137
178

 

HTHS

THE ELECTRODEF’OSITION
OF BREGHT COPPER

Thesisfer the Degree of M‘ S.
MICHIGAN STATE COLLEGE
Henry Vincent Pfeuffer jr

E947

m
_
A.

 

 

 

 

This is to certify that the

thesis entitled

THE ELECTRODEPOSITION
OF BRIGHT COPPER

presented by

Henry Vincent Pfeuffer Jr.

has been accepted towards fulfillment
of the requirements for

Mdegree in Chemistry
(Physical)

 

 

THE ELECTRODEPOSITION OF BRIGHT COPPER

by
' HENRY VINCENT PFEUFFER Jr.

A THESIS
Submitted to the School of Graduate Studies of Michigan
State college of Agriculture and Applied Science
in partial fulfillment of the requirements

for the degree or

MASTER OF SCIENCE

Department of’Chemietry
1947

\\

Acknowledgements
The writer wishes to thank Dr. D. 1‘. Ewing, Pro-
tensor of. rhysioal Chemistry, for his assistance and
suggestions throughout the course of this investiga-
tion. The writer'is also indebted to the Keeler

Brass Oompam of. Grand Rapids, Michigan, for the
grant of a fellas-hip which made this work possible.

187890

Two major’types of solutions are available for the elec-
trodeposition of cOpper. These are: 1. Acid solutions of
cepper salts; 2. Alkaline solutions of coPper salts. The
electrodeposition of bright capper is possible in both types
of the above mentioned solutions, the majority being of the
alkaline type solution.

The acid type bright cOpper solutions may be classified
as follows:

- 1. Solutions containing cupric sulphate, sulphuric acid,
and brightening agents.

2. Solutions containing cuprous capper salts.

3. Solutions of capper salt of sulfbnic type acids.

4. Solutions of cepper salt of dibasic organic acids.

Alkaline bright capper solutions fall into the follow-
ing classes:

1. Ouprocyanide solutions containing brightening agents.

2. Solutions of capper amines.

3. Capper pyroPhosphate solutions.

4. Capper sulfamate solutions.

This investigation is limited to the first three types
of alkaline bright capper solutions. One typical solution of
the cyanide type and perphosphate type was investigated for
the effects on brightness of temperature, current density, pH,
and metallic impurities. The same effects were studied for
two types of capper amine solutions, nauwly, the ethylene dia-
mine and diethylene triamine solutions. A further study was
made of the ethylene diamine solution in an effort to improve

the throwing power, smoothness of deposit, and brightness of

I

deposit.

The electrodeposition of bright cOpper has been exten-
sively studied since 1939. Prior to this time various modi-
fications and additions were made to the existing capper so-
lutions without any notable degree of success in obtaining
lustrous, smooth deposits. Kern (l) and Bennett (2) found
that the addition of certain colloidal substances and reduc-
ing agents to the acid sulphate solution improved the physical
appearance of the deposit. Gelatin, tannic acid, glue, and
tin were the colloids found beneficial, while pyrogallol,
bensoic acid, hydroxylamine, and sugar were the reducing a-
'gents used. MCCullough and Gilchrist (3), by the addition of
Rochelle salts to the cyanide copper bath, improved the bright-
ness, smoothness, and cathode current efficiency. Work of
this nature was carried on intermittently until 1936 when
Brockman and his oo-workers (4,5,6) published the results of
a series of investigations on various copper-amine complexes.
This research stimulated the subject of bright capper elec-
trodeposition to a considerable extent. Various solutions con-
taining mono, di, and tri ethanolamine, ethylene diamine, and
diethylene triamine were studied. The triethanolamine solu-
tion, when used in conjunction with sodium oxalate, was found
to be applicable for striking steel preparatory to plating in
a conventional solution. The ethylene diamine and diethy-
lene solutions, however, gave lustrous deposits even for high
current densities. Greenspan (7) improved Brockman's diethy-
lane triamine bath, modifying it by the addition of ammonium

sulphate, ammonium.hydrozide, and a wetting agent. Similar

$1

modifications have been made to the ethylene diamine solution
by Wilson (8) and Hartford (9). Wilson added boric acid and
lactic acid to the original Brockman solution while Hartfbrd
approxina tely tripled the original constituents. Coincident
with the work on the amine solutions was the development of
two successful solutions for bright cOpper electrodeposition.
One was a product of the duPont company (10) and was essen-
tially a cyanide solution.containing cOpper cyanide, potas-
sium cyanide, potassium hydroxide, a brightener (sodium thi-
ocyanate), and an.antipitting agent. The solution, when used
hot, gave bright deposits up to high current densities. A
solution was described by Starek (11) and Coyle (12) and con-
sisted of copper pyrophosphate, potassium.plerphosphate, amp
monia, and citric acid. Starek has disclosed the use of'di-
basic organic acids or their ammonium or fixed alkali salts
as brighteners in this solution. Additional brighteners and
addition agents listed are the disulfbnic acids of phenol or
napthalene and the chlorides of arsenic, bismuth, iron, chro-
mium, tin, zirconium, lead, cadmium, and the alkali metals.
The use of’a double salt of sodium and copper perphosphate
as the major constituent of a copper solution has been des-
cribed by Gamov and Pomenko (13). Other solutions of recent
develOpment which are claimed to give bright deposits are as
follows: 1. acid cepper bath containing thiourea and molas-
ses (14); 2. oxalate-copper complex bath (l5); 3. cuprous
chloride-sodium thiosulfate solution (16); 4. copper-alkane
sulfonic acid solution.(17). The latter solution was discussed

in an article recently and appears to be applicable for the high

.3

speed deposition of bright capper. A bright cyanide solution
was recently deve10ped by Mac Dermid Incorporated (18) con-
taining a salt similar to Rochelle salts and a brightener.

