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6/01 c-JCIRC/DateDuepes-p. 1 5

 

THE ELECTROLYTIC DEPOSITION 0F CADMIUM.

THE ELECTROLYTIC DEPOSITION OF CADMIUIJ.

A THESIS

SUBMITTED TO THE FACULTY OF

MICHIGAN STATE COLLEGE

IH PARTIAL FIEFILLMENT OF THE REQUIRED}?

FOR THE DEGREE OF

MASTER OF SC IENCE

BY

HERBERT WILLIAM SCHMIDT

1925.

TABLE 9;; c ommrs.

Introduction.

Review of Literature.

The Principles of Electrodepoeition.

Method of Procedure.

Apparatus and Materials.

Pretreatment of Cathode Material.

Experimental Work.

General Summary and Discussion.

Recommendations for a Bath.

INTR ODUC TI ON .

The electrolytic deposition of cadmium is by no
means a recent discovery. Smee appears to have been one of
the first, if not the first, to deposit cadmium electro-
lytically. Since the publication of his results, the
matter has received very little attention.

About this time, Woolrich and Russell were granted
a patent in England in 1849, or nine years after the
discovery of silver plating. Their solution was made‘by
dissolving cadmium in anoz, precipitating Cd 003, with
Nagcos, washing with water, and redissolving in KGB.

Within the last few years, there has been a narked
activity in the electrolytic deposition of cadmium. The
reason for this is quite apparent When one considers that
in cadmium, there is, to a very high degree, the protective
value of zinc and.the pleasing appearance of nickel.

It might be well at this time to review a few of
the properties or! this metal. Cadmium is always found in
nature associated with zinc. In the extraction of the zinc,
the cadmium distills first, since its boiling point (778°C)
is considerably less than that of zinc (930°C). The
distillate is collected, mixed with coke or charcoal, and
distilled at about 800°C. In.this way a metal of over
99.6% purity is obtained. The chief source of cadmium is
America. It is estimated that production could.be brought

up to 500 tens or more a year if necessary to supply the

market.
A Cadmium has a silver white color wim a bluish tinge

and a bright luster, which dulls somewhat on exposure to
air. The cast metal is' crystalline which when etched reveals
polygonal crystals. It has a specific gravity of 8.65 at
20°C. Cadmium has a Brinnell hardness of 29.0. It can be
easily cut with a knife and is very flexible, ductile, and
malleable.

Cadmium is strongly electro-pcsitive as shown by
the following table of electrode potentials at 25°C.

Zinc ---------- 9.758
Cadmium ------ - +.398
Iron ---------- +.441
Nickel -------- 4.220
Hydrogen ------ .000

The relative position of iron and cadmium are in
question. Althc, according to the electromotive force,
cadmium should be below iron in the series, its chemical
and electrochemical behavior and its pcsi ticn in the
periodic system would lead one to correctly place it above
iron. Unless cadmium is above iron, it can hardly be
expected to protect ircn against corrossion. That it does
protect iron has been shown by Blassett, (1).

However, since it lies so close to iron it cannot
be expected to give as much intrinsic protection as zinc,
and consequently will not protect as large areas as will
zinc. It follows that a deposit of cadmium must be nearly

impervious in order to furnish continued protection.

However, cadmium will not corrode as rapidly as zinc, will
preserve a better appearance, and will protect the iron
longer than will a similar plate of zinc, provided the iron
is not exposed because of porosity or abrasion.

As the potential of cadmium is much closer to
nickel than is zinc, it is more advisable to plate nickel
over cadmium than zinc, since there would be less tendency
to deposit nickel by imnersion and if the cadmium is
subsequently exposed, there would be less tendency for it
to corrode and cause peeling of the nickel. By plating
successively with cadmium and nickel it may be possible to
materially increase the protective value of the nickel
without sacrificing its desirable prOperties.

Whether the theoretical advantages of cadmium as
compared with zinc can be realized comm ercially, and whether
they will Justify the added cost of the cadmium, can only

be determined after more experience.

REVIEW gr; LITERATURE.

A review of the literature ahowed that altho there
has been some investigation, the majority of this has been
of an analytical nature only. In.any investigation in
electroanalysis, the problem is to remove all of the desired
metal quantitatively, and in an.adherent form. No reference
to this kind of“work will be made as it was deemed of little
value in relation to electrOplating. mathers and Marble (2),
give a complete abstract of the electrolytic deposition of
cadmium. Mathers and.Marble investigated cadmium deposition
using a very lOW'current density (0.4 amperes per square
decimeter), and.allcwing the deposition to continue over a
long period of time. Their'work, consequently, was in.reality
one of the refining of’cadmium rather than that of plating.
They used a great number of different solutions among which
were the sulphate, chloride, nitrate, acetate, ammoniacal,
cyanide, bromide, iodide, fluosilicate, fluoborate, fluoride,
and the perchlorate. In the case of the sulphate bath,
they Obtained only crystalline deposits after a few different
addition agents had'been used and so abandoned it as'hopeless.

As far as could be determined the only bath in
use at the present time for depositing cadmium is the
cyanide solution.

The Udylite Process Company (3), covers the
electrolysis of iron, steel, and other metals in a neutral
or basic solution of cadmium cyanide‘with anodes of graphite,

carbon, or other insoluable and non-polarizing materials.

