US3669766A - Formation of coating on copper containing materials - Google Patents

Abstract

A METHOD OF INDUSTRIALLY FORMING VERDIGRIS ON A SURFACE OF AN ARTICLE OF COPPER OR AN ALLOY THEREOF WITHIN A SHORT PERIOD, WHICH RESEMBLES THAT NATURALLY FORMED, SO AS TO PREVENT THE SURFACE FROM CORROSION AND TO GIVE A DECORATIVE AND ARTISTIC APPEARANCE, BY TREATING SUCH A SURFACE WITH A SOLUTION CONTAINING AMMONIUM SULPHATE AND MERCURIC CHLORIDE OR FURTHER TREATING WITH AN ETHYL NITRATE SOLUTION.

Description

United States Patent 3,669,766 FORMATION OF COATING ON COPPER CONTAINING MATERIALS Mitsunosuke Fukawa, 20-21, l-chome, Matsugaoka, Kugenuma, Fujisawa-shi, Kanagawa-ken, Japan; and Haruo Oishi, 21-7, S-chome, Nakano-ku; Kicllitaro Saruya, 7-14, Z-chome, NIinami-cho, Tanashi-shi; and Akira Nagai, 17, Z-chome, Fukuro-machi, Kita-ku, all of Tokyo, Japan; and Yoshitaro Nagai, 13-3, l-chome, Nishikamata, Ota-ku, Japan No Drawing. Filed Nov. 28, 1969, Ser. No. 880,929 Int. Cl. C23f 7/00 US. Cl. 148-624 1 Claim ABSTRACT OF THE DISCLOSURE A method of industrially forming verdigris on a surface of an article of copper or an alloy thereof within a short period, which resembles that naturally formed, so as to prevent the surface from corrosion and to give a decorative and artistic appearance, by treating such a surface with a solution containing ammonium sulphate and mercuric chloride or further treating with an ethyl nitrate solution.

BACKGROUND OF THE INVENTION It is well known that in the atmosphere oxygen, steam carbonic acid gas, sulphides, and the like act on copper and copper alloys to form basic copper salts which constitute verdigris having an elegant colour tone. However, recently in cities and town, it is impossible to expect the formation of a beautiful film of verdigris naturally due to the fact that a clean copper surface is blackened. Under these circumstances, an artificial formation of verdigris is required. Meantime, many methods have been well known for forming verdigris artificially on the industrial art works by employing chemicals. In one of these methods copper salts and ammonium chloride are used.

The copper salts are dissolved in water or an acid material is provided for replenishing copper ion which constitutes the formation of verdigris. The ammonium chloride or a substitute thereof reacts with copper to produce blue copper hydroxide. In addition, alum, arsenous acid, and the like are added to accelerate the reaction of the copper ion and improving the durability of the verdigris.

However, even if it is possible to treat small numbers of the industrial art works or the like by the prior art, it is substantially impossible to treat large areas such as those of roofs and walls of a religious, monumental building, or the like by the conventional method.

SUMMARY OF THE INVENTION This invention relates to chemical methods of forming verdigris on a surface of an article of copper or an alloy of which the main constituent is copper, which is of industrial application.

The object of this invention is to provide a method of forming verdigris which resembles that naturally formed, on a surface of an article of copper or an alloy of which the main constituent is copper, so as to form a film of verdigris within a short period which is effective for preventing the surface from undesirable deterioration such as corrosion and giving the surface a decorative and artistic appearance.

The invention provides a process of forming verdigris on the surface of an article which comprises either copper or an alloy of which the main constituent is copper, comprising bringing the surface into contact with a solution containing ammonium sulphate and mercuric chloride. The solution preferably contains copper sulphate. Preferably the pH of the solution is from 4 to 5 and the concentration of ammonium sulphate is above 25 grams per litre.

By virtue of this invention, the drawbacks inherent to the conventional method are removed or mitigated and the formation of verdigris may be carried out industrially and mass-productively in response to the above-mentioned requirement.

:In the process of the invention an amalgam of copper and mercury is formed from the main constituent and the solution of the invention so that the substance of the verdigris film is produced by combining copper sulphate and others within a short period to convert a film into the verdigris film which resembles that naturally formed. The verdigris film formed as above may subsequently be treated with a solution containing an alkyl (particularly ethyl) nitrite so as to convert the film into another verdigris film having a colour tone which is nearer to that of the naturally formed verdigris without aging, and a stability.