Several theories for the mechanism of bright electrodep-
osition have been prOposed. Taft (19), Bancroft (20), and
Kern (21) are of the opinion that addition agent or bright-
ening action falls into one of two classes, namely, adsorption
of a colloidal particle with the metal, or reduction of the
metal by the particle with no co-deposition. mathers (22)
proposes a compleg ion formation resulting in a refined grain
size. Hunt (23) and Hendrick (24) state that the interfer-
ence film formed at the cathode interface determines the
grain size and thereby the brightness of the deposit. The
ratio of this film to the cepper ion is said to be the deter5
mining factor on the ultimate grain size.

EXPERIMENTAL

Because of the number of processes investigated, cache
solution.will be discussed separately as regards composition

purification, apparatus, and discussion of results.

lEhrlsue_liaains_§clsiicu - The composition of the solu-
tion used in each case was as follows:
011304 . SHZO " 50 g./1 (6.8 03/831.)

Ethylene Diamine (60%) 42 cc./1(5.4 " )
10 g./l (1.4 " )
Ammonium.Hydroxide - 23 cc./l(3.l " )

pH (electrometric) - 10.0

Ammonium.3ulphate

This is essentially the Brockman (6) solution with ammon-
ium sulphate added as suggested by Greenspan (7). The ammon-
ium hydroxide, cOpper sulphate, and ammonium sulphate used
were of O. I. grade. The ethylene diamine was the Eastman.Prs'
actical grade.

The chemicals were dissolved in 1 liter of water in the
order given. The solution was then purified by filtering hot
(60°C) througha flurrey of filter aid and activated carbon.
This treatment removed organic impurities and suspended matter.
The metallic impurities were removed by electrolysing a dummy
cathode of large area at a current density of 2-6 amps/sq.ft.
for 5 amp.-hcurs.

The data for Table II was determined in a 1 liter bat-

tery jar. The cathode was suspended between 2 rolled cepper

\

anodes at a distance of 2.5 inches from each anode.

All runs in Tables I, III, and IV were made in the Hull
cell using 250 cc. of solution. The cathodes used through-out
were steel panlele, 4 inches by 2.5 inches. The steel panels
were well buffed and electrocleaned clmthcdically in a hot
solution containing 8 ounces per gallon of Northwest 30-45
cleaner. .After being electrocleaned, the plates were firm;
rinsed in cold running water followed by an acid dip in 50%
hydrochloric acid by volume and finally were rinsed again in
cold running water. They were then given a copper strike in
a cyanide bath. The criteria used to determine the cleanness
of the plate was the water film test. If the plates showed no
break in the water film they were immediately placed in the
plating solution with the current on. This procedure was
used throughout the entire investigation. After each run the
solution was filtered through filter aid and the pflichecked.
A11 pH determinations were made with the Beckman pH Meter, MOd-
el G. To obtain pH values below 8.3, 50% sulphuric acid by
volume was added until_the value desired was reached. When
the preceding run was completed, the solution was discarded
and the pl'values above 8.3 were obtained by the addition of
ethylene diamine (60%). In all cases the free ammonium.hydrox~
ide was maintained.

After a preliminary determination of the effect of agi-

tation on the deposit, moderate mechanical agitation corres-
ponding to approximately 20-40 ft./minute was used.

The metallic impurities were added by means of standard
solutions of their sulphate salts containing 1 mg/cc. of the

metal. (After each run the solution was purified by filtration

and electrolysis.

Table I
Ethylene Diamine

THE EFFECT OF TEMPERATURE 0N BRIGHT RANGE OF DEPOSIT

n.“ In.

OGQOOIfiNNl-I'

Time-ten minutes, Hull 0e11, Current-l ampere

Temp. in 0° Condition of Deposit
25° Bright Range-5 to 25 amps/rte
30 ' ' -Same
35 ' ' ~Same
40 o o -6 to so
45 " " -5 to 45
50 ' " -5 to 55-very bright
55 " " -5 to 55
60 " " -5 to 50
65 " " -5 to 40-mlky
Table II

Ethylene Diamine

THE EFFECT OF CURRENT DENSITY ON BRIGHTNESS OF

Dlate No.
10
ll
12
13
14
15
16

Temperature-50-6000, Time-ten.minutes
condition.of'Deposit

Current Density
5 amps/ftz
10
15
20
25
3O
35

DEPOSIT

Bright-even

Plate No.

17
18
19
20
21

Current Density

40 amps/ft2

45
50
55
60

Table II (cont'd)

Table III

Condition of Deposit

Very Bright
w w
n n
w n

Milky-burned on edges

Ethylene Diamine

THE EFFECT OF pH ON BRIGHTNESS RANGE OF DEPOSIT

Temperature-50°C, Current-l ampere, Time-ten minutes

Plate No.
22
23
24
25
26
27
28
29
3O
31
32
33
34

pH

7.4
7.6
7.8
8.0
8.2
8.4
8.6
8.8
9.0
9.2
9.4
9.6
9.8

* O. D. -current density

Condition of Deposit

Non adherent-milky
Rough-burned at high 0. D.*
Non adherent-burned

streaked-brittle

1' H
I! W
n N

Milky-brittle

N '9

Bright Range 15-25 amps/ft2

” " 10-30 '
” " 10-45
" " 10-55

Plate No.
35
36
37
38

Table III (cont'd)

pH Condition of Deposit
10.0 Bright Range 10-55
10.2 T " 10.55
10.4 " ” 10-50
10.6 Streaked-rough

Table IV

 

Elena Diamine
THE EFFECT OF METALLIC IEPURITIES 0N BRIGHT RANGE

Temperature-50°C, Current-l ampere, Time-ten minutes

1 e Hiokel

Plate No.
39 I
40
41
42
43
44
45
46
47
48
49

2. Zinc

Plate No.
50
51

Conc. of'Ni(mg./l)

1

2 .

