CA1043734A

CA1043734A - Method of electroplating gold and gold plating baths containing amido-polyphosphate

Info

Publication number: CA1043734A
Application number: CA224,943A
Authority: CA
Inventors: John M. Deuber; George R. Lurie
Original assignee: Oxy Metal Industries Corp
Current assignee: Oxy Metal Industries Corp
Priority date: 1974-04-19
Filing date: 1975-04-18
Publication date: 1978-12-05
Also published as: DE2516252C3; FR2268093B1; DE2516252A1; FR2268093A1; GB1506496A; CH606504A5; US3898137A; JPS50143734A; DE2516252B2; JPS5510672B2

Abstract

METHOD OF ELECTROPLATING GOLD AND GOLD
PLATING BATHS CONTAINING AMIDO-POLYPHOSPHATE
ABSTRACT OF THE DISCLOSURE

Disclosed is an aqueous composition suitable for plating gold deposits of improved brightness, and a method of plating therewith. An amido-polyphosphate compound is added to a plat-ing bath containing a gold complex, and the resulting deposits exhibit a substantial improvement in brightness. The visual quality of the deposits improves further by the additional in-clusion of a polyphosphate compound. Still further improve-ments may be obtained by the inclusion in a bath containing a gold cyanide complex of a small quantity of cobalt or nickel ion. In addition to improved brightness, the latter bath also exhibits improved hardness, an important characteristic for many applications.

Description

` S-1~,172 _ACI~GI~OUND ~F Tllr Nv~lrrI~N
This invcntion rclatcs to the art o~ platinc~ gold deposits.
More specifically, it relates to the electrodeposition of goId deposits exhibiting improved brightness.
Numerous platiny baths have been proposed for the electro-deposition of gold deposits. Foremost are those baths contain-ing the gold as a cyanide complex, and those containing gold as the sulfite complex. Pertinent to the cyanide baths are U.S.
Patent Nos. 2,905,601; 3,373,094; 2,765,269; 2,812,299; and RE. 25,883. The sulfite comp]ex baths are described for example in U.S. Patent Nos. 3,057,789 and 3,666,640.
The foregoing patents describe generally the parameters for plating using the gold complex compounds, and describe various brightening agents which may be included in the plating bathsO
Suggested brighteners include hydrazine and piperazine deriva-tives, as well as small quantities of arsenic, antimony, and selenium ions.
As generally practiced, the gold cyanide baths are adjusted to a pH of 3.5 or greater. The sulite baths are adjusted to a pH of ~rom 5.5 to 10.5 and often rely on the pres~nce o an amine compound in order to maintain stability at the lower pH's.
SUMMARY OF THE INVENTION
According to the present invention, an aqueous gold plating bath containing gold in the form of a complex is provided with a quantity o an amido-polyphosphate compound sufficient to im-prove the brightness of the deposits obtained by electroplating therewith. In a preferred embodiment, the aqueous plating solu-tion additionally contains at least l g/l of a polyphosphate compound. In the case of a cyanide complex bath, a further im-provement in bri:ghtness and an improvement of hardness in the deposit can be obtained by urther including at least 0.0l g/l of Gobalt or nickel ion.

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The invention relates to an aqueous gold electro-plating bath containing gold in an electrodepositable form ~ ;
adjusted to a pH suitable for plating. The bath includes an amido-polyphosphate compound differing from a normal poly~
phosphate compound in that one or more of the oxygen linkages between phosphorus atoms is replaced by an -NH-linkage in a .
sufficient quantity to effect a brighter deposit. . -~

