Experimental Details · 2014-05-20 · Surface Treatment. Computer Methods and Experimental Measurements 49 Experimental Details 10 x 2 cm samples were cut from 1.5 mm thick carbon

Physical and electrochemical characterisation of

electroless nickel coatings on carbon steelC. Kerr, D. Barker and F. Walsh

& f /z j/ca/ Sa'fMcej, [/m've rjz'rr. Mzc/za /'j Bw/dmg,

Abstract

Various electrolyte and deposit parameters were investigated to assess the performance of

electroless nickel coatings deposited from baths aged in the range 0-6 metal bath turnovers.

The properties studied included: measurement of internal stress, analysis of orthophosphiteconcentration in the plating solution and determination of phosphorus content in the deposit.

The effect of bath ageing on the hardness of the deposit in the as-plated condition, and after

heat treatment, was also examined. Changes in the deposit mainly appeared in the range of 3-

5 metal turnovers, suggesting that the life expectancy of these electroless nickel platingsolutions should not exceed 6 metal bath turnovers. The corrosion potential (E ) was

measured and the corrosion current density (i) of coated samples was determined by

extrapolation of polarisation vs. log current density (Tafel) plots in 0.125M P SOj. at 22°C.

Introduction and Literature Survey

Electroless nickel coatings on steel have properties such as excellent throwing

power and high hardness which have resulted in a wide range of industrialapplications, such as valves for fluid handling, hydraulic cylinders and

medical equipment [1-3]. The deposits exhibit good corrosion resistance in a

wide range of environments in the absence of defects present in the coating.However, nickel is more noble than ferrous substrates and severe corrosion

can result at the base of any through-pores due to the adverse condition of a

Transactions on Engineering Sciences vol 17, © 1997 WIT Press, www.witpress.com, ISSN 1743-3533

48 Surface Ireatment, Computer Methods and Experimental Measurements

large cathode area to a small anode area. Defects in the galvanic metal coating

can seriously reduce the design life and the range of service environments.

Porosity in electroless deposits has been attributed to improper pre-

treatment processes [4-8], surface roughness of the component being plated

[9], an adverse composition of the plating bath [10], design features of the

component and surface defects on the substrate prior to coating [11]. Traces

of soils remaining after cleaning will prevent the uniform autocatalytic

reduction of nickel from the solution and efficient cleaning of the ferrous

metal is vital. Rough surfaces tend to promote the development of pores due

to an increase in substrate surface area, entrapment of particles (such as

alumina from polishing pre-treatment processes) and the trapping of hydrogen

gas bubbles in the deep recesses on the surface [12-14].

A coating with a high internal stress is hazardous to cathodic deposits

as they can lead to crack formation and expose the substrate to the attacking

environment, or peel leading to poor adhesion of the coating. In the early

stages of deposit growth, the nature of the stress may have an important

bearing on the final levels of coating porosity found within the plated deposit.

A high compressive stress may not only help reduce porosity but also improve

deposit adhesion as electroless nickel coatings tend to have a relatively low

ductility. In the presence of surface defects or soil residues on te steel, an

electroless nickel coating can develop high tensile internal stresses, resultingin poor adhesion. When the component is subjected to applied loads, theinternal stresses within the deposit may have an important influence on the

time to failure such as in stress corrosion cracking and corrosion fatigue

conditions. The presence of a high tensile stress within the coating may bedetrimental to both deposit and substrate [15]; stressed areas are more likely tocorrode or to produce coating defects.

A phosphorus content of 11-13% is considered to result in a

compressive stressed deposit but lower phosphorus contents produce a tensile

internal stress. Baldwin and Such reported [16] that the cause and effect of

internal stress within electroless nickel deposits were a result of physical

changes in the electroless bath, e.g., pH, temperature and phosphite

concentration. Their results indicated a change from compressive to tensile

internal stress at pH 4.65; this was atributed to an increase in orthophosphiteconcentration as the bath aged. The results underline the importance ofcontrolling bath composition and operational parameters to optimise plating.

As part of a study to determine the factors affecting the porosity and

corrosion resistance of electroless nickel coatings, we have examined the

importance of operational parameters, particularly deposition time (and hence

deposit thickness and bath age) on the electrolyte composition, internal stress,

hardness, phosphorus content and corrosion stability of deposits using both

physical measurements and electrochemical techniques.


