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Publication numberUS3367853 A
Publication typeGrant
Publication dateFeb 6, 1968
Filing dateAug 26, 1965
Priority dateAug 26, 1965
Publication numberUS 3367853 A, US 3367853A, US-A-3367853, US3367853 A, US3367853A
InventorsKarl Schumpelt
Original AssigneeSel Rex Corp
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Acid-gold electroplating bath
US 3367853 A
Abstract  available in
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Claims  available in
Description  (OCR text may contain errors)

United States Patent Office 3,367,853 Patented Feb. 6, 1968 3,367,853 ACID-GOLD ELECTROPLATING BATH Karl Schumpelt, Union, N.J., assignor to Sel-Rex Corporation, Nutley, N.J., a corporation of New Jersey No Drawing. Continuation-impart of application Ser. No. 424,496, Dec. 31, 1964. This application Aug. 26, 1965, Ser. No. 482,903

7 Claims. (Cl. 20446) This application is a continuation-in-part of US. application Ser. No. 424,496, filed Dec. 31, 1964, now abandoned.

This invention relates to the art of metal coating With particular reference to a process and method for electrodepositing gold.

In years past it was customary to electrodeposit gold from an aqueous solution containing an alkali gold cyanide and some excess alkali cyanide with or without additional conducting salts. Such solutions Were well on the alkaline side. About the middle of the twentieth century several gold plating baths, sans free cyanide, were invented, and these were operated at what was essentially a neutral pH. About ten years later, Rinker and Duva discovered that potassium gold cyanide was stable at much lower pH values than theretofore known. These baths, as disclosed in U.S. Patents Nos. 2,905,601 and 3,104,212, contain 1- 30 g./l. of gold added as alkali metal gold cyanide and -150 g./l. of an organic acid partially neutralized to provide a pH of 3-6.

Among the objects of this invention is to provide a bath which makes it possible to plate from the aforementioned acid gold solution, a gold deposit characterized by being harder and more abrasion resistant.

Another object is to provide a method for obtaining a deposit from an acid gold bath which is smoother and somewhat brighter than deposits obtained from the bath described in US. Patent No. 3,104,212.

This invention is based on my discovery that the addition of an alum to a gold bath containing a weak organic acid partially neutralized with sodium, potassium, or ammonium hydroxide, or a combination of these alkalies, to provide a pH of 3.06.0 modifies the structure of the gold electrodeposit obtained therefrom to give a finer grained texture which is also harder. The amount of alum is not very critical, 1 to 100 g./l. having been found useful. It is preferred, however, to add 10 to grams to each liter of plating solution.

The term alum will be understood to define compounds such as are obtained by crystallizing the sulfates of aluminum, chromium and gallium with the sulfates of ammonium, cesium, potassium, rubidium, sodium and thallium and with Water in which the molar ratio,

M22804: M2 (SO4)3 i H2O is 1:1:24, where M is the monovalent metal and M is the trivalent metal.

Surprisingly, I have been unable to detect any chromium, aluminum, or gallium in deposits prepared in such a gold plating solution even though the increased hardness would indicate some codeposition. Apparently, the trivalent metal is complexed in such a manner as not to be plated out with the gold. On the other hand, if trivalent metal sulfate is added to the bath the deposit becomes very bright and hard. Chromium, for example, can easily be identified by X-ray fluorescence.

The unexpected stability of these alums in this acid gold plating system leads to the production of a high-purity gold deposit with improved physical properties with respect to hardness and smoothness.

It will be understood that the buffered acid solutions of the invention can be obtained by mixing free acid and neutralizing alkaline salts or by dissolving acid reacting salts of the weak acids to form the solution or by mixing the free acid and salts of the free acid. The acidic nature of the bath is denoted by its pH of 3 to 6.5.

The following examples will explain the composition of the bath and method of plating.

Example 1 A bath was prepared as follows:

Gold (added as KAu(CN) g./l 8.2 Ammonium citrate ((NHQ C H O g./l 50 Chrome alum (NH C1'(SO .12H O) g./l 20 pH 5.0

A brass panel 3 /2 x 1" was plated at 0.5 amp/dm. at 50 C. to a thickness of about 25 microns. The deposit was smooth and semi-bright. The hardness was found to be kg./mm. (Knoop with 25 g. load).

