Embed Size (px)
Citation preview
REVIEW ARTICLE
Recent developments in the volatile corrosion inhibitor (VCI)coatings for metal: a review
Sukanya Gangopadhyay, Prakash A. Mahanwar
� American Coatings Association 2018
Abstract Corrosion is a crucial worldwide problemthat strongly affects metals. Out of the several ways toprevent corrosion, volatile corrosion inhibitors (VCIs)are predominantly used as a method of temporaryprotection. These compounds have the ability tovaporize and condense on the surface of the ferrousor nonferrous material and make the substrate lesssusceptible to corrosion but work only in a confinedspace. VCI compounds form a monomolecular layerover the metal surface, thereby preventing the elec-trochemical reactions on the metal surface which leadto corrosion. This review article outlines the use ofvolatile corrosion inhibitors (VCIs) as a temporarycorrosion protection technique, their working mecha-nisms and the various compounds used as VCI. It alsoanchors on the latest research works which have beencarried out on VCI coatings along with a glimpse of theworks that were carried out in the past. The variousfactors affecting the volatile corrosion inhibitors alongwith the merits of VCI coatings are discussed in thispaper. Formulations for both strippable and perma-nent VCI coatings are also reported with the varioustesting methods. Lastly, an overview of the recentdevelopments of VCI coatings along with the variousgreen VCI is given.
Keywords Corrosion, Volatile corrosion inhibitor,Temporary protection, VCI coatings, Green VCI
Introduction
A process that leads to the gradual destruction ofmaterials, mostly metals by chemical and/or electro-chemical reactions with their environment, is termed ascorrosion. Corrosion is a destructive phenomenon thatcauses huge economic losses, along with being detri-mental to the appearance of metals, and at times cancause equipment failure.1 The latest estimate of annualcosts of corrosion in the USA is $276 billion, more than3 times of the amount reported by the NationalAssociation of Corrosion Engineers (NACE) in1998.2 Corrosion can be of various types dependingon the environment to which the metal is exposed suchas atmospheric corrosion, water- or soil-induced cor-rosion, or corrosion induced by high temperature.3,4
The metal surfaces are mostly attacked by atmosphericcorrosion mainly during packaging, storage, and trans-portation due to the omnipresence of air in theatmosphere.5 This results in great economic lossesand also the loss of the aesthetic value of the metal.Atmospheric humidity and gaseous pollutants presentin the atmosphere such as sulfur dioxide (SO2),
6
chlorine (Cl2),7 hydrogen sulfide (H2S), carbon dioxide
(CO2), nitrogen oxides (NO and NO2), and ozone (O3)lead to the electrochemical reactions on the metalsurface and thus cause corrosion as depicted in Fig. 1.
Corrosion can be inhibited either by changing themetal composition, by separating the metal from thecorrosive environment, or by modifying the environ-ment. With the main focus being on prevention ofatmospheric corrosion, separation of metal from thecorrosive environment is the most cost-effectivemethod.4 Now, this can be achieved by two methodssuch as permanent protection techniques and tempo-rary protection techniques. Permanent techniquesinclude the use of alloys, metallic coatings, permanentcoatings,8–10 plating, cathodic protection,11,12 anodicprotection,13 while the temporary techniques involve
S. Gangopadhyay, P. A. Mahanwar (&)Department of Polymer and Surface Engineering,Institute of Chemical Technology, Matunga, Mumbai,Maharashtra 400019, Indiae-mail: [email protected];[email protected]
S. Gangopadhyaye-mail: [email protected]
J. Coat. Technol. Res.
https://doi.org/10.1007/s11998-017-0015-6
coating with waxes, greases, oils,14 volatile corrosioninhibitors,15 and desiccants like silica gel which absorbmoisture.16 Most effective and economic means ofatmospheric corrosion prevention involves the use ofvolatile corrosion inhibitors coatings17,18 as shown inFig. 2. In this review, our objective is to provide aperspective on wide volatile corrosion inhibitorcoating used as a protection barrier for metal. Alsothe overview of volatile corrosion inhibitor-basedcoatings is focused from mechanism to applicationarea.
Volatile corrosion inhibitors
The corrosion inhibitors generally with vapor pressureabove 10�5 mm Hg and with the ability to volatilizeeasily and reach the inaccessible parts of the metalsurface are termed as volatile corrosion inhibitors(VCIs).19–23 Nonvolatile compounds which releasesuch volatile components on hydrolysis can also beused as VCI. VCIs for temporary protection can beused in the form of packaging materials such as VCIfilms and VCI papers, porous emitters (VCI desic-cants), inhibited air, or in special forms intended forthe protection of specific product types.24,25 VCIs canalso be used for protection of metal articles within
polymer coatings (paints) and working liquids (hy-draulic, cooling liquids, etc.).26
The main concept of VCI is focused on the protec-tion of metal parts during processing, transporta-tion and storage without causing any residualcontamination on the protected metal surface.27–33
This form of protection has permitted the immediateuse of packaged items without the tedious proceduresnormally associated with the removal of oil or greasepreservatives before stored or packaged equipment isplaced in service. The savings in man-hours on reac-tivation of equipment are greater in many cases thanthe initial cost of packaging. Complicated metallicassemblies, such as electronic equipment, may beprotected by this method.
Use of VCI is advantageous as it is compatible withother corrosion prevention techniques such as cathodicprotection, and when used in combination with it, itlowers the corrosion rate of metals such as steel, zinc,mild steel,34 aluminum,35 and also lowers the usage ofthe electric power necessary for the cathodic protec-tion.36
In contrast, it is difficult to predict the shelf life ofVCI; moreover, it also does not indicate the corrosionprotection remaining, thus making its use difficult.37
The typically used VCI compounds are sodiumnitrite, benzotriazole, dicyclohexylammonium nitrite,
Fe(OH)2
O2++
O2
H2O
H2O
Rust
1/2 + 2e− 2OH−+
CathodeSteelElectrons
flow
Irondissolves
Water
Anode
Fe2−
Fig. 1: Electrochemical reactions causing corrosion
Without VCIpackaging VCI packaging
Fig. 2: Metal packaging with and without VCI
J. Coat. Technol. Res.
dicyclohexylammonium benzoate, cyclohexylaminebenzoate, etc.
VCI coatings are user-friendly replacements forsolvent- and oil-based corrosion inhibitor paints.38
Unlike sticky or tacky products, the VCI coatings donot attract dirt or dust on metal parts. It is safe to useboth on ferrous and nonferrous metals as well as onmost elastomers or plastics. It is ideal for small parts inlarge quantities (nuts and bolts, fasteners, hardware) orodd-shaped parts that cannot be placed into bags orwrap. The main markets currently using VCI coatingsinclude automotive, construction/agriculture, metalmachining, electronics, military, oil and gas, aerospace,steel, and steel service centers.
Literature review
This section gives a review of the past literature ofusing VCI coatings as a method of temporary protec-tion of metals against corrosion during processing,transport, and storage without causing any residualcontamination on the protected metal surface. Itdescribes the working mechanism of the VCI coatings,various compounds used as VCI along with the variousfactors affecting the volatile corrosion inhibitors, andthe merits of VCI coatings. It also anchors on the latestresearch works that have been carried out on VCIcoatings and provides a glimpse into the works thatwere carried out in the past.
Volatile corrosion inhibitors (VCIs)
The corrosion inhibitors generally with vapor pressureabove 10�5 mm Hg and with the ability to volatilizeeasily and reach the inaccessible parts of the metalsurface are termed as volatile corrosion inhibitors(VCIs).24–27 Nonvolatile compounds which releasesuch volatile components on hydrolysis can also beused as VCI. VCIs for temporary protection can beused in the form of packaging materials28 (VCI films29
and VCI papers), porous emitters (VCI desiccants),inhibited air, or in special forms intended for theprotection of specific product types. VCIs can also beused for protection of metal articles within polymercoatings (paints) and working liquids (hydraulic, cool-ing liquids, etc.).30
History
At the beginning of the 20th century, ammonia wasused as a volatile corrosion inhibitor in steam boilercircuits to protect both immersed and exposed parts. Itwas not until the early 1940s that less odorous, moreeffective, and little less dangerous active substancesbegan to be used industrially, e.g., salts of dicyclohexy-lamine. Papers impregnated with these types of active
substances, known as VPI papers, are still in circulationin Europe.
Today there are more than 1000 types of VCIcompounds known, but only a fraction of them areacceptably efficient, cost-effective, and environmentfriendly.
During World War II, the VCI compounds wereused and tested for the first time by the US Navy topreserve the military equipment and similar structureson warships as it became necessary to protect militaryequipment and replacement parts against rusting dur-ing storage under all climatic conditions. The existingindustrial packaging procedures were found inade-quate, as these packaging procedures were expensiveand time-consuming, and considerable trouble andexpense were required to remove such preservativesbefore the equipment was placed in service. The vapor-phase inhibition obtained by the use of amine nitritesopened a completely new avenue for attack onpackaging problems.
The first VCIs were anodic corrosion inhibitors(sodium nitrite, sodium benzoate). They were devel-oped for protection of ferrous metals. Anodic VCIsrestrict the anodic reactions by the mechanism ofanodic passivation when a thin film of VCI preventscorrosion of the metal. Anodic VCIs are hazardoussubstances. They also may attack nonferrous alloys.
Later, mixed (ambiodic) volatile corrosion inhibitors(VCIs) were developed. They are capable of combin-ing the effects of both anodic and cathodic inhibitors.A depression of the cathodic reaction is achieved dueto the restriction of the oxygen transportation.
An idea that started in the 1940s is now the standardprocedure for protecting the metal parts used by themanufacturers and metal parts fabricators around theworld. Today, the military, the automotive, marine,transportation, aerospace, HVAC, heavy equipment,powdered metal, metal casting, metal stamping, springand coil, gear, precision machining, firearms, precisionmachining, and general industrial industries all con-tinue to benefit from the use of VCI, specialty coatings,and corrosion preventatives.
