US3442810A - Chemical polishing composition and method - Google Patents

Description

3,442,810 Patented May 6, 1969 in practice and have suffered from certain shortcomings 3,442,810 in that the y do not impart a uniformly bright surface to CHEMICAL g g ggggg copper and brass articles, and also, do not produce a Charles H. Elbreder, St. Louis, Mo., assignor to Garman Company, Incorporated, Lemay, Mo., a corporation of copper, brass or alloys of high copper content. However, such compositions have not proved entirely satisfactory smooth, level surface substantially free of projections and other surface irregularities. Upon examination, it is seen Missouri 5 that the surface of copper and brass articles to be polished No Drawing. Filed Feb. 25, 1966, Ser. No. 529,950 is consistently irregular in profile. These irregularities conlut- Cl- C23f 3/04 sist of projections and depressions or peaks and valleys US. Cl. 252-79.4 12 Claims on the f A high degree of smoothness and brightness of the surface of copper articles is desirable particularly where ABSTRACT OF THE DISCLOSURE such articles are to be nickel plated. When the surface An improved aqueous polishing composition which is a P hf f is smooth h h i no effective for use in polishing articles composed of copper, surface irregularities, considerably less nickel 15 required brass or alloys of high copper content consists f a 15 to obtain a high luster for the plated article. There rechmmtum compound Such as chromium triexide or maths, therefore, an unfulfilled need for an improved m provides a concentration of polishing composition which does not exhibit the afore- 25% by weight of chromic acid in aqueous solution, a mehhohed E source of elemental bromine such as sodium bromide In the presehhmvehhohi has h which provm weight of bromine in aqueheen found that improved results in the chemical pol1shous solution and either sulfamic acid or sulfuric acid in mg of copper and t cles may be achieved through an amount mm to The the use of a composition containing a chromium comcomposition may be prepared in dry form and then dis- PPuhd whfch Fonverted Into chroimc acid h bemg sdlved in water to form an aqueous polishing eompesi dissolved in acidified Wat er, an alkali metal bromide and tion. The copper article is contacted with the aqueous lf he1hg dlssolved m which h h a composition for a brief period and the reddish brown composition Provldes, an t y afluwus 'pohshmg film which forms thereon istthen removed by dipping the composition for chemically polishing articles composed of article in an acid or alkaline medium or by heating the copper brass h Y of f f I h article to a temperature above 180 F. The resulting article fshtmd that the pollshmg P of my mvemwn displays a smooth bright finish having a high degree of simultaneously effect macropolishtng (i.e., the removal of lusten coarse PIOjCCtlOIlS from and leveling of the surface) and micropolishing (i.e., the dissolving of smaller surface irregularities and polishing of the surface), and thereby h mvehhoh relates to chemlcal Pohshmg and {hora impart smoothness and brightness, respectively, to the particularly to compositions and methods for chemically Surface of the eopper article Phlishihg articles composed of copper, brass or alloys of It is believed that the presence of elemental bromine hlgh F PP contemand chromic acid in an aqueous solution having a low y the P Q mvenhon 15 dlrected to a f pH value is responsible for imparting unique leveling P ith hf ahhqhews Pohshlhg and chemical polishing characteristics to the surface of composition for s Ph amcles composed P 40 the article treated therewith. The elemental bromine is FQPP brass alloys of hlgh QPP I content f provided by adding elemental bromine per se to the aque mg chrhmlhm corhpohhd Whlch 1S {ohverted lhto ous solution or by incorporating an alkali metal bromide chromic acid upon being dissolved in acidified water, an ht the drv composition Whteh is added to Water to form alkali metal bromide and sulfamic acid. The invention my aqueeus polishing composition The alkali metal is also directed to aqueous polishing compositions formed mtdes, such as Sodium and potassium bromides, are by dlssolvlhg dry .composlhohs of the abPve type water dized and release free bromine in an aqueous solution havand to methods of chemical polishing utilizing such aquethe a low PH 0115 P t The chromic acid in the aqueous composition is pro- Among the py hl of the hh may he vided by incorporating in the dry composition a chroh f provfslhh of Improved composlhohs for use mium compound which is converted into chromic acid m pcfhshlhg arhclhs composed of Fh brass or upon being dissolved in acidified water. Preferably, chro- Q hlgh Q PPF content; the P of such h mium trioxide is employed as the chromium compound tio s which impai 't to copper articles a smooth, brigh as this is readily converted into chromic acid upon being finish having a high degree of l ster; the pr f of dissolved in water. However, it will be understood that composlhohs of type which slmhhaheously achieves 55 alkali metal chromates such as sodium chromate and po removal of coarse Projections and dissolving of Smaller tassium chromate and alkali metal dichromates such as surface irregularities Ff' the Surface of the themed sodium dichromate and potassium dichromate, may also P P and the of i h of chemically be employed to provide chromic acid in the aqueous polpolishing copper articles with compositions of the type ishihg composition of my invention metitioned whieh may be conveniently carried out and In order to provide the low PH for the aqueous which f rehahle rcsuhsoiher ohiectF and features position containing the chromic acid and elemental bro- Y be in Part apparent and In P Polhted out here mine, either sulfamic acid or sulfuric acid may be inlhafterg cluded. Sulfamic acid is preferred since it has been found The invention accordingly comprises the products and t0 give a Somewhttt better Surface fi i h to the eophet methods herei after described, the scope of th lnven' 5 article being treated. Moreover, being a solid, sulfamic hoh P md'cated h the h h h acid may be incorporated in the dry composition dc As is known, chemical polishing or brightening comscribed above positions have been formulated and used heretofore for In the Practice of the invention, it has been found the P p Of Polishing and imparting a brightened that the amount of free bromine present in aqueous soluface to articles h as fittings, for p p d of tion with chromic acid and sulfamic or sulfuric acid should be between approximately 0.05% and 3.5% by weight in order to achieve enhanced chemical polishing .ing composition may be prepared by dissolving the individual components in the necessary amount of water. In the latter case, of course, it is possible to use elemental bromine as the source of bromine and sulfuric acid to provide a low pH whereas these particular components may not be incorporated in the dry composition.

