Hindawi Publishing CorporationISRN CorrosionVolume 2013 Article ID 464710 9 pageshttpdxdoiorg1011552013464710

Research ArticleCorrosion Study of Powder-Coated Galvanised Steel

Manish Kumar Bhadu Akshya Kumar Guin Veena Singh and Shyam K Choudhary

RampD and Scientific Services TATA Steel Ltd Jamshedpur 831001 India

Correspondence should be addressed to Manish Kumar Bhadu mkbhadugmailcom

Received 31 December 2012 Accepted 3 February 2013

Academic Editors C-H Hsu and S Umoren

Copyright copy 2013 Manish Kumar Bhadu et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

In general steel is protected from corrosive environments by conversion coatings that is phosphating chromating and so forthand then followed by different layers of paints Nowadays strict pollution laws and regulations are creating significant challengesfor coating experts to develop an environmentally friendly product Powder coatings have demonstrated their ability as alternativeto traditional solvent-borne coatings In the present work polyester-based two coating systems have been investigated and theirperformances have been evaluated for surface topographical properties by Scanning electron microscope (SEM) and energydispersive spectrometry (EDX) accelerated corrosion resistance by salt spray test and impedance property by electrochemicalimpedance spectroscopy Coating adhesion with the steel and hardness were evaluated by bond strength cross cut adhesion andpencil hardness This paper explains the results and performance of the coatings by the above two systems

1 Introduction

Galvanised steel is widely used in construction automobileand white goods sector Zinc coating is the most effectiveand economic means to protect the steel substrate exposedto atmospheric corroding environments It protects the steelsubstrate by acting as a barrier against the corrosive envi-ronment and by sacrificially corroding themselves to providecathodic protection

Protective ability of galvanised (GI) steel may beenhanced by employing thicker zinc coatings or by paintingthe metallic substrate [1] Paints improve the surface lifeof underlying zinc coating acting as a barrier against zincreaction with environmental agents Cracks crater and pinholes occurring in the paint are sealed by corroded zincproducts Moreover corroded zinc products occupy a 20ndash25 more volume than zinc while iron oxides (corrosionproduct of steel) occupy a volume several times larger thanthe steel thus expansive forces are reduced at the zinc-paintinterface compared to those at the steel-paint one [2] Themain practical problem concerning painting of zinc-coatedsurface lies in achieving good bond strength that is goodadhesion of polymer with GI sheet Often adhesion lookssatisfactory immediately after painting but it prematurelydegrades after water oxygen and other corrosive ingredients

diffuse through the polymeric coating Several pretreatmentprocesses were reported to improve coating adhesion Themain function of pretreatment for GI steel surface is to forma very stable passive film which will enhance the adhesionwith subsequent polymeric film [3] There are a number ofpretreatment processes like phosphating chromating andcoating of rust preventing compounds by chemical andphysical vapor deposition and diffusion coating and so forthSome of these pretreatment processes do not contain a filmformingmaterial that is nonpriming and hence they shouldbe compatible with the rest of the painting system [4]Primers contain a film forming material and are expected toact as the anchorage of the paint system [5] Some of thesecoatings are toxic and pose concerns to the environment

Powder thermoset coatings are solvent-free and unlikethe conventional liquid coatings have zero volatile organiccontent (VOC) Thus they could offer the coating formula-tors a robust and a highly promising approach to produceeco-friendly coatings Moreover not only powder coatingsare easier to apply than solvent-based coatings but they alsoprovide a thicker and more uniform coating If we take intoaccount the economical advantages of powder coatings likecost savings in water disposal high yield and cheap mainte-nance the total operating cost of a powder application plantis lower than that of traditional solvent-based liquid paints

2 ISRN Corrosion

Phosphated layer (4 120583)

Zinc coating (60 gsm)

Steel substrate

Epoxyepoxy-polyester layer (60120583)

Figure 1 Schematic diagram of different coating layers with thickness

Furthermore a wide variety of finishes such as structuredwrinkled metallic and antique finishes are available withpowder coatings [6ndash9]

Although it is possible to achieve high-gloss and smoothcoatings with excellent adhesion flexibility and hardness byepoxy powder coating they however exhibit poor toleranceto heat and light resulting in a pronounced tendency to fade[10] In order to overcome this shortcoming polyesterepoxyblends-based coating technology has been developed whichshows excellent film smoothness appropriate mechanicalproperties and adherence characteristics [11] Interestinglyblend coatings show a broader degradation temperatureinterval and they volatilize to a substantially less extentcompared to pure epoxy and polyester powder coatingEpoxy-polyester powder coating is a hybrid of epoxy andpolyester powder coating These hybrids have propertiessimilar to those of epoxy powders however their additionaladvantage is that they have improved resistance to fading andimproved weather resistance [11]

Hybrid powders are now regarded as the main backboneof the powder coating industry The objective of the presentwork is to find out a suitable powder coating system for GIsurface A comparative study was made in between polyesterand epoxy-polyester powder coating process Adhesion onGI steel was assessed by suitable standardized adhesion testsAnticorrosive behaviour was evaluated by salt spray andelectrochemical impedance spectroscopy (EIS) method

2 Experimental Details

Zero-spangle GI (120 gm2) sheet was used as the basesubstrate These sheets were degreased to remove oil andgrease followed by phosphating in tricationic phosphate basesolution to obtain a thin coating of dry film thickness (DFT)sim4micron The polyester and epoxy-polyester powder coatingof DFT 60micron was applied by electrostatic sprayingmethod on phosphate GI sheet referred to as system-1 andsystem-2 respectively Coated panels were allowed to standfor 7 days at room temperature for curing before any testingThe microstructure and surface morphology of the coatedsamples were observed by a scanning electron microscope(SEM) equipped with energy dispersive spectrometry (EDX)The energy used for analysis was 15 KeV

Corrosion resistance of the samples was evaluated byelectrochemical impedance spectroscopy (EIS)TheEISmea-surements were carried out by using the VersaSTAT MCA typical three-electrode system was employed in these

tests The samples acted as the working electrode (1 cm2of the exposed area) saturated calomel electrode (SCE) asthe reference and graphite as counter electrode 35 NaClsolution was used as an electrolyte in all the measurements

The EIS measurement was carried out in the frequencyrange of 100KHz to 001Hz and the applied voltage was5mV Salt spray tests were carried out by exposing the scribedsamples (610158401015840 times 410158401015840) in a salt spray chamber as per the ASTMB-117 test method The panels were checked at a regularinterval of time and results were noted down in terms ofblisters creep and red rustThe adhesion hardness and bondstrength measurements were performed on the coated steelsample as per the ASTMD3359 ASTMD 3363 and ASTMD4541 respectively

3 Results and Discussion

31 Morphology The schematic diagram of the differentcoating layers on the steel substrate is shown in Figure 1The cross-sectional SEM photographs of phosphate steelwith polyester powder coated and epoxy-polyester powdercoated are shown in Figures 2 and 3 respectively It can beseen that coating formed by epoxy-polyester appears to beuniform without any surface defects and cracks From theSEM photograph it is clearly visible that the epoxy-polyesterpowder coating is highly dense and it strongly adheres tosurface whereas some visible cracks appear on polyester-coated sheet and are not so strongly adherent to surfacecompared to the epoxy-polyester-coated surface

EDX spectra of polyester powder-coated and epoxy-polyester powder-coated samples are also shown in Figures2 and 3 The peaks of different pigments materials like zincsilica phosphorus and oxygen are predominant in bothcases

32 Bond Strength Two major pieces of information areobtained from the bond strength test The first is the pull-offstrength that is bond strength of coating on substrate andthe second one is about the point where the split occurredin the paint system The split could be an adhesive break acohesive break a combination of both or a failure of the glue

From Table 1 cohesive failure is observed in polyesterpowder-coated sample whereas adhesive failure is observedin epoxy-polyester system Epoxy-polyester system compar-atively adheres strongly with phosphated steel substrate andneeds more than 5MPa force for any type of delamination

ISRN Corrosion 3

90120583m Electron image 1

(a)

0 1 2 3 4 5 6 7 8 9 10(keV)

Zn Zn Zn

Fe

Fe

Fe

C

Point 1Full-scale 5718 cts cursor minus0018 (353 cts)

(b)

0 1 2 3 4 5 6 7 8 9 10(keV)

Zn

Zn

Zn

OTi

Ti Ti

Fe Fe

FeC S

Point 3Full-scale 5718 cts cursor minus0018 (297 cts)

(c)

1 2 3 4 5 6 7 8 9 10(keV)

C

O

Fe

Fe FeZn

Zn Zn

Si

S

Ba

Ba

Ba

BaBaBa

Point 7

Full-scale 1613 cts cursor 0048 (306 cts)

(d)

Figure 2 (a) Cross-sectional SEM image of polyester powder-coated sheet (system-1) (b) (c) and (d) show EDX analysis of three respectivepoints 1 3 and 7 shown in (a)

The failure in the case of system-2 is from the glue itselfBut polyester coating system shows failure from interface andneeds only 4MPa force for any type of coating delaminationThis improvement in system-2 is due to the formation ofstrong and crack-free bonding of epoxy-polyester hybridwith steel substrate whereas polyester coatingweakly adhereswith the presence of internal crack as noticed from SEMphotograph and hence needs minimum force to delaminatefrom the surface as compared to epoxy-polyester coating [12ndash14]

33 Corrosion Resistance Property by ElectrochemicalImpedance Spectroscopy The electrochemical properties ofpolyester and epoxy-polyester on phosphate steel substratewere examined by EIS measurements The main role of EISin the characterization of an organic coating is to provideinformation about the properties of the protective system

such as defects adhesion and barrier properties as wellas to determine the onset and progression of corrosionprocess on metal substrate underneath the organic coatingFor the EIS measurements elements were selected througha model equivalent circuit (see Figure 4) to represents thesystems under study The systems undergo a charge transfercontrol according to this circuit where119877s represents solutionresistance 119877p coating resistance 119862c coating capacitance 119877ctcharge transfer resistance and 119862dl double layer capacitance

The Bode representations of the impedance data havebeen analyzed with VersaSTAT MC and ZSimpWin soft-ware of Princeton applied research Single slope in themidfrequency range shows the existence of a single timeconstant and the impedance data have been analyzed usingthe equivalent circuit

The impedance behavior of coating system-1 and coatingsystem-2 on steel substrate after initial study 144 h and 264 h

4 ISRN Corrosion

Table 1 Bond strength and nature of failure of galvanised coated substrate

System Bond strength (in MPa) Nature of failure Photographs

1 4 Failure from top coat and adhesive

2 5 Failure from top coat and adhesive

Table 2 Impedance parameters of wash primer and epoxy primer and top coated GI in 35 NaCl solution

Time hSystem-1 System-2

resistance (Ωcm2) resistance (Ωcm2)Initial 8835 times 106 1166 times 106

24 h 7203 times 104 1446 times 105

96 h 7367 1185 times 105

144 h 7166 1633 times 104

264 h 5504 1576 times 104

Table 3 Cross-hatch adhesion and pencil hardness results of system-1 and system-2

System Cross-hatch Percentage of area removed Pencil hardness (at 45∘)1 5B 0 7H2 5B 0 9H

of immersion in 35 NaCl solution is shown Figures 5(a)ndash5(c) with overlay The individual impedance behaviours withinitial time 24 h 96 h 144 h and 264 h are shown in Figures6 7 8 9 and 10 respectively The coating resistance andcapacitance values derived from these figures are given inTable 2 It is clear from Figures 6 7 8 9 and 10 and Table 2that in the beginning of experiment the coating resistance ofpolyester- and epoxy-polyester-coated samples is in the samerange Impedance of coating system-1 containing polyesterpowder coating shows 8835 times 106Ωcm2 against the 1166 times10

6Ωcm2 resistance of coating system-2The coating resistance value of system-1 decreases from8835times10

6Ωcm2 to 5504 times 103Ωcm2 after 264 h of immer-

sion whereas coating resistance value of system-2 decreasesfrom 1166 times 106Ωcm2 to 1633 times 104Ωcm2 in 144 h ofimmersion and to 1576 times 104Ωcm2 in 264 h of immersionGenerally the high impedance value of polyester-coatedsample shows a fast reduction in the first 24 h of immersiondue to the development of conductive pathways inside thefilm Comparatively a slow decrease in the impedance valuewas observed for the epoxy-polyester powder-coated steel

sheet followed by a small recovery after 24 h of immersion[15 16]

Penetration of water and movement of ionic speciesthrough the coating layermay be responsible for the observeddecrease in coating resistance value [17] Other reasonscould be a weaker ionic resistance and a lower-cross linkingdensity The dielectric constants of organic coating and waterare about 6 and 80 respectively at ambient temperatureTherefore permeation of a small amount of water throughthe coating can contribute to a relatively large change in thepore resistance It is known that diffusion of electrolyte waterand ions through the epoxy-polyester powder-coated sampleis much lower than the polyester powder-coated sample Thehigher corrosion protection by epoxy-polyester powder coat-ing on steel surface is due to the higher cross-linked densityof epoxy-polyester network comparingwith polyester systemin addition to high cross-linking density the additional freehydroxyl group that is ndashOH of epoxy-polyester coatingsystem (as compared to only polyester system) forms a strongbondwith phosphate and steel surfaceThehigh cross-linkingdensity and strong adhesion of epoxy group with phosphate

ISRN Corrosion 5

90 120583m Electron image 1

(a)

1 2 3 4 5 6 7 8 9 10

OMn

Mn

Mn

Fe

Fe

Fe

Zn

Zn

ZnNiNi Ni

P

S

Ba

Ba

Ba

BaBa

Ba

Point 6

(keV)Full-scale 785 cts cursor 0028 (359 cts)

