GB2031463A - Process for electrodeposition of iron-nickel alloys - Google Patents

Abstract

A process for electrodepositing a layer of a ferro-nickel alloy uses as a soluble anode an anodic basket filled with granules of ferro-nickel having a composition substantially identical with that of the layer that it is desired to deposit and such that the mass ratio of nickel plus cobalt to iron plus nickel plus cobalt is between 20 and 90%.

Description

SPECIFICATION Process for electrodeposition of iron-nickel alloys This invention relates to a process for the electrodeposition of iron-nickel alloys and is a development of that described and claimed in the Specification of our earlier Application No.

32960/76 (Serial No. ) which is hereinafter referred to as the "earlier Specification".

Claim 1 of our earlier Specification is in the following terms:- A process of electrodepositing a layer of a ferro-nickel alloy using as a soluble anode an anodic basket (subsequently referred to as a panode) filled with granules of ferro-nickel which are ductile when crushed, have been made by pouring molten metal into a bath of water, and have a composition such that their iron/nickel ratio is substantially identical to that of the layer which it is desired to deposit.

The earlier Specification states that the teaching relating to those ferro-nickels whose nickel content is in the region of 77%, is applicable to ferro-nickels having a nickel content of from 20 and 90%. The present invention has arisen from a study of attempts to apply the process of our earlier Specification to ferro-nickels whose nickel content is between 20 and 60%, and to determine the optimum conditions for such processes.

According to this invention, the process according to the earlier Specification can advantageously be used by filling the panodes with granules whose composition is such that the ratio of nickel plus cobalt to iron plus nickel plus cobalt is between 20 and 90%.

Advantageously, the proportion of impurities contained in the granules is not more than 0.2%, while the proportion of granulating adjuvants may vary from 0 to 1%. The term "granulating adjuvants" is used to denote silicon, manganese, magnesium, aluminium, and carbon.

During the studies leading up to this invention, it was found that in order to produce low sludge ratios it is advantageous to provide the panodes with granules, the structure of which is basaltic or equiaxed without a dendritic sub-structure produced by inter-dendritic segregation.

The particle joints are fine. The basaltic structure gives better results than those obtained with equiaxed structure particles. The dimension of the particles (the major diameter) is preferably between 1 and 1 5 mm.

For a definition of basaltic and equiaxed structures reference should be made to "Metals handbook Volume 8-Metallography, structures and phase diagrams" published by "The American Society for Metals" and "A concise encyclopedia of metallography" by A. D.

Merriman, published by Elsevir Publishing Company-Amsterdam-i 965-page 121.

Aqua regia as defined in US Standard ASTM E 407-70 No. 12, may be used to show the structure of the granules and the following reagent may be used to show the particle substructure: 400 ml HCI (density = 1.2) 8 9 Curl2 28 g FeCI3 20 ml HNO3(density = 1.4) 800 ml methanol 400 ml H20.

Since it is difficult to determine quentitatively whether a structure is basaltic or equiaxed with or without a dendritic substructure, a test has been perfected whereby it is possible to tell by means of a simple hand-vice to tell whether a batch of granules gives a high sludge ratio. The test comprises simply subjecting to compression test between the jaws of a hand-vice a sample of granules with a size of preferably between 10 and 1 5 mm. If the granules subjected to this test do not disintegrate under a compression which reduces their major diameter by at least onethird, and if the sum of the adjuvants and impurities does not exceed 1 %, the sludge ratio may be expected to be less than 1.5%. The test carried out by the average person is equivalent to a compression test of about 2 to 2.5 tonnes.

However, since this is only semi-quantitative, a new test was perfected using a compression machine. If the granules do not disintegrate under a compression of 5 tonnes, and if the sum of the adjuvants and of the impurities is not more than 1%, the sludge ratio will be less than 1%.

If the first crack does not appear until a value above 2 tonnes, and if the sum of the adjuvants and of the impurities does not exceed 0.5%, the sludge ratio will be less than 0.5%.

