THE ELECTRO-DEPOSITION
OF NICKEL

Thesis for the Degroe of M. 3..
MICHIGAN STATE COLLEGE

StanIey S. Krentel
I941

 

 

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THE ELECTRODEPOSITION OF NICKEL

by

Stanley Still Krentel

A THESIS
Submitted to the Graduate School of Michigan
State College of Agriculture and Applied
Science in partial fulfilment of the
requirements for the degree of

MASTER OF SCIENCE

Department of Chemistrz

1941

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The purpose of this investigation is to determine what
effect the compounds commonly associated with nickel sulfate in a
nickel plating solution have upon the quality of the plated sur-
face. The temperature and pH were varied so that their effect
could be noted and current efficienc; studies were.made. As a
follow-up of this sork a bright nickel solution was prepared and
the bright range was ascertained using the temperature and pH as
variables.

Several research workers have studied similar aspects
of this same problem. M. A. Brochet (1) states that a solution
of nickel salt alone cannot be used for electrolysis: in the
case of the chloride, nickel hydroxide forms on the cathode.
With nickel sulfate the solution becomes acid upon electrolysis,
as the nickel anode being passive, sulfuric acid is formed.
Addition of chlorides suppresses this anodic passivity but forms
anions of nickel tetrachloride with the tendency toproduce nickel
peroxide. A better method to suppress the acidity is to add
slightly dissociable salts, such as sodium citrate. The most
convenient to use is boric acid, which serves to compensate the
action of the hydroxide.

Jeseph Haas (2) conducted a series of experiments to
determine the effect of adding various salts and acids to a bath
containing 90 grams per liter of nickel sulfate. He found that
the electrolysis of the nickel sulfate solution alone yielded no
electrodeposited.metallic nickel, but produced instead a gelat-
inous precipitate of nickel hydroxide. The addition of ammonium

chloride and sodium citrate to the nickel sulfate solution gave

i230

pa
CL:
9

good deposits of nickel, while sodium chloride and magnesium
sulfate as addition agents prohibited the deposition of nickel.
The inorganic acids nitric, hydrochloric and sulfuric caused
excessive hydrogen evolution and produced brittle deposits of
nickel. Phosphoric acid gave a precipitate of nickel phosphate,
while borio acid gave satisfactory results both in color and
character of the deposits.

As the effect of zinc as an addition agent was studied
it is relevant to note the results of an investigation carried
out by Vbzdvizhenskii and Makolkin (3). They found that satis-
factory deposits of nickel can be produced up to a concentration
of zinc of 0.45% of the nickel present, at various bath tempers
atures and at a current density of 0.05 to 1.0 amperes per square
decimeter. At a higher zinc concentration, between 0.45 and
0.65% streaky deposits can be avoided by increasing the temper-
ature to 40°, but at concentrations of zinc above 0.65% streaky
deposits are inevitable. The pH around the cathode increases
with increasing concentration of zinc salts, reaching such a high
value that a colloidal basic precipitate of nickel salts occurs.
The positively charged particles of this colloid are transported
to the cathode surface and deposited as a dark layer, this con-
dition is facilitated by the stream of evolved hydrogen at the
cathode.

M. Waite (4) found that the equilibrium pH of nickel
chloride decreased with increased concentration of nickel
chloride. Harder deposits were obtained with increased concen-
tration of nickel chloride and the effects are reversed as the

temperature is raised.

M. R. Thompson's (5) results indicate that in general
good nickel deposits are secured when the cathode current effic-
iency is high. He also found that at a low pH better deposits
are obtained at a high rather than at a low current density.
Also, deposits from a solution having a low pH are apt to be
brighter, harder, finer grained and more brittle.than those from
a solution of high pH. With any pH above 6.0 the deposits were
found to be dark colored and cracking and curling was apt to
occur.

Experimental Procedure: Before the actual results are
presented the method observed in preparing the surface for
electrodeposition will be given. The steel plates were first
polished using a saponifiable emery compound, then they were
cleaned electrolytically in a proprietary cleaner containing 6
ounces per gallon of Matawan #2. The plates were then rinsed in
running water. They were then copper plated in a copper cyanide
solution having the following composition: copper cyanide, 3
ounces per gallon; sodium cyanide, 4.5 ounces per gallon and
sodium carbonate, 2.0 ounces per gallon. After being copper
plated they were rinsed, dried and buffed using tripoli for the
buffing compound. Then the panels were colored using Acme white
finish.

The next step was to clean the copper plates electro-
lytically in a similar cleaner to the one used for the steel,
the difference being that the concentration of Matawan 52 was 2
ounces per gallon. The panels were then rinsed in water, dilute

sulfuric acid and then dried by first immersing the plates for

one minute in boiling water and allowing the moisture to evaporate
in the air. The plates were next weighed to 0.0001 grams using
analytical balances. Following that they were recleaned and
plated in the nickel solution, dried and reweighed.

A stock solution of nickel sulfate was prepared con-
taining a concentration of 32 ounces per gallon of the salt.
Panels were run frmm the stock solution alone and then from
solutions containing the stock solution plus the addition agent.
In other words, pairs of compounds were used in all solutions
used for electrodeposition except the first which contained only
nickel sulfate.

In each series the pH was varied from 6.0 to 1.0, using
sulfuric acid to lower the value and nickel carbonate to raise
the pH. The pH values were determined electrometrically using a
quinhydrone electrode. Two temperatures were used: namely, 25
and 40°.

The baths consisted of 1% liters of solution in 2 liter
museum jars. It was possible to operate four solutions at the
same time by utilizing a water bath especially constructed for
this purpose.

