Coated graphite members and process for producing the same

Claim 2

A composite structure comprising a. a substrate comprising a fine grained isotropic graphite member of a density of at least about 1.75 gr./cc., of a coefficient of thermal expansion of the order of 7.5 to 8.3 inch per inch per °C×10 - 6 , in which the grains are of a maximum particle size of less than 0.001 inch, and characterized by a relatively uniform distribution of many interconnected fine pores of an average diameter of about 5 microns and less, the pores extending to the surface of the member, an ash content not exceeding about 10 ppm, and b. a refractory metal carbide coating of a thickness of at least 0.1 mil firmly bonded to and conforming to the surface of the isotropic graphite member, said coating comprising at least one metal carbide selected from the group consisting of niobium carbide, zirconium carbide, titanium carbide, hafnium carbide, tantalum carbide, molybdenum carbide, and chromium carbide, the refractory metal carbide coating and the isotropic graphite member having closely matching coefficients of thermal expansion.

Claim 3

The composite structure of claim 1, wherein the coating is at least 0.3 mil in thickness.

Claim 4

An anode suitable for use in an electrical device comprising a. a substrate comprising a fine grained isotropic graphite member of a density of at least about 1.75 grams per cc., and a coefficient of thermal expansion of the order of 7.5 to 8.3 inch per inch per °C×10 - 6 , in which the grains are of a maximum particle size of less than 0.001 inch, and characterized by a relatively uniform distribution of many interconnected fine pores of an average diameter of about 5 microns and less, the pores extending to the surface of the member, and an ash content of less than about 10 ppm, a surface of the substrate being subject to a stream of electrons and high temperatures when in use in the electrical device, and b. the said surface of the substrate having applied thereto a refractory metal carbide coating of a thickness of at least 0.1 mil firmly bonded and conforming to said surface, said coating comprising at least one metal carbide selected from the group consisting of niobium carbide, zirconium carbide, titanium carbide, hafnium carbide, tantalum carbide, molybdenum carbide, and chromium carbide, the refractory metal carbide coating and the isotropic graphite member having closely matching coefficients of thermal expansion.

Claim 5

An anode suitable for use in an electrical device comprising a. a substrate comprising a fine grained isotropic graphite member of a density of at least about 1.75 grams per cc., and a coefficient of thermal expansion of the order of 7.5 to 8.3 inch per inch per °C×10 - 6 , in which the grains are of a maximum particle size of less than 0.001 inch, and characterized by a relatively uniform distribution of many interconnected fine pores of an average diameter of about 5 microns and less, the pores extending to the surface of the member, and an ash content of less than about 10 ppm, a surface of the substrate being subject to a stream of electrons and high temperatures when in use in the electrical device, and b. the said surface of the substrate having applied thereto a refractory metal carbide coating of a thickness of at least 0.1 mil firmly bonded and conforming to said surface, said coating comprising at least one metal carbide selected from the group consisting of niobium carbide, zirconium carbide, titanium carbide, hafnium carbide, tantalum carbide, molybdenum carbide, and chromium carbide, the refractory metal carbide coating and the isotropic graphite member having closely matching coefficients of thermal expansion.

Claim 6

A rotating anode for an X-ray tube comprising a rotatable shaft and the anode being mounted on the shaft for rotation therewith, the anode comprising a composite member comprising a. a substrate comprising a fine grained isotropic graphite member of a density of at least about 1.75, and a coefficient of thermal expansion of the order of 7.5 to 8.3 inch per inch per °C×10 - 6 , in which the grains are of a maximum particle size of less than 0.001 inch, and characterized by a relatively uniform distribution of many interconnected fine pores of an average diameter of about 5 microns and less, the pores extending to the surface of the member, and an ash content of less than about 10 ppm, b. a refractory metal carbide coating of a thickness of at least 0.1 mil firmly bonded to and conforming to the exposed surfaces of the graphite member, the coating comprising at least one metal carbide selected from the group consisting of niobium carbide, zirconium carbide, titanium carbide, hafnium carbide, tantalum carbide, molybdenum carbide, and chromium carbide, the refractory metal carbide coating and the graphite member having closely matching coefficients of thermal expansion, and c. a peripheral refractory metal ring in good thermal contact with the refractory metal carbide coated graphite member, the refractory metal ring adapted to have a beam of electrons projected thereagainst thereby heating it up, and the contacting refractory metal coated graphite member enabling the heat generated in the metal ring to be conducted to it for dissipation.

