Abstract: 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 A1N 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 ceramografically not detectable as separate phase(s) up to a manification of 2400 times. The molded bodies have a bending strength measured according to the 4-point method, at room temperature and up to about 1400.degree. C., of at least 500 N/mm.sup.2, a predominantly transcrystalline rupture modulus and a thermal conductivity at 300 K of at least 150 W/mK.

Abstract: 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 AlNup to 0.35% by weight residual oxygenup to 0.35% by weight residual carbon andup to 0.03% 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 caromografically not detectable as separate phase(s) up to a magnification of 2400 times. The molded bodies have a bending strength measured according to the 4-point method, at room temperature and up to about 1400.degree. C., of at least 500 N/mm.sup.2, a predominantly transcrystalline rupture modulus and a thermal conductivity at 300 K of at least 150 W/mK.