(b)

1 2 3 4 5 6 7 8 9 10

Point 7

OFe

Fe

Fe

Zn

Zn

Zn

(keV)Full-scale 4830 cts cursor 0028 (359 cts)

(c)

1 2 3 4 5 6 7 8 9 10

Point 9

Fe

Fe

Fe

(keV)Full-scale 3118 cts cursor 0093 (196 cts)

(d)

Figure 3 (a) Cross sectional SEM image of epoxy-polyester powder-coated sheet (system-2) (b) (c) and (d) show EDX analysis of threerespective points 6 7 and 9 shown in (a)

119877s

119877p

119877ct

119862c

119862dl

Figure 4 Electrical equivalent circuit for the polyester and polyester-epoxy coating on the galvanised sheet

and steel substrate create an impermeable surface for waterand other corrosive ingredients on the coated surface[18ndash20]

34 Corrosion Resistance Property by Salt Sprat Test Per-formance of steel coated sheet after 1608 h exposure in saltspray chamber is shown in Figure 11 It can be seen that

epoxy-polyester powder-coated sample (system-2) is foundto have less white rust even after 1608 h of exposure insalt spray chamber (ASTM B 117) Whereas coating system-1 containing polyester powder coating fails after 1200 h ofexposure in salt spray chamber (ASTM B117) There are anumber of blisters in and around the edges of the scribe areain the case of system-1

6 ISRN Corrosion

25M

2M

15M

1M

500k

0

10m 100m 1 10 100 1k 10k 100 kFrequency (Hz)

System-1System-2

|119885|

(ohm

s)

(a)

10m 100m 1 10 100 1k 10k 100 kFrequency (Hz)

System-1System-2

15k

10k

5k

|119885|

(ohm

s)

(b)

10m 100m 1 10 100 1k 10k 100 kFrequency (Hz)

System-1System-2

200 k

150k

100 k

50k

0

|119885|

(ohm

s)

(c)

Figure 5 (a) (b) and (c) show EIS overlap diagram of samples immersed for time intervals beginning 144 h and 264 h respectively

5101520253035404550556065707580

Ang

le (d

eg)

1119864+07

1119864+06

1119864+05

1119864+0410000010000100010010101001

Frequency (Hz)

|119885|

(ohm

)

(a)

510152025303540455055

Ang

le (d

eg)

1119864+07

1119864+06

1119864+05

1119864+0410000010000100010010101001

Frequency (Hz)

minus50

|119885|

(ohm

)

(b)

Figure 6 Bode plot of (a) system-1 and (b) system-2 at initial time

35 Adhesion andHardness Cross hatch and pencil hardnessof system-1 and system-2 were performed according to theASTMD3359 and ASTMD3363-05 The results of these testsare shown in Table 3 which compares the adhesion andhardness properties of the two systems

The result of the x-cut adhesion test was satisfactory forboth the systems providing 5Bwith no observed flaking in thecross-cut area Therefore no adhesion losses appeared in anyinterfacesThe adhesion of primer to the steel surface and theadhesion of the top coats to the primer bothwere satisfactory

ISRN Corrosion 7

10000010000100010010101001Frequency (Hz)

024681012141618202224262830323436

Ang

le (d

eg)

100000

10000

1000

|119885|

(ohm

)

(a)

10000010000100010010101001Frequency (Hz)

05101520253035404550

1119864+06

1119864+05

1119864+04

1119864+03

Ang

le (d

eg)

|119885|

(ohm

)

(b)

Figure 7 Bode plot of (a) system-1 and (b) system-2 at 24 h time

10000010000100010010101001Frequency (Hz)

02468101214161820222426283032

Ang

le (d

eg)

100000

10000

1000

|119885|

(ohm

)

(a)

10000010000100010010101001Frequency (Hz)

Ang

le (d

eg)

1000000

100000

10000 051015202530354045

|119885|

(ohm

)

(b)

Figure 8 Bode plot of (a) system-1 (b) system-2 at 96 h time

Ang

le (d

eg)

10000010000100010010101001Frequency (Hz)

10000

1000 01234567891011121314

|119885|

(ohm

)

(a)

051015202530354045

Ang

le (d

eg)

10000010000100010010101001Frequency (Hz)

100000

10000

|119885|

(ohm

)

(b)

Figure 9 Bode plot of (a) system-1 and (b) system-2 at 144 h time

4 Conclusion

The powder coatings protect galvanised steel substrates bythe introduction of a barrier layer with relatively high ohmicresistance between the metallic substrate and the corrosiveenvironment Also it is indicated that the cross-link densityappears only to affect ionic conductivity of the film and

due to the higher cross-linked density of epoxy-polyesternetwork comparing with polyester system the permeabilityof water and ions through the coating film becomes lessand it leads to a more impervious film with a more resistantstructure to corrosion It is indicated that the polyester film ismore porous due to the less cross-link density of cured poly-mer comparedwith epoxy-polyester powder-coated samples

8 ISRN Corrosion

0510152025303540

Ang

le (d

eg)

100000

100000

10000100010010101001Frequency (Hz)

10000

1000

|119885|

(ohm

)

(a)

051015202530354045

Ang

le (d

eg)

100000

10000010000100010010101001Frequency (Hz)

10000

1000000

minus5

|119885|

(ohm

)

(b)

Figure 10 Bode plot of (a) system-1 and (b) system-2 at 264 h time

(a) System 1 (b) System 2

Figure 11 Salt spray photographs of coated substrate (a) polyester-coated sample after 1200 h of salt spray test (b) epoxy-polyester-coated sample after 1608 h of the salt spray test

SEM micrograph and bond strength suggest that epoxy-polyester coating is more firmly adherent to the phosphatesubstrate than polyester coating due tomore hydroxyl groupsin epoxy-polyester bonding with phosphate substrate Pro-tective properties of fully cured organic coatings on metallicsubstrate may be attributed to a barrier andor an activeinhibition mechanism

Acknowledgment

The authors would like to thank the staff of the corrosion labfor helping them during experiments

References

[1] A K Guin S Nayak T K Rout N Bandyopadhyay and D KSengupta ldquoCorrosion resistance nano-hybrid sol-gel coating onsteel sheetrdquo ISIJ International vol 51 no 3 pp 435ndash440 2011

[2] A S Khanna Introduction to High Temperature Oxidation andCorrosion ASM International 1997

[3] B V Jegdic J B Bajat J P Popic and V B Miskovic-StankovicldquoCorrosion stability of polyester coatings on steel pretreatedwith different iron-phosphate coatingsrdquo Progress in OrganicCoatings vol 70 no 2-3 pp 127ndash133 2011

[4] A M P Simoes R O Carbonari A R Di Sarli B del Amoand R Romagnoli ldquoAn environmentally acceptable primerfor galvanized steel formulation and evaluation by SVETrdquoCorrosion Science vol 53 no 1 pp 464ndash472 2011

[5] R Mafi S M Mirabedini M M Attar and S Moradian ldquoCurecharacterization of epoxy and polyester clear powder coatingsusing Differential Scanning Calorimetry (DSC) and DynamicMechanical Thermal Analysis (DMTA)rdquo Progress in OrganicCoatings vol 54 no 3 pp 164ndash169 2005

[6] D Maetens ldquoWeathering degradation mechanism in polyesterpowder coatingsrdquo Progress in Organic Coatings vol 58 no 2-3pp 172ndash179 2007

[7] J B Bajat J P Popic and V B Miskovic-Stankovic ldquoTheinfluence of aluminium surface pretreatment on the corrosionstability and adhesion of powder polyester coatingrdquo Progress inOrganic Coatings vol 69 no 4 pp 316ndash321 2010

[8] M A J Batista R P Moraes J C S Barbosa P C Oliveiraand A M Santos ldquoEffect of the polyester chemical structure onthe stability of polyester-melamine coatings when exposed toaccelerated weatheringrdquo Progress in Organic Coatings vol 71no 3 pp 265ndash273 2011

[9] F L Duivenvoorde J Laven and R Van der Linde ldquoDiblockcopolymer dispersants in polyester powder coatingsrdquo Progressin Organic Coatings vol 45 no 2-3 pp 127ndash137 2002

[10] S Radhakrishnan N Sonawane and C R Siju ldquoEpoxy powdercoatings containing polyaniline for enhanced corrosion protec-tionrdquo Progress in Organic Coatings vol 64 no 4 pp 383ndash3862009

[11] V C Malshe and G Waghoo ldquoWeathering study of epoxypaintsrdquo Progress in Organic Coatings vol 51 no 4 pp 267ndash2722004

[12] R Van der Linde E G Belder and D Y Perera ldquoEffect of phys-ical aging and thermal stress on the behavior of polyesterTGICpowder coatingsrdquo Progress in Organic Coatings vol 40 no 1ndash4pp 215ndash224 2000

[13] Technical Data Sheet of Ridoline 1352 BA of Ms HenkelChembond India Ltd

ISRN Corrosion 9

[14] Technical Data Sheet of Granodine of Ms Henkel ChembondIndia Ltd

[15] M Ozcan I Dehri and M Erbil ldquoEIS study of the effectof high levels of SO

2on the corrosion of polyester-coated

galvanised steel at different relative humiditiesrdquo Progress inOrganic Coatings vol 44 no 4 pp 279ndash285 2002

[16] R Naderi MM Attar andM HMoayed ldquoEIS examination ofmill scale on mild steel with polyester-epoxy powder coatingrdquoProgress in Organic Coatings vol 50 no 3 pp 162ndash165 2004

[17] R Mafi S M Mirabedini R Naderi and M M Attar ldquoEffectof curing characterization on the corrosion performance ofpolyester and polyesterepoxy powder coatingsrdquo CorrosionScience vol 50 no 12 pp 3280ndash3286 2008

[18] G Wuzella A Kandelbauer A R Mahendran and ATeischinger ldquoThermochemical and isoconversional kineticanalysis of a polyester-epoxy hybrid powder coating resin forwood based panel finishingrdquo Progress in Organic Coatings vol70 no 4 pp 186ndash191 2011

[19] M Barletta and A Gisario ldquoAn application of neural networksolutions to laser assisted paint stripping process of hybridepoxy-polyester coatings on aluminum substratesrdquo Surface andCoatings Technology vol 200 no 24 pp 6678ndash6689 2006

[20] R Naderi MM Attar andM HMoayed ldquoEIS examination ofmill scale on mild steel with polyester-epoxy powder coatingrdquoProgress in Organic Coatings vol 50 no 3 pp 162ndash165 2004

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2 ISRN Corrosion

Phosphated layer (4 120583)

Zinc coating (60 gsm)

Steel substrate

Epoxyepoxy-polyester layer (60120583)

Figure 1 Schematic diagram of different coating layers with thickness

Furthermore a wide variety of finishes such as structuredwrinkled metallic and antique finishes are available withpowder coatings [6ndash9]

Although it is possible to achieve high-gloss and smoothcoatings with excellent adhesion flexibility and hardness byepoxy powder coating they however exhibit poor toleranceto heat and light resulting in a pronounced tendency to fade[10] In order to overcome this shortcoming polyesterepoxyblends-based coating technology has been developed whichshows excellent film smoothness appropriate mechanicalproperties and adherence characteristics [11] Interestinglyblend coatings show a broader degradation temperatureinterval and they volatilize to a substantially less extentcompared to pure epoxy and polyester powder coatingEpoxy-polyester powder coating is a hybrid of epoxy andpolyester powder coating These hybrids have propertiessimilar to those of epoxy powders however their additionaladvantage is that they have improved resistance to fading andimproved weather resistance [11]

Hybrid powders are now regarded as the main backboneof the powder coating industry The objective of the presentwork is to find out a suitable powder coating system for GIsurface A comparative study was made in between polyesterand epoxy-polyester powder coating process Adhesion onGI steel was assessed by suitable standardized adhesion testsAnticorrosive behaviour was evaluated by salt spray andelectrochemical impedance spectroscopy (EIS) method

2 Experimental Details

Zero-spangle GI (120 gm2) sheet was used as the basesubstrate These sheets were degreased to remove oil andgrease followed by phosphating in tricationic phosphate basesolution to obtain a thin coating of dry film thickness (DFT)sim4micron The polyester and epoxy-polyester powder coatingof DFT 60micron was applied by electrostatic sprayingmethod on phosphate GI sheet referred to as system-1 andsystem-2 respectively Coated panels were allowed to standfor 7 days at room temperature for curing before any testingThe microstructure and surface morphology of the coatedsamples were observed by a scanning electron microscope(SEM) equipped with energy dispersive spectrometry (EDX)The energy used for analysis was 15 KeV

Corrosion resistance of the samples was evaluated byelectrochemical impedance spectroscopy (EIS)TheEISmea-surements were carried out by using the VersaSTAT MCA typical three-electrode system was employed in these

tests The samples acted as the working electrode (1 cm2of the exposed area) saturated calomel electrode (SCE) asthe reference and graphite as counter electrode 35 NaClsolution was used as an electrolyte in all the measurements

The EIS measurement was carried out in the frequencyrange of 100KHz to 001Hz and the applied voltage was5mV Salt spray tests were carried out by exposing the scribedsamples (610158401015840 times 410158401015840) in a salt spray chamber as per the ASTMB-117 test method The panels were checked at a regularinterval of time and results were noted down in terms ofblisters creep and red rustThe adhesion hardness and bondstrength measurements were performed on the coated steelsample as per the ASTMD3359 ASTMD 3363 and ASTMD4541 respectively