Cost of corrosion: market survey
VCIs are generally used in a closed environment, andthey disperse when in contact with the metal surface,the vapor of these inhibitors (typically salts) condensesand reacts with moisture producing protective species.Amine-based compounds are commonly used as VCIs.Over the years, the number of fields using VCIs haswidened, now covering electronics, packaging, processindustries, reinforced concrete, coatings, and metal-working fluids.
Corrosion inhibitors (CIs) are either organic orinorganic chemicals, or more commonly, formulationsthereof that are added in small amounts (parts permillion, ppm) to a corrosive environment in order to
J. Coat. Technol. Res.
delay or decrease the corrosion process of the surfaceto be protected.39
Due to the fact that equipment constructed withmaterials resistant to corrosion is very expensive, it iscommon to use corrosion inhibitors as a practical,economical, and simple alternative.
A recent study in the USA indicated that theirindustries spent about $276 billion/year and around 900million/year on about 200 million tons of CIs. Thismarket is shared by about 40% of inorganic inhibitorssuch as sulfonates and phosphonates (for coolingtowers) and 60% of organic inhibitors, i.e., amines,cyclic amines, quaternary amidoamines, dietilamines,imidazolines, and fatty acids, which are primarily usedas CIs in the petroleum industry, in the production ofgas, refineries, oil pipelines, and products.
The CI formulations generally are made up of oneor more active ingredients and suitable vehicles (otheradditives and solvents) that encourage compatibilitywith the environment and make viable the activetransport to the area to be protected (metal surface).
Figure 3 shows the percentage contribution of thefive industries to the total cost of corrosion as per theNACE report.
According to the current US corrosion study, thedirect cost of metallic corrosion is $276 billion on anannual basis. This represents 3.1% of the US GrossDomestic Product (GDP).40
As can be seen, corrosion strongly affects a coun-try’s GDP and therefore steps need to be taken toprevent corrosion. Out of the various sectors whichcorrosion affects, corrosion during transportation andstorage also accounts for a huge percentage, which canbe prevented by using methods for temporary corro-sion prevention such as VCI coatings.
Table 1 gives the estimate of the annual cost ofcorrosion spent on army ground vehicles, navy ships,and marine ground vehicles which is on an average
around $3–4 billion, which can be easily prevented byusing volatile corrosion inhibitor.40,41 Thus, VCI as amode of temporary corrosion prevention significantlyreduces the cost of corrosion, thereby adding to thecountry’s GDP.
Volatile corrosion inhibitor (VCI) compounds
Volatile corrosion inhibitors (VCIs) are substancemolecules that vaporize at a significant pressure andthen are adsorbed on the metal surface forming a thincorrosion protection layer.42,43 Most volatile corrosioninhibitors are aminocarboxylates—products of reactionbetween organic acids with an amine or amine deriva-tives.
Table 2 gives the list of the typical volatile corrosioninhibitors used commercially.
VCIs are substances whose vapor pressure is suffi-cient in enclosed spaces to protect the metal surfaceswithout necessarily being in direct contact with themetal surface but by condensing on the metal surface.Selection of a suitable inhibitor for a particular metaland environment depends on the vapor pressures ofthe compounds. The vapor pressure of an effectiveVCI should be less than 1 mmHg to prevent too rapidevaporation of the VCI. Saini, Yadav and Kannanstudied the effective use of VCI for mild steel undervarious conditions.44–46
For example, morpholine47 and cyclohexylaminecarbonate (CHC),48 which is used as a corrosioninhibitor, have a vapor pressure of 10 mmHg at 23�Cand 0.40 mmHg at 25�C, respectively; various ureaamines and tertiary amine compounds are also used asVCI.49,50
Dicyclohexylammonium nitrite with vapor pressure0.00001 mmHg is used as a VCI for corrosion-preven-tive packaging of steel, owing to its chemical stability,compatibility, volatility, vapor transport, diffusion,solubility, and corrosion inhibition properties. Theabsence of undesirable effects with nonmetallic mate-rials, nonferrous metals, bimetallic couples and inhandling by people also add to its practical impor-tance.51
Bis-piperidiniummethyl-urea (BPMU) and polya-mine compounds have been proven to be a goodvolatile corrosion inhibitors for the (temporary pro-tection) prevention of atmospheric corrosion of mildsteel as well as carbon steel, by references (52–54).
Morpholine and its derivatives, such as morpholineborate, sorbate, laurate, succinate, azelate, and seba-rate, were used and tested as VCI by Vuorinen for mildsteel.55 Reference (56) reported a series of morpholineMannich base derivatives as VCIs for steel. Reference(57) synthesized and evaluated some salts of 1,6-diaminohexane as VCIs for aluminum, zinc, and mildsteel. 1,3-Di-morpholin-4-yl-propan-2-ol (DMP) and1,3-bis-diethylamino-propan-2-ol (DEAP) were syn-thesized and used as VCI by reference (58).
Infrastructure16.4%
($22.6 billion)
Government14.6%
($20.1 billion)
Production andmanufacturing
12.8%($17.6 billion) Transportation
21.5%($29.7 billion)
Utilities34.7%
($47.9 billion)
Fig. 3: Percentage and dollar contribution to the total costof corrosion for the five industry categories analyzed.($137.9 Billion)
J. Coat. Technol. Res.
Vapor-phase corrosion inhibitor composition con-sisting essentially of sodium nitrite and sodium phos-phate in packaging materials has proven to be effectiveagainst atmospheric corrosion for protecting metalarticles.59–61 Benzotriazole is one of the most effectiveVCIs for nonferrous metals.62–64
Quraishi65 synthesized six organic volatile corrosioninhibitors (VCIs) using lauric hydrazide with variousacids such as cinnamic acid, succinic acid, nitrobenzoicacid, phthalic acid, and maleic acid and evaluated ascorrosion inhibitors of mild steel, copper, brass, zinc,and aluminum.
Murray66 developed VCI and also the method ofincorporating/deposition of it on the metal surface tobe protected. It was comprised of reacting a stronglybasic amine and a weak acid on the metal surface suchthat it forms a salt of the amine (in situ) on the metalsurface and the said weak acid being in the vapor stateat the time of application and being present in thevapor in a concentration of at least fifteen percent,acting as VCI and protecting the surface againstcorrosion.
Table 3 depicts the saturated vapor pressures ofsome common VCI compounds.
Types of volatile corrosion inhibitor compounds
There are various types of VCI compounds which areused for the protection of the various types of metalsand alloys and can be broadly classified as:
1. Volatile corrosion inhibitors for steel, for example,
• Nitrite of amines• Carboxylate of amines• Chromate of amines• Ester of carboxylic acid
2. Volatile rust inhibitor for coppers and copperalloys, for example:
• Hetero cyclic compounds• Triazole ring• Pyrole ring• Pyrazole ring• Thiazole ring• Compounds with imidazole ring• Thiourea ring• Compounds with mercapto group
Various forms of VCI compounds
As a mode of temporary corrosion prevention,volatile corrosion inhibitor compounds can be usedin various forms depending on the area of applicationleading to better accessibility and corrosion preven-
Table 1: Cost of corrosion studies
Study year Data baseline Study segment Annual cost of corrosion
2005–2006 FY2004 Army ground vehicles $1.5 BillionFY2004 Navy ships $3.4 Billion
2006–2007 FY 2005 DoD Facilities and Infrastructure $1.4 BillionFY 2005 Army Aviation and Missiles $1.7 BillionFY 2005 Marine Crops Ground Vehicles $0.5 Billion
2007–2008 FY 2005-06 Navy and Marine Crops Aviation $4.5 BillionFY 2005-06 Coast Guard Aviation and Vessels $0.3 Billion
2008–2009 FY 2006-07 Air Force $4.9 BillionFY 2006-07 Army ground vehicles $2.6 BillionFY 2006-07 Navy Ships $2.6 BillionFY 2006 DoD—other equipment $5.1 Billion
2009–2010 FY 2007-08 Marine Crops Ground Vehicles $0.4 BillionFY 2007-08 DoD Facilities and Infrastructure $1.9 BillionFY 2007-08 Army Aviation and Missiles $1.6 Billion
2010–2011 FY 2008-09 Air Force $5.7 BillionFY 2008-09 Navy and Marine Crops Aviation $3.9 Billion
2011–2012 FY 2009-10 Navy ships $3.9 BillionFY 2009-10 Army ground vehicles $1.9 Billion
2012–2013 FY 2010-11 Marine Crops Ground Vehicles $0.4 BillionFY 2010-11 DoD Facilities and Infrastructure $3.0 BillionFY 2010-11 Army Aviation and Missiles $2.0 BillionFY 2009 DoD—other equipment $3.6 Billion
J. Coat. Technol. Res.
tion results. The various forms in which the VCIcompounds are commercially used include VCI films,VCI paper, VCI coating, VCI oils67 and VCI desic-cants.
VCI film
VCI films combine the benefit of barrier packagingwith anticorrosion protection in an easy-to-use form
allowing for safe, clean, and dry packaging of metalproducts. VCI films are made from incorporation ofthe VCI concentrate into the resin mix during theblowing, casting, or extrusion coating processes.68 Themost common resins are low-density, linear-low-den-sity, or high-density polyethylene, because they arerecyclable, low cost, good barrier to moisture, lightweight, and highly resistant to most solvents.69 Theyare environmentally friendly and approved by theFDA for indirect contact with food.
Table 2: Volatile corrosion inhibitor compounds
Sr. no. Volatile corrosion inhibitor Abbreviation Structure
1. Benzotriazole BTA
N NN
H
2. Dicyclohexylammonium nitrite DICHAN
NH-HNO2
3. Dicyclohexylammonium salicylate DICHA-SA
NH HOOCOH
4. Monoethanolamine benzoate MEA-BA HO(CH2)2NH2-HOOC
5. Dicyclohexylammonium benzoate DICHA-BA
NH-HOOC
6. Diisopropyl ammonium benzoate DIPA-BA CH3
CH3
CH2
NH-HOOC
7. Cyclohexylamine benzoate CHA-BA NH2HOOC
8. Dicyclohexylammoniumcyclohexane carboxylate
DICHA-CHC
NH-HOOC
9. Cyclohexylamine cyclohexanecarboxylate
CHA-CHC NH2-HOOC
10. Dicyclohexylammonium acrylate DICHA-AA
NH-HOOC–CH = CH2
11. Cyclohexylamine acrylate CHA-AA NH2-HOOC–CH = CH2
12. Sodium Nitrite NaNO2
J. Coat. Technol. Res.
Markets Automotive, construction, metal machin-ing, electronics, military, oil and gas, aerospace, steel,and steel service centers.
