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The study examines the effect which the composition of hotpressed electroconductive ceramics has on their structure, mechanical properties, and oxidation behavior, for ceramics of the type AIN-AlzO~-42 wt% TIN, differing in the AIN/A1203 ratio. The results are physico-mechanical property data, including density, hardness, strength, fracture toughness, and wear resistance. A correlation was found between the wear resistance and fracture toughness. The analysis of oxidation products revealed the formation of aY-AI2O3 and rutile in the temperature range from 600" to 1100°C and also aluminum titanate above 1200°C. The spallation of the oxide layer caused low oxidation resistance of Alz03-rich composites above 1250°C. The oxidation of composites was compared with the oxidation of pure TIN. The relationship is discussed between material properties,

Mullite-based composites can be made by an in situ reaction process using silica-coated alumina (SCA) powder as a mullite precursor. In this paper we present the combined effects of zirconia and premullite seeds on the crystallization process and microstructure development. When zirconia is added without seeding, mullite formation proceeds through the formation of transient zircon. This phase provides a lower energy barrier for mullite nucleation and thus lowers the mullitization temperature. The presence of yttria as a stabilizer in zirconia reduces the activation energy for zircon formation and thus promotes the transient reaction. The addition of premullite seeds results in the nucleation of mullite from alumina and silica, and zircon does not form. At low seeding levels mullitization remains nucleation-controlled; however, once the seeding level exceeds 1-2%, this is no longer the case.