Experimental Results: The first series was prepared
using a portion of the stock solution, which contained 32 ounces
per gallon of nickel sulfate. To determine whether there was an
advantage in using the chemically pure nickel sulfate or whether
the commercial grade was suitable, duplicate series were made.
The commercial nickel sulfate was purified preceding operation

of the solution by raising the pH with a nickel carbonate treat-

ment. This treatment consists of heating the solution to 60° C.
followed by the addition of a thin paste of nickel carbonate.
The solution was then agitated mechanically for one hour and
allowed to stand over night. The solution is then filtered from
the excess nickel carbonate and from the metallic hydroxides
that have precipitated. Accompanying the actual precipitation
of impurities there is some adsorption of organic and inorganic
contaminants on the surface of the freshly prepared nickel hydrox-
ide. The pH obtained by this method was determined to be between
6.5 and 6.4. This preliminary purification of commercial nickel
sulfate produced a solution which electrodeposited nickel
identical in appearance to plates secured from a solution prepared
from chemically pure nickel sulfate. Consequently commercial
nickel sulfate was utilized throughout the project being purified
first with nickel carbonate.

It is observed in Table 1 that a pH of 6.2 produces
deposits of lower current efficiency than a solution having a
pH of 5.7. This is due to the increased alkalinity of the cathode
layer which facilitates precipitation of basic nickel compounds
having a lower weight than metallic nickel. As the pH is
decreased the current efficiency decreases also. This is due to
the fact that the h drogen overvoltage on nickel decreases with
increasing acidity of the solution.

Electrolysis of the nickel sulfate solution at a pH of
2.0 results in a slight increase in current efficiency over the
efficiencies of the solution at higher pH values, namely, 3.0 to

4.0. At this pH either the hydrogen overvoltage on nickel

increases somewhat or the nickel overvoltage on nickel decreases.
No investigation was made of the true reason for this phenomenon
in this study.

It is also observed that an increase in current density
with the temperature remaining constant, namely, 25°, results in
a dimunition of the current efficiency. This is a reasonable
effect in consideration of the fact that the conductivity of
nickel sulfate solution alone is low. Any factor that would
increase the conductivity of the solution would be expected to
raise the current efficiency. Thus, elevating the temperature
of the solution to 40° and in this manner increasing the conduc-
tivity will increase both the current efficiency and the quality
of the deposit.

Fig. 2 shows the results obtained in this series. It
is observed that the deposits are uniformly poor until a pH of
2.0 is attained. At that point metallic nickel of good color and
quality is deposited over the entire surface of the test panel.
It is also noticed that the plates at a low current density are
better in appearance than those at the higher current density.
Above a pH of 2.0 at room temperature and a current densitv of 20
amperes per square foot, the plates are very black.

The fact that the area of metallic nickel deposits
first in the center of the plate emphasizes the low conductivity
of the single salt solution. Since the current distribution is
least in the center of the plate the conditions at that partic-
ular area on the test panel tends to favor precipitation of the
metal.

A reduction in pH improves the quality of the plate by

improving the conductivity of the solution.

The polarization required for the deposition of nickel
decreases with rise of temperature but the hydrogen overvoltage
behaves in the same way. Therefore, whatever the current density
or the temperature a low pH will result in an appreciable evolu-
tion of hydrogen and the current efficiency will be low. However,
the increased allowable rate of deposition and improved quality
of the deposit greatly discount the small loss in current
efficiency.

Raising the temperature to 46° increases the whiteness
of the deposits and completely eliminates all burning the deposit
at the high current density areas. At a pH of 5.5 the deposit
botained is cracked as well as being streaked with vertical black
lines. At a pH of 5.0 the dark lines have appreciably diminished,
and at a pH of 2.6 they are l cated at the edge of the test panel.
Below a pH of 2.6 the deposits have good ph sical characteristics
and possess more luster than deposits from.a solution having a

higher PH.

Table I

 

 

Series A
NiSO4 °7H20 32 oz./gal.
Current Weight of
Plate Density Temperature Time in Deposit % Current
Number Amps/sift Degrees 0. Minutes pH in grams Efficiency
1. 10 25 20 6.2 .2746 75
2. 10 a 25 20 5.7 .3446 90
3. 10 25 20 3.8 .2889 79
4. 10 25 20 3.1 .2875 78
5. 10 25 20 2.5 .2810 77
6. 10 25 20 2.0 .3069 84
7. 10 25 20 1.3 .0801 22
8. 20 25 20 6.3 .3638 49
9. 20 25 20 5.5 .3113 46
10. 20 25 20 4.4 .4030 55
11. 20 25 20 3.7 .4471 61
12. 20 25 20 2.0 .4744 65
13. 20 25 20 1.5 .2886 39
14. 20 46 20 5.5 .6690 92
15. 20 46 20 5.0 .6862 94
16. 20 46 20 2.6 .5986 82
17. 20 46 20 2.0 .6132 84

18. 20 46 20 1.5 .5110 70

 

In Series H the effect of boric acid additions upon the
quality of nickel deposited from the sulfate solution is deter-
minted. One of the primary observations that was made in the
comparison of Table 2 with Table l is that the cathodic current
efficiencies are greater in this series.

In the first series in the increase in temperature from
25° to 46° resulted in a marked difference in the appearance and
current efficiency of the deposit obtained. However, in the
present series these differences were not noted.

