Bath for galvanic deposition of gold and gold alloys

Abstract

Galvanic baths are provided for the deposition of gold or gold alloy coatings, such baths containing in combination aldehyde and nitrogen compounds with arsenic compounds.

Description

The invention relates to a bath for the galvanic deposition of gold coatings and gold alloy coatings, containing a combination of organic compounds on a base of aldehydes and nitrogen compounds with arsenic compounds.

The use of nitrogen-containing compounds, such as hydrazine and derivatives thereof, in gold electrolytes for reducing the internal stresses of the coatings deposited therefrom is known, cf., German Pat. Nos. 1,215,467, 1,218,248 and 1,222,347.

It is further known that soluble arsenic compounds are added to gold electrolytes in order thereby to achieve an improved luster of the gold coatings. Cf., German Nos. 2,042,127, 1,621,172 and 1,621,068.

An essential disadvantage of these electrolytes, however, is that their smoothing or leveling action is not satisfactory.

It is, therefore, an object of the present invention to avoid the disadvantages of the known electrolytes and to provide galvanic baths from which smooth coatings of gold and the alloys can be deposited.

This is achieved according to the present invention by providing a bath which is characterized by a content of

A. at least one compound of the general formula R -- CHO

in which R signifies hydrogen, methyl or the group --CHO, or one of its addition compounds and

B. at least one compound of the general formula R.sub.2 N--(R'--NR).sub.m --(R').sub.n --NR.sub.2

in which the radicals R are identical or different and represent hydrogen, possibly alkyl substituted by hydroxy groups with preferably 1 to 4 carbon atoms or aryl and R' alkylidene radicals with preferably 1 to 5 carbon atoms, m and n being 0 or representing integers from 1 to 3, or one of their salts and

C. at least one alkali salt of arsenic or arsenous acid, such as sodium and potassium arsenite or sodium and potassium arsenate.

In the general formula under (B) above, the radicals R signify for example methyl, ethyl, propyl, butyl or isobutyl, and the radicals R', signify methylene, ethylidene, propylidene, butylidene, pentylidene and the like, the alkyl radicals being preferably substituted with up to 2 hydroxy groups.

The components (A), (B) and (C) seem to influence each other synergistically in the bath, for when used alone they are completely ineffective.

The concentrations required for a high-gloss gold deposition or a chromatic gold alloy deposition are, for the aldehydes, i.e., component A, about 0.005 to 50 g/liter, for the nitrogen compounds, i.e., component B, about 0.1 to 50 g/liter, and for the arsenic compounds, i.e., component C, about 0.001 to 5 g/liter.

As aldehyde components there are suitable preferably formaldehyde, acetaldehyde and glyoxal, which can be used per se or in the form of their addition compounds, i.e., as bisulfites.

Nitrogen compounds that are especially suitable, are hydrazine or methyl hydrazine, which are to be used according to invention either by themselves or in the form of their salts, such as the chlorides or sulfates, or alone or in a mixture with one another. In addition, prropyl hydrazine as well as phenyl hydrazine and the substitution products thereof and their salts have proved to be suitable.

Further nitrogen compounds that may be used according to the invention are, for example, N-(3-propyl-1,2-diol)-diethylene triamine, triethylene tetramine, ethylene diamine, diethylene triamine, triethylenetetramine and tetraethylene pentamine, of which the first two in particular have been found to be very favorable with respect to their smoothing action.

Also, these compounds can be used by themselves as such, as well as in the form of their salts, for example, the chlorides or acetates.

Suitable arsenic compounds that are effective are the alkali salts of arsenic and arsenous acid, such as sodium and potassium arsenate or arsenite.

It is understood that the components (A), (B) and (C) may be used either by themselves alone, or in the form of their mixtures.

As a bath, there is generally used an aqueous solution which contains a water-soluble gold salt, preferably a complex compound of gold, in particular potassium dicyanoaurate (I), in concentrations of about 1 to 50 g/liter.

If gold alloy coatings are to be deposited, there are added to the bath the alloy metals silver, copper, zinc, cadmium, manganese, cobalt, nickel, palladium, indium, antimony or tin, in the form of their water-soluble compounds, preferably in the form of the complex compounds, such as the chelate or the cyano complexes, in total concentrations of about 0.01 to 200 g/liter. Depending on whether binary, ternary or quaternary alloy coatings are intended, corresponding mixtures of the metal compounds are used.

It has been found particularly appropriate if the bath contains boric acid and a polyvalent alcohol, preferably ethylene glycol, namely more particularly in a ratio by weight of about 1:1 to 1:2 and in a concentration of about 10 to 200 g/liter of boric acid or of about 10 to 2000 g/liter of alcohol.