Bio articles are then washed in water and baked for acne
hours at a temperature of 150°C to 200°C, or up to 250°C,
if the plates are imbedded in Ca(OH)2. The electrolyte
may contain from.l.25 to 15%rcadmium and l - 25% Na ON.
The cadmium is precipitated as Cd (OH)2 and redissolved
in.NaCN or KCN. A slight excess of cyanide is allowable.
Cadmium is added to the solution in the form of Cd (0mg.
With an electrolyte containing 10.5% cadmium, a current
density of 25 - 100 amperes per square foot may be used.

Wm..A. Wissler'and.c. H. Humphreys (4), control
a patent for practically the same process. .

The Udylite Process Company, of Kokomo, Indians,
have developed a commercial method for depositing cadmium
and are prepared to grant licenses for its industrial use.

The writer was of the opinion that cadmium could
be deposited from a slightly acid solution of cadmium
sulphate by means of suitable addition agents.

Blum.and Hagaboom in their'recent book, ”Principles
of ElectrOplating and Electroforming", say "It is possible
to deposit cadmium.from.slightly acid chloride or sulphate
solutions, but the deposits are coursely crystalline and
entirely unsuited for electrOplating unless some suitable
addition agents are present.

This investigation was undertaken to determine the
effect of various addition agents on the electrolytic

deposition of cadmium from a sulphate solution.

THE PRINCIPLES 921 EECT'RODEPOSITION.

 

It might be well to review some ed? the theoretical
considerations in regard to the character of deposits as
influenced by various factors. In electrOplating as in
other lines of work, there are a good many factors entering
whose effects are not known.

There is no single case where one factor governing
electrodeposition can be changed without changing quite a
number of other factors. For instance, if we have a solution
of a metallic salt in water and we add some acid, we now
have changed the acidity, both actual and total, the
conductivity, and the metal ion concentration slightly, as
well as other factors. It can be readily seen that the
problen of addition agents is a very complex one, and a
consideration of principles, in so far as they are known,
is of the utmost importance. These principles have as yet
not‘been proven to be absolutely true in all cases but they
are merely advanced as an aid to the electrodeposition of
metals. /.

If the process of electrodepositing metals depends
upon the formation of crystals, it seems reasonable that
the principles or ordinary crystal growth must apply in
some degree to the formation of crystals by electrodeposition.
A consideration of these principles led W. D. Bancnft (5),
to state certain "axioms" regarding the structure of

electrodeposited metals.

These "axioms" were stated by Dr. Bancroft in
the following terms:

1. Bad deposits are due to excessive admixtures
of come compounds or to excessively large crystals.

2. Excessive admixture of am compound can be
eliminated by changing the conditions so that the compound
cannot precipitate.

3. Increasing the current density, increasing the
potential difference at the cathode, or. lowering the
temperature, decreases the size of the crystals.

4. The crystal size is decreased whm there are
present, at the cathode surface, substances which are
absorbed by the deposited metal.

5. If a given solution will give a good deposit at
any current density, provided the conditions at the
cathode surface are kept constant.

6. Tracing is facilitated by a high potential drop
thru the solution and by conditions favorable to the formation

of large crys tal s.

No time will be taken for a discussion of these
"axioms" but they will be referred to in the conclusion and
discussion of the experimental work.

Wm. Blum, of the Bureau of Standards (6), discusses
and gives experimental evidence of these axioms and also
advances a theory of crystal formation.

Mathers and Marble in the discussion of their

paper say, "that a good deposit is the result of the

additive preperties of me acid ion and the additive
substance. A stronger statement of the theory is that
any metallic salt will give a good deposit for the prOper
addition agent is used." They attempt to prove this
statement by the experimental work of their paper.

The above principles are Just some of the theories
concerning the charadter of electrolytic deposits and will
be referred to later in this thesis.

METHOD 9;: Psocsbugp.

Solutions of various concentrations of Cd 804
were made and electrolytic deposits obtained from each
of them at various conditions. Thai to these solutions
were added various salts at different concmtrations and
the results noted. Finally, the commonly called organic
colliods and reducing agents were added and their effects
noted.

After cleaning and washing, which method will be
described in detail later, the specimen to be plated was
placed in the solution under observation. The current was
always on before any plate touched the solution; thereby
preventing to a great degree any tendency to deposit by
imnersion. The voltage of the cell and ampa'age flowing
thru the cell was regulated as desired by means of a
rheostat. As a means of comparison a fixed time of 15
minutes was allowed for each plate. The current density
was varied for different plates to observe that effect.
Some plates were made to show the effect of agitating the
solution wiih air (1' by stirring mechanically. The
taperauire was the same as room temperature and varied
I from 18° to 27° as maximum limits. After plating, the plates
were rinsed in cold water and filed in a rack to dry. The
crystal size and surface of the plates were compared by
means of a microscope using a direct illumination from a

150 watt electric light. The magnification was set at

100 diameters. For the purpose of demonstration, photo
micrOgraphs of various plates were made but the mefidod

is included elsewhere in this thesis.

10

11
APPARATUS AND MATERIAL S .

APPARATUS.

The apparatus used in this investigation consisted
of a 250 cc beaker, two anodes of cadmium and a support for
the cathode. All solutions used were made up to 250 cc

volume.

CHEMICALS .

All chemicals used were of the purity commonly
called "C.P." except in the case of some of the organic

addi ti on agents.

same.

The anodes used were of cast cadmium in the form

of rods and were of high purity.

CA'IHODE MATERIALS.

Two different kinds of sheet metal were used.
One was what is known as blue steel because of the blue
scale on the surface and the other was known as Russian
Iron. The former was 24 gauge in thickness and the latter
was 28 gauge. Very little difference was noticed in
plating with these two kinds of metal. The metal was cut

12
into strips approximately 4 cm. wide by 15 cm. long.