3 Results and Discussion

31 Morphology The schematic diagram of the differentcoating layers on the steel substrate is shown in Figure 1The cross-sectional SEM photographs of phosphate steelwith polyester powder coated and epoxy-polyester powdercoated are shown in Figures 2 and 3 respectively It can beseen that coating formed by epoxy-polyester appears to beuniform without any surface defects and cracks From theSEM photograph it is clearly visible that the epoxy-polyesterpowder coating is highly dense and it strongly adheres tosurface whereas some visible cracks appear on polyester-coated sheet and are not so strongly adherent to surfacecompared to the epoxy-polyester-coated surface

EDX spectra of polyester powder-coated and epoxy-polyester powder-coated samples are also shown in Figures2 and 3 The peaks of different pigments materials like zincsilica phosphorus and oxygen are predominant in bothcases

32 Bond Strength Two major pieces of information areobtained from the bond strength test The first is the pull-offstrength that is bond strength of coating on substrate andthe second one is about the point where the split occurredin the paint system The split could be an adhesive break acohesive break a combination of both or a failure of the glue

From Table 1 cohesive failure is observed in polyesterpowder-coated sample whereas adhesive failure is observedin epoxy-polyester system Epoxy-polyester system compar-atively adheres strongly with phosphated steel substrate andneeds more than 5MPa force for any type of delamination

ISRN Corrosion 3

90120583m Electron image 1

(a)

0 1 2 3 4 5 6 7 8 9 10(keV)

Zn Zn Zn

Fe

Fe

Fe

C

Point 1Full-scale 5718 cts cursor minus0018 (353 cts)

(b)

0 1 2 3 4 5 6 7 8 9 10(keV)

Zn

Zn

Zn

OTi

Ti Ti

Fe Fe

FeC S

Point 3Full-scale 5718 cts cursor minus0018 (297 cts)

(c)

1 2 3 4 5 6 7 8 9 10(keV)

C

O

Fe

Fe FeZn

Zn Zn

Si

S

Ba

Ba

Ba

BaBaBa

Point 7

Full-scale 1613 cts cursor 0048 (306 cts)

(d)

Figure 2 (a) Cross-sectional SEM image of polyester powder-coated sheet (system-1) (b) (c) and (d) show EDX analysis of three respectivepoints 1 3 and 7 shown in (a)

The failure in the case of system-2 is from the glue itselfBut polyester coating system shows failure from interface andneeds only 4MPa force for any type of coating delaminationThis improvement in system-2 is due to the formation ofstrong and crack-free bonding of epoxy-polyester hybridwith steel substrate whereas polyester coatingweakly adhereswith the presence of internal crack as noticed from SEMphotograph and hence needs minimum force to delaminatefrom the surface as compared to epoxy-polyester coating [12ndash14]

33 Corrosion Resistance Property by ElectrochemicalImpedance Spectroscopy The electrochemical properties ofpolyester and epoxy-polyester on phosphate steel substratewere examined by EIS measurements The main role of EISin the characterization of an organic coating is to provideinformation about the properties of the protective system

such as defects adhesion and barrier properties as wellas to determine the onset and progression of corrosionprocess on metal substrate underneath the organic coatingFor the EIS measurements elements were selected througha model equivalent circuit (see Figure 4) to represents thesystems under study The systems undergo a charge transfercontrol according to this circuit where119877s represents solutionresistance 119877p coating resistance 119862c coating capacitance 119877ctcharge transfer resistance and 119862dl double layer capacitance

The Bode representations of the impedance data havebeen analyzed with VersaSTAT MC and ZSimpWin soft-ware of Princeton applied research Single slope in themidfrequency range shows the existence of a single timeconstant and the impedance data have been analyzed usingthe equivalent circuit

The impedance behavior of coating system-1 and coatingsystem-2 on steel substrate after initial study 144 h and 264 h

4 ISRN Corrosion

Table 1 Bond strength and nature of failure of galvanised coated substrate

System Bond strength (in MPa) Nature of failure Photographs

1 4 Failure from top coat and adhesive

2 5 Failure from top coat and adhesive

Table 2 Impedance parameters of wash primer and epoxy primer and top coated GI in 35 NaCl solution

Time hSystem-1 System-2

resistance (Ωcm2) resistance (Ωcm2)Initial 8835 times 106 1166 times 106

24 h 7203 times 104 1446 times 105

96 h 7367 1185 times 105

144 h 7166 1633 times 104

264 h 5504 1576 times 104

Table 3 Cross-hatch adhesion and pencil hardness results of system-1 and system-2

System Cross-hatch Percentage of area removed Pencil hardness (at 45∘)1 5B 0 7H2 5B 0 9H

of immersion in 35 NaCl solution is shown Figures 5(a)ndash5(c) with overlay The individual impedance behaviours withinitial time 24 h 96 h 144 h and 264 h are shown in Figures6 7 8 9 and 10 respectively The coating resistance andcapacitance values derived from these figures are given inTable 2 It is clear from Figures 6 7 8 9 and 10 and Table 2that in the beginning of experiment the coating resistance ofpolyester- and epoxy-polyester-coated samples is in the samerange Impedance of coating system-1 containing polyesterpowder coating shows 8835 times 106Ωcm2 against the 1166 times10

6Ωcm2 resistance of coating system-2The coating resistance value of system-1 decreases from8835times10

6Ωcm2 to 5504 times 103Ωcm2 after 264 h of immer-

sion whereas coating resistance value of system-2 decreasesfrom 1166 times 106Ωcm2 to 1633 times 104Ωcm2 in 144 h ofimmersion and to 1576 times 104Ωcm2 in 264 h of immersionGenerally the high impedance value of polyester-coatedsample shows a fast reduction in the first 24 h of immersiondue to the development of conductive pathways inside thefilm Comparatively a slow decrease in the impedance valuewas observed for the epoxy-polyester powder-coated steel

sheet followed by a small recovery after 24 h of immersion[15 16]

Penetration of water and movement of ionic speciesthrough the coating layermay be responsible for the observeddecrease in coating resistance value [17] Other reasonscould be a weaker ionic resistance and a lower-cross linkingdensity The dielectric constants of organic coating and waterare about 6 and 80 respectively at ambient temperatureTherefore permeation of a small amount of water throughthe coating can contribute to a relatively large change in thepore resistance It is known that diffusion of electrolyte waterand ions through the epoxy-polyester powder-coated sampleis much lower than the polyester powder-coated sample Thehigher corrosion protection by epoxy-polyester powder coat-ing on steel surface is due to the higher cross-linked densityof epoxy-polyester network comparingwith polyester systemin addition to high cross-linking density the additional freehydroxyl group that is ndashOH of epoxy-polyester coatingsystem (as compared to only polyester system) forms a strongbondwith phosphate and steel surfaceThehigh cross-linkingdensity and strong adhesion of epoxy group with phosphate

ISRN Corrosion 5

90 120583m Electron image 1

(a)

1 2 3 4 5 6 7 8 9 10

OMn

Mn

Mn

Fe

Fe

Fe

Zn

Zn

ZnNiNi Ni

P

S

Ba

Ba

Ba

BaBa

Ba

Point 6

(keV)Full-scale 785 cts cursor 0028 (359 cts)

(b)

1 2 3 4 5 6 7 8 9 10

Point 7

OFe

Fe

Fe

Zn

Zn

Zn

(keV)Full-scale 4830 cts cursor 0028 (359 cts)

(c)

1 2 3 4 5 6 7 8 9 10

Point 9

Fe

Fe

Fe

(keV)Full-scale 3118 cts cursor 0093 (196 cts)

(d)

Figure 3 (a) Cross sectional SEM image of epoxy-polyester powder-coated sheet (system-2) (b) (c) and (d) show EDX analysis of threerespective points 6 7 and 9 shown in (a)

119877s

119877p

119877ct

119862c

119862dl

Figure 4 Electrical equivalent circuit for the polyester and polyester-epoxy coating on the galvanised sheet

and steel substrate create an impermeable surface for waterand other corrosive ingredients on the coated surface[18ndash20]

34 Corrosion Resistance Property by Salt Sprat Test Per-formance of steel coated sheet after 1608 h exposure in saltspray chamber is shown in Figure 11 It can be seen that

epoxy-polyester powder-coated sample (system-2) is foundto have less white rust even after 1608 h of exposure insalt spray chamber (ASTM B 117) Whereas coating system-1 containing polyester powder coating fails after 1200 h ofexposure in salt spray chamber (ASTM B117) There are anumber of blisters in and around the edges of the scribe areain the case of system-1

6 ISRN Corrosion

25M

2M

15M

1M

500k

0

10m 100m 1 10 100 1k 10k 100 kFrequency (Hz)

System-1System-2

|119885|

(ohm

s)

(a)

10m 100m 1 10 100 1k 10k 100 kFrequency (Hz)

System-1System-2

15k

10k

5k

|119885|

(ohm

s)

(b)

10m 100m 1 10 100 1k 10k 100 kFrequency (Hz)

System-1System-2

200 k

150k

100 k

50k

0

|119885|

(ohm

s)

(c)

Figure 5 (a) (b) and (c) show EIS overlap diagram of samples immersed for time intervals beginning 144 h and 264 h respectively

5101520253035404550556065707580

Ang

le (d

eg)

1119864+07

1119864+06

1119864+05

1119864+0410000010000100010010101001

Frequency (Hz)

|119885|

(ohm

)

(a)

510152025303540455055

Ang

le (d

eg)

1119864+07

1119864+06

1119864+05

1119864+0410000010000100010010101001

Frequency (Hz)

minus50

|119885|

(ohm

)

(b)

Figure 6 Bode plot of (a) system-1 and (b) system-2 at initial time

35 Adhesion andHardness Cross hatch and pencil hardnessof system-1 and system-2 were performed according to theASTMD3359 and ASTMD3363-05 The results of these testsare shown in Table 3 which compares the adhesion andhardness properties of the two systems

The result of the x-cut adhesion test was satisfactory forboth the systems providing 5Bwith no observed flaking in thecross-cut area Therefore no adhesion losses appeared in anyinterfacesThe adhesion of primer to the steel surface and theadhesion of the top coats to the primer bothwere satisfactory

ISRN Corrosion 7

10000010000100010010101001Frequency (Hz)

024681012141618202224262830323436

Ang

le (d

eg)

100000

10000

1000

|119885|

(ohm

)

(a)

10000010000100010010101001Frequency (Hz)

05101520253035404550

1119864+06

1119864+05

1119864+04

1119864+03

Ang

le (d

eg)

|119885|

(ohm

)

(b)

Figure 7 Bode plot of (a) system-1 and (b) system-2 at 24 h time

10000010000100010010101001Frequency (Hz)

02468101214161820222426283032

Ang

le (d

eg)

100000

10000

1000

|119885|

(ohm

)

(a)

10000010000100010010101001Frequency (Hz)

Ang

le (d

eg)

1000000

100000

10000 051015202530354045

|119885|

(ohm

)

(b)

Figure 8 Bode plot of (a) system-1 (b) system-2 at 96 h time

Ang

le (d

eg)

10000010000100010010101001Frequency (Hz)

10000

1000 01234567891011121314

|119885|

(ohm

)

(a)

051015202530354045

Ang

le (d

eg)

10000010000100010010101001Frequency (Hz)

100000

10000

|119885|

(ohm

)

(b)

Figure 9 Bode plot of (a) system-1 and (b) system-2 at 144 h time

4 Conclusion

The powder coatings protect galvanised steel substrates bythe introduction of a barrier layer with relatively high ohmicresistance between the metallic substrate and the corrosiveenvironment Also it is indicated that the cross-link densityappears only to affect ionic conductivity of the film and

due to the higher cross-linked density of epoxy-polyesternetwork comparing with polyester system the permeabilityof water and ions through the coating film becomes lessand it leads to a more impervious film with a more resistantstructure to corrosion It is indicated that the polyester film ismore porous due to the less cross-link density of cured poly-mer comparedwith epoxy-polyester powder-coated samples

8 ISRN Corrosion

0510152025303540

Ang

le (d

eg)

100000

100000

10000100010010101001Frequency (Hz)

10000

1000

|119885|

(ohm

)

(a)

051015202530354045

Ang

le (d

eg)

100000

10000010000100010010101001Frequency (Hz)

10000

1000000

minus5

|119885|

(ohm

)

(b)

Figure 10 Bode plot of (a) system-1 and (b) system-2 at 264 h time

(a) System 1 (b) System 2

Figure 11 Salt spray photographs of coated substrate (a) polyester-coated sample after 1200 h of salt spray test (b) epoxy-polyester-coated sample after 1608 h of the salt spray test

SEM micrograph and bond strength suggest that epoxy-polyester coating is more firmly adherent to the phosphatesubstrate than polyester coating due tomore hydroxyl groupsin epoxy-polyester bonding with phosphate substrate Pro-tective properties of fully cured organic coatings on metallicsubstrate may be attributed to a barrier andor an activeinhibition mechanism

Acknowledgment

The authors would like to thank the staff of the corrosion labfor helping them during experiments

References

[1] A K Guin S Nayak T K Rout N Bandyopadhyay and D KSengupta ldquoCorrosion resistance nano-hybrid sol-gel coating onsteel sheetrdquo ISIJ International vol 51 no 3 pp 435ndash440 2011

[2] A S Khanna Introduction to High Temperature Oxidation andCorrosion ASM International 1997

[3] B V Jegdic J B Bajat J P Popic and V B Miskovic-StankovicldquoCorrosion stability of polyester coatings on steel pretreatedwith different iron-phosphate coatingsrdquo Progress in OrganicCoatings vol 70 no 2-3 pp 127ndash133 2011

[4] A M P Simoes R O Carbonari A R Di Sarli B del Amoand R Romagnoli ldquoAn environmentally acceptable primerfor galvanized steel formulation and evaluation by SVETrdquoCorrosion Science vol 53 no 1 pp 464ndash472 2011