These compression tests were carried out with granules, each major diameter end of which was formed with a flat of an area of about 1 5 mm2.

Compression tests of this kind give a deformation value Ae as a function of the load applied.

From the discontinuities found on this curve it is possible to measure with fairly good accuracy the values corresponding to disintegration and to first cracking.

This test is a fairly reliable means of determining the sludge ratio.

Obviously the test should be carried out on a representative sample of the batch of granules intended for use for electroplating.

During the study leading up to this invention it was found that granules containing silicon and at least two adjuvants selected from the group comprising manganese, magnesium, aluminium and carbon, in the following respective proportions: Silicon : from 0.02 to 0.5% Carbon : from 0.03 to 0.2% Magnesium : from 0.02 to 0.4% Manganese : from 0.01 to 0.1% Aluminium : from 0.01 to 0.1% give sludge ratios less than 1 % if the sum of the various adjuvants meets the following requirements:When the granules with which the panodes are provided are of a composition such that the mass ratio of nickel plus cobalt to iron plus nickel plus cobalt is between 20 and 50%, the sum of the adjuvants contained in the granules must be between 0.1 and 1%; when the grannles with which the panodes are provided are of a composition such that the mass ratio of nickel plus cobalt to iron plus nickel plus cobalt is between 50 and 70%, the sum of the adjuvants must be between 0.2 and 1 %; when the granules with which the panodes are provided are of a composition such that the mass ratio of nickel plus cobalt to iron plus nickel plus cobalt is between 70 and 90%, the sum of the adjuvants must be between 0.1 and 1%.

Preferably, the sum of the magnesium, manganese and aluminium contained in the granules is at least 0.05%.

To obtain a sludge ratio less than 0.5%, the panodes are advantageously provided with granules which contain silicon and at least two other adjuvants selected from the group comprising manganese, magnesium, aluminium and carbon in the following respective proportions: Silicon : from 0.04 to 0.2% Carbon : from 0.03 to 0.1% Magnesium : from 0.02 to 0.1% Manganese : from 0.01 to 0.6% Aluminium : from 0.01 to 0.06%.

The sum of the adjuvants present in the granules must be between 0.2 and 0.3%.

Preferably, the sum of the magnesium, manganese and aluminium contained in the granules is between 0.07 and 0.2%. The top value of the range is imperative only to the extent that it is required to keep the concentration of these metals at low levels.

Advantageously, if the mass ratio of nickel plus cobalt to iron plus nickel plus cobalt in the ferro-nickels is between 70 and 80%, the preferred ranges are as follows: Silicon : from 0.04 to 0.1 % Carbon : from 0.03 to 0.05% Magnesium : from 0.02 to 0.08% Manganese : traces Aluminium : traces In the case of ferro-nickels whose mass ratio of nickel plus cobalt to iron plus nickel plus cobalt is between 50 and 70%, the preferred ranges are as follows: Silicon : from 0.1 to 0.2% Carbon : from 0.03 to 0.1 % Magnesium : from 0.03 to 0.08% Manganese : from 0.01 to 0.08% Aluminium : from 0.02 to 0.06% The values of the ranges are given with an indetermination of the order of 0.01 % for the individual ranges and 0.02% for the sum ranges.

At this point it should be noted that the quality of the metal coating produced by electroplating depends very much on the ratio between the ferric ions and the total amount of iron dissolved in the electrolyte. If this ratio is very high, the deposit contains iron hydroxide which occurs ih the form of numerous spots of rust colour. If the iron stabilizer is a complexing agent, as is the case in the examples, this ratio should not be more than 40%, and is preferably less than 20%. It is very difficult to keep the ratio inside the above-indicated limits and the ratio is generally around 50%.

The process according to this invention solves this problem. The ratio between the ferric iron and the total quantity of iron dissolved in the electrolyte can be kept at about the preferred limits, simply by using ferro-nickel granules, because none of the numerous measurements of this ratio taken hitherto has exceeded 20%.