All plates were numbered for record.

SOURCE 9;: CURRENT.

The current was obtained from a 6 - 12 volt
motor generator set thru a switchboard provided with an
ammeter and voltmeter. The current was varied by means

of a resistance in series wiih the bath.

15

PRETREATMENT Q: CATHO'DE MATERIAL.

The pretreatment of the cathode material is
of very great importance since all oil, grease, rust or
any other kind of foreign matter must be thoroughly
renoved before attempting to e1 ectrOplate,or a complete
failure will be the inevitable result.

All Specimens, before plating, were given the
following preliminary treatment:- If Specimen was covered
with a heavy layer of oil, this was removed by C 014 or
CH 013, then wiped with cloth. To remove the black scale,
or in numerous cases to reuse plates previously plated
with cadmium, the specimens were placed in a hot solution
of the following composition: Sn 012, 50 gm.; Tartaric
Acid, 2 gm.; I120, 1000 cc. The specimens were allowed
to remain in this solution until thoroughly cleaned,
rinsed in cold water, and wiped dry with a cloth. This
treatment was used to quite a number of plates at a time
so that before they were finally used they became covered
with rust again.

Just before plating the following procedure was
used: The plates were first boiled in a strong alkaline
solution to remove any remaining oil or grease, rinsed in
hot water, and wiped dry. They were given a thorough
cleaning with a. fairly fine scratch brush on a motor driven
buffing lathe to remove any rough spots and also any
adhering loose material. The plates were immersed in a

10% solution of H2304, to renove the thin layer of rust

l4

accumulated, rinsed in cold water, and given a 10 second
dip in the following bright dip solution; RN03 conc.;
25% by volume; 33304 conc.; 50% by volume; and B20, 25%
by volume. The plates were washed clean in water. The
surface of the metal then had a very bright color and was
clean.

The plates were next placed in a hot alkaline
solution for about. 5 minutes, washed in hot water, cold water,
and were then ready for plating. The alkaline solution was

of the following composition:

Ra2003, 165 gms. per liter; NaOH, 15 gms. per liter.

15

Lemons F33 MAKING moromcaoczmeas.

 

The apparatus used was a Bosch and Lomb Photo-
Micrographic camera. The illumination was obtained
from a high power electric lamp focused directly on the
plate rather than the usual method of using an
illuminator. It was found that by using the direct
method of illumination a better picture was obtained.

A magnification of twenty diameters was used. All
exposures were for 15 seconds, and developed for about

8 minutes.

16

EXPER IME NTAL WORK.

In order that the experimmtal work of this
thesis might be presented in as clear a manner as possible,
the work has been divided into several parts, each of which
will be presented and discussed separately. The photo-
micrographs found elsewhere are of value in getting a clearer
insight into sane of the subject matter. Whenever possible,
concentrations have been expressed in terms of normality.
In some cases, however, it was deemed advisable in express
the additions in terms of the quantity added for bath of
250 cc. In the case of liquids, these additions are expressed
in terms of cc of addition agent for 250 cc of solution.

In presenting the effects of a bath on the deposit,
it should be renembered that the comparison is always drawn
from a bath which does not contain the addition agent under

cons id era ti on.

EFFECT 3!: ADDITION g: NON-METALLIC SALTS WIEOUT FREE ACID.

The standard for comparison was a bath containing
simply Cd 304 (1.0151). The deposit was coarsely crystalline.
The color was fair; the cover poor; and the adhesion very
poor. There was considerable treeing on the edges.

(NH4)2 304 (0.251“. The deposit was coarsely
crystalline with larger crystals than those of the
Cd 304 (1.011). The color was improved some. The cover was

poor, and adhesion was very poor. This bath was also tried

17

giving the sample a preliminary dip for about 5 seconds
in the following arsenic dip; 60 gms. Aszoz per liter

of concentrated HCl. The crystal size was decreased
considerably. The color and cover were about the same as
was the adhesion.

”(34).? 804 (0.50M. The crystal size was
decreased somewhat. The color was darker; the cover and
adhesion were poor. The amount of treeing was decreased
considerable but there was still a tendency for the edges
to get rough. There was also a decided tendemy for the
surface of the plate to become rough which was more
pronounced if the time was increased to 50 minutes.

(N34) 01 (0.25151). The deposit was crystalline
with a slight increase in the size of the crystals. The
color was darker; the cover and adhesion were poor. There
was an excessive treeing on the edges.

N114 Cl (0.50m. there was an increase in the
crystal size. The color was darker than with (0.251“. The
cover and adhesion were poor.

Nag 804 (0.251”. A crystalline deposit with
practically no change in crystal size was obtained. The
color was Slightly darker; the cover was fair and the
adhesion was impr0ved. There was considerable tracing.

Na 304 (0.5011). The crystal size was decreased

2
slightly. The color was improved; the cover was fair and

the adhesion was better but still poor. The treeing was only
slight but the edges was rough.

Na CI (0.251“. The crystal size was increased

18

slightly. The color was darker; the cover was poorer, and
the adhesion was also poor. Considerable tre eing was
observed.

Na 01 (0.501”. The crystal size was decreased
slightly. The cover was poor; the color was slightly
darker, and adhesion was poor.

K2 304 (0.8515). The crystal size appeared
about the same; . the color darker; the cover and adhesion
were poor. There was a decided tendency to Sponge. There
was some tracing and the edges were rough.