DESORIPT ION OF THE PREFERRED EMBODIMENTS In accordance with the present invention, an A liquor is used, which comprises such constituents as 50 to 150 g. of ammonium sulphate, 2 to 8 g. of cupric sulphate, and 5 to 15 g. of mercuric chloride, dissolved in one litre of water, of which pH value is adjusted in the range from 4.0 to 5.0 by adding 28 percent aqueous solution ammonia thereto. A C liquor may also be used, which comprises one litre of water containing such solutes as 5 to 20 g. of ammonium chloride, 20 to 60 g. of sodium chloride, and 50 to g. of copper nitrate mixed with 30! to 100 cc. of 15 percent alcoholic ethyl nitrite solution.

In operation, a cleaned surface of a copper article is sprayed with or immersed in the A liquor and allowed to stand in the atmosphere to dryness. The dried surface is again treated as above. A film of verdigris having a more bluish colour tone than that of naturally formed verdigris is formed, which becomes more to resemble to the latter by aging. In order to obtain an artificial verdigris more resembling the natural one just after the treatment, the article may be sprayed with or immersed in a C liquor in a similar manner as the treatment with the A liquor. 1

Now the treatment in accordance with this invention will be explained from the chemical point of view. The cleaned surface of copper or an alloy thereof reacts with the A liquor as follows:

Volts CuCu ++2e 0.34 HgHg ++2e 0.86

Copper (amalgamated copper) and ammonium sulphate in the A liquor react with atmospheric oxygen as follows, yielding ammonia:

A part of the ammonium is expelled into the atmosphere in the gaseous state and another part reacts with copper sulphate as follows, yielding cupric hydroxide and regenerating ammonium sulphate.

CuSO +2NH OH-Cu(OH) +(NH4) SO (3) The cupric hydroxide combines with copper sulphate on the instant of formation thereof, yielding basic copper sulphate which forms the substance of the blue verdigris.

The ammonium sulphate is one of the essential ingredients to the A liquor. The use of ammonium sulphate of the concentration below 50 g./l. cannot provide the blue verdigris of the desired thickness because of the insufiicient yield of ammonia and, hence, cupric hydroxide. Thus, below 50 g./l. there is no substantial eifect of the ammonium sulphate concentration, but the use of a com centration higher than 150 g./l. is not necessary.

It is clear that the reaction in accordance with the Formula 2 requires oxygen. Therefore, not only the mode of contact of the article to be treated with the A liquor is important, but also the drying condition for the treated article is essential. In view of our experiments, it is preferred to naturally dry for a period of 15 to 20' minutes conditional on that the humidity is 50 to 60% and the temperature is 15 to 30 C.

The reaction for forming verdigris is greatly affected by the concentration of mercuric chloride in the A liquor. Even in the absence of Hg, the reaction as the Formula 1 would arise. But in such a condition as above, the reaction velocity would be slow, and a little quantity of ammonium would be produced so as to form a little verdigris. The mercuric chloride can be used in a concentration range from 5 g./l. to 15 g./l. to ensure the formation of sufiicient amounts of the amalgam and cupric hydroxide; however, no significant effect is obtained with a concentration of higher than 15 g./l. of mercuric chloride. The amalgam of copper separated on the surface thereof is likely to serve as a bonding material for the verdigris film. By virtue of the amalgam, the verdigris film becomes well adhesive. It is sufiicient that the A liquor has copper sulphate in concentration of 0.5 to 2 g./litre as Cu. In most cases, a concentration of l g./litre Cu is appropriate. Of course, copper sulphate is an indispensable constituent for the treatment. However, too much copper sulphate would result a too thick film which would be apt to peel. On the contrary, too little copper sulphate would form too little subject of verdigris so that it is impossible to form a verdigris film having a desired thickness and a desired colour tone. The ammonium sulphate in the A liquor is also an indispensable constituent. In the absence of this constituent, verdigris is not formed. It is not necessary to define the concentration of ammonium sulphate in the A liquor appreciably strictly. However, it is necessary to contain at least 25 g. thereof in one litre of the A liquor.

The A liquor may be used at the normal temperature, and the pH value thereof suitable for the process is between 4.0 and 5.0. The amount of formation of verdigris becomes less as the pH value rises. The amount of formation and quality of verdigris become extremely bad at a pH value higher than 7.0 and as the pH value decreases below 4.0, there are the additional bad effect of poor adhesion of verdigris to the substrate. The verdigris film may be formed by giving attention to the conditions as above.

