US2409295A - Porous metal article - Google Patents

Description

Gd. 15, 1945. J, RVI r 2,409,295

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Filed Dec. 8. 1941 2 Sheets-Sheet 2 l I I I I I I I I I '1 I, I J' I! I/I/IIIIII 1/,

THUR ATI'ORN Patented Oct. 15, 1946 POROUS METAL ARTICLE John '1. Marvin and Roland R-Koehrlng, Dayton, Ohio, assignors to General Motors Corporation, Detroit, Mich, a corporation of Dela- Ware Application December 8, 1941, Serial No. 422,138

3 claims. 1

This invention relates to porous metal articles and is particularly concerned with the surface treatment of such articles for providing characteristics on the entire porous surface of the articles making them suitable for specific uses.

An object of the invention is to provide a method whereby porous metal articles may have their entire porous surface plated with another metal which gives more desirable characteristics to the article.

Another object of the invention is to provide a method for coating, or plating, the entire surface of the porous metal article with another metal wherein the porous metal article may be made from an inexpensive material and have a thin plate of inexpensive metal thereover whereby the character of the plated metal is imparted to the porous metal surface thereby reducing the cost of manufacture of the specific article.

Another object of the invention is to provide a method for plating the surface of the porous metal articles by deposition wherein the position of the metals in the electro-chemical series is utilized.

A further object of the invention is to provide a method for coating the surface of a porous metal article with another metal which is capable of being vaporized or sublimed and then deposited on the surface ofv the porous metal article and diffused to some extent into the porous metal article if desired.

In carrying out the above objects it is a further object of the invention to provide a method wherein the entiresurface of the porous metal article is plated or coated by means of expedients wherein the plating or coating metal in suitable form is caused to pass through the porous metal article whereby every surface of each pore is coated or plated.

Another object of the invention is to provide a new article of manufacture which consists of a matrix of one metal coated completely thereover with another metal whereby the second metal imparts its characteristics to the surface of the article.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein preferred embodiments of one form of the present invention is clearly shown.

In the drawings:

Fig. 1 is a diagrammatic view, shown in section, showing an apparatus used in the plating of porous metal articles by deposition.

Fig. 2 is a view taken on the line 22 of Fig. Fig. 3 is a fragmentary and greatly enlarge sectional view of the porous metal article after treatment of the apparatus shown in Fig. 1.

Fig. 4 is a view of another type of apparatus used in the treatment of the metal article with metal vapors.

Fig. 5 is a view taken on the line 5-5 of Fig. 4.

Fig. 6 is a fragmentary viewon a greatly enlarged scale taken through line 6-6 of Fig. 5.

Porous metal articles due to their relatively large surface are in many cases attacked by oxidizing fluids such as water, air containing moisture, and the like. It has been found, for example, that porous iron is more readily oxidized in the atmosphere than is solid iron made by conventional practice. This may be explained by the fact that porous iron presents a relatively greater surface area per unit volume than does iron made by conventional practices. For this reason, it is often highly desirable to protect such articles whether they be made from porous iron or other porous metals which are attacked by the air or fluids which may pass therethrough. For example, porous bronzes, porous ferrous alloys, porous nickel alloys, porous aluminum alloys and the like may, by surface treatment, all be improved for certain intended uses thereof wherein the surface treatment provides a protective film or layer. It should be understood, however, in many instances the intended use of the article has no deleterious effect thereon and such surface treatments are therefore unnecessary.

Further .it is often possible by using surface treatment to reduce the cost of the manufacture of the part. For example, in some cases a porous copper alloy part may be highly desirable from an oxidation standpoint but due to the cost such a part may not be economical. By utilizing the invention described herein it is possible to provide a ferrous part and then plate the entire surface thereof with copper thereby reducing the cost of the part and making the use thereof economical while the surface has all of the characteristics of copper due to the copper plate thereon. Thus it will be apparent that there are many commercial uses for the present invention.

The problems present in plating or coating of the porous metal parts are many due to the large surface areas and the tortuous, serpentine paths of the pores. Such porous articles do not lend themselves to electroplating'since the throwing power of the electrolyte does not penetrate to any great depth and gassing at the adjacent surfaces of-the pores also prevents a uniform electrodeposition.