K2 {:304 (0.501“. The crystal size decreased. The
color was slightly darker; the cover ani adhesion were poor.
There was still a tendency to Sponge, but there was no
treeing.

K Cl (0.2511). The crystal size did not appear to
be changed; the color was slightly darker; the cover was
poor and the adhesion was poor. Treeirg was excessive.

K 01 (0.5ON). The crystals appeared to increase
in size with a rougher surface. The cover was poor; the
color slightly darker, and the adhesion was poor. A slight

treeing was oh 8 erved .
SUMMARY.

Practically all of the above addition agents gave
tracing to a more or less degree. The crystal size was not
changed to any great extent. The cover and adhesion were

poor in all cases. It appeared that the SO4-ion is better

19

than the Cl-ion as an addition agent. Rag 304 +(NH4)2 804

are the best addition agents of this class.
DISCUSSION.

In the first case without addition agents the
deposit was crystalline with considerable treeing.
Reasoning from Bancroft's sixth ”Axiom” by increasing the
conductivity we should decrease treeing. Altho the
conductivity was harassed by addition of the salts the
terdency to tree was still quite pronounced. It is evident
that treeirg in this case must be greatly influenced by
the second part of the sixth "axiom". We might further
increase the concentration of the salts but this was thought
inadvisable. Howeva‘, we can imrease the concentration of

the Cd $04. This will be discussed later.

EFFECT CF Hg 804 AND NON-BETALLIC SALTS.

 

 

 

With no non-metallic salt, as the acid was added
gassing started at the cathode and increased with increased
concentration of the acid. The tendency to tree, however,
decreased with increased concentration. The crystal size
appeared to decrease also. Sponginess was noticable on some
of the plates. The color does not seen to stay constant as
some plates are darker than others. The cover was about the

suns for all concentrations but only fair.

20

The adhesion was fair, improving slightly with concentration.
The naximum acid cornentration appeared to be about 8 cc. cone.
H2 304 per 250 cc. solution as cadmium scene to redissolve

as fast as it is plated out.

(NH4)2 304 (0.2511). cm increasing the concentration
of acid, the crystal size appeared to decrease, but
sponginess appeared. The adhesion improved with the concen-
tration. The cover was fair. The color was about the same
thruout. The tracing decreased with increased concentration
of the acid. Cathode gassing imreased with increase of
acidity.

(N34)2 304 (0.5ON). 0n increasing the concentration
of the acid the crystal size appeared to decrease. The
tendency to Sponge was observed at concentrations over .2 cc.
The tendency to tree decreased at the higher concentration
until the edges were Just rough. Adhesion improved with
increase concentration of acid as did the color. Cathode
gassing increased with increased concentration of acid.

N84 Cl (0.2511). 0n imreasing the comentration
of acid, the crystal size decreased. In all cases the
color was considerably (darker. thanwith the Cd 804 alone or
with (R34)2 304. The adhesion was fair, improving with
the concentration at acid. The cover was poor, and the
treeing decreased with increased concentration of acid.

Rough edges were observed on all plates. Cathode gassing
increased with acid concentration. Sponginess appeared at

the higher concentrations of acid. The best condition

appeared to be at an acid concentration of Ice.

21

N34 01 (0.501“. 0n increasing the acidity about
the same results as above were noted. Increasing the
concentration of N34 Cl appeared to have very little effect.

Nag 804 (0.251“. 0n imreasing the acid
concentration, the crystal size decreased. The color
appeared to be slightly darker. Adhesion was fair, and
treeing decreased with increasing concentration of acid.

The edges were not very rough. The cover was poor without
acid,‘but improved with concentration.of acid. maximum
concentration of acid was less than 1 cc as deposit could be
seen anly cn.ohe side.

N32 304 (0.50M). About the same effects as
noted above were observed except that the maximum concentration
was 2.00 cc. Increasing the concentration of Nag 804 from
(0.25 to 0.5011), decreased crystal size and as well as
treeing. .

Na 01 (0.25N). Increased concentration of acid
decreased the crystal size. The colorwwas darker and the
cover was fair- Considerable treeing was observed without
acid but this decreased with increased concentration of
acid. The adhesion was poor but improved with acid
cone en trati on.

NaCl (0.50N). Increased concentration of acid
produced abdut the same effect as noted above except that
the deposit @peared somewhat denser.

with K2 804 (0.25m. Increasing the comentration
of acid decreased the crystal size and.improved the cover

and adhesion. The color was darker. A slight tracing was

22

observed, decreasing with increased concentration of
acid. The edges were rough, and sponginess was obsa‘ved
on sane of the plates.

K2 804 (0.501“. Increased concentration of
acid produced about the same effects as were noted above.
The mximum concentration at acid was about 0.5 cc.

K01 (0.25m. Increasing the acidity decreased
the crystal size but improved the adhesion am cover. The
color was dark. Considerable treeing was noted but this
decreased with increase of the acidity.

K01 (0.50m. Increased concentration of acid
producediabout the same effects as were noted above.

The best concentration noted was .04 cc. Except for color,
this was the best deposit in the series. Above this

ccncentrati on there was a tendency to sponginess and rough

0‘18 68.
SWY.

In all cases, as soon as H2 804 was added,
cathode gassing started'and increased with increase of
the acidity. In nearly all cases the crystal size was
increased with the addition of a salt. There appeared to
-be a definite acidity for this type of bath and was
approximtely 0.1 - 0.2 cc. The color with (rage 304 was
the best and with Nag 304 second. K01 (0.50N) gave the
finest crystals with .04 cc acid but the color was dark.

