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Engineering Ceramics from Polymers
Abstract Conventional processing of Si-based, covalent, non-oxide ceramics includes deagglomeration and mixing of starting powders, drying and sieving of the resulting mixtures, moulding into green bodies and subsequent liquid phase sintering at temperatures between 1700°C–2100°C. These materials have application limits where oxidation and creep resistance at elevated temperatures is required. These limitations result from the used processing process and basically can be attributed to the following points: (i) commercial Si3N4 parts can be applied in oxidizing environments only up to temperatures in the range of 1200 to 1300°C. At higher temperatures, the material creeps [1] and is oxidized [2,3] even in the bulk. This behavior is related to the presence of sintering promoting compounds like MgO, A12O3 or Y2O3 which react with SiO2 formed during the oxidation reaction to give low viscous silicates, (ii) the use of conventionally processed secondary phase free SiC in the high temperature field is limited to low strength applications [4,5], due to the reduced flaw tolerance caused by the low fracture toughness of additive free SiC, (iii) liquid phase sintered SiC reveals a higher sensitivity towards oxidation owing to the reaction of the used sintering aids with the oxide product formed on the SiC surface [6]. (iv) the conventional fabrication of dense Si3N4/SiC-composites is difficult due to the distinct sintering behavior of the Si3N4 and SiC powder particles used as the starting materials [7,8].
Engineering Ceramics from Polymers
Abstract Conventional processing of Si-based, covalent, non-oxide ceramics includes deagglomeration and mixing of starting powders, drying and sieving of the resulting mixtures, moulding into green bodies and subsequent liquid phase sintering at temperatures between 1700°C–2100°C. These materials have application limits where oxidation and creep resistance at elevated temperatures is required. These limitations result from the used processing process and basically can be attributed to the following points: (i) commercial Si3N4 parts can be applied in oxidizing environments only up to temperatures in the range of 1200 to 1300°C. At higher temperatures, the material creeps [1] and is oxidized [2,3] even in the bulk. This behavior is related to the presence of sintering promoting compounds like MgO, A12O3 or Y2O3 which react with SiO2 formed during the oxidation reaction to give low viscous silicates, (ii) the use of conventionally processed secondary phase free SiC in the high temperature field is limited to low strength applications [4,5], due to the reduced flaw tolerance caused by the low fracture toughness of additive free SiC, (iii) liquid phase sintered SiC reveals a higher sensitivity towards oxidation owing to the reaction of the used sintering aids with the oxide product formed on the SiC surface [6]. (iv) the conventional fabrication of dense Si3N4/SiC-composites is difficult due to the distinct sintering behavior of the Si3N4 and SiC powder particles used as the starting materials [7,8].
Engineering Ceramics from Polymers
Dressler, W. (author) / Riedel, R. (author)
1997-01-01
11 pages
Article/