4

e
16
as
64
128
256
500

l g./1

Cone. of Zn(mg/1)
1
2

Condition of Deposit

'Bright Range 5-55 amps/ftz, even

" ' same "
H I II I!
i! I I! If
w fl '0 I!
I! II n I!
II V! I! I!
I! II I I
I! R D I!
N I. w w
n I! ll '0

Condition of Deposit
Bright Range 5-55 amps/ftz, even

Table IV (cont'd)

2. Zinc

Plate No. Conc. of Zn(mg./1) Condition of Deposit
52 4 Bright Range 5-55 amps/ftz, even
58 8 ' ” Same ”
54 , 15 w w n w
55 52 n w w w
‘56 54 e w w e
57 - 128 o v e w o
58 266 " " " '
59 506 Rough at high 0. D.
60 1 g./1 Tread at high 0. D.-rough

3. Iron

Plate No. Cone. of Fe(mg./l) Condition of Deposit

61 1 Bright range 5-55 amp/ftz, even-

. smooth

62 2 " " . Same '

63 4 I! I! W W

64 8 " H II I1

65 15 Bright range 19-50 amp/rt2

66 32 fitted-same bright range

67 64 Brittle and pitted-same bright
range

68 128 " 7 '

69 1 g./1 Tread at high €.:D.-p1tted

Discussion of Resultg.--The optimum operating conditions
evident from the data are as follows:
Temperature - 50 to 55°C
Current Density - 20 to 55 amps/sq. ft.
pH - 9.8 to 10.2

[(3

0f the three above variables the one requiring the most
careful control is pH. A variation from the 9.8 to 10.2
range causes poor deposits especially if the maximum value of
10.2 is exceeded. pH is, in fact, a measure of the amine to
copper ratio, the value of which should be kept at or near
0.8 (f; 0.03).

Other factors that were found to affect the condition and
appearance of the deposit were anode area, ammonia content,
and agitation. The anode area required is approximately twice
that of the cathode, too little anode area resulting in salt
formation on the anode and a resulting decrease in anode cor-
rosion. Addition of ammonia is required frequently as the
high temperatures used promote decomposition and subsequent
loss of the ammonia.

The brightness of the plate is unaffected by lack of ag-
itation, however, mild agitation is required to prevent the
formation of wire-like growths on.the cathode. Excess agi-
tation causes streaked deposits.

The deposits from this solution may be classed as lustrous
bright and are ductile when free from impurities. Nickel and
zinc, in concentrations normally encountered, have little or
no effect upon.the appearance or preperties of the deposit,
however, iron, in amounts as low as 15 mg./l, has a harmful ef-
fect. The chief effects of iron in concentrations over 32 mg/l
are pitting, embrittlement, loss of brightness at low current
densities, and treeing at high current densities due to the solid
ferric hydroxide particles.

At the optimum Operating conditions, the cathode current

I (

efficiency is 107%, indicating some deposition from the cup-
rous state. The throwing power of the solution is considerably

less than that of the standard cyanide solution in spite of the

high current efficiency.

Diethylene Trialmine Solution.--The composition of the so-

lution used in each case was as follows:

Cu804 ' 5820 - 119 g/l (16 oz/gal)
Diethylehe Triamine - 89 " (12 os/gal)
Ammonium Sulphate - 18.6 " (2.5 " )
Ammonium.Hydroxide - 30 " (4 " )

Tergitol 08 (wetting agent) 2.2 " t .s o )
pH (electrometric) - 9.8

This solution (7) is made up in the order shown and puri-
fied. The procedure for purifying this solution is identical
with that used for the ethylene diamine solution, e.g., fil-
traticn through filter aid and activated carbon renewed by
-e1ectrclysis at 2 to 5 amps/sq.ft. for 5 ampere hours.

A17 liter solution was used for the determination of the
effects of temperature and current density upon the deposit
(Tables 7 and VI). This large volume was necessitated by the
fact that preliminary investigation showed that abnormal and
harmful effects were produced if the current passed exceeded
1 ampere/liter for long periods of time. It was necessary to
pass current up to u amperes thereby necessitating a large vol-
ume. The cathodes used were steel plates with an area of 0.1
square foot. The plates were given a preliminary copper strike
in a cyanide bath. Rolled copper anodes were used having an
area twice that of the cathode. The anodes were bagged to pre-
vent contamination of the solution by suspended matter. The
cathode was suspended in the center of the tank at a distance
of 5-3/16 inches from.each anode.

The investigation of the effects of pH and impurities was

carried out in a 1 liter beaker using a bent cathode, 1 inch
by 4 inches, with a lip 1 square inch in area. The Hull cell
was not used because of the inconsistency of results due to
contamination from the anode and excessive current used. The
cathode was given a preliminary cepper strike in a cyanide sol-
ution due to iron contamination caused by exposed steel. The
procedures for cleaning plates, adding impurities, and varying
pH, are similar to those used for theethylene diamine solution.
moderate mechanical agitation was used in all cases. Air
agitation.was attempted but was found to contaminate the sol-
ution through the formation of solid oxidation products.
Table V
Diefiflllene Triamine
THE EFFECT OF TEMTEHATURE 0H BRIGHTNESS RANGE OF DEPOSIT
Time-ten minutes

Current

Plate No. Density Temp. in 6° Condition o£.Deposit
1 40 amp/ftz 25 Dull-burned on edges
2 40 50 Even-s1 ight mininess
3 40 35 ” " "
4 4o 40 Semi-bright
5 40 45 Slightly brighter than #4
6 40 50 Very bright-even
7 50 55 ” ‘ '
8 50 60 (Dull
9* 50 60 Very bright-even

10 50 65 " " "

* ‘(’ 30 co. ammonium hydroxide (conc.)

/L(

Plate No.