Surface Treatment. Computer Methods and Experimental Measurements 49

Experimental Details

10 x 2 cm samples were cut from 1.5 mm thick carbon (Pyrene) steel platesweighed and subjected to the following stringent sequence:

1) Alkaline soak cleaning (Duraprep 115-20 g drn ). The panels were

immersed for 5-10 minutes at a temperature of 55-60 C.

2) Rinsing (x 2) in deionised water at a temperature of 22°C, for 30-60 s.3) Pickling - HC1 (activation). The acid bath was a 25% vol HC1 (S.G.

1.18) and de-ionised water. Panels were immersed for 60 s at 22 C.4) Rinsing (x 2).

5) Repeating steps 1-4.

6) Duraposit 90 electroless nickel plating at 90-92°C, the plating rate forbeing approximately 12-14 (jm h~l.

The electroless nickel plated samples used in electrochemical tests were

covered with an acid resistant tape, exposing 1 cm? of metal. This enabled the

current measurements to be easily converted to current densities.Electrochemical measurements were carried out in 0.125M H SC at 22°C.

The cell and experimental arrangement for polarisation measurements

are described in more detail elsewhere [22]. A three-compartment glass cell

was used having a working electrode compartment volume of approximately

100 crrA The SCE reference electrode was connected to the cell via a luggin

capillary while the counter electrode (platinum foil, 3.4 cm?) was isolated

from the cell by means of a Nafion 324 (DuPont) cationic membrane. This

prevented any products generated at the counter electrode interfering with the

electrochemical measurements. A microcomputer-controlled EG & Gpotentiostat (model 273A) was used, with a scan rate of 1 mV s-l for Tafel(potential vs. log current density) plots.

The stress within an electroless nickel deposit was determined by theuse of a Brenner-Senderoff spiral contractometer [19]. This instrumentconsisted of a strip of stainless steel (2.54 x 30 x 0.15 cm thick) wound in the

shape of a helix (2.5 cm diameter). Its interior was coated with a lacquer thuspreventing the deposition of electroless nickel inside of the helix. The helix

was fixed at one end of the spiral contractometer while the other end was free

to rotate, thereby, moving a pointer on the dial. From the direction of rotation

(clockwise for tensile and anti-clockwise for compressive stress) and amount

of deflection recorded, the type and extent of internal stress was then

measured. The spirals were chemically treated prior to electroless nickelplating (with times and conditions as for the mild steel pre-treatment):1. Alkaline soak cleaning, (Duraprep 115).2. Rinsing (x 2) in deionised water.

3. Pickling, (hydrochloric acid).


50 Surface Treatment. Computer Methods ana bxpenmental Measurements

4. Rinsing (x 2) in deionised water.

5. Woods Nickel strike (nickel chloride 240 g , HC1 (S.G. 1.18) 86 crn^

made up to 1 dnr^ with deionised water). The spiral was immersed for

1-2 minutes at a temperature of 22°C and was electroplated at acurrent density of 5 A dm--.

6. Rinsing (deionised water), washing, (alcohol), drying and weighing.

7. Electroless nickel deposition, (Duraposit 90).

8. Rinsing (deionised water), washed, (alcohol), dried and reweighed.

The procedure adopted for the analysis of the sodium orthophosphite

concentration followed the instructions in the manufacturer's data sheet for

Duraprep and Duraposit, which are trade names for chemicals supplied by

Shipley Europe Ltd.. The phosphorus content within electroless nickel

deposits was determined as follows. A sample of electroless nickel foil was

prepared by passivating the steel substrate in chromic acid (1100 g dm'3).

After through rinsing to remove any excess chromic acid, the passivated steelwas plated in various aged electroless nickel baths for 1 hour at 92°C. Once

plated, the nickel-phosphorus foil was stripped from the steel, dried and

weighed; phosphorus content was determined by ion chromatography.

The hardness of various aged electroless nickel deposits was

determined using a M41 Vickers microhardness instrument utilising a

diamond pyramid indenter. The samples were etched to distinguish the

electroless nickel deposit from the mild steel substrate using 1% nital (1%

nitric acid (S.G. 1.42) in ethanol). A 50-100 g load was used and an average

Knoop hardness for 10 measurements was taken. The area of interest wasviewed under low magnification (x 40) before the pyramid indenter was

placed over the deposit. This procedure was repeated for the samples heattreated at 400°C for 1 hour.

