the effect of cyanide cadmium plating bath compositions on steel hydrogenation

Electrodeposition and Surface Treatment Elsevier Sequoia S.A., Lausanne - Printed in Switzerland

213

THE EFFECT OF CYANIDE CADMIUM PLATING BATH COMPOSITIONS ON STEEL HYDROGENATION

V. N. KUDRYAVTSEV, K. S. PEDAN and A. T. VAGRAMYAN

Institute of Physical Chemistry, Academy of Sciences of the U.S.S.R,, Moscow (U.S.S.R.)

(Received June 20, 1972)

SUMMARY *

The effect of cyanide cadmium electrolyte main components in a wide range of concentrations (Cd 15-40 g/l; NaCN 52-157 g/l; NaOH 10-120 g/l; Ni O-O.3 g/l) on steel hydrogenation has been studied. It is recorded that at high cadmium concentration in the solution the quantity of hydrogen absorbed by the steel sharply decreases. The introduction of nickel brightener (up to 0.3 g/l) in the solution leads to a significant hydrogenation increase. It is shown that a change of NaCN concentration (in most cases) (52-157 g/l) and NaOH (lo-40 g/l) in the conventional limits produces a negligible effect on hydrogen absorption. On the basis of the obtained experimental data a tentative calculation method is suggested, with the help of which it is possible to estimate the relative influence of each component of the electrolyte on hydrogenation.

INTRODUCTION

It is well known that significant hydrogenation and a deterioration in the mechanical properties of steel parts may occur when they are electroplated with cadmium from cyanide electrolytes. Many attempts have been made to replace these last-named by less hydrogenating, but equally effective electrochemically non-cyanide electrolytes, but none can be said to have been completely successful. So the problems of hydrogenation and hydrogen embrittlement elimination under cadmium cyanide electroplating are still very acute. In order to solve these problems it is necessary to know how a change in the content of the main components in the solution influences hydrogenation. The available information relating to the influence of separate components of cyanide cadmium electrolyte on hydrogenation and the mechanical properties of steel is scarce, and it is contradictory. Thus, Sachs and Melbourne’, in a study of bend ductility on spring steel specimens,

* R&urn& en fran$ais & la fin de l’article. Deutsche Zusammenfassung am Schluss des Artikels.

Electrodepos. Surface Treat., I (1972173)

214 V. N. KUDRYAVTSEV, K. S. PEDAN, A. T. VAGRAMYAN

discovered that hydrogenation during cadmium electroplating is lower from an

electrolyte with a small content of free sodium cyanide (2.4 g/l), than from one

with a large content of sodium cyanide (22.5 g/l). According to Sink2, however, at

constant cadmium concentration (15, 22.5, 30 and 37.5 g/l) an increase of sodium

cyanide in the electrolyte of from 50 to 100-125 g/l decreases rather than increases

hydrogenation, and it is only when the NaCN concentration is raised to over

125 g/l that hydrogenation increases. At a cadmium concentration of 45 g/l,

too, an increase in the NaCN content causes the hydrogenation to increase.

Cotton3 and also Geyer, Lawless and Cohen4 indicate that an increase of

cadmium concentration in the electrolyte leads to the lowering of hydrogenation.

The data obtained by Sink2 show that at NaCN concentrations of 100, 125 and

150 g/l an increase of Cd content in the electrolyte from 15 to 30 g/l results in a

decrease of hydrogenation, while further increases in concentration lead to an

increase of hydrogenation.

Dingley, Bednar and Roger&’ present data demonstrating a significant

influence of alkali on hydrogenation during cadmium electroplating processes.

They believe that the origin of hydrogen embrittlement is mainly connected with

the unstable nature of cyanide electrolytes, which is due to the low alkali concentra-

tion in conventional cyanide electrolytes. To diminish hydrogenation it is recom-

mended that the alkali content in cyanide cadmium electrolytes be increased so

that the OH- and the CN- ion concentrations are equal. However, it should be

noted that the comparative compositions of “stable” and “unstable” electrolytes,

given by the authors, had unequal cadmium content. In “stable” electrolytes the

cadmium concentration was higher5, which as some other authors believe3,4

exerted a decisive influence on hydrogenation.

To improve the quality of the deposit it is recommendeda, !’ that a nickel salt

additive be introduced into the cyanide electrolyte. The effect of such an additive

on hydrogenation has not been studied.

