Method Of Producing Substrate Having A Particulate Metallic Coating

Abstract

A method of producing a substrate having a particulate coating of high surface area to mass ratio, said method comprising in sequence the steps of: I. disposing particles between a substrate and an intermediate body wherein the particles are harder than the substrate; and the intermediate body is softer than the particles but is harder than the substrate; Ii. compressing the substrate and intermediate body, with particles therebetween whereby the intermediate body pushes the particles into the substrate; and Iii. removing the intermediate body from the particles leaving them embedded in the substrate. The coating substrates produced by the process of the present invention find utility as catalytic devices to accelerate or retard chemical reactions, as getter devices to sorb residual gases in closed vessels such as electronic tubes, and with further processing as capacitors.

Parent Case Text

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No. 527,906 filed Feb. 16, 1966, now abandoned, the disclosure of which is incorporated herein by reference.

Description

Processes for producing substrates having thereon a particulate metallic coating are notoriously well known in the art. However, most prior processes require the use of a binder to hold the metal particles to the substrate. In an effort to avoid the use of a binder it has been suggested to place the metal particles on the substrate to be coated and then pass these between the nip or rotating rolls to embed the particles in the surface of the substrate. However, such processes suffer from a number of disadvantages. One disadvantage is the wear of the rolls which is especially acute when the metal particles are hard. This wear of the rolls necessitates their frequent replacement with a concurrent expense. However, an even more troublesome effect of the wear of the rolls is their inability to exert an even pressure on the particles with the result that only a portion of the substrate is coated or alternatively an uneven coating results. Another disadvantage of the use of rolls in contact with metal particles is that the action of the rolls on the particles substantially reduces their total surface area. This is especially troublesome when the desired coated substrate is one preferably having a high surface area to mass ratio of the coating particles.

Many of the prior processes require the use of superambient temperatures increasing expense and the necessity for elaborate controls. Many other prior processes do not produce a coated substrate having physical characteristics rendering it suitable for the intended use. Examples of such physical characteristics include among others a high heat transfer coefficient between the metal particles and the substrate, a resistance of the coated substrate to mechanical shocks, to ultrasonic vibrations, and to thermally induced stresses such as are caused by heating the coated substrate to high temperatures such as those of 1,000.degree. C. and higher. Many of these coated substrates lack freedom from loose particles which may be created by separation of particles of the metallic coating from the substrate.

Because of the above described disadvantages such processes have been found unsuitable for the production of getter devices, catalytic devices, and capacitors.

It is therefore an object of the present invention to provide an improved method for producing a substrate having a particulate metallic coating thereon which method is substantially free of one or more of the disadvantages of prior methods.

Another object is to provide an improved method which does not require the use of a binder.

A further object is to provide an improved method which can be practiced at ambient temperatures.

A still further object is to provide an improved method employing rolls which are not subject to wear.

Yet another object is to provide an improved method for producing a coated substrate such as those suitable to be used as catalytic devices, getter devices, or capacitors.

Still another object is to provide an improved method for producing a coated substrate which has the above described desirable physical characteristics.

Still another object is to provide a method for producing an improved getter device having a high surface area to mass ratio of the getter metal and which is free of loose particles.

Additional objects and advantages of the present invention will be apparent to those skilled in the art by reference to the following detailed description thereof and drawings wherein:

FIG. 1 is a cross-sectional view with an enlargement of about 300 diameters of a coated substrate produced by the method of the present invention wherein the coating has a thickness approximately equal to one particle diameter and;

FIG. 2 is a cross-sectional view with an enlargement of about 300 diameters of a coated substrate produced by the method of the present invention wherein the particulate metallic coating has a thickness of approximately 3 particle diameters, this figure being a drawing corresponding to a microphotograph representing the structure taken along line 2--2 of FIG. 4 and;

FIG. 3 is a cross-sectional view with an enlargement of about 1,300 diameters of a coated substrate produced by the method of the present invention wherein the original substrate comprised a hard base having a softer metallic coating thereon and;

FIG. 4 is a schematic representation of an apparatus suitable for practicing the method of the present invention.