Boric acid has long been used for a buffer in nickel
plating solutions. In this respect it acts both upon the bulk of
the solution and also in the electrode-electrolyte interfacial
surfaces to restrict changes in pH due to electrolysis of the
solution. Boric acts in another manner in addition to its buffer
action because below a pH of 4.9 it exhibits no buffer action.
However, acid nickel solutions of the sulfate type about which
this investigation is concerned produce excellent matte deposits
at pH values ranging from.1.0 to 5.5. The presence of boric acid
in the nickel sulfate solution permits a higher current density
without burning or precipitation of basic nickel salts on the
cathode.than can be obtained under the same conditions without
it.

Fig. 3 shows that all the plates secured in this series

were good matte deposits.

Table II

 

 

Series H
NiSO4.7H20 32 oz./gal.
H3303 4 oz./gal.
Current Weight of
Plate Density Temperature Time in Deposit % Current
Number amps/sq ft Degrees C. Minutes p§_ in pgrams Efficiency
1. 10 25 20 5.6 .3504 96
2. 10 25 20 5.0 .3472 95
3. 10 25 20 4.3 .3491 95
4. 10 25 20 3.5 .3395 93
5. 10 25 20 2.9 .3358 92
6. 10 25 20 2.5 .3285 90
7. 10 25 20 2.1 .2920 80
8. 10 25 20 1.8 .2154 89
9. 10 25 20 1.0 .0219 6
10. 20 25 20 5.5 .6059 83
11. 20 25 20 4.7 .7300 100
12. 20 25 20 ' 4.0 .7081 97
13. 2O 25 20 3.5 .6935 95
14. 20 25 20 2.5 .8790 93
15. 20 25 20 2.0 .6220 85
16. 20 25 20 1.8 .6165 84

17. 20 25 20 1.0 .0999 13

 

Table II - Continued

Series H - cont'd.

NiSO4.7H20 32 oz./ga1.
H.3303 4 oz./gal.
Current ' weight of
Plate Density Temperature Time in Deposit % Current

 

Number Amps/sqft Degrees C. Egnutes pH; in grams Efficiency

18. 20 46 ' 20 . 5.2 .7300 100
19. 20 46 20 4.5 .6555 90
20. 20 46 20 4.2 .7300 100
21. '20 46 20 3.6 .7115 98
22. 20 46 20 2.0 .6220 85

23. ' 20 46 20 1.1 .2285 31

 

 

The effect upon the quality of the plate caused by the
addition of nickel chloride to the nickel sulfate solution is
illustrated in Fig. 4. It is noticed that the plates are very
similar in appearance to the ones obtained from the nickel
sulfate solution containing no addition agents.

The cathode current efficiency values are higher in
this series than they were in Table I. The addition of nickel
chloride to the nickel plating solution is made to provide for
adequate anode solution. It is the chloride ion which is active
in this reapect. The chloride ion has been added as sodium,
potassium and ammonium chloride and as hydrochloric acid. It is
added as the nickel salt for two reasons in the first place using
nickel chloride no foreign cations are added and secondly, it
tends to replenish the nickel ion concentration. In addition to
these reasons and perhaps or more paramount importance is the
fact that a nickel sulfate solution electrolyzed with no halogen
ions present becomes acid. This is due to the production of
sulfuric acid at the anode and the volution of oxygen, caused by
the passivity of the anode. The chloride overcomes the passive
condition of the anode by acting as an anodic depolarizer. The
fact that nickel chloride is highly ionized aids the conductivity
of the nickel sulfate solution.

Nickel anodes are believed to be passive in a nickel
sulfate bath due to the formation of a film of oxygen or an oxide
which has a low oxygen overvoltage.

In a recent publication by W. A. Wesley and

J. W. Carey (7) on the electrodeposition of nickel from nickel

chloride solutions they find that the deposit from a bath of
this type (nickel chloride and boric acid) is finer grained,
harder, stronger and somewhat less ductile than deposits from the
ordinary nickel sulfate plating solution. The advantages claimed
for this solution are: (1) low tank voltage; (2) ease of buffing;
(3) greater smoothness of thick deposits; (4) ease of control;
(5) freedom.from.pitting; (6) high cathode efficiency; (7) the
solution has less tendency to overheat due to the passage of large
currents.

The disadvantages are: (l) greater corrosiveness of
the solution; (2) loss of ductility; (3) the cost is slightly

higher.

Table III

 

 

Series D
NiSO4.7H20 32 oz./ga1.
N1012 4 oz./gal.
Current Weight of
Plate Density Temperature Time in Deposit % Current
Number Amps/sqpft_Degrees C. Minutes Ip§_ in grams Efficiency
1. 10 25 20 6.3 .2597 71
2. 10 25 20 5.1 .2671 73
3. 10 25 20 4.9 .2957 81
4. 10 25 20 4.2 .2739 75
5. 10 25 20 3.5 .2991 81
6. 10 25 20 2.9 .3000 82
7. 10 25 20 2.0 .2906 79
8. 10 25 20 1.6 .2143 58
9. 10 25 20 1.1 .1349 36
10. 20 25 20 6.0 .4138 57
11. 20 25 20 5.5 .4166 58
12. 20 25 20 5.2 .3697 50
13. 20 25 20 4.1 .4081 56
14. 20 25 20 3.6 .2842 39
15. 20 25 20 3.3 .4185 57
16. 20 25 20 2.2 .4515 62

17. 20 25 20 1.6 .5407 75

 

 

Table III - Continued

Series D - cont'd.