The present paper is devoted to the study of the influence of the concentra-

tion of cyanide cadmium electrolyte main components on steel hydrogenation.

EXPERIMENTAL PROCEDURE

To investigate hydrogenation a direct method was used for determining the

quantity of hydrogen adsorbed by the steel base during electroplatinglo.

The procedure used was as follows. Steel specimens were chemically stripped

of Cd deposit in 40-50% NH,NO, solution, cooled with ice to 5-10°C, washed

in distilled water, degreased in acetone and then placed in the device for vacuum

extraction. The content of electrolytic hydrogen in steel was estimated at 400°C

and residual pressure of 1O-6 mm Hg.

The specimens used throughout this investigation had been produced from a

quenched spring steel Type Y-8A of the following composition (%): C 0.8; Si 0.2;


STEEL HYDROGENATION 215

Mn 0.22; P 0.018; S 0.02; Cr 0.15; Ni 0.12. The Rockwell C hardness was 50.

This steel was chosen on account of its wide use in industry, inclination to hydrogen

embrittlement, good reproducibility of results (the value of relative error being not

more than 5-10%) and, also, because of the constant and minimum content of

metallurgical hydrogen in the steel (at an extraction temperature of 400°C it does

not exceed 0.05 cm3/100 g). The specimens used in the estimation of hydrogen in

steel after cadmium electrodeposition were 90 x 8 x 0.3 (mm) in size.

The main plating solutions were prepared from Cd0 and NaCN by way of

their dissolution in distilled water. NaOH or Ni (in the form of NiS0,.7H,O salt)

was added to the main solutions in sufficient quantities. All the salts were chemi-

cally pure. Prior to the experiment the solutions were subjected to pre-electrolysis

(at c.d. = 0.75 amp/dm2) for a time sufficient to allow the passage of at least 5

amp-h per 1 1 of the solution.

Cadmium electrodeposition was performed in 0.8 I of bath in a thermostatic

glass cylindrical cell at 20°C without agitation, the electroplated area being 15 cm2.

The anodes were made of cadmium type “Cd-00”. To avoid anode passivation in

the process of electrolysis the anodic current density was not more than 1.5 amp/

dm2. Cadmium current efficiency was determined with the help of a cupric coulo-

meter.

From time to time the electrolytes were filtered and analysed to detect any

changes in composition and, where necessary, a content correction was made.

After each correction the solution was again subjected to pre-electrolysis (cd. =

0.75 amp/dm2) for a time sufficient to allow the passage of at least 1 amp-h per

1 1 of solution.

Prior to the electroplating the specimens were degreased in alkaline solution

of the following composition (g/l): Na,PO, 30; NaOH 10; Na,CO, 30; OP 7 = 3

at 40°C in an ultrasonic field. The degreased specimens were thoroughly rinsed in

hot running water and then in distilled water, and electroplated with cadmium,

the thickness of the deposit being 0.4 mil in all experiments. Prior to cadmium

electrodeposition the degreased and rinsed specimens were kept in cyanide electro-

lyte for 40-60 set in order to improve the adhesion of the deposit. No other pre-

plating operations which could lead to additional hydrogenation of steel were

conducted. The influence of sodium cyanide (total and free) on steel hydrogena-

tion was studied in the solutions with constant cadmium concentration (Table 1).

Solutions containing 104.8 g/l NaCN and 15 and 30 g/l Cd were used for

the study of Ni and alkali influence on hydrogenation.

EXPERIMENTAL RESULTS AND DISCUSSION

1. E#ect of sodium cyanide

The dependences of steel hydrogenation on total cyanide concentration

during electroplating from electrolytes with cadmium contents of 15 and 30 g/l

Electrodepos. Surface Treat., I (1972/73)

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Fig. 1. Quantity of hydrogen absorbed by the steel during cadmium electroplating depending on sodium cyanide concentration. (a) Cd concentration = 15 g/l = const. Curve 1, 0.5 amp/dmz; curve 2, 1.0 amp/dm*; curve 3, 1.5 amp/dma; curve 4, 2.0 amp/dm*. (b) Cd concentration = 30 g/l = const. Curve 1,0.5 amp/dme; curve 2, 1.0 amp/dma; curve 3, 1.5 amp/dm*; curve 4, 2.0 amp/dm2.