In accordance with the present invention there is provided a method of producing a substrate having a particulate metallic coating of high surface area to mass ratio and usually greater than 2 cm..sup.2 /mg. The method comprises in sequence the steps of:

I. disposing metal particles between a substrate and an intermediate body wherein the particles are harder than the substrate; and the intermediate body is softer than the particles but is harder than the substrate;

II. compressing the substrate an intermediate body, with particles therebetween whereby the intermediate body pushes the particles into the substrate; and

III. removing the intermediate body from the particles leaving them embedded in the substrate.

Referring now to the drawings and in particular to FIG. 1 there is shown a substrate 1 of stainless steel having an upper coating 2 and a lower coating 3 comprising metal particles of a zirconium alloy partially embedded in the surface of the substrate 1. FIG. 2 shows an iron substrate 4 having coatings 5 and 6 wherein these coatings 5 and 6 have a total thickness which is approximately equal to three times the diameter of a single particle. As can be seen the metal particles in contact with the substrate 4 are partially embedded therein whereas the other particles are attached to one another or held in place by small cold microwelds (not shown) between the individual particles. FIG. 3 discloses a base 7 of iron having aluminum thereon which actually forms the substrate 8. The particles forming the coating 9 are partially embedded in this substrate 8.

Referring now to FIG. 4 there is shown an apparatus 10 suitable for practicing the process of the present invention. In the practice of this process loose metal particles 11 and 12 are disposed respectively between a substrate 13 and an upper intermediate body 14 and the substrate 13 and a lower intermediate body 15. Most conveniently the metal particles 11 are placed on the substrate 13 whereas the metal particles 12 are placed on the lower intermediate body 15 to form a composite structure which is passed between the nip of two rolls 16 and 17 rotating respectively in the direction of arrows 18 and 19. The apparatus 10 is provided with means for maintaining the distance between the rolls less than the combined thickness of the substrate 13, particles 11 and 12, and intermediate bodies 14 and 15. In the preferred embodiment wherein the intermediate bodies 14 and 15 are work-hardenable the rolls 16 and 17 press the intermediate bodies 14 and 15 with a force such that the intermediate bodies 14 and 15 undergo plastic deformation with concurrent work-hardening while effectively pushing the metal particles 11 and 12 into the substrate 13 without substantially reducing the total surface area of the metal particles 11 and 12.

The entire composite structure then leaves the nip between rolls 16 and 17 with the intermediate bodies 14 and 15 adhering to the metal particles 11 and 12 which are embedded in the substrate 13 and are welded to one another by cold microwelds. The intermediate bodies 14 and 15 are then removed leaving behind the coated substrate 20. By virtue of the above described relationship in hardness between the metal particles 11 and 12, the substrate 13 and the intermediate bodies 14 and 15 the metal particles 11 and 12 adhere substantially completely to the substrate 13 rather than to the intermediate bodies 14 and 15. This relationship in hardness is critical to the successful practice of the method of the present invention. For example, if the intermediate bodies 14 and 15 are of the same hardness as the substrate 13 the particles 11 and 12 will be randomly embedded in the substrate 13 and the intermediate bodies 14 and 15. On the other hand if the substrate 13 is harder than the intermediate bodies 14 and 15 the particles will preferentially embed themselves into the intermediate bodies 14 and 15. If the particles 11 and 12 are softer than either the intermediate bodies 14 and 15 or the substrate 13 they will be plastically deformed losing their surface area and will not become embedded in the substrate 13.

The metal particles can be of widely varying particle sizes but are generally those which pass through a U.S. standard screen of 10 mesh per inch and are preferably those which pass through a U.S. standard screen of 100 mesh per inch and are retained on a screen of 600 mesh per inch.

Broad and preferred ranges of Vickers hardness for the intermediate body, the metallic particles and the substrate are given in the following table:

Vickers Hardness Component Broad Preferred Example Range Range (kg/mm.sup.2) (kg/mm.sup.2) (kg/mm.sup.2) Intermediate body 10-600 100-300 180 Particles 100-.infin. 200-800 400 Substrate 1-400 10-200 90

The values given in this table are non-limiting in the sense that specific values within the above ranges must be chosen while maintaining the herein-described hardness relationship. In a preferred embodiment of the present invention the intermediate body has a Vickers hardness at least 50 and preferably at least 100 kg./mm..sup.2 less than the particles; and the substrate has a Vickers hardness of at least 40 and preferably at least 80 kg./mm..sup.2 less than the intermediate body.