 

 

NiSO4.7H20 32 oz. /gal .
NiClz ' 4 oz./gal.
Current 5 Weight of

Plate Density Degrees C. Time in Deposit % Current
Number Amps/sq ft Temperature Minutes ‘p§_ in grams Efficiency
18. 20 ‘46 20 5.9 .7097 97

19. 20 46 20 4.8 .7018 96

20. 20 46 20 2.9 .7095 97

21. 20 46 20 2.0 .6352 87

22. 20 46 20 1.5 5245 72

 

Fig. 5 shows the results obtained by adding sodium
benzene disulfonate to the nickel sulfate solution. It is observed
that three of the plates at the lower temperatures have bright
areas. These plates occur at the pH values of 4.7, 2.4 and 1.5
with the plate from.the solution at a pH of 1.5 bright over nearly
the whole surface. It is also noted that at 46° there is no
bright area at all. In Table 4 we notice that the current
efficiency is not materially affected by this addition. The
important fact is that the quality of the plated surface is
markedly improved.

Salts of this type, pelysulfonates, have been advocated
by many investigators as being capable of producing lustrous
plates from nickel sulfate solutions containing nickel sulfate,
nickel chloride and.boric acid. The bright plates occur at the
lower pH values due to the fact that the polysulfonates tend to
decompose at high pH values. Even at a pH of 4.0 the cathode
layer is more alkaline than the remainder of the solution. Part
of the brightening action of sodium benzene disulfonate may be
due to the presence of the sodium ion, but the same brightening
action has been observed when nickel benzene disulfonate or

benzene disulfonic acid has been used in place of the sodium salt.

Table VIII

 

 

Series I!
NiSO4.7H20 32 oz./gal.
Zn 100 mg./l.
Current Weight of
Plate Density Temperature Time in Deposit % Current
Number Amps/sq ft Degrees C. Minutes pg in grams Efficiency
1. 20 25 20 6.2 .3167 , 43
2. 2O 25 20 4 .9 .4685 64
3. 20 25 20 4.3 .2821 38
4. 2O 25 20 3.9 .2210 30
5. 20 25 20 2.4 .4255 58
6. 20 25 20 1.5 .4538 63
'7. 20 46 20 6.3 .7163 ' 98
a.“ 20 46 20 3.8 .6275 85
9. 20 46 20 3.3 .6779 93

10. 20 46 20 2.6 .6299 87

 

Series J, M. R and P are grouped together because they
deal with the effect of adding zinc in varying concentrations to
the nickel sulfate solution. Series J contained 50 milligrams per
liter, Series M had 100 milligrams per liter, Series B 200 milli-
grams per liter and Series P 500 milligrams per liter of zinc.

Referring to the tables, it is noted that the addition
of zinc up to a concentration of 200 milligrams per liter tends
to slightly increase the current efficiency at 25?. At a concen-
tration of 500 milligrams per liter and an Operating temperature
of 25° the current efficiency drops off somewhat. However, at
46° the cathodic current efficiency is nearly the same irrespec-
tive of the zinc concentration.

Figures 6, 7, 8 and 9 show that increasing the zinc
concentration improves the quality of the plates up to a concen-
tration of 200 milligrams per liter of zinc at 25° and above that
value it has the opposite effect. At 46° 500 milligrams per liter
of zinc gives the best results in quality and current efficiency.
at 25° and at low zinc concentrations there is a darkening of the
deposit that is diminished as these two variables are increased.
The zinc was added as the sulfate in all cases. The purpose for
adding zinc to a nickel bath is for the production of lustrous
plates. An aromatic sulfonated compound is added in conjunction
with zinc when bright plates are desired. Zinc is deposited with

nickel but in a low percentage.

Table VII

 

 

Series R
NiSO4.7H20 32 oz. /gal.
2n 200 mg./l.
Current Weight of
Plate Density Temperature Time in Deposit % Current
Number Amps/sq ft Degrees 0; Minutes '25. in ggrams Efficiency
1. 20 I 25 20 6.2 .5556 76
2. 20 25 20 4.4 .3544 49
3. 20 25 20 3.6 .4600 63
4. 20 25 20 2.9 .3869 53
5. 20 25 20 1.5 .2419 33
6. 20 46 20 - 5.8 .7300 100
7. 20 46 20 5.0 .6665 91
8. 20 46 20 4.3 .6875 94
9. 20 46 20 3.5 .6839 94
10. 20 46 20 2.8 .7000 96
ll. 20 46 20 2.0 .7003 96

12. 20 46 20 1.6 .5058 70

 

 

 

 

 

A resume of the results obtained discloses several
interesting points. In the first place, deposits of nickel can
be obtained from a bath containing only nickel sulfate in a con-
centration of 32 ounces per gallon. At the higher p H values
there is a preferential deposition of basic nickel salts on the
cathode. However, at approximately a pH of 2.0 the quality and
appearance of the plate is good. If the bath is operated at a
pH above 2.5 the tendency is for the solution to become more acid.
Operation of the bath below a pH of 2.5 causes only a slight
change in pH. It is apparent that the relative cathode and anode
efficiencies are nearly identical below a pH of 2.5, thereby
maintaining a constant pH in the solution.

An increase in temperature caused the cathode current
efficiency to increase by diminishing the tendency for the
deposition of basic salts. An increase in the current density at
25° caused the cathode current efficiency to decrease because the
poor conductivity of the solution promoted a greater deposition
of basic salts on the cathode.

The addition of nickel chloride tended to darken the
deposit. However, the provision for efficient anode corrosion
maintained the pH at a more constant value upon electrolysis of
the solution. Variations in the temperature, pH and current
density produced essentially the same results that were obtained
in the nickel sulfate solution with no addition agents. It was
again noted that at a pH of 2.5 to 2.0 the deposit improves
greatly due to total elimination of all traces of basic salt

precipitation on the cathode. An increased temperature again

improved the current efficiency and appearance of the plated
specimens.