are shown in Fig. 1. From the data given (Fig. la) it follows that at low Cd con-

centration (15 g/l) a simple dependence of steel hydrogenation on cyanide con-

centration at different current densities is not detected. Thus, at low current density

(0.5 amp/dm2) with an increase in NaCN concentration of from 52.4 to 131 g/l

(at the same time the content of free cyanide also increases), hydrogenation grows

and at 1.5 and 2 amp/dm2 the dependence of hydrogenation on NaCN concentra-

tion goes through a maximum. The change of NaCN concentration in the solution

with higher Cd content (30 g/l) at all current densities has little effect on steel

hydrogenation (Fig. lb). Analogous results were obtained at a cadmium concen-

tration of 20 g/l.

Thus, in the majority of the electrolytes studied the wide range increase of

both free and total cyanide did not produce a significant effect on the quantity of

hydrogen absorbed by the steel when electroplated.

The study of hydrogenation at cathodic polarisation of steel in 0.5 M

NaOH solution (in the absence of Cd ions) containing different NaCN concentra-

tions was also conducted. It was found (Fig. 2) that the introduction of relatively

3.0

G

8 2.0 . %s E

” 1.0 I

IIfI.I 0 0.5 I.0 1,8

C NaCN(M/‘)

Fig. 2. Steel hydrogenation at cathodic polarisation in 0.5 MNaOH solution depending on NaCN concentration. Current density 1.5 amp/dme, time of polarization 15 min.

Electrodepos. Surface Treat., I (1972/73)


small quantities of NaCN up to 15 g/l (0.3 m/l) results in a significant growth of

steel hydrogenation, this latter being negligible in the concentration range of

15-25 g/l (0.3-0.5 m/l). The increase of cyanide concentration upwards of 25 g/l

has almost no effect on the quantity of hydrogen absorbed by the steel. These data

also show that at free cyanide concentrations above 25 g/l (0.5 m/l), the hydrogena-

tion-promoting effect of the CN--anions does not increase.

2. EfSect of cadmium concentration

The change of cadmium concentration, unlike that in the case of cyanide,

produces a significant and simple effect on hydrogenation. The investigation show-

ed that in the solutions with constant concentration of total cyanide (Figs. 3a and

3b) at all current densities the increase of Cd concentration resulted in a hydro-

genation decrease. Thus, the increase of cadmium concentration from 15 to 30

g/l led to a 2-5 times decrease in hydrogenation. Analogous dependences were

obtained in all other solutions. The lowest hydrogenation took place in the solu-

tion with the highest cadmium content. The data, given in Table 2, confirm the

predominant effect of Cd concentration on steel hydrogenation as compared with

the effect produced by free and total cyanide. As can be seen, with the rise of cad-

mium concentration in the solution, in spite of the simultaneous growth of free and

total cyanide, hydrogenation falls markedly at all current densities, this fall being

obviously due to cadmium influence.

The study of Cd current efficiencies reveals a simple relation between current

efficiency and concentration of hydrogen absorbed by the steel: an increase of the

former results in a decrease of the latter, and vice versa. As an example, in Table 2

(a) (b)

- I

0 15 25

CCd k/l )

Fig. 3. Quantity of hydrogen absorbed by the steel at cadmium electroplating depending on cadmium concentration. (a) NaCN concentration = 78.5 g/l = const. Curve 1, 0.5 amp/dm*; curve 2, 1.0 amp/dm2; curve 3, 1.5 amp/dm*; curve 4, 2.0 amp/dm2. (b) NaCN concentration = 104.8 g/l = const. Curve 1, 0.5 amp/dm2; curve 2, 1.0 amp/dmz; curve 3, 1.5 amp/dm*; curve 4, 2.0 amp/dm*.

Electrodepos. Surface Trent., I (1972/73)


TABLE 2

DEPENDENCE OF STEEL HYDROGENATION ON CYANIDE ELECTROLYTE COMPOSITION

Electrolyte composition Hydrogen content in steel Cadmium current

(gll) (cm3/100 g) at c.d. (ampldm=) eficiencies ( %)

Cd NaCN Total Free

0.5 1.0 1.5 0.5 1.0 1.5

15 18.6 52.4 0.50 0.63 1.02 97 86.3 80.1 30 104.8 52.4 0.25 0.30 0.35 98.3 95.1 93.4 40 131 61.0 0.18 0.14 0.22 98.8 98.3 98.2

there are given Cd current efficiencies for three electrolytes. In reality, a current

efficiency increase, stipulated by the growth of Cd concentration in the solution,

results in a sharp decrease in hydrogenation.

