CA1075190A

CA1075190A - Process for the electrodeposition of ferro-nickel alloys

Info

Publication number: CA1075190A
Application number: CA258,674A
Authority: CA
Inventors: Armand Limare; Guy Plancquel
Original assignee: Societe Metallurgique Le Nickel SLN SA
Current assignee: Societe Le Nickel SLN SA
Priority date: 1975-08-13
Filing date: 1976-08-09
Publication date: 1980-04-08
Also published as: BE844841A; FR2320996A1; DE2636552C3; DE2636552B2; DE2636552A1; IT1062718B; JPS5222529A; ES450678A1; GB1552837A; FR2320996B1

Abstract

ABSTRACT

A process of electrodepositing a layer of ferro-nickel alloy using a soluble anode consisting of anodic baskets filled with granules of ferro-nickel of composition substan-tially identical to that of the layer which it is desired to deposit.

Description

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The invention relates to a new process for the electro-deposition of ferro-nickel alloys, and is particularly concerned with the use of soluble anodes of ferro-nickel.
Until recent years, nickel-plating consisted solely of covering the pieces with a layer of pure nickel. New techniques have very recently appeared in the nickel-pLating industry in which the nickel is partially replaced by iron. Ferro-nickel alloys of an iron content of up to 40~ may be deposited, where-by the replace~ent of an expensive metal, nickel, by a consider-ably cheaper metal allows the net cost of nickel plating to be reduced quite sharply. These processes, which are described in U.S. Patents Nos. 3,795,591, 3,806,429 and 3,812,516, and in Prench Patent No. 2,226,479, aim essentially at replacing the soluble nickel anode of the conventional process by two anodes respectively made of iron and nickel. However, the use of two different anodic materials causes a large number of disadvan-tages; these include the problems of storage and of handling whilst renewing the anodes and the difficulty of finding a commercial ma~erial suitable for electroplating.
Moreover, it has been thought that materials used for this /
should be products of high purity, such as for example o ARMC0 iron with less than 0.15~ impurities and of electrolytic nickel.
It has been found, for example, that the presence of carbon can be troublesome in the nickel anode.
In order to form uniform plated layers it i5 necessary that the composition of the bath and especially the iron/nickel .
ratio should not vary during the electrolytic deposition of the ~; ~ alloy layer.