Application Domestic shipment, export shipment,inventory storage, in-process operations, during shutdowns, long-term storage.
VCI paper
A high-quality neutral natural kraft paper is usuallyused as a substrate. Paper can be impregnated orcoated with the VCI chemical solution, which usuallyconsists of two parts—the VCI chemical itself and aspecial binder, usually acrylic based. It is essential inkeeping the shipments, stored items, and in-processmetals protected and corrosion-free for years. VCIpapers can be impregnated either on one side or onboth sides. VCI papers are environmentally safe, fullyrecyclable and repulpable, biodegradable, and nontox-ic.
Markets Automotive, construction/agriculture, me-tal machining, electronics, military, silver, copper,precious metals, oil and gas, aerospace, steel, and steelservice centers.
Applications Domestic shipment, export shipment,inventory storage, in-process operations, during shutdowns, long-term storage.
VCI coating
VCI coating is a user-friendly replacement for solvent-and oil-based corrosion inhibitors. At ambient condi-tions, this clear protective coating will dry-to-touchwithin a maximum of 20 min. Unlike sticky or tackyproducts, this coating does not attract dirt or dust onmetal parts. It is safe to use on ferrous metals andstainless steel and will not harm most elastomers orplastics. It can be a water-based system and can beused for ferrous metals and represents a significantadvancement in corrosion prevention technology.
Application VCI coatings provide excellent indoorprotection but are not recommended for outdoor useunless used in combination with other VCI productsthat contain UV inhibitors. It is ideal for small parts inlarge quantities (nuts and bolts, fasteners, hardware) orodd-shaped parts that cannot be placed into bags orwrap.
Markets Automotive, construction/agriculture, me-tal machining, electronics, military, oil and gas, aero-space, steel, and steel service centers.
VCI desiccant
Desiccants are drying agents used to control thehumidity levels inside a container through the processof adsorption.70 Hydrogels are used as desiccants whichadsorb water and reduce the water level inside thecontainer, thereby inhibiting corrosion.71 Hydrogelsare basically water-absorbent polymers which absorbmoisture, thus preventing electrochemical reactionsleading to corrosion.72 Then, these desiccants releasethe anticorrosive volatile corrosion inhibitors. Desic-cants work in conjunction with VCI nanotechnology toeliminate corrosion and rust on metal surfaces.
Markets Automotive, construction/agriculture, me-tal machining, electronics, military, silver, copper,precious metals, oil and gas, aerospace, steel, and steelservice centers.
VCI working mechanism
Volatile corrosion inhibitors are substances whosemolecules vaporize at a significant pressure and thenare adsorbed on the metal surface forming a thincorrosion protection layer. VCI are capable of reduc-ing corrosion in enclosed spaces (e.g., package bags).
The protective vapor is emitted by a VCI-containingmaterial, and then it is distributed throughout thespace migrating to the part surface and penetrating
Table 3: Saturated vapor pressures of common VCI compounds
Sr. no Substance Temperature (�C) Vapor pressure (mm Hg) Melting point (�C)
1. Morpholine 20 8.0 –2. Benzylamine 29 1.0 –3. Cyclohexylamine carbonate 25.3 0.397 –4. Diisopropylamine nitrite 21 4.84 9 10�3 1395. Morpholine nitrite 21 3 9 10�3 –6. Dicyclohexylamine nitrite 21 1.3 9 10�4 1797. Cyclohexylamine benzoate 21 8 9 10�5 –8. Dicyclohexylamine caprylate 21 5.5 9 10�4 –9. Guanadine chromate 21 1 9 10�5 –10. Hexamethyleneimine benzoate 41 8 9 10�4 6411. Hexamethyleneamine nitrobenzoate 41 1 9 10�6 13612. Dicyclohexylamine benzoate 41 1.2 9 10�6 210
J. Coat. Technol. Res.
into crevices, cracks, small holes, and other hard-to-reach regions. The vapors condense on the metalsurface in the form of microscopic crystals, whichdissolve in the moisture film present on the surface.
The volatile corrosion inhibitors are made up ofcompounds that in addition to corrosion protectingproperties also have a vapor pressure.73 Due to theevaporation properties, the corrosion inhibitor transi-tions into the gas phase and fills the entire volumewithin the storage system with a continuous chemicalcloud.74 When the vapor concentration reaches acertain level, equilibrium is established (provided thepackage is air tight) and some crystals condense rapidlyonto the surface of the item and a monomolecularlayer is formed on the surface which inhibits theelectrochemical processes, leading to corrosion andthereby preventing corrosion75 as shown in Fig. 4. VCImolecules also decrease the diffusion of oxygen to themetal surface and control the pH level in the elec-trolyte. The attraction of the VCI molecules is strongerthan that of water molecules, thereby repelling mois-ture and preventing corrosion,76,77 as shown in Fig. 5.
After removing the VCI packaging, the VCI com-ponents escape without residue from the metal surfacesuch that no subsequent cleaning of the metal objects isrequired before the further use thereof. This is adecisive advantage of a packaging containing VCI asopposed to other methods of temporary corrosionprotection, such as the oiling/lubricating of compo-nents.
Similar is the case with VCI coatings, the VCIcomponent incorporated in the VCI coatings beingvolatile slowly comes to the surface of the metal and onvaporization forms an invisible coating layer, therebypreventing corrosion.
Saini44 investigated the various modes of function-ing of corrosion inhibition by the VCIs:
• By reducing the relative humidity below the criticalvalue
• By alkalizing the medium to a pH value at whichthe rate of corrosion becomes significantly low.
• By reducing the corrosion current density to aminimum value by rendering the metal surfacehydrophobic which prevents the reaction of metalwith the environment.
• The presence of a greater number of lone pairs inthe inhibitor enhances their inhibition efficiency,but the presence of unsaturation and bulky alkylgroups near the lone pair carrier atom retards theiraction due to the resonance stabilization and sterichindrance, respectively.
Figure 5 depicts the case of metal protected usingVCI, and the active substance contained in the VCIvaporizes and fills the atmosphere confined within thepackage and gets adsorbed on the metal surfaceforming the primary oxide layer (POL), therebyblocking penetration of water molecules and prevent-ing electrochemical reactions, thus protecting metalsurface from corrosion.
Figure 6 depicts the case of corrosion of an unpro-tected metal surface, i.e., the metal surface withoutVCI protection. The water molecules condense on themetal surface and thereby initiate electrochemicalreaction, leading to corrosion.
Effectiveness and factors affecting volatilecorrosion inhibitors
The effectiveness of the volatile corrosion inhibitorcompounds depends on various factors such as thevapor pressure, pH, corrosion protection radius, con-centration of VCI compound and the application time.
Metal surface
VCI moleculesVaporization
VCI coating
Absorbed VCI molecules
Fig. 4: VCI working mechanism
J. Coat. Technol. Res.
All these factors and their effect on the performanceof the VCI are discussed below with reference to thelatest literature.
The efficiency of the VCI compounds is mainlydependent on the vapor pressure emitted by thecompounds and their adsorption strength on the metalsurface. The better the adsorption strength, the morestrongly the VCI molecules adhere on the metalsurface, thereby repelling water molecules and pre-venting corrosion.
Koehler78 found that the inhibition by VCI com-pounds mainly depends on their ability to vaporize to asufficient extent and the ferrous metals protection by
VCIs in packages is more effective under neutral toslightly alkaline conditions than with strong alkalineconditions.
The effectiveness of VCI depends on their vaporpressure. Too high vapor pressure allows fast evapo-ration and distribution of the inhibitor in the sur-rounding atmosphere. However, the resultingprotective layer is unstable. Its molecules have atendency to vaporize from the metal surface. Too lowvapor pressure produces a stable protective layer, butthe process of its formation is very slow.
Figure 7 shows the basic properties of the two VCIswith different vapor pressures. Along with being
Metal protected using VCI
Anodic zone
FeCathodic zone
Metal(steel)
POL
VCI packaging
VCI vapors
Water
Oxygen(Air)
Fig. 5: With VCI protection
Corrosion of Unprotected Metal i.e. without VCI Protection
Anodic zoneCathodic zone
Metal(steel)
POL
Oxygen(Air)
Water
2H2O 2OH++2OH−
Fe2+
Fe(OH)2
Iron oxide
H2
+
2 e−
Fig. 6: Without VCI protection
J. Coat. Technol. Res.
dependent on the vapor pressure, the efficiency of VCIalso depends on the amount of water permeation.Therefore, corrosion can begin before a low-vapor-pressure VCI compound can begin to protect thesurface, and hence a VCI compound with adequatevapor pressure can only help in corrosion prevention.
The effectiveness of the volatile corrosion inhibitorcompounds also depends on the corrosion protectionradius, which is defined as the distance away from theVCI source from which the VCIs can still havesufficient corrosion protection properties. The radiusis dependent on the vapor pressure of the VCI, but theservice life of the VCI compound also depends on thevapor pressure. Figure 8 depicts the dependence of theVCI effectiveness on the corrosion protection radius.
The efficiency of a selected combination of VCIcompounds mainly depends on two parameters79,80:
1. Their vapor pressure (more exactly their tendencyto sublime) under atmospheric conditions shouldbe high enough to allow significant vapor-phasetransport of the compounds within an enclosedspace to the metal surface.
2. Their adsorption strength should be high on theoxide-covered metal surface (directly or afterdissolving in the condensed water film) inhibitingthe metal corrosion during storage and transportby interaction with the surface.
Figure 9 shows the efficiency and corrosion rate as afunction of concentration of VCI and as a function oftime after application of the VCI. Efficiency refers tothe decrease in the corrosion rate of the metal underVCI protection. While designing a particular VCIsystem, the concentration of the VCI and the length ofthe time following application are important parame-ters which need to be considered. The corrosionprotection mechanism depends on the VCI compoundsused and the characteristics of the metal beingprotected.