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T~L'. I'~ILED D~.~CRIrTION OF T~IE INVENTION
I;l accordance with the state of the art, ~old plating solu-tions commonly contain between 1 and 100 g/l gold in the form of a complex. In order to minimiæe losses due to draqout, the concentration of gold is preferably maintained between 1 and 20 g/l. In the case of the sulfite complex, the gold is normally provided as an ammonium, amine, or alkali metal gold sulfite.
In the case of the cyanide complex, the gold is normally pro-vided in the form of an ammonium or alkali metal gold cyanide.
For solubility reasons, the potassium salts are the most pre-ferred. Common alloying metals may also be present in the solution.
The essential component of the plating baths of the pre-sent invention is an amido-polyphosphate compound. This com-pound differs from the normal polyphosphate compounds in thatone or more of the oxygen linkages between phosphorus atoms has been replaced by an -NH- linkage. As is the case with polyphosphate compounds, the amido-polyphosphates may be added either as the ammonium or alkali salts. Compounds of this type may be made in various ways, for example, by the reaction of dry ammonia with a phosphoric anhydride compound as described in U.S. Patent No. 2,122,122. These compounds may be made by reacting anhydrous ammonia with phosphorus p~ntoxide and heating the reaction mixture in the presence of excess anhy-drous ammonia at a temperature of at least about 150C. fora sufficient period of time to effect a molecular condensation with loss of ammonia from the product, forming a substantially neutral product in which 'he atomic ratio of nitrogen to phos-phorus is less than 1.5 to 1. The amido-polyphosphates have ' ' .:: . ` , , ` . `: ` .
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S-10,172 ~ P2O5 equivalent phosphorus content o~ ~rom 65 to 80Q by weight-and an NH3 equivalent amide nitrogen content of from about 5 to 12% by weight. Where thP ammonium salt is employed, the NH3 equivalent ammonium nitrogen content should be from about 8 to 22% by weight. One commercially available ammonium salt of an amido-polyphosphate is sold by the Stauffer Chemical Company under the trademar~ "Victamide". The product contains approxi-mately 76~ P2Os equi~alent phosphorus, 7% NH3 e~uivalent amide nitrogen, and 15.4% NH3 e~uivalent ammonium. The compound ex-hibits an average phosphorus content of about 4 to 5 atoms per molecule.
The precise concentration of the amido-polyphosphate - compound in tha gold plating solution depends to some extent on the nature and concentrations of the other components pre-sent. It appears, however, that at least 1 g/l is necessary to obtain any appreciable effect and a quantity in excess of 100 g/l does not provide any further improvement in brightness.
In general, sufficient brightening effect can be obtained by employing quantities between 5 and 40 g/l.
In a preferred embodiment of this invention, it has -been found desirable to include a polyphosphate compound in the solution as well. The amido-polyphosphata and the poly-phosphate apparently co-act in some matter to further enhance the brightness of the dep~sit. When it is desired to nclude the polyphosphate compound in the soiution, at least 1 g/l should be included in order to obtain beneficial effects. Ex-amples of suitable compounds include the ammonium and alkali metal salts of the pyrophosphate, tripolyphosphate, and tetra-.. ~ . .. . .. .

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metapolyphosphate anions. Quantities in excess of 20 g/l are preferred.
When the platin~ solution contains the gold cyanide complex in the acid pH range, a still further preferred emhodi-ment is the inclusion of a small ~uantity of cobalt or nickel in depositable form. While addition of the amido-polyphosphate and the polyphosphate compound improve the brightness of the deposit, the final inclusion of cobalt and nickel ion brings the deposit to full brightness. The inclusion of cobalt or nickel is thus preferred wherever brightness is of extreme im-portance as in the case of jewelry manufacture. As demonstrated in the examples, the inclusion of cobalt and nickel has the ad-ditional advantage of improving the hardness of the gold deposit.
The precise concentration of cobalt and nickel ions re-quired in order to obtain the foreoging advantages depends upon the concentration of the other components of the solution. Since it is desirable to minimize the amount of cobalt or nickel in the final deposit, it is, of course, desirable to include no more co~alt in the solution than is necessary to obtain the desired brightness. The minimum cobalt concentration required appears to vary in proportion to the concentration of the amido~
polyphosphate compound in the solution. Cobalt concentrations of 100 mg/l and less have been found effective, whereas amounts as high as 1.1 g/l have also been found effective without in-2S creasing the cobalt content of the deposit beyond 0.5%.
In order to simplify reporting in the following examples, -a numerical scale ha~ been adopted in order to describe the de-gree of brightness exhibited by a gold deposit:

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' ' 3'7 5 10,172 1. Bright --- Details of a reflected imagQ
are distinct.