11
12
13

Table V'(cont'dl

Current
Density Temp. in c° condition of Deposit
60 amp/ftz 70 Cloudy on edges
60 75 n w n
so so Milky
Table VI

Diethzlene Triamine

THE EFFECT OF CURRENT DENSITY ON BRIGHTNESS OF DEPOSIT

Plate No.

i 14
15
16
17
1e
19

' so
21
22
23
24.
25
so
27

Temperature-60°C, Time-ten minutes

Current Density Condition of Deposit
5 Semi-bright
10 Very bright
15 n I 1
20 " '
25 " "
30 ' '
35 ' '
‘0 u e
45 ' '
50 " "
55 " ”
50 ' '
65 ' '
70 Burned on edges

Table VII
Diethylene Triamine
THE EFFECT OF pH OH BRIGHTNESS RANGE OF DEPOSIT

Temperature-60°C, Bent cathode, Time-ten minutes

Plate No. pH Condition of Deposit
28 8.6 Brittle-dull-dark
29 8.8 " " "
30 9.0 Bright Range 5-40 am a
per ft
31 9.2 " " 5-40
32 9.4 " " 5-40
33 9.6 " " 5-70
34 9.8 ” ” 5-70
35 10.0 " " 5-60
36 10.2 " " 5-30
37 10.5 Low conductivity-burned
at high 0. D., milky at
others
.ggble VIII

 

Diethyiene Triamine
THE EFFECT OF METALLIC IMRURITIES ON BRIGHT RANGE OF DEPOSIT
Temperature-60°C, Time-ten min., Current-1 amp., Bent cathode
l. Nickel
Plate No. Cone. of Ni(mg/l) Condition oi’Deposit

38 0 Bright range 5-70 amps/ftz, even
39 2 " " Same "
4o 4 n N n I!
41 8 " " " pitted

42 16 n N N N

Table VIII (cont'dl
Plate No. Cone. of Ni(mg/l) Condition of Deposit

43 52 Bright range 5-70 amps/ftz-
pitted
44 64 " " Same "
45 128 Bright range 5-50 amps/ftz
46 256 " " Same
47 1 g/1 " " n
2 Zinc

Plate No. Cone. of Zn(mg/l) Condition of Deposit

48 0 Bright range 5-55 ampe/ft3
49 2 " " Same
50 4 n w n
51 s n n n
52 16 n n w
55 52 a n w
54 64 " w n
55 128 v n n
56 256 n n n
57 1 g./1 Slight Cloudiness
3 Iron

Plate No. Conc. of Fe(mg/l) Condition of Deposit

58 0 Bright Range 5-70 amps/fta-
. even

59 2 " " Same

60 4 II fl 1'

61 8 N n W

62 16 Bright Range 10-55-brittle

Table VIII (cont'dl
Plate No. Cone. of Pe(mg/1) Condition of Deposit

63 32 Bright Range 15-55 amps/ft3
pitted at all C. D.

64 64 Bright Range 25-50-Fe de-
posit low at C. D.

65 128 Poor plate-milky and pitted

Discussion.--The Optimum operating conditions as seen
from the data are as follows:
Temperature . -50 to 60°C
'Current Density ~20 to 70 amps/sq.ft.
pH -9.5 to 10.0
This solution is extremely sensitive to certain soluble
impurities and snapended matter. Iron is the most common im-
purity and in small amounts produces brittleness and pitting
and must be entirely removed before satisfactory deposits
may be obtained. Oil, even in small amounts, is taken into
solution from the presence of the wetting agent and agitation
and causes milky, streaked deposits. The suspended impurities
may be introduced through unbagged anodes, exposed steel, and
imprOper filtering technique. Their effect is to cause a
general roughness and pitting on the deposit and treeing at
high current densities. All of these impurities may be re-
moved by filtration and electrolysis treatment. The effect
of the wetting agent, "Tergitol 08" is to increase the toler-
ance for solid impurities.
As in the ethylene diamine solution the ammonia content
is rapidly depleted and must be replenished periodically. A

low ammonia content causes a narrowing of the bright range,

while an excess, as determined by odor, has no harmful effect.

The deposits produced in this solution.nny'be classed as
lustrous bright, and are the brightest deposits encountered in
any of the solutions investigated. The solution has good
throwing power and has a cathode current efficiency of 109%
at the Optimum operating conditions.

As in the case of the ethylene diamine solution, pH is an
indication of the amine to cOpper ratio. When the pH falls
below 9.0, dark brittle deposits result. At pH values over
10.0, a narrowing of the bright range is evident.

The following summary gives precautions and operating
conditions necessary for satisfactory results from the die-
thylene triamine solution.

1. Anodes must be bagged at all times.

2. Anodes must be removed from solution.When not in use,

to prevent dissolving action of solution.

3. Excess ammonia content must be maintained.

4. Current should not exceed 3 amperes/gallon.

5. Solution must be free from organic impurities and
metallic impurities, especially iron. Continuous
filtration is recommended.

6. Best pH range is 9.5 to 10.0.

7. Best Operating temperature is 60°C (140°F).

8. maximum current density at the above temperature is
70 amps/sq. ft.

9. Mechanical or solution agitation is necessary for
Operation at high current densities. Air agitation

is unsatisfactory.

{9

10. Steel and zinc work should be given a preliminary

cyanide strike.
11. An anode area approximately twice that of the

cathode area is recommended.

gerphosphate Solution-- The composition of the solution
used in each case was as follows:
copper Perphosphate (Cu2P207 ' 5520) ~110 g./1 (14.7 oz/g)
Potassium Perphosphate (K4P207' 10H20) -404 " (50.9 oz/g)

Ammonium.Hydroxide - 3 " ( 0.4 oz/g)
citric Acid - 10 n ( 1.5 Oz/g)
pH (electrometric) - 8.5

This solution is the same perphosphate solution de-
veloped by Starek(ll).

All of the chemicals used were of C. P. grade. Rolled
capper anodes were used. The chemicals were mixed in the or-
der shown, heated to 50°C, and filtered through filter aid
and activated carbon. The solution was then electrolyzed
from 2 to 5 amp-hours at a current density of 5 amps/sq.ft to
remove all metallic impurities.

The Hull cell was used in all cases, with the exception
of Table I. In this case, a 1 liter beaker containing 750 m1.
of solution.was used with the cathode suspended between 2
anodes. The anode-cathode distance was 2 inches. Steel plates
4 inches by 2.5 inches were used and were subjected to the
same cleaning treatment as in the ethylene diamine procedure.
The methods of adding the metallic impurities is also similar

to that used for the ethylene diauune bath.

The pH was varied by means of potassium hydroxide and
sulfuric acid.

MOderate mechanical agitation.was used in all cases.