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cau~es numerou3 difficulties relatin~ to the iron/nlcl~el rat:i.o .in the electrolyte; in order for this rat:Lo to be constant, the ratio of the respective anodic suxfaces of the two metals should be kept constant, a slight alteration in the anodic surface of the iron c~n change the composition of the bath quite significantly because of the greater speed of dissolution of iron relative to nickel~ When the electroplating apparatus ceases operation, the iron anode i.5 covered by a layer of nickel which can reach or even exceed a thick-ness of 1 mm, thus causing a considerable variation in ~he iron/
nickel ratio of the electrolyte. All this causes a lack o~ flexi-bility in the electroplating apparatus and requires a greater supervi~ion thereof.
O~e of the objects Or the invention is therefore to simpli~y the process of deposition of iron-nickel alloys.
~ nother object of the invention is to provide a nickel-plating process which can be stopped without difficulty and without this causing variations in the composition of the bath.
A ~urther object of the present invention is to provide a process of the t~pe mentioned above in which an electrolytic coat-. i~g of high quality is obtained.
hese and other objects ~hich will become apparent ~rom the ~ollowing description are attai~ed according to the in~ention by a process of electrolytically depositing a layer of a ferro-nickel alloy which comprises using as a soluble anode.an anodic basket ~- filled with ferro-nickel granules of a compositio~ substantially . identical to that o~ the layer which it is desired to deposit. The ~ ~ expression "substantially identical'! indicates that only the iron/`~ nickel ratio is importa~t and that the presence of a certain numbero~ impurities in the ferro-nickel starting material can be tolerated, since the impurities are not generally found in the layer of alloy which is deposited on the cathode. ~hese impurities either . ~ .;
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remain clissolved in the bath or are precipitated in the electrolysis tank in the form of a sediment.
The expression "substantially identical" also means that there are only small variations between the nickel content of the initial ferro-nickel, disregarding the impurities, and the nickel content o~ the plated deposit. These variations are generally within the limits o~ analysis error (0.5 % by weight absolute error).
This possibility of tolerating a relatively increased amount of impurities by using ferro-nickel in place of nickel and iron is one of the more surprising and interesting features of the process. The amount of impurities which can be tolerated clearly varies with the nature of the impurities. In general, the impurities which, like silicon, are precipitated as a sediment at the bottom of the electrolysis tank or of anodic bags provided for that purpose, are much more tolerable than those which are soluble in the electrolyte. Of the latter sort, however, cobalt, the amount of which can reach several percent (by weight) should be considered separately ^ 20 since it cannot easily be considered as an "impurity"; it is deposited on the cathode at the same time as the iron and nickel and does not in any way harm the quality of the plated deposit, a~d therefore should not really be considered as an impurity.
It must be added that it is the appreciation of this tolerance of impurities which has allowed us to use ferro-nickel in electroplating.
This possibility has already been cons:idered in the Patents listed above as a poor alternative to the use of several anodes ~ ~ 5~
of pure ~netal, but, to our knowledge, no experimentation thereon has been performed. This should be explalned by the absence of commercially available nickel of a purity equivalent to that of electrolytic nickel and in a form suitable for electroplating.
It seemed useless to seek for granulating adjuvants, since such adju~ants added during the granulating operation became the impurities in the electro-deposition operation.
Thus the process of the invention, in providing a new technique for the use of ferro~nickel in electroplating, is a significant technical advance in the nickel-plating industry, the economic effects of which could be considerable.
This advance could only have been brough~ abou~ by showing that the commonly held opinion regarding the purity of the materials intended for electroplating has not been completely justified in the case of ferro-nickel.
It is however clear that, despite this tolerance, it is more practical to work with materials which are as pure as possible.
The granules are made by pouring the molten metal into a bath of water and in order that the granules produced should have a suitable shape it is necessary to select granulating adjuvants for this type of alloy. On ~his subject reference should be ~ade to our Pate~t Applicatio~ S~rial No. 258,683 filed August 9, 1976 entitle~ "Process for making ferro~nickel gran-ules for electroplating". ~he first granulatiIlg adjuvants tried were aluminium and mag~e sium; however, the use of the granules thus obtained was not completely satisfactory: the appearance in a ver~ appreciable quantity of sediment in the anodic bags was noted. A more detailed study has shown that _ 5 _ ' ~ .
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the granules obtained from the ba-ths enriched with aluminium and magnesium had a granular microstructure. At the time of the anodic dissolution, a significant proportion of these grains is broken down to form a sediment of a composition similar to that of the initial ferro~nickel.
One can determine in advance if a batch of granules will give a significant amount of sediment with the aid of a simple test. ~his test consists of evaluating the crushing resista~ce of a granule from the batch that is desired to be used by clamping in a hand vice. If the granule is only lightl~ deformed, remains whole and beha~es like a ductile metal, then the batch of granules will give very little sediment~ On the other hand, if it is deformed with crumbling, thus behaving like a brittle metal, the amount of sedi~ent will be hi~h~ unless the operating conditions are modified (for example, by using a high current density).
~he above difficulties Can largely be avoided by adjusti~g the operating conditions and especially the current density. How-e~er, according to a preferred method of operation of -the process almost these difficulties can be/eliminated by using the granules obtained from a metallic bath to which is added a granulating adjuvant ; ~ containing silicon and/or cal~bon~ ~he silicon is preferably introduced into the bath as ~erro-silicon. ~he selection of the amount of silicon in the bath is extremely delicate; indeed two ; re~uirements act in contrary directions: thus to ~void the formation of a sledIment caused by silicon, it is necessary to limit as far as possible the amo~nt of silicon, but to improve the shape of the gr~lules it is necessary to increase it. It is therefore prefer:red to keep the amount of silicon (in the granules)

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The process thus described has, among other advantages, ea~e of operation due to replacement of two materials by one and the use of granules.
The use of ferro-nickel granules ensures moreover a con-stant and uniform dissolution of the two metals (nickel and iron) with a Faraday anodic yield near to unit7, which facilitates the control and maintenance of the iron-nickel ratio in the elctro-lyte and ensures a good Yersatility of operation in allowing stopping of the process without major difficulties. ~he dis solution of the alloy is complete and does not cause formation of a large amount of sediment.
The quality of the metal coating obtained b~ electro-deposition depends greatly on the ratio of ferric iron to the total amount of iron in the electrol~te. If this ratio is too high~ the coating will contain inclusions of ferric h~droxide, which shows as numerous specks of rust colour. Thus, when the iron stabiliser i3 a complexing agent (as in the Examples) this ferric iron ratio should not be more than 40~, and is preferably less than 20%o It has been difficult to keen the ratio within the above limits, andconventiona~ly, such ratios are often near 50%.
~he process according to the invention presents a solution to this problem. ~he simple fact of using gra~ules of ferronickel permits one to obtai~ a ratio of ferric iron in the solution within the above preferred limits~ and~in many measurements ~f the ratio of ferric iron, none have exceeded 20%. -`
Another factor influenci~g the quality of the cathodic ooating is the~ cleanliness and the porosit~ of the anodic ba~s (sacs) surrounding the anodes which retain the sediment which ~ 7 ,:

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otherwise would fall to -the ~oot of the electrolytic tank. If these anodic bags are not changed frequently, the cathodic coat-ing may have very irreg~lar thickness. '~his problem is par-ticularly acute when small ~uantities o~ sulphur are added to the nickel anodes to facilitate dissolution. ~he present inven-tion also presents a solution -to this problem, since when using ' ferro-nickel granules, the anodic bags retain satisfactory porosity and cleanliness, and excel'lent cathodic coatings can be obtained without the nece~sity to change the anodic bags frequent-ly.
Finally~ the ferro-rlickel granules are very soluble, and th'is hi~h solubility avoids the necessity for solubilising a~ents and enables the quantity of chloride ions in the 'ba-th to be reduced to between`lo to 40 g/l.
It i~ interesting to note -that none o~ the advantages described above are ment'ioned in the Patents which allude to , the possi~ility of using ferro-nic~el. This, whatever its explanation, shows well the surprising results of'the use of ferro-nickel in the form of granules.
~he invention will now be illu~trated by the following examples in which all percentages are b~ weight.
Example Fer~o-nickel granules containing 7~/~ of nickel, called hexei~ "FN 77" were prepared fro;m a bath enriched with aluminium and ma~ne~ium, as described in Example 1 of the above-mentioned copending Patent Applica-tion filed on the same day as the~present Application .
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The chemical analysis was as follows:
Ni = 77 . 2 Yo Fe - 21 . 9 %
Co c 0.38 %
Si - 0.00~3 %
Mn = 0.007 %
Mg = O . 00()2~/o Al = O.OOL~ %
C ~ 0.002 %
'10 Solubilit;y tests were carried out in a 12 litre ta~c in a bath of the following composition:
NiS04~ 6H20 = 75 g/l NiCl~. 6H20 = 75 g/l FeS04. 7H20 = 10 g/l 3 3 = 45 g/l Commercial products of the Ud;s~lite Compan~:
Brighteners ~N 1 = 25 cc/litre ~: ~ , ;, ,, ' .
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* FN 2 a 2.5 cc/litre ' * 84 = 18 cc/litre Stabilizer NF = 25 g/litre Wetting Agent 62A = 1 cc/litre The operating conditions were:
- anodic current density 10 Amps/dm2 - total anodic surface 3.8 dm2 _ p~ = 3.7 - length of test = 235 hours (correspondin~ to a quantity of current 8694 Amp-hours).
The results were as follows. After 83 hours of operation, i.e. a current amount of 3082 Amp-hours, a residue remained in -the baskets consisting o metallic grains,the quantity of which correspo.lded to 4.4~ of the weight of granules consumed. Chem-ical analysis of the residue showed that the latter was composed of grains of alloy of the same content of nickel-iron. At the end o the test the amount of residue was 5. 240 ~
Howe~er, the Faraday yield of the anodic dissolution was near to 1.0 and after 1300 Amp-hours the ratio ~total iron/
~20 iron ~ nlckel) in the electrolyte was stable and almost lO~o.
The bath had then attained equilibrium.
At the end of the test the amount o~ iron in the plating was 21.6~. -The quality of the cathodic plating was excellent. ~ -Example 2 ; The same granules as in Example 1 were tested in the same type of bath, but with an anodic current density of 3.8 Amps/dm~
with a total anodic surface of 2 dm2 for 432 hours, correspond-~ . :
~ ng to a quan~ity of current of 3427 Amp-hours, as in Example :
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, ~'75 ~ bove-mentio~ed 2 of our/copending Patent Application filed on the same day as the present Application. The amount oE residue in the anode baskets was then 13~ and its chemical analysis showed the nickel/iron ratio to be substantially identical to ~hak of the initial granules.
The Faraday anodic yield was near 1Ø
The Faraday cathodic yield was near 0.95.
The quality of the cathodic plating was excellent.
Example 3 A fresh bath of granules was prepared from a bath of liquid alloy enriched with aluminium and magnesium.
The analysis of the granules was as follows:
Ni - 77.05 ~0 C = 0.004 ~u Co - O.S ~ Al = 0.015 %
Mg = 0.002 ~ ~i = 00008%
Mn = 0.013 ~ Fe - re~ai~der These granules were then tested in the same type of ba~h as in the previous examples, under an anodic current density of 2.7 Amps!dm2 for 132 hours (total quantity of current = 1044 Amp-hours).
The amount of sediment collected in the anodic baskets was then 15.6~. However the ratio (total iron/iron + nickel) was constant and near to 11~. The concentration of nickel +
iron was near 33 g/l~
The quality of the cathodic coating was excellent.
Fxample~4 Other granules were made from a bath o alloy enriched above-me~tioned with silicon and manganese, as in ~xample 4 of our/copending ~ ~ .