As additional additives, the bath may contain common conducting salts, for example ammonium sulfate or alkali salts of sulfuric acid, nitric acid or hydrochloric acid, pH-regulating substances, appropriately the organic and/or inorganic buffer mixtures commonly used for this purpose such as, mixtures of citric acid and potassium citrate or sodium hydrophosphate and sodium dihydrophosphate as well as surface-active substances, such as ethylhexylsulfate and N-ethoxyhexylamine.

The pH value of the bath may be from about 5 to 10, preferably 6.8 to 7.5. It is operated appropriately at temperatures of about 20.degree. to 70.degree. C, preferably at temperatures between 25.degree. to 30.degree. C, current densities from about 0.1 to 5 amp.dm.sup.2 being used.

The bath according to the invention is suitable in particular for the galvanic deposition of high-gloss gold coatings and chromatic gold alloy coatings with excellent smoothing appearance.

Another advantage of the invention consists in the extraordinary adhesion of the coatings, which, surprisingly, far exceeds that of the coatings produced by the usual, known methods. Thus, for example, even the lead containing brass alloy, which is very difficult to galvanize or plate, can be gold plated directly without the previous deposition of an intermediate layer by means of the bath according to this invention resulting in a substantial saving of material and time.

It should be stressed further that the bath of the invention permits the use of high current densities and at good current efficiency shorter exposure times, whence special advantages result for the practice.

The following examples will illustrate the invention, without limitation thereof.

EXAMPLE 1

g/liter ______________________________________ Potassium dicyanoaurate (I), K(Au(CN).sub.2) 18.0 Ammonium sulfate, (NH.sub.4).sub.2 SO.sub.4 60.0 Boric acid, H.sub.3 BO.sub.3 40.0 Ethylene glycol, HO--CH.sub.2 --CH.sub.2 --OH 80.0 Formaldehyde, CH.sub.2 O 5.0 Hydrazine hydrate, N.sub.2 H.sub.4.sup.. H.sub.2 O 15.0 Sodium arsenite Na.sub.3 AsO.sub.3 0.07 pH value: 6.8 which is adjusted with sulfuric acid Applicable current density: from 0.1 to maximum 2.0 amp.dm.sup.2 Temperature: 20 to 70.degree. C The rate of deposition at 1 amp/dm.sup.2 : 1 micron in 4 ______________________________________ minutes.

This electrolyte composition according to the invention is suitable for the deposition of nearly 24 carat gold. The coatings deposited from this electrolyte are of high luster, saturated gold color, and have a hardness of about 170 microvickers.

With the electrolyte, lead containing brass can be proviced, without an intermediate layer, with a gold coating which is of high luster from about 8 micron on.

EXAMPLE 2

g/liter ______________________________________ Potassium dicyanoaurate (I), K(Au(CN).sub.2) 12.0 Ammonium sulfate, (NH.sub.4).sub.2 SO.sub.4 70.0 Boric acid, H.sub.3 BO.sub.3 40.0 Ethylene glycol, HO--CH.sub.2 --CH.sub.2 --OH 80.0< Copper sulfate, CuSO.sub.4.sup.. 5H.sub.2 O 8.0 Ethylene diamine tetraceticacid dipotassium salt 9.5 Formaldehyde, CH.sub.2 O 5.0 Hydrazine hydrate N.sub.2 H.sub.4.sup.. H.sub.2 O 12.0 Sodium arsenite, Na.sub.3 ASO.sub.3 0.045 ______________________________________

By means of this electrolyte, about 18 carat coatings can be deposited, which have the color of rolled gold. The coatings are of high gloss and tarnish resistant.

EXAMPLE 3

g/liter ______________________________________ Potassium dicyanoaurate, (I), K(Au(CN).sub.2) 12.0 Ammonium sulfate, (NH.sub.4).sub.2 SO.sub.4 30.0 Boric acid, H.sub.3 BO.sub.3 60.0< Ethylene glycol, HO--CH.sub.2 --CH.sub.2 --OH 60.0 Cadmium sulfate CdSO.sub.4.sup.. 8/3 H.sub.2 O 3.5 Ethylene diamine tetracetic acid dipotassium salt 4.0 Formaldehyde, CH.sub.2 O 10.0 Hydrazine sulfate, N.sub.2 H.sub.4.sup.. H.sub.2 SO.sub.4 30.0 Sodium arsenite, Na.sub.3 ASO.sub.3 0.5 pH value: 8.0 Applicable current density: From 0.1 to 1.5 amp/dm.sup.2 Temperature: 20 to 60.degree. C Rate of deposition at 1 amp.dm.sup.2 : 1 micron in 4 minutes. Intensive agitation of electrolyte or cathode is effected. ______________________________________

This electrolyte furnishes light yellow, about 20 carat coatings. The coatings deposited from this electrolyte are high gloss and tarnish resistant.