”4/
{’K

Table IX
gyrophosphate
THE EFFECT OF TEMPERATURE ON BRIGHT RANGE OF DEPOSIT

Time-ten minutes, Hull Cell, Current-l ampere

Plate No. Temp. in 00 Condition of Deposit
l 21 Black at high C. D.
2 25 Bright Range-10-35 amps£ft2
3 30 Same without burning
4 55 n n n
5 40 Bright Rmnge-5-40
5 45 w w n
7 50 Bright Range-5-50
8 55 . " V 0-55
9 60 " " 0-60

10 65 " " 0-60
11 70 " " 0-60
Table I
gerphosphate

 

THE EFFECT OF CURRENT DENSITY 0N BRIGHTNESS 0F DEPOSIT

Temperature-60°C, Time-ten minutes

Plate No. Current Density Condition of Deposit
12 10 amps/rt2 Smooth-bright-even
15 20 w " " ,,
14 3O " " "
15 40 " " "
16 50 " " "
17 55 " " "

18 60 fl '1 fl

Plate No.
19
20
21
22

Table X'(cont'd1

 

Current Density Condition of Deposit
6O amps/ft2 Smooth-bright-even
70 n n w
75 Burned at high C. D.
80 Same plus rough and dull
Table II
Ezrgphosphate

 

THE EFFECT OF pH ON BRIGHT RANGE OF DEPOSIT

Temperature-50°C,

Plate No.
23
24
25
26
27
28
29
3O
31
32
33
34
35
36
37

pH
7.0
7.5
7.8
8.0
8.2
8.4
8.5
8.6
8.8
9.0
9.2
9.4
9.6
9.8
10.0

Hull Cell, Time-ten minutes

Condition of Deposit
Bright Range 5 to 10 amps/rt2

" " Same

n n n

w n w

w n n

w n n

n n w

n w w

n w w

w n n

" " 5 to 60-rough

Same-duller

N :1

Bright Range 5 to 55

Table XI (cont'dl

 

Plate No. pH Condition of Deposit
38 10.5 Bright Range 5 to 55
39 11.0 Semi Bright Range 5 to 55
40 11.5 " " " "
41 12.0 Entire pla te milky
Table XII
gerphosphate

 

THE EFFECT OF METALLIC IMPURITIES ON BRIGHT RANGE OF DEPOSIT

l. Nickel--Nickel was added up to concentrations of 1 gram
per liter with no deletereous effects upon the smoothness,
brightness or ductility of the deposit. I
2. Zinc--The effect of’zinc up to concentrations of 1 gram
per liter is Edentical with that of nickel.
3. Iron

Temperature-60°C, Hull Cell, Time-ten minutes
Plate No. Cone. of Fe(mg/l) Condition of Deposit

42 2 Bright Range 5-70 amps/ftz-
87911

43 4 " ” Same

44 8 n n n

45 16 w " w

46 52 " " "

47 64 " " "

48 128 n " W

49 256 Cloudy at low C. D.

50 500 " " " w

51 1 g./1 Bright Range 15-70 amps/it2

I'M

Discussion-~The Optimum operating conditions for this so-

lution are as follows: ‘
Temperature - 60°C
Current Density - 20 to 65 amps/ft2
pH - 8.5

This solution is very stable and may be Operated for con-
siderable periods of time without requiring replacement of
chemicals except for those lost through drag-out. The solue
tion as made up is a very heavy and viscous causing consid-
erable drag-out in normal use.

The deposits obtained from this solution are bright,
smooth, and ductile. The solution has good throwing power
and has a cathode current efficiency of 100% at the Optimum
operating'conditions.

The tolerance of the solution.fOr metallic impurities is
very good, as shown.by the data. The chief effect of iron.ie
a diminution of brightness at low current densities at concen-
trations over 256 mg/l.

An unusual pH range, over which good deposits may be ob-
tained, is an advantageous characteristic of this solution.
Another advantage is the good adherence of the copper when

plated directly on steel.

Cygnide Bright COpper Solution.--The composition of the
solution.used in each case was as follows:
Potassium Cyanide - 74 g./1 (9 Oz/gal.)
COpper Cyanide - 49 " (6 oz/gel.)

Potassium Hydroxide 8.2 " (2 " )

Rocheltex - 5% by volume
Brightener - 2% "

pH (electrometric) 15.0

This (18) is a cyanide solution modified by the addition
of brightening agents (18). The OOpper cyanide was of techni-
cal grade while the potassium cyanide and potassium hydroxide
were of C. P. grade. The composition of the "Rocheltex" and
the brightener solution were unknown. Both solution were fur-
nished macdermid Incorporated.

The chemicals were added in the order shown. The solu-
tion.was then purified by the usual filtration through filter
aid and activated carbon followed by an electrolysis using a
low current density (2 to 5 amps/sq.ft.).

Steel plates, 4 inches by 2.5 inches were used as cathodes
and were prepared by the same procedure as previously mentioned.

Moderate mechanical agitation was used. The solution was
filtered and the pH checked after each run.

The data for Tables XIII, XV, XVI, and XVII was deter-
mined in a Hull cell. The data for current density effect
was accomplished by the same procedure used in the perphos-
phate solution; e.g., a 1 liter beaker, 750 cc. of solution,

anode-cathode distance of 2 inches.

Table XIII

Cyanide
THE EFFECT OF TEMPERATURE 0N BRIGHT RANGE OF DEPOSIT
Time-ten minutes, Hull Cell, Current-l ampere

Plate No. Temp. in c° Condition of Deposit

 

1 25 Burned
2 50 "
3 35 Burned at high C.D., milky at low
4 40 Bright Range to 10 amps/ft“g
5 45 7 7 ' 7 14
6 50 " " " 18
7 55 " " w 30
8 50 " " " 40
9 55 " " " 48
10 70 " " " 50
Table XIV
Cyanide

THE EFFECT OF CURRENT DENSITY ON BRIGHTNESS OF DEPOSIT

Temperature-60°, Time-ten minutes

Plate No. Current Density Condition of Deposit
11 10 amps/sq.ft. Bright-even
12 20 " "
13 30 " "
14 35 " "
15 40 " ”
16 45 Rough at high 6. D.