The particles of the metal to be embedded in the substrate are chosen with respect to the desired end use of the product. Thus if a getter device is desired particles of a non-evaporable getter metal are employed whereas if a catalytic device is desired particles of a catalyst metal are chosen. Finally if a capacitor is desired metallic particles are employed which are electrically conductive. In the broadest aspect any prior known non-evaporable getter metal can be employed in the production of getter devices. Examples of suitable getter metals include among others zirconium, titanium, tantalum, niobium, vanadium mixtures thereof and alloys thereof with one another and with other metals which do not materially reduce the gas sorptive capacity of these getter metals. The preferred getter metal is an alloy of 5 to 30 and preferably 13 to 18 weight percent aluminum balance zirconium. When it is desired to produce catalytic devices the metal particles are those which have heretofore been found to catalyze the particular chemical reaction. Examples of suitable catalytic materials include among others platinum, zirconium, vanadium, and tantalum. Examples of electrically conductive particles suitable for producing capacitors include among others iron, silver, copper and preferably aluminum.

The substrate and the intermediate bodies can be of any metal which has the herein described hardness relationship. Examples of suitable metals include among others soft iron, steel, and stainless steel. It must be emphasized that the chemical nature of the elements making up the alloys employed as substrates and intermediate bodies is not critical. In fact it is conceivable that alloys of identical chemical composition can be employed as both provided that they have differing hardnesses. As is apparent to those skilled in the art differing hardnesses can be imparted by conventional metallurgical techniques such as heat treatment, cold rolling and the like.

The invention is further illustrated by the following examples in which all parts and percentages are by weight unless otherwise indicated. These non-limiting examples are illustrative of certain embodiments designed to teach those skilled in the art how to practice the invention and to represent the best mode contemplated for carrying out the invention.

EXAMPLE 1

This example illustrates the method of the present invention wherein the resulting structure is a getter device.

Referring to FIG. 4 finely divided particles of a non-evaporable getter alloy available from SAES Getters S.p.A. as "St 101" is placed on an iron substrate 0.010 inches thick. The St 101 is an alloy of 16 percent aluminum, balance zirconium and passes through a screen of 100 mesh per inch and is retained on a screen of 600 mesh per inch. The particles of St 101 in their sheet form exhibit a Vickers hardness of 400 kg./mm..sup.2. The substrate has a Vickers hardness of 90 kg./mm..sup.2. A single intermediate body of iron having a Vickers hardness of 180 kg./mm..sup.2 and a thickness of 0.010 inches is placed on top of the metal particles and the resultant composite passed between the nip of two rotating rolls. The intermediate body is then removed leaving the particles embedded in the substrate.

EXAMPLE 2

This example illustrates the process of the present invention wherein the resultant product is a catalytic device.

The procedure of Example 1 is repeated except that the particles of St 101 are replaced with platinum and the substrate is replaced with one of aluminum having a Vickers hardness of 50 kg./mm..sup.2 and the intermediate body is replaced by one of iron having a Vickers hardness of 170 kg./mm..sup.2. The resultant catalytic device functions satisfactorily to increase the reaction rate of a chemical reaction.

Although the invention has been described in considerable detail with reference to certain preferred embodiments thereof, it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described above and as defined in the appended claims.

Claims

We claim:

1. A mechanical method of producing a metallic substrate having a metallic particulate coating of high surface area to mass ratio, said method comprising in sequence the steps of:

I. disposing metallic particles between the metallic substrate and an intermediate body wherein the particles are harder than the substrate; and the intermediate body is softer than the particles but is harder than the substrate;

Ii. employing a compressing means in order to compress the substrate and intermediate body, with particles therebetween whereby the intermediate body pushes the particles into the substrate; and

Iii. removing the intermediate body from the particles leaving them embedded in the substrate.

2. The process of claim 1 wherein the particles are placed on the substrate, and wherein an additional amount of particles are placed on a second intermediate body which is on the side of the substrate opposite the first intermediate body in order to produce a structure having particles embedded on both sides of the substrate.