[5] R Mafi S M Mirabedini M M Attar and S Moradian ldquoCurecharacterization of epoxy and polyester clear powder coatingsusing Differential Scanning Calorimetry (DSC) and DynamicMechanical Thermal Analysis (DMTA)rdquo Progress in OrganicCoatings vol 54 no 3 pp 164ndash169 2005

[6] D Maetens ldquoWeathering degradation mechanism in polyesterpowder coatingsrdquo Progress in Organic Coatings vol 58 no 2-3pp 172ndash179 2007

[7] J B Bajat J P Popic and V B Miskovic-Stankovic ldquoTheinfluence of aluminium surface pretreatment on the corrosionstability and adhesion of powder polyester coatingrdquo Progress inOrganic Coatings vol 69 no 4 pp 316ndash321 2010

[8] M A J Batista R P Moraes J C S Barbosa P C Oliveiraand A M Santos ldquoEffect of the polyester chemical structure onthe stability of polyester-melamine coatings when exposed toaccelerated weatheringrdquo Progress in Organic Coatings vol 71no 3 pp 265ndash273 2011

[9] F L Duivenvoorde J Laven and R Van der Linde ldquoDiblockcopolymer dispersants in polyester powder coatingsrdquo Progressin Organic Coatings vol 45 no 2-3 pp 127ndash137 2002

[10] S Radhakrishnan N Sonawane and C R Siju ldquoEpoxy powdercoatings containing polyaniline for enhanced corrosion protec-tionrdquo Progress in Organic Coatings vol 64 no 4 pp 383ndash3862009

[11] V C Malshe and G Waghoo ldquoWeathering study of epoxypaintsrdquo Progress in Organic Coatings vol 51 no 4 pp 267ndash2722004

[12] R Van der Linde E G Belder and D Y Perera ldquoEffect of phys-ical aging and thermal stress on the behavior of polyesterTGICpowder coatingsrdquo Progress in Organic Coatings vol 40 no 1ndash4pp 215ndash224 2000

[13] Technical Data Sheet of Ridoline 1352 BA of Ms HenkelChembond India Ltd

ISRN Corrosion 9

[14] Technical Data Sheet of Granodine of Ms Henkel ChembondIndia Ltd

[15] M Ozcan I Dehri and M Erbil ldquoEIS study of the effectof high levels of SO

2on the corrosion of polyester-coated

galvanised steel at different relative humiditiesrdquo Progress inOrganic Coatings vol 44 no 4 pp 279ndash285 2002

[16] R Naderi MM Attar andM HMoayed ldquoEIS examination ofmill scale on mild steel with polyester-epoxy powder coatingrdquoProgress in Organic Coatings vol 50 no 3 pp 162ndash165 2004

[17] R Mafi S M Mirabedini R Naderi and M M Attar ldquoEffectof curing characterization on the corrosion performance ofpolyester and polyesterepoxy powder coatingsrdquo CorrosionScience vol 50 no 12 pp 3280ndash3286 2008

[18] G Wuzella A Kandelbauer A R Mahendran and ATeischinger ldquoThermochemical and isoconversional kineticanalysis of a polyester-epoxy hybrid powder coating resin forwood based panel finishingrdquo Progress in Organic Coatings vol70 no 4 pp 186ndash191 2011

[19] M Barletta and A Gisario ldquoAn application of neural networksolutions to laser assisted paint stripping process of hybridepoxy-polyester coatings on aluminum substratesrdquo Surface andCoatings Technology vol 200 no 24 pp 6678ndash6689 2006

[20] R Naderi MM Attar andM HMoayed ldquoEIS examination ofmill scale on mild steel with polyester-epoxy powder coatingrdquoProgress in Organic Coatings vol 50 no 3 pp 162ndash165 2004

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

ISRN Corrosion 3

90120583m Electron image 1

(a)

0 1 2 3 4 5 6 7 8 9 10(keV)

Zn Zn Zn

Fe

Fe

Fe

C

Point 1Full-scale 5718 cts cursor minus0018 (353 cts)

(b)

0 1 2 3 4 5 6 7 8 9 10(keV)

Zn

Zn

Zn

OTi

Ti Ti

Fe Fe

FeC S

Point 3Full-scale 5718 cts cursor minus0018 (297 cts)

(c)

1 2 3 4 5 6 7 8 9 10(keV)

C

O

Fe

Fe FeZn

Zn Zn

Si

S

Ba

Ba

Ba

BaBaBa

Point 7

Full-scale 1613 cts cursor 0048 (306 cts)

(d)

Figure 2 (a) Cross-sectional SEM image of polyester powder-coated sheet (system-1) (b) (c) and (d) show EDX analysis of three respectivepoints 1 3 and 7 shown in (a)

The failure in the case of system-2 is from the glue itselfBut polyester coating system shows failure from interface andneeds only 4MPa force for any type of coating delaminationThis improvement in system-2 is due to the formation ofstrong and crack-free bonding of epoxy-polyester hybridwith steel substrate whereas polyester coatingweakly adhereswith the presence of internal crack as noticed from SEMphotograph and hence needs minimum force to delaminatefrom the surface as compared to epoxy-polyester coating [12ndash14]

33 Corrosion Resistance Property by ElectrochemicalImpedance Spectroscopy The electrochemical properties ofpolyester and epoxy-polyester on phosphate steel substratewere examined by EIS measurements The main role of EISin the characterization of an organic coating is to provideinformation about the properties of the protective system

such as defects adhesion and barrier properties as wellas to determine the onset and progression of corrosionprocess on metal substrate underneath the organic coatingFor the EIS measurements elements were selected througha model equivalent circuit (see Figure 4) to represents thesystems under study The systems undergo a charge transfercontrol according to this circuit where119877s represents solutionresistance 119877p coating resistance 119862c coating capacitance 119877ctcharge transfer resistance and 119862dl double layer capacitance

The Bode representations of the impedance data havebeen analyzed with VersaSTAT MC and ZSimpWin soft-ware of Princeton applied research Single slope in themidfrequency range shows the existence of a single timeconstant and the impedance data have been analyzed usingthe equivalent circuit

The impedance behavior of coating system-1 and coatingsystem-2 on steel substrate after initial study 144 h and 264 h

4 ISRN Corrosion

Table 1 Bond strength and nature of failure of galvanised coated substrate

System Bond strength (in MPa) Nature of failure Photographs

1 4 Failure from top coat and adhesive

2 5 Failure from top coat and adhesive

Table 2 Impedance parameters of wash primer and epoxy primer and top coated GI in 35 NaCl solution

Time hSystem-1 System-2

resistance (Ωcm2) resistance (Ωcm2)Initial 8835 times 106 1166 times 106

24 h 7203 times 104 1446 times 105

96 h 7367 1185 times 105

144 h 7166 1633 times 104

264 h 5504 1576 times 104

Table 3 Cross-hatch adhesion and pencil hardness results of system-1 and system-2

System Cross-hatch Percentage of area removed Pencil hardness (at 45∘)1 5B 0 7H2 5B 0 9H

of immersion in 35 NaCl solution is shown Figures 5(a)ndash5(c) with overlay The individual impedance behaviours withinitial time 24 h 96 h 144 h and 264 h are shown in Figures6 7 8 9 and 10 respectively The coating resistance andcapacitance values derived from these figures are given inTable 2 It is clear from Figures 6 7 8 9 and 10 and Table 2that in the beginning of experiment the coating resistance ofpolyester- and epoxy-polyester-coated samples is in the samerange Impedance of coating system-1 containing polyesterpowder coating shows 8835 times 106Ωcm2 against the 1166 times10

6Ωcm2 resistance of coating system-2The coating resistance value of system-1 decreases from8835times10

6Ωcm2 to 5504 times 103Ωcm2 after 264 h of immer-

sion whereas coating resistance value of system-2 decreasesfrom 1166 times 106Ωcm2 to 1633 times 104Ωcm2 in 144 h ofimmersion and to 1576 times 104Ωcm2 in 264 h of immersionGenerally the high impedance value of polyester-coatedsample shows a fast reduction in the first 24 h of immersiondue to the development of conductive pathways inside thefilm Comparatively a slow decrease in the impedance valuewas observed for the epoxy-polyester powder-coated steel

sheet followed by a small recovery after 24 h of immersion[15 16]

Penetration of water and movement of ionic speciesthrough the coating layermay be responsible for the observeddecrease in coating resistance value [17] Other reasonscould be a weaker ionic resistance and a lower-cross linkingdensity The dielectric constants of organic coating and waterare about 6 and 80 respectively at ambient temperatureTherefore permeation of a small amount of water throughthe coating can contribute to a relatively large change in thepore resistance It is known that diffusion of electrolyte waterand ions through the epoxy-polyester powder-coated sampleis much lower than the polyester powder-coated sample Thehigher corrosion protection by epoxy-polyester powder coat-ing on steel surface is due to the higher cross-linked densityof epoxy-polyester network comparingwith polyester systemin addition to high cross-linking density the additional freehydroxyl group that is ndashOH of epoxy-polyester coatingsystem (as compared to only polyester system) forms a strongbondwith phosphate and steel surfaceThehigh cross-linkingdensity and strong adhesion of epoxy group with phosphate

ISRN Corrosion 5

90 120583m Electron image 1

(a)

1 2 3 4 5 6 7 8 9 10

OMn

Mn

Mn

Fe

Fe

Fe

Zn

Zn

ZnNiNi Ni

P

S

Ba

Ba

Ba

BaBa

Ba

Point 6

(keV)Full-scale 785 cts cursor 0028 (359 cts)

(b)

1 2 3 4 5 6 7 8 9 10

Point 7

OFe

Fe

Fe

Zn

Zn

Zn

(keV)Full-scale 4830 cts cursor 0028 (359 cts)

(c)

1 2 3 4 5 6 7 8 9 10

Point 9

Fe

Fe

Fe

(keV)Full-scale 3118 cts cursor 0093 (196 cts)

(d)

Figure 3 (a) Cross sectional SEM image of epoxy-polyester powder-coated sheet (system-2) (b) (c) and (d) show EDX analysis of threerespective points 6 7 and 9 shown in (a)

119877s

119877p

119877ct

119862c

119862dl

Figure 4 Electrical equivalent circuit for the polyester and polyester-epoxy coating on the galvanised sheet

and steel substrate create an impermeable surface for waterand other corrosive ingredients on the coated surface[18ndash20]

34 Corrosion Resistance Property by Salt Sprat Test Per-formance of steel coated sheet after 1608 h exposure in saltspray chamber is shown in Figure 11 It can be seen that

epoxy-polyester powder-coated sample (system-2) is foundto have less white rust even after 1608 h of exposure insalt spray chamber (ASTM B 117) Whereas coating system-1 containing polyester powder coating fails after 1200 h ofexposure in salt spray chamber (ASTM B117) There are anumber of blisters in and around the edges of the scribe areain the case of system-1

6 ISRN Corrosion

25M

2M

15M

1M

500k

0

10m 100m 1 10 100 1k 10k 100 kFrequency (Hz)

System-1System-2

|119885|

(ohm

s)

(a)

10m 100m 1 10 100 1k 10k 100 kFrequency (Hz)

System-1System-2

15k

10k

5k

|119885|

(ohm

s)

(b)

10m 100m 1 10 100 1k 10k 100 kFrequency (Hz)

System-1System-2

200 k

150k

100 k

50k

0

|119885|

(ohm

s)

(c)

Figure 5 (a) (b) and (c) show EIS overlap diagram of samples immersed for time intervals beginning 144 h and 264 h respectively

5101520253035404550556065707580

Ang

le (d

eg)

1119864+07

1119864+06

1119864+05

1119864+0410000010000100010010101001

Frequency (Hz)

|119885|

(ohm

)

(a)

510152025303540455055

Ang

le (d

eg)

1119864+07

1119864+06

1119864+05

1119864+0410000010000100010010101001

Frequency (Hz)

minus50

|119885|

(ohm

)

(b)

Figure 6 Bode plot of (a) system-1 and (b) system-2 at initial time

35 Adhesion andHardness Cross hatch and pencil hardnessof system-1 and system-2 were performed according to theASTMD3359 and ASTMD3363-05 The results of these testsare shown in Table 3 which compares the adhesion andhardness properties of the two systems

The result of the x-cut adhesion test was satisfactory forboth the systems providing 5Bwith no observed flaking in thecross-cut area Therefore no adhesion losses appeared in anyinterfacesThe adhesion of primer to the steel surface and theadhesion of the top coats to the primer bothwere satisfactory

ISRN Corrosion 7

10000010000100010010101001Frequency (Hz)

024681012141618202224262830323436

Ang

le (d

eg)

100000

10000

1000

|119885|

(ohm

)

(a)

10000010000100010010101001Frequency (Hz)

05101520253035404550

1119864+06

1119864+05

1119864+04

1119864+03

Ang

le (d

eg)

|119885|

(ohm

)

(b)

Figure 7 Bode plot of (a) system-1 and (b) system-2 at 24 h time

10000010000100010010101001Frequency (Hz)

02468101214161820222426283032

Ang

le (d

eg)

100000

10000

1000

|119885|

(ohm

)

(a)

10000010000100010010101001Frequency (Hz)

Ang

le (d

eg)

1000000

100000

10000 051015202530354045

|119885|

(ohm

)

(b)

Figure 8 Bode plot of (a) system-1 (b) system-2 at 96 h time

Ang

le (d

eg)

10000010000100010010101001Frequency (Hz)

10000

1000 01234567891011121314

|119885|

(ohm

)

(a)

051015202530354045

Ang

le (d

eg)

10000010000100010010101001Frequency (Hz)

100000

10000

|119885|

(ohm

)