17 50 Burned-rough

if,,
a
.2
l

Table XV

Cyanide
THE EFFECT OF pH 0N BRIGHT RANGE OF DEPOSIT

Temperature-60°, Hull Cell, Time-ten minutes

Plate No. pH Condition of Deposit
18 11.5 Rough-milky
19 12.0 7 7
20 12.6 7 7
21 12.5 Bright Range 15-25 amps/ft2
22 15.0 7 7 15-40 ~
25 15.2 7 7 Same
24 15.4 7 7 7
Table XVI

 

THE EFFECT OF METALLIC IMPURITIES ON BRIGHT RANGE OF DEPOSIT
1. Nickel-~No detrimental effect was noticed up to a concen-
tration of 1 gram/liter of’nickel if the free cyanide is allowed
to fall below 0.5 ounces/gallon, concentrations of nickel over
16 ag/liter cause rough, streaked deposits due to the formation
of suspended nickel hydroxide.
2. Zinc--The results are the same as for nickel.
3. Iron--

Temperature-60°C, Hull Cell, Time-ten minutes
Plate No. cone. of Iron tug/1) condition of Deposit

25 1 Bright Range-to 4O amps/ftz-even
26 2 " " " Same "
27 4 n n n n W
28 8 Rough at high 0. D.

29 15 . Bright Range 5-40

Plate No.
30
31
32
33
34

Table XVI (cont'dl

Cone. of Iron (

mg/l) Condition of Deposit

Bright Range 5-40 amps/ftz-rough

 

32
64 Rough-milky
128 Treed-rough-milky
256 " "
1 g./1 7 7
Table XVII
Cyanide

THE EFFECT OF FREE CIANIDE 0N BRIGHT RANGE OFJDEPOSIT

Temperature-60°C,

Plate NO.

35
36
37
38
39
4O
41
42
43
44
45
46
47

Free Cyanide

(oz/gal.)
(12
(L5
CL4
0.5
CLO
0.7
(L9
1.0
1.2
1.4
1.6
1.8
2.0

Hull Cell,

Milky-pitted

Time-ten minutes

Condition of’Deposit

Bright Range 5-20 amps/rt2

fl

7'

I!

5-35
5-40

Same

77

Semi Bright Range 5-30

" 5-15

Discussions-The Optimum operating conditions for the

solution are as follows:

7‘(

Temperature - 50 to 70°C
Current Density - 20 to 40 amps/rt2
pH - 13 to 13.5

The free cyanide content must be maintained within the
limits, 0.6 to 1.8 ounces/gallon, to insure bright smooth de-
posits. An excess of anode area (2:1) is desired to prevent
burning Of the anode.

By the use of the above conditions, bright, smooth de-
posits may be obtained up to 40 amps/ftz. Continued use of
the solution at temperature over 50°C causes a depletion of
the free cyanide content through the formation of carbonates,
resulting in a pitted, milky deposit. This effect may be
avoided by the use of lower temperatures and current densities.
The "Rocheltex" and brightener solutions are consumed rather
slowly but must be replaced periodically in order to prevent
decreased brightness of the deposit. The analysis fer 7R0-
cheltex" is identical with that used fer Rochelle salts.

The solution has very good throwing power and has a
cathode current efficiency of 100% at the optimum operating
conditions.

Btgyiene Diamine Solutions (Improved )--Ths effect of var-
iation in concentration of the solution's original constitu-
ents, e.g., cOpper sulphate, ethylene diamine, ammonium hy-
droxide, and ammonium sulphate, was first determined. After
arriving at an Optimum composition, various compounds, noted
for their brightening action or buffering action, were added
in an effort to improve the physical characteristics of the
deposit and the throwing power of the solution.

All determinations were made in the Hull cell with the
exception of the cOpper sulphate-ethylene diamine procedure,
the data for which was determined in a 1 liter beaker. The
addition agents were added directly to the cell and were dis-
solved, in the case of solids, before the determination was
made. A constant volume was restored by evaporation. The ad-
dition agents were added in small amounts until an effect was
noticed on the deposit. Freshly prepared solutions were used
for each addition agent. Chemicals of C. P. grade were used
for all cases with the exception of the ethylene diamine
which was the Eastman Practical grade.

Cathodes of steel plate, 4 inches by 2.5 inches were used.
The plates were cleaned in the same manner as previously men-
tioned and were given a preliminary cyanide strike.

Moderate mechanical agitation was used in all cases.

Copper Sulphate-Ethylene Diamine Ratio--A water solution
containing 120 grams/liter of copper sulphate was prepared and
diluted to 500 cc. Ethylene diamine was added until a deep
blue coloration was formed. Aliquot 10 cc. portions of ethylene

diamine were then added until a total of so cc./1iter had been

Bf

added. Test plates were run after each addition. The deposits
in all cases were milky and rough. The solution was then dil-
uted with water, added in portions of 100 00., until 1 liter
had been added. The effect of the dilution was noted a fter each
addition. Bright deposits were obtained at concentrations of
50 to 60 grams/lit er of copper sulphate. In order to study

the effect of ethylene diamine concentration upon the deposit,

a solution containing 60 grams/liter of capper sulphate was
chosen.

Table XVIII

Ethylene Diamine (Improved)
Temperature-24°C, Hull c611, Time-ten minutes

 

Plate No. Ethylene Diamine Condition of Deposit
1 50 oe./1 Bright Range 10-15-emp- /ft3
2 35 " " Sonic
3 4O “ " " ~darker
4 45 4 Bright nge 15-30
5 50 " " Sane
6 55 Dark
7 60 Dark-burmd

The optimum composition was 60 grams/liter ofc0pper sul-
phet. and 50 cc./1iter of ethv1ene diamine. This oonposiuon
was used throughout the remainder of the inestigation.

