Method for producing refractory carbide coatings on graphite

Claim 2

THE PROCESS FOR COATING GRAPHITE WITH AN ADHERENT, CONTINOUS LAYER OF METALLIC CARBIDE COMPRISING THE STEPS OF DISPOSING A QUANTITY OF A REFRACTORY, CARBIDE FORMING METAL TO BE CARBURIZED IN CONTIGUOUS, GENERALLY SPACED RELATION WITH A SMOOTH GRAPHITE SURFACE, SAID SPACING BEING SUFFICIENT TO PERMIT FLOW OF A GAS BETWEEN SAID SURFACE AND SAID METAL, ENCLOSING SAID ASSEMBLY WITH A NONREACTING GASEOUS ATMOSPHERE CONTAINING METHANE, HEATING SAID ASSEMBLY TO A TEMPERATURE ABOVE THE DECOMPOSITION POINT OF SAID METHANE AND SLIGHTLY ABOVE THE SOFTENING POINT OF SAID METAL, WHEREBY A QUANTITY OF SAID METHANE UNDERGOES PYROLYSIS AND DEPOSITS CARBON ON SAID GRAPHITE AND SAID METALLIC SURFACES, AND QUICKLY RAISING THE TEMPERATURE OF SAID ASSEMBLY TO A POINT AT WHICH CARBURIZATION OCCURS.

Claim 3

A process for reacting graphite with a refractory metal to produce an adherent, continuous layer of metallic carbide comprising the steps of disposing a quantity of a metal selected from the group consisting of molybdenum, zirconium, and niobium in contiguous, generally spaced relation with a smooth graphite surface, said spacing being sufficient to permit flow of a gas between said surface and said metal, degassing said assembly, enclosing said assembly with a nonreactive gaseous atmosphere containing less than about 20% methane, heating said assembly to a temperature of above about 1,700* C, whereby a quantity of said methane decomposes, and quickly raising the temperature of said assembly to a point at which carburization occurs.

Claim 4

A process for reacting graphite with a refractory metal to produce an adherent, continuous layer of metallic carbide comprising the steps of disposing a quantity of a metal selected from the group consisting of molybdenum, zirconium, and niobium in contiguous, generally spaced relation with a smooth graphite surface, said spacing being sufficient to permit flow of a gas between said surface and said metal, degassing said assembly, enclosing said assembly with a nonreactive gaseous atmosphere containing less than about 20% methane, heating said assembly to a temperature of above about 1,700* C, whereby a quantity of said methane decomposes, and quickly raising the temperature of said assembly to a point at which carburization occurs.

Claim 5

A process for coating graphite with an adherent, continuous layer of metallic carbide comprising the steps of disposing a sheet of metal foil selected from the group consisting of molybdenum, zirconium, and niobium in a contiguous generally spaced relation with a smooth graphite surface, said spacing being sufficient to permit flow of a gas between said surface and said metal, heating and degassing said assembly at a temperature below 1,700* C, enclosing said assembly within a nonreactive gaseous atmosphere containing 10 to 20% methane, heating said assembly to a temperature of above about 1,700* C, whereby a quantity of said methane decomposes, and quickly raising the temperature of said assembly to a point at which carburization occurs, cooling and removing said assembly from said furnace.

Claim 6

A process for coating graphite with an adherent, continuous layer of metallic carbide comprising the steps of disposing a sheet of metal foil selected from the group consisting of molybdenum, zirconium, and niobium in a contiguous generally spaced relation with a smooth graphite surface, said spacing being sufficient to permit flow of a gas between said surface and said metal, heating and degassing said assembly at a temperature below 1,700* C, enclosing said assembly within a nonreactive gaseous atmosphere containing 10 to 20% methane, heating said assembly to a temperature of above about 1,700* C, whereby a quantity of said methane decomposes, and quickly raising the temperature of said assembly to a point at which carburization occurs, cooling and removing said assembly from said furnace.

Claim 7

The process of claim 3 in which the metal foil is held in contiguous gas permeable relation with said graphite piece by means of a second graphite piece.