The dependence obtained may be explained by taking into account the fact

that the concentration polarization by ions of discharging metal (Cd) is prevalent

in cyanide cadmium solutions. It is only natural that an increase of cadmium in the

solution should lead to a sharp decrease in concentration limitations, to an in-

crease of Cd current efficiency and, hence, to a reduction of the quota of current

going for hydrogen discharge. This last-named results in diminishing the degree

of growing deposit surface coverage by adsorbed hydrogen atoms and produces

a decisive effect on steel hydrogenation elimination.

3. The effect of alkali concentration

No simple dependence of steel hydrogenation on alkali concentration was

detected during cadmium electroplating from the solutions with different alkali

(b)

Fig. 4. Quantity of hydrogen absorbed by the steel depending on NaOH concentration. (a) Cd concentration 15 g/l, NaCN 104.8 g/l. Curve 1, 0.5 amp/dm*; curve 2, 1.0 amp/dm*; curve 3, 1.5 amp/dm2; curve 4, 2.0 amp/dm2. (b) Cd concentration 30 g/l, NaCN 104,8 g/l. Curve 1, 0.5 amp/dm2; curve 2, 1.0 amp/dm2; curve 3, 1.5 amp/dm8; curve 4,2.0 amp/dma.

Electrodepos. Surface Treat., 1 (1972173)


concentrations (Fig. 4). With an increase of alkali concentration hydrogenation

may either fall (curve 1) or rise (curves 3 and 4), depending on current density.

It can be seen that in all cases a change of alkali concentration in the range of

lo-40 g/l (i.e. in the conventional concentration range) produces little effect on

hydrogenation. In the majority of the experiments the growth of alkali concentra-

tion above 40-50 g/l results in hydrogenation increase, the most significant one

taking place in electrolytes with a cadmium concentration of 15 g/l. It is only at

low current density (0.5 amp/dm2) that the increase of alkali content leads to some

hydrogenation decrease. It should be noted that there is no correlation between

alkali concentration and hydrogenation on the one hand and cadmium current

efficiencies on the other hand. Thus, for example, in the solution with 15 g/l Cd

at c.d. = 1 amp/dm2, with an alkali concentration increase of from 10 to 80 g/l

hydrogenation increases to double its value; however, current efficiencies in all

these solutions are almost equal and add up to 90-91%. Since in cyanide solutions

with high alkali content a significant growth of steel hydrogenation is not followed

by a decrease in cadmium current efficiency, the possible mechanism of alkali

influence, apparently, differs from the mechanism of cadmium concentration

influence.

Kabanov et c~l.ll-~~ showed that cadmium cathodic polarisation as well as

that of Zn, Pb, Ag and other metals in alkali solutions may be followed by electro-

chemical intrusion of alkali metal cations (Naf, Li +, K-i-, Csf) in the cathode,

with the formation of intermetallic compounds by the reaction:

nCd + Na-‘- + e j NaCd, (1)

The authors give data according to which such a reaction is possible also in the

process of cadmium electroplating at potentials more negative than - 1.4 V. As

recent investigations have shown l4 the intermetallic compounds formed interact ,

partly with water with atomic hydrogen formation according to the reaction :

NaCdn + H,O --f nCd + Na+ + OH- + ‘/2 H, (2)

Since cyanide cadmium electroplating is carried out at potentials more negative

then -1.2 V, at high NaOH concentrations, reactions (1) and (2) are likely to

take place in the solution, with the formation of atomic hydrogen, which may be

the source of additional steel hydrogenation.

It should be noted that the above-made assumption explains not only the in-

crease in hydrogenation under alkali concentration growth in the solution, but

also the lack of this increase at a current density of 0.5 amp/dm2 (Fig. 3). Indeed,

as it has been shown before15, during cadmium deposition from electrolytes with

the same composition of main components (Cd and NaCN) as in Fig. 3A, the

cathodic potential, being at c.d. = 0.5 amp/dm2 -1.2 V, at current density in-

crease (l-2 amp/dm2) sharply shifts to the negative side up to - 1.8-I .9 V. Since

the formation of an intermetallic component by reaction (1) is most likely to occur

Elecfrodepos. Surface Treat., I (1972/13)


at potentials more negative than -1.4 V, it is possible that at a current density of

0.5 amp/dm2, because of the relatively low cathodic potential, the formation of an

intermetallic compound hardly takes place and, accordingly, hydrogenation does

not increase.