Table XIX

Eihylene Diamine ( Improved )

THE EFFECT OF AMMONIUM SULPHATE CONCENTRATION ON DEPOSIT

Temperature-50°C, Hull Cell, Tine ~ten minutes
Plate No. Cons. of (554)2504 Condition of Deposit

 

8 5 g/l Dark-poor-throwing power

Table XIX (cont‘d)

Plate No. Cone. of (N24)2SO4 Condition of Deposit
9 1o g/1 Dark-better T. 2.7
10 15 Bright Range 10-20 aupsé
11 20 " " 10-25 ft
12 25 Tra d-burned at high C.P.
13 50 I N I I! I

The best results were obtained at a concentration of 20
grams/liter of qmonium sulphate. This com entration was used
for the investigation of addition agents classed as brighteners.
*T. P.--throwing power

Table XX
Ethylene Diamine (Igmved)
THE EFFECT OF AMMONIUM HYDROXIDE CONCENTRATION ON DEPOSIT
Temperature-50°C, Hull Cell, Time-ten minutes

Plate No. Cone. of NH40H Condition of Deposit
14 5 ce./1 Bright Range 10-40 amp/ftz
15 10 " " Same
16 15 " " 5-60
17 20 " '27. Same
18 25 " " 15-30
19 30 Burned-peer T. P.

The Optimum concentration of amonium hydroxide was 15 to
20 cc./1iter and this concentration was used through out the
rest of the investigation.

The previous results were combined giving the following
solution for the determination of the effect of brighteneing

CgODtB e

pk)

U 5

cuso4~5ago - 60 g./l
Ethylene Diamine - 50 cc ./1
Ammonium Sulphate - 20 g./1
Ammonium Hydroxide 20 cc./l
pH - 10.5

The bright range of this solut ion was 5-60 amps /sq.ft.

The following compounds gave matte, burned deposits when
present in concentrations over 0.5 grams/liter; l-naphthylamine-
-5-sulfonic acid, urea, acetonitrile, sulfan ilic acid, tartaric
acid, peptone, albumin, naphthol, acetylsalicic acid, saccharin,
and furfurol. Twi wetting agents, "Dmmol" and "Tergitol"
were added and were found to give milky, streaked deposits at
concentrations over 0.01 grams/liter.

Table XXI
Eylene Diamine (vaed)
THE EFFECT OF CERTAIN'ADDITION.AGENTS ON BRIGHTNESS 0F DEPOSIT
Temperature-500e, Hull Cell, Time- ten minutes

 

1. Formaldehyde

Plate No. Conc. of H030 Condit ion of Deposit
20 0.4 cc/l Bright Rm ge 5-60 amps/ft2
21 0.8 7 7 Same-brighter
22 1.2 2811 git nge 5-60-brigiter
23 1.6 7 ' Sane
24 2.0 " " "
25 2.4 " ' "
26 2.8 7 7 Rough
27 5.2 Bright Range 5-5

Concentrations of formaldehyde up to 2.4 ecu/liter increase

”N r
'1
57')

7

the brightness of the deposit.
2. Sodium Formate

Plate No. Cone. of NaHC03 Condition of Deposit

' 28 4 g/l Bright Range 5-60 amps/rtz
29 8 " " Same
3O 16 " " " milky
51 ' a: 7 7 7 T.P. better
32 24 " " " milk:
33 m w n u w
34 32 Burned at high C.D.~dark

Sodium formats, in concentrations of 20 to 28 grams/liter,
increased the throwing power of the solution but decree sad the
brightness of the deposit. Additions of farmaldehyde up to 30
cc./1iter to the solution containing 24 grams/liter of sodium
forsate, had no beneficial effect won the deposit.

3. Amonium Citrate

Plate No. Gene. of (NH‘)3063507 Condition of Deposit
55 2 g/l Bright Rm ge 5-60 amps/rt?-
36 4 " " Some
57 6 7 7 7 brighter
38 8 " " " T.P. better
39 10 " 7 "
40 12 " " " lustrous
41 14 w w 77 w
42 16 " " " milky
43 18 " " " at to dep-

osit
Ammonium citrate increased the brigiinen of deposit and

the throwing power of the solution up to concentrations of 14
grams/liter. Replacement of ammonium sulphah by ammonium ci-
trate gave dull, burned deposits. Cit'ic acid, up to 4) grams/
liter, had no beneficial effect when combimd w ith ammonium
citrate, at any Of the concentrations of ammonium citrate shown
in Table XXI.

4. Rochelle Salts (Sodium Potassium Tartrate)

Plate No. Cone. of Rochelle Salts Condition of Deposit

44 1 g./l Bright Range 5-60 amps/ft3
45 2 " " Same

45 3 n w u

47 4 w w w

43 5 w w w

49 6 7 7 7 brigiter
50 7 " " " T.P. better
51 8 7 7 7 brighter
52 9 n n ' .w

53 10 " " "

54 ll Burned on edges

55 12 " " " and at high

current density
Rochelle salts, in concentrations .of 7 to 10 grams/liter,
gave the most satisfactory deposits of all the addition agents
used. The throwing power of the solution, although inferior to
that of the cyanide solutions, was notably better than that of
the standard ethylene diamine solution.

5. Tin
Tin, added as stannic sulphate, formed a colloidal suspens-

ion which caused an increase of the brightmss of the deposit

at concentrations below 10 mg./1.

J J
«a

GENERAL DISCUSSION

All of the solutions investigated give bright deposits.
The throwing power, tolerance for impurities, ease of main-
tenance, and conditions necessary for satisfactory deposition,
however, vary considerably. The throwing power and bright-
ness of the ethylene diamine solution is improved by the ad-
dition of ammonium citrate and Rochelle salts. Tin and for-
maldehyde improved the brightness but have no effect on the
throwing power of the solution. Rochelle salts give the most
satisfactory deposits in a solution of the following compo-

sition:
cuso4- 5320 - so g./1
Ethylene Diamine (60%) - 50 cc./l
.Ammonium Sulphate - 20 g./l
Ammonium.Hydroxide - 20 cc./l
Rochelle Salts - 8 g./l
pH - 10.0

This solution will be referred to as ethylene diamine (B).

