DE2445537A1 - BATH FOR GALVANIC DEPOSITION OF GOLD - Google Patents

Description

SCHERiNG AG

Industrial property legal protection

Berlin, 'Sept. 18, 1974

BATH FOR GALVANISGHEN DEPOSITION OF GOLD

The invention relates to a cyanide-free bath for electrodeposition of gold.

Alkaline cyanide baths for galvanic gold plating are already known »They are characterized by their excellent stability and Kobustheit and are often used. Your disadvantage however, lies in the extraordinary toxicity of the cyanides they contain, which makes them more hygienic and "wastewater technology." Seem questionable.

Neutral gold electrolytes have also become known Polygamy an aurocyanide, trivalent arsenic and as a sulfur donor contain an alkali metal thiosulphate (DQ) -OS 20 10 725). These However, electrolytes also contain cyanide and have the other Disadvantage, neither glaus-forming nor gloss-retaining and not either to have a leveling effect.

Finally, alkaline, cyanide-free gold baths have already been proposed v / elche gold as sulphite and luster-enhancing additives included (DT-OS 16 21 180). Such gold sulfitokoxaplexes however, have an unsatisfactory stability and form even with an extremely high excess of free. Sulfite ions for long

609815/1073

SCHERING AG

Commercial law school

-2- Sept. 18, 1974

Gerern standing of the solution elemental gold, making the solution unusable will.

The object of the present invention is therefore to develop a stable bath, which overcomes the disadvantages of the known gold baths and the relatively non-toxic galvanic deposition of Gold with good technological and decorative properties with a high degree of purity at the same time.

The object is achieved according to the invention by a bath that is characterized is due to a content of gold in the form of a l'hiosulfato complex.

Such thiosulfato complexes are to be understood as complexes changing composition with gold as the central atom and at least a thiosulfate ligand. The approximate composition these complexes can be of the formula

^M 3 - 12 & ^U 1 - 2 ( ^S 2 ^{J <} V 2 - 7 ^ correspond, in which M is a metal equivalent, e.g. sodium. These gold thiosulphato complexes are known per se or can be prepared by processes known per se .

Sodium dithiosulfatoaurate (I) (Na-, l ~ Au (S ₂ O ₅ ) ^ J. 2 H ₂ O) can be z. B. by ecduction of sodium tetrachloroaurate (III) in neutral aqueous solution with thiosulfate and precipitation of the ge

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SCHERING AG

Intellectual Property

Sept. 18, 197 ^

formed complex with alcohol.

In a similar way, the compound sodium heptathiosulfate diaurate (I) (Na ^ ₂ [Au ₂ ( ^S 2 ° 3 ^ 7 ~ P) can be prepared and isolated from aqueous solution.

The gold thiosulfato complexes to be used according to the invention are readily soluble in water. The concentration of gold in the invention The bath can expediently be from 0.1 g gold / liter to saturation, preferably from 3 g to 30 g gold / liter. The gold thiosulfato complexes are either prefabricated in the bath Form added or made in this itself. Advantageously, the solution can also contain excess thiosulfate contained in a weight ratio of metal: thiοsulphate up to to about 1:20. The concentration of thiosulfate in the solution is expediently at least 1 g / liter, preferably from 20 g to 500 g / liter.

Thiosulfate is to be understood here as meaning the ammonium and / or alkali salts, preferably the sodium or potassium salts, thio sulfur acids or their adducts with basic compounds such as B-, with amines or polyamines.

Since gold is difficult to dissolve anodically in thiosulphate solutions and one therefore with insoluble anodes, such as. B. with platinum-coated titanium "works, you can add reducing agents to the bathroom if you want, such as B. nitrite or sulfites, preferably in the form of their Alkali salts, such as ζ. B. the sodium or potassium salts.

609815/1073 ~ ' ^] "

SCHERING AG

Intellectual Property

Sept. 18, 1974-

The bath can also contain conventional constituents as further additives. These are e.g. B. electrolyte salts, such as ammonium or alkali salts of inorganic or weak organic acids, such as. B. sulfuric acid, sulphurous ·; Acid ₈ carbonic acid, boric acid, sulfamic acid, acetic acid, citric acid and others. In addition, the bath can contain substances that regulate the pH, expediently the organic and / or inorganic buffer mixtures customary for this purpose, such as. B. disodium phosphate, alkali metal carbonate, alkali borate, alkali acetate ₉ contain alkali metabisulphite or a mixture of boric acid and ethylene glycol. It is preferably of 20 °, expediently operated at temperatures of about 10 ° to 80 ° C ₅ to 55 ° C, with current densities come from about 0.1 to 2 A / dm "to the application.

The bath according to the invention is used in a manner known per se Way.

The gold coatings deposited from the bath of the invention are high gloss and are characterized by their excellent ductility, especially with thicker coatings. The bathroom works beyond that also leveling from 5 mm and is for the separation suitable for both thin and thick gold layers.

When using low current densities, e.g. B. 0.1-0.5 A / dm one high purity gold plating with excellent electrical

Conductivity. If you electrolyze with 0.4 - 1.2 A / dra, the result is .t.i or on

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SCHERiNG AG

Intellectual Property

Sept. 18, 1974

animal gold coatings of higher hardness (120 - 1GO Vickers) with good Abrasion resistance. Finally, as a particular advantage, the bath according to the invention offers a cyanide-free and therefore relatively non-toxic one Mode of operation, which improves occupational hygiene and reduces the work involved in wastewater treatment is achieved.

The following examples serve to illustrate the invention.