Along with depending on the concentration of theVCI, the efficiency of the VCI depends on the length oftime as depicted in Fig. 10.
Adherence of VCI coating
One of the important factors affecting the effectivenessof the VCI coating is its adherence on the metalsurface. The better the adherence of the coating,the better is the corrosion protection of the metalsurface. Depending on the chemical properties of theVCI compounds, they inhibit corrosion either bypassivating the electrochemical reactions leading tocorrosion or by precipitating on the surface.
Volatile corrosion inhibitors can be divided intopassivation-, adsorption-, and precipitation-type inhi-bitors with respect to their main inhibition mechanism.Passivating inhibitors like nitrites develop a goodprotection effect, especially on iron (steel) materialsby forming a passive layer in cooperation with
0 1 2 3 4Time (h)
20
40
60
80
100E
ffici
ency
%
1
3
2
Fig. 7: 1. Low vapor pressure �1023 Pa, 2. high vaporpressure �103 Pa, 3. mixed VCIs
10-1 10-2Vapor pressure
Temperature (°C)
0
0 100
0
(X) 5
Pro
tect
ion
radi
us (P
R, m
)
Ser
vice
life
(SL,
Yea
rs)SL
PR SL
PR
Fig. 8: Relationship between corrosion protection radius,service life, and vapor pressure
1
2
3
4
Application time (AT)
Cor
rosi
on ra
te (C
R)
Fig. 9: 1 = mild steel without VCI, 2 < 3 < 4 increasing VCIconcentration
J. Coat. Technol. Res.
oxygen.81 However, passivating inhibitors have littleeffect on nonferrous metals such as zinc, aluminum,and magnesium.
M.A. Quraishi and D. Jamal revealed that thecorrosion-inhibiting action of diaminohexanes is attrib-uted to the presence of an amino group and carboxylateanions. In addition to this, para-electrons and a lone pairof electrons present on the N atom of the aminohexanemolecules also facilitate adsorption of inhibitor mole-cules onto the metal surface, as shown in Fig. 11.57 Thecorrosion-inhibiting action of the nitrobenzoates wasattributed to thepresenceof a nitro group, aromatic ring,and carboxylate anion. Inhibitive action of orthophos-phate was attributed to the presence of p-electrons,which facilitated the adsorption of inhibitor moleculesonto the metal surface.
The vapor corrosion inhibition properties of bis-piperidiniummethyl-urea (BPMU) and monopiperi-diniummethyl-urea (MPMU) were compared for thecorrosion inhibition of mild steel by reference (52).The results show that BPMU has the better protection
effect compared with MPMU. It was shown that oneBPMU molecule has two N atoms to coordinate withone Fe atom and that one MPMU molecule has one Natom to coordinate with one Fe atom.
Hence, it can be concluded that the presence of theunpaired electrons or lone pair of electrons in the VCIcompounds leads to better adsorption of the com-pounds on the metal surface, leading to better passi-vation of the electrochemical reactions which lead tocorrosion. Better adsorption of the compounds alsoforms a strong monomolecular layer on the metalsurface, thereby repelling water molecules preventingcorrosion.
Merits of volatile corrosion inhibitor coatings
Various types of paints, or rather coatings, are usedtraditionally to protect metal surfaces against corro-sion. The majority of these coatings are solvent-basedwhich are not environmentally friendly, and alsovarious solvents are used during removal, which inturn affects the metal surface. However, in the case ofVCI coatings, a monomolecular layer is formed on themetal surface which protects the metal even if the paintgets disrupted, exposing the bare metal. Anotheradvantage is that since VCIs are volatile, they reachand cover even the inaccessible parts and crevices ofthe metal surface, protecting them against corrosionwhich the conventional paints are unable to do.Further merits of the VCI coatings are discussedbelow, as per the latest literature.
Baseman82 showcased the main difference betweenconventional paints and the paints containing VCI.Experiments revealed that the VCI component in thepaint migrates through the paint film to form anadditional, continuous coating on the metal surface toprotect the same, with the advantage that even if thepaint film is disrupted, exposing a part of the metalsurface, some corrosion inhibitors migrate from theportion of the film adjacent to disruption to coat thebare metal and inhibit corrosion thereof.
Knell3 proved that the VCI solutions are effectiveeven when the coating is applied to a previouslypainted or damaged metal surface as the VCImolecules can migrate all over the metal surface andprovide the required protection.
The use of VCI coatings for the prevention ofatmospheric corrosion is advantageous as it does notinvolve the use of oils whose removal before the use ofcoated metal involves additional time and economicfactor. Moreover, removal of the protective oil coat-ings involves the use of organic solvent- or water-baseddetergents whose disposal is a problem contraveningenvironmental regulations. Marshakov83 compared theatmospheric corrosion-inhibitive properties of VCIcompounds and conventional corrosion-inhibitive oils.
The vapor diffusing properties of such corrosion-inhibiting formulations offer an important advantage
Application time (AT)
0
100E
ffici
ency
%
Fig. 10: Efficiency of VCI versus application time
Metal surface
VCI molecules
VCI carrier −−coating
Fig. 11: Adherence of VCI molecules on the metal surface
J. Coat. Technol. Res.
over conventional inhibitor coatings since the traces ofthese gas molecules penetrate into inaccessible cre-vices, gaps, and slots, reaching the surfaces of complex-shaped articles that are difficult to coat. They areadsorbed onto the surface of the metal to form acorrosion-inhibiting protective layer that is just a fewmolecules thick. VCI products may also include acidgas-absorbing chemicals in the packaging material toact as a barrier and add another dimension to theprotection of the metal content. The scavengingchemicals react and neutralize the polluted air thatmay diffuse through the VCI material.
Concentrations of VCIs in VCI products (e.g., VCIplastics) are very low (< 1 wt%). When the packingmaterial has reached the end of its life cycle, VCIconcentrations are minimal and VCI plastic can berecycled. The trend in the VCI plastics industry is touse environmentally safe compounds that are eitherphotodegradable or biodegradable.
Volatile corrosion inhibitor (VCI) coatings
Volatile corrosion inhibitor coatings are a user-friendlyreplacement for the solvent- and oil-based coatingswhich are conventionally used for protection of themetals from corrosion. Based on the area of applica-tion, VCI coatings can broadly be classified as perma-nent VCI coating and temporary (or strippable) VCIcoating. Permanent VCI coatings are the ones whichare useful for corrosion prevention during the workinghours of the metal usually at the place of its installa-tion, while the strippable coatings provide temporaryprotection to the metal surface during processing,transportation, and storage. Various VCI coatings havebeen developed which are discussed as per the latestliterature.
Jeffrey84 developed a coating containing benzotria-zole as a VCI material and an antiwetting barrierhaving a nanoparticle composite structure. In thiscoating, a vapor corrosion inhibitor layer is providedon the substrate and an antiwetting barrier comprisinga nanoparticle composite structure deposited on thesubstrate surface using a liquid deposition process, toform an ionic barrier with super-hydrophobic proper-ties on the substrate. This coating acts as a replacementfor the usual anticorrosive barrier layers includingpaints, polymers, and organic coatings of urethanes,epoxies, acrylics with a typical thickness of around 25to 125 lm.85
Baseman82 patented a novel paint compositioncomprising an organic solvent-based solid film-formingcomponent such as alkyd esters with an organic volatilecorrosion inhibitor dicyclohexylammonium nitrite.
Martenson86 disclosed a water-based coating com-position which forms a readily strippable protectivefilm on metal surfaces. The composition includes a filmformer ingredient which is a terpolymer of polyvinylbutyral, polyvinyl alcohol, and polyvinyl acetate withbenzotriazole as the volatile corrosion inhibitor. TheT
able
4:Volatile
corrosioninhibitorcoatings
Sr.
no.
Auth
or
Title
/year/
pate
nt
no
VC
Iused
Coatings
develo
ped
1.
Chin
net
al.
Surf
ace
Coating,
US
2010/0
08095
Benzotr
iazole
Super-
hyd
rophobic
coatin
gw
itha
nanopart
icle
com
posi
test
ruct
ure
isdeposi
tedon
the
subst
rate
surf
ace
usi
ng
liquid
deposi
tion
pro
cess
2.
Maurice
S.
Basem
an
Pain
tC
om
positio
nC
onta
inin
gV
ola
tile
Corr
osio
nIn
hib
itor,
US
1989/4
812503
Dic
yclo
hexyla
mm
oniu
mnitrite
The
org
anic
solv
ent-
based
solid
film
-form
ing
pain
tsuch
as
alk
yd
este
rsw
ith
an
org
anic
vola
tile
corr
osio
nin
hib
itor
3.
Irvin
W.
Mart
enson
Corr
osio
nC
oating
Com
positio
n,
US
1988/4
792464
Benzotr
iazole
Aw
ate
r-base
dst
rippable
coatin
gco
mposi
tion
com
-prisi
ng
ate
rpoly
mer
of
poly
vinyl
buty
ral,
poly
vinyl
alc
ohol,
and
poly
vinyl
ace
tate
with
added
VC
I4.
Alv
inJ.
Conner
Meta
lC
orr
osio
nIn
hib
itor,
US
1978/4
,116,7
01
Sodiu
mnitrite
and
am
moniu
mbenzoate
VC
Icoating
with
am
ixtu
reof
sodiu
mnitrite
and
am
moniu
mbenzoate
ina
nitro
genous
base
such
as
ure
ato
wate
ras
the
VC
I5.
Walla
ce.
J.
Murr
ay
Vapor
Corr
osio
nIn
hib
itio
n,
US
1954/2
,914,4
24
Morp
holin
e,
morp
holin
ecarb
am
ate
VC
Icoating
form
ed
by
the
depositio
nof
the
vapor-
phase
inhib
itors
by
insitu
reaction
of
the
reacta
nts
,pre
fera
bly
invapor
sta
teover
the
meta
lsurf
ace
tobe
coate
d
J. Coat. Technol. Res.
advantage of such strippable coatings is that thecoating can be easily stripped off whenever requiredand does not involve the use of solvents for cleaningthe metal surface which at times causes more damageto the metal than corrosion.