Results

The electrode potential of the sample was adjusted to a value 0.25 V more

negative than the open circuit value then the potential was scanned to a value0.25 V more positive than the open circuit. The 1 cm^ area of the sample

allowed current readings to be directly expressed as current density ()J A crrr ).

Figure 1 shows the E vs. log i plots for uncoated steel and various electroless

nickel deposits. The value of i or %od ^COT extrapolated from this figure, areshown in the inset graph of Figure 1 and in Table I.

The value of E^r becomes more noble as the deposit thicknessincreases which agrees with the corrosion potential vs. time behaviour seen

earlier. The value of corrosion current density decreases, however, from a


Surface Treatment, Computer Methods and Experimental Measurements 51

value of 55 pA crrr? (uncoated steel), to 8 pA cnr-for a pore-free, 24 pm

nickel deposit. Porous deposits of nickel on steel showed intermediate values.

00

-02

•£

I

- 1 u m deposit j-Sum deposit I- G u m deposit !- 12 u m deposit!- 18 pi m deposit I- 24 u m deposit j

- 6 - 5 ^ - 3

Log(i/mAcm^)

Figure 1: Cathodic Tafel plot of mild steel and various electrolessnickel deposits from in 0.125M P SO at 22 C.

The inset shows data obtained for a range of plated deposits.

Deposit thickness

/pm

24

18

12

6

3

1

0

Corrosion potential

Ecor vs. SCE/v

-0.205

-0.230

-0.388

-0.423

-0.425

-0.447

-0.539

Corrosion current

ICOF/pA cm"

7

5

9

30

30

30

61

density

2

Table I Tafel analysis of electroless nickel deposits of various thickness.


:>z Surface treatment. Computer Methods and Experimental Measurements

If two electrodes, one of pure iron and one of pure electroless nickel(i.e., a pore free deposit) are joined, the nickel electrode becomes the cathode

while the iron becomes the anode and corrodes. This can be analogous to the

cathodic protection of ferrous structures by sacrificial anodes such as

aluminium or zinc. In the electroless nickel-iron couple, the iron will have to

corrode at a rate greater than I^t to depress the potential of the electroless

nickel into the zone of immunity, i.e., Ep^ for nickel. This is illustratedschematically in Figure 2.

EvsSCE/ V-0.0-

-0.1-

-0.2-j

Eprot - L-0.3

-0.4

-0.5

(e)

(d)(c)

Ni/Ni

Log (I / A)

Figure 2:

-5 -4

A schematic, Evans diagram illustrating the cathodic protection

of the electroless nickel deposit. The corrosion potential, E p,

becomes more noble and the corrosion current density, i ofalls for thicker deposits.

(a) Uncoated steel substrate, (b) 3 jam electroless nickel deposit.

(c) 12 jam electroless nickel deposit, (d) 18 jam electroless nickel deposi

Below this value of Ep , the electroless nickel will be 100 % cathodic and

thereby protected. Pores within the electroless nickel deposit on the steel

substrate may be considered as sacrificial anode sites. If these sites aresufficiently large they can confer protection to the electroless coating. The

coverage of the steel by even a thin coating of electroless nickel, e.g., 2 |am,

will reduce the area of iron available to cathodically protect the electroless

nickel. This lowers the anodic current produced by iron dissolution and the


iicaimenu computer ivietnoas and hxpenmental Measurements 53

mixed potential of the iron-electroless nickel moves in a positive (i.e., more

noble) direction as illustrated in Figure 2. This mixed potential is in reality, the

value of E^r measured experimentally. Increasing the deposit thickness

further reduces the anodic area of the pore and the subsequent anodic currents;the mixed couple potential moves in a more noble direction.

The corrosion rates obtained form the Tafel experiments decreased

with increased deposit thickness. The value of corrosion potentials where the

current became zero were very slightly different to those from simple

immersion tests [22]. This is not surprising as these results were taken after 50

hours in the 0.125M sulphuric acid while in the Tafel experiments, the

potential was estimated after approximately 15 minutes. In addition, the

cathodic scan will possibly reduce oxide films which might be on the surface

of the nickel and/or the steel. This will also cause the potentials to be slightlydifferent between the two techniques.

Figure 3 shows the results of the stress measurements. Initially, the

fresh bath produces a compressive internal stress of 37-24 MPa at 0-1 metal

turnovers. The stress decreases with increased number of metal turnovers, and

after 3 turnovers, the stress becomes tensile. The value of this tensile stress

increases as the bath ages reaching a value of 241 MPa after 6 metal turnovers.