4. The efect qf nickel concentration

The investigation of nickel brightener influence shows that the increase of

steel hydrogenation is strongly dependent upon the introduction of a nickel

brightener in cyanide cadmium electrolytes. Thus, for example, in the solution

with 15 g/l of Cd (Fig. 5) even 0.04 g/l of Ni at all current densities increases steel

hydrogenation by 15-20x. With an increase of Ni content in the solution steel

adsorbs still greater quantities of hydrogen and at a Ni concentration of 0.3 g/l

(which corresponds to 1.5 g/l NiS0,.7H,O) at current densities of 1 and 1.5

amp/dm2 hydrogenation is about twice as high as that in a solution with no

brightener.

The data obtained from the electrolyte with a Cd concentration of 30 g/l

were analogous to those given above. The introduction of 0.3 g/l Ni into the solu-

tion gave a hydrogenation increase of 5%60%. It should be noted that in all cases

current efficiencies of the metal became slightly lower as the nickel content in the

electrolyte was increased.

Analysis of the deposit composition showed that during cadmium electro-

deposition nickel was included in the deposit, the nickel percentage in it increasing

(in the range of 0.1--0.4%) with an increase of nickel concentration in the solution.

Since hydrogen evolution overvoltage on nickel is significantly lower than on

cadmium, it is only natural that, the more nickel there is in the deposit, the greater

is the increase of hydrogen current efficiency and, hence, of hydrogenation. In

addition, nickel belongs to a transitional group of metals which are able to adsorb

significant quantities of atomic hydrogen, which in its turn may lead to an increase

of degree of growing deposit surface coverage with atomic hydrogen and, ac-

cordingly, to an increase in the quantity of absorbed hydrogen.

Fig. 5. Quantity of hydrogen absorbed by the steel depending on Ni concentration. Cd concentration 15 g/l, NaCN 104,8 g/l. Curve 1,0.5 amp/dme; curve 2, 1.0 amp/dm*; curve 3, 1.5 amp/dma; curve 4,2.0 amp/dm2.

Electrodepos. Surjizce Treat., I (1972173)


COMPARATIVE ESTIMATES OF THE DEGREE OF THE CYANIDE ELECTROLYTE

COMPONENTS INFLUENCE ON HYDROGENATION

All the results obtained were considered and it was recorded that a variation of

cyanide electrolyte components concentrations leads to a change, to this or that

degree, in the quantity of hydrogen absorbed by the steel. However, as in the

experiments all components concentrations varied by different amounts, it was

difficult to compare mutually their effect on hydrogenation. Therefore it seemed

reasonable to compare the influence of all cyanide electrolyte components at

equal changes of their concentrations. It is advisable to express these variations in

mol/l, as the equal molarities correspond to the equal number of atoms or mole-

cules of the component.

If it is known that an increase in the component concentration in the solu-

tion of from C, to Cz mole/l [C,- C, = AC] leads to a steel hydrogenation varia-

tion of from V, to V, cm3/100 g [V2 V1 = AV], it is obvious that the relation

AV/AC = Vm cm3/100 g per mole/l will be numerically equal to the steel hydroge-

nation variation under the increase of component concentration per 1 mole/l. The

value V, characterises the influence of the electrolyte component on steel hydroge-

nation in the concentration range of from C, to Cz. In case the component concen-

tration increases hydrogen absorption, V, is the positive value (+ Vm); if, on the

other hand, it decreases hydrogenation, then Vm is the negative value (- V,). Thus, having from the experimental data calculated Vm values at the change of

each component concentration, we have the opportunity (a) to estimate, corn- paring

Vm signs, the influence trend of the component given (whether it increases or de-

creases hydrogenationin the predetermined range ofconcentrations), and (b) to com-

pare the degrees of components influence among themselves by Vm absolute value.

