US3092559A - Gold plating - Google Patents

Description

United States Patent 3,092,559 GOLD PLATING Donald Gardner Foulke, Watchung, and Edwin Cornell Rmker, Morristown, N..i., assiguors to Sel-Rex Corpoi-anon, Nutley, N.J., a corporation of New Jersey No Drawing. Filed May 1, 1961, Ser. No. 106,541 9 Claims. (Cl. 204-43) This invention relates to gold plating and more particularly to the deposition of bright, relatively low-carat deposits.

Although there are a number of processes for the deposition of bright 24-carat gold and near-24-carat gold deposits, processes are not available for the deposition of bright lower carat electroplates. The obvious advantage of a low-carat deposit is the reduced cost of the deposit per unit of thickness, with the electroplate still retaining the corrosion and tarnish resistance of gold alloys as well as the color to a considerable extent.

One method for providing bright gold deposits was described by Rinker (US. Reissue No. 24,582). However, when the amount of silver in the deposit exceeds about two percent the deposits become greenish in color and are lacking in attractiveness.

Among the objects of this invention is to provide a composition and process for obtaining bright deposits of about 14 to about 23.5 carat gold with improved color.

This invention is based on the discovery that the addi tion of a small amount of an alkali soluble titanium compound to an alkali cyanide gold plating bath containing silver not only leads to an extended bright range and more brilliant deposits, but the addition of this addition agent also leads to deposits less green in color than those obtained from baths containing larger quantities of silver than as described under said US. Reissue Patent No. 24,582. Exceptionally brilliant gold-silver alloy deposits are obtained when the titanium compound is added in conjunction with a small amount of an alkali-soluble selenium compound.

This invention is carried out most advantageously by employing a typical cyanide gold plating solution containing 4-32 g./l. of gold, 10 to 200 grams per liter of alkali cyanide, and 0.1 to 12 g./l. of potassium silver cyanide. The prefer-red composition and limiting concentrations are shown in Table 1 (below) from which it is obvious that a wide range for each constituent is possible. Obviously, the ratio of silver to gold in the deposit will vary considerably dependent upon the AuzAg ratio in the bath, but wide variations can be accomplished by manipulation of the brightener content due to varying effects upon the polarization curves for gold and silver. Most striking is the development of low carat deposits going from gold to white with little evidence of the green color common to low-carat, gold-silver alloys.

Any titanium compound soluble in the bath may be employed, but particularly satisfactory results have been obtained by adding titanium coordination compounds having at least one ligand selected from the class consisting of polyols and alkanolamines, since these compounds are unusually stable for titanium salts in aqueous solution. The aminoalcohol titanates which may be employed in the practice of the present invention include the titanate esters of aminoalcohols which have the formula,

wherein R is selected from the group consisting of ethylone and alkyl substituted ethylene radicals and R and R" are selected from the group consisting of hydrogen, alkyl hydrocarbon groups, B-amino-alkyl and B-hydroxy alkyl "ice radicals. These aminoa-lcohol esters are stabilized in solution by the addition to said ester of a compound selected from the group consisting of inositol, sucrose and the more or less related saturated and/ or unsaturated straight chain aliphatic alcohols and monocarboxylic acid derivatives thereof containing 3 to 7 carbon atoms and 3 to 6 hydroxy groups such as gluconic, sorbic, aconitic, glucoheptonie acids and the alkali salts thereof. The mechanism of the stabilization may involve the formation of a coordination compound between the aminoalcohol titanates and the polyhydroxy compounds. The exact structure is not known, but in general the greater the number of hydroxy groups, the more efilective is the compound as a stabilizer.

Aminoalcohol titanates, per se, are disclosed in US. Patent No. 2,894,966 but the following Examples A-C illustrate specific methods of producing such titanium compounds.

EXAMPLE A A suitable stabilized ethanolamine titanate may be prepared by adding 1 mole of ethanolamine to mole of isopropyl titanate. The solution will become warm, then mole of sorbitol hemihydrate in 100 ml. of water is added and the mixture is heated to drive oil. the isopropyl alcohol after which the stabilized ethanolamine titanate is taken up in 250 ml. of water. The aqueous solution serves as the addition agent for the gold bath.

EXAMPLE B The triethanolamine titanate was prepared by the same process as set forth in Example A by substituting 1 mol of triethanolamine for the ethanolamine.

EXAMPLE C The solution of titanates of Examples A or B may also be stabilized by substituting or" a mol of inositol, sodium gluconate, sodium glucoheptonate, or similar polyliydroxy compound for the sorbit-ol.

The gold bath normally is made up with potassium salts according to Table I, but sodium salts may be substituted in which case somewhat less brilliancy may be expected.

When the selenium compound is added a minimum of about .03 g./l. is required to enhance the result noticeably.

The following specific examples of the gold plating bath compositions yielding bright deposits support the ranges given in Table I.