Conner61 developed a VCI coating with a mixture ofsodium nitrite and ammonium benzoate in a nitroge-nous base such as urea to water as the VCI. Thismixture is applied as a mist or spray to the exposededges of coiled and cut length sheets of steel to protectthe steel during storage and shipping.
Murray66 developed a mechanism of depositing thevapor-phase inhibitors by in situ reaction of thereactants, preferably in vapor state over the metalsurface to be coated. The method involves the forma-tion of a vapor-phase corrosion inhibitor on enclosedmetal surfaces which will adhere to the metal atelevated temperatures, and working efficiency isnot affected by the air velocity over the metal surface.The VCI film formed on the metal surface will becontinuous and of even thickness and protects themetal surface not only against corrosion due to contactwith air and water but also against that due to theproducts of combustion encountered in engines and jetmotors. The vapor-phase inhibitors are also hydropho-bic in nature. The products (VCIs) formed also beingin the vapor phase easily penetrate into the intricateregions of the metal surface providing protectionagainst corrosion.
Table 4 gives the summary of all the VCI coatingsbased on the patent literature.
Types of volatile corrosion inhibitor coating
VCI coatings can be classified into various types suchas strippable and permanent VCI coatings based on
their area of application, solvent- and water-based VCIcoatings based on their solubility, and green VCIcoatings.
Table 5 gives an overview of the various types ofVCI coatings.
Based on area of application
Based on the area of application, VCI coatings can beclassified as temporary (strippable) coatings and per-manent coatings. The strippable coatings are mainlyused for corrosion prevention during transportationand storage, while permanent VCI coatings are typi-cally useful for corrosion prevention during the work-ing hours of the metal, at the place of its installation.
Strippable VCI coatings are used generally for thetemporary protection of the metal surface. The mainapplication of these coatings is generally during trans-portation, processing, and storage of the metals asthese coatings give the advantage of being able toeasily peel off as and when required. These coatings donot require the use of solvents for their removal,thereby not affecting the metal surface.
Strippable VCI coatings typically consist of the resinmaterial that can be easily peeled off from the metalsurface, with VCI compounds incorporated in the resinwhich provides the desired corrosion protection.
Strippable coating formulations can be either sol-vent-based or water-based emulsions containing re-lease agents that limit the adhesion they have todifferent substrates. Grogan87 developed an aqueous-based strippable coating composition, with poly (vinylbutyral), poly (vinyl formal), poly (vinyl acetates), poly(vinyl chloride) as the polymeric resin materialblended with surfactants such as TRITON X-100(nonionic surfactant) and plasticizers such as dibutyl
Table 5: Types of VCI coatings
Sr. no. Type of coating Example of the coatings developed
1. Strippable VCI coatings87 Coating formulations either solvent-based or water-based emulsioncan be made strippable by adding release agents that limit theadhesion they have to the different substrates. Resin materialsused for strippable coatings include poly (vinyl butyral), poly (vinylformal), poly (vinyl acetates), poly (vinyl chloride) blended withsurfactants and VCI with respect to the metal to be protected
2. Permanent VCI coatings3 Coating formulations such as alkyd esters or two-part polyamideepoxy primer paints with added 2–3 wt% of VCI solids in the finaldry film can be used as permanent VCI paints
3. Water-based VCI coatings88 These coatings consist of water-soluble VCI compounds such assodium nitrite or VCI incorporated into waterborne coatings byemulsification, adding co-solvents
4. Solvent-based VCI coatings82 It mainly consists of VCIs that are solvent soluble, such as in mineralspirits, incorporated in a solvent-based coating system
5. Green VCI coatings89,90 These coatings contain natural compounds such as menthol, woodbark oil, used as VCIs in the coatings for temporary corrosionprevention
J. Coat. Technol. Res.
phthalate to form water-based emulsion. This clear,strippable coating formed a temporary protectivecoating which is strippable for about one year bothby mechanical pulling and by water spray.
Suitable VCIs can be added into these coatings withrespect to the substrate/metal to be protected, ulti-mately leading to the strippable VCI coating.
The various other resins which are used for thestrippable coating formulations include emulsion-gradepolyvinyl chloride (PVC) which forms the plastisolcoatings and the water-based acrylic emulsion.
PVC plastisol coatings essentially consist of emul-sion-grade PVC particles, with particle size in therange of 0.5–2 lm. These are then dispersed in thesuitable plasticizer, usually phthalates such as dioctylphthalate, with added heat stabilizers which intercepthydrochloride from PVC decomposition and preventthe PVC from further degradation.91 Common stabi-lizers are made from barium-cadmium-zinc, cadmium-zinc, or octyl-tin compounds. Table 6 presents a typicalPVC plastisol coating formulation. The added merits ofPVC plastisol strippable coatings include high flexibil-ity of the coatings along with low permeability,resisting water and water vapor to permeate throughthe coatings.
With the emerging environmental concerns, water-based strippable coatings are being prepared. Water-based acrylic emulsion92,93 is one of the resins typicallyused for the preparation of the water-based strippablecoatings. This resin cures at room temperature with theevaporation of water giving a strippable coating on themetal surface. The hardness of the acrylic emulsion-based coatings can be improved by the addition of thestyrene monomer. The main advantages of suchcoatings include high scratch resistance. The coatingsare also highly resistant to water and other chemicals.The flexibility of the coatings can be improved by theaddition of phthalate plasticizers such as dioctyl phtha-late (DOP) along with release agents such as paraffinwax emulsion which make the coatings easily strip-pable from the metal surface.
Permanent VCI coatings are typically useful forcorrosion prevention during the working hours of themetal, at the place of its installation. These provideprotection to the metal surface or equipment againstboth corrosion and mechanical damage such as scratchwhen it is in use.
These coatings do not involve the use of typicalcorrosion inhibitor chemicals such as phosphates,mercapto compounds, azole derivatives which are toxicand fatal for humans.
The main advantage of such coatings is that theycontinue to protect the metal even if there is a smallscratch on the coated surface, due to the presence ofthe VCI compounds which form an invisiblemonomolecular layer on the metal, thereby protectingit against corrosion.
Knell3 developed an amine carboxylate-type VCIsolution and then incorporated it in the Part A of atwo-part polyamide epoxy primer paint to achieve a 2–3 wt% of amine carboxylate VCI solids in the final dryfilm when the parts A and B are combined and thepaint is applied to a metal surface and allowed to dryand cure. The coating containing long-chain VCIcompounds gave similar corrosion protection on whitesteel as the primer with added zinc phosphate. How-ever, the primer with added zinc phosphate wasinferior in exhibiting a lower degree of adhesion towhite and rusted steel panels than panels coated withthe epoxy primer with VCI added.
Long oil alkyd resins with added VCI compoundsare also used as permanent VCI coatings.94–96 Thealkyd resin can be modified as per the application areaof the coatings with the use of various curing mecha-nisms.97,98 The alkyd resin can be either air-dried withthe use of various driers such as zirconium drier, leaddrier, cobalt drier, or a combination of all three driers,or the alkyd resin can be heat-cured using melamineformaldehyde as the curing agent. The advantage ofalkyd resin coatings is that they provide a gloss to thecoatings along with high water resistance and goodmechanical properties.
Types of VCI coating based on solubility
The VCI coatings can be further classified based ontheir solubility in water as water-based VCI coatingsand solvent-based VCI coatings. Water-based VCIcoatings involve the use of water-based emulsions orwater-soluble resins as the main film-forming resinmaterials, while the solvent-based VCI coatings in-volve the use of resins such as polyvinyl butyral (PVB)which are soluble in certain solvents to be used as themain film-forming ingredient.
Water-based VCI coatings consist of water-solubleVCI compounds or VCI incorporated into waterbornecoatings by emulsification, adding co-solvents, etc.Tack can be eliminated by adding pigments, waxes,hard resins, or curing agents in some cases. Suchcoatings usually cure at room temperature, with theevaporation of water.
Solvent-based VCI coatings mainly consist of VCIsthat are soluble in certain solvents, such as in mineralspirits, tetrahydrofuran (THF), etc. The film-formingingredient is also solvent-based and usually involves
Table 6: Typical PVC formulation
Material Parts per hundred resin (phr)
PVC resin 60–100Plasticizer 30–100Stabilizer 0.5–5Pigments 0–5Lubricants 0–2Solvents 0–10Other additives 0–5
J. Coat. Technol. Res.
the use of thermal curing techniques for solventvaporization and curing of the coating.
Mode of application of VCI coating
VCI coatings can be applied to the substrate by dippingand fogging. New metal parts may be dipped in a VCIsolution, oil or water based, dried, and put on a shelfwith no corrosion concerns for extended periods oftime. Sprayed or fogged VCI coatings vaporize in thetank, vessel, or container; saturating the interioratmosphere, a portion of them condenses on thesurface, providing corrosion protection.
Green volatile corrosion inhibitors
Owing to the toxic nature of few of the amines (themain ingredient in the VCI compounds),99 naturalcompounds100 such as menthol101 can be used as avapor-phase corrosion inhibitor for temporary protec-tion of mild steel in NaCl environment.
Various such natural compounds can be extractedvia various processes such as liquid–liquid extractionand then purified to be used as the VCI. The lowtoxicity and good corrosion-inhibiting properties ofsuch compounds make them commercially applicable.
The highly volatile wood bark oils89 of Casia siamea-gonrai, Cassia auriculata, Crataeva religiosa, andStrychnos nuxvomica extracted from the dry bark canalso be used as a vapor-phase corrosion inhibitors formild steel and copper in sodium chloride and sulfurdioxide environments.
Chyhyrynets90 studied the anticorrosive propertiesof the volatile fractions of the isopropanol extract ofrapeseed (Brassicaceae family) oil cake. It is demon-strated by the Chyhyrynets90 and Vorobyova102 thatthe corrosion rate of steel decreases as its concentra-tion increases due to the blocking of the metal surfaceby chemically adsorbed molecules.
