DE1696087A1 - Electrolyte for the deposition of gold-copper alloys - Google Patents

Description

The invention relates to an electrolyte from which shiny, hard gold-copper alloys with a pink hue can be deposited. _h ., - ■ - ■ -, ----

There are already acidic gold baths for the deposition of pure gold with a pH between 3 and 5 respectively. 3 and 6.5 known. It is also already known that one shiny hard gold layers can get if the gold arrives at the same time with an accompanying metal for the deposition (here e.g. U.S. Patent 2,9o5,6o1). One of the most difficult colors in gold plating from acid baths is shiny pale pink shades. These difficulties arise from the fact that copper is the main concern

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sliding element for pink hues and copper ions are sensitive to changes in concentration, so that Uniform and easily reproducible coatings from gold copper alloys are only available with careful Monitoring of the electrolyte and the working conditions, However, after a certain time it comes to a slight veil on the coverings of such baths. This becomes more significant with increasing Age of the bath.

The invention now relates to an electrolyte and a method for producing uniformly reproducible, shiny, hard coatings made of a gold-copper alloy with a pale pink color » The composition of the electrolyte according to the invention is a further development of an acidic phosphate electrolyte for gold alloys * 1-8 g / l Au are preferred for the electrolyte according to the invention 4 g / l Au (added as alkali gold cyanide), 2 - Io g / l Cu, preferably 5 g / l Cu (added as a copper complex), 0.5 - 10 g / l Sb, preferably 1.5 g / l Sb (added as antimony salt e.g. as tartrate), 5 - 60 g / l, preferably 20 g / l of a chelating agent, 2o 12o g / l »preferably contain 60 g / l of a weak acid or its salt, the pH being on 4 »5 - 6, preferably 5.3, is set. The inventive Electrolyte works flawlessly at

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a current density between 0.5 and 2, preferably 1.5 Amp / dm and at a temperature between 4o and 60 ° C, preferably 50 ° C.

With the electrolyte according to the invention you can Coatings with a thickness of 25 / U and above in obtained high-gloss form. The pale pink coatings are decorative and corrosion-resistant.

A copper salt of any chelating or complexing agent with a stability constant can be added to the electrolyte as a copper complex for copper, bring in about 17 or less. Such complexing agents are e.g. Ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, ΪΓ-hydroxyethylethylenediamine triacetic acid or their alkali salts. The alkali salts can also be used as chelating agents in the electrolyte according to the invention apply these substances. ™

The usual weak acids which have a pK value of more than about 3, in particular organic acids or phosphoric acid, can be used as weak acids. If a polybasic acid is used, the acidic salts or mixtures thereof can be used instead. The primary potassium phosphate respectively. "Sodium, lithium or ammonium phosphate can be used in this connection in the electrolyte according to the invention. 109883/1333 is also suitable

also the primary potassium citrate.

Antimony can be introduced in the form of any soluble salt, preferably antimonyl tartrate.

Although copper is the essential alloy metal for a pink shade from alkali gold cyanide electrolytes and would already be sufficient for a pink shade, antimony, which is also important for a pink shade, is also used according to the invention. “ ₌ This measure achieves excellent results in acidic gold baths. Layers with 75-85 fo gold, 14-24 fo copper and 0.5-1.5 <fo antimony are obtained. The Knoop hardness is about 23o-280 kg / mm with a load of 25 g.

It was found that a small addition of lead fc the tendency to fogging with insufficient Decreases bath movement and current density. So you can according to the invention any soluble lead salt, such as the lead acetate, in an 'amount up to 2oo mg / l, preferably 15-2oo mg / l, use.

The mechanism by which lead is effective in preventing haze is not yet complete

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Enlightened, However, because of the small amount required, this appears to be an influence on diffusion to act. Lead is preferably used as acetate, but a complex one can also be used Use lead salt like that of ethylenediaminetetraacetic acid

The following examples explain the invention:

example 1

The electrolyte is prepared with the following substances ι

Salt metal

Gold Fk Au (CH) ₉ I.
L 'J MeA 4 g / l Copper (m ₂ EDTA) * 25 g / l 5 g / l Ant imony11 art council 4.5 g / l 1.5 g / l Na ₂ EDTA 2o g / l KH ₂ PO ₄ "60 g / l # EDTA = ethylenediaminetetraacetic acid

From this electrolyte, brass test sheets were coated with a coating of 25 / rev at an electrolyte temperature of 5o C and a current density γοη about 1 _f 5 Amp / dm. The coatings were pale pink in color and glossy. Hardness according to Viokers about

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24ο - 25o. Alloy Composition: about 8o # Au,
18.9 i ° Ou and 1 fo Sb,

In a modification of this experiment, tetrasodium pyrophosphate was used instead of the primary potassium phosphate
and / or tripolyphosphoric acid neutralized to a pH of 5 applied. The same results are obtained. In a series of tests, the acid content went down to 2o g / l and up to 12o g / l. Weak acids partially neutralized
pH values between 4.5 and 6 produced essentially the same results. Citric acid did not have as high a gloss as inorganic acids, but the layers are still very decorative
Tartaric acid neutralized with sodium hydroxide is satisfactory, but there is sometimes a slight excretion of tartar when the gold is added as potassium gold cyanide. Good results are also obtained with potassium or sodium acetate.

Example 2

An electrolyte was prepared according to the following recipe:

Gold [K Au (CN) ₂ J 3 g / l

Copper (NA ₂ EDTA) 4 g / l

Antifflonyl tartrate 3 g / l

Na ₂ EDTA 2ο g / l

KH ₂ PO ₄ 60 g / l

Lead [Pb (C ₂ H ₃ Og) _{2 63} <g] 0 _t o15 g / l

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ο With an electrolyte temperature of 5o C and one

A current density of about 10 amps / dm was obtained on brass test sheets a 25 / U thick coating that has a high-gloss finish and was light pink *

An increase in the lead content up to 2oo mg / l leads only to a higher gloss and a leveling effect.

Instead of the phosphate mentioned you can also Use tetrasodium polyphosphate or potassium polyphosphate and comes to similar results.

With citric acid and buffered to a pH value 5 the results are not quite as good as with inorganic acids, but the coatings are still very decorative. With tartaric acid there is a slight precipitation of tartar when the gold is used as potassium gold cyanide was introduced. Acetic acid and potassium acetate lead to precipitation of one in some cases a small part of antimony, but lead to good coatings.

Claims

109883/1333

Claims (1)

Claims 1. Electrolyte for shiny, hard gold-copper alloys with a light pink shade containing 1-8 g / l Au, added as alkali gold cyanide, 2-1 o g / l Cu, added as a copper complex, o, 5-1o g / l antimony, added as Antimony salt, 5-6o g / l chelating agent with a pH value of 4 to 5 »6 adjusted with a weak acid or their salt for working temperatures 4o to 6o ° C and one. Current density between 0.5 and 2 Amp / dm. 2 _β electrolyte according to claim 1 with 4 g / l Au, 5 g / l Cu, 1.5 g / l Sb, 20 g / l chelating agent, 6o g / l primary potassium phosphate with a pH value of about 5.3 for a working temperature of about 5o G and a current density 2
of about 1.5 amp / dm, 3 · Electrolyte according to claim 1 or 2 with an additional content of up to 2oo mg / l Pb, added as soluble lead compound. 4 · Electrolyte according to 3 characterized by an additional content of 15-2oo mg / l Pb. 109883/1333