US3008812A

US3008812A - Method for chemical polishing of copper

Info

Publication number: US3008812A
Application number: US749597A
Authority: US
Inventors: Spahn Heinz; Frederick H Wells
Original assignee: Albright and Wilson Mfg Ltd
Current assignee: Albright and Wilson Mfg Ltd
Priority date: 1957-08-20
Filing date: 1958-07-21
Publication date: 1961-11-14
Anticipated expiration: 1978-11-14

Description

United States Patent Ofiice 3,008,812 Patented Nov. 14, 1961 3,008,812 METHOD FOR CHEMICAL POLISHING OF COPPER Heinz Spiihn, Darmstadt, Germany, and Frederick H. Wells, Erdington, England, assignors to Alh'right and Wilson (Mfg) Limited, Birmingham, England No Drawing. Filed July 21, 1958, Ser. No. 749,597

Claims priority, application Great Britain, Aug. 20, 1957 4 Claims. (Cl. 156---20) This invention relates to the chemical polishing of copper and its alloys.

A bath for chemically polishing metal surfaces has been proposed in United States Patent No. 2,446,060 consisting of concentrated solutions of from 5% to 85% by volume of nitric acid of about 1.42 specific gravity, admixed with from to 95% by volume of phosphoric acid of about 1.7 specific gravity and from 0% to 90% by volume of acetic acid of about 1.05 specific gravity. It was stated that the maximum amount of water which may be added to baths containing nitric acid and phosphoric acids alone, the composition of which could be varied from to 75% nitric acid and 95% to 25% phosphoric acid, was by volume since at proportions of water above this, the polish obtained would be impaired.

It was further stated in British Patent No. 73 8,744 that where no acetic acid was present in the bath, but only phosphoric acid and nitric acid, the presence of water is essential in order to obtain a satisfactory polish and a bath for the chemical polishing. of copper, nickel and alloys of those metals, with or without the addition of zinc, was proposed which comprises from 5% to 83% of phosphoric acid, from 2% to 50% of nitric acid, and from to 45% of water.

It has now been found that very much improved polishing is obtained using baths containing arsenic acid together with phosphoric acid and nitric acid. The baths of the present invention give a specular polish considerably superior to that obtained using any bath previously known.

According to the present invention there is provided a solution for the chemical polishing of copper and its alloyswhich comprises from 5% to 40% arsenic acid (of a concentration of 80% by weight in water), from 2% to 50% nitric acid of specific gravity 1.5 and from 5% to 75% phosphoric acid of specific gravity 1.75; preferably the solution also contains glacial acetic acid and/or up to water. The foregoing percentages are all quoted by volume.

The preferred solutions contain from 10% to 30% arsenic acid,.from 20% to 30% phosphoric acid, from 30% to 50% acetic acid, from 10% to 15% nitric acid, and from 0% to 10% water, all percentages being by volume and the strengths of the acids being as hereinbefore defined.

It has been found that the polishing rate of the solutions is controlled by the quantity of glacial acetic acid present. If no acetic acid i present, the polishing rate tends to be too high, and if more than 70% is present, the rate is too slow for most practical purposes. If more than 75% of phosphoric acid is present, the metal is etched. If more than 30% of nitric acid is present, the polish obtained, although bright, is not very specular, and if more than 40% of arsenic acid is present, the surface of the immersed metal becomes pitted.

The solutions will continue to polish without requiring regeneration until they contain up to about 90 grams per litre of dissolved metal. When regeneration is necessary, that is when polish is impaired or the polishing rate is appreciably altered, it may be achieved merely by the addition of any constituent which is found to be deficient after analysis of the polishing solution. It is usually sufficient to add nitric acid and acetic acid and it has not been found necessary to add further quantities of arsenic acid.

In use, the solutions are preferably maintained at a temperature of from 50 C. to C. and with the preferred solutions of this invention satisfactory polish is obtained in about three minutes.

The solutions of the present invention may satiss factorily be stored in vesselsmade, of such materials as glass, chemical stoneware, stainless steel or polyvinyl resins.