Table 3 sets out the Vm values, calculated on the basis of experimentally

obtained data on hydrogen absorption in the range of the electrolyte components

concentrations (g/l): Cd 15-40; NaCN 52-157; NaOH 10-120; Ni O-O.3 at catho-

dic current densities of 0.5-2 amp/dm2.

As will be seen from Table 3, the signs and absolute values confirm obvi-

ously the above-made conclusions as to the influence of electrolyte components

on steel hydrogenation. Indeed, the effect of NaCN concentration on hydrogena-

tion is unsignificant and ambiguous. About one-half of all V, values in the whole

studied NaCN concentrations range (52-157 g/l) are positive (number _1- V, -=

15), the other half negative (number - V,, = 12).

A sharp decrease in hydrogenation during cadmium concentration increase

is illustrated by negative signs and their large absolute values. The influence of

alkali in the wide range of concentrations, as well as NaCN, is ambiguous (25

positive and 15 negative Vm). A very high hydrogenating effect is produced by

nickel. All Vm values for nickel (except one) are positive; their absolute values are

the highest (40-258).



TABLE 3

THE CHANGE OF VII, VALUES IN THE WIDE CONCENTRATION RANGE OF ELECTROLYTE COMPONENTS

No of Electrolyte components concerztrations Current density (amp/dmz) electrolyte groups Constant g/l Variation Variation 0.5 1.0 1.5 2.0

range IgIl) value (mole)

I -

1 Cd = 15

Cd = 20

Cd = 30

NaCN NaCN VUI Ym Y, V,

52.3-78.5 0.535 +0.24 +0.06 +0.13 +0.02 78.5-104.7 0.535 +0.24 +0.04 -0.47 -0.11

104.7-131 0.535 +0.54 +0.13 -0.21 -0.37

78.5-104.7 0.535 +0.02 +0.09 +0.02 -0.51 104.7-131 0.535 -0.02 -0.02 +0.06 -0.02

104.7-131 0.535 +0.32 -0.04 +0.08 -0.06 131-157.2 0.535 0 -0.15 -0.11 +0.17

Cd Cd VIII VIII V* VIII

2 NaCN = 78.5 15-20 0.0445 -5.17 -4.7 -11.0 -7.2 2&30 0.089 -0.45 -1.4 -1.7 -3.82

NaCN = 104.7 15-20 0.0445 -5.4 -4.0 -5.63 -11.9 2&30 0.089 -1.58 -1.9 -0.9 -0.9

NaCN = 131 15-20 0.0445 -12.1 -5.85 -3.82 -4.72 20-30 0.089 +0.25 -0.80 -0.11 -2.58 3040 0.089 -2.7 -2.8 -2.93 -1.0

3

Cd = 15 NaCN = 104.7

Cd = 30 NaCN = 104.7

4 Cd = 15 NaCN = 104.7

Cd = 30 NaCN = 104.7

NaOH NaOH VIII VIII VlU VIII

lo-20 0.25 +0.16 +0.48 -0.12 -0.08 20-30 0.25 -0.48 -0.16 -0.04 -0.72 30-40 0.25 +0.12 +0.48 +0.4s +0.04 40-60 0.50 -0.20 +0.54 +0.14 +0.16 60-80 0.50 +0.20 +0.40 +0.76 +0.54 80-120 1.00 -0.13 $0.80 +0.58 +0.83

2040 0.5 -0.14 -0.1 +0.52 +0.28 4cMO 0.5 -0.06 -0.08 +O.l -0.22 6680 0.5 -0.04 +0.04 +0.06 +0.2 80-120 1.0 -0.04 +0.38 +0.14 +0.27

Ni Ni VIII VIII VIII VIII

O-0.04 0.7 x 10-a +114 +258 +228 t-228 0.04-0.20 2.8 x 1O-8 +96.5 +125 +118 0 0.2-0.3 1.75 x 10-a t-57 +4Q +74 +40

WI.3 5.25 x 1O-s +3.s +48 +46 +51


224 V. N. KUDRYAVTSEV, K. S. PEDAN. A. T. VAGRAMYAN

As, according to the above-given definition, Vm = AV/AC, proceeding from

this dependence it is possible to estimate steel hydrogenation during electrolyte

composition variation, with reference to some initial composition, hydrogenation

degree of which is taken as unit. Of course, one should make the reservation that

such an estimation will naturally be only approximate*.

