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Silicon carbonitride monoliths derived from polymer powder compacts via polymer pyrolysis represent a new class of structural ceramic materials due to the complete coalescence of the powder particles during polymer decomposition and the formation of a uniform ceramic matrix free from any grain boundaries or secondary phases. The submicron pore channel system penetrating the material can be minimized in volume by infiltration of liquid polysilazane solution or by post-HIPing so that relative densities of 96 % can be reached. The monoliths are oxidation resistant up to 1600 OC in air due to the formation of a highly pure silica oxidation layer and they exhibit a creep rate of 1-10-6 s-1 at 1650°C and 30 MPa load. Initially x-ray amorphous silicon carbonitride can be crystallized in nitrogen or in air to form Si3N4ISiC or Si3N4ISiClC nanocomposites.

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