Testing methods for VCI coatings
Evaluation of the performance of vapor corrosioninhibitors is done in the laboratory under controlledconditions and in the field under natural or serviceconditions.103 Both the laboratory and field testing canbe performed by utilizing direct metal loss measure-ments, by electrochemical tests of the corrosion pro-cess and determined parameters such as corrosioncurrent, corrosion potential, polarization resistance,electrochemical impedance spectra and by electro-chemical noise measurements.104–107
Resistance probes (Corrosometer) can also be usedto detect the rate of the corrosion process by measur-ing the change in the resistance of a wire as the wirecorrodes. Monitoring of the corrosion process by using
a Corrosometer follows the kinetics of the corrosion/protection-developing processes.108
Usually, laboratory testing includes several proce-dures to evaluate the effect of different conditions onthe VCI performance.109
In general, laboratory tests of VCI products consistof:
• Preconditioning the metal specimen. The VCIemitter is placed in a testing chamber by normalconditions to obtain the VCI’s adsorption–desorp-tion equilibrium at the metal surface.
• Subjecting a ‘control’ and the VCI-protected spec-imens to various corrosive atmospheres. Variationsinclude elevated temperatures and relative humid-ity levels; cycling of condensation and evaporationof the moisture; corrosive salt solutions and indus-trial contaminants (sulfur dioxide, hydrogen sulfide,hydrogen chloride, ammonia).
• Evaluation of the test results.
A multi-metal corrosion test evaluates the protec-tion provided by a packaging material against galvaniccorrosion. Carbon steel, copper, galvanized steel,aluminum, brass, or other metals are attached to astar-shaped holder. These metal panels are connectedwith conductive wire and are kept inside the VCI filmor paper bag. The temperature cycle uses 20 h at roomtemperature (conditioning), 0.5 h at 80�C, 1.5 h atroom temperature, and 0.5 h at 80�C. Humidity insidethe bag is provided by a piece of paper saturated withwater, inserted inside this package.
The results of the test shall be presented using thescale:
• No corrosion-promoting effects• Slight/strong corrosion-promoting effect• No protective effect• Slight/average/good protective effect
The various mechanical properties of the coatingssuch as the flexibility, scratch hardness, impact resis-tance, adhesive strength, hardness, toughness are alsoevaluated as per the ASTM standards.110
The VCI compounds can be analyzed for the groupsleading to corrosion prevention and their stability forhigh-temperature range using FTIR and thermal anal-ysis.111,112
Future trends in VCI coatings
Boris88 developed a synergetic multi-layer defense ofcorrosion resistance through passivation, ion-scavenging,and film formation by modifying the waterborne acrylic-based paints by incorporation of a combination of nano-VCIs with a nontoxic metal complex inhibitor which
J. Coat. Technol. Res.
significantly improves the long-term corrosion protectionof acrylic paints that are applied directly to metal.
Leuders73 developed packaging material for corro-sive metallic objects, it comprised of a plastic filmforming a package on the outer surface, an inner layer,and an adhesive layer bonding the plastic film to theinner layer, wherein the adhesive layer comprises avolatile corrosion inhibitor and the inner layer has ahigh permeability for the corrosion inhibitor on thepackage outer surface as compared to the plastic film.
Adelman113 developed a padded packaging sheet forguarding against rust and corrosion, which incorpo-rates a coating of volatile corrosion inhibitor on apliable layer of a sealed-cell microporous foam. TheVCI can be incorporated into a cohesive non-adhesivecoating on the microporous in the absence of suchcohesive coating. The effectiveness of the VCI can befurther enhanced by incorporating in the padded sheeta vapor barrier such as, for example, aluminum foil, ora film of hydrophobic polymer such as a silicone orpolyester like Mylar (polyethylene terephthalate). Awater-repellent layer can also be added. The sheet canbe made antistatic and/or opaque and strengthenedwith fibers that make it almost impossible to tear.
Conclusion
Corrosion is the most widespread problem affectingmetal storage, transportation, and processing. Of thevarious alternatives available, the use of volatilecorrosion inhibitor (VCI) as a means of temporarycorrosion protection and its working mechanism alongwith the various factors affecting its adherence on themetal surface has been reviewed in this paper. Thevarious compounds used as VCIs in the coatings alongwith the advantages of using the VCI coatings over theconventional corrosion-inhibitive paints have also beendiscussed. This review article provides an emphasis onboth temporary and permanent VCI coatings usedpresently along with an overview of the past develop-ments. The future trends in the VCI coatings and theupcoming use of green VCIs to overcome the toxicnature of the VCIs have also been studied. Toconclude, VCI coatings can be used as a means oftemporary corrosion protection in metal packagingduring transportation and storage.
References
1. Charng, T, Lansing F, ‘‘Review of Corrosion Causes andCorrosion Control in a Technical Facility,’’ DSN Engi-neerign Section. p. TDA Progress Report, 42–69 (1982)
2. Gerhardus, HK, Brongers, MPH, Thompson, NG, Virmani,YP, Payer, JH ‘‘Corrosion Costs and Preventive Strategiesin the United States’’, Publication No. FHWA-RD-01-156
3. Timothy Alan Knell, RW, ‘‘Corrosion Resistant Coatingsfor Metal Surfaces.’’ Patent No: US 2016/0077886 A1, pp.1–8, 2016
4. Allcock, BW, Lavin, PA, ‘‘Novel Composite CoatingTechnology in Primary and Conversion Industry Applica-tions.’’ Surf. Coat. Technol., 163 (164) 62–66 (2003)
5. Shreir, LL, ‘‘1.05: Basic Concepts of Corrosion.’’ Shreir’sCorros., 1 89–100 (2010)
6. Subramanian, A, Rajendran, P, Natesan, N, Balakrishnan,K, Vasudevan, T, ‘‘Anti-Corrosion Methods and MaterialsEmerald Article: Corrosion Behaviour of Metals in SOEnvironment and Its Prevention by Some VolatileCorrosion Inhibitors Contributed Papers Corrosion Beha-viour of Metals in SO2 Environment and Its Preventionby Some.’’ Anti Corros. Methods Mater., 5 346–348(1999)
7. Kannan, P, Lavanya, K, Natesan, M, ‘‘Study the Perfor-mance of Volatile Corrosion Inhibitors in Protection ofMild Steel in Cl 2 Gas Environments.’’ Res. J. Chem. Sci., 2(9) 50–55 (2012)
8. Sorensen, PA, Kiil, S, Dam-Johansen, K, Weinell, CE,‘‘Anticorrosive Coatings: A Review.’’ J. Coat. Technol.Res., 6 (2) 135–176 (2009)
9. Carneiro, JO, Teixeira, JO, Azevedo, S, Maltez-da CostaM, ‘‘Smart Self-Cleaning Coatings for Corrosion Protec-tion,’’ Handbook of Smart Coatings for Materials Protec-tion, pp. 489–509 (2014)
10. Zubielewicz, M, Gnot, W, ‘‘Mechanisms of Non-toxicAnticorrosive Pigments in Organic Waterborne Coatings.’’Prog. Org. Coat., 49 (4) 358–371 (2004)
11. Fitzgerald, JH III, ‘‘Engineering of Cathodic ProtectionSystems,’’ Uhlig’ Corros. Handb., 1001–1011 (2011)
12. Franke, G, Heinzelmann, U, ‘‘Internal Cathodic Protectionof Water Tanks and Boilers.’’ Handb. Cathod. Prot. 441–463 (1997).
13. Sastri VS, ‘‘3. Adsorption in Corrosion Inhibition.’’ GreenCorros. Inhib. Theory Pract. 103–138 (2011).
14. Mary Anbarasi, AKC, Rajendran, S, Pandiarajan, M, ‘‘AnEncounter with Corrosion Inhibitor.’’ Eur. Chem. Bull., 2(4) 197–207 (2013)
15. Georg Reinhard, UL, Hahn, G, Lautner, S ‘‘Vapor-PhaseCorrosion Inhibitors and Methods for their Production.’’Patent No: US 6,540,959 B1, vol. 1, no. 12, pp. 0–4,2003.
16. Dariva, CG, Galio, AF, ‘‘Corrosion Inhibitors – Principles,Mechanisms and Applications.’’ 2014. https://doi.org/10.5772/57255.
17. Miksic, BA, Miller, RH, ‘‘Fundamental Principles ofCorrosion Protection with Vapor Phase Inhibitors,’’ 5thEuropean Symp. Corrosion Inhibitors, pp. 1–20. EuropeanFederation of Corrosion, Italy (1980)
18. Georg Reinhard, GH, Ludwig, U, ‘‘Vapor Phase CorrosionInhibitors and Method for their Production.’’ Patent No:US007824482B2, vol. 2, no. 12, pp. 1–9, 2010.
19. Baker, HR, ‘‘Volatile Rust Inhibitors.’’ Ind. Eng. Chem., 46(12) 2592–2598 (1952)
20. Vasanth, KL, ‘‘Vapor Phase Corrosion Inhibitors for NavyApplications,’’ National Association of Corrosion Engi-neers, Paper # 179, pp. 1–9, 1997
21. Fodor, GE, ‘‘The Inhibition of Vapor-Phase Corrosion: AReview.’’ U.S. Army Belvoir Research and DevelopmentCenter Materials, Fuels and Lubricants Laboratory, InternalReport BFLRF No. 209, no. 209, pp. 1–66, 1986.
22. Gandhi, A, ‘‘Storage Tank Bottom Proptection UsingVolatile Corrosion Inhibitors.’’ Mater Perform, 1 (January)28–30 (2001)
23. Rowden, S, ‘‘Vapour-Phase Corrosion Inhibitors.’’ Anti-Corros. Methods Mater., 5 (4) 117–126 (1958). https://doi.org/10.1108/eb019433.