Claim 7

A rotating anode for an X-ray tube comprising a rotatable shaft and the anode being mounted on the shaft for rotation therewith, the anode comprising a composite member comprising a. a substrate comprising a fine grained isotropic graphite member of a density of at least about 1.75, and a coefficient of thermal expansion of the order of 7.5 to 8.3 inch per inch per °C×10 - 6 , in which the grains are of a maximum particle size of less than 0.001 inch, and characterized by a relatively uniform distribution of many interconnected fine pores of an average diameter of about 5 microns and less, the pores extending to the surface of the member, and an ash content of less than about 10 ppm, b. a refractory metal carbide coating of a thickness of at least 0.1 mil firmly bonded to and conforming to the exposed surfaces of the graphite member, the coating comprising at least one metal carbide selected from the group consisting of niobium carbide, zirconium carbide, titanium carbide, hafnium carbide, tantalum carbide, molybdenum carbide, and chromium carbide, the refractory metal carbide coating and the graphite member having closely matching coefficients of thermal expansion, and c. a peripheral refractory metal ring in good thermal contact with the refractory metal carbide coated graphite member, the refractory metal ring adapted to have a beam of electrons projected thereagainst thereby heating it up, and the contacting refractory metal coated graphite member enabling the heat generated in the metal ring to be conducted to it for dissipation.

Claim 8

The rotating anode of claim 4, wherein the refractory metal coating is at least 0.3 mil in thickness.

Claim 9

A rotating anode for an X-ray tube comprising a rotatable shaft, in combination, a refractory metal disk adapted to be affixed to the shaft for rotation therewith, the outer periphery of the refractory metal disk having a surface to be exposed for impingement of a beam of electrons thereagainst during operation of the X-ray tube, at least one refractory metal carbide coated graphite body affixed to the lower surface of the refractory metal disk and in close conductive thermal contact with the metal disk whereby to enable heat developed by the electron beam to be conducted to the graphite body for radiant energy dissipation therefrom, the graphite body comprising a. a substrate comprising a fine grained isotropic member of a density of at least about 1.75, and a coefficient of thermal expansion of the order of 7.5 to 8.3 inch per inch per °C×10 - 6 , in which the grains are of a maximum particle size of less than 0.001 inch, and characterized by a relatively uniform distribution of many interconnected fine pores of an average diameter of about 5 microns and less, the pores extending to the surface of the member, and an ash content of less than about 10 ppm, and b. a refractory metal carbide coating of a thickness of at least 0.1 mil firmly bonded to and conforming to the surface of the isotropic graphite member, the coating comprising at least one metal carbide selected from the group consisting of niobium carbide, zirconium carbide, titanium carbide, hafnium carbide, tantalum carbide, molybdenum carbide, and chromium carbide, the refractory metal carbide coating and the isotropic graphite substrate having closely matching coefficients of thermal expansion.

Claim 10

A rotating anode for an X-ray tube comprising a rotatable shaft, in combination, a refractory metal disk adapted to be affixed to the shaft for rotation therewith, the outer periphery of the refractory metal disk having a surface to be exposed for impingement of a beam of electrons thereagainst during operation of the X-ray tube, at least one refractory metal carbide coated graphite body affixed to the lower surface of the refractory metal disk and in close conductive thermal contact with the metal disk whereby to enable heat developed by the electron beam to be conducted to the graphite body for radiant energy dissipation therefrom, the graphite body comprising a. a substrate comprising a fine grained isotropic member of a density of at least about 1.75, and a coefficient of thermal expansion of the order of 7.5 to 8.3 inch per inch per °C×10 - 6 , in which the grains are of a maximum particle size of less than 0.001 inch, and characterized by a relatively uniform distribution of many interconnected fine pores of an average diameter of about 5 microns and less, the pores extending to the surface of the member, and an ash content of less than about 10 ppm, and b. a refractory metal carbide coating of a thickness of at least 0.1 mil firmly bonded to and conforming to the surface of the isotropic graphite member, the coating comprising at least one metal carbide selected from the group consisting of niobium carbide, zirconium carbide, titanium carbide, hafnium carbide, tantalum carbide, molybdenum carbide, and chromium carbide, the refractory metal carbide coating and the isotropic graphite substrate having closely matching coefficients of thermal expansion.

Claim 11

The rotating anode of claim 6, wherein a second refractory metal carbide coated graphite body is disposed in good conductive thermal contact with the upper surface of the refractory metal disk except for the surface to be exposed for impingement thereon of the beam of electrons, the second refractory metal carbide coated graphite body comprising: a. a substrate comprising a fine grained isotropic graphite member of a density of at least about 1.75, and a coefficient of thermal expansion of the order of 7.5 to 8.3 inch per inch per °C×10 - 6 , in which the grains are of a maximum particle size of less than 0.001 inch, and characterized by a relatively uniform distribution of many interconnected fine pores of an average diameter of about 5 microns and less, the pores extending to the surface of the member, and b. a refractory metal carbide coating of a thickness of at least 0.1 mil firmly bonded to and conforming to the surfae of the isotropic graphite member, the coating comprising at least one metal carbide selected from the group consisting of niobium carbide, zirconium carbide, titanium carbide, hafnium carbide, tantalum carbide, molybdenum carbide, and chromium carbide, the refractory metal carbide coating and the isotropic graphite substrate having closely matching coefficients of thermal expansion.