Another factor which influences the quality of the cathode coating is the cleanness and the porosity of the anodic sacs which surround the anodes and which retain the sludges, which would otherwise fall to the bottom of the tank. Unless these anodic sacs are changed frequently, the cathodic coating may have a very irregular thickness. This problem is particularly acute when small quantities of sulphur are added to the nickel anodes to facilitate dissolution.

This problem appears to be solved simply by using ferro-nickel granules according to the invention, since it has never been met in numerous tests carried out with ferro-nickel granules.

Finally, the ferro-nickel granules are highly soluble and this high solubility means that there is no need to use solubilizers, and the amount of chloride ions in the electrolyte can be reduced to a value of between 10 and 40 g per litre.

The use of ferro-nickel granules also enables baths to be used with a sulphate ion and chloride ion concentration ratio of between 2.5 and 4 expressed as g per litre.

The following non-limitative examples are intended to enable the skilled addressee readily to determine the operating conditions advantageously used for each specific case.

Example 1 A batch of granules having the following composition: Nickel : 76.7% Cobalt 0.50% Silicon 0.13% Carbon 0.02% Sulphur . 0.01% Iron : to make up to 100%, was used to carry out a test in an 80 litre electrolytic tank containing the same electrolytes as that described in Example 4 in the earlier Specification, at a temperature of 60"C with air nitrogen. This test was continuously carried out for 2200 hours with a current density of 2.5 amps per square decimetre, corresponding to a total current of 109 000 amps per hour. The panode charge had to be renewed four times for this test.

The results obtained were as follows: Sludge ratio: 0.9%; ratio of iron III to total iron was constant between 12 and 20%.

Example 2 Another test was carried out in a 2500 litre tank using the same granules and the same electrolyte as in Example 1, with a pH of 3.2 and a temperature of 60'C, agitation being carried out mechanically.

The test was carried out intermittently for a period of 8 months with a current density ranging from 0.5 to 3 amperes per square dm corresponding to a current of about 500 000 amps per hour.

The results were as follows: The Fe III: total iron ratio kept constant between 2 and 9%; the sludge ratio was negligible.

No problem was found (unlike the techniques used in the prior art) and after the panode charge had been consumed and renewed there was no need to clean the anodes, the anodic sacs or the anodic cells.

Examples 3 to 29 Examples 3 to 22 were carried out in the same way as in Examples 1 and 2, the tests lasting for about 200 hours with a current density of about 5 amperes per square dm with the same bath as that used in Example 4 of the earlier Specification.

The same samples of granules were also tested in a bath having the same mineral consitituents but with the following organic compounds: Sodium saccharinate : 5 g per litre 1 ,3,6-naphthalene-trisulphonic acid . 5 g per litre Ascorbic acid : 0.35 g per litre Sodium lauryl sulphate : 1 cc per litre The anode yield was of the order of 100%. The cathode yield was of the order of 95%. The quality of the coating was excellent and identical to that obtained with the bath similar to that of Example 4 of the earlier Specification.

The tests corresponding to Examples 23 to 29 were carried out under same conditions as in the previous Examples but because of the small size of the electrolysis cell these tests were only dissolution tests and not cathodic deposition tests.

The results corresponding to Examples 3 to 29 are shown in the following Table.