25

DI SCUS SI ON.

The addition of acid decreased the hydrogen
overvoltage at the cathode so that hydrogen was more
easily released. Altho the addition of salts of this
type deminished the tendency to tree, the crystal size
did not appear to be affected to a very great degree.
There was also a more pronounced tendency to produce a
spongy deposit. The effect of the addition of the non-
metallic compounds used appeared to be of a detrimental
nature, either alone or with a slight acidity.

ADDITIOIIS or METALLIC caIDmmDs mm ADDITIONS or 32304

 

 

 

 

T0 ca 304 (1.011).

A12 (304)3 (0.251”. Without the addition of acid
or with not over 0.1 cc, 32804 was only slightly crystalline
and of a fine texture. The adhesion was good and the color
was very good with a high luster. Increasing the acidity
the crystal size increased. Gassing started with an acid
concentration above 0.1 cc. Treeing was observed but slightly
without acid and gradually decreased with increased
concentration of acid. The edges were slightly rough.

With 5 cc of acid the deposit showed no marked attack by
the acid.

Mg 804I (0.251“. The color was about the same as
with A12 (304)5. The crystal size was slightly finer than

24

without Mg 804. The cover was not very good and there was
a' tendency for the surface to be rough with protruding
crystals. There was a slight treeing and the adhesion
was poor. 0n adding acid the crystal size decreased
considerably for the first .04 cc. but then the decrease
was slight. There was also an improvement in cover and a
slight treeing. Increasing the concentration of acid
above 1.0 cc, there was a tendency to produce sponginess
and also an indication of excess acidity.

A12 (804,3 gave finer crystals than Mg 804 and
better cover.

Mn 304 (0.1K). The crystal size was decreased
and the cover was improved. The color was slightly lighter,
and a good adhesion was noted, but there was considerable
treeing. Increasing the concentration of acid decreased
the crystal size slightly, as well as decreasing the
tendency to tracing.

0r2 (304)5 (0.111). the crystal size was fine
and the cover was good giving a more even deposit. The
color was lighter and the adhesion was poor until the acid
concentration was 0.2 cc. Increasing the acidity decreased
the crystal size but appeared to give a less even deposit.

Or 015 (0.111). The deposit was very finely
crystallined. The cover was good but the deposit was
uneven or rough with considerable voids. The color was
about the same as without Or 013 and the adhesion was good.

Increasing the current density seemed to increase the

as
roughness of the surface. Increasing the concentration
of acid appeared to increase the crystal size. The cover
was good in all cases but the surface appeared to get
rougher and more uneven with increased acidity, while
Sponginess was observed on some plates.

Increasing the concentration of Ce 013 tot0.2N)
tended to increase the crystal size slightly and gave a more
uneven deposit.

Further increase of concentration to (0.411)
increased the crystal Size more.

Fe 804 (0.1!). No change in the crystal size
was observed. The color was considerably darker; the cover
was poor; the surface was uneven, and the adhesion was poor.
Increasing the acidity seemed to increase the crystal size
but the adhesion was poor thruout and the surface was rough,
with a fair cover. All deposits were somewhat spongy but
this tendency increased with the acidity.

SULEIARY.
Arranging the addition agents in order of their
increasing effect on the crystal size we get
Cr 013 erg ($04)3 A12 (304)5 mg 304

The cover was good with Alg(SO4)5, fair with
org (304%, but poor in the rest. The color was excellent

26

with A12 (SO4)5, not as good with the chromium salts,

and darker with Fe 304, Mg 304, and Mn $04. The surface
with the A12 (304)3 and chromium salts was slightly

rough but the rest are very rough with a tendency of
grouping crystals. In all cases of the addition of acid,
cathode gassing was evident, and the crystal size decreased.
The color and cover remained about the same.as noted above.
The surface showed a marked improvement with Aluminum, and
both chromium salts while the rest were rather rough, but
the crystals were less grouped or rather there were more
crystals. A12 (804) appeared to be of sane value as an

addi ti on agent.
DISCUSSION.

In using A12 (304)3 after the salt has dissolved
the usual apoleseence was observed, due to hydrolysis, .but
this disappeared upon standing, probably due to an
equilibrium being established. The aluminum sulphate
seemed to possess that additive property which when used
with Cd 304 produced more nearly the condition required for
a good deposit. A12 (804)95 is the first addition agent
that appears to have any marked tendency to give a good

dep osi t.

2?

EFFECT OF CONCENTRATION 0? Cd 304 WITH 32304.

 

 

Increasing the concentration of Cd SO4 fran
(1.011) to (2.0N), the crystal size was about the same,
but the cover was improved and a denser deposit was
obtained. The color was about the same but the adhesion
was improved. Increasing the acidity to 0.1 co the crystal
sizedecreased but above 0.1 cc Sponginess appeared.

In the case of 0d 804 1.511 the crystal size was
slightly smaller than with (LON). The cover was poor but
the color and adhesion were fair. A slight treeing was
observed, the edges were rough and there was a tendency

to produce a spongy deposit.

DISCUSSION.

It is rather difficult to say at this time
which concentration would be of the most value. The effect
of addition agents seems to vary considerably with the
concentration as will be shown later. However, a higher
concentration of 0d 304 than (1.01!) is necessary in order
to eliminate the tendency to give treeing.

MISCELLANEOUS ADDITIONS EQ_Cd 804 1.0N.

casomc ACID (2 Es.)

