DENSE MOLDED BODIES OF POLYCRYSTALLINE ALUMINUM NITRIDE AND PROCESS FOR PREPARATION WITHOUT USE OF SINTERING AIDS

摘要

The invention is a molded body of polycrystalline aluminum nitride having a density of at least 99.8% TD and comprising: at least 99 % by weight AlN up to 0.35 % by weight residual oxygen up to 0.35 % by weight residual carbon and up to 0.30 % by weight metallic impurities (Fe, Si, Ca, Mg). In the molded body, the aluminum nitride is present in the form of a single phase, homogeneous, isotropic microstructure having a maximum grain size of 5 .mu.m. The residual oxygen and the residual carbon are present in the form of a solid solution in the aluminum nitride lattice and ceramographically not detectable as separate phase(s) up to a magnification of 2400 times. The molded bodies have a bending stength measured according to the 4-point method, at room temperature and up to about 1400.degree.C, of at least 500 N/mm2, a predominantly transcrystalline rupture mode and a thermal conductivity at 300 K of at least 150 W/mK. The molded body is produced from a porous, deoxidized green body having a maximum density of 70% TD and the same chemical composition as the final product, by isostatic hot pressing in a vacuum sealed casing at a temperature of from 1700.degree. to 2100.degree.C and a pressure of from 100 to 400 MPa in a high-pressure zone using an inert gas as a pressure transmitting agent.