IE41859B1

IE41859B1 - Improvements in or relating to the electrodeposition of gold

Info

Publication number: IE41859B1
Application number: IE2018/75A
Authority: IE
Original assignee: Schering Ag
Priority date: 1974-09-20
Filing date: 1975-09-16
Publication date: 1980-04-09
Also published as: YU36050B; ZA755978B; IT1042698B; FR2285473B1; FR2285473A1; YU106175A; AT335813B; HU172424B; IE41859L; JPS5147539A; RO69581A; CH614240A5; DD118124A5; ES438407A1; SE408436B; CA1053174A; AR206828A1; DE2445537A1; SE7510455L; SU923375A3

Abstract

The bath is free of cyanide and contains the gold in the form of a thiosulphato complex. In this bath, gold is electrodeposited as a levelling, non-porous layer at pH values between 4 and 13 and at temperatures between 10 and 80 DEG C with a current between 0.1 and 2 A/dm<2> onto a suitable substrate.

Description

This invention relates to the electrodeposition of gold in cyanide-free baths.

Alkaline cyanidic baths for electrogilding are known.

They are distinguished by their excellent stability and robustness, and are frequently used. However, their disadvantage lies in the extraordinary toxicity of the cyanides contained therein, as a result of which they pose a health hazard to those working with them and the disposal of their waste liquors gives rise to technical TO problems.

Neutral gold electrolytes that contain an aurocyanide, trivalent arsenic and, as sulphur donor, an alkali metal thiosulphate, are also known (German Offenlegungsschrift 20 10 725). However, these electrolytes also contain cyanide and have the further disadvantage of being neither gloss-forming nor gloss-maintaining, and having no levelling effect. .

Finally, cyanide-free gold baths that contain gold in the form of sulphite, and gloss-increasing additives, have been proposed (German Offenlegungsschrift 16 21 180).

However, such gold sulphito-complexes are not sufficiently stable, and when the solution stands for a long time elementary gold is formed, even with a very large excess -241859 of free sulphite ions, with the result that the solution becomes unusable.

Patent Specification tto. described and claims a process for the electro5 deposition of a noble metal alloy, wherein the electric current is passed through an electrodeposition bath free from cyanide ions and containing the noble metal in the form of a thiosulphato-complex.

The present invention provides a process for the electro10 deposition of gold, wherein the electric current is passed through an electrodeposition bath free from cyanide ions and containing the gold in the form of a, thiosulphatocomplex. The bath may contain one or more conventional additives, e.g. reducing agents, buffers and conductive salts.

The present invention also provides a bath for the electrodeposition of gold, wherein the bath is free from cyanide ions and contains the gold in the form of a thiosulphato-complex, and contains a reducing agent,·buffer or conductive salt or two or more such additives.

This bath is generally stable and substantially overcomes the disadvantages of the known gold baths. Thus, it is -341859 generally possible by a relatively non-toxic electrodeposition process to obtain gold deposits having good technological and decorative properties and at the same time, a high degree of puri ty.

As such gold thiosulphato-complexes there are to be understood complexes of variable composition containing gold as the central atom and at least one thiosulphate ligand. The approximate composition of these complexes may correspond to the formula 10 M3-12 Bu1 -2^S2°3^2-7j ’ in which M represents one equivalent of a metal, for example a sodium atom. These gold thiosulphato-complexes are known and may be made by methods in themselves known.

Sodium dithiosulphato-aurate (1) (Na3 {au(S2O3)^J .2H20) may be made, for example, by the reduction of sodium tetrachloroaurate (III) in neutral aqueous solution with thiosulphate, and. precipitation of the resulting complex with alcohol. -441859 In a similar manner, the compound sodium heptathiosulphatodiaurate (I) may be made and isolated from aqueous solution.

The gold thiosulphato-complexes to be used in accordance with the invention generally dissolve well in water. The concentration of gold in the bath of the invention may advantageously be from 0.1 gram of gold per litre up to saturation, and preferably from 3 grams to 30 grams of gold per litre.

The gold thiosulphato-complexes may be added performed to the bath or may bq produced in the bath itself.

