Method of making a silicon carbide article of less than full density

A method of making a silicon carbide article which comprises the steps of:

• 1. mixing (a) 26 to 58 parts by weight of silicon carbide particles having a size less than about 80 microns, (b) 44 to 26 parts by weight of silicon particles of less than about 180 microns, and (c) 30 to 17 parts by weight of a thermosetting, polymeric material which (i) originally contains aromatic components or produces such aromatic components upon pyrolysis and (ii) is in a flowable, liquid phase at temperatures of a plastic molding operation;
• 2. injection molding said mixture formed in step 1, said injection molding carried out by (a) preheating said mixture to a temperature whereat said polymeric material is in a liquid phase, (b) introducing said heated mixture into a mold for an injection molding process, (c) filling said mold with said introduced mixture, and (d) developing a uniform, constant pressure throughout said mixture within said mold thereby to develop a matrix of said polymeric material throughout said mold with a greater amount of said polymeric material near the surface of said mold;
• 3. stiffening said mixture introduced into said mold to form a molded article, said stiffening of said mixture being accomplished by cross linking said thermosetting, polymeric material to at least a degree sufficient to permit said molded article to be removed from said mold without substantial distortion thereof;
• 4. pyrolyzing said polymeric material of said molded article to produce a porous body in which said silicon carbide particles and silicon particles are bonded together by substantially pure carbon;
• and
• 5. siliciding said porous body produced in step 4 with said silicon particles of said body by heating said body in a suitable atmosphere to a temperature at which said silicon particles melt to form liquid silicon which reacts with said carbon thereby to form a finished article of substantially pure silicon carbide, which article has a dense skin and a porous core.

A method of making a silicon carbide article which comprises the steps of:

• 1. mixing (a) 26 to 58 parts by weight of silicon carbide particles, (b) 44 to 25 parts by weight silicon particles, (c) 30 to 17 parts by weight of a thermosetting, polymeric material which originally contains aromatic components or produces such aromatic components upon pyrolysis and (d) a small amount of a blowing agent;
• 2. molding said mixture formed in step 1, said molding carried out by (a) preheating said mixture to a temperature whereat said polymeric material is in a liquid phase, (b) introducing said heated mixture into a mold, (c) filling less than all of said mold with said introduced mixture, and (d) reacting said blowing agent to developing a uniform, constant pressure throughout said mold;
• 3. stiffening said mixture introduced into said mold to at least a degree sufficient to permit said molded article to be removed from said mold without substantial distortion thereof;
• 4. pyrolyzing said polymeric material of said molded article to produce a body in which said silicon carbide particles and said silicon particles are bonded together by substantially pure carbon;
• and
• 5. siliciding said carbon of said body produced in step 4 with said silicon particles of said body to form a finished article of substantially pure silicon carbide, said body being of less than full density.