Method for the preparation of silicon carbide platelets

A method of producing free-flowing single crystal silicon carbide platelets, which comprises the steps:

• preparing a mixture of silicon dioxide particles and carbon particles, said silicon dioxide particles having an average diameter of no greater than about minus 60 mesh and said carbon particles having an average diameter no greater than about 40 micrometers, said mixture having a weight ratio of SiO.sub.2 to carbon of about 1.75:1 to about 2.75:1 and a packing density less than about 1.0 g/cm.sup.3 ;
• heating said mixture to a first temperature of about 1600.degree..+-.100.degree. C. in a furnace for a time duration of about 5 to about 10 hours to produce a silicon carbide prefire material, followed by cooling to room temperature;
• mixing said prefire material with up to about 12 parts of a finely divided platelet-enhancing material selected from the group consisting of a fine carbon source, powdered aluminum metal, anhydrous boric oxide and mixtures thereof;
• heating said mixture of prefine material and platelet-enhancing material to a second temperature of about 1900 to about 2400.degree. C. in a furnace for about 2 to about 10 hours to produce said silicon carbide platelets;
• and
• maintaining gaseous products of the reaction during said heating at said first and second temperatures at a substantially steady state by flowing a substantially inert gas through said furnace at a selected rate.

A method of producing free-flowing single crystal alpha phase silicon carbide platelets having a thickness of about 0.5 to about 5 microns and a diameter of about 5 to about 75 microns, which comprises the steps:

• preparing a mixture of silicon dioxide particles and carbon particles, said silicon dioxide particles having an average diameter of no greater than minus 40 mesh and said carbon particles having an average diameter no greater than about 40 micrometers, said mixture having a weight ratio of Si.sub.2 O to carbon of about 1.75:1 to about 2.75:1 and a packing density less than about 1.0 g/cm.sup.3 ;
• heating said mixture of silicon dioxide and carbon particles to a first temperature of about 1600.degree..+-.100.degree. C. in a furnace for a time duration of about 5 to about 10 hours to produce a silicon carbide prefire material;
• mixing said prefire material with about 8-12 parts of finely divided graphite powder, based upon 100 parts of said prefire material;
• heating said mixture of prefire material and graphite powder to a second temperature of about 2150.degree..+-.250.degree. C. in a furnace for about 2-10 hours at a loading of about 0.3-0.4 g/cm.sup.3 ;
• and
• maintaining gaseous products of the reaction during said heating at said first and second temperatures at a substantially steady state by flowing argon gas through said furnace at a selected rate.

A method of producing free-flowing single crystal alpha-phase silicon carbide platelets having a thickness of about 0.5 to about 5 microns and a diameter of about 5 to about 75 microns, which comprises the steps:

• preparing a mixture of silicon carbide whiskers and carbon black in a ratio of about 100 parts silicon carbide whiskers and about 1-12 parts carbon black;
• heating said mixture of silicon carbide whiskers and carbon black in a furnace at about 2150.degree..+-.250.degree. C. for about 8-10 hours;
• and
• maintaining gaseous products of the reaction during said heating at a substantially steady state by flowing argon gas through said furnace at a selected rate.