With this bath the deposit became covered with
a loose, black, spongy mass. This may have'been due to
excessive chromic acid so a'bath was tried containing
chromic acid (0.005 gms.). In.this case the deposit:was
very rough and spongy and similar to the above.

BORIC ACID.

 

With 1 gm. boric acid the crystal size decreased
slightly but the cover was poor and the deposit contained
some voids. The color was about the earn as without the
acid and the adhesion was fair.

Increasing the Boric acid content to 2 gms. the
crystal size increased Slightly but sponginess appeared.
0n adding 32804 to this bath the sponginess disappeared,
and with 0.1 cc a fairly fine crystalline deposit was
obtained with no Sponginess.

Increasing the boric acid in the same bath to
5 gms. the crystal size was further decreased. The voids
were smaller while the color remained the same. Increasing
the 32804 to 0.2 cc decreased the crystal size but the
deposit still contained considerable voids. With a further
increase in acidity to 1.0 co, the voids seemed to

increase.

29

DISCUSSION.

Apparently the chromic acid praiuced the
conditions noted in Bancroft's first "axiom”. Chromic
acid has a detrimental effect on the deposit.

Boric acid did not seem to be of any particular
value in the simple bath with acidity. Boric acid is used
in plating sclutions as a buffer to control the actual

acidity. It may prove to be of value later.

ADDITIONS OF NON-METALLIC SALTS TO BATH 0F Cd 304 1.0N,

 

 

 

w

AND A12 (304)3 (0.25N).

(N34)2 804 (0.25N). There*was an increase in
the crystal size due to the (NH4)2 804 but the deposit
was very fine. The color'was good but a little darker.
The adhesion and cover were good but there was a slight
tracing and some voids. Increasing the current density
decreased the crystal size, improved the cover, but gave
an excessive treeing.

Increasing the (NH4)2 $04 concentration to
(0.50N), there was no material change except that treeing
was decreased.

N82 804 (0.25N and 0.50N) gave about the same
results as for (NH4)2 304.

With N34 01 (0.50N) the crystal size seemed larger

than with either of the above. The color was slightly

30

darker, the cover was fair but the adhesion was poor.
DISCUSSION.

As noted before, the addition of (N34)2 304 or
similar salts tend to increase crystal size but decrease
treeing. Whether or not an adjustment of concentrations
will be found so that this addition will be of any value

remains to be seen.

MISCELLANEOUS ADDITIONS TO 2.0N Cd 304.

 

Crz (304)3 (0.05N). The crystal size decreased
but there were voids in the surface. The color and
adhesion were good. There was no treeing but the edges
were rough. Adding 0.1 Cr 32304 decreased crystal size
slightly with a less tendency to form voids. The cover and
color were good. Increasing the current density increased
the crystal size and more voids were observed.

Or 015 (0.1N). The crystal size decreased but the
color was darker. Adhesion and cover were good but there
were considerable voids and a slight tracing on the corners.

The addition of 112804 decreased the crystal size
slightly with but little change in the surface to decrease
voids. The tendency to sponge was quite pronounced. The

addition of 2.0 gms. Boric acid had very little effect on

the deposit.

31

(N114)2 SO4 (0.50N). There was no appreciable
change in the crystal size. The color was the same. The
cover was good but the adhesion was poor. The surface
was uneven but dense. The addi ticn of Hg§04 decreased the
crystal size somewhat. In all cases there was a decided
tendency to sponge. Increasing the concentration of
(NH4)2 $04 to (1.0N) did not affect the above condition to
a very great degree, except that the adhesion was improved.
In all the deposits with (IIH4)2 804 the bath had a tendency
to produce sponginess.

A12 (SO4)3 (.25N). The crystal size was fairly
fine but there was a tendency to leave voids. The color
and cover were good as was the adhesion. No treeing was
observed but the edges were rough. Increasing the current
density, decreased the crystal size and improved the cover
so that a more uniform deposit was obtained. There was no
tendency to sponge. Increasirg the acidity tended to
increase the crystal size but improved the cover. The
adhesion was good.

A12 (SO4)3 (1.0N). The deposit was finer in
texture and the color was very good. The cover was better
than with the lower concmtration of aluminum. Cohesion was
good but there was a slight treeing and the edges were rough.
Increased current density decreased the crystal size to a
very fine uniform deposit but the tendency to tracing was
excessive. Increasing the acidity decreased the crystal

size but the deposit was not as good as without the acid.

32

With an acidity above 2.0 cc spongi ness appeared. The
concentration of aluminum was probably excessive.

A12 (304)3 (0.25N) and (n34)2 so4 (0.50w).
The crystal size was increased slightly due to (NH4)2 SO

4
The color and cover were good but there were some voids on

the surface. There was no treeing but the edges were
slightly rough. Increased current density decreased the
crystal size but sponginess was observed.

'Alg (804)5 (0.2511), (NI-14);; 804 (1.0N). The crystal
size was slightly larger. Otherwise, the effects were the
same as noted above.

A18 (304)3 (0.5ow), (N34)2304'(0.50N). The crystal
size was slightly snaller than in the case of A12 (304')5
(0.25N) ”134,2 804 (0.5010. The other effects were about

the same as noted above. No treeing was noted.

SUMMARY.

 

The most unifonn deposit as well as having the
best color was obrained by using only the A12 (304),,
as an addition agent. The addition of (NH4)2 804 had the
detrimental effect noted previously.

It appears that with 0d 304 2.0N the best
assition is A13 (5104):, (0.50N).

33

VARIOUS ADDITIONS TO cc so4 (1.5m.