{ The present invention further provides a mixture of compounds suitable for making up a bath free from cyanide ions for the electrodeposition of gold, which comprises a gold thiosulphato-complex or its precursors and one or more ingredients selected from reducing agents, buffers and conductive salts.

Advantageously, the electrodeposition bath or mixture for its preparation may contain an excess of thiosulphate, for example in a ratio by weight of metal: thiosulphate of -541859 of up to 1:20. The concentration of thiosulphate in the bath solution is advantageously at least 1 g/1 and preferably 20 to 500 g/1.

As thiosulphate there is to be understood the ammonium 5 and/or alkali metal salts, preferably the sodium or potassium salts, of thiosulphuric acid or their adducts with basic compounds such, for example, as amines or polyamines.

Where the mixture of compounds for making up the bath con10 tains excess thiosulphate, the mixture may include cyanide-containing salts, provided the thiosulphate is sufficient to convert the cyanide into the less.toxic thiocyanate in the bath.

As the anodic solubility of gold in thiosulphate solutions is poor, insoluble anodes, for example, platinised titanium, should generally be used and, if desired, reducing agents, for example nitrites, oxalates or sulphites, preferably the alkali metal salts, for example the sodium or potassium salts, may be added -to1 the bath.

The bath may also contain one or more conductive salts, e.g. ammonium or alkali metal salts of inorganic or weak organic acids such, for example, as sulphuric acid, sul-641859 phurous acid, carbonic acid, boric acid, sulphamic acid, acetic acid and citric acid. The bath may also contain substances that regulate the pH-value, advantageously the usual organic and/or inorganic buffer mixtures such, for example, as disodium phosphate, alkali metal carbonate, alkali metal borate, alkali metal acetate or citrate, alkali metal metabisulphite or a mixture of boric acid and ethylene glycol.

The pH-value of the bath may be in the range of from 4 to 13, and preferably 5 to 11. It is advantageous to work at a temperature in the range of from 10 to 80°C, preferably 20 to 55°C, and at a cathodic current density of from 0.1 to 2 amperes per dm .

The bath of the invention may be used in a manner in itself known.

The gold coatings deposited from the bath of the invention are generally highly glossy and show outstanding ductility in thick coatings. Furthermore, the bath also has a levelling effect even from 3 pm, and is suitable for the deposition of both thin and thick gold layers. By using low cathodic current densities, for example, 0.1 - 0.5 ρ amperes per dm , highly pure gold coatings of excellent electrical conductivity may be obtained. When carrying out electrolysis at 0.4 - 1.2 amperes per dm , gold coatings of -741889 high hardness (120-160 Vickers) coupled with good resistance to abrasion are obtained. Finally, the bath of the invention.has the special advantage of a cyanidefree and thus relatively non-toxic method of operation, whereby a reduction in health risks and a decrease in expenditure in disposing of waste liquors are achieved.

The following Examples illustr case an aqueous bath was used.

Example Bath composition: Gold in the form of sodium Sodium thiosulphate Na2S203 . 5H20: Sodium sulphite Na2S03: Sodium borate Na4B40? . lOHgO: Operating conditions: pH-value (adjusted with Temperature: te the invention. In each dithiosulphato-aurate (I) 0.04 molar =7.9 gm of gold/ 1itre. 0.5 molar = 119 gm/litre. 0.06 molar = 7.6 gm/litre. 0.015 molar = 6.4 gm/litre.

NaOH): 9.0 25°C. -841859 Stirring the electrolyte and cathode movement.

? Cathodic Current density: 0.1 to 1.5 A/dm Anode platinised titanium.

A carefully defatted watch lunette of lead-containing 5 brass was immersed in the above solution and electrolysed for about 20 minutes under the above operating conditions. A 6 to 7 pm thick glossy gold layer free from pores was deposited therein.

EXAMPLE 2 10 Bath composition: Gold in the form ^a12 ^υ2^2θ3' of sodium heptathiosulphato-diaurate (I .10H20: 0.04 molar = 15.7 gm of go!d/1i tre. 15 Potassium thiosulphate KgSgOg: 0.8 molar = 240 gm/litre. Sodium sulphite Na2$03: 0.1 molar = 12.6 gm/litre. Boric acid B(OH)3: 0.3 molar = 18.6 gm/litre. 20 Ethylene glycol -941859 H0-CH2-CH2-0H: 0.6 molar = 37.2 gm/litre.