J. Coat. Technol. Res.
24. Singh, DDN, Banerjee, MK, ‘‘Vapour Phase CorrosionInhibitors: A Review.’’ Anti-Corrosion, 31 (June) 4–8(1984)
25. Boyle, R, Miksic, BWB, ‘‘Efficacy of Vapor Phase Corro-sion Inhibitor Technology in Manufacturing.’’ Corrosion, 60(6) 515–522 (2004)
26. Bavarian et al., B, ‘‘Comparison of the Corrosion Protec-tion Effectiveness of Vapor Corrosion Inhibitors and DryAir System.’’ NACE International Corrosion Conferenceand Expo, Paper No. 5449, pp. 1–12, 2015.
27. Pucic, I, Madzar, T, Jaksic, M, ‘‘PIXE Spectroscopy forDetermination of Volatile Corrosion Inhibitor Concentra-tion in Anticorrosion Polymer Films.’’ Monatshefte furChemie, 137 (7) 953–961 (2006)
28. Estevao, LRM, Nascimento, RSV, ‘‘Modifications in theVolatilization Rate of Volatile Corrosion Inhibitors byMeans of Host-guest Systems.’’ Corros. Sci., 43 (6) 1133–1153 (2001)
29. Valdez, SB, et al., ‘‘Rapid Method for Corrosion ProtectionDetermination of VCI Films.’’ Anti-Corros. MethodsMater., 53 362–366 (2006)
30. McConnell, R, ‘‘Volatile Corrosion Inhibitors Offer Effec-tive Protection for Processing and Shipment of Metal-BasedProducts.’’ Metal Finish., 106 (9) 23–27 (2008)
31. Holden et al., J, ‘‘Vapor Corrosion Inhibitors in Hydro-Testing and Long Term Storage Applications.’’ NACEInternational Corrosion Conference and Expo, Paper No.10405, no. 10405, pp. 1–14, 2010
32. Furman, AY, Kharshan, M, Chandler, CJ, ‘‘Performanceand Testing of Vapor Phase Corrosion Inhibitors.’’ Corro-sion, 2004 1–12 (2004)
33. Subramanian, A, Natesan, M, Muralidharan, VS, Balakr-ishnan, K, Vasudevan, T, ‘‘Vapor Phase Corrosion Inhibi-tors.’’ Corrosion, 56 (2) 144–155 (2000)
34. Saini, V, Kumar, H, ‘‘Synergistic Effect of CTAB as VPCIfor Mild Steel.’’ Int. J. Chem. Phys. Sci., 3 (5) 52–69 (2014)
35. Lenard, DR, Moores, JG, ‘‘The Effects of Vapor PhaseCorrosion Inhibitors on the Galvanic Corrosion of Alu-minium.’’ Corros. Sci., 34 (5) 871–880 (1993)
36. Dwivedi, SK, ‘‘Corrosion in Fuel Tank and Its Preventionby Volatile Corrosion: A Review.’’ AKGEC Int. J. Tech-nol., 4 (1) 48–53 (2013).
37. Eibl, S, Reiner, D, ‘‘Correlation of Content and CorrosionProtection of Volatile Corrosion Inhibitors in PackagingMaterial: Regaining Trust in VCI.’’ Mater. Corros., 62 (8)745–752 (2011)
38. Andreev, NN, Goncharova, OA, Vesely, SS, ‘‘VolatileInhibitors of Atmospheric Corrosion. IV. Evolution ofVapor-Phase Protection in the Light of Patent Literature.’’Int. J. Corros. Scale Inhib., 2 (3) 162–193 (2013)
39. Saji, VS, ‘‘A Review on Recent Patents in CorrosionInhibitors.’’ Recent Patents Corros. Sci., 2 (1) 6–12 (2010)
40. Brongers, MPH, Koch, GH, ‘‘Corrosion Costs and Preven-tive Strategies in the United States.’’ NACE, 10, 2010.
41. Zairyo, ‘‘Survey of Corrosion Cost in Japan,’’ Zairyo-to-Kankyo, vol. 58, no. 12, pp. 402–428, 2009.
42. Three Bond, ‘‘Volatile Corrosion Inhibitor (VCI),’’ vol.1987, no. 7, pp. 1–10, 1987.
43. Kumar, H, Yadav, V, ‘‘BIA, DPA, MBTA and DMA asVapour Phase Corrosion Inhibitors for Mild Steel UnderDifferent Atmospheric Conditions.’’ Int. Lett. Chem. Phys.Astron., 1 52–66 (2014)
44. Kumar, H, Saini, V, Yadav, V, ‘‘Study of Vapour PhaseCorrosion Inhibitors for Mild Steel Under DifferentAtmospheric Conditions.’’ Int. J. Eng. Innov. Technol., 3(3) 206–211 (2013)
45. Kumar, H, Yadav, V, ‘‘Corrosion Characteristics of MildSteel Under Different Atmospheric Conditions by VapourPhase Corrosion Inhibitors.’’ American Journal of MaterialsScience and Engineering, 1 (3) 34–39 (2013)
46. Kannan, P, Jithinraj, P, Natesan, M, ‘‘Multiphasic inhibitionof mild steel corrosion in H2S gas environment.’’ Arab. J.Chem. 11 (3) 388–404 (2013)
47. Zhang, D, Guoding, Z, ‘‘Study of Morpholinium Oligomeras a Novel Vapor Phase Inhibitor.’’ Corrosion, 2003 (April)1–8 (2003)
48. Henriksen, JF, ‘‘The Distribution of a Volatile CorrosionInhibitor (CHC) on Corroded Fe.’’ Corros. Sci., 12 (5) 433–436 (1972)
49. Zhang, DQ, Gao, LX, Zhou, GD, ‘‘Self-assembled Urea-Amine Compound as Vapor Phase Corrosion Inhibitor forMild Steel.’’ Surface and Coatings Technology, 204 (9–10)1646–1650 (2010)
50. Gao, G, Liang, CH, Wang, H, ‘‘Synthesis of TertiaryAmines and Their Inhibitive Performance on Carbon SteelCorrosion.’’ Corros. Sci., 49 (4) 1833–1846 (2007)
51. Skei, T, Stillman, N, Wachter, A, ‘‘DicyclohexylammoniumNitrite, A Volatile Inhibitor for Corrosion PreventivePackaging.’’ Corrosion, 7 (9) 284–294 (1951)
52. Quan Zhang, D, Xun An, Z, Yi Pan, Q, Xin Gao, L, DingZhou, G, ‘‘Comparative Study of Bis-piperidiniummethyl-urea and Mono-piperidiniummethyl-urea as Volatile Cor-rosion Inhibitors for Mild Steel.’’ Corros. Sci., 48 (6) 1437–1448 (2006)
53. Zhang, DQ, Gao, LX, Zhou, GD, ‘‘Polyamine Compoundas a Volatile Corrosion Inhibitor for Atmospheric Corro-sion of Mild Steel.’’Materials and Corrosion, 58 (8) 594–598(2007)
54. Zhang, D, An, Z, Pan, Q, Gao, L, Zhou, G, ‘‘VolatileCorrosion Inhibitor Film Formation on Carbon SteelSurface and Its Inhibition Effect on the AtmosphericCorrosion of Carbon Steel.’’ Applied Surface Science, 2531343–1348 (2006)
55. Vuorinen, E, Ngobeni, P, Van der Klashorst, GH, Skinner,W, de Wet, E, Ernst, WS, ‘‘Derivatives of Cyclobexylamineand Morpholine as Volatile Corrosion Inbibitors.’’ BritishCorrosion Journal, 29 (2) 120–121 (1994)
56. Skinner, W, ‘‘A New Method for Quantitative Evaluationof Volatile Corrosion Inhibitors.’’ Corros. Sci., 35 (5–8)1491–1494 (1993)
57. Quraishi, MA, Jamal, D, ‘‘Development and Testing of allOrganic Volatile Corrosion Inhibitors.’’ Corrosion, 58 (5)387–391 (2002)
58. Gao, G, Liang, CH, ‘‘1,3-Bis-diethylamino-propan-2-ol asVolatile Corrosion Inhibitor for Brass.’’ Corros. Sci., 49 (9)3479–3493 (2007)
59. Kean, RT, Fnace BAM, ‘‘Improved Packaging MaterialsMade FromBarrier CoatedPaper IncorporatingVapor PhaseCorrosion Inhibitors.’’ NACE International Corrosion Con-ference and Expo, Paper No. 5575, no. 5575, pp. 1–7, 2015.
60. Philip, T, Shick, E, ‘‘Vapor Phase Corrosion Inhibition.’’Patent No: 3,433,577, pp. 3–4, 1969.
61. Conner, AJ, ‘‘Metal Corrosion Inhibitor.’’ Patent No:4,116,701, pp. 3–6, 1978.
62. Korpics, CJ, ‘‘Vapor Phase Inhibitor Containing Benzotri-azole and Tolyltriazole Mixtures.’’ Patent No: 3,791,855, pp.1–10, 1974.
63. Finsgar, M, Milosev, I, ‘‘Inhibition of Copper Corrosion by1,2,3-benzotriazole: A Review.’’ Corros. Sci., 52 (9) 2737–2749 (2010)
64. Chen, Z, Huang, L, Zhang, G, Qiu, Y, Guo, X, ‘‘Benzo-triazole as a Volatile Corrosion Inhibitor During the Early
J. Coat. Technol. Res.
Stage of Copper Corrosion Under Adsorbed Thin Elec-trolyte Layers.’’ Corros. Sci., 65 214–222 (2012)
65. Quraishi, MA, Bhardwaj, V, Rawat, J, ‘‘Prevention ofMetallic Corrosion by Lauric Hydrazide and Its Salts UnderVapor Phase Conditions.’’ J. Amer. Oil Chem. Soc., 79 (6)603–609 (2002)
66. Murray, WJ, ‘‘Vapor Phase Corrosion Inhibition.’’ PatentNo: 2914424, pp. 2–4, 1959.
67. Vapor-Tek Ltd., ‘‘The Role of Volatile Corrosion InhibitorOil.’’ Anti-Corros. Methods Mater., 31 (4) 6 (1984). https://doi.org/10.1108/eb060850.