3. The process of claim 1 wherein the particles are susceptible to cold welding to one another and to the substrate.

4. The process of claim 1 wherein the particles are of a size such that they pass through a U.S. standard screen of 10 mesh per inch.

5. The process of claim 1 wherein the substrate has a Vickers hardness of 10 to 200 kg./mm..sup.2.

6. The process of claim 1 wherein the intermediate body has a Vickers hardness of 100 to 300 kg./mm..sup.2.

7. The process of claim 1 wherein the metallic particles have a Vickers hardness of 200 to 800 kg./mm..sup.2.

8. The process of claim 1 wherein the intermediate body has a Vickers hardness at least 50 kg./mm..sup.2 less than the particles.

9. The process of claim 1 wherein the substrate has a Vickers hardness at least 40 kg./mm..sup.2 less than the intermediate body.

10. A mechanical method of producing a structure of high surface area having particles of metal embedded in a metallic substrate, said method comprising in sequence the steps of:

I. disposing loose particles of metal between the metallic substrate and a work hardenable intermediate body wherein the particles are harder than the substrate; and the intermediate body is softer than the particles but is harder than the substrate;

Ii. passing the substrate and intermediate body, with loose particles therebetween, between the nip of two rotating rolls wherein the distance between the rolls in less than the combined thickness of the substrate the intermediate body and the mass of loose particles; whereby the intermediate body undergoes plastic deformation with the concurrent work hardening while effectively pushing the particles into the substrate without substantially reducing the total surface area of the particles; and

Iii. removing the intermediate body from the particles leaving them partially embedded in the substrate.

11. The process of claim 1 wherein the distance between the surfaces of the rolls is sufficiently small that the intermediate body and the substrate both exhibit plastic deformation, but is not so small as to substantially reduce the total surface area of the particulate material.

12. A mechanical method of producing a getter device having particles of a non-evaporable getter metal embedded in a metallic substrate, said method comprising in sequence the steps of:

I. disposing particles of a non-evaporable getter metal between the metallic substrate and an intermediate body wherein the particles are harder than the substrate and the intermediate body is softer than the particles but is harder than the substrate;

Ii. passing the substrate and intermediate body, with particles therebetween, between the nip of two rotating rolls whereby the intermediate body pushes the particles into the substrate; and

Iii. removing the intermediate body from the particles leaving them embedded in the substrate.

13. The process of claim 12 wherein the non-evaporable getter material is a zirconium-aluminum alloy.

14. The process of claim 13 wherein the zirconium-aluminum alloy contains 5 to 30 weight percent aluminum balance zirconium.

15. A mechanical method of producing a getter device having particles of a non-evaporable getter metal embedded in a metallic substrate, said method comprising in sequence the steps of:

I. disposing loose particles of a non-evaporable getter metal between the metallic substrate and an intermediate body wherein the particles are harder than the substrate and the intermediate body is softer than the particles but is harder than the substrate and is in a work-hardenable condition;

Ii. passing the substrate and intermediate body, with loose particles therebetween, between the nip of two rotating rolls wherein the distance between the rolls is less than the thickness of the substrate and intermediate body with loose particles therebetween; whereby the intermediate body undergoes plastic deformation with concurrent work hardening while effectively pushing the particles into the substrate without substantially reducing their surface area; and

Iii. removing the intermediate body from the particles leaving them partially embedded in the substrate.

16. A mechanical method of producing a getter device having particles of a non-evaporable getter metal embedded in a metallic substrate, said method comprising in sequence the steps of:

I. disposing loose particles of a non-evaporable getter metal consisting essentially of an alloy of 13 to 18 weight percent aluminum balance zirconium between the substrate and a work hardenable intermediate body wherein the intermediate body has a Vickers hardness at least 100 kg./mm..sup.2 less than the particles and the metallic substrate has a Vickers hardness at least 80 kg./mm..sup.2 less than the intermediate body;

Ii. passing the substrate and intermediate body, with loose particles therebetween, between the nip of two rotating rolls wherein the distance between the rolls is less than the thickness of the substrate and intermediate body with loose particles therebetween; whereby the intermediate body undergoes plastic deformation with concurrent work hardening while effectively pushing the particles into the substrate without substantially reducing their surface area; and

Iii. removing the intermediate body from the particles leaving them partially embedded in the substrate.