(b)

Figure 9 Bode plot of (a) system-1 and (b) system-2 at 144 h time

4 Conclusion

The powder coatings protect galvanised steel substrates bythe introduction of a barrier layer with relatively high ohmicresistance between the metallic substrate and the corrosiveenvironment Also it is indicated that the cross-link densityappears only to affect ionic conductivity of the film and

due to the higher cross-linked density of epoxy-polyesternetwork comparing with polyester system the permeabilityof water and ions through the coating film becomes lessand it leads to a more impervious film with a more resistantstructure to corrosion It is indicated that the polyester film ismore porous due to the less cross-link density of cured poly-mer comparedwith epoxy-polyester powder-coated samples

8 ISRN Corrosion

0510152025303540

Ang

le (d

eg)

100000

100000

10000100010010101001Frequency (Hz)

10000

1000

|119885|

(ohm

)

(a)

051015202530354045

Ang

le (d

eg)

100000

10000010000100010010101001Frequency (Hz)

10000

1000000

minus5

|119885|

(ohm

)

(b)

Figure 10 Bode plot of (a) system-1 and (b) system-2 at 264 h time

(a) System 1 (b) System 2

Figure 11 Salt spray photographs of coated substrate (a) polyester-coated sample after 1200 h of salt spray test (b) epoxy-polyester-coated sample after 1608 h of the salt spray test

SEM micrograph and bond strength suggest that epoxy-polyester coating is more firmly adherent to the phosphatesubstrate than polyester coating due tomore hydroxyl groupsin epoxy-polyester bonding with phosphate substrate Pro-tective properties of fully cured organic coatings on metallicsubstrate may be attributed to a barrier andor an activeinhibition mechanism

Acknowledgment

The authors would like to thank the staff of the corrosion labfor helping them during experiments

References

[1] A K Guin S Nayak T K Rout N Bandyopadhyay and D KSengupta ldquoCorrosion resistance nano-hybrid sol-gel coating onsteel sheetrdquo ISIJ International vol 51 no 3 pp 435ndash440 2011

[2] A S Khanna Introduction to High Temperature Oxidation andCorrosion ASM International 1997

[3] B V Jegdic J B Bajat J P Popic and V B Miskovic-StankovicldquoCorrosion stability of polyester coatings on steel pretreatedwith different iron-phosphate coatingsrdquo Progress in OrganicCoatings vol 70 no 2-3 pp 127ndash133 2011

[4] A M P Simoes R O Carbonari A R Di Sarli B del Amoand R Romagnoli ldquoAn environmentally acceptable primerfor galvanized steel formulation and evaluation by SVETrdquoCorrosion Science vol 53 no 1 pp 464ndash472 2011

[5] R Mafi S M Mirabedini M M Attar and S Moradian ldquoCurecharacterization of epoxy and polyester clear powder coatingsusing Differential Scanning Calorimetry (DSC) and DynamicMechanical Thermal Analysis (DMTA)rdquo Progress in OrganicCoatings vol 54 no 3 pp 164ndash169 2005

[6] D Maetens ldquoWeathering degradation mechanism in polyesterpowder coatingsrdquo Progress in Organic Coatings vol 58 no 2-3pp 172ndash179 2007

[7] J B Bajat J P Popic and V B Miskovic-Stankovic ldquoTheinfluence of aluminium surface pretreatment on the corrosionstability and adhesion of powder polyester coatingrdquo Progress inOrganic Coatings vol 69 no 4 pp 316ndash321 2010

[8] M A J Batista R P Moraes J C S Barbosa P C Oliveiraand A M Santos ldquoEffect of the polyester chemical structure onthe stability of polyester-melamine coatings when exposed toaccelerated weatheringrdquo Progress in Organic Coatings vol 71no 3 pp 265ndash273 2011

[9] F L Duivenvoorde J Laven and R Van der Linde ldquoDiblockcopolymer dispersants in polyester powder coatingsrdquo Progressin Organic Coatings vol 45 no 2-3 pp 127ndash137 2002

[10] S Radhakrishnan N Sonawane and C R Siju ldquoEpoxy powdercoatings containing polyaniline for enhanced corrosion protec-tionrdquo Progress in Organic Coatings vol 64 no 4 pp 383ndash3862009

[11] V C Malshe and G Waghoo ldquoWeathering study of epoxypaintsrdquo Progress in Organic Coatings vol 51 no 4 pp 267ndash2722004

[12] R Van der Linde E G Belder and D Y Perera ldquoEffect of phys-ical aging and thermal stress on the behavior of polyesterTGICpowder coatingsrdquo Progress in Organic Coatings vol 40 no 1ndash4pp 215ndash224 2000

[13] Technical Data Sheet of Ridoline 1352 BA of Ms HenkelChembond India Ltd

ISRN Corrosion 9

[14] Technical Data Sheet of Granodine of Ms Henkel ChembondIndia Ltd

[15] M Ozcan I Dehri and M Erbil ldquoEIS study of the effectof high levels of SO

2on the corrosion of polyester-coated

galvanised steel at different relative humiditiesrdquo Progress inOrganic Coatings vol 44 no 4 pp 279ndash285 2002

[16] R Naderi MM Attar andM HMoayed ldquoEIS examination ofmill scale on mild steel with polyester-epoxy powder coatingrdquoProgress in Organic Coatings vol 50 no 3 pp 162ndash165 2004

[17] R Mafi S M Mirabedini R Naderi and M M Attar ldquoEffectof curing characterization on the corrosion performance ofpolyester and polyesterepoxy powder coatingsrdquo CorrosionScience vol 50 no 12 pp 3280ndash3286 2008

[18] G Wuzella A Kandelbauer A R Mahendran and ATeischinger ldquoThermochemical and isoconversional kineticanalysis of a polyester-epoxy hybrid powder coating resin forwood based panel finishingrdquo Progress in Organic Coatings vol70 no 4 pp 186ndash191 2011

[19] M Barletta and A Gisario ldquoAn application of neural networksolutions to laser assisted paint stripping process of hybridepoxy-polyester coatings on aluminum substratesrdquo Surface andCoatings Technology vol 200 no 24 pp 6678ndash6689 2006

[20] R Naderi MM Attar andM HMoayed ldquoEIS examination ofmill scale on mild steel with polyester-epoxy powder coatingrdquoProgress in Organic Coatings vol 50 no 3 pp 162ndash165 2004

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

4 ISRN Corrosion

Table 1 Bond strength and nature of failure of galvanised coated substrate

System Bond strength (in MPa) Nature of failure Photographs

1 4 Failure from top coat and adhesive

2 5 Failure from top coat and adhesive

Table 2 Impedance parameters of wash primer and epoxy primer and top coated GI in 35 NaCl solution

Time hSystem-1 System-2

resistance (Ωcm2) resistance (Ωcm2)Initial 8835 times 106 1166 times 106

24 h 7203 times 104 1446 times 105

96 h 7367 1185 times 105

144 h 7166 1633 times 104

264 h 5504 1576 times 104

Table 3 Cross-hatch adhesion and pencil hardness results of system-1 and system-2

System Cross-hatch Percentage of area removed Pencil hardness (at 45∘)1 5B 0 7H2 5B 0 9H

of immersion in 35 NaCl solution is shown Figures 5(a)ndash5(c) with overlay The individual impedance behaviours withinitial time 24 h 96 h 144 h and 264 h are shown in Figures6 7 8 9 and 10 respectively The coating resistance andcapacitance values derived from these figures are given inTable 2 It is clear from Figures 6 7 8 9 and 10 and Table 2that in the beginning of experiment the coating resistance ofpolyester- and epoxy-polyester-coated samples is in the samerange Impedance of coating system-1 containing polyesterpowder coating shows 8835 times 106Ωcm2 against the 1166 times10

6Ωcm2 resistance of coating system-2The coating resistance value of system-1 decreases from8835times10

6Ωcm2 to 5504 times 103Ωcm2 after 264 h of immer-

sion whereas coating resistance value of system-2 decreasesfrom 1166 times 106Ωcm2 to 1633 times 104Ωcm2 in 144 h ofimmersion and to 1576 times 104Ωcm2 in 264 h of immersionGenerally the high impedance value of polyester-coatedsample shows a fast reduction in the first 24 h of immersiondue to the development of conductive pathways inside thefilm Comparatively a slow decrease in the impedance valuewas observed for the epoxy-polyester powder-coated steel

sheet followed by a small recovery after 24 h of immersion[15 16]

Penetration of water and movement of ionic speciesthrough the coating layermay be responsible for the observeddecrease in coating resistance value [17] Other reasonscould be a weaker ionic resistance and a lower-cross linkingdensity The dielectric constants of organic coating and waterare about 6 and 80 respectively at ambient temperatureTherefore permeation of a small amount of water throughthe coating can contribute to a relatively large change in thepore resistance It is known that diffusion of electrolyte waterand ions through the epoxy-polyester powder-coated sampleis much lower than the polyester powder-coated sample Thehigher corrosion protection by epoxy-polyester powder coat-ing on steel surface is due to the higher cross-linked densityof epoxy-polyester network comparingwith polyester systemin addition to high cross-linking density the additional freehydroxyl group that is ndashOH of epoxy-polyester coatingsystem (as compared to only polyester system) forms a strongbondwith phosphate and steel surfaceThehigh cross-linkingdensity and strong adhesion of epoxy group with phosphate

ISRN Corrosion 5

90 120583m Electron image 1

(a)

1 2 3 4 5 6 7 8 9 10

OMn

Mn

Mn

Fe

Fe

Fe

Zn

Zn

ZnNiNi Ni

P

S

Ba

Ba

Ba

BaBa

Ba

Point 6

(keV)Full-scale 785 cts cursor 0028 (359 cts)

(b)

1 2 3 4 5 6 7 8 9 10

Point 7

OFe

Fe

Fe

Zn

Zn

Zn

(keV)Full-scale 4830 cts cursor 0028 (359 cts)

(c)

1 2 3 4 5 6 7 8 9 10

Point 9

Fe

Fe

Fe

(keV)Full-scale 3118 cts cursor 0093 (196 cts)

(d)

Figure 3 (a) Cross sectional SEM image of epoxy-polyester powder-coated sheet (system-2) (b) (c) and (d) show EDX analysis of threerespective points 6 7 and 9 shown in (a)

119877s

119877p

119877ct

119862c

119862dl

Figure 4 Electrical equivalent circuit for the polyester and polyester-epoxy coating on the galvanised sheet

and steel substrate create an impermeable surface for waterand other corrosive ingredients on the coated surface[18ndash20]

34 Corrosion Resistance Property by Salt Sprat Test Per-formance of steel coated sheet after 1608 h exposure in saltspray chamber is shown in Figure 11 It can be seen that

epoxy-polyester powder-coated sample (system-2) is foundto have less white rust even after 1608 h of exposure insalt spray chamber (ASTM B 117) Whereas coating system-1 containing polyester powder coating fails after 1200 h ofexposure in salt spray chamber (ASTM B117) There are anumber of blisters in and around the edges of the scribe areain the case of system-1

6 ISRN Corrosion

25M

2M

15M

1M

500k

0

10m 100m 1 10 100 1k 10k 100 kFrequency (Hz)

System-1System-2

|119885|

(ohm

s)

(a)

10m 100m 1 10 100 1k 10k 100 kFrequency (Hz)

System-1System-2

15k

10k

5k

|119885|

(ohm

s)

(b)

10m 100m 1 10 100 1k 10k 100 kFrequency (Hz)

System-1System-2

200 k

150k

100 k

50k

0

|119885|

(ohm

s)

(c)

Figure 5 (a) (b) and (c) show EIS overlap diagram of samples immersed for time intervals beginning 144 h and 264 h respectively

5101520253035404550556065707580

Ang

le (d

eg)

1119864+07

1119864+06

1119864+05

1119864+0410000010000100010010101001

Frequency (Hz)

|119885|

(ohm

)

(a)

510152025303540455055

Ang

le (d

eg)

1119864+07

1119864+06

1119864+05

1119864+0410000010000100010010101001

Frequency (Hz)

minus50

|119885|

(ohm

)

(b)

Figure 6 Bode plot of (a) system-1 and (b) system-2 at initial time

35 Adhesion andHardness Cross hatch and pencil hardnessof system-1 and system-2 were performed according to theASTMD3359 and ASTMD3363-05 The results of these testsare shown in Table 3 which compares the adhesion andhardness properties of the two systems

The result of the x-cut adhesion test was satisfactory forboth the systems providing 5Bwith no observed flaking in thecross-cut area Therefore no adhesion losses appeared in anyinterfacesThe adhesion of primer to the steel surface and theadhesion of the top coats to the primer bothwere satisfactory

ISRN Corrosion 7

10000010000100010010101001Frequency (Hz)

024681012141618202224262830323436

Ang

le (d

eg)

100000

10000

1000

|119885|

(ohm

)

(a)

10000010000100010010101001Frequency (Hz)

05101520253035404550

1119864+06

1119864+05

1119864+04

1119864+03

Ang

le (d

eg)

|119885|

(ohm

)

(b)

Figure 7 Bode plot of (a) system-1 and (b) system-2 at 24 h time

10000010000100010010101001Frequency (Hz)

02468101214161820222426283032

Ang

le (d

eg)

100000

10000

1000

|119885|

(ohm

)

(a)

10000010000100010010101001Frequency (Hz)

Ang

le (d

eg)

1000000

100000

10000 051015202530354045

|119885|

(ohm

)

(b)

Figure 8 Bode plot of (a) system-1 (b) system-2 at 96 h time

Ang

le (d

eg)

10000010000100010010101001Frequency (Hz)

10000

1000 01234567891011121314

|119885|

(ohm

)

