Method of hot pressing reactive materials

Claim 1

A method of hot pressing agglomerated Si 3 N 4 comprising powdered materials in a pressing assembly having graphite walls the carbonaceous decomposition products of the walls reactive with the material to be pressed under the temperature and pressure conditions to be experienced at the interface between the material and reactive walls, comprising: (a) forming a plurality of generally flat stackable billets of said powdered material; (b) stacking said billets in said hot pressing assembly aligned with the direction of pressing; (c) interposing a barrier wall between the interface of said billets with said pressing assembly and along at least a zone of said assembly in which a temperature of 1600°-1750° C. and a pressure of at least 1000 psi will be experienced at said interface during hot pressing, said barrier wall being effective to prevent a chemical and physical reaction between the Si 3 N 4 of said billets and the decomposition products of said graphite walls of said pressing assembly; and (d) hot pressing said billets within said assembly to achieve a desired density in each of said billets.

Claim 2

A method of hot pressing agglomerated Si 3 N 4 comprising powdered materials in a pressing assembly having graphite walls the carbonaceous decomposition products of the walls reactive with the material to be pressed under the temperature and pressure conditions to be experienced at the interface between the material and reactive walls, comprising: (a) forming a plurality of generally flat stackable billets of said powdered material; (b) stacking said billets in said hot pressing assembly aligned with the direction of pressing; (c) interposing a barrier wall between the interface of said billets with said pressing assembly and along at least a zone of said assembly in which a temperature of 1600°-1750° C. and a pressure of at least 1000 psi will be experienced at said interface during hot pressing, said barrier wall being effective to prevent a chemical and physical reaction between the Si 3 N 4 of said billets and the decomposition products of said graphite walls of said pressing assembly; and (d) hot pressing said billets within said assembly to achieve a desired density in each of said billets.

Claim 4

A method of hot pressing agglomerated powdered materials in a pressing assembly having graphite walls reactive with the material to be pressed under the temperature and pressure conditions to be experienced by the material and said walls in hot pressing, comprising: (a) preparing a plurality of silicon nitride comprising billets, each having silicon nitride and oxygen carrying crystallites, and containing up to 0.5% by weight free silicon and unreacted oxides, and up to 0.2% by weight cation impurities, each billet having a density of at least 2.0 gm/cm 3 ; (b) stacking said billets in a predetermined aligned order within said pressing assembly; (c) prior to or subsequent to the stacking of said billets in said assembly, interposing a solid barrier wall therebetween at a zone of said assembly in which a temperature of 1600°-1750° C. and a pressure of at least 1000 psi, as will be experienced during hot pressing, said barrier wall being effective to act as a mechanical barrier to the transport of carbonaceous gaseous reaction products of said graphite walls therethrough; and (d) hot pressing said plurality of stacked billets to achieve a desired density in each of said billets and a composition consisting substantially of beta form silicon nitride.

Claim 5

A method of hot pressing agglomerated powdered materials in a pressing assembly having graphite walls reactive with the material to be pressed under the temperature and pressure conditions to be experienced by the material and said walls in hot pressing, comprising: (a) preparing a plurality of silicon nitride comprising billets, each having silicon nitride and oxygen carrying crystallites, and containing up to 0.5% by weight free silicon and unreacted oxides, and up to 0.2% by weight cation impurities, each billet having a density of at least 2.0 gm/cm 3 ; (b) stacking said billets in a predetermined aligned order within said pressing assembly; (c) prior to or subsequent to the stacking of said billets in said assembly, interposing a solid barrier wall therebetween at a zone of said assembly in which a temperature of 1600°-1750° C. and a pressure of at least 1000 psi, as will be experienced during hot pressing, said barrier wall being effective to act as a mechanical barrier to the transport of carbonaceous gaseous reaction products of said graphite walls therethrough; and (d) hot pressing said plurality of stacked billets to achieve a desired density in each of said billets and a composition consisting substantially of beta form silicon nitride.