B ice Piel 1

'Bath composition:'

Gold as sodium dithiosulfatoaurate (I)

0.04 molar = 7.9 g gold / liter Sodium thio sulfate

. 5 HpO 0.5 molar

0.06 molar - sodium t etr from ο r at

0.015 molar = 6.4 g / liter

Well, JAu (S ₂ O,) £]. 2 sodium sulfite Na ₀ SO,

2 5

119; g / liter - 7 »6 g ./liter

Na ₄ B ₄ O ₇ . 10

Working conditions: pH value (adjusted with NaOH): 9.0

Temperature; 25C

Electrolyte circulation and cathode movement

Current density: anode:

0.1 to 1.5
platinum-coated titanium

609815/1073

SCHERING AG

Intellectual Property

Sept. 18, 1974

Result:

If you immerse a carefully degreased watch bezel in this solution made of leaded brass and electrolyzed for about 20 minutes, a 6 to 7 µm thick shiny gold layer is obtained on it, which is free from ponen.

example

Bath composition: gold as sodium heptathiosulfatoaurate (I)

Potassium thio _{sulfate K 2} S ₂ O ₃ sodium sulfite Na ₂ SO ₅ boric acid

Ethylene glycol HO-CH ₂ -CHp-OH

p ^ value: temperature; Anodes: current density:

.

0.04 molar = 15.7 g gold /

liter

0.8 molar = 240 g / liter

0.1 molar «12.6 g / liter

0.3 molar = 18.6 g / liter

0.6 molar = 37.2 g / liter

Working conditions:

6.8 23 ⁰ C platinized titanium Ο, 3 to 1.5 A / dm ²

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SCHERING AG

Intellectual Property

-7- Sept. 18, 1974-

Result:

A scratched copper sheet with an area of about 1 dm takes 15 minutes

gold-plated in this electrolyte. The ones caused by the scratching fine grooves are then clearly leveled.

Example 3

Bath composition:

Gold as sodium dithiosulfatoaurate (I)

Na, FAu (S ₀ O ^) ₀ I. 2 H ₀ O 0.05 molar = 10 g gold /

^ ^{L d} ■ * ^{dA d} ■ liters

Sodium thiosulfate

Na ₂ S ₂ O ^ 0.5 molar = 119 g / liter

Sodium sulfite

Na ₂ SO ₇ 0.05 molar = 6.3 g / liter

Potassium dihydrogen phosphate

KH ₂ PO ^ x 0.02 molar = 2.7 g / liter

Potassium metabisulfite

K ₂ S ₂ 0 _r 0.05 molar = 11.1 g / liter

Working conditions:

pH 6.9

Temperature: 20 ⁰ C

Anode: 'coal

Current density: 0.1 to 1.2 A / dm

Result:

A printed circuit with a total area of approx. 0.7 dm is made

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SCHERING AG

Intellectual Property

Sept. 18, 1974

gold-plated in this solution for 6 minutes. The gold coating, which is about 2.5 P ^ thick, is pore-free and can be soldered excellently.

Example 4

B ad to s a m en s e tio n;

Gold as sodium dithiosulfatoaurate (l)

Ha, IAu (SpO ^) ₉ j. 2 H ₉ O 0.05 molar = 9 »85 g gold /

⁵ L ^d * ^d 4 ^d liters

Sodium thiosulfate

Na ₉ S ₉ O;, 1.0 molar = 156 g / liter

Sodium sulfite

Na ₂ SO ₅ 0.1 molar = 12.6 g / liter

Potassium metabisulfite

^K 2 ^S 2 ° 5 ^{0) 01 raolar = 2} » ² S / liter

Boric acid

B (OH), O ₉ 15 molar = 18.6 g / liter

Ethylene glycol

HO-CH ₂ -CH ₂ -OH 0.3 molar » 37.2 g / liter

Working conditions:

PH value! 6.5

Temperature. · 22 ⁰ C

Anodes; platinum-coated titanium

Result:

In a drum, diode feeds with an overall upper

-.9. 609815/1073

SCHERiNG AG

, Commercial legal slot

^{¥ Sep} 18, 1974-

P 2

area of 1 m with an average current density of 0.1 A / dm gold plated. The 2 µm thick coatings are pore-free and can be used well even after a long storage period of a few months soldering.

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Claims (8)

SCHERING AG Intellectual Property Law -10- Sept. 18, 1974 PATENT CLAIMS 1. Cyanide-free bath for galvanic deposition of gold, thereby characterized that it is the gold as a thiosulfato complex contains. 2. Bath according to claim 1, characterized in that the gold in a concentration of 0.1 g gold / liter to saturation, preferably from 3 g to 30 g gold / liter. 3 · bath according to claims 1 and 2, characterized in that it Contains excess thiosulfate. 4. Bath according to claim 3 »characterized in that the thiosulfate as ammonium or alkali thiosulfate, preferably as Sodium or potassium thio sulfate. 5 · bath according to claim 4, characterized in that the thiosulfate is contained in concentrations of at least 1 g / Litex, preferably from 20 g to 500 g / liter. 6. A method for the galvanic deposition of gold using a bath according to claims 1 to 5 · 7. The method according to claim 6 _5, characterized in that the bath at pH values of 4 to 13? preferably from 5 "to 11. -11- 609815/1073 SCHERING AG Intellectual Property " ^ΛΛ ~ . Sept. 18, 1974- 8. The method according to claim 7 »characterized in that the bath" at temperatures of about 10 ° and 80 ⁰ C, preferably of 20 ° Ms 55 ⁰ C, is operated. 809815/1073