 

(N34)2 304 (0.50N). The crystal size increased
slightly. The color and cover were poor but the adhesion
was improved. There was no tendency to tree except with
the higher current densities.

Al,3 (304)55 (0.25N). The crystal size was fine.
The cover was good and the color very good with a high
luster. The adhesion was good. There was no noticable
tracing except with the higher current densities but the
edges were slightly rough. Increasing the current density
decreased the size of the crystals and also decreased the
formation of voids and gave a more even deposit.

A12 (804)?) (0.50N). The deposit appeared
denser but the surface was rougher in that more voids
were observed.

A12 (304):5 (0.25N), (N114)2 304 (0.50N). The crystal
size was increased. The cover am color were not as good
and there was a slight tendency to give a spongy deposit.

A12 (304,5 (0.25N), Cr 013 (0.1N). The crystal
size was decreased and a denser deposit was obtained. The
color was slightly darker. The cover was fair but the
adhesion was poor. Agitation with air decreased treeing.

A12 (304)5 (0.25N), Fe 013 (5 gms.). The crystal
size increased considerable and the color was darker. The
adhesion was poor but the cover was fair. There was no

treeing but rough edges were observed.

A12 (304)3 (c.25r), Na 023302 3 gm. The crystal
size was fairly large with a tendency to exist as
individual crystals. The color was darker and the cover

was poor while the adhesion was fair.
SIHI'HRY.

The best deposit observed up to the present time
was Obtained from a bath containing Cd 804 (1.5N), and
A12 ($04)3 (0.25r).

armor: pg; VARIOUS ACIDS..

The bath used for this observation was as follows:
Cd 804 (1.5N), (N34)2 804 (0.50N), A12 ($04)3 (0.25N).

The acids were added in very small quantities and the
effects noted in each case.

32304. The crystal size was increased but was
more uniform and there were less voids.

30211502. The crystal size increased considerable
with increased concentration of acid. The cover was good
but the color was darker. There was a tendency to produce
Sponginess.

H0104. The crystal size increased considerably
with increased concentration of acid. There was a decided
tendency to produce sponginess.

Crystal size was increased considerably

H5P04.

with increased concentration of acid. The adhesion was poor,

a.

a decided tendency to produce sponginessmas observed.

H5P04. Crystal size was increased considerably
with increased concentration of acid. The adhesion was
poor and there was a decided tendency to produce
Sponginess.

320304 (1 gm). The crystal size was increased
slightly. The cover was fair but the re were considerable
voids. There was no treeing but the adhesion was poor

while the color was darker.

Citric Acid (1 gm.). The effects noted were the

same as under H20204.
SUMMARY.

In all cases the addition of the acids had a
very detrimental effect on the deposit. It would appear
that the electrolytic deposition should be carried out in
a neutral or very slightly acid solution.

EFFECT pg" ORGANIC ADDITION AGENTS.

The bath used consisted of Cd 304 (1.511), and
A12 (304)5 0.25N to which was added the following organic

compounds.
H CH0 (0.1 cc). There was a decrease in the
crystal size but the color was slightly darker. The adhesion

 

36

and cover were fair. There was no treeing but the edges
were rough and there was a decided tendency to form a
streaked deposit. Increasing the concentration of ECHO
to 0.5 cc increased the size of the crystals but did not
appear to effect the other factors.

033 030 (0.1 cc). The deposit was rather coarsely
crystalline. The color was darker-and the adhesion poor.
Agitation decreased treeing as well as the crystal size,
but Sponginess was more noticable.

CH3 CHO (0.5cc). The deposit was coarsely
crystalline even with agitation. The color was lighter than
the above. Adhesion and cover were poor.

0235 OH (1.00 cc). There was a decrease in crystal
size but no other change was noticed. Increasing the
concentration of 0235 OH to 5 cc increased the¢32ystal size
but this was decreased by adding H2304 0.5 cc. There was
a noticable tendmcy to striate the deposit. Further
additions of acid had little effect eXpect to increase
cathode gassing.

Clove Oil (2 drops). The crystal size was decreased
considerably so that a very fine deposit was obtained,
except for some voids. The color was excellent. The cover
was good but the adhesiOn was fair. There was no treeing
but the edges were rough.

Clove Oil in.alcohol (%-drop oil to 1.0 cc alchhol).(l cc
There was no change observed. (2 cc). The crystal size

decreased very slightly. There was a noticable tendency to

57

give a striated deposit.

011 adding H2804 0.5 co, the crystal size
decreased slightly and there was no tendency to form a
striated deposit.

Gelatin (0.1 3111.). A very fine deposit was
obtained. The cover and adhesion were good. The color
was about the same as that obtained from a cyanide bath.
At low current densities there was no treeing and the edges
were only slightly rough which was eliminated by agitation.
At higher current densiti es the edges were rougher but the
deposit was better.

Gelatin (0.02 gm.). The deposit was slightly
rougher and the color and adhesion were not as good as above.

Cd 804 (1.51!) A12 (804‘):3 (0.50N). The crystal
size was fine and decreased with increased current density,
but the edges becmne corre8pondingly rougher. The color was
darker but the adhesion and cover were good. The deposit
was finer but darker than with 0.02 gm. Gelatin was rougher
than with 0.1 gm.

4’3
The deposit was about the same as noted just above.

Dextrose (0.02 gm.). This addition had very little
effect, except to make the color slightly darker.

Dextrose (1.0 gun). The crystal size was increased
considerably even at relatively high current densities.