Table I-Analysis of granules (% by weight) TEST Ni Co Si C Mg Mn Al S Boues % 3 76,5 0,48 0,05à 0,0035à traces traces" 0,003 0,0110 6 a 7 0,07 0,0157 4 76,6 0,50 0,12a 0,0035à traces traces 0,003 0,0110 5,4 0,22 0,0157 5 75 à 0,50 0,10a 0,0035à traces traces 0,003 0,0110 3,597 76 0,60 0,0157 6 76 à 0,55 0,05à 0,005 à traces < 0,05 0,002 0,0100à 2,5 à 5 77 0,20 < 0,020 0,0120 7 76,5 0,49 0,38 0,11 traces < 0,05 traces 0,0110 5 8 76,5 0,49 0,06 traces traces traces 0,05 0,0100 6 a 7 9 76,3 0,47 0,32 0,025 traces traces traces 0,0120 2,1 10 75 0,48 < 0,05 traces 0,05 < 0,05 traces 0,0100 1,3 11 75,4 0,46 < 0,05 traces 0,08 < 0,05 traces 0,0100 1,1 12 75,6 0,48 < 0,05 traces 0,006 0,090 traces 0,0110 1,1 13 75 0,48 < 0,05 0,29 0,07 < 0,05 traces 0,0100 1,2 14 75,5 0,45 0,05 0,11 0,07 < 0,05 traces 0,0100 0,9 15 74,8 0,47 0,05 0,07 0,08 < 0,05 traces 0,0100 0,7 16 74,6 0,44 0,05 traces 0,08 0,06 traces 0,0100 0,3 17"" 74,8 0,44 0,05 traces 0,01 à 0,05 à traces 0,0100 0,7 0,25 0,20 18 74,2 0,46 0,5 traces 0,1 0,07 traces 0,0100 0,3 19 75,2 0,48 0,05 0,04 0,08 < 0,01 < 0,01 0,0100 < 0,2 20 74,8 0,43 < 0,05 traces 0,225 0,10 traces 0,0110 0,7 21 74,8 0,42 < 0,05 traces 0,42 0,20 traces 0,0100 0,7 22 59,7 0,57 0,14 0,036 0,067 0,00620,026 0,0150 < 1 23 59,7 0,55 0,070 0,30 0,060 0,0062traces 0,0150 7 24 59,5 0,5 0,14 0,018 0,050 < 0,01 0,029 0,0170 0,72 25 59,8 0,54 0,15 0,023 0,060 < 0,01 traces 0,0210 0,26 26 59,7 0,56 0,16 0,021 0,068 < 0,01 0,025 0,0190 0,12 27 60 0,45 < 0,09 0,104 0,030 < 0,01 0,030 0,0120 0,2 28 28,2 0,78 0,060 0,011 traces 0,017 0,040 0,0210 0,5 29 24,6 0,75 0,03 0,002 traces 0,19 0,01 0,0130 < 1 traces: < 0,001 % This example is equivalent to a mean value of several tests; the composition of the granules varies in such manner that the sum of the magnesium and manganese is between 0.2 and 0.3%.

Example 30 The above-described compression tests were carried out on the granules of Examples 4, 8, 14, 19, 23, 24, 27 and 29 by means of a model TTDM INSTROM machine at a speed of 5 mm per minute and under an increasing load of from 0 to 10 tonnes.

Granules of a size of between 10 and 1 5 mm were selected for these tests.

Two parallel plane surfaces of about 1 5 square mm were produced by abrasion to ensure the stability of the granule between the two plates of the machine. The applied load was at the top of the range.

The above test gives the deformation value he (e for thickness) against the applied load. This value enables the load required to produce the first crack and for crushing (disintegration) to be measured.

The results are given in the following Table: Table 2 Load at which first Test Sludge ratio % crack appears Disintegration load 11 5 1 3 15 7 0.5 0.5 19 0.9 0.5 to 0.7 > 5 24 0.2 2 > 5 28 0.9 to 1 1.5 > 5 29 7.3 0.9 1.2 32 0.26 3 > 5 34 0.20 4 > 5 It will be seen from the above that this test is a very reliable means of determining the sludge ratio.