2. Semi-bright --- A reflected imag2 is visible, though hazy.

3. Lustrous --- The deposit exhibits a low~level reflectance, although details of an image are not visible.

4. Dull, smooth yellow --- The deposit appears smooth, although there is no ordered light reflection.

5. Dull, yellow --- The deposit exhibits no light reflection and gives a matte appear-ance.

6. Brownish-yellow --- The deposit has lost its-normal yellow color and gives a matte appear-ance.

7. Dull, dark brown --- The deposit is dark brown and gives a matte appearance~

EXAMPLE
, A ~old plating bath was prepared as follows:

COMPONENT G/L
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Au as Na3~Au(so3)2] 8 ~a25O3 3Q
Ammonium amido-poly- 25 phosphate NaOH to p~ 9.0 Plating on cathodic brass panel~ was performed at approximately 120F. and 3 ASF with perî~dic replenishment for a period of 6~1/2 hours. Deposits oh~ained exhibitad an average visual rating of 2. Where th~ same bath was em-ployed without the amido-polyphosphate, ~e visual rating of : ~ -the deposit was 4.

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. E~AMPLE II
A gold plating bath was prepared as follOW5:

COMPONENT G/L
Au as KAu(CN)2 8 K2HPO~ 60 Ammonium amido-poly- 20 phosphate H3PO4 to pH 7.0 Plating on cathodic brass panels at approximately 120F.
to 1~0F. and 3 ASF with periodic replenishment for a period of i-l/2 days. Deposits obtained exhibited an average visual rat-ing of 4O When the same bath was employed without the amido-polyphosphate the visual rating of the deposit was 5.

EXA~PLE III
15. A gold plating bath was prepared as follows:

COMPONENT G/L
Au as Na3[Au(So3)2] 8 Na2S03 . 10 Ammonium amido-poly 20 phosphate Na4P27 30 .
NaOH to pH 8.5 Plating was performed on cathodic brass panels at approx~mately 120F. and 3 ASF with periodic replenishment for a period of over two days. Deposits obtained exhibited an average visual rating of 1. The use of the pyrophosphate improves the visual quality as compared to the system con-taining neither the amido-polyphosphate nor the pyrophosphate - 6 - :

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- (k ratin~3) ~nd as co;n~ared to the system containing onl~ the amido-polyphosphate (2 rating) in E`xample I. Identical re-sults were obtained where Na5P301o and Na4P40~2 were substi-tuted for the sodium pyrophosphate. An additional advantage is that t~e pyrophosphate permits one to maintain the bright-ening effect for a longer period of time and buffers the solu-tion to impart stability.

EXAMPLE IV
A gold plating bath was prepared as follows:

COMPONENT G~L
K4P~07 100 Ammonium amido-poly- 10 phosphate Au as KAu(CN)2 8 Co as CoS0~7H20 0.1 H3P04 to pH 4.0 Plating was performed on cathodic brass panels at ap-proximately 100F. and 10 ASF. The deposit exhibited a visual rating of 1 compound tc a rating of 4 without the cobalt. As the amido-polyphosphate concentration was increased, the con-centration of cobalt required to produce a 1 rating gradually increased. At an amido-polyphosphate content of 100 g/l the cobalt concentration required to obtain a 1 rating was. in ex-cess of 0.5 g/l, although lesser quantities did improve the brightness to some extent. An analysis of the deposits obtain-ed indicated a cobalt content not exceeding 0.5%. Similar re-sults were obtained when nickel as NiS04-6H20 was used in place of the cobalt.