68. Ebadi-Dehaghani, H, ‘‘Diffusion of 1,2,3-Benzotriazole as aVolatile Corrosion Inhibitor through Common PolymerFilms Using the Molecular Dynamics Simulation Method.’’Journal of Macromolecular Science, Part B, 55 (3) 310–318(2016)
69. Dorfman, AM, Zolotovitskii, YM, Lyakhovich, AM, Cha-lykh, AE, Reshetnikov, SM, ‘‘The Desorption of a VolatileCorrosion Inhibitor from Polyethylene.’’ Protection ofMetals, 37 (1) 9–12 (2001)
70. Gross, JR, The Evolution of Absorbent Materials, Vol 8, 2nded. Elsevier Inc., London (1990)
71. Niu, H, Wang, F, Weiss, RA, ‘‘Hydrophobic/HydrophilicTriblock Copolymers: Synthesis and Properties of Physi-cally Cross-Linked Hydrogels.’’ Macromolecules, 48 (3)645–654 (2015)
72. Po, R, ‘‘Water-Absorbent Polymers: A Patent Survey.’’ J.Macromolecular Sci., Part C: Polymer Reviews, 34 (4) 607–662 (1994)
73. Wachs, T, Leuders, J, Leuders, J, ‘‘Packing Material forCorrosible Metallic Objects.’’ Patent No: US8461063B2,vol. 1, no. 12, 2013
74. Persiantseva, BP, Terentiev, PB, Rosenfeld, IL, ‘‘Mecha-nism of Metal Protection by Volatile Inhibitors.’’ NACECorros., 20 222t (1964)
75. Haruhito Sato, KO, ‘‘Vapor Phase Corrosion InhibitorCompositions and Method of Inhibiting Corrosion usingSaid Compositions.’’ Patent No: US 4308168, pp. 0–4, 1981
76. Miksic, BBA, ‘‘Some Aspects of Metal Protection by VaporPhase Inhibitors,’’ NACE Int. J. 1–10, 1975
77. Vuorinen, E, Kalman, E, Focke, W, ‘‘Introduction toVapour Phase Corrosion Inhibitors in Metal Packaging.’’Surf. Eng., 20 (4) 281–284 (2004)
78. Rammelt,U,Koehler, S,Reinhard,G, ‘‘Use ofVapourPhaseCorrosion Inhibitors in Packages for Protecting Mild SteelAgainst Corrosion.’’ Corros. Sci., 51 (4) 921–925 (2009)
79. Koehler, S, Reinhard, G, ‘‘VCI Containing Package Mate-rials-Mode of Functioning.’’ Int. J. Corros. Scale Inhib., 3(4) 286–306 (2014)
80. Bastidas, DM, Cano, E, Mora, EM, ‘‘Volatile CorrosionInhibitors: A Review.’’ Anti Corros. Methods Mater., 52 71–77 (2005)
81. Andreev, NN, Kuznetsov, YI, Fedotova, TV, ‘‘On Corro-sion Protection of Steel with Solutions of Volatile Inhibi-tors.’’ Prot. Metals, 37 (1) 1–8 (2001)
82. Baseman, MS, ‘‘Paint Composition Containing a VolatileCorrosion Inhibitor.’’ Patent No: US 4812503, pp. 1–4, 1989
83. Mikhailovskii, YN, Popova, VM, Marshakov, AI, ‘‘Fieldand Accelerated Tests of Contact and Volatile Inhibitors ofAtmospheric Corrosion with Various Metals.’’ Prot. Metals,36 (5) 546–551 (2000)
84. Jeffrey, RG, Chinn, D, ‘‘Surface Coating.’’ Patent No: US2010/0080957 A1, pp. 1–39, 2010
85. Sanyal, B, ‘‘Organic Compounds as Corrosion Inhibitors inDifferent Environments: A Review.’’ Prog. Org. Coat., 9 (2)165–236 (1981)
86. Martenson, IW, ‘‘Corrosion Coating Composition.’’ PatentNo: US 4792464, pp. 0–5, 1988
87. Boyd, RH, Grogan GW, ‘‘Aqueous Based, StrippableCoating Composition and Method.’’ Patent No:USOO5143949A, pp. 1–6, 1992
88. Boris, ARC, Fnace, M, Kharshan, M, ‘‘Water-Based Coat-ings Powered by Nanoparticle Vapor Corrosion Inhibitors.’’Mater. Perf., June 20–23 (2015)
89. Poongothai, N, Rajendran, P, Natesan, M, Palaniswamy, N,‘‘Wood Bark Oils as Vapour Phase Corrosion Inhibitors forMetals in NaCl and SO2 Environments.’’ Indian J. Chem.Technol., 12 (6) 641–647 (2005)
90. Chyhyrynets, OE, Vorob’Iova, VI, ‘‘Anticorrosion Proper-ties of the Extract of Rapeseed Oil Cake as a VolatileInhibitor of the Atmospheric Corrosion of Steel.’’ Mater.Sci., 49 (3) 318–325 (2013)
91. Von Moody, HLN, ‘‘Polyvinyl Chloride Plastisol Coating.’’Tufted Carpet 115–123 (2004)
92. Guo, Z, et al., ‘‘High-Quality Hollow Closed-Pore SilicaAntireflection Coatings Based on Styrene-Acrylate Emul-sion @ Organic-Inorganic Silica Precursor.’’ ACS Appl.Mater. Interfaces, 8 (18) 11796–11805 (2016)
93. Zhang, Y, et al., ‘‘A Lightweight Geo-Workflow Manage-ment System.’’ J. Power Sources, 78 (1) 427–436 (2016)
94. Prenosil, M, ‘‘Volatile Corrosion Inhibitor Coatings.’’Mater. Perform., 40 14–17 (2001)
95. Vaso, K, Dema, M, ‘‘Preparation of the AnticorrosivePaints with Long Oil Alkyd Resins Modified with MaleicAnhydride and Phthalic Anhydride.’’ Zastita Mater., 51 (1)87–93 (2010)
96. Badran, BM, Abdel Fattah, AA, Abdul Azim, AA, ‘‘NewCorrosion Inhibitors Based on Fatty Materials-II. Epoxi-dized Fatty Materials Modified with Aromatic Amines.’’Corros. Sci., 22 (6) 525–536 (1982)
97. Abd El-Ghaffar, MA, Youssef, EAM, Abo-Shosa, MMH,Ibrahim, NA, ‘‘Articles Modified Alkyd Resin as Binder forPaints.’’ 1996.
98. Malik, WU, Aggarwal, LK, ‘‘Studies on the CorrosionProtection Efficiency of Some Alkyd Based Anti-corrosivePaints.’’ pp. 12–14, 1976
99. Palou, RM, Olivares-Xomelt, O, Likhanova, NV, ‘‘Envi-ronmentally Friendly Corrosion Inhibitors.’’ Green Corros.Inhib. Theory Pract. 257–303 (2011).
100. Scott, J, ‘‘Biodegradable Vapor Corrosion Inhibitor Prod-ucts.’’ Patent No: EP 0990676 A1,’’ no. 19, pp. 1–10, 2000.
101. Premkumar, P, Kannan, K, Natesan, M, ‘‘Evaluation ofMenthol as Vapor Phase Corrosion Inhibitor for Mild SteelIN NaCl.’’ Arab. J. Sci. Eng., 34 (2) 71–79 (2009)
102. Chygyrynets’, OE, Vorobyova, VI, Galchenko, GY,Roslik, IG, ‘‘Investigation of the Efficiency of Inhibitorsof Atmospheric Corrosion.’’ Metall. Min. Ind., 4 (2) 100–106 (2012)
103. Wan, H, Huang, H, Zhang, M, Li, Z, ‘‘A modified method forevaluation of materials containing volatile corrosion inhibi-tor.’’ J. Cent. South Univ. Technol., 12 (4) 406–410 (2005)
104. Pereira, EA, Tavares, MFM, ‘‘Determination of VolatileCorrosion Inhibitors by Capillary Electrophoresis.’’ J.Chromatogr. A, 1051 (1–2) 303–308 (2004)
105. Clifford, P, Moore, G ‘‘Instrumentation for Measurementof the Effectiveness of Vapor Corrosion Inhibitors C.’’NACE, National Association of Corrosion Engineers, Cor-rosion, Paper #490, pp. 1–8, 1995
106. Subramanian, A, Natesan, M, Gopalan, A, Balakrishnan, K,Vasudevan, T, ‘‘A Modified Cell Design for the Quantita-tive Evaluation of Vapour Phase Corrosion Inhibitors.’’Bull. Electrochem., 15 (2) 54–55 (1999)
J. Coat. Technol. Res.
107. Martin, P, Arsenal, RI, ‘‘Vapor Pressures of VolatileCorrosion Inhibitors by the Torsion-Eff usim Method’’.’’J. Chem. Eng. Data, 1 292–294 (1965)
108. James Henderson, EYLA, ‘‘Evolving Standard Test Meth-ods for Vapor Inhibiting Ability (Via) for Corrosion Protec-tion.’’ NACE International Corrosion Conference and Expo,Paper No. 10146, vol. 215, no. 244, pp. 1–10, 2010.
109. ‘‘Laboratory Test to Evaluate the Vapor-Inhibiting Abilityof Volatile Corrosion Inhibitor Materials for TemporaryProtection of Ferrous Metal Surfaces,’’ NACE Interna-tional-TM0208, no. 21253, 2008.
110. Koleske, JV, ‘‘Mechanical Properties of Solid Coatings.’’Encycl. Anal. Chem. 1–15 (2001)
111. Pieterse, N, Focke, WW, Vuorinen, E, Racz, I, ‘‘Estimatingthe Gas Permeability of Commercial Volatile CorrosionInhibitors at Elevated Temperatures with Thermo-Gravimetry.’’ Corros. Sci., 48 (8) 1986–1995 (2006)
112. Focke, WW, Nhlapo, NS, Vuorinen, E, ‘‘Thermal Analysisand FTIR Studies of Volatile Corrosion Inhibitor ModelSystems.’’ Corros. Sci., 77 88–96 (2013)
113. Adelman, HB, ‘‘Sheet Packaging Material.’’ Patent No: US4321297,’’ vol. 2176, no. Vii, pp. 4761–4763, 1982
J. Coat. Technol. Res.
