US3123544A

US3123544A - Electrodeposition of ruthenium

Info

Publication number: US3123544A
Authority: US
Priority date: 1961-04-18
Publication date: 1964-03-03
Anticipated expiration: 1981-03-03
Also published as: GB938164A

Description

United States Patent 3,123,544 ELECTRODEPOSITION 0F RUTHENIUM Joyce Cresswell Blake, London, England, asslgnor to The International Nickel Company, Inc., New York, N.Y., a corporation of Delaware No Drawing. Filed Apr. 10, 1962, Ser. No. 186,318 Claims priority, application Great Britain Apr. 18, 1961 7 Claims. (Cl. 204-47) The present invention relates to electrodeposition and, more particularly, to the electrodeposition of ruthenium.

Hitherto, ruthenium has usually been electrodeposited cathodically from a fused electrolyte. The electrolyte has consisted of a fused mixture of sodium and potassium cyanides that has been charged with ruthenium by alter nating current electrolysis between ruthenium electrodes. This gives satisfactory, coherent coatings up to 0.0015 inch thick, but has the disadvantage that a temperature of about 500 C. must be used to maintain the bath molten.

This disadvantage can be overcome by the use of an aqueous electrolyte and it has been proposed to use an acid aqueous solution of a ruthenium salt containing a nitroso group. It is, however, difiicult to make such solutions with reproducible properties. Although attempts were made to overcome the foregoing disadvantage, none, as far as I am aware, was entirely successful when carried into practice commercially on an industrial scale.

It has now been discovered that by the use of a special plating method including a novel electroplating bath, advantageous ruthenium electrodeposits can be produced from an aqueous medium.

It is an object of the present invention to provide a novel process for the electrodeposition of ruthenium.

Another object of the invention is to provide a novel ruthenium electroplating bath.

Other objects and advantages will become apparent from the following description.

According to the invention, ruthenium is electrodeposited from an aqueous acidic solution of a soluble tetrasulphamato nitrosyl ruthenate, preferably the sodium salt. Such solutions can be prepared with satisfactory reproducibility from sodium tetranitro nitrosyl ruthenate, which is precipitated as fine yellow needles of definite composition by treating a boiling solution of ruthenium chloride in normal hydrochloric acid with twice the theoretical amount of sodium nitrite and allowing the reaction mixture to cool. On warming an aqueous solution of the crystals to 100 C. with solid sulphamic acid, nitrogen is evolved in an amount that corresponds, when reaction is complete, to the replacement of all four nitro groups by sulphamato groups. The product of the reaction is a clear deep-red solution which gives very reproducible results when used as an electrolyte for the deposition of ruthenium.

The ruthenium content of the solution used for the electrolysis is advantageously about 2.5 to about 20 grams per liter (g.l.). At lower concentrations than 2.5 g./l., ruthenium tetroxide is evolved at the anode and we prefer to use a solution containing about g./l. of ruthenium. Increasing the ruthenium concentration above this, decreases the cathode efliciency and increases both the cost of the bath and the losses of ruthenium by drag-out.

The acidity of the solution is not critical, but advantageously from 10 to 50 g./l. of free sulphamic acid is present. This may be partly or wholly replaced by sul-. phuric acid. The remainder of the bath is essentially water.

The bath can be used from room temperature up to boiling point. The cathode efficiency of the bath increases with temperature and a suitable working temperature range is from 50 C. to 90 C., advantageously about 3,123,544 Patented Mar. 3, 1964 "ice 70 C. Increasing the current density decreases the cathode efiiciency and advantageously the cathode current density is about 2 to about 8 amperes per square decimeter (amps./dm.

By way of example, a bath containing 5 g./l. of ruthenium as sodium tetrasulphamato nitrosyl ruthenate and 30 g./l. of free sulphamic acid was used to plate copper discs 2 square inches in total area which had previously been given a thin electrodeposit of copper from an acid copper sulphate bat'h followed by a flash coating of gold or palladium. The ruthenium plating bath was maintained at a temperature of 70 C. and ruthenium was electrodeposited on the discs at a current density of 8 amps./dm. using insoluble anodes of platinum foil. The deposition rate was about 0.00015 inch/hour and the cathode efficiency was 5%. The deposits were bright and substantially crack-free up to a thickness of 0.0002 inch. Their surfaces showed a very faint crack pattern but this did not show up when the deposits were sectioned. At a thickness of 0.00045 inch the deposits were bright and frosted.

At a thickness of 0.0001 inch, one or" the deposits had an internal tensile stress of 25.7 tons/sq. inch and at a thickness of 0.0005 inch it had a hardness of about 900 DPN.

A similar bath operated under similar conditions but using a current density of 4 amps./dm. electrodeposited ruthenium on a cathode at a deposition rate of 0.00009 inch/ hour with a cathode efliciency of 5.5%.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

I claim:

1. A process for the electrodeposition of ruthenium which comprises oathodically depositing ruthenium from an aqueous acidic bath containing at least about 2.5 grams per liter of ruthenium dissolved therein as a tetrasulphamato nitrosyl ruthenate at a cathode current density of about 2 to about 8 amperes per square decimeter.

2. A process as defined in claim 1 wherein the bath contains up to about 50 grams per liter of an acid selected from the group consisting of sulphuric acid, sulphamic acid and mixtures thereof.

3. A process as defined in claim 2 wherein the bath contains about 2.5 to about 20 gna-ms per liter of ruthenium and is maintained at a temperature of about 50 C. to about C.

4. A process as defined in claim 2 wherein the bath contains at least about 10 grams per liter of acid.

5. A ruthenium electroplating bath comprising an aqueous acidic solution of at least about 2.5 grams per liter of ruthenium as a tetrasulphamato nitrosyl ruthenate.

6. A ruthenium electroplating bath comprising an aqueous acidic solution of about 2.5 to about 20 grams per liter of ruthenium as a tetrasulphamato nitrosyl ruthenate.

7. A ruthenium electroplating bath as defined in claim 6 which contains about 10 to about 50 grams per liter of an acid selected from the group consisting of sulphuric acid, sulphamic acid and mixtures thereof.

References Cited in the file of this patent UNITED STATES PATENTS 2,600,175 Volterra June 10, 1952 FOREIGN PATENTS 466,126 Great Britain May 18, 1937

Claims

1. A PROCESS FOR THE ELECTRODEPOSITION OF RUTHENIUM WHICH COMPRISES CATHODICALLY DEPOSITING RUTHENIUM FROM AN AQUEOUS ACIDIC BATH CONTAINING AT LEAST ABOUT 2.5 GRAMS PER LITER OF RUTHENIUM DISSOLVED THEREIN AS A TETRASULPHAMATO NITROSYL RUTHENATE AT A CATHODE CURRENT DENSITY OF ABOUT 2 TO ABOUT 8 AMPERES PER SQUARE DECIMETER.