Abstract: A method is disclosed of making a plurality of dimensionally accurate hot pressed ceramic bodies. A plurality of Si.sub.3 N.sub.4 plates having a thickness to width ratio of 1:3 to 1:40 are stacked in a hot pressing assembly (40-41-42-43). The plates are arranged in groups of progressively decreasing number so that (a) for a plate group (10-11-12-13-14) residing in a zone of compression (15) that will experience the least movement along the pressing direction the stacked number of plates is greatest within such group, and (b) for a plate group residing in a zone of compression (22) that will experience the most movement along the pressure direction the stacked number of plates (21) within such group is the lowest, each group being separated from adjacent groups by an inert rigid spacer.

Abstract: A method is disclosed for simultaneously and uniformly densifying a plurality of semidense ceramic powder bodies. The bodies are hinged together with a uniform space therebetween to form a cluster. The spaces in each cluster are filled with an isostatic pressure medium and then the clusters are stacked in a predetermined alignment along a pressing axis and hot pressed to substantially full density. The bodies are then ruptured from said clusters so as to be in a condition for use as a tool.

Abstract: A method is disclosed for hot pressing agglomerated materials in a pressing assembly having walls which can be reactive with the material to be pressed under the environmental, temperature, and pressure conditions to be experienced by the material at the interface with the pressing assembly walls. After a plurality of generally flat stackable billets (10-20) of the powdered material are formed and stacked in a pressing assembly (21) in a predetermined aligned order, a barrier wall (30) is interposed between the interface of the billets and pressing assembly along at least a zone (26) in which a temperature of 1600.degree.-1750.degree. C. and a pressure of at least 3000 psi will be experienced at the interface during hot pressing. The billets are then hot pressed to a desirable density and removed, leaving the assembly walls in a substantially unreacted condition.