A comparative discussion of the solutions investigated
as to brightness of deposit, bright current density range,
throwing power, impurities, and general operating conditions,
follows:

'grightness of’Depggitr-The deposits encountered in this
investigation may be divided into two classes, namely, lus-
trous bright and bright. The lustrous bright deposits are
mirror-like and are characteristic of the amine type solu-
tions, the diethylene triamine solution producing the brightest

1"“

‘2?
l L}

a

deposits of the two. The pyrcphosphate and cyanide solutions
give bright deposits which lack the high luster of the amine
deposits.

Bright Current Density Range-~At the optimmm.operating
conditions, the following bright current density ranges were
obtained for the solutions investigated:

Table XXII

Diethylene Triamine - 5-te 70 amps/sq.ft.

Perphosphate - 5 to 70

Ethylene Diamine - 5 to 50

Ethylene Diamine (B) - 5 to 50

Cyanide - 5 to 40

Throwing Power--The throwing power of the cyanide and pye

rcphosphate solutions is very good at all current densities.
The diethylene triamine solution has fair throwing power al-
though less than the cyanide and pyrophosphate solutions. The
ethylene diamine solution has poor throwing'power. The addi-
tion of Rochelle salts improves the throwing power of the ethy-
lene diamine solution.

Impurities--The cyanide and pyrophosphate solutions have

a very wide tolerance for iron, zinc, and nickel. Harmful
effects are produced by the above impurities only when they are
present in large amounts sufficient to form.suspended hydrox-
ides. These amounts are over 500 mg./liter. The amino solutions
are tolerant to zinc and nickel but are extremely sensitive to
iron in amounts over 16 mg./liter. Constant purification of

‘ the amine solutions is required due to iron contamination of the

solution from the chemicals used andfrom.exposed steel surfaces.

\BW

An electrolysis treatment, using low current densities, is
the only satisfactory method found completelyt'purify the amine
solutions. Organic impurities, either in the form of amine
decomposition products or foreign material, e.g., oil, grease,
cleaner solution, and buffing compound, produce milky, dull
. deposits in the amine solutions when present in smaller amounts.
No trouble is encountered in the cyanide or pyrophosphate so-
lutions by organic contamination.

General Operating Conditions--Table XXIII illustrates the
optimum operating conditions and cathode current efficiencies

for the solutions under discussion.

Table m1:

Cathode Max.
Solution Temp. pH Efficiency 0.1).
Diethylene Triamine eo°c 9.3 109% 70 amps/fizz
Ethylene Diamine 50 10.0 107 50
Ethylene Diamine (B) 50 10.0 102 50
Pyrcpho sphate 60 8 . 5 100 70
Cyanide 50 13. 0 100 40

The amine solutions require bagged anodes in order to pre-
vent suspended material, formed at the anode, from contaminat-
ing the solutions. In all solutions investigated an excess of
anode area (2:1) is recommended to prevent burning of the anode.
High anode current densities in the amine solutions promote loss
of brightness and a decrease in the solution conductivity. Air
agitation, harmful in the amine and cyanide solutions, may be
used in the pyrophosphate solution, due to its chemical stabil-
ity. Air agitation, used with the cyanide and amine solutions,

causes the formation of solid oxidation products. A preliminary
ngj '

is

copper strike on steel parts in unnecessary when using the py-
rophosphate or cyanide solutions, Deposition in the amine so-
lutions, however, requires preliminary covering of the steel,
due to the rapid corrosion of steel in amine type solutions.

The amine solutions give lustrous bright, smooth deposits
but require careful control and maintenance. Conversely, the
perphosphate and cyanide solutions, while giving less lustrous
deposits, are easily controlled and maintained.

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

13.

14.

15.

16.

1?.

LITERATURE CITED
Kern, B. F., Trans. Electrochem. Soc., _1_5_, 441 (1909).
Bennett, c. w., Trans. Electrochem. Soc., pg, 233 (1913).
McCullough and Gilchrist, U. 5. 1,853,559, June 21, 1932.
Brockman, C. J. and Brewer, A. 1... Trans. Electrochem.
Soc., _5_g, 535 (1935).
Brockman, C. J., Trans. Electrochem. Soc., 11, 251, 255
(1937).
Brockman, C. J. and Mote, J. H., Trans. Electrochem. Soc.,
19, 355,371 (1938).
Greenspan, I... U. S. 2,195,454, April 2, 1940; Trans. Elec-
trochem. Soc., 33. 303 (1940).
Wilson, E. D., U. 8. 2,411, 674, Nov. 26, 1946.
Hartford, C. G., U. 8. 2,555,070, Aug. 8, 1944.
Potassium High Speed Cepper Plating Process (RH551), B. I.
du Pont de Nemours a. 00., Wilmington, Del. (undated).
Starek, J., U. 8. 2,250,556, July 29, 1941.
Coyle, T. 6)., Proc. Am. Electroplaters' Soc., 114;, 113.
Gamov, M. I. and Pomenko, z. 8., Russian Pat. 54,546 (Peb-
ruary 28, 1929); C. A., §_6_, 2800 (1941).
Clifton, P. L. and Phillips, W. H., Proc. Am. Eleotroplaters'
Soc., .1342, 92.
Levin, A. I. and Co-workers, J. Applied Chem. (USSR), lg,
595 (194.0); c. 1., g. 3535, (1941).
Games, I). C., Lorenz, G. A. and Montillon, G. H., Trans.
Electrochem. Soc., 31, 177 (1940). r
Faust, C. I... Agruss, B., and Combs, E. 1... Monthly Rev.
Am. ElectrOplaters‘ Soc., 34, 541 (1947).

. "7.
L! J;

18.
19.
20.
21.
22.

Leaver, H., Materials and Methods, g._5_, 82 (1947).

Taft, R., Trans. Electrochem. Soc., 5_3_, 75 (1933).

Kern, E. D., Trnas. Electrochem. Soc., 15, 441 (1909).
Bandroft, w. 2., Trans. Electrochem. Soc., _5_, 27(1904).
Mather-s, F. 0., Proc. Am. Electroplaters' Soc., _21, 134
(1939).

Hunt, 1. 13., J. Phys. Chem., :15, 1005,2259 (1932).
Hendrick. J. 1... Trans. Electrochem. Soc., pg, 113 (1942).

IV}

 

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