Operating conditions: pH-value: Temperature: Anode: Cathodic Current density: 6.8 23°C platinised titanium 0.3 to 1.5 A/dm^ A Scratched copper plate having an area of about 1 dm was gilded in the above electrolyte under the above operating conditions for 15 minutes. The fine grooves caused by the scratching were distinctly levelled out.

Example 3 Bath composition: Gold in the form of sodium dithiosulphato-aurate (I) Na^Jau(S203)^ .2H20: 0.05 molar=10gm/litre Sodium thiosulphate Na2S203.5H20: 0.5 molar=119 gm/litre Sodium sulphite Na2S03: 0.05 molar=6.3 gm/litre Potassium dihydrogen phosphate -1041859 ΚΗ2Ρ04: 0.02 molar=2.7 gm/litre Potassium metabisulphite K2S2°5: 0.05 molar=ll.l gm/litre.

Operating conditions: pH-value: 6.9 Temperature: 20°C Anode: carbon Cathodic Current density : 0.1 to 1.2 A/dm A printed circuit having a total area of about 0.7 dm was gilded in this solution under the above conditions for 6 minutes. The gold coating about 2.5 pm thick was pore-free and could be soldered extremely well.

Example 4 Bath composition: Gold in the form of sodium dithiosulphato-aurate (I) Na3 Jau(S203)^ .2H20: 0.05 molar=9.85 gm/litre Sodium thiosulphate Na2S2°3: 1.0 molar=156 gm/litre Sodium sulphite -1141859 Na2S03: 0.1 molar=12,6 gm/litre Potassium metabisulphite K2S2°5: 0.01 molar= 2.2 gm/litre Boric acid B(0H)3: 0.3 molar=18.6 gm/litre Ethylene glycol .H0-CHZ-CHZ-OH: 0,6 molar=37.2 gm/litre Operating conditions: pH-value Temperature Anode: 6.5 22°C. platinised titanium. o Diode leads having a total surface area of 1 m were gilded in a drum at an average cathodic current density of 0.1 A/dm under the above conditions. The 2 pm thick coatings were pore-free and could be soldered well even after a long storage period of a few months.

Claims

1. A process for the electrodeposition of gold, wherein -1241859 the electric current is passed through an electrodeposition bath free from cyanide ions and containing the gold in the form of a thiosulphato-complex.

2. A process as claimed in claim 1, wherein the concentration 5 of the gold in the bath is from 0.1 g/1 to saturation.

3. A process as claimed in claim 2, wherein the concentration of gold is from 3 to 30 g/1.

4. A process as claimed in any one of claims 1 to 3, wherein the bath contains excess thiosulphate. 10 5. A process as claimed in claim 4, wherein the concentration of thiosulphate in the bath is at least 1 g/1. 6. A process as claimed in claim 5, wherein the concentration of thiosulphate is from 20 to 500 g/1. 7. A process as claimed in any one of claims 4 to 6, 15 wherein the thiosulphate is present in the form of ammonium thiosulphate or an alkali metal thiosulphate. 8. A process as claimed in claim 7, wherein the alkali metal thiosulphate is sodium or potassium thiosulphate. 9. A process as claimed in any one of claims 1 to 8, -1341859 wherein the bath contains a reducing agent. 10. A process as claimed in claim 9, wherein the reducing agent is an alkali metal nitrite, oxalate or sulphite.

5. 11. A process as claimed in any one of claims 1 to

6. 10, wherein the bath contains a conductive salt.

7. 12. A process as claimed in any one of claims 1 to 11, wherein the bath contains a buffer.

8. 13. A process as claimed in claim 12, wherein the pH of 10 the bath is in the range of from 4 to 13.

9. 14. A process as claimed in claim 13, wherein the pH is in the range of from 5 to 11.

10. 15. A process as claimed in any one of claims 1 to 14, wherein the electrodeposition is carried out at a temperature 15 in the range of from 10 to 80°C.

11. 16. A process as claimed in claim 15, wherein the temperature is in the range of from 20 to 55°C.

