Process for preparing silicon carbide by carbothermal reduction
AssigneeThe Dow Chemical Company
InventorsAlan W. Weimer, William G. Moore, William Rafaniello, Raymond P. Roach
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Abstract
A process for preparing silicon carbide by carbothermal reduction is disclosed. This process involves rapidly heating a particulate reactive mixture of a silica source and a carbon source to form a product which shows improved uniformity of crystal size. The product of this process can be used to form a densified part.
Claims32
A process for preparing silicon carbide by carbothermal reduction which comprises passing a particulate reactive mixture of a silica source and a carbon source through a heating zone such that substantially all of the particles of the reactive mixture are individually heated at a heating rate of at least about 100.degree. C./second to a temperature within a range of from 1400.degree. C. to 2400.degree. C. and maintained within that range for a time period of from 0.2 to 10 seconds to form a product which, after removal of at least a portion of excess carbon and oxygen, is at least 80 weight percent silicon carbide crystals which have a size distribution such that at least 50 weight percent of the silicon carbide crystals is from 0.4 to 1.6 times the median crystal size.
A process for preparing silicon carbide crystals by carbothermal reduction which comprises:
- (1) passing a particulate reactive mixture of a silica source and a carbon source into a reactor having
- (a) a reactant transport member, the reactant transport member having a wall defining a hollow conduit, the wall having a cooling means and being further characterized as having a concentric inner wall defining an inner annular space, the inner annular space having an inlet and being open at the bottom such that a gas can be flowed therethrough;
- (b) a reactor chamber, the reactor chamber having a wall defining a reaction zone, the chamber being in fluid communication with the reactant transport member:
- (c) a heating means, the heating means being suitable for heating the particulate reactive mixture in the reaction zone;
- and
- (d) a cooling chamber, the cooling chamber having a wall defining a cooling zone, the wall having a cooling means, the cooling chamber being in fluid communication with the reactor chamber;
- the temperatures of the reactant transport member, reactor chamber, and cooling chamber being independently controllable:
- such that the particulate reactive mixture can be fed continuously through the reactant transport member into the reactor zone and then into the cooling zone;
- (2) heating the silica source and the carbon source in the reaction zone at a heating rate of at least about 100.degree. C./second to a temperature from 1400.degree. C. to 2400.degree. C. to form a product aerosol;
- and
- (3) cooling the product aerosol in the cooling zone to form a product which, after removal of at least a portion of excess carbon and oxygen, is at least 80 weight percent silicon carbide crystals which have a size distribution such that at least 50 weight percent of the silicon carbide crystals is from 0.4 to 1.6 times the median crystal size.
A composition which, after removal of at least a portion of excess carbon and oxygen, comprises at least 80 weight percent silicon carbide crystals having a size distribution such that at least 80 weight percent of the silicon carbide crystals is from 0.1 to 0.4 micrometer in size and at least 50 percent of the silicon carbide crystals is from 0.4 to 1.6 times the median crystal size.
A process for producing silicon carbide by carbothermal reduction comprising passing a particulate reactive mixture of a silica source and a carbon source through a heating zone such that substantially all of the particles of the reactive mixture are individually heated at a heating rate of at least about 100.degree. C./second to a sufficient temperature and for a sufficient length of time to form a product which, after removal of at least a portion of excess carbon and oxygen, is at least about 80 weight percent silicon carbide crystals which have a size distribution such that at least about 50 weight percent of the silicon carbide crystals is within a size range from about 0.4 to about 1.6 times the median crystal size.
Dependencies are inferred from the claim text.