(/)CLif)$(%

40000

36000

30000

•<£<_ijj

20000

15000

10000

5000

0

-5000

-10000

', ' ' ' ' I • I ' 1 • 1 r- 1

—• — Ex pen mental j O- O- Manufacturer's guideline |

-= Compressive stress-*• = Tensile stress -O

- "~*mr ^/X x/

0'" /,''*— — •

- ,-_._-•/ ;

• — -* - o-

— ' ' 1 . 1 , I . . . , . , "2 3 4Number of metal tumo/ers

Figure 3: Variation of the internal stress in the electroless nickel deposit

with increased number of bath metal turnovers for a highphosphorus electroless nickel plating solution


54 Surface Treatment, Computer Methods and Experimental Measurements

This result is consistent with other workers [10] and the supplier's data for the

electroless nickel bath but in disagreement with the findings of Bleeks and

Brindisi [20] and Keene [21]. The high phosphorus electroless nickel system

investigated by Bleeks and Brindisi showed that the internal stress of the

deposits, measured by a gearless spiral contractometer, remained compressive

even after 6 metal turnovers. Work carried out by Keene also showed that the

internal stress within deposits plated from a high phosphorus electroless nickel

bath remained compressive up to 6 metal turnovers.

The plating rate vs. the number of bath metal turnovers is illustrated in

Figure 4. The plating rate remains fairly consistent until 4.5 metal turnovers

when the plating rate suddenly starts to fall. This lowering of the plating rate

coincides with higher values of tensile stress found after 4-5 metal turnovers.

150 —•— High phosphoruselectroiess nickel

14.5

14.0

fcS" 135

E 130<D

120

11.52 3 4

Number of metal turnovers

Figure 4: Plating rate of a high phosphorus electroless nickel solution

from baths aged by 0-6 metal turnovers.

Results of the analysis of the bath for orthophosphite concentration areshown in Figure 5 as a linear relationship between the concentration of the

orthophosphite ion and the number of bath metal turnovers. During electroless

nickel deposition, hypophosphite is oxidised to orthophosphite. As the bathages, the concentration of the orthophosphite in the plating solution must

increase. A comparison of Figure 5 with Figure 3 indicates that the high

levels of tensile stress maybe associated with orthophosphite concentrations inexcess of 125 g dm-3. This corresponds to a bath metal turnover of

approximately 4.5 at which point the plating rate begins to fall (see Figure 4).


Surface Treatment. Computer Methods and Experimental Measurements 55

Where;m = 34.19054 (sd 0.59652), c = 0.32112 (sd 1.88399)R = 0.9987, N = 10, SD = 3.51515 & P = 95312 x

3 4NaofMe&tLmM-rs

Figure 5: Variation of the sodium orthophosphite concentration with

increased number of metal turnovers of a high phosphorus

electroless nickel bath.

The phosphorus content of the deposit was found to be in the range of

11.3-13.3% wt (c.f. 11-13% wt, which is the expected range quoted by the

manufacturer). This value was maintained throughout irrespective of the

number of metal turnovers. The amount of phosphorus incorporated withinthe deposit, however, gradually increased with the number of metal turnovers.

This is illustrated in the plot of weight % phosphorus vs. number of metal

turnovers (Figure 6). This may not be directly related to the age of the

solution, but as a result of the plating rate. Factors which alter the plating rate

also tend to effect the amount of phosphorus incorporated within the deposit.

A increase in the deposition rate coincides with a fall in the phosphoruscontent although the reason for this is still uncertain. As shown in Figure 4,

the plating rate falls with increased orthophosphite levels and this may explain

the gradual increase of phosphorus observed in the deposits plated from bathswith a higher number of metal turnovers.

Figure 7 shows that the values of Knoop hardness, H%, found in the as-

plated condition (H^ 550-600) remain consistent for a 12-14 jam deposit plated

from various electroless nickel solutions (0-6 metal bath turnovers). Heattreated coatings show a marked increase in hardness compared to the as plated


56 Surface Treatment, Computer Methods and bxpenmental Measurements

120

11.5

11.0

105O0_

100

9.0

I—wt%P

1 2 3 4


Figure 6: Phosphorus content of an electroless nickel deposit

plated from baths aged in the range 0-6 metal turnovers.