12. 17. A process as claimed in any one of claims 1 to 16, ό wherein a cathodic current density of from 0.1 to 2 A/dm -1441859 is used.

13. 18. A process as claimed in any one of claims 1 to 17, wherein a platinised titanium anode is used.

14. 19. A process as claimed in any one of claims 1 to 5 18, wherein the gold thiosulphato-complex has the formula M 3-12 C AU 1 -2 S 2°3)2-7^ 3 in which M represents one equivalent of a metal.

15. 20. A process as claimed in any one of claims 1 to 19, wherein the gold thiosulphato-complex is prepared in the 10 electrodeposition bath.

16. 21. A process as claimed in claim 1, carried out substantially as described in any one of the Examples 1 to 4 herein.

17. 22. A substrate having a gold coating produced by a 15 process as claimed in any one of claims 1 to 21.

18. 23. A bath for the electrodeposition of gold, wherein the bath is free from cyanide ions and contains the gold in the form of a thiosulphato-complex, and contains a reducing agent, buffer or conductive salt or two or more 20 such additives. -1541859

19. 24. A bath as claimed in claim 24, wherein the concentration of gold is from 0.1 g/1 to saturation.

20. 25. A bath as claimed in claim 24, wherein the concentration of gold is from 3 to 30 g/l. 5

21. 26. A bath as claimed in any one of claims 23 to 25, which contains excess thiosulphate. »

22. 27. A bath as claimed in claim 26» wherein the concentration of thiosulphate is at least 1 g/1.

23. 28. A bath as claimed in claim 27, wherein the 10 concentration of thiosulphate is from 20 to 500 g/1.

24. 29. A bath as claimed in any one of claims 26 to 28, wherein the thiosulphate is present in the form of ammonium thiosulphate or an alkali metal thiosulphate.

25. 30. A bath as claimed in claim 29, wherein the alkal 15 metal thiosulphate is sodium or potassium thiosulphate.

26. 31. A bath as claimed in any one of claims 23 to 30, which contains a reducing agent.

27. 32. A bath as claimed in claim 31, wherein the reducing agent is an alkali metal nitrite, oxalate -1641859 or sulphite.

28. 33. A bath as claimed in any one of claims 23 to 32, which contains a conductive salt.

29. 34. A bath as claimed in any one of claims 23 to 33, 5 which contains a buffer.

30. 35. A bath as claimed in claim 34, wherein the pH is in the range of from 4 to 13.

31. 36. A bath as claimed in claim 35, wherein the pH is in the range of from 5 to 11. 10

32. 37. A bath as claimed in any one of claims 23 to 36, wherein the gold thiosulphato-complex has the formula M 3-12 β υ 1 -2^ S 2°3)2-7~j ’ in which M represents one equivalent of a metal.

33. 38. A bath as claimed in claim 23, substantially as 15 described in any one of the Examples 1 to 4 herein.

34. 39. A mixture of compounds suitable for making up a bath free from cyanide ions for the electrodeposition of gold, which comprises a gold thiosulphato-complex or its -17418S9 precursors and one or more ingredients selected from reducing agents, buffers or conductive salts.

35. 40. A mixture as claimed in claim 39, which contains excess thiosulphate. 5

36. 41. A mixture as claimed in claim 40, which contains ammonium thiosulphate or an alkali metal thiosulphate.

37. 42. A mixture as claimed in claim 41, wherein the alkali metal thiosulphate is sodium or potassium thiosulphate.

38. 43. A mixture as claimed in any one of claims 39 to 10 42, which contains a reducing agent.

39. 44. A mixture as claimed in claim 43, wherein the reducing agent is an alkali metal nitrite, oxalate or sulphite.

40. 45. A mixture as claimed in any one of claims 39 to 44, 15 which contains a conductive salt.

41. 46. A mixture as claimed in any one of claims 39 to 45 which contains a buffer,

42. 47. A mixture as claimed in any one of claims 39 to 46 -1841859 wherein the gold thiosulphato-complex has the formula M 3-l2 f Au l-2( S 2°32-7] ’ in which M represent one equivalent of a metal.

43. 48. A mixture as claimed in claim 39, substantially as 5 described in any one of the Examples 1 to 4 herein.