EXAMPLE 4

g/liter ______________________________________ Potassium dicyanoaurate (I) K(Au(CN).sub.2) 10.0 Ammonium sulfate (NH.sub.4).sub.2 SO.sub.4 50.0 Boric acid H.sub.3 BO.sub.3 30.0< Ethylene glycol, HO--CH.sub.2 --CH.sub.2 --OH 60.0 Palladium cyanide, Pd(CN).sub.2 4.5 Nickel sulfate NiSO.sub.4.sup.. 7H.sub.2 O 10.0 Ethylene diamine tetracetic acid dipotassium salt 12.0 N-(3-propyl-1,2-diole)-diethylene triamine, (CH.sub.2 --OH--CHOH--CH.sub.2 NH--CH.sub.2 --CH.sub.2 --NH--CH.sub.2 --CH.sub.2 --NH.sub.2 1.0 Sodium arsenate, Na.sub.3 AsO.sub.4 0.2 Formaldehyde, CH.sub.2 O 7.5 pH value: 6.5 Applicable current density: from 0.2 to 1.0 amp/dm.sup.2 Temperature: 20 to 70.degree. C The rate of deposition at 1 amp/dm.sup.2 is 1 micron in 8 ______________________________________ minutes.

This electrolyte furnishes almost white, high-gloss coatings. The deposited alloy is approximately 16 carat.

EXAMPLE 5

g/liter ______________________________________ Potassium dicyanoaurate (I), K(Au(CN.sub.2) 15.0 Ammonium sulfate, (NH.sub.4).sub.2 SO.sub.4 80.0 Boric acid, H.sub.3 BO.sub.3 50.0 Ethylene glycol, HO--CH.sub.2 --CH.sub.2 --OH 100.0 Cobalt sulfate, CoSo.sub.4.sup.. 7H.sub.2 O 3.0 Nickel sulfate NiSO.sub.4.sup.. 7H.sub.2 O 2.0 Indium sulfate, In.sub.2 (SO.sub.4).sub.3 0.5 Methyl hydrazine CH.sub.3 --NH--NH.sub.2 0.1 Ethylene diamine tetracetic acid dipotassium salt 6.0 Formaldehyde, CH.sub.2 O 3.0 Sodium arsenite, Na.sub.3 AsO.sub.3 0.3 pH value: 5.0 Applicable current density: from 0.1 to 2.5 amp/dm.sup.2 Temperature: 20 to 35.degree. C Rate of deposition at 2 amp/dm.sup.2 : 1 micron in 2 minutes ______________________________________

According to the invention an alloy of good electrical properties and excellent abrasive strength can be deposited with this bath.

The coatings are of high gloss and have a fineness of 23 carat. The current efficiency is 40 to 60%. The content of alloy metals can be greatly influenced by varying the current density and the speed of goods or by electrolyte agitation. From a layer thickness of about 5 micron on, a smoothing effect can already be observed.

Claims

1. An aqueous bath for the electrodeposition of gold or gold alloys having a high gloss, said bath having a pH of from about 5 to 10 and an amount of components, A, B and C to provide a coating having high gloss and extraordinary adhesion, said bath comprising

A. from about 0.005 to 50 grams per liter of at least one compound of the general formula RCHO wherein R is selected from the group consisting of hydrogen, methyl, and the group - CHO, and an aldehyde bisulfite addition compound thereof, and

B. from about 0.1 to 50 grams per liter of at least one compound of the general formula R.sub.2 N--(R'--NR).sub.m --(R').sub.n --NR in which each R is selected from the group consisting of hydrogen, alkyl having from 1 to 5 carbon atoms and hydroxy-substituted alkyl having from 1 to 5 carbon atoms, m and n is 0 or an integer from 1 to 3, and

C. from about 0.001 to 5 grams per liter of at least one alkali metal salt of a member of the group consisting of arsenic acid and arsenious acid, and

D. a water soluble gold compound in an amount of about 1 to 50 grams per

2. A bath adding to claim 1 which contains about 10 to 200 grams per liter of boric acid and about 10 to 200 grams per liter of a polyvalent alcohol, the ratio of boric acid to polyvalent alcohol being from about 1:1 to

3. A bath according to claim 2 wherein the polyvalent alcohol is ethylene

4. A bath according to claim 1 wherein component A is selected from the group consisting of formaldehyde, acetaldehyde and glyoxal and component B is selected from the group consisting of hydrazine, methyl hydrazine, N-(3-propyl-1,2-diol)-diethylene triamine, triethylene tetramine and salts

5. A bath according to claim 1 for electrodeposition of gold alloy containing at least one alloy metal selected from the group consisting of silver, copper, zinc, cadmium, cobalt, nickel, palladium, indium, manganese, antimony and tin wherein the alloy-metals are added to the bath in the form of water-soluble compounds in amounts of about 0.01 to 200 grams per liter.