Electrochemical deposition by the utilization of salt solutions of various metals has not heretofore been satisfactory since by the time the salt solution passes through the interstices of the porous metal article, the salt of the metal in solution has been depositioned out adjacent the external surfaces of the porous metal article and therefore insufficient metal remains in the salt solution to accomplish satisfactory deposition and plating. In the present invention we propose to cause a metal salt solution to flow through porous metal articles at a sufiicient rate to providefor adequate surface plating of the entire. porous surface. To this end an apparatus 20 may be employed wherein a plurality of porous metal plates 22,'for example, are held in a fixture 24 which fixture is clamped between two members 26 and 28 by means of clamps 30. The member 26 is substantially conical and is connected to a pipe 32 which leads from a pump which issupplied through pipe 38 from a salt solution tank 88 containing a salt solution 40. Salt solution 40 is forced by pump 34 into member .26 and through porous. metal article 22 whence it enters member 28 and passes bygravity therefrom through pipe 42 back into the tank 38. Thus continual circulation of the salt solution through the. porous metal articles may be accomplished and concentration of the metal in the salt solution may be closely controlled to keep the concentration at a substantially uniform figure. After a suitable time, which is best determined by examination of the porous article, it will be found that the entire porous surface thereof will be plated with the metal in the salt solution. After making a trial run it is then pos- 54 on a suitable hearth ll. The furnace is like-' wise preferably includes a water cooled baflie chamber 82 or condenser which may be connected to an exhaustblower 84 if insumcient flow is experienced. I In the use of the apparatus, the

a metal in pan 50, for example'cadmium, is heated sible to produce articles without further ex amination by maintaining the flow of salt solution therethrough for a predetermined time period. A number of articles 22 may be treated at the same time. The articles, for example, are porous iron and the salt solution may be copper sulphate, since it is possible to coat copper directly on the iron. Likewise, by referring to the electrochemical series it is possible to choose various salt solutions which will deposit their metal upon another metal in the article to be plated. Thus, any metal in the electrochemical series may be coated with any metal found lower in the same series due to the fact that as onereads downwardly in the series the rate of ease, of reduction increases, or stated differently, the metals in the series .reading downwardly increase in activity as oxidizing agents, such phenomenon being well known in electrochemistry. It should be understood that after the solution is contaminated with the metal being replaced to a suificient degree, which is also best determined by trial, it should either be purified by any well known method, or replaced. I

Fig. 3 shows a portion of the porous metal article after plating wherein 44 indicates the matrix portion, or in the present case, the porous iron, and. 46 indicates the copper plating thereover.

In many instances it may be desirable to partially diffuse the plating metallurgically into the matrix after treatment which may be accomplished by suitable heat treatment. However, for most purposes the plating is sufficient.

above its boiling point and vaporized and is drawn by blower 84 through the furnace and likewise-through the porous metal articles II. In order to provide sufficient atmosphere within the furnace it may be necessary in some cases to include a non-oxidizing or reducing atmosphere which may be admitted through the pipe 68 in limited amouts and which may be used as a carrier for a metallic vapor. It is desirable to maintain the furnace portion in which the porous metal articles are disposed at a temperature but slightly above the boiling point of the metal being vaporized and this may be accomplished by utilizing a suitable heating means. After the atmosphere containing the metallic vapor has passed through the furnace and entered the chamber 82 it is cooled below the boiling point whereby the metal is condensed within the chamberdand may be recovered periodically and reuse In the present instance the coating of cadmium, zinc, etc., which depositson the porous metal articles may be completely or partially difl'used therein by use of suitable heat treatment and maintenance thereof during or after the coating operation has been completed. In many instances this diffusion is not required although it should be understood that such diffusion may be accomplished if desired.

From the foregoing it is manifest that we have provided a method for coating or plating the entire surface of porous metal articles with another metal which metal acts to change the characteristics of the surface of the porous metal articles for specific purposes and uses. In this manner, non-corrosive surfaces may be deposited on porous metal articles or surfaces having desired physica1 and/or chemical characteristics. The method is inexpensive and easy to accom- Plish.

While the embodiments of the present invention as herein disclosed, constitute preferred forms, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

1. A method of coating the entire porous surface of a porous metal article having pores passing completely through the article with a metal lower in the electrochemical series than the metal of the article'andwherein the coating is metallurgically bonded to the surface of the article, the

0 steps comprising; continuously circulating solely There are several metals which may be easily vaporized, such as cadmium, zinc, selenium, etc. These metals often provide a very desirable suring the article at a temperature below the melting point of the coating metal for a time sumcient to cause at least partial metallurgical difiusion of the coating metal into the metal of the article whereby the surface characteristics of the porous metal article are those of the metal deposited on the surfaces of the walls of the pores without destroying the porosity. of the article.

2. A method of coating the entire porous surface of a porous metal article with another metal which is below the metal oi the article in the electrochemical series and wherein the pores of said article pass completely therethrough, the step of circulating an electrolyte containing the metal to be deposited on the surface of the porous metal article through said pores or said porous metal article through pumping and for a time sufiicient to cause the metal in said electrolyte to deposit to a desired thickness upon the entire porous surface of the article to be coated whereby the surface characteristics of the porous metal article are those of the metal deposited on the sur faces of the walls of the pores without destroying the porosity of the article,

3. The method as claimed in claim 2 including the added step of heating the coated article to a temperature and for a time sumeient to cause at least partial metallurgical difiusion of the coating metal into the metal of the article.

- JOI-m T. MARVIN.

ROLAND P, KQELEING.

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