Claim 12

The rotating anode of claim 6 wherein a refractory metal disk is affixed to the rotatable shaft, an outer ring of tungsten or a tungsten base alloy affixed to the periphery of the refractory disk, the outer ring having a surface to be exposed to a beam of electrons in the X-ray tube, at least one graphite body affixed in close thermal contact with one face of the refractory metal disk between the ring and the shaft, the graphite body comprising: a. a substrate comprising a fine grained isotropic graphite member of a density of at least about 1.75, and a coefficient of thermal expansion of the order of 7.5 to 8.3 inch per inch per °C×10 - 6 , in which the grains are of a maximum particle size of less than 0.001 inch, and characterized by a relatively uniform distribution of many interconnected fine pores of an average diameter of about 5 microns and less, the pores extending to the surface of the member, and b. a refractory metal carbide coating firmly bonded to and conforming to the surface of the isotropic graphite member, the refractory metal carbide coating and the isotropic graphite substrate having closely matching coefficients of thermal expansion.

Claim 13

In the process of applying a refractory metal carbide coating to a graphite member to produce a composite structure, the steps comprising: a. heat treating at a temperature of from about 1,700°C to 2,400°C an isotropic graphite body comprising fine grained isotropic graphite of a density of at least 1.75 and having a coefficient of thermal expansion of about 7.5 to 8.3 inch per inch per °Centigrade ×10 - 6 , the graphite grains being of a maximum particle size of less than 0.001, and characterized by a relatively uniform distribution of many interconnected fine pores of an average diameter of about 5 microns and less, the pores extending to the surface of the body, the heating being applied for at least an hour in a halogen atmosphere, the heat-treatment purifying the body, b. machining the heat treated isotropic graphite body to a member of predetermined shape and surface condition, c. ultrasonically cleaning the machined body in a liquid cleaning fluid to remove loose surface particles, and d. vapor depositing on the surfaces of the cleaned isotropic graphite member a refractory metal carbide coating of a thickness of at least 0.1 mil.

Claim 14

In the process of applying a refractory metal carbide coating to a graphite member to produce a composite structure, the steps comprising: a. heat treating at a temperature of from about 1,700°C to 2,400°C an isotropic graphite body comprising fine grained isotropic graphite of a density of at least 1.75 and having a coefficient of thermal expansion of about 7.5 to 8.3 inch per inch per °Centigrade ×10 - 6 , the graphite grains being of a maximum particle size of less than 0.001, and characterized by a relatively uniform distribution of many interconnected fine pores of an average diameter of about 5 microns and less, the pores extending to the surface of the body, the heating being applied for at least an hour in a halogen atmosphere, the heat-treatment purifying the body, b. machining the heat treated isotropic graphite body to a member of predetermined shape and surface condition, c. ultrasonically cleaning the machined body in a liquid cleaning fluid to remove loose surface particles, and d. vapor depositing on the surfaces of the cleaned isotropic graphite member a refractory metal carbide coating of a thickness of at least 0.1 mil.

Claim 15

The process of claim 9 wherein the refractory metal carbide vapor deposition step (d) comprises passing a reactive gas mixture of refractory metal halide vapor, hydrogen, and an inert gas over the graphite member while the graphite member is at a temperature of at least about 1,500°C whereby refractory metal is deposited on the graphite member from contact of the gas mixture therewith, the deposited metal and the graphite react to form the carbide and additional carbon diffuses into the applied coating to react with subsequently deposited refractory metal.

Claim 16

The process of claim 10, wherein the refractory metal halide is a halogen composed of at least one element of the group consisting of zirconium, hafnium, titanium, tantalum, molybdenum, chromium and niobium.

Claim 17

The process of claim 9, wherein the refractory metal carbide coating step (d) comprises heating the cleaned isotropic graphite member to at least about 1,000°C and passing over the heated member a reactive gas mixture comprising a refractory metal halide, hydrogen and a hydrocarbon, whereby a coating of the refractory metal carbide is deposited on the graphite member.

Claim 18

The process of claim 12, wherein the reactive gas mixture comprises an inert gas.

Claim 19

The process of claim 12, wherein the refractory metal halide is a halogen compound of at least one element of the group consisting of zirconium, hafnium, titanium, tantalum, molybdenum, chromium and niobium.