(a)

051015202530354045

Ang

le (d

eg)

10000010000100010010101001Frequency (Hz)

100000

10000

|119885|

(ohm

)

(b)

Figure 9 Bode plot of (a) system-1 and (b) system-2 at 144 h time

4 Conclusion

The powder coatings protect galvanised steel substrates bythe introduction of a barrier layer with relatively high ohmicresistance between the metallic substrate and the corrosiveenvironment Also it is indicated that the cross-link densityappears only to affect ionic conductivity of the film and

due to the higher cross-linked density of epoxy-polyesternetwork comparing with polyester system the permeabilityof water and ions through the coating film becomes lessand it leads to a more impervious film with a more resistantstructure to corrosion It is indicated that the polyester film ismore porous due to the less cross-link density of cured poly-mer comparedwith epoxy-polyester powder-coated samples

8 ISRN Corrosion

0510152025303540

Ang

le (d

eg)

100000

100000

10000100010010101001Frequency (Hz)

10000

1000

|119885|

(ohm

)

(a)

051015202530354045

Ang

le (d

eg)

100000

10000010000100010010101001Frequency (Hz)

10000

1000000

minus5

|119885|

(ohm

)

(b)

Figure 10 Bode plot of (a) system-1 and (b) system-2 at 264 h time

(a) System 1 (b) System 2

Figure 11 Salt spray photographs of coated substrate (a) polyester-coated sample after 1200 h of salt spray test (b) epoxy-polyester-coated sample after 1608 h of the salt spray test

SEM micrograph and bond strength suggest that epoxy-polyester coating is more firmly adherent to the phosphatesubstrate than polyester coating due tomore hydroxyl groupsin epoxy-polyester bonding with phosphate substrate Pro-tective properties of fully cured organic coatings on metallicsubstrate may be attributed to a barrier andor an activeinhibition mechanism

Acknowledgment

The authors would like to thank the staff of the corrosion labfor helping them during experiments

References

[1] A K Guin S Nayak T K Rout N Bandyopadhyay and D KSengupta ldquoCorrosion resistance nano-hybrid sol-gel coating onsteel sheetrdquo ISIJ International vol 51 no 3 pp 435ndash440 2011

[2] A S Khanna Introduction to High Temperature Oxidation andCorrosion ASM International 1997

[3] B V Jegdic J B Bajat J P Popic and V B Miskovic-StankovicldquoCorrosion stability of polyester coatings on steel pretreatedwith different iron-phosphate coatingsrdquo Progress in OrganicCoatings vol 70 no 2-3 pp 127ndash133 2011

[4] A M P Simoes R O Carbonari A R Di Sarli B del Amoand R Romagnoli ldquoAn environmentally acceptable primerfor galvanized steel formulation and evaluation by SVETrdquoCorrosion Science vol 53 no 1 pp 464ndash472 2011

[5] R Mafi S M Mirabedini M M Attar and S Moradian ldquoCurecharacterization of epoxy and polyester clear powder coatingsusing Differential Scanning Calorimetry (DSC) and DynamicMechanical Thermal Analysis (DMTA)rdquo Progress in OrganicCoatings vol 54 no 3 pp 164ndash169 2005

[6] D Maetens ldquoWeathering degradation mechanism in polyesterpowder coatingsrdquo Progress in Organic Coatings vol 58 no 2-3pp 172ndash179 2007

[7] J B Bajat J P Popic and V B Miskovic-Stankovic ldquoTheinfluence of aluminium surface pretreatment on the corrosionstability and adhesion of powder polyester coatingrdquo Progress inOrganic Coatings vol 69 no 4 pp 316ndash321 2010

[8] M A J Batista R P Moraes J C S Barbosa P C Oliveiraand A M Santos ldquoEffect of the polyester chemical structure onthe stability of polyester-melamine coatings when exposed toaccelerated weatheringrdquo Progress in Organic Coatings vol 71no 3 pp 265ndash273 2011

[9] F L Duivenvoorde J Laven and R Van der Linde ldquoDiblockcopolymer dispersants in polyester powder coatingsrdquo Progressin Organic Coatings vol 45 no 2-3 pp 127ndash137 2002

[10] S Radhakrishnan N Sonawane and C R Siju ldquoEpoxy powdercoatings containing polyaniline for enhanced corrosion protec-tionrdquo Progress in Organic Coatings vol 64 no 4 pp 383ndash3862009

[11] V C Malshe and G Waghoo ldquoWeathering study of epoxypaintsrdquo Progress in Organic Coatings vol 51 no 4 pp 267ndash2722004

[12] R Van der Linde E G Belder and D Y Perera ldquoEffect of phys-ical aging and thermal stress on the behavior of polyesterTGICpowder coatingsrdquo Progress in Organic Coatings vol 40 no 1ndash4pp 215ndash224 2000

[13] Technical Data Sheet of Ridoline 1352 BA of Ms HenkelChembond India Ltd

ISRN Corrosion 9

[14] Technical Data Sheet of Granodine of Ms Henkel ChembondIndia Ltd

[15] M Ozcan I Dehri and M Erbil ldquoEIS study of the effectof high levels of SO

2on the corrosion of polyester-coated

galvanised steel at different relative humiditiesrdquo Progress inOrganic Coatings vol 44 no 4 pp 279ndash285 2002

[16] R Naderi MM Attar andM HMoayed ldquoEIS examination ofmill scale on mild steel with polyester-epoxy powder coatingrdquoProgress in Organic Coatings vol 50 no 3 pp 162ndash165 2004

[17] R Mafi S M Mirabedini R Naderi and M M Attar ldquoEffectof curing characterization on the corrosion performance ofpolyester and polyesterepoxy powder coatingsrdquo CorrosionScience vol 50 no 12 pp 3280ndash3286 2008

[18] G Wuzella A Kandelbauer A R Mahendran and ATeischinger ldquoThermochemical and isoconversional kineticanalysis of a polyester-epoxy hybrid powder coating resin forwood based panel finishingrdquo Progress in Organic Coatings vol70 no 4 pp 186ndash191 2011

[19] M Barletta and A Gisario ldquoAn application of neural networksolutions to laser assisted paint stripping process of hybridepoxy-polyester coatings on aluminum substratesrdquo Surface andCoatings Technology vol 200 no 24 pp 6678ndash6689 2006

[20] R Naderi MM Attar andM HMoayed ldquoEIS examination ofmill scale on mild steel with polyester-epoxy powder coatingrdquoProgress in Organic Coatings vol 50 no 3 pp 162ndash165 2004

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

ISRN Corrosion 5

90 120583m Electron image 1

(a)

1 2 3 4 5 6 7 8 9 10

OMn

Mn

Mn

Fe

Fe

Fe

Zn

Zn

ZnNiNi Ni

P

S

Ba

Ba

Ba

BaBa

Ba

Point 6

(keV)Full-scale 785 cts cursor 0028 (359 cts)

(b)

1 2 3 4 5 6 7 8 9 10

Point 7

OFe

Fe

Fe

Zn

Zn

Zn

(keV)Full-scale 4830 cts cursor 0028 (359 cts)

(c)

1 2 3 4 5 6 7 8 9 10

Point 9

Fe

Fe

Fe

(keV)Full-scale 3118 cts cursor 0093 (196 cts)

(d)

Figure 3 (a) Cross sectional SEM image of epoxy-polyester powder-coated sheet (system-2) (b) (c) and (d) show EDX analysis of threerespective points 6 7 and 9 shown in (a)

119877s

119877p

119877ct

119862c

119862dl

Figure 4 Electrical equivalent circuit for the polyester and polyester-epoxy coating on the galvanised sheet

and steel substrate create an impermeable surface for waterand other corrosive ingredients on the coated surface[18ndash20]

34 Corrosion Resistance Property by Salt Sprat Test Per-formance of steel coated sheet after 1608 h exposure in saltspray chamber is shown in Figure 11 It can be seen that

epoxy-polyester powder-coated sample (system-2) is foundto have less white rust even after 1608 h of exposure insalt spray chamber (ASTM B 117) Whereas coating system-1 containing polyester powder coating fails after 1200 h ofexposure in salt spray chamber (ASTM B117) There are anumber of blisters in and around the edges of the scribe areain the case of system-1

6 ISRN Corrosion

25M

2M

15M

1M

500k

0

10m 100m 1 10 100 1k 10k 100 kFrequency (Hz)

System-1System-2

|119885|

(ohm

s)

(a)

10m 100m 1 10 100 1k 10k 100 kFrequency (Hz)

System-1System-2

15k

10k

5k

|119885|

(ohm

s)

(b)

10m 100m 1 10 100 1k 10k 100 kFrequency (Hz)

System-1System-2

200 k

150k

100 k

50k

0

|119885|

(ohm

s)

(c)

Figure 5 (a) (b) and (c) show EIS overlap diagram of samples immersed for time intervals beginning 144 h and 264 h respectively

5101520253035404550556065707580

Ang

le (d

eg)

1119864+07

1119864+06

1119864+05

1119864+0410000010000100010010101001

Frequency (Hz)

|119885|

(ohm

)

(a)

510152025303540455055

Ang

le (d

eg)

1119864+07

1119864+06

1119864+05

1119864+0410000010000100010010101001

Frequency (Hz)

minus50

|119885|

(ohm

)

(b)

Figure 6 Bode plot of (a) system-1 and (b) system-2 at initial time

35 Adhesion andHardness Cross hatch and pencil hardnessof system-1 and system-2 were performed according to theASTMD3359 and ASTMD3363-05 The results of these testsare shown in Table 3 which compares the adhesion andhardness properties of the two systems

The result of the x-cut adhesion test was satisfactory forboth the systems providing 5Bwith no observed flaking in thecross-cut area Therefore no adhesion losses appeared in anyinterfacesThe adhesion of primer to the steel surface and theadhesion of the top coats to the primer bothwere satisfactory

ISRN Corrosion 7

10000010000100010010101001Frequency (Hz)

024681012141618202224262830323436

Ang

le (d

eg)

100000

10000

1000

|119885|

(ohm

)

(a)

10000010000100010010101001Frequency (Hz)

05101520253035404550

1119864+06

1119864+05

1119864+04

1119864+03

Ang

le (d

eg)

|119885|

(ohm

)

(b)

Figure 7 Bode plot of (a) system-1 and (b) system-2 at 24 h time

10000010000100010010101001Frequency (Hz)

02468101214161820222426283032

Ang

le (d

eg)

100000

10000

1000

|119885|

(ohm

)

(a)

10000010000100010010101001Frequency (Hz)

Ang

le (d

eg)

1000000

100000

10000 051015202530354045

|119885|

(ohm

)

(b)

Figure 8 Bode plot of (a) system-1 (b) system-2 at 96 h time

Ang

le (d

eg)

10000010000100010010101001Frequency (Hz)

10000

1000 01234567891011121314

|119885|

(ohm

)

(a)

051015202530354045

Ang

le (d

eg)

10000010000100010010101001Frequency (Hz)

100000

10000

|119885|

(ohm

)

(b)

Figure 9 Bode plot of (a) system-1 and (b) system-2 at 144 h time

4 Conclusion

The powder coatings protect galvanised steel substrates bythe introduction of a barrier layer with relatively high ohmicresistance between the metallic substrate and the corrosiveenvironment Also it is indicated that the cross-link densityappears only to affect ionic conductivity of the film and

due to the higher cross-linked density of epoxy-polyesternetwork comparing with polyester system the permeabilityof water and ions through the coating film becomes lessand it leads to a more impervious film with a more resistantstructure to corrosion It is indicated that the polyester film ismore porous due to the less cross-link density of cured poly-mer comparedwith epoxy-polyester powder-coated samples

8 ISRN Corrosion

0510152025303540

Ang

le (d

eg)

100000

100000

10000100010010101001Frequency (Hz)

10000

1000

|119885|

(ohm

)

(a)

051015202530354045

Ang

le (d

eg)

100000

10000010000100010010101001Frequency (Hz)

10000

1000000

minus5

|119885|

(ohm

)

(b)

Figure 10 Bode plot of (a) system-1 and (b) system-2 at 264 h time

(a) System 1 (b) System 2

Figure 11 Salt spray photographs of coated substrate (a) polyester-coated sample after 1200 h of salt spray test (b) epoxy-polyester-coated sample after 1608 h of the salt spray test

SEM micrograph and bond strength suggest that epoxy-polyester coating is more firmly adherent to the phosphatesubstrate than polyester coating due tomore hydroxyl groupsin epoxy-polyester bonding with phosphate substrate Pro-tective properties of fully cured organic coatings on metallicsubstrate may be attributed to a barrier andor an activeinhibition mechanism

Acknowledgment

The authors would like to thank the staff of the corrosion labfor helping them during experiments

References

[1] A K Guin S Nayak T K Rout N Bandyopadhyay and D KSengupta ldquoCorrosion resistance nano-hybrid sol-gel coating onsteel sheetrdquo ISIJ International vol 51 no 3 pp 435ndash440 2011

[2] A S Khanna Introduction to High Temperature Oxidation andCorrosion ASM International 1997

[3] B V Jegdic J B Bajat J P Popic and V B Miskovic-StankovicldquoCorrosion stability of polyester coatings on steel pretreatedwith different iron-phosphate coatingsrdquo Progress in OrganicCoatings vol 70 no 2-3 pp 127ndash133 2011

[4] A M P Simoes R O Carbonari A R Di Sarli B del Amoand R Romagnoli ldquoAn environmentally acceptable primerfor galvanized steel formulation and evaluation by SVETrdquoCorrosion Science vol 53 no 1 pp 464ndash472 2011