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Patent Application filed on the same day as the present Appli-cation.
The chemical analysis of these granules was as follows:
Ni + Co = 7:3.6 Co = 0.5 Mn = 0.27 ~
Si ~ 0.16 C = 0 . 020~o Fe = remainder Theso granules were tested in the same type of bath as previously under a current density of 2.5 Amps/dm2 ~total anodic surface 0.69 dm2) for 375 hours (total of 645 Amp-hours).
The Faraday anodic yield was near l.0 and the amount of residue formed was very low. This residue consisted of a black-ish sedirnent containing silicon.
The manganese content in the bath rose from 0.003 g/l to 0.162 g/l at the end of the test.
In this example a bath at equilibrium for an alloy of 77~ Ni was fed with a 74~ alloy, which invo~ved an increase in ~he ratio (total iron/iron + nickel) in the bath of from 11 to 18~.
The concentration of nickel ~ iron in the bath remained practically sonstant at about 37 gll-The quality of the cathodic coating was excellent.Example S
Another batch of granules was prepared from a bath enriched above-men~ioned with silicon and carbon, as in Éxample S of our/copending Patent App~lication filed on the same day as the present Application.
The~chemica:l analysis of the granules was:
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Ni -~ Co = 76.85 Co - 1.25 ~
Si = 0.20 %
C = 0.17 %
S = 0.22 %
Mn = 0.05 ~
Fe = remainder These granu]es were tested at an anodic current density of 2.4 ~mps/dm2 for 200 hours ~total current of 942 ~mp-hours).
The Faraday anodic yield was always near 1.0 and the amount of residue formed was not measurable.
There was no increase of silicon in the electrolyte.
The quality of the cathodic coati~g was excellent.
Example 6 Another batch of granules was made rom a bath of alloy enriched with silicon and carbon according to the technique already described in Examples 4 and 5.
The chemical analysis was as followjs:
Ni = 76 Co = 0.50 ~
Si = 0.35 %
C - 0.10 %
Mn = 0.05 %
I Fe = remainder . .
A solubility test was carried out in a 100 litre tank in a bath having the following composition in g/l:
NiS04. 6 H20 = 105 NiC12. 6 H20 = 60 ~ ~ ~eS04. 7 H20 = 10 :` ~ 13 : -.~ 7 5~ ~
H~03 ~ L~5 Stabili~er Por iron and Or~anic proclucts were employed as in Examnle 6 of our above-mentioned Patent ~pplication filed on the same day as the present Application.
~ he anodic current densit~y was 3 Amps/dm2 and the duration of the test was 330 hours corre,~ponding to a cur~ent quantity of 5100 ~mp-hours.
At the end of the test the residue was only 0~2% with respect to the amount of granules cons~edA -.
~he quality of the cathod:ic coating was excellent.
~he amount of sediment observed in Examples 2 and 3 was scarcely acceptable, for it represented a serious loss of start-ing material; however beyond the fact that the sediment did not at all harm the electrolysis a~d the quality of the plating~
Example 1 and other tests not described ha~e showed the possi~
bility of reduoing the amount of sediment to lev~ls e~tirely acceptable, by optimising the operating co~ditions.
In particular the use of higher current densities than 10 ~mps/dm2 permit reduction of such residue to acceptable levels.
On the other hand it should be noted that the residues from the baskets may be dissolved followiIIg the electrodepositionO
~lthough these examples relate essentially to ~erro-nickel in which the amount of nickel is from about 74 to 7~/o~ it will .
be clear to those skilled in the art that this teaching is applic-able to ~erro~nickels of various nickel contents (e~g. 20 to 90%
by weight).
, ;~ Xt will also be clear to those skilled in the art that the tolerance of i:mpurities such as has been shown by these tests :: :

