Method of making silicon carbide

Claim 1

A method of making beta-silicon carbide powder, comprising mixing carbon powder with silica powder, as reactants, the method comprising the steps of: ,(i) heating the reactants in a reaction chamber under a non-reactive gas pressure which is equal to or greater than atmospheric pressure, which maintains a carbon monoxide partial pressure sufficient to prevent significant loss of silicon monoxide until the reactants reach a temperature of between 1200 and 2000 degrees C; and (ii) subsequently maintaining the temperature of the reactants between 1200 and 2000 degrees C. to cause the reactants to react to form silicon carbide and carbon monoxide, and simultaneously applying a subatmospheric pressure to the reactants which is from about 50 millitorrs to about 500 millitorrs (i), which pressure is sufficient to remove carbon monoxide gas from the reaction chamber, while agitating the reactants to allow for passage of carbon monoxide therefrom, whereby the removal of the carbon monoxide drives the reaction to substantial completion.

Claim 2

A method of making beta-silicon carbide powder, comprising mixing carbon powder with silica powder, as reactants, the method comprising the steps of: ,(i) heating the reactants in a reaction chamber under a non-reactive gas pressure which is equal to or greater than atmospheric pressure, which maintains a carbon monoxide partial pressure sufficient to prevent significant loss of silicon monoxide until the reactants reach a temperature of between 1200 and 2000 degrees C; and (ii) subsequently maintaining the temperature of the reactants between 1200 and 2000 degrees C. to cause the reactants to react to form silicon carbide and carbon monoxide, and simultaneously applying a subatmospheric pressure to the reactants which is from about 50 millitorrs to about 500 millitorrs (i), which pressure is sufficient to remove carbon monoxide gas from the reaction chamber, while agitating the reactants to allow for passage of carbon monoxide therefrom, whereby the removal of the carbon monoxide drives the reaction to substantial completion.

Claim 9

A method as claimed in claims 4, 6 or 7, wherein the pressure of the non-reactive gas is at least 0.034 MPa above atmospheric pressure.

Claim 10

A method as claimed in claims 2, 3 or 4 wherein the carbon and silica powder mixture is either continuously or intermittently agitated, and agitation is carried out during at least the step of maintaining the temperature whilst applying a subatmospheric pressure.

Claim 11

A method as claimed in claims 2, 3 or 4 wherein the reactants are agitated by rotating the reaction chamber.

Claim 12

A method as claimed in claims 1, 2, 3, 4 or 5 wherein the temperature at which the reactants are maintained whilst the subatmospheric pressure is applied is in the range 1400°-1800 degrees C.

Claim 13

A method as claimed in claims 6 or 7 wherein the temperature at which the reactants are maintained while the subatmospheric pressure is applied is in the range of 1400°-1800 degrees C.

Claim 14

A method as claimed in claims 2, 3 or 4, which is carried out in a reaction chamber formed from graphite, silicon carbide or molybdenum.

Claim 15

A method of making submicron size beta-silicon carbide, the method comprising the steps of: (i) mixing, as reactants, a submicron size carbon powder with silica powder having a particle size not exceeding 45 microns; (ii) continuously heating the reactants in a reaction chamber under a non-reactive gas pressure which is equal to or greater than atmosphere pressure, until the reactants reach a temperature between 1400-1800 degrees C. whilst maintaining the partial pressure of carbon monoxide at a level sufficient to prevent significant loss of silicon monoxide; and (iii) subsequently maintaining the temperature of the reactants between 1400-1800 degrees C. to cause the reactants to react to form silicon carbide and carbon monoxide, whilst applying a subatmospheric pressure to the reactants in the reaction chamber in the range 50-100 millitorrs which is less than that in step (i) and which is sufficient to remove carbon monoxide gas from the reaction chamber and to drive the reaction to substantial completion and agitating the reactants to prevent agglomeration, prevent any pressure differential of carbon monoxide developing within the reactants which would inhibit the reaction and promote heat transfer to the reactants.

Claim 16

A method of making submicron size beta-silicon carbide, the method comprising the steps of: (i) mixing, as reactants, a submicron size carbon powder with silica powder having a particle size not exceeding 45 microns; (ii) continuously heating the reactants in a reaction chamber under a non-reactive gas pressure which is equal to or greater than atmosphere pressure, until the reactants reach a temperature between 1400-1800 degrees C. whilst maintaining the partial pressure of carbon monoxide at a level sufficient to prevent significant loss of silicon monoxide; and (iii) subsequently maintaining the temperature of the reactants between 1400-1800 degrees C. to cause the reactants to react to form silicon carbide and carbon monoxide, whilst applying a subatmospheric pressure to the reactants in the reaction chamber in the range 50-100 millitorrs which is less than that in step (i) and which is sufficient to remove carbon monoxide gas from the reaction chamber and to drive the reaction to substantial completion and agitating the reactants to prevent agglomeration, prevent any pressure differential of carbon monoxide developing within the reactants which would inhibit the reaction and promote heat transfer to the reactants.

Claim 17

A method as claimed in claims 2, 4 or 14, wherein the carbon powder is formed from carbon black or petroleum coke.

Claim 18

A method as claimed in claims 2, 4 or 14, wherein, after forming the silicon carbide, the silicon carbide is subjected to a temperature not exceeding 750 degrees C. in the presence of oxygen to oxidize the carbon.

Claim 19

A method as claimed in claims 1, 2 or 4, in which the subatmospheric pressure within the reaction chamber and/or rate of gas production from the reactants is monitored, to determine when the reaction has been driven to substantial completion.