The addition of boric acid very positively improved the
quality of the plate and the current efficiency of the solution
under all conditions investigated. The presence of the borie
acid enabled maintenance of pH values above 4.9 by effectively
buffering the solution. Below a pH of 4.9 its buffering value
is very limited. In all cases the deposit was white in color and
.matte in character. In this series the improvement in current
efficiency upon increasing the temperature was not appreciable.

The addition of sodium.benzene disulfonate produced
bright areas on the test panels at 25° and pH values of 4.7, 2.4
and 1.5. At a leof 1.5 the bright area covered nearly the whole
plate. Increasing the temperature resulted in loss of the bright
area but increased current efficiency.

The addition of formaldehyde produced poor plates when
the pH of the solution was in excess of 2.5. An increase in
operating temperature did not improve the quality of the deposits.
At 25° and a pH of 2.5 a bright area occurred that was not present
in any of the other panels. At 46° and above a pH of 2.2 the
deposits obtained were ridged vertically. A peculiar point con-
cerning this addition agent was the fact that at room temperature
the current efficiency increased as the pH decreased, indicating
quite clearly the fact that formaldehyde acts as a cathodic de-
polarizer and is most effective in this respect at a low pH.

Concentrations of zinc in the nickel sulfate solutions

up to 200 milligrams per liter improves the quality of the plated

surface and the current efficiency when the Operating temperature,
is 25°. A concentration of 500 milligrams per liter of zinc and
a solution temperature of 25° had the Opposite effect. At 46’the
current efficiency is approximately the same at all concentrations
of zinc, but the quality of deposits from the solution having a
concentration of 500 milligrams per liter of zinc were superior.
An increase in temperature improved all the deposits somewhat.

With regard to the results that were obtained at low pH
values, Dr. A. Kenneth Graham (8) published an article indicating
that a Watts type bath Operated at a pH range of 1.0 to 2.5 rather
than the customary range of 5.6 to 6.0, can be operated at current
densities well in excess of 100 amperes per square foot and still
produce satisfactory results. The current efficiency drops at
the low pH values advocated but the increase in allowable current
density favors.more rapid deposition and the wider plating range
produced deposited plate less subject to cracking and roughness
at the edges.

The advantages that Graham claims are: (1) increased
plating range, which embodies decreased time and increased
current density; (2) better anode corrosion; (3) no turbidity.
The disadvantages are: (1) lower cathode efficiency; (2) too
high anode corrosion in some instances; (3) the high temperatures
used restrict some types of tank linings; (4) for bright nickel
plating the low pH bath gives the best results at a low tempera-
ture; (5) low pH solutions are not suitable for plating zinc
base die castings.

S. Makaieva (9) investigated the effect of the composi-

tion Of the electrolyte, current density and bath temperature
upon the properties of electrolytic nickel and recorded the
following data. He deposited nickel on polished copper cathodes
under two different conditions, (1) current density of 0.1
amperes per square decimater at 20°, (2) a current density of 5
amperes per square decimeter at 60°. The electrolyte was not
agitated, the pH was constant at 5.3 and the luster, hardness,
porosity, microstructure and crystal orientation of nickel layers
20 microns thick were determined for various current densities.
temperatures and bath compositions. All the nickel deposits from
chloride baths had a yellow tinge, were less lustrous, less orien-
tated, but considerably harder and more porous than deposits
obtained under the same conditions from.sulfate baths. The
differences in prOperties were more pronounced at 60°. By in—
creasing the current density the hardness of the nickel deposit
obtained from.the sulfate baths decreased and the luster improved,
but for nickel deposited from the chloride baths the opposite
effects were Obtained at 60°.

A summary Of the results obtained by the author in his
investigation is as follows:

1. (a) Nickel sulfate in a concentration of 32 ounces per
gallon can successfully be utilized with no addition
agents for the production of electrodeposits Of
nickel if the pH is maintained below 2.5.

(b) An increase in current density at 25° decreases
the current efficiency.

(c) Increasing the temperature to 46° improves the

2.

3.

4.

5.

6.

7.

current efficiency and the quality of the deposit.
(d) Above a pH of 2.5 the solution becomes more acid

upon electrolysis.
The addition of nickel chloride causes the anodes to
corrode, helps to maintain pH values and causes a
darkening of the deposit.
Boric acid improves the quality of the deposit, improves
the current efficiency and acts as a buffer above a
pH Of 4.9.
Sodium benzene disulfonate at 25° produced deposits
having bright areas at pH values Of 4.7, 2.4 and 1.5.
The addition of zinc at 25° improved the current effic-
iency and plate quality up to a concentration of 200
milligrams per liter, above that opposite effects were
produced. At 46° the current efficiency was approximately
the sens in all cases. At 460 the plate quality is
improved as the zinc concentration is increased and is
best at a concentration of 500 milligrams per liter.
The addition of formaldehyde to the nickel sulfate
solution produced a lustrous plate at a pH of 2.5 and
at an operating temperature of 25°. It also resulted
in increasing the current efficiency at 25° as the pH
decreased.
In general good deposits were secured from all bath
compositions at pH values below 2.5 and at both 25°and
46°. The exception was the nickel sulfate solution con-
taining boric acid as an addition agent in this series

all the deposits were satifactory.