In carrying out the invention, a dry composition containing a chromium compound convertible into chromic acid upon being dissolved in acidified water, an alkali metal bromide and sulfamic acid is first dissolved in water to provide an aqueous solution having a pH within the limits stated above and containing chromic acid and free bromine. Alternatively, such an aqueous solution may be formed by dissolving chromium trioxide or an alkali metal chromate or dichromate in water together with elemental bromine or an alkali metal bromide and either sulfamic or sulfuric acid. In either event, the amount of components employed should be within the ranges hereinbefore stated. The copper or brass article to be treated is then immersed in the aqueous solution for a relatively short period of time which may range from a few seconds to about five minutes. Immediately after immersion, it will be observed that a reddish brown film is formed on the surface of the metal article. After the de sired immersion period the article or metal part is removed from the aqueous solution and preferably rinsed in water to wash away the aqueous polishing solution remaining thereon.

Next, the reddish brown film is removed and this is preferably effected by dipping the article in an alkaline or acid medium. It has been found that the reddish brown film formed on the surface of the copper article is insoluble in cold water and only slightly soluble in hot water. However, the film is readily soluble in alkaline and acid media. Any of the conventional acid or alkaline media may be used. For example, a solution containing between 2% and by weight of sodium hydroxide or one containing between 2% and 10% by weight of sulfuric acid or sulfamic acid has been found satisfactory for this purpose.

If desired, the reddish brown film may be removed by heating the article to a temperature of at least 180 F., preferably a temperature between 180 F., and 200 F.

Folowing removal of the film, the article may be given a final water rinse to wash away traces of the acid or alkaline media used in removing the film. The surface of the article thus produced through the practice of the invention exhibits a high degree of luster and polish and is substantially smooth and free of projections and irregularities.

Although the exact nature of the reddish brown film formed on the surface of the article is not known, it is believed the film consists of a cupric chromate complex compound having the formula CuCrO -2CuO2I-l O. This film is somewhat gelatinous in nature and forms uniformly over the entiresurface being treated. It is believed that the metal being treated becomes anodic upon being submersed in the above described aqueous solution and that the film is responsible for micropolishing of the surface by chemical oxidation. The film apparently allows the necessary exchange of electrons between the metal being polished and the ions in solution. In any event, the resulting surface is smooth and bright.

The following examples illustrate the invention.

Example 1 An aqueous solution was prepared containing 10% by weight of chromium trioxide and 10% by weight of sulfamic acid. Upon being dissolved in water, the chromium trioxide was converted into chromic acid. The solution had a pH of 0.5. To the solution was added 0.2% by weight of elemental bromide. A copper fitting was immersed in the resulting solution whereupon a reddish brown film immediately formed on the surface thereof. After three minutes, the fitting was removed from the solution and rinsed in water. The fitting was next dipped in a 2% sodium hydroxide solution to remove the reddish brown film. The fitting was then given a final water rinse. The resulting fitting exhibited a high degree of luster, brightness and smoothness.

Example 2- A dry composition soluble in water to form an aqueous polishing composition for use in polishing articles composed of copper, brass or alloys of high copper content, was prepared having the following composition by weight- Component: Percentage by weight Chromium trioxide 53.8 Sulfamic acid 44.8 Potassium bromide 1.4

Example 3 The composition of Example 2 was dissolved in water to form the following aqueous polishing composition Component: Percentage by weight Chromium trioxide 12.0 Sulfamic acid 10.0 Potassium bromide 0.3 Water 77.7

This aqueous polishing composition was used as described in Example 1 to polish a copper article with good results.

Example 4 An aqueous polishing composition was prepared having the following composition by weight Component: Percentage by weight Chromium trioxide 18.0 Sulfuric acid 5.0 Bromine 0.3 Water 76.7

The composition was prepared by dissolving the chromium trioxide, sulfuric acid and bromine in water. The composition was used as described in Example 1 with good results.