Knoop hardness /H %

1000

900

800

TO)

600

500

400

qm

1 ' I ' 1 ' 1 ' 1 ' I ' I

"*~~" \ -""' ~~~~— — -.- _• .-

—O— Knoop hardness (H ) as plated High phosphorus electroless nickel (EN)— •— Knoop hardness (H ) Pyrene steel— •— Knoop hardness (H ) High phosphorus EN heat treated @ 400 °C for 1 hr— O— Knoop hardness (H ) Pyrene steel heat treated @ 400 °C for 1 hr

-

U " \^ _ G— — __ n-—" -^" • .r-i ~

^^Q Q -O— Q Q Q O

™ • • • -•— — _ ^ ^ ** ~## ^ w ^

1 , 1 , 1 , 1 , 1 , 1 . 12 3 4


Figure 7: Knoop hardness measurements taken from samples plated

from solutions aged by 0-6 metal turnovers before and after

heat treatment (1 hour at 400°C).


sunace ireaimem, computer ivietnoas ana experimental Measurements :> /

condition and there is no noticeable difference in H% value (H^ 900-1000)

between deposits plated from 0-6 metal turnovers. Hardness properties are,

therefore, not dependent on factors influencing the ageing process of

electroless solutions. Hardness is attributed to the phosphorus content of thedeposit, and this present work has illustrated that the phosphorus content

within the coating remains fairly constant, whether it is plated from a fresh

bath or an aged solution. With the levels of deposit phosphorus remaining

consistent irrespective of bath age the level of hardness of these deposits was

also found to follow the same trend.

The present research has shown the characterisation of electroless

nickel deposits from acid baths alters as the bath ages. The ageing of the bath

is directly related to metal turnover additions. Between 4 and 5 metal

turnovers, this change is most noticeable as can clearly be seen in Figure 8

with the plating rate decreasing from 14 to 9.5 jam hr*. This decline in plating

rate can be attributed to the build-up in concentration of sodium

orthophosphite, a by-product of the oxidation process. The level of sodium

orthophosphite builds up on a linear scale as the bath ages rising to a

maximum level of 190 g dm-3 after 6 metal turnovers, when the solution has

reached the end of its useful working life.

The internal stress within the deposit becomes highly tensile between

metal turnovers 4 and 5, and this demonstrated in Figure 8.

200

180

160

140

120

100

80

60

40-

3D-

0

Pfetingrate mh^-T 16

—<*—- R^Jngtime/mn —a—9ress/MF£• Crthcphasphte core. —A— wt % P

--15

E 140--

^ 80-

iiterrcl stress /IVPar120

9.02 3NuTter cf metal turcMers

Figure 8: Various physical parameters , number of metal turnovers.


58 Surface Treatment, Computer Methods and Experimental Measurements

The internal stress measured within the deposit is thought to be associated

with the amount of phosphorus included in the coating. There are conflicting

reports in the literature on the role of phosphorus. Results presented in this

paper closely mirror those reported by Riedel and his co-workers but are in

disagreement with those published by Bleeks and Brindisi [20] and by Keene

[21]. The latter work showed that, for high phosphorus alloys, the internal

stress remains compressive in deposits plated from solutions aged by 0-6

metal turnovers. Analysis of electroless nickel foils indicated that the ageing

process had little effect on the weight % phosphorus found with levels rising

slightly, with increased number of metal turnovers.

Conclusions

The use of electrochemical measurements in the detection of pores in

electroless deposits has been demonstrated to be an effective alternative to the

conventional corrosion or chemical tests. Tafel polarisation measurements

have been shown to be able to identify the presence of pores through the

coating to the underlying steel substrate. The shape of the corrosion current

density vs. coating thickness plots have a very similar resemblance to the

coating thickness vs. percentage porosity curves as shown in a previous study

using the sulphur dioxide corrosion test [4], Good agreement has beenobtained between these exposure tests and electrochemical measurements inpredicting the presence of pores with the widely employed sulphur dioxide

test. The electrochemical tests can give an estimation of the presence of pores

in a matter of hours compared with days for the sulphur dioxide test i.e., Tafel

analysis can be rapidly carried out, once the sample has been prepared.

The characterisation of electroless nickel deposits from acid baths is

dependent on the bath age, which is related to metal turnovers. Between 4 and

5 metal turnovers, this change is most noticeable, with the plating rate

decreasing from 14 to 9.5 jam h~*. This decline in plating rate can be attributed

to the build-up in concentration of orthophosphite. The level of orthophosphite

builds up linearly with time as the bath ages, rising to a maximum level of 190g dm-3 after 6 metal turnovers, when the solution has reached the end of its

useful working life.