The next section of this study was a bright range
investigation. In this part the current density in all tests
was kept at a constant value of 25 amperes per square foot. The
variables were pH, temperature and brightener concentration. The
object was to determine the best operating conditions for the
production of lustrous deposits from.e bath having the following
composition: nickel sulfate, 32 ounces per gallon; boric acid, 4 :
ounces per gallon; nickel chloride, 4 ounces per gallon; sodium
lauryl sulfate, 67 milligrams per liter; zinc, 200 milligrams per
liter; benzene disulphonic acid, 5 grams per liter.

The cathodes were 0.1 square foot steel plates which
were plated in a cyanide OOpper solution and then color buffed.
The buffed copper plates were electrocleaned in a solution con-
taining 2 ounces per gallon of Matawan #2, rinsed in distilled
water, given an acid dip in 20% sulfuric acid, rinsed again in
distilled water and were then electroplated in the nickel
solution.

The functions of the constituents were as follows:
ihe nickel sulfate was present to provide the main source of '
nickel; the nickel chloride furnished nickel ions, improved the
conductivity of the bath and provided for adequate anode
corrosion; boric acid improved the quality Of the deposit,
increased the current efficiency and acted as a buffer between
a pH of 4.9 and 6.0; sodium lauryl sulfate decreased the surface
tension of the solution and in that way eliminated pitting of the
deposit due to adhesion of hydrogen on the surface of the cathode
during deposition; the zinc and benzene disulfonic acid were the

brighteners.

The pH of the solution was lowered with sulfuric acid
and was raised with nickel carbonate. Tb determine the pH an
electrometric.method was used which was composed of a quinhydrone-
calomel cell.used in conjunction with a Leeds and Northrop
potentimmeter.

The temperature range studied was between 87° and 135°
F. The pH range was from 5.5 to 1.0 Figure ll shows a graph
outlining the range within which the most lustrous deposits were
secured. I

.The bath as originally prepared had a lOw pH and was
raised using nickel carbonate to a pH of 5.9. At this pH the
deposit has a tendency to be streaked and burned in the tempera-
ture range of 75° to 90° F. and in addition are pitted. Between
95° and 120° F. the deposits are not streaked or burned and the
pitting is approximately eliminated but the plates are very gray
in color. Despite the grayness of the deposit the appearance is

more lustrous than a matte nickel deposits.

 

 

 

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The effect of lowering the pH to 5.0 was to improve the
brightness of the plates in the low temperature range, 75° to
100°, but the panels were still burned on the edges until a
temperature of 90° was attained. Above 90° the plates were all
pitted and became increasingly more gray as the temperature was
increased.

The pH was then decreased to 4.0 and the result was to
further improve the brightness of the low temperature deposits,
which again became progressively grayer as the temperature was
raised. Even the plates secured below a temperature of 110° had
a slight surface cloudiness that eliminated any from the category
of bright nickel deposits. The degree of pitting was appreciably
reduced and burning was noticed only on the plate at 750 . The
burning in this instance was not the black deposit hitherto
secured but had instead a matte appearance.

At a pH Of 3.6 the deposits were all good and below
110° were quite lustrous except in the center of the panel where
a cloudiness was still observed. The pitting was entirely
eliminated.

Again reducing the pH this time to 3.1 produced plates
in the temperature range 85° to 92° upon which only an extremely
faint cloud could be observed. The depth of grayness still
increases with increasing temperature. Even at a temperature Of
122° they were more lustrous than any plates secured down to a pH
of 4.0.

At a pH of 2.5 the grayness was appreciably diminished

throughout the temperature range. The deposits secured between

95° and 115° were the most lustrous so far obtained.

When the pH was reduced to 1.9 it was impossible to
perceive any trace of cloudiness on the surface except above
temperatures of 110°. Even deposits above 1100 were only slightly
cloudy. However, the extreme edges were matte in appearance
until a temperature of 110° was reached. A reduction in current
density from 25 to 20 amperes per square foot eliminated this
condition without adversely affecting the brightness.

At a pH of 1.5 practically the same results were Obtain-
ed as were secured with a pH of 1.9. The differences between
the results secured in this trial and at a pH of 1.9 were that
the bright deposits could be secured at 132° and the matte condi-
tion on the edges was more pronounced at the low temperatures.

The effect of increasing the zinc concentration to 300
milligrams per liter and the benzene disulfonic acid to 10 grams
per liter aided slightly so a new bath was prepared using the
increased brightener concentrations and the entire series was
repeated. The results obtained were essentially identical to
the results secured in the first series.

The cloudiness mentioned was believed to be due to the
presence of copper in the solution. It was proven that copper
was present by immersing a nickel plated cathode in the solution
for ten hours. At the end of that time observation of the

electrode disclosed the fact that a visible amount of copper had
deposited on the nickel by immersion. The copper present was
largely removed by Operation of the bath at a pH of 1.5 and

utilizing a current density of 0.5 amperes per square foot for 15

to 20 hours. Plates secured after this treatment were more
lustrous than those Obtained while copper was present. The
surface cloud was eliminated approximately 95%. Hewever, when
the pH was raised the cloudiness of the deposit reappeared. The
source of copper was definitely determined to be in the Bakers
C. P. nickel carbonate used to raise the pH.

A summary Of the results obtained in this study is as
follows:

(1) The bright range for the solution studied appears

to be between 100°-130° F., the current density is
25 amperes per square foot and the pH range is 1.5
to 2.5.

(2) The presence of OOpper is a definite contaminant

and causes the deposits to be milky.

