Production and sintering of reaction bonded silicon nitride composites containing silicon carbide whiskers or silicon nitride powders

Claim 1

A method for producing a sintered reaction bonded silicon nitride composite which contains silicon nitride, is reinforced with silicon carbide whiskers, or both, which method comprises mixing powdered silicon having an average particle size not greater than 5 μm with a suitable amount of a sintering aid and (a) from 10 to 35 percent of silicon carbide whiskers, (b) from 15 to 50 percent of silicon nitride, or (c) from 10 to 35 percent of silicon carbide whiskers and from 15 to 50 percent of silicon nitride, pressing a shape from the resulting mixture, heating the shape in a nitrogen atmosphere at a pressure of about 1 atmosphere absolute, and controlling the heating rate: (d) until a predetermined temperature is reached, so that reaction between nitrogen and the shape is substantially complete at any given temperature before the shape is heated above that temperature, the predetermined temperature being one at which it has previously been determined that the consumption of nitrogen by reaction between silicon of the shape and nitrogen is complete when the heating is conducted so that reaction between nitrogen and the shape is substantially complete at any given temperature before the shape is heated above that temperature, and (e) thereafter heating the shape rapidly from said predetermined temperature to a temperature sufficiently high to produce, by reaction involving the sintering aid, a sufficient amount of a glass to produce a Si 3 N 4 body having from 65 to 85 percent of theoretical density, wherein the suitable amount of a sintering aid is from 3 to 7 percent each of MgO and CeO 2 , 2 to 8 percent of Y 2 O 3 , 6 percent of Y 2 O 3 and 2 percent of Al 2 O 3 , 2 to 8 percent of MgO, BeO, HfO 2 or ZrO 2 , or 1 to 5 percent of CaO.

Claim 2

A method for producing a sintered reaction bonded silicon nitride composite which contains silicon nitride, is reinforced with silicon carbide whiskers, or both, which method comprises mixing powdered silicon having an average particle size not greater than 5 μm with a suitable amount of a sintering aid and (a) from 10 to 35 percent of silicon carbide whiskers, (b) from 15 to 50 percent of silicon nitride, or (c) from 10 to 35 percent of silicon carbide whiskers and from 15 to 50 percent of silicon nitride, pressing a shape from the resulting mixture, heating the shape in a nitrogen atmosphere at a pressure of about 1 atmosphere absolute, and controlling the heating rate: (d) until a predetermined temperature is reached, so that reaction between nitrogen and the shape is substantially complete at any given temperature before the shape is heated above that temperature, the predetermined temperature being one at which it has previously been determined that the consumption of nitrogen by reaction between silicon of the shape and nitrogen is complete when the heating is conducted so that reaction between nitrogen and the shape is substantially complete at any given temperature before the shape is heated above that temperature, and (e) thereafter heating the shape rapidly from said predetermined temperature to a temperature sufficiently high to produce, by reaction involving the sintering aid, a sufficient amount of a glass to produce a Si 3 N 4 body having from 65 to 85 percent of theoretical density, wherein the suitable amount of a sintering aid is from 3 to 7 percent each of MgO and CeO 2 , 2 to 8 percent of Y 2 O 3 , 6 percent of Y 2 O 3 and 2 percent of Al 2 O 3 , 2 to 8 percent of MgO, BeO, HfO 2 or ZrO 2 , or 1 to 5 percent of CaO.