Claim 8

The process of claim 3 in which the metal foil is zirconium and said nonreactive gas is helium.

Claim 9

The process of claim 3 in which the metal foil is niobium and said nonreactive gas is nitrogen.

Claim 10

The process of claim 3 in which the metal foil is molybdenum and said nonreactive gas is 5-15% hydrogen in helium.

Claim 11

A process for coating a graphite tube with an adherent, continuous layer of zirconium carbide comprising the steps of disposing a sheet of zirconium metal tightly and evenly about a graphite mandrel, said mandrel being sized for a close tolerance between said foil and said bore when inserted therein together with said foil, inserting said foil and mandrel within said tube, degassing said assembly at a temperature below 1,700* C, enclosing said graphite-metal interface within a nonreactive gaseous atmosphere containing 10 to 20% methane, heating said assembly to a temperature of about 1,700* C, whereby a quantity of said methane decomposes, quickly raising the temperature of said assembly to a point at which carburization occurs, cooling and removing said tube from said furnace, and removing said mandrel from said tube by mechanical means.

Claim 12

A process for coating a graphite tube with an adherent, continuous layer of zirconium carbide comprising the steps of disposing a sheet of zirconium metal tightly and evenly about a graphite mandrel, said mandrel being sized for a close tolerance between said foil and said bore when inserted therein together with said foil, inserting said foil and mandrel within said tube, degassing said assembly at a temperature below 1,700* C, enclosing said graphite-metal interface within a nonreactive gaseous atmosphere containing 10 to 20% methane, heating said assembly to a temperature of about 1,700* C, whereby a quantity of said methane decomposes, quickly raising the temperature of said assembly to a point at which carburization occurs, cooling and removing said tube from said furnace, and removing said mandrel from said tube by mechanical means.

Claim 13

The process of claim 8 in which said zirconium foil about said mandrel is within the range of from 1 to 20 mils thick.

Claim 14

The process of claim 8 in which a tolerance of about 1 mil exists between the zirconium foil and the tube prior to decomposition of the methane.

Claim 15

The process of claim 8 in which the partial pressure of the methane is at least 3 to 5 psig.

Claim 16

A process for coating a graphite tube with an adherent, continuous layer of zirconium carbide comprising the steps of disposing a sheet of zirconium metal 1 to 20 mils thick about a graphite mandrel, said mandrel being sized for a tolerance of the order of 1 mil between said foil and said tube when inserted therein together with said foil, inserting said foil covered mandrel within said graphite tube, evacuating said assembly to a pressure of 100 microns Hg, flushing said assembly with helium, repeating said evacuating and flushing steps at least two times, pressurizing said assembly with helium of about 50 psig combined with methane of about 5 psig, heating said assembly for about 9 minutes at about 1,800* C, whereby at least part of said methane decomposes and deposits carbon on said tube and said foil, thereafter raising the temperature to about 2,100* C for a time of the order of at least 5 minutes, whereby the metal coating carburizes, cooling and removing said tube from said furnace, and removing said mandrel from said tube by mechanical means.

Claim 17

A process for coating a graphite tube with an adherent, continuous layer of zirconium carbide comprising the steps of disposing a sheet of zirconium metal 1 to 20 mils thick about a graphite mandrel, said mandrel being sized for a tolerance of the order of 1 mil between said foil and said tube when inserted therein together with said foil, inserting said foil covered mandrel within said graphite tube, evacuating said assembly to a pressure of 100 microns Hg, flushing said assembly with helium, repeating said evacuating and flushing steps at least two times, pressurizing said assembly with helium of about 50 psig combined with methane of about 5 psig, heating said assembly for about 9 minutes at about 1,800* C, whereby at least part of said methane decomposes and deposits carbon on said tube and said foil, thereafter raising the temperature to about 2,100* C for a time of the order of at least 5 minutes, whereby the metal coating carburizes, cooling and removing said tube from said furnace, and removing said mandrel from said tube by mechanical means.