This problem.of bright nickel has held the attention of
investigators for many years. Colloids were first used as bright-
eners. Joseph Underwood (10) states that glues, gums, etc., act
as brighteners in nickel plating solutions, but they are difficult
to control and cause trouble unless the amounts used are small.

A slight excess causes peeling and cracking. He suggests that
cadmium acts as brighteners and give less trouble. The use Of
cadmium as the chloride produces the best results.

Marcel Ballay (11) in an investigation of the production
of bright nickel deposits by the use of colloids records the
following material. Upon electrolysis of a nickel sulfate solu-
tion containing small amounts Of chloride and borate with a

cathode over the surface of which the current density varies

considerably, bright nickel deposits are secured in certain
areas, where the pH is just below that favoring precipitation of
nickel hydroxide or basic salt in the immediate proximity of the
cathode. The addition of some organic colloids, e. g., starch,
dextrin, gum arabic, agar-agar, gelatin (2.5 milligrams per liter
suffices with a pH Of 6.5, but 0.4 grams per liter is necessary
with a pH of 8.0) egg albumin and casein also gives bright
deposits which are somewhat more uniform and obtainable with a
greater range of current density than those obtained with inor-
ganic additions.

It is generally known that bright deposits obtained by
the use of gelatin, casein, various gums, etc., are too brittle
and the operating conditions are too crhical for commercial use.

.Max Schlotter (12) states that bright deposits of
nickel are Obtained from solutions containing alkali or alkaline
earch halides, eg., sodium chloride, potassimm chloride,.magnes-
ium chloride, magnesium bromide, sodium iodide and aromatic
sulfonic acids or their salts. The total amount of halogen and
other inorganic acid radicals present should be more than equiv-
alent to the sulfonic acid radical and the pH should be from 3.5
to 5.3, though more acid solutions may be used with higher
current densities. Nickel may be introduced into the bath as
nickel sulfate, nickel carbonate and/or nickel hydroxide. In
examples the aromatic sulfonic acid compounds used are sodium
toluenedisulfonate, sodium trisulfonate, naphthalenedisulfonic
acid and sodium benzenedisulfonate.

Priston and Garden (13) found that nickel was deposited

in a smooth, lustrous form.from a bath containing an organic
sulfonate in addition to a colloidal substance, e. g., gelatin
and/or lysalbic acid. The monosulfonates were found to be
particularly suitable. The sodium sulfonates of benzene, toluene,
ethylbenzene, iso propylnaphthalene, triphenylpentane, alkyl
naphthalene, tetrahydronaphthalene and pyridine are specified.
They also recommend that the pH may be buffered by the addition
of boric acid, acetic acid, formic acid and adipic acid or their
salts.

W. Machu (14) states that colloids and substances Of
high molecular weight are adsorbed on the cathode during electro-
deposition, forming a porous diaphragm with a "pincushion"
structure. The discharge of the cations and the deposition of
the metal is believed to occur in the intermicellar spaces in
the diaphragm. Since the pores are small the crystal nuclei are
small and their number is high and thus they give a fine-grained
deposit. Growth of the nuclei is hindered by the reduced rate of
diffusion of ions in the colloidal diaphragm. Uniformity Of
structure is attributed to restriction by the pores in the
direction of growth of the metal crystals.

At the present thme bright nickel solutions based
upon the addition of aromatic sulfonic acid compounds or their
salts and used in conjunction with a metal such as zinc are in
wide use in commercial plating. They are in general quite
satisfactory and have a pH range of 2.5 to 3.5, a temperature
range of 120°-l45° F. and a current density variable extending

from 20 to 100 amperes per square foot. The most widely used

purification of these baths consists in two operations (1) of
organic contaminants by filtering through activated charcoal or
an appropriate clay and (2) purification of metallic impurities
by raising the pH with nickel carbonate and precipitating the
contaminating metals as their hydroxides. Another type of
purification applicable to metallic impurities is advocated by
Louis Weisberg which consists of plating out the impurities using
low current densities and a low pH.

Another bright nickel solution obtains lustrous deposits
by plating a cobalt-nickel alloy. The brightness of this deposit
depends upon the presence of formaldehyde and a formats in the
solution. Louis Weisberg (15) states that ammonium.sulfate
enhances the brightness of the deposit in prOper amounts but an
excess results in embrittlement. Formaldehyde acts as a depitter
and depolarizer. The combination of sodium formats and formalde-
hyde increases the effectiveness of the brighteners.

Cadmium is used in another bright nickel solution to
produce deposits of high luster. E. Raub and M. Wittum (16)
find that the cathode potential-current density curves Obtained
in baths containing 144 grams of nickel sulfate and 10 grams of
boric acid per liter with a cadmium content varying between 1.3
and 12.7% of the total metal content indicate decreasing throwing
power with increasing cadmium content. Considerable amounts of
cadmium are deposited with the nickel, which increase with the
cadmium content of the bath and decrease with increasing current
density. It is concluded that cadmium additions for bright

nickel baths are less suitable than organic brighteners.

Regarding the cause of the production Of lustrous
deposits of nickel from.some baths R. Springer (17) states that
the principal conditions for producing bright nickel deposits
are: the microcrystals of the deposits should be so orientated
that one of the reflecting surfaces lies in the plane of the
surface of the object and should be smaller than the shortest
wave length of light incident upon the surface.

VOzdvizhenski and Suliemanova (18) believe that the
luster of bright nickel is due to an increased hydrogen content
in the deposit, leading to the formation of an inner strain
which causes a disintegration of the metal during the process of
deposition.

