In situ grown SiC coatings on carbon materials

Abstract

A -SiC coating made by the method of mixing SiO.sub.2 with carbon and heating the mixture in vacuum wherein the carbon is oxidized to CO gas and reduces the SiO.sub.2 to SiO gas and reacting a carbon material, comprising stainless steel with a carbon coating, with the SiO gas at a temperature in the range of 1300 to 1600 C. resulting in a SiC coating on the stainless steel.

Claims

1. A -SiC coating directly contacting stainless steel formed by the method comprising: mixing SiO.sub.2 with carbon; placing the SiO.sub.2 and carbon mixture in a reaction vessel; separately placing a carbon substrate in the reaction vessel containing the SiO.sub.2 and carbon mixture, wherein the carbon substrate is stainless steel with a carbon coating; and heating the reaction vessel in vacuum at a temperature in the range of 1300 to 1600 C., wherein the carbon is oxidized to CO gas and reduces the SiO.sub.2 to SiO gas, wherein the carbon coating on the stainless steel is converted to a -SiC coating resulting in a -SiC coating directly contacting the stainless steel.

2. The -SiC coating formed by the method of claim 1, wherein the carbon substrate comprises graphite, vitreous carbon, amorphous carbon, diamond, or any combination thereof.

3. -SiC coating formed by the method of claim 1, wherein SiO.sub.2 is a powder, an alkoxide precursor, a crystalline or glassy morphology, or any combination thereof.

4. The -SiC coating formed by the method of claim 1, wherein the carbon mixed with the SiO.sub.2 comprises graphite, vitreous carbon, activated carbon, carbon black, carbon containing organic compounds, or any combination thereof.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows an uncoated vitreous carbon disk (left) and an SiC coated vitreous carbon disk (right).

(2) FIG. 2 is an XRD pattern of an as-received vitreous carbon disk (bottom) and a vitreous carbon disk that was run at 1600 C. for 4 hours showing the formation of a -SiC coating (top) C-vitreous carbon, --SiC.

(3) FIG. 3 shows an uncoated crucible (left) and an SiC-coated crucible (right).

DETAILED DESCRIPTION OF THE INVENTION

(4) The present invention pertains to forming -SiC on a carbon containing substrate. The SiC can be in the form of a coating or can completely replace the carbon material with -SiC. It is also possible to coat a material not containing carbon by first coating said material with carbon and then reacting the carbon coating to form -SiC.

(5) The -SiC can be deposited on a carbon substrate by reacting said carbon substrate with SiO gas. A carbon substrate is defined as all materials that are made up of carbon such as, but not limited to graphite, vitreous carbon, amorphous carbon, and diamond. The SiO directly reacts at temperatures of 1300-1600 C. with the carbon to form a coating or if the material is sufficiently thin (<50 microns) the entirety of the material can be converted to -SiC.

(6) The SiO gas is formed by mixing SiO.sub.2 with carbon and heating in vacuum. The carbon is oxidized to CO gas and reduces the SiO.sub.2 to SiO gas which flows over the carbon substrate and forms SiC. SiO.sub.2 includes but is not limited to powder, alkoxide precursors, crystalline or glassy morphologies. Carbon includes any material that can supply carbon to the reaction such as graphite, vitreous carbon, activated carbon, carbon black, and carbon containing organic compounds such as sugar, fructose, and sucrose.

(7) The material can be heated in a sintering furnace capable of operating in vacuum. The reaction vessel can be as simple as a lidded crucible with the part to be coated suspended inside the crucible. A more complex vessel would have a reaction zone for the SiO.sub.2 and C and a fixture for the substrate to be coated. The vessel is loaded with the SiO.sub.2+C charge and the substrate. The vessel is sealed and placed in the furnace. The furnace is ramped at 5 C./minute to the operating temperature and held. The result will be a SiC coated substrate.

(8) Alternatively the substrate can be a porous carbon material. In this case the entirety of the carbon may be converted to SiC due to the thinness of the carbon structural units in the porous material.

(9) New designs of the reaction vessel can be envisioned to coat multiple samples at once. It may also be possible to form the SiO gas at one temperature while the material to be coated is at a much lower temperature. It may be possible to form the SiO gas using other reactants that do not involve the reduction of SiO.sub.2 by carbon.

Example 1

(10) SiO.sub.2 powder and activated carbon are mixed with a mortar and pestle. The mixture is placed in a vitreous carbon reaction vessel. A vitreous carbon disk is placed in the vessel. The vessel is placed in a graphite vacuum furnace and heated to 1600 C. at 5 C./min and held for 4 hours. FIG. 1 shows a photograph of the disk before and after coating with SiC. FIG. 2 is an X-ray diffraction pattern of the vitreous carbon disk before and after coating.

Example 2

(11) Tetraethylorthosilicate (TEOS) which is an alkoxide precursor for SiO.sub.2 is mixed with dissolved sugar and dried. The dried mixture is placed in a vitreous carbon crucible having a large height to diameter ratio. The crucible is caped, placed in a vacuum furnace and heated at 5 C./minute to 1600 C. for 10 hours. FIG. 3 shows an uncoated crucible and a SiC-coated crucible.

Example 3

(12) This example is the same process as either example 1 or 2 with the exception that a porous carbon material is placed in the reaction vessel. The result is a SiC porous material.

Example 4

(13) This example uses an alternative host, in this case Al.sub.2O.sub.3, although it could be any other substrate, which was coated with a carbon coating. The surface was then reacted in a similar manner to example 1. This converted the carbon coating to SiC.

Example 5

(14) This example uses an alternative host, in this case stainless steel, which was coated with a carbon coating. The surface was then reacted in a similar manner to example 1. This converted the carbon coating to SiC.

(15) The above descriptions are those of the preferred embodiments of the invention. Various modifications and variations are possible in light of the above teachings without departing from the spirit and broader aspects of the invention. It is therefore to be understood that the claimed invention may be practiced otherwise than as specifically described. Any references to claim elements in the singular, for example, using the articles a, an, the, or said, are not to be construed as limiting the element to the singular.