Peptone (0.1 gm.). The crystal size was very

fine, but there were considerable voids. The color was darker

58

and the adhesion and cover were fair. There was no
treeing but the edges were slightly rough.

Blood Fibrin (0.1 gm. ). The deposit was very
coarsely crystalline and about the same as the simple
salt solution with no additions.

Egg Albumin (0.1 gm.). The crystal size was
very fine but the plate was pit ted. The color was very
dark but the cover and adhesion were good. The edges were
slightly rough and the plate had a slight tendency to striate.

Egg Albumin (0.02 gm.). The crystal size increased
some, but the color was much lighter, but as yet slightly
dark. The adhesion and cover were good. The depos it was
rough and had a pronounced tendency to striate.

Licorice Root (0.2 gm.). The root was cut into
fine shreads and allowed to soak in the solution over night.
The crystal size was very fine. The color was excellent.
The cover was good and the adhesion was very good.

Gum Tragacanth (0.05 gn. ) 1 There was very little
change in crystal size but the tendency to Sponge was very
pronounced. The cover was fair but the adhesion was poor.
The color was slightly darker.

Gum Arbic. The crystal size was fairly fine but
there was a decided tendency to give Sponginess. The cover
and adhesion were poor. Adding Na H3 P04 (10. gms.)
increased the crystal size very much. The cover and adhesion
were poor. The color was darker.

Glue (0.05 gm.). The crystal size was very fine,

but there was a decided tendency to give Sponginess. The

59

cover and adhesion were poor and the color was darker.

Uric Acid (0.05 gm.). The crystal size was
considerably increased. The cover was poor, the color
darker; and the adhesiOn, fair.

B. Naphthol (0.05 gm.). As this solution was
used it became slightly colored probably due to a reaction
of the B. Naphthol. The deposit was very fine. The color,
cover and adhesion were good. There was no treeing and the
edges were smooth, except at the higher current densities.
Excessive rough edges were elinimated by using mechanical

agi tati on.

SUMI‘JARY .

Reducing agents such as aldehydes did not produce
a sufficiently good deposit. 0f the addition agents used the
most likely ones to be of any use were, gelatin, and B.
Naphthol and Licorice Root. The other addition agents
were more or less detrimental to the deposit. Agitation

reduced or eliminated any tendency to form rough edges.

40

GENERAL SUI-MARYme DISCUSSIOLI.

The use of salts of the type of (NH4)2 SO4
appeared to be more of a detriment. Altho treeing was
deminished to a great extent by their use the increase in
crystal size outweighted any advantage. No combinations
were found in which the addition of these salts would
prove successful.

0f the various salts used A12 (304):3 was deemed
of the most value al the Ge 013 might be used to advantage.
The color due to the preseice of the A12 (304)3 was
very good and better than that of arm others. Other than
the organic compounds, no additions were found that would
be advantageous to use in connection with A12 (804)5.

0f the organic compounds; Licorice Root, gelatin,
and B. Haphthal were the only ones to produce a deposit
that could be of any value. Of these, B. Naphthol and
gelatin produced the highest color but the licorice root

gave a slightly better deposit.

in

pi
e.“
v

41

HECOWATIONS FOR _A_ BATH.

The electrolytic deposition of cadmium can be
accomplished to give satisfactory deposits. In any plating
bath it is important that the solution be as simple as
possible. In the case of cadmium, the bath should have

the following composition: 0d 804 1.5N, A13 (304) 0.25N,

with an.organic addition agent. 0f the organic adiition
agents any one of the following should be used: Gelatin 0.1 gm.,
(licorice root 0.2 gum, or B. Naphthol 0.05 gm.

A cathode current density of 1.5 - 2.2 amperes
per square decimeter should be used. The anode area should
be from 1.5 - 2.0 times as great as the cathode area. The
temperature should be approximately that of ordinary room
temperature. The solution should be agitated mechanically

for successful Operation.

FIGURE

10

11

Cd

Cd

Cd

Cd

Cd

Cd

Cd

Cd

Cd

Cd

Cd

42

KEY‘TQ,PHOTOMICROGRAPHS.

E
w

1.0N.

1.5K.

2.0N.

1.5N,

1.5K,

1.5N,

1.5K,

1.5K,

1.5N,

1.5m,

1.5K,

(NH4)2 304 0.50N.
A12 ($04)3 0.25N.
(n34)2 so4 0.50N, A12 ($04)3 0.25N.

A12 ($04)3 0.25N, Gelatin 0.1 gm.

A12 (304)3 0.25N, B. Naphthol 0.05 gm.

A12 (304)3 0.25N, Licorice Root 0.2 gm.

A12 (304),, 0.25m Egg Albumin 0.1 gm.

A12 (304)3 0.25N, Clove Oil 2 dr0ps.

'u. T»
*“H'fl’r
' I

3
l‘,‘ ...l 1 {‘0
o

 

Figure 6.

45

Figure 8.

 

Figure 10.

 

 

Figure 11.

44

I.

II.

III.

VI.

45

BIBL I OGPAIL .

 

Blassett, Metal Industry 9, 25, 1911.

.Mathers and marble, Trans. American Electrochemical

Society, 25, 519, 1914.

The Udylite Process Company. British Patent.
NO. 178422, march.ll, 1922.

W . A. Wissler and C. H. Humphreys, Canadian Patent
No. 230277, April 10, 1923.

W. D. Bancroft, Trans. American Electrochemical

Society, 6, 27, 1904; ibid. 25, 266, 1915.

Wm. Blum, Trans. American Electrochemical

Society, 36, 215, 1919; 44, 597, 1925.

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