Another theory advanced by M. Schlotter is that bright
electrolytic deposits of metals have an extremely small grain
size, Of the order of the wave length of light. In controlling
the grain size it is found that the anions of hydrolysis products
of the salts in the electrolyte is of major importance, since
these anions may be deposited with the metal and thereby influence
the manner of grain formation. The greater the volume of the
anion the greater the rate of grain growth of the metal and the
smaller the number of nuclei formed; hence the greater the grain
size.

Hothersall and Gardam (19) in an investigation on the
structure and properties of bright nickel deposits state that
three types of deposits were investigated: (2) nickel-cobalt
alloy deposited from a bath containing sodium formats and

formaldehyde, (b) nickel deposited from a bath containing 5 grams

per liter of nickel naphthalenedisulfonate, (c) nickel deposited
from.a bath containing 30 grams per liter of isopropylnaphthalene
sulfonate. Ordinary nickel deposits appear matte, they claim,
because the surface consists of irregular mounds which scatter
reflected light. The mounds do not have plane surfaces or
crystal facets. Bright nickel deposits have a very small grain
size and the surfaces are very smooth. The luster of thin
deposits was highest on a smooth fine-grained surface. On
coarse-grained surfaces the deposits had to be .0004" to appear
fully lustrous. The bright deposits show no definite microstruc-
ture. The etched cross-section showed large numbers of lines
parallel to the cathode surface. These lines are depressions
caused by preferential deposition, but no explanation is advanced.
These lines were not found on deposits from solutions (b) and (c)
which had been annealed in vacuo at 300°. When the annealing was
done at 1000° in Vacuo all three bright deposits obtained a fair
grain size. The stress in the deposits was determined by the
bending of a thin steel strip which was plated on only one side.
Deposits from solutions (a) and (c) had a higher stress
than ordinary dull nickel, but the deposit from solution (b) had
practically no stress. By a bend test deposit (a) was found to
be almost as ductile as ordinary nickel. Deposits (b) and (c)
were brittle. eray examination of (a) and (c) yielded a
diffuse reflection indicating a smaller grain size matte nickel
deposits. Deposit (a) showed some orientation of the crystals,
but (c) die not. The porosity of bright deposits was about the

same as matte deposits, except when the bright deposits contained

cracks.

The above references represent a fairly complete survey
of the literature on bright nickel plating and are included to
indicate the study that is being done on this problem. The
subject is still comparatively new and a great deal of work needs
to be done not only to clarify the mechanism by which bright
deposits are secured but also development of control methods and
analyses. Subsequent investigations will doubtless answer many,

if not all, of the questions about which we may now only theorize.

Bibliography

(1)

(2)

(3)

(4)

(5)

(6)

(7)

(8)

(9)

(10)

(11)

(12)

(13)

(l4)

(15)

M. A. Brochet, 0n the Reactions of the Nickel Plating Bath.
Compt. Rend. 145, 627-8

Joeseph Haas, Survey Of Nickel Solutions. Metal Industry

G. S. Vbsdvizhenskii and I. A. Makolkin, Nature and Mechan-
ism Of the Formation of Streaky Nickel Deposits.
Is Applied Chem. (Us Se Se Re) 2, 1423 ‘ 26e

V. Waite, The Effect of Nickel Chloride in Nickel Plating
Solutions. Monthly Rev. Electroplaters Soc. ‘24, 183 (1937)

M. R. Thompson, The Acidity Of Nickel Depositing Solutions.
Trans. Electrochem. Soc. ‘31, 333 (1922)

Mathers, Stuart and Sturdevand, Nickel Plating.
Trans. Electrochem. Soc. (adv copy) (1915)

W. A. Wesley and J. W. Carey, The Electrodeposition Of Nickel
from.Nickel Chloride Solutions. Trans. Electrochem. Soc.
'15, 179-201 (1939)

A. K. Graham, The Deposition of Nickel at a Low pH.
Metal Industry 22, 118 (1931)

S. Makaieva, Effect of Composition of Electrolyte, Current
Density, and Bath Temperature on the Properties Of Electro-
lytic Nickel. Bull. Acad. Sci. (U. S. S. R.) 1938, 1223-4
(1938)

Joseph E. Underwood, Production of Bright Nickel Deposits.
Metal Cleaning and Finishing 1929, 435-6 (1929)

Mercel Ballay, Electrolytic Deposition Of Bright Nickel in
the Presence of Colloids. Compt. Rend. 199, 60-2 (1934)

Max Schlotter, Electrodeposition of Nickel. Brit. 459,887

H. R. Priston and G. E. Gardam, Electrodeposition of Nickel
Brit. 506,332, May 23, 1939

W..Machu, Influence Of Colloids on the Structure of Electro-
deposits. Osterr. Chem. Ztg. 22, 244-7 (1939)

Louis Weisberg, Deposition Of Cobalt-Nickel Alloys. Trans.
Aline Electrochem. SOCe E. 435 " 40 (1937)

Bibliography - cont'd.

(16)

(1'7)

(18)

(19)

E. Raub and M. Wittum, Cadmium.and Arsenic in Nickel Baths.
Korrosion and Metallschutz‘lg, 127-30 (1939)

R. Springer, Bright Nickel Plating. Oberflachentech. '14.
49-51 (1937)

G. S. VOzdvizhenskii and Suliemanova, Bright Deposits on
Unpolished Surfaces. J. Applied Chem. (U. S. S. R.).g,
1416-22 (1936)

A. W. Hothersall and G. E. Gardam, The Structure and Prop~
erties of Bright Nickel Deposits. J. Electrodepositors
Tech. Soc. _]_.§_, 127-40 (1939)

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