Thus, for example, taking for the unit a steel hydrogenation in the electro-

lyte of the composition (g/l): Cd 15; NaCN 50; NaOH 10; Ni 0.04, at a current

density of 1.5 amp/dm2, it is possible to estimate the change of hydrogenation

degree in the electrolyte of the following composition (g/l); Cd 40; NaCN 150;

NaOH 30; Ni 0.3 at a current density of 1.5 amp/dm2, using the simple relation:

v2 = VI + K(C,tC*) . AC&+ CV~,~,+C,GWN~CN+ [Vm(C,t~,)ACsINaoH+[~m(C,tC,)AC41Ni (3)

where V, = initial electrolyte hydrogenation (conditionally equal to 1 cm3/100 g);

V, = unknown quantity of hydrogenation (cm3/100 g); Vmcc,+c,j = steel hydro-

genation variation under the increase of component concentration per 1 mol/l

for the given range of concentrations C,tC, [cm3/100g per mole/l]; ACr; AC2; AC,;

AC, = components concentrations variation (mole/l). For our example AC by

components are, accordingly, equal (g/l): [ACI]cd = 25; [AC21NaCN = 100:

w3 INaOH = 20; [ACJNi = 0.26.

Since in this example the electrolyte components concentrations change over a

very wide range, while in Table 3 values VmtC,tC,j are given for the narrower

concentration range, in order to estimate more accurately the hydrogenation

change in the second electrolyte, the summing up Vmtc,+c,j AC values by compo-

nent concentrations ranges, given in Table 3, should be done. For cadmium such

summing up is carried out in the following way:

[v~~~,+~,~ AC,lCd = Vym(lai2o) AC,’ + Vm(zo+30) AC;+

m(3040) AC,“’ (4)

where AC, = AC,’ + AC,” + AC,“’ (mole/l).

Substituting into eqn. (4) numerical values Vm~c,-.-cs~ according to the concentra-

tions ranges of AC,‘; AC1”; AC,“’ from Table 3, we obtain:

[Vmmi+-lo) AC&d = (-11) 0.0445 + (-1.7) 0.089 + (-2.93) 0.089

= -0.9 cm3/100 g

Having carried out such summing up for all other components of the electrolyte,

the obtained partial values of hydrogen variations for each component are sub-

* A more accurate calculation may be carried out by statistical methods, developed on the theory of experiment planning. However, in this case the calculations are cumbersome and need the use of computers.



stituted in the general equation (3)* and the final value of hydrogenation in the second electrolyte is :

v, = 1 + [-0.91,, + [+ 0.061,,,, + [+ 0.261,,,, + + [0.211Ni = 0.63 cm3/100 g.

As can be seen from the above calculation, the increase of cadmium concentration in the second electrolyte results in a tenfold decrease of steel hydrogenation as compared with the first electrolyte, but since other components of the electrolyte contribute to hydrogenation increase, the resulting decrease is not so high (37%).

An analogous estimation was carried out, using the data of Dingley, Bednar and Rogerss. In the work two electrolytes of the following composition are de- scribed (g/l): I. Cd 17.1; NaCN 124. 5; NaOH 9.6; brightener 0.8. II. Cd 34.5; NaCN 98.3; NaOH 80.3; brightener 0.8.

Assuming that the degree of hydrogenation in the first electrolyte equals 1 cm3/100 g (100x), we shall obtain for the second electrolyte after a corresponding calculation :

Vz = 1 + [-0.4],, + [-0.161NaCN + [-0.16],,,, = 0.28 cm3/100g **

The result obtained completely coincides with the authors’ conclusions that the second electrolyte hydrogenizes steel to a smaller degree than does the first one (the decrease is 72%). However, as can be seen from the calculations, the main quota of hydrogenation decrease is connected with the increase of cadmium and not with the high concentration of alkali.

REFERENCES

1 K. Sachs and S. M. Melbourne, Trans. Znsf. Metal Finishing, 36, NQ (1959) 142. 2 G. T. Sink, Pfuting, 55, N5 (1968) 449. 3 W. L. Cotton, PIating, 47, N2 (1960) 169. 4 N. M. Geyer, G. M. Lawless and B. Cohen, Tech. Proc. Am. Electroplaters’ Sot., 47 (1960) 143. 5 J. Bednar, W. Dingley and R. R. Rogers, Electrochem. Tech., 4, N 9-10 (1966) 497. 6 W. Dingley, J. Bednar and R. R. Rogers, Can. Mining Met. Bulk, 60, N658 (1967) 224. 7 R. R. Rogers, Metal Progr., June (1968) 91. 8 L. R. Westbrook, Trans. Am. Electrochem. Sot., 55 (1929) 333. 9 V. 1. Lainer and N. T. Kudryavtsev, Osnovi Galvanostegii, Metalurgizdat, Moscow, 1953.