[5] R Mafi S M Mirabedini M M Attar and S Moradian ldquoCurecharacterization of epoxy and polyester clear powder coatingsusing Differential Scanning Calorimetry (DSC) and DynamicMechanical Thermal Analysis (DMTA)rdquo Progress in OrganicCoatings vol 54 no 3 pp 164ndash169 2005

[6] D Maetens ldquoWeathering degradation mechanism in polyesterpowder coatingsrdquo Progress in Organic Coatings vol 58 no 2-3pp 172ndash179 2007

[7] J B Bajat J P Popic and V B Miskovic-Stankovic ldquoTheinfluence of aluminium surface pretreatment on the corrosionstability and adhesion of powder polyester coatingrdquo Progress inOrganic Coatings vol 69 no 4 pp 316ndash321 2010

[8] M A J Batista R P Moraes J C S Barbosa P C Oliveiraand A M Santos ldquoEffect of the polyester chemical structure onthe stability of polyester-melamine coatings when exposed toaccelerated weatheringrdquo Progress in Organic Coatings vol 71no 3 pp 265ndash273 2011

[9] F L Duivenvoorde J Laven and R Van der Linde ldquoDiblockcopolymer dispersants in polyester powder coatingsrdquo Progressin Organic Coatings vol 45 no 2-3 pp 127ndash137 2002

[10] S Radhakrishnan N Sonawane and C R Siju ldquoEpoxy powdercoatings containing polyaniline for enhanced corrosion protec-tionrdquo Progress in Organic Coatings vol 64 no 4 pp 383ndash3862009

[11] V C Malshe and G Waghoo ldquoWeathering study of epoxypaintsrdquo Progress in Organic Coatings vol 51 no 4 pp 267ndash2722004

[12] R Van der Linde E G Belder and D Y Perera ldquoEffect of phys-ical aging and thermal stress on the behavior of polyesterTGICpowder coatingsrdquo Progress in Organic Coatings vol 40 no 1ndash4pp 215ndash224 2000

[13] Technical Data Sheet of Ridoline 1352 BA of Ms HenkelChembond India Ltd

ISRN Corrosion 9

[14] Technical Data Sheet of Granodine of Ms Henkel ChembondIndia Ltd

[15] M Ozcan I Dehri and M Erbil ldquoEIS study of the effectof high levels of SO

2on the corrosion of polyester-coated

galvanised steel at different relative humiditiesrdquo Progress inOrganic Coatings vol 44 no 4 pp 279ndash285 2002

[16] R Naderi MM Attar andM HMoayed ldquoEIS examination ofmill scale on mild steel with polyester-epoxy powder coatingrdquoProgress in Organic Coatings vol 50 no 3 pp 162ndash165 2004

[17] R Mafi S M Mirabedini R Naderi and M M Attar ldquoEffectof curing characterization on the corrosion performance ofpolyester and polyesterepoxy powder coatingsrdquo CorrosionScience vol 50 no 12 pp 3280ndash3286 2008

[18] G Wuzella A Kandelbauer A R Mahendran and ATeischinger ldquoThermochemical and isoconversional kineticanalysis of a polyester-epoxy hybrid powder coating resin forwood based panel finishingrdquo Progress in Organic Coatings vol70 no 4 pp 186ndash191 2011

[19] M Barletta and A Gisario ldquoAn application of neural networksolutions to laser assisted paint stripping process of hybridepoxy-polyester coatings on aluminum substratesrdquo Surface andCoatings Technology vol 200 no 24 pp 6678ndash6689 2006

[20] R Naderi MM Attar andM HMoayed ldquoEIS examination ofmill scale on mild steel with polyester-epoxy powder coatingrdquoProgress in Organic Coatings vol 50 no 3 pp 162ndash165 2004

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

6 ISRN Corrosion

25M

2M

15M

1M

500k

0

10m 100m 1 10 100 1k 10k 100 kFrequency (Hz)

System-1System-2

|119885|

(ohm

s)

(a)

10m 100m 1 10 100 1k 10k 100 kFrequency (Hz)

System-1System-2

15k

10k

5k

|119885|

(ohm

s)

(b)

10m 100m 1 10 100 1k 10k 100 kFrequency (Hz)

System-1System-2

200 k

150k

100 k

50k

0

|119885|

(ohm

s)

(c)

Figure 5 (a) (b) and (c) show EIS overlap diagram of samples immersed for time intervals beginning 144 h and 264 h respectively

5101520253035404550556065707580

Ang

le (d

eg)

1119864+07

1119864+06

1119864+05

1119864+0410000010000100010010101001

Frequency (Hz)

|119885|

(ohm

)

(a)

510152025303540455055

Ang

le (d

eg)

1119864+07

1119864+06

1119864+05

1119864+0410000010000100010010101001

Frequency (Hz)

minus50

|119885|

(ohm

)

(b)

Figure 6 Bode plot of (a) system-1 and (b) system-2 at initial time

35 Adhesion andHardness Cross hatch and pencil hardnessof system-1 and system-2 were performed according to theASTMD3359 and ASTMD3363-05 The results of these testsare shown in Table 3 which compares the adhesion andhardness properties of the two systems

The result of the x-cut adhesion test was satisfactory forboth the systems providing 5Bwith no observed flaking in thecross-cut area Therefore no adhesion losses appeared in anyinterfacesThe adhesion of primer to the steel surface and theadhesion of the top coats to the primer bothwere satisfactory

ISRN Corrosion 7

10000010000100010010101001Frequency (Hz)

024681012141618202224262830323436

Ang

le (d

eg)

100000

10000

1000

|119885|

(ohm

)

(a)

10000010000100010010101001Frequency (Hz)

05101520253035404550

1119864+06

1119864+05

1119864+04

1119864+03

Ang

le (d

eg)

|119885|

(ohm

)

(b)

Figure 7 Bode plot of (a) system-1 and (b) system-2 at 24 h time

10000010000100010010101001Frequency (Hz)

02468101214161820222426283032

Ang

le (d

eg)

100000

10000

1000

|119885|

(ohm

)

(a)

10000010000100010010101001Frequency (Hz)

Ang

le (d

eg)

1000000

100000

10000 051015202530354045

|119885|

(ohm

)

(b)

Figure 8 Bode plot of (a) system-1 (b) system-2 at 96 h time

Ang

le (d

eg)

10000010000100010010101001Frequency (Hz)

10000

1000 01234567891011121314

|119885|

(ohm

)

(a)

051015202530354045

Ang

le (d

eg)

10000010000100010010101001Frequency (Hz)

100000

10000

|119885|

(ohm

)

(b)

Figure 9 Bode plot of (a) system-1 and (b) system-2 at 144 h time

4 Conclusion

The powder coatings protect galvanised steel substrates bythe introduction of a barrier layer with relatively high ohmicresistance between the metallic substrate and the corrosiveenvironment Also it is indicated that the cross-link densityappears only to affect ionic conductivity of the film and

due to the higher cross-linked density of epoxy-polyesternetwork comparing with polyester system the permeabilityof water and ions through the coating film becomes lessand it leads to a more impervious film with a more resistantstructure to corrosion It is indicated that the polyester film ismore porous due to the less cross-link density of cured poly-mer comparedwith epoxy-polyester powder-coated samples

8 ISRN Corrosion

0510152025303540

Ang

le (d

eg)

100000

100000

10000100010010101001Frequency (Hz)

10000

1000

|119885|

(ohm

)

(a)

051015202530354045

Ang

le (d

eg)

100000

10000010000100010010101001Frequency (Hz)

10000

1000000

minus5

|119885|

(ohm

)

(b)

Figure 10 Bode plot of (a) system-1 and (b) system-2 at 264 h time

(a) System 1 (b) System 2

Figure 11 Salt spray photographs of coated substrate (a) polyester-coated sample after 1200 h of salt spray test (b) epoxy-polyester-coated sample after 1608 h of the salt spray test

SEM micrograph and bond strength suggest that epoxy-polyester coating is more firmly adherent to the phosphatesubstrate than polyester coating due tomore hydroxyl groupsin epoxy-polyester bonding with phosphate substrate Pro-tective properties of fully cured organic coatings on metallicsubstrate may be attributed to a barrier andor an activeinhibition mechanism

Acknowledgment

The authors would like to thank the staff of the corrosion labfor helping them during experiments

References

[1] A K Guin S Nayak T K Rout N Bandyopadhyay and D KSengupta ldquoCorrosion resistance nano-hybrid sol-gel coating onsteel sheetrdquo ISIJ International vol 51 no 3 pp 435ndash440 2011

[2] A S Khanna Introduction to High Temperature Oxidation andCorrosion ASM International 1997

[3] B V Jegdic J B Bajat J P Popic and V B Miskovic-StankovicldquoCorrosion stability of polyester coatings on steel pretreatedwith different iron-phosphate coatingsrdquo Progress in OrganicCoatings vol 70 no 2-3 pp 127ndash133 2011

[4] A M P Simoes R O Carbonari A R Di Sarli B del Amoand R Romagnoli ldquoAn environmentally acceptable primerfor galvanized steel formulation and evaluation by SVETrdquoCorrosion Science vol 53 no 1 pp 464ndash472 2011

[5] R Mafi S M Mirabedini M M Attar and S Moradian ldquoCurecharacterization of epoxy and polyester clear powder coatingsusing Differential Scanning Calorimetry (DSC) and DynamicMechanical Thermal Analysis (DMTA)rdquo Progress in OrganicCoatings vol 54 no 3 pp 164ndash169 2005

[6] D Maetens ldquoWeathering degradation mechanism in polyesterpowder coatingsrdquo Progress in Organic Coatings vol 58 no 2-3pp 172ndash179 2007

[7] J B Bajat J P Popic and V B Miskovic-Stankovic ldquoTheinfluence of aluminium surface pretreatment on the corrosionstability and adhesion of powder polyester coatingrdquo Progress inOrganic Coatings vol 69 no 4 pp 316ndash321 2010

[8] M A J Batista R P Moraes J C S Barbosa P C Oliveiraand A M Santos ldquoEffect of the polyester chemical structure onthe stability of polyester-melamine coatings when exposed toaccelerated weatheringrdquo Progress in Organic Coatings vol 71no 3 pp 265ndash273 2011

[9] F L Duivenvoorde J Laven and R Van der Linde ldquoDiblockcopolymer dispersants in polyester powder coatingsrdquo Progressin Organic Coatings vol 45 no 2-3 pp 127ndash137 2002

[10] S Radhakrishnan N Sonawane and C R Siju ldquoEpoxy powdercoatings containing polyaniline for enhanced corrosion protec-tionrdquo Progress in Organic Coatings vol 64 no 4 pp 383ndash3862009

[11] V C Malshe and G Waghoo ldquoWeathering study of epoxypaintsrdquo Progress in Organic Coatings vol 51 no 4 pp 267ndash2722004

[12] R Van der Linde E G Belder and D Y Perera ldquoEffect of phys-ical aging and thermal stress on the behavior of polyesterTGICpowder coatingsrdquo Progress in Organic Coatings vol 40 no 1ndash4pp 215ndash224 2000

[13] Technical Data Sheet of Ridoline 1352 BA of Ms HenkelChembond India Ltd

ISRN Corrosion 9

[14] Technical Data Sheet of Granodine of Ms Henkel ChembondIndia Ltd

[15] M Ozcan I Dehri and M Erbil ldquoEIS study of the effectof high levels of SO

2on the corrosion of polyester-coated

galvanised steel at different relative humiditiesrdquo Progress inOrganic Coatings vol 44 no 4 pp 279ndash285 2002

[16] R Naderi MM Attar andM HMoayed ldquoEIS examination ofmill scale on mild steel with polyester-epoxy powder coatingrdquoProgress in Organic Coatings vol 50 no 3 pp 162ndash165 2004

[17] R Mafi S M Mirabedini R Naderi and M M Attar ldquoEffectof curing characterization on the corrosion performance ofpolyester and polyesterepoxy powder coatingsrdquo CorrosionScience vol 50 no 12 pp 3280ndash3286 2008

[18] G Wuzella A Kandelbauer A R Mahendran and ATeischinger ldquoThermochemical and isoconversional kineticanalysis of a polyester-epoxy hybrid powder coating resin forwood based panel finishingrdquo Progress in Organic Coatings vol70 no 4 pp 186ndash191 2011

[19] M Barletta and A Gisario ldquoAn application of neural networksolutions to laser assisted paint stripping process of hybridepoxy-polyester coatings on aluminum substratesrdquo Surface andCoatings Technology vol 200 no 24 pp 6678ndash6689 2006

[20] R Naderi MM Attar andM HMoayed ldquoEIS examination ofmill scale on mild steel with polyester-epoxy powder coatingrdquoProgress in Organic Coatings vol 50 no 3 pp 162ndash165 2004

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

ISRN Corrosion 7

10000010000100010010101001Frequency (Hz)

024681012141618202224262830323436

Ang

le (d

eg)

100000

10000

1000

|119885|

(ohm

)

(a)

10000010000100010010101001Frequency (Hz)

05101520253035404550

1119864+06

1119864+05

1119864+04

1119864+03

Ang

le (d

eg)

|119885|

(ohm

)

(b)

Figure 7 Bode plot of (a) system-1 and (b) system-2 at 24 h time

10000010000100010010101001Frequency (Hz)

02468101214161820222426283032

Ang

le (d

eg)

100000

10000

1000

|119885|

(ohm

)

(a)

10000010000100010010101001Frequency (Hz)

Ang

le (d

eg)

1000000

100000

10000 051015202530354045

|119885|

(ohm

)

(b)

Figure 8 Bode plot of (a) system-1 (b) system-2 at 96 h time

Ang

le (d

eg)

10000010000100010010101001Frequency (Hz)

10000

1000 01234567891011121314

|119885|

(ohm

)