Example 31 Comparative tests were carried out in a bath, the initial composition of which was as follows: NiSo4 6H2O : 200 g/l NiCI2 6H20 70 g/l FeSO4 7H2O 11 gel H3BO3 45 g/l Stabilizer 20 g/l Brightener 1 25 cc/l Brightener 2 2.5 cc/l Brightener 3 1 8 cc/l Wetting agent 1 cc/l pH = 3.5 Two 80 litre tanks were filled with the same initial bath, one having four titanium baskets (panodes) filled with granules (tank A) and having an area of 6.66 square dm, the other (tank B) having three baskets filled with nickel (area = 5 square dm) and another filled with iron (area = 1.66 square dm). These two tanks were connected in series and a 50 amp current was passed through the tanks, equivalent to a mean anode density of 3 amps per square dm, with identical air agitation in both tanks. The tests took 300 hours.The temperature was about 60"C.

The concentration of the metals in the two baths was deliberately left to develop freely.

The anode yield in the case of tank A was almost 100%, while in tank B it was more than 100% (about 103%), showing a chemical dissolution of about 400 g of iron on the 2360 g of iron dissolved.

The cathode yield of the deposit in tank A was slightly better than than in tank B, and was about 94%.

At the end of the tests, the mean composition of the coating was very close to that of the granules in the case of tank A (nickel 73%, iron 27%) while that of the deposits obtained in tank B was close to 82% nickel and 17% iron.

The nickel plus iron concentration in tank B was of the order of 87 g per litre while in tank A it was of the order of 80 g per litre (a fault in controlling the level in tank B resulted in a dilution of the bath which limited the differences at the end of the tests).

The nickel concentration in tank B was about 83.5 g per litre at the end of the tests while in tank A it was about 75 g per litre.

The ratio of total iron to nickel plus iron after 2500 Ah was 6 + 0.5% in tank A while in tank B it was less than 20% and about 10% + 2.5% after 10 000 Ah and up to the end of the tests, while in tank B it was 38% after 2500 Ah, falling to about 20% with fluctuations of + 7.5%. The total acid consumption used to keep the pH of the bath constant during the test period was substantially the same in both tanks to within the measuring accuracy. Measurement of the density of the two baths in tanks A and B showed a more rapid increase in density in tank B (1206 in the case of tank A and 1212 in the case of tank B after 9 000 Ah, while the density of the initial bath in both tanks was 1170), thus confirming the greater nickel concentration increase in the case of tank B.

Other comparative tests carried out under conditions similar to those described above showed that sampling of the bath had to be more frequent in tank B (sampling of approximately 2 litres of solution out of 80 litres of bath and replacement by about 2 litres of water) to keep the bath density constant: Tanks with separate anodes: about 4 to 5 samplings per 10 000 Ah.

Tanks with granule anodes: about 2 to 3 samplings per 10 000 Ah.

The above examples show the advantage of using granules to facilitate operation of the bath and give deposits of the required composition.

These examples also show the difficulty of determining the proper anodic area ratio of the nickel baskets and of the iron baskets in the case of separate anodes.

It should be pointed out that other studies have shown that it is preferably for the oxygen, sulphur and copper contents not to exceed 0.03, 0.02 and 0.03% respectively.

Claims (25)

1. A process for electrodepositing a layer of ferro-nickel alloy using as a soluble anode a anodic basket filled with granules of ferro-nickel having a composition substantially identical to that of the layer which it is desired to deposit and such that the mass ratio of nickel plus cobalt to iron plus nickel cobalt is between 20 and 90%.

2. A process according to Claim 1, wherein said granules contain granulating adjuvants in a proportion of from 0 to 1% and impurities in a proportion of from 0 to 0.2%.

3. A process according to Claim 1, wherein the granulating adjuvants are selected from silicon, manganese, magnesium, aluminium and carbon.

4. A process according to any one of Claims 1 to 3, wherein said granules have a basaltic structure, the particle joints of which are fine.

5. A process according to any one of Claims 1 to 3, wherein said granules have an equiaxed structure, the particle joints of which are fine and the substructure of which is only slightly dendritic.