10 V. N. Kudryavtsev, K. S. Pedan and A. T. Vagramyan, Zachitu MetuNov, 6, Nl (1970) 67. 11 B. N. Kabanov, I. I. Astachov and I. G. Kiseleva, Usp. Khim., 34, NlO (1965) 1813. 12 B. N. Kabanov, I. G. Kiseleva, I. I. Astachov and N. N. Tomashova, Elektrokhim., I, N9

(1965) 1023. 13 I. G. Kiseleva, B. N. Kabanov and D. N. Matchavariani, Elektrokhim., 6, N7 (1970) 905. 14 N. N. Tomashova, I. G. Kiseleva and B. N. Kabanov, Elektrokhim., 7, N3 (1971) 438. 15 V. N. Kudryavtsev, K. S. Pedan, N. K. Baraboshkina and A. T. Vagramyan, Zachitu

MetaNov, 8, Nl (1972) 56.

* In order to estimate the effects of NaCN, NaOH and Ni concentration variations, V, values (Table 3) for cadmium concentration of 30 g/l were used. * * Since the authors in their study used barrel cadmium electroplating, we consider the cathodic current density used as being not more than 0.5 amp/dma.

Electradepos. Surface Treat., I (1972173)


L’inJEuence des composants du bain de cadmiage electrolytique cyanur& sur l’hydrogenation d’acier

Nous avons Ctudie l’influence des composants du bain de cadmiage electro-

lytique cyanurt dans une large intervalle des concentrations (Cd 15-40 g/l; NaCN

52-157 g/l; NaOH 10-120 g/l; Ni O-O.3 g/l) sur I’hydrogenation fragilisante

d’un acier. On constate que lors de concentration haute du cadmium dans la solu-

tion, la quantitt d’hydrogene absorbte par l’acier est diminute d’une man&e

brusque. Le presence du brillanteur nickel dans la solution (jusqu’a 0,3 g/l) aug-

mente nettement l’hydrogenation.

11 est montre que la variation de la concentration NaCN (le plus souvent)

(52-157 g/l) et de la concentration NaOH (10-40 g/l) aux limites ordinaires exerce

une influence peu importante sur l’adsorption d’hydrogene.

Sur la base des donnees une methode approximative Ctait proposee a l’aide

de laquelle il est possible d’estimer l’influence relatif de chaque composant de la

solution sur l’hydrogtnation.

Der EinJluss der Badformulierung cyanidischer Kadmierungselektrolyte auf die Wasserstoffaujtiahme von Stahl

Es wurden der Einfluss der Basiskomponenten eines cyanidischen Kad-

mierungselektrolyten innerhalb breiter Konzentrationsbereiche (Cd 15 bis 40 g/l,

NaCN 52 bis 157 g/l, NaOH 10 bis 120 g/l, Ni 0 bis 0.3 g/l) und ihr Einfluss auf die

Wasserstoffaufnahme von Stahl untersucht und festgestellt, dass die von Stahl

absorbierte Wasserstoffmenge bei hohen Kadmiumkonzentrationen stark ab-

nimmt. Die Wasserstoffversprijdung nimmt stark zu, wenn als Glanzbildner

Nickel (bis 0.3 g Ni/l) im Elektrolyten vorhanden ist. Es wird bewiesen, dass die

Konzentrationsverschiebung an NaCN (52 bis 157 g/l) und die an NaOH (10 bis

40 g/l) im iiblichen Bereich auf die Wasserstoffabsorption einen nur geringen Ein-

fluss ausiibt. Aufgrund dieser Untersuchungsergebnisse wird eine Methodik zur

ungeftihren Berechnung vorgeschlagen, nach der der relative Einfluss einer jeden

Elektrolytkomponente auf die Wasserstoffverspriidung abzuschatzen ist.


the effect of cyanide cadmium plating bath compositions on steel hydrogenation

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