Example 2 A bath was prepared containing:

Gold (added as KAu(CN) g./l 16.5 Ammonium citrate ((NHg C H O g./l 50 Chrome alum (NH Cr(SO .12H O) g./l 50 pH 5.5

A brass panel 3 /2 x 1 was plated at 1.0 arnp/dm. at 50 C. to a thickness of 20 microns. The hardness was 118 kg./rnm. Knoop at 25 g. load.

In other experiments the ammonium citrate was varied from 10 to grams per liter and various amounts of sodium and potassium citrate were added with no apparent effect on the deposit. The acid or acid anion need not be citric or citrate but may be any stable organic acid with a pK value such that the acid will be an effective buffer in the pH range of about 3 to about 6.5.

KOH to provide a pH 5.0

A brass panel 3 /2" x 1" Was plated at 10 amp/dm. at 50 C. to a thickness of 5 microns. The hardness was 110 kg./mm. and the product was smooth and semi bright.

Panels plated with the aluminum alums and mixtures of the aluminum, chromium and gallium alums show substantially the same brightness and hardness.

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. An aqueous electrolyte for electrodepositing smooth, hard, 24-karat gold containing about 130 g./l. of gold added as a soluble alkali metal gold cyanide, about 10 150 g./l. of a stable, organic acid selected from the class having a pK value effectively buffering at a pH of 3 to 6.5, partially neutralized with an alkaline material to yield a salt of said acid selected from the class consisting of sodium, potassium, lithium and ammonium salts and combinations thereof and to provide a pH of 3 to 6.5, and 1 to 100 g./l. of an alum.

2. An electrolyte as claimed in claim 1 in which said organic acid is citric acid.

3. An electrolyte as claimed in claim 1 in which said alum is a compound of the formula Where M is a monovalent cation selected from the group consisting of ammonium, cesium, potassium, rubidium, sodium and thallium and M is a trivalent metal selected from the group consisting of aluminum, chromium and gallium.

4. An electrolyte as claimed in claim 1 in which said alum is alkali metal chromium disulfate decahydrate.

5. An electrolyte as claimed in claim 1 in which said alum is ammonium chromium disulfate decahydrate.

References Cited UNITED STATES PATENTS 8/1880 Lisenmayer 204-43 9/1963 Rinker et al. 20446 HOWARD S. WILLIAMS, Primary Examiner.

G. KAPLAN, Assistant Examiner.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US231064 *Apr 29, 1880Aug 10, 1880 Electro-deposition of aluminium and gold alloy
US3104212 *May 21, 1959Sep 17, 1963Sel Rex CorpElectroplating smooth ductile gold
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3856638 *Apr 26, 1973Dec 24, 1974Auric CorpBright gold electroplating bath and method of electroplating bright gold
US3893896 *Jul 2, 1973Jul 8, 1975Handy & HarmanGold plating bath and process
US4069113 *Jul 19, 1973Jan 17, 1978Oxy Metal Industries CorporationElectroplating gold alloys and electrolytes therefor
Classifications
U.S. Classification205/251, 205/268, 205/247
International ClassificationC25D3/48, C25D3/02
Cooperative ClassificationC25D3/48
European ClassificationC25D3/48
Legal Events
DateCodeEventDescription
Nov 20, 1983ASAssignment
Owner name: MANUFACTURERS HANOVER TRUST COMPANY, A CORP OF NY
Free format text: SECURITY INTEREST;ASSIGNOR:INTERNATIONAL CORPORATION, A CORP OF DE;REEL/FRAME:004201/0733
Effective date: 19830930
Oct 6, 1983ASAssignment
Owner name: OMI INTERNATIONAL CORPORATION, 21441 HOOVER ROAD,
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:OCCIDENTAL CHEMICAL CORPORATION;REEL/FRAME:004190/0827
Effective date: 19830915
May 5, 1983ASAssignment
Owner name: OCCIDENTAL CHEMICAL CORPORATION
Free format text: CHANGE OF NAME;ASSIGNOR:HOOKER CHEMICAS & PLASTICS CORP.;REEL/FRAME:004126/0054
Effective date: 19820330
Apr 19, 1982ASAssignment
Owner name: HOOKER CHEMICALS & PLASTICS CORP.
Free format text: MERGER;ASSIGNOR:OXY METAL INDUSTRIES CORPORATION;REEL/FRAME:004075/0885
Effective date: 19801222
Mar 16, 1982ASAssignment
Owner name: OXY METAL INDUSTRIES CORPORATION
Free format text: CHANGE OF NAME;ASSIGNOR:OXY METAL FINISHING CORPORATION;REEL/FRAME:003967/0084
Effective date: 19741220