The action and effect of the C liquor are as follows. When a film formed by the action of the A liquor is sprayed with the C liquor, ethyl nitrite contained in the C liquor acts as a reductant, so that basic copper sulphate in the film and copper nitrate in the C liquor are converted into basic copper nitrite and the cupric ion is reduced to the cuprous ion so asto form a basis cuprous salt which constitutes yellowish green verdigris. It is necessary that the C liquor contains at least g. of ethyl nitrite as C H ONO per one litre thereof, while the allowable upper limit of the concentration of ethyl nitrite is indefinite.

The ammonium chloride and sodium chloride in the C liquor serve as a source of chlorine ion by means of which the color of verdigris is changed from bluish green to yellowish green. This change of color does not occur in the absence of chlorine ion, even if the ethyl nitrite is present in the system. The concentration of ammonium chloride to be used may be 5-20 g./l., but it is not so critical. The sodium chloride having the color-changing function mentioned above should be used at a concentration from 20 g./l. to 60 g./l. The concentration below 20 g./l. cannot impart sufiicient color-changing function to the C liquor. The copper nitrate is suitably used at a concentration of from 50 g./l. to 100 g./l. The use of copper nitrate in excess of 100 g./l. results in the formation of too thick a film of verdigris which is liable to peel off, and less than 50 g./l. affects the deepness of the color.

By virtue of the C liquor, the colour tone of the verdi-,.

gris is converted and the adhesion to the base metal is improved.

Examples of the process of the invention will now be given.

were dissolved in water which was then diluted to one litre and adjusted to a pH from 4.0 to 5.0 by 28 percent ammonia solution.

A cleaned surface of copper was sprayed with 200 to 500 cc./m. of the A liquor composed as above at normal temperature and allowed to dry naturally.

The condition for drying in this case is very important. It is most preferable that the natural drying requires a period of about 15 to 20 minutes at a temperature of from 15 to 30 C., and a humidity of from 50 to 60%. Stagnant excess liquid formed by the spraying operation will result in a verdigris film inferior in adhesion, if left as it is on the sheet. Accordingly, it is necessary to suck away such stagnant excess liquid by a sucking means.

The film formed was sprayed with the A liquor repeatedly three times.

Except in the initial operation, the spraying and drying operation do not require such strict conditions.

Example 2 A liquor: G. Ammonium sulphate (NH SO 50 Copper sulphate CuSO -5H O 5 Mercuric chloride HgCl 8 were dissolved in water which was then diluted to one litre and adjusted to a pH from 4.0 to 5.0 by 28 percent ammonia solution.

C liquor: G. Ammonium chloride NH.,C1 15 Sodium chloride NaCl 50 Copper nitrate Cu(NO -3H O 100 The three constituents were dissolved in water which was then diluted to one litre, and then 100 cc. of 15 percent alcoholic ethyl nitrate solution were added. Asurface of copper plate, cleaned by means of liquid honing, was sprayed with the A liquor at normal temperature at the rate of from 200 to 500 cc. per square meter. Stagnant excess liquid was sucked away. The plate was naturally dried for 10 to 30 minutes at a humidity from 50 to percent and a temperature from 5 to 35 C.

The, film yielded by treating with the A liquor was sprayed with C liquor at a normal temperature at the rate of to 200 cc. per square meter and naturally dried. The length of the drying period does not substantially aifect to the formation of the verdigris. The treatment with the C liquor was repeated once more and the again sprayed plate was naturally dried. It is not necessary to wash the treated plate with water, but it is rather preferred to allow it to stand as it is for a period of two or three days.

What is claimed is:

1. A method of producing on the surface of an article having copper as the main constituent, a large scale yellowish green verdigris, which comprises the steps of:

(a) treating the surface of the article with an aqueous solution comprising 50 to 150 grams per liter ammonium sulfate, 5 to 15 grams per liter mercuric chloride and 2 to 8 grams per liter copper sulfate, the pH of which is adjusted to 4.0 to 5.0; and

(b) treating the verdigris thus formed with an aqueous 10 solution comprising 50 to 100 grams per liter copper nitrate, 10 grams per liter or more of ethyl nitrite in a 15% alcoholic solution, and a chlorine ion donor of 5 to 60 grams per liter.

References Cited UNITED STATES PATENTS 1,951,304 3/1934 Freeman et al 1486.24 3,473,970 10/1969 Robey 1486.24 X

OTHER REFERENCES Hopkins, Scientific American Cyclopedia of Formulas, Scientific Am. Pub. Co., 1925, p. 441.

RALPH S. KENDALL, Primary Examiner US. Cl. X.R. 148-6. 14