6. A process according to Claim 4 or 5, wherein the major particle dimension is between 1 and 15 mm.

7. A process according to any preceding Claim, wherein said granules can withstand a compression test which reduces the major diameter by at least one-third without disintegration.

8. A process according to any preceding Claim, wherein said granules can withstand a compression test of more than 5 tonnes without disintegration.

9. A process according to any one of Claims 1 to 7, wherein said granules can withstand a compression test of more than 2 tonnes without the first crack appearing.

10. A process according to any one of Claims 3 to 9, wherein said granules contain silicon and at least two other adjuvants selected from manganese, magnesium, aluminium and carbon in the following respective proportions: Silicon : from 0.02 to 0.5% Carbon : from 0.03 to 0.2% Magnesium : from 0.02 to 0.4% Manganese : from 0.01 to 0.1% Aluminium : from 0.01 to 0.1%.

11. A process according to Claim 10, wherein said granules are of a composition such that the mass ratio of nickel plus cobalt to iron plus nickel plus cobalt is between 20 and 50% and the sum of the adjuvants contained in the granules is between 0.1 and 1%.

1 2. A process according to Claim 10, wherein said granules are of a composition such that the mass ratio of nickel plus cobalt to iron plus nickel plus cobalt is between 50 and 70% and the sum of the adjuvants contained in the granules is between 0.1 and 1%.

1 3. A process according to Claim 10, wherein said granules are of a composition such that the mass ratio of nickel plus cobalt to iron plus nickel plus cobalt is between 70 and 90% and the sum of the adjuvants contained in the granules is between 0.1 to 1%.

14. A process according to any one of Claims 10 to 13, wherein the sum of the magnesium, manganese and aluminium contained in the granules with which the panodes are provided is at least 0.05%.

1 5. A process according to any one of Claims 10 to 14, wherein said granules contain silicon and at least two other adjuvants selected from manganese, magnesium, aluminium and carbon in the following respective proportions: Silicon : from 0.04 to 0.2% Carbon : from 0.03 to 0.1% Magnesium : from 0.02 to 0.1% Manganese : from 0.01 to 0.6% Aluminium : from 0.01 to 0.06%.

16. A process according to any one of Claims 10 to 15, wherein the sum of the adjuvants present in the granules is between 0.2 and 0.3%.

1 7. A process according to any one of Claims 10 to 16, wherein the sum of the magnesium, manganese and aluminium contained in said granules is between 0.07 and 0.2%.

1 8. A process according to any one of Claims 1 to 10 and 1 3 to 17, wherein said granules are of a composition such that the ratio of nickel plus cobalt to iron plus nickel plus cobalt is between 70 and 80% and the adjuvants in the granules are present in the following proportions: Silicon : from 0.04 to 0.1% Carbon : from 0.03 to 0.05% Magnesium : from 0.02 to 0.08% Manganese : traces Aluminium : traces.

19. A process according to any one of Claims 1 to 10, 12 and 14 to 17, wherein said granules are of a composition such that the ratio of nickel plus cobalt to iron plus nickel plus cobalt is between 50 and 70%, and silicon and at least two other adjuvants are present in the following respective proportions: Silicon : from 0.1 to 0.2% Carbon : from 0.03 to 0.1% Magnesium : from 0.03 to 0.08% Manganese : from 0.01 to 0.08% Aluminium : from 0.02 to 0.6%.

20. A process according to any one of Claims 1 to 19, wherein the chloride ion content in the electrolytic bath is between 10 and 40% g per litre.

21. A process according to any one of Claims 1 to 20, wherein the ratio between the sulphate ion and chloride ion concentrations expressed in g per litre is between 2.5 and 4.

22. A process according to Claim 1 and substantially as herein described.

23. A process for the electrodeposition of a ferro-nickel alloy substantially as herein described with reference to any one of the foregoing Examples.

24. An article plated by a process as claimed in any preceding Claim.

25. The features as herein described, or their equivalents, in any novel selection.