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and in the description does not extend to a~y soluble metals of less reducing power than iron and nickel.
~ e 7 Another batch of granules having the following chemical analysis was prepared:~
Ni - 76.7 %
Co - 0.50 %
Si ~ ~.13 %
C - 0.02 %
S - 0.01 %
Fe - remain-ler A test was performed iII an 80 litre tank containing the same electrolyte as ~n Example 6 (o~ pH 3.2) at a temperature of 6~C using air agitation.
~he test was per~ormed continuously 24 hours a day ~or ?200 hours (3 months) using a~ anodic current density of 2,5 Amps/dm2, which corresponded to a current ~uantity o~ 109,000 Amp~hours. In this time the amount of ~ickel consumed corres-ponded to a fourfold renewal o~ the i~itial chaxge in the baskets.
The results were as fol}ows:
Amount of sediment - 0.~/0, which is very good for such a long test~ -~e III : ~otal Fe ratio between 12 and 2~/o Another test was performed in a 2500 litres tank using granules ~nd electrolyte as in Example 7, at a pH of 3.2 and a temperature of 50C, using mechanical agitation.
he test(8as catrhried out intermittently over the period Deoember to Jul~of the ~ollowing year~ with a current density ., , ~ .,, . ., , . -.
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~ 75~0 which varied ~rom 0.5 to 3 ~mps/dm2,'corre~ponding to a total curent quantity of about 500~000 Amps.H, The results were as follows:
Fe III : total Fe ratio between 2 and 9~
No problems were encountered ~unlike in prior art techniques),and after the charge in the anodic baskets had been consumed and renewed, there was still no need to wash the baskets or the bags, which shows the undoubted advantages of the present invention.
Example 9.
Another test was performed in a 2000 litres tank using grarlules and electrolyte as in Example 7, at a p~ o~ 3.2 and a temperature of 60C, using agitation by air.
The test was carried out continuously for 24 hours a day for 2 months, using an anodic current density which varied from O.S to 3 Amps/dm2, corresponding to a totAl curren~ quantity of about 650~000 Amps.H. In t:his time the initial charge in the anodic baskets was completely renewed ~hree times.

The sediment prc~uced was negligible, and the Fe III :
total Fe ratio was 19 %.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process of electrodepositing a layer of a ferro-nickel alloy using a soluble anode consisting of anodic baskets filled with granules of ferro-nickel of a composition substantially identical as to iron nickel ratio and as to nickel content to that of the layer which it is desired to deposit.

2. A process as claimed in Claim 1, wherein the ferro-nickel granules are derived from cast alloy with the addition of a granulating adjuvant containing silicon, said granules containing 0.1 to 005% silicon.

3. A process as claimed in Claim 1 or 2, wherein the ferro-nickel granules are derived from a cast alloy with the addition of a granulating adjuvant containing carbon.

4. A process as claimed in Claim 1 or 2, wherein the ferro-nickel granules are derived from a cast alloy with the addition of a granulating adjuvant containing manganese.

5. A process as claimed in Claim 1 or 2, wherein the ferro-nickel granules are derived from a cast alloy with the addition of a granulating adjuvant containing aluminium.

6. A process as claimed in Claim 1 or 2, wherein the ferro-nickel granules are derived from a cast alloy with the addition of a granulating adjuvant containing magnesium.

7. A process as claimed in Claim 1 or 2, wherein the granules have a nickel content in the range of 20 to 90% by weight.

8. A process as in Claim 2, wherein the silicon is added in the form of ferro-silicon.

9. A process as in Claim 1 or 2, wherein the amount of ferric iron to total iron is not greater than 40%.

10. A process as in claim 1 or 2, wherein the amount of ferric iron to total iron is not greater than 20%.

11. A process of electrodepositing a layer of a ferro-nickel alloy using a soluble anode consisting of anodic baskets filled with granules of ferro-nickel of a composition substantially identical as to iron-nickel ratio and as to nickel content to that of the layer which it is desired to deposit, the ferro-nickel granules being derived from cast alloy with the addition of a granulating adjuvant containing silicon, said granules containing 0.1 to 0.5% silicon, the granules having a nickel content in the range of 20 to 90% by weight, and the amount of ferric iron to total iron being not greater than 20%.

12. A process as in Claim 11, wherein the ferro-nickel granules are derived from a cast alloy with the addition of a granulating adjuvant also containing carbon.