US3156635A

US3156635A - Gold plating

Info

Publication number: US3156635A
Application number: US133301A
Authority: US
Inventors: Foulke Donald Gardner
Original assignee: Sel Rex Corp
Current assignee: Occidental Chemical Corp; Sel Rex Corp
Priority date: 1961-08-23
Filing date: 1961-08-23
Publication date: 1964-11-10
Anticipated expiration: 1981-11-10
Also published as: GB928087A; BE620596A; CH399863A; DE1215467B

Description

United States Patent 3,156,635 GOLD PLATING Donald Gardner Foullre, Watchung, Piainfield, N.J., assignor to Sci-Rex Corporation, Nutley, N.J., a corporation of New Jersey N0 Drawing. Filed Aug. 23, 1%1, Ser. No. 133,301 Claims. (Cl. 20446) This invention is concerned with the deposition of gold and specifically with the deposition of gold from a bath relatively free of organic compounds, resulting in minimum codeposition of organic materials with the gold.

From the early beginning of gold plating until very recently gold plating has been done from a cyanide electrolyte almost exclusively. Some plating was done from the acid trivalent gold complex, HAuCl but this solution is highly corrosive and not at all suitable for production work. More recently gold has been plated from a bath on the acid side of the pH range, pH 3.5-6.0, to which was added considerable amounts of organic acids and their salts. Although this formulation circumvented the ageold problem of eliminating the build-up of undesirable cyanide decomposition products characteristic of the conventional hot cyanide gold baths, obviously considerable organic material is present in the solution, some of which may co-deposit with the gold.

This invention is based on the discovery that it is possible to obtain 24-carat gold deposits essentially free of organic inclusions by employing a gold bath containing potassium gold cyanide and conducting salts consisting of phosphates or phosphites adjusted to a pH of 36. Gold deposition from such solutions proceeds at an efficiency of less than 100 percent resulting in some loss of hydrogen with the result that the phosphorous acidphosphite solution is somewhat more suitable from a buffer standpoint. Polyphosphoric acids may also be used although they gradually convert to orthophosphate.

The deposits obtained from this solution are not bright, being yellow matte to semi-bright, but they are smooth and of high purity.

An object of this invention, therefore, is to provide an acid gold plating bath which is low in organic material so that there is little tendency to codeposit organic compounds with gold.

A second object of this invention is to provide a gold plating bath which is low in cyanide, thereby minimizing the tendency to build up a concentration of cyanide break-down products in the bath. Obviously, some alkali cyanide will develop in the bath over a period of time, but at a pH of 36 the concentration is maintained at a low value. However, I have found that the introduction of hydrazine or substituted hydrazines tends to prevent this cyanide build-up and to provide improved electrodeposits.

The hydrazine compounds which may be employed are comprised of the water soluble hydrazine salts which is the sulfate, N H .H SO the hydrochloride, N H .2HCl, etc., the water soluble organic hydrazine, hydrazono, and hydrazo compounds, etc. Approximately /2 to 20 g./l. of the hydrazine or hydrazine compound are satisfactory in preventing the build-up of cyanide products.

The gold content of the bath is not very critical but very satisfactory deposits are obtained with from 4 to 36 g./l. of soluble gold salt.

3,156,635 Patented Nov. 10, 1964 ice The phosphate or phosphite anions are present in the bath in the proportion of about 5 to 200 g./l. The phosphate and phosphate anions, may be added to the bath as acids in which case, the pH is adjusted to the range of 36 by the addition of alkali.

Examples of the method of carrying out this invention are as follows:

Example 1 A bath of the following composition was prepared:

KAu(CN) 12 KH PQ, 30

dm. The efficiency was 120 mg./ amp minute.

Example 2 A bath was made up as follows:

KAu(CN) g./l 12 Phosphorous acid (30%) ml 200 KOH to pH=3.5.

Brass panels plated in this bath were similar in appearance to those obtained from the phosphoric acid phosphate bath. The addition of methyl hydrazine in one case and dimethyl hydrazine in another case gave brighter deposits. Potassium phosphite could be substituted for the equivalent amount of KOH and phosphorous acid to make this bath.

Example 3 A bath was made up according to Example 1, except that only 2 g./l. of gold (as sodium gold cyanide) were added. Satisfactory deposits were obtained up to 0.6 amp/dm. Increasing the phosphate content to 200 g./l. had no observable effect on the deposit, but the voltage drop across the cell was lowered.

Example 4 A bath was prepared as follows:

G./l. KAu(CN) 12 Polyphosphoric acid KOH to pH=3.5.

Deposits similar to those in Examples 1 and 2 were obtained, except the deposits were brighter. Increasing the gold to 24 g./l. extended the permissible current density range upwards, at a pH of 6.0 the deposits continued to be ductile and were somewhat brighter.

The features and principles underlying the invention described above in connection with specific exemplifications will suggest to those skilled in the art many other modifications thereof. It is accordingly desired that the appended claims shall not be limited to any specific feature or details thereof.

I claim:

1. The method of electrodepositing gold which coma prises electrolyzing an aqueous solution containing an alkali metal gold cyanide in the amount of 4 g./l. to 36 g./l., a nitrogen compound selected from the group consisting of hydrazine, water soluble substituted hydrazine compounds and salts of hydrazine, and a combination of acidic anions selected from the group consisting of phosphoric, phosphorous and polyphosphoric acid anions and sufiicient alkali to give a pH of 3.0-6.0.

2. The process as claimed in claim 1 in which the acid anion is phOSphate anion and is present in the proportion of about 5 to 200 g./l.

3. The process as claimed in claim 1 in which the acid anion is phosphite anion and is present in the proportion of about 5 to 200 g./l.

4. A plating solution for plating approximately 24k 15 selected from the group consisting of phosphoric, phosphorous and polyphosphoric acid anions,

sufficient alkali to provide a pH of 3 to 6 and an amount up to about 20 g./l. of a hydrazine compound selected from the group consisting of hydrazine, hydrazine salts and Water soluble substitution products of hydrazine. 5. A plating solution as claimed in claim 4 comprising 1 to 10 g./l. of hydrazine sulfate.

References Cited in the file of this patent UNITED STATES PATENTS 2,176,668 Egeberg et a1 Oct. 17, 1939 2,654,702 De Long Oct. 6, 1953 2,812,299 Volk Nov, 5, 1957 2,978,390 Atwater et al Apr. 4, 1961

Claims

1. THE METHOD OF ELECTRODEPOSITING GOLD WHICH COMPRISES ELECTROLYZING AN AQUEOUS SOLUTION CONTAINING AN ALKALI METRAL GOLD CYANIDE IN THE AMOUNT OF 4 G/1 TO 36 G./L., A NITROGEN COMPOUND SELECTED FROM THE GROUP CONSISTING OF HYDRAZINE, WATER SOLUBLE SUBSITUTED HYDRAZINE COMPOUNDS AND SALTS OF HYDRAZINE, AND A COMBINATION OF ACIDIC ANIONS SELECTED FROM THE GROUP CONSISTING OF PHOSPHORIC, PHOSPHOROUS AND POLYPHOSPHORIC ACID ANIONS AND SUFFICIENT ALKALI TO GIVE A PH OF 3.0-6.0