EXAMPLE 1 A bath containing 4 g./l. of gold as KAu(CN) 0.04 g./l. of silver as KAg(CN) 0.05 g./l. of titanium as stabilized triethanolamine titanate and 10 g./l. of free potassium cyanide gave bright, yellowish gold deposits on a 2.5 x 10 cm. brass panel plated at .2 ampere/dmP'.

EXAMPLE 2 A gold plating solution containing 8 g./l. of gold (as potassium gold cyanide), 3 g./l. of silver (as potassium silver cyanide), g./l. of potassium cyanide, 0.1 g./l. of titanium (as the ethanolamine titanate of Example A) and 0.1 g./l. of selenium diethyldithio-carbamate. De-

posits were obtained on 2.5 x 10 cm. panels which were bright at 0.4, 0.6, 1.2, and 1.8 amperes/dmF.

EXAMPLE 3 A bath was made up containing 8 g./l. of gold added as potassium gold cyanide, 4 gl/l. of silver, added as potassium silver cyanide, 90 g./l. of potassium cyanide and carbon-treated with 1 g./lite-r of carbon. At 0.6, 0.8 and 1.2 amperes/dm. the deposit was hazy. The 0.1 g./'l. of titanium as triethanolamine titanate of Example B and 0.1 g./l. of selenium as sodium selenite was added. The deposit became brilliant at 0.6, 0.8 and 1.2 amperes/dmf EXAMPLE 4 A bath was made up containing 8 g./l. of gold, added as potassium gold cyanide, 4 g/l. of silver, added as potassium silver cyanide and 90 g./l. of potassium cyanide. As in Example 3 the deposits were hazy at 0.6, 0.8 and 1.2 amperes/dmf". The addition of 0.1 g./l. of titanium as stabilized triethanolamine titanate eliminated the hazy condition at 0.6 and 0.8 amperc/dmF.

EXAMPLE 5 A gold plating solution was prepared as for Examples 2 and 3. A characteristic haxy golden deposit was brightened considerably by as little as 0.05 g./l. of stabilized triethanolamine titanate and became brilliant when 0.1 g./l. of selenium diethyldithi-o-carbamate was also added.

EXAMPLE 6 A bath was made up containing 32 g./l. of gold as KAu(CN) =12 g./ l. of silver added as KAg(CN) 90 g./l. of potassium cyanide along with 0.1 g./l. of titanium as stabilized triethanolamine titanate and 0.025 g./l. of selenium as metallic selenium was added to the bath. Bright, white gold deposits were obtained at 4, 6, 8 and 10 amperes/dmfi. At 20 amperes/clrn. the deposit was slightly hazy.

The features and principles underlying the invention described above in connection with specific exemplifica- 'tions 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.

We claim:

1. An aqueous alkali cyanide gold plating bath containing about 4 to 32 g./l. of gold, about 0.04 to 12 g./l. of silver, about 10 to 200 g./l. of alkali cyanide and about 0.05 to 5 g./l. of a water-soluble titanium compound.

2. The gold plating bath of claim 1 in which the titanium compound is an aminoalcohol titanate.

3. The gold plating bath of claim 2 in which the aminoalcohol titanate is stabilized by the addition of polyaleohol compound.

4. An aqueous alkali cyanide gold plating bath containing about 4 to 32 g./-l. of gold, about 0.04 to 12 g./l. of silver, about 10 to 200 g./l. of alkali cyanide, about 0.05 to 5 g./l. of stabilized amin'oaloohol titanium compound and about 0:03 to 3 g./l. of a bath-soluble selenium compound.

5. An aqueous cyanide gold plating bath according to claim 4 wherein the bath-soluble titanium compound is a stabilized triethanolamine titanate and the gold and silver are present as potassium gold cyanide and potassium silver cyanide, respectively.

6. A process of producing a bright gold alloy which comprises electrodepositing a gold-silver alloy of about 23.5 to about 14-ca1'at from an aqueous solution containing from about 4 to 32 g./l. of gold added as alkali gold cyanide, about 0.4 to 12. g./l. of silver added as alkali silver cyanide, about 10 10,200 g./l. of free alkali cyanide and about 0.05 to 5 g./l. of a soluble titanium compound.

7. A process as claimed in claim 6 wherein the soluble titanium compound is an alcoholamine titanate.

8. A process according to claim 6 comprising adding to said bath, in addition, 0.03 to 3 g./l. of selenium.

9. A process according to claim 8 wherein the titanium compound is t-riethanolamine titanate and the selenium compound is diethyldithio-carbamate.

References Cited in the file of this patent UNITED STATES PATENTS Re. 24,582 Rinker Dec. 23, 1958' 1,731,212 Davignon Oct. 8, 1929

Claims (1)

1. AN AQUEOUS ALKALI CYANIDE GOLD PLATING BATH CONTAINING ABOUT 4 TO 32 G./L. OF GOLD, ABOUT 0.04 TO 12 G./L. OF SILVER, ABOUT 10 TO 200 G./L. OF ALKALI CYANIDE AND ABOUT 0.05 TO 5 G./L. OF A WATER-SOLUBLE TITANIUM COMPOUND.