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EXAMPLE V
A bath was prepared in ~xample 4 hut containing 25 g/l amido-polyphosphate and 0.35 g/l cobalt. Plating was performed under the conditions of the prior example and deposits exhibit-ing a visual rating of 1 and containing from 0.2 to 0.3~ cobalt were obtained. The Knoop hardness of these deposits was in the range of 147-159. Without the inclusion of cobalt, hard-ness values ranged from 60 to 90.

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Claims

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

1. In an aqueous gold electroplating bath containing gold in an electrodepositable form adjusted to a pH suitable for plating, the improvement comprising including an amido-polyphosphate compound differing from a normal polyphosphate compound in that one or more of the oxygen linkages between phosphorus atoms is replaced by an -NH-linkage in a sufficient quantity to effect a brighter deposit.

2. The bath of claim 1 wherein said amido-polyphosphate compound has a P2O5 equivalent phosphorus content of from about 65 to 80 weight percent, and an NH3 equivalent amide nitrogen content of from about 5 to 12 weight percent.

3. The bath of claim 2 wherein said amido-polyphosphate is an ammonium salt.

4. The bath of claim 3 wherein said amido-polyphosphate compound has an NH3 equivalent ammonium nitrogen content of from about 8 to 22 weight percent.

5. The bath of claim 1 additionally containing at least 1 g/l of normal polyphosphate compound.

6. The bath of claim 1 wherein said amido-polyphosphate compound is present in a concentration of from 1 to 100 g/l.

7. The bath of claim 1 wherein said gold is present in the form of a gold cyanide complex, the pH of the bath is maintained at a value of at least 3.5, and the bath contains at least 0.01 g/l of a metal selected from the group consisting of cobalt and nickel in co-depositable form.

8. The bath of claim 1 wherein said gold is present in the form of a gold sulfite complex and the pH of the bath is maintained at a value of from 5.5 to 10.5.

9. A method of electroplating a gold layer on a metallic article comprising electrolyzing with said article as cathode an aqueous gold electroplating solution containing gold in an electrodepositable form adjusted to a pH suitable for plating, said solution including an amido-polyphosphate compound differ-ing from a normal polyphosphate compound in that one or more of the oxygen linkages between phosphorus atoms is replaced by an -NH-linkage in a sufficient quantity to effect a brighter deposit.

10. In an aqueous gold electroplating bath containing gold in an electrodepositable form adjusted to a pH suitable for plating, the improvement comprising including an amido-poly-phosphate compound obtained by reacting anhydrous ammonia with phosphorus pentoxide and heating the reaction mixture in the presence of excess anhydrous ammonia at a temperature of at least about 150°C. for a sufficient period of time to effect a molecular condensation with loss of ammonia from the product, forming a substantially neutral product in which the atomic ratio of nitrogen to phosphorus is less than 1.5 to 1 in a quantity sufficient to effect a brighter deposit.

11. The bath of claim 10 wherein said amido-polyphosphate compound has a P2O5 equivalent phosphorus content of from about 65 to 80 weight percent, and a NH3 equivalent amide nitrogen content of from about 5 to 12 weight percent.

12. The bath of claim 11 wherein said amido-polyphosphate is an ammonium salt.

13. The bath of claim 10 additionally containing at least 1 g/l of a normal polyphosphate compound.

14. The bath of claim 10 wherein said amido-polyphosphate compound is present in a concentration of from 1 to 100 g/l.

15. The bath of claim 10 wherein said gold is present in the form of a gold cyanide complex, the pH of the bath is maintained at a value of at least 3.5, and the bath contains at least 0.01 g/l of a metal selected from the group consist-ing of cobalt and nickel in codepositable form.

16. The bath of claim 10 wherein said gold is present in the form of a gold sulfite complex and the pH of the bath is maintained at a value of from 5.5 to 10.5.