Example 5 A dry composition was prepared having the following composition by weight Component: Percentage by weight Sodium dichromate 52.6 Sulfamic acid 42.1 Potassium bromide 5.3

Example 6 The composition of Example 5 was dissolved in water to form the following aqueous polishing composition Component: Percentage by weight Sodium dichromate 15.0 Sulfamic acid 12.0 Potassium bromide 1.5

Water 71.5

The resulting aqueous polishing composition was used as described in Example 1 with good results.

Example 7 An aqueous polishing composition was prepared having the following composition by weight A dry composition was prepared having the following composition by weight Component: Percentage by weight Chromium trioxide 56.7 Sulfamic acid 39.0 Sodium bromide 4.3

Example 9 The composition of Example 8 was dissolved in water to form the following aqueous polishing composition- Component: Percentage by weight Chromium trioxide 15.0 Sulfamic acid 11.0 Sodium bromide 2.2

Water 71.8

The resulting aqueous polishing composition was used as described in Example 1 with good results.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could be made in the above methods and products without departing from the scope of the invention, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A dry composition soluble in water to form an aqueous polishing composition for use in polishing articles composed of copper, brass or alloys of high copper content consisting essentially of a chromium compound selected from the group consisting of chromium trioxide, alkali metal chomates and alkali metal dichromates, an alkali metal bromide and sulfamic acid, the amount of said chromium compound in the composition providing a concentration of between 2% and 25% by weight of chromic acid in aqueous solution, the amount of said alkali metal bromide in the composition providing between 0.05% and 3.5% by weight of bromine in aqueous solution and the-amount of sulfamic acid in the compo sition being sufiicient to provide a pH of approximately 0.1 to 2.0 for the aqueous solution formed by dissolving the composition in water.

2. A dry composition as set forth in claim 1 in which the chromium compound is chromium trioxide and the alkali metal bromide is potassium bromide.

3. A dry composition as set forth in claim 1 wherein the chromium compound is sodium dichromate.

4. An aqueous polishing composition for use in polishing articles composed of copper, brass or alloys of high copper content consisting essentially of water, a chromium compound selected from the group consisting of chromium trioxide, chromic acid, alkali metal chromates and alkali metal dichromates, a source of bromide selected from the group consisting of elemental bromine and'alkali metal bromides and an acid selected from the group consisting of sulfamic acid and sulfuric acid, the amount of said chromium compound in the composition providing a concentration of between 2% and 25% by weight of chromic acid in aqueous solution, the amount of said source of bromine in the composition providing between 0.05% and 3.5% by weight of bromine in aqueous solution and the amount of said acid in the composition being suflicient to provide a pH of approximately 0.1 to 2.0 for the composition.

5. An aqueous polishing composition as set forth in claim 4 wherein the chromium compound is chromic acid, the source of bromine is elemental bromine and the acid is sulfamic acid.

6. An aqueous polishing composition as set forth 'in claim 4 wherein the chromium compound is chromium trioxide and the alkali metal bromide is potassium bromide. x

7. An aqueous polishing composition as set forth in claim 4 wherein the chromium compound is sodium dichromafe.

8. Themethod of chemically polishing an article composed of copper, brass or alloys of high copper content ,to impart a smooth, bright finish having a high degree of luster which comprises the steps of contacting said article with an aqueous polishing composition consisting esseniially of water, a chromium compound selected from the group consisting of chromium trioxide, chromic acid, alkali metal chromates and alkali metal dichromates, a source of bromine selected from the group consisting of elemental bromine and alkali metal bromides and .an acid selected from the group consisting of sulfamic acid and sulfuric acid, the amount of said chromium compound in the composition providing a concentration of between 2% and 25% by weight of chromic acid in aqueous solution, the amount of said source of bromine in the composition providing between 0.05% and 3.5 by weight of bromine in aqueous solution and the amount of said acid in the composition being suflicient to provide a pH of approximately 0.1 to 2.0 for the composition, and thereafter removing the film formed on said article by subjecting the article to treatment with an alkaline or acid medium or by heating the article to a temperature of about to 200 F.

9. The method of chemically polishing as set forth in claim 8 wherein the chromium compound is chromic acid, the source of bromine is elemental bromine and the acid is sulfamic acid.

10. The method of chemically polishing as set forth in claim 8 wherein the article is given a water rinse before and after removal of said film therefrom.

11. The method of chemically polishing as set fort in claim 8 wherein the alkaline medium is sodium hydroxide.

12. The method of chemically polishing as set forth in claim 8 wherein the acid medium is sulfamic acid.

(References on following page) References Cited UNITED STATES PATENTS Rich et a1. 212-792 XR Pryor et a1. 106-3 Post et a1. 212-792 XR Alderuccio et a1. 156-18 XR Szkudlapski 212-793