The role of phosphorus, the part it plays on the internal stresses withinthe Ni-P deposit and the influence of operational parameters are not well

understood in the electroless nickel system and further work is required to

understand the interactions amongst: electrolyte composition, operatingconditions, the kinetics of depostiion and the physical properties of the deposit


References

1. B.D. Barker, "Electroless deposition of metals",Trans. Inst. Metal Fin.,(1993), 71 (3), 121-124.

2. A. Brenner, "Electroless plating comes of age-part 1", Metal Finishing,(1954), 52 (11), 68-76.

3. A. Brenner, "Electroless plating comes of age-part 2", Metal Finishing,(1954), 52 (12), 61-68.

4. C. Kerr, B.D. Barker and F.C. Walsh, "Porosity of electroless nickeldeposits on ferrous substrates", Trans. Inst. Metal Fin.., (1996), 74 (6)214-220.

5. D. Haywood, "Surface preparation techniques for metals to be coated forcorrosion control", Corros. Coatings S. Africa, (1992), 19 (1), 11-18.

6. H.G. Darkin, "Chemicals for cleaning - Why such a wide selection?"Product Finishing, Feb., (1990), 6-8.

7. G.J. Shawhar, " Surface preparation prior to electroless nickel plating ofsteel", Metal Finishing, (1988), 86 (6), 87-89.

8. H. Deng and P. Moller, "Effects of pretreatment on the structure andproperties of Electroless Nickel coatings", Proc. 79th AESF AnnualCW.., (1992), 2, 803-819.

9. S.S. Tulsi, "Properties of electroless nickel", Trans. Inst. Metal Fin..,(1986), 64,73-76.

10. W. Riedel, "Electroless Nickel Plating", Finishing Publications Ltd.,Stevenage, England, (1991).

11. S.M. Garte, "Effect of substrate roughness on the porosity of goldelectrodeposits", Plating, (1966) 53, (11), 1335-1339.

12. U.R. Evans and S.C. Shome, "Studies in the discontinuities inelectrodeposited metallic coatings", /. Electrodepositors Tech. Soc.,(1950), 26, 137-160.

13. I.M. Notter and D.R. Gabe, "Porosity of electrodeposited coatings: Itscause, nature, effect and management", Corr. Rev., (1992), 10, 217-280.

14. F. Ogburn and D.W. Ernst, "The nature, cause and effect of the porosityin electrodeposits-pt. 3. microscopic detection of porosity", Plating,(1949), 46 (7), 831-833.

15. R. Walker, "Engineering aspects of internal stress in electrodeposits",Metallurgia, (1968), Oct., 131-135.

16. C. Baldwin and T.E. Such, "The plating rates and physical properties ofelectroless nickel / phosphorus alloy deposits", Trans. Inst. Metal Fin ,(1968), 46, 73-80.

17. J.W. Dini, "Electrodeposition. The Material Science of Coatings andSubstrates", Noyes Publications Ltd., New Jersey, (1993).

18. J.B. Kushner, "A new instrument for measuring stress inelectrodeposits", 41st Annual Technical Proceedings, AmericanE/fcfmp/affrj&)C., (1954), 188.

19. A. Brenner and S. Senderoff, "A spiral contractometer for measuringstress in electrodeposits", Proc. American Electroplaters Soc., (1948)35,53-78.

20. T.W. Bleeks and F. Brindisi, Jr., "The properties and characteristics ofelectroless nickel coatings applied to gas turbine engine components",Presented at the Gas Turbine and Aeroengine Congress and Exposition -June 4-8, 1989, Toronto, Ontario, Canada. (ASME 89-GT-4).

21. R.H. Keene, "Application and control of electroless nickel processes atNorth West Airlines", Plating and Surface Finishing, Dec. 1988.

22. C. Kerr, B.D. Barker and F.C. Walsh, "Electrochemical techniques forthe evaluation of porosity and corrosion rate for electroless nickeldeposits on steel", Trans. Inst. Metal Fin.., (1997), 75 (2), 81-87.


Documents

Experimental Details · 2014-05-20 · Surface Treatment. Computer Methods and Experimental Measurements 49 Experimental Details 10 x 2 cm samples were cut from 1.5 mm thick carbon