It has not been found that the presence of arsenic acid in the polishing solution introduces any danger in the form of toxic fumes or deposits on the polished metal surfaces. No arsine has been detected in the fumes from the solutions even in the absence of nitric acid and no appreciable deposit of arsenic compounds has been found on the surface of the polished metal.

It is to be noted that the method of chemically polishing metal surfaces according to the invention consists in merely immersing them, as distinct from processes in Which the metal is made the anode in the polishing solution as electrolyte. The baths of the present invention are not suitable for use in electro-polishing.

The following examples serve to illustrate the manner in which the invention may be performed, the percentages in each case being by volume and the concentrations of the acids used being as hereinbefore stated. It is to be understood that the percentages of Water refer to added Water, excluding the water already present in the acids before mixing.

Example 1 A solution was prepared containing 20% phosphoric acid, 15% arsenic acid, 45% acetic acid, 10% nitric acid and 10% Water, and the metal articles to be polished were immersed in it for three minutes at a temperature of 6080 C. A reasonably good polish was obtained, being better on copper and nickel silver than on brass.

Example 2 A solution was prepared containing 20% phosphoric acid, 30% arsenic acid, 40% acetic acid, 10% nitric acid and no added water. A very good polish was obtained on brass articles immersed for three minutes at 60 80 C. A good polish was obtained on gilding metal immersed for three minutes at 50-60 C. but no polish at all was obtained on copper or nickel silver.

Example 3 Example 4 A solution was prepared containing 20% phosphoric acid, 30% arsenic acid, 35% acetic acid, 15 nitric acid and no added water. A good polish was obtained on brass articles immersed for three minutes at 6080 C. but the metal solution rate was rather high. A fair polish was obtained on gilding metal immersed for three minutes at 70 C. but no polish was obtained on nickel silver.

In the foregoing examples the brass used was composed of 70% by weight of copper and 30% by weight of zinc and the gilding metal was composed of from 80 %90% by weightrof copper and from 20%-10% by weight of zinc.

We claim:

1. The method of chemically polishing articles of a metal of the class consisting of copper and alloys of copper, which comprises immersing the article in a solution comprising from to 30% by volume of arsenic acid of a concentration of 80% by weight in Water, from to by volume of phosphoric acid of specific gravity 1.75, from 30% to 50% by volume of glacial acetic acid, from 10% to 15% by volume of nitric acid of specificgravity 1.5 and from 0% to 10% by volume of additional water.

2. The method as claimed in claim 1 in which said solution is maintained at a temperature in the range of from 50 C. to 80 C.

3. The method of chemically polishing articles of a metal of the class consisting of copper and alloys of copper, which comprisesimrnersing the article in a solution comprising from 5% to 40% of arsenic acid of a concentration of 80% by Weight in water, from 2% to 4 by volume of nitric acid of specific gravity 1.5, and from 5% to by volume of phosphoric acid of specific gravity 1.75.

4. The method as claimed in claim 3 in which the nitric acid is present in an amount not exceeding 30% by volume.

References Cited in the file of this patent UNITED STATES PATENTS 2,005,780 Gravell June 25, 1935 2,172,171 Meyer Sept. 5, 1939 2,282,351 Faust May 12, 1942 2,446,060 Pray et -al July 27, 1948 2,456,947 Jermstedt Dec. 21, 1948 2,650,157 Cochran Aug. 25, 1953 2,729,551 Cohn M Jan. 3, 1956

Claims

1. THE METHOD OF CHEMICALLY POLISHING ARTICLES OF A METAL OF THE CLASS CONSISTING OF COPPER AND ALLOYS OF COPPER, WHICH COMPRISES IMMERSING THE ARTICLE IN A SOLUTION COMPRISING FROM 10% TO 30% BY VOLUME OF ARSENIC ACID OF A CONCENTRATION OF 80% BY WEIGHT IN WATER, FROM 20% TO 30% BY VOLUME OF PHOSPHORIC ACID OF SPECIFIC GRAVITY 1.75, FROM 30% TO 50% BY VOLUME OF GLACIAL ACETIC ACID, FROM 10% TO 15% BY VOLUME OF NITRIC ACID OF SPECIFIC GRAVITY 1.5 AND FROM 0% TO 10% BY VOLUME OF ADDITIONAL WATER.