(a)

051015202530354045

Ang

le (d

eg)

10000010000100010010101001Frequency (Hz)

100000

10000

|119885|

(ohm

)

(b)

Figure 9 Bode plot of (a) system-1 and (b) system-2 at 144 h time

4 Conclusion

The powder coatings protect galvanised steel substrates bythe introduction of a barrier layer with relatively high ohmicresistance between the metallic substrate and the corrosiveenvironment Also it is indicated that the cross-link densityappears only to affect ionic conductivity of the film and

due to the higher cross-linked density of epoxy-polyesternetwork comparing with polyester system the permeabilityof water and ions through the coating film becomes lessand it leads to a more impervious film with a more resistantstructure to corrosion It is indicated that the polyester film ismore porous due to the less cross-link density of cured poly-mer comparedwith epoxy-polyester powder-coated samples

8 ISRN Corrosion

0510152025303540

Ang

le (d

eg)

100000

100000

10000100010010101001Frequency (Hz)

10000

1000

|119885|

(ohm

)

(a)

051015202530354045

Ang

le (d

eg)

100000

10000010000100010010101001Frequency (Hz)

10000

1000000

minus5

|119885|

(ohm

)

(b)

Figure 10 Bode plot of (a) system-1 and (b) system-2 at 264 h time

(a) System 1 (b) System 2

Figure 11 Salt spray photographs of coated substrate (a) polyester-coated sample after 1200 h of salt spray test (b) epoxy-polyester-coated sample after 1608 h of the salt spray test

SEM micrograph and bond strength suggest that epoxy-polyester coating is more firmly adherent to the phosphatesubstrate than polyester coating due tomore hydroxyl groupsin epoxy-polyester bonding with phosphate substrate Pro-tective properties of fully cured organic coatings on metallicsubstrate may be attributed to a barrier andor an activeinhibition mechanism

Acknowledgment

The authors would like to thank the staff of the corrosion labfor helping them during experiments

References

[1] A K Guin S Nayak T K Rout N Bandyopadhyay and D KSengupta ldquoCorrosion resistance nano-hybrid sol-gel coating onsteel sheetrdquo ISIJ International vol 51 no 3 pp 435ndash440 2011

[2] A S Khanna Introduction to High Temperature Oxidation andCorrosion ASM International 1997

[3] B V Jegdic J B Bajat J P Popic and V B Miskovic-StankovicldquoCorrosion stability of polyester coatings on steel pretreatedwith different iron-phosphate coatingsrdquo Progress in OrganicCoatings vol 70 no 2-3 pp 127ndash133 2011

[4] A M P Simoes R O Carbonari A R Di Sarli B del Amoand R Romagnoli ldquoAn environmentally acceptable primerfor galvanized steel formulation and evaluation by SVETrdquoCorrosion Science vol 53 no 1 pp 464ndash472 2011

[5] R Mafi S M Mirabedini M M Attar and S Moradian ldquoCurecharacterization of epoxy and polyester clear powder coatingsusing Differential Scanning Calorimetry (DSC) and DynamicMechanical Thermal Analysis (DMTA)rdquo Progress in OrganicCoatings vol 54 no 3 pp 164ndash169 2005

[6] D Maetens ldquoWeathering degradation mechanism in polyesterpowder coatingsrdquo Progress in Organic Coatings vol 58 no 2-3pp 172ndash179 2007

[7] J B Bajat J P Popic and V B Miskovic-Stankovic ldquoTheinfluence of aluminium surface pretreatment on the corrosionstability and adhesion of powder polyester coatingrdquo Progress inOrganic Coatings vol 69 no 4 pp 316ndash321 2010

[8] M A J Batista R P Moraes J C S Barbosa P C Oliveiraand A M Santos ldquoEffect of the polyester chemical structure onthe stability of polyester-melamine coatings when exposed toaccelerated weatheringrdquo Progress in Organic Coatings vol 71no 3 pp 265ndash273 2011

[9] F L Duivenvoorde J Laven and R Van der Linde ldquoDiblockcopolymer dispersants in polyester powder coatingsrdquo Progressin Organic Coatings vol 45 no 2-3 pp 127ndash137 2002

[10] S Radhakrishnan N Sonawane and C R Siju ldquoEpoxy powdercoatings containing polyaniline for enhanced corrosion protec-tionrdquo Progress in Organic Coatings vol 64 no 4 pp 383ndash3862009

[11] V C Malshe and G Waghoo ldquoWeathering study of epoxypaintsrdquo Progress in Organic Coatings vol 51 no 4 pp 267ndash2722004

[12] R Van der Linde E G Belder and D Y Perera ldquoEffect of phys-ical aging and thermal stress on the behavior of polyesterTGICpowder coatingsrdquo Progress in Organic Coatings vol 40 no 1ndash4pp 215ndash224 2000

[13] Technical Data Sheet of Ridoline 1352 BA of Ms HenkelChembond India Ltd

ISRN Corrosion 9

[14] Technical Data Sheet of Granodine of Ms Henkel ChembondIndia Ltd

[15] M Ozcan I Dehri and M Erbil ldquoEIS study of the effectof high levels of SO

2on the corrosion of polyester-coated

galvanised steel at different relative humiditiesrdquo Progress inOrganic Coatings vol 44 no 4 pp 279ndash285 2002

[16] R Naderi MM Attar andM HMoayed ldquoEIS examination ofmill scale on mild steel with polyester-epoxy powder coatingrdquoProgress in Organic Coatings vol 50 no 3 pp 162ndash165 2004

[17] R Mafi S M Mirabedini R Naderi and M M Attar ldquoEffectof curing characterization on the corrosion performance ofpolyester and polyesterepoxy powder coatingsrdquo CorrosionScience vol 50 no 12 pp 3280ndash3286 2008

[18] G Wuzella A Kandelbauer A R Mahendran and ATeischinger ldquoThermochemical and isoconversional kineticanalysis of a polyester-epoxy hybrid powder coating resin forwood based panel finishingrdquo Progress in Organic Coatings vol70 no 4 pp 186ndash191 2011

[19] M Barletta and A Gisario ldquoAn application of neural networksolutions to laser assisted paint stripping process of hybridepoxy-polyester coatings on aluminum substratesrdquo Surface andCoatings Technology vol 200 no 24 pp 6678ndash6689 2006

[20] R Naderi MM Attar andM HMoayed ldquoEIS examination ofmill scale on mild steel with polyester-epoxy powder coatingrdquoProgress in Organic Coatings vol 50 no 3 pp 162ndash165 2004

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

8 ISRN Corrosion

0510152025303540

Ang

le (d

eg)

100000

100000

10000100010010101001Frequency (Hz)

10000

1000

|119885|

(ohm

)

(a)

051015202530354045

Ang

le (d

eg)

100000

10000010000100010010101001Frequency (Hz)

10000

1000000

minus5

|119885|

(ohm

)

(b)

Figure 10 Bode plot of (a) system-1 and (b) system-2 at 264 h time

(a) System 1 (b) System 2

Figure 11 Salt spray photographs of coated substrate (a) polyester-coated sample after 1200 h of salt spray test (b) epoxy-polyester-coated sample after 1608 h of the salt spray test

SEM micrograph and bond strength suggest that epoxy-polyester coating is more firmly adherent to the phosphatesubstrate than polyester coating due tomore hydroxyl groupsin epoxy-polyester bonding with phosphate substrate Pro-tective properties of fully cured organic coatings on metallicsubstrate may be attributed to a barrier andor an activeinhibition mechanism

Acknowledgment

The authors would like to thank the staff of the corrosion labfor helping them during experiments

References

[1] A K Guin S Nayak T K Rout N Bandyopadhyay and D KSengupta ldquoCorrosion resistance nano-hybrid sol-gel coating onsteel sheetrdquo ISIJ International vol 51 no 3 pp 435ndash440 2011

[2] A S Khanna Introduction to High Temperature Oxidation andCorrosion ASM International 1997

[3] B V Jegdic J B Bajat J P Popic and V B Miskovic-StankovicldquoCorrosion stability of polyester coatings on steel pretreatedwith different iron-phosphate coatingsrdquo Progress in OrganicCoatings vol 70 no 2-3 pp 127ndash133 2011

[4] A M P Simoes R O Carbonari A R Di Sarli B del Amoand R Romagnoli ldquoAn environmentally acceptable primerfor galvanized steel formulation and evaluation by SVETrdquoCorrosion Science vol 53 no 1 pp 464ndash472 2011

[5] R Mafi S M Mirabedini M M Attar and S Moradian ldquoCurecharacterization of epoxy and polyester clear powder coatingsusing Differential Scanning Calorimetry (DSC) and DynamicMechanical Thermal Analysis (DMTA)rdquo Progress in OrganicCoatings vol 54 no 3 pp 164ndash169 2005

[6] D Maetens ldquoWeathering degradation mechanism in polyesterpowder coatingsrdquo Progress in Organic Coatings vol 58 no 2-3pp 172ndash179 2007

[7] J B Bajat J P Popic and V B Miskovic-Stankovic ldquoTheinfluence of aluminium surface pretreatment on the corrosionstability and adhesion of powder polyester coatingrdquo Progress inOrganic Coatings vol 69 no 4 pp 316ndash321 2010

[8] M A J Batista R P Moraes J C S Barbosa P C Oliveiraand A M Santos ldquoEffect of the polyester chemical structure onthe stability of polyester-melamine coatings when exposed toaccelerated weatheringrdquo Progress in Organic Coatings vol 71no 3 pp 265ndash273 2011

[9] F L Duivenvoorde J Laven and R Van der Linde ldquoDiblockcopolymer dispersants in polyester powder coatingsrdquo Progressin Organic Coatings vol 45 no 2-3 pp 127ndash137 2002

[10] S Radhakrishnan N Sonawane and C R Siju ldquoEpoxy powdercoatings containing polyaniline for enhanced corrosion protec-tionrdquo Progress in Organic Coatings vol 64 no 4 pp 383ndash3862009

[11] V C Malshe and G Waghoo ldquoWeathering study of epoxypaintsrdquo Progress in Organic Coatings vol 51 no 4 pp 267ndash2722004

[12] R Van der Linde E G Belder and D Y Perera ldquoEffect of phys-ical aging and thermal stress on the behavior of polyesterTGICpowder coatingsrdquo Progress in Organic Coatings vol 40 no 1ndash4pp 215ndash224 2000

[13] Technical Data Sheet of Ridoline 1352 BA of Ms HenkelChembond India Ltd

ISRN Corrosion 9

[14] Technical Data Sheet of Granodine of Ms Henkel ChembondIndia Ltd

[15] M Ozcan I Dehri and M Erbil ldquoEIS study of the effectof high levels of SO

2on the corrosion of polyester-coated

galvanised steel at different relative humiditiesrdquo Progress inOrganic Coatings vol 44 no 4 pp 279ndash285 2002

[16] R Naderi MM Attar andM HMoayed ldquoEIS examination ofmill scale on mild steel with polyester-epoxy powder coatingrdquoProgress in Organic Coatings vol 50 no 3 pp 162ndash165 2004

[17] R Mafi S M Mirabedini R Naderi and M M Attar ldquoEffectof curing characterization on the corrosion performance ofpolyester and polyesterepoxy powder coatingsrdquo CorrosionScience vol 50 no 12 pp 3280ndash3286 2008

[18] G Wuzella A Kandelbauer A R Mahendran and ATeischinger ldquoThermochemical and isoconversional kineticanalysis of a polyester-epoxy hybrid powder coating resin forwood based panel finishingrdquo Progress in Organic Coatings vol70 no 4 pp 186ndash191 2011

[19] M Barletta and A Gisario ldquoAn application of neural networksolutions to laser assisted paint stripping process of hybridepoxy-polyester coatings on aluminum substratesrdquo Surface andCoatings Technology vol 200 no 24 pp 6678ndash6689 2006

[20] R Naderi MM Attar andM HMoayed ldquoEIS examination ofmill scale on mild steel with polyester-epoxy powder coatingrdquoProgress in Organic Coatings vol 50 no 3 pp 162ndash165 2004

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

ISRN Corrosion 9

[14] Technical Data Sheet of Granodine of Ms Henkel ChembondIndia Ltd

[15] M Ozcan I Dehri and M Erbil ldquoEIS study of the effectof high levels of SO

2on the corrosion of polyester-coated

galvanised steel at different relative humiditiesrdquo Progress inOrganic Coatings vol 44 no 4 pp 279ndash285 2002

[16] R Naderi MM Attar andM HMoayed ldquoEIS examination ofmill scale on mild steel with polyester-epoxy powder coatingrdquoProgress in Organic Coatings vol 50 no 3 pp 162ndash165 2004

[17] R Mafi S M Mirabedini R Naderi and M M Attar ldquoEffectof curing characterization on the corrosion performance ofpolyester and polyesterepoxy powder coatingsrdquo CorrosionScience vol 50 no 12 pp 3280ndash3286 2008

[18] G Wuzella A Kandelbauer A R Mahendran and ATeischinger ldquoThermochemical and isoconversional kineticanalysis of a polyester-epoxy hybrid powder coating resin forwood based panel finishingrdquo Progress in Organic Coatings vol70 no 4 pp 186ndash191 2011

[19] M Barletta and A Gisario ldquoAn application of neural networksolutions to laser assisted paint stripping process of hybridepoxy-polyester coatings on aluminum substratesrdquo Surface andCoatings Technology vol 200 no 24 pp 6678ndash6689 2006

[20] R Naderi MM Attar andM HMoayed ldquoEIS examination ofmill scale on mild steel with polyester-epoxy powder coatingrdquoProgress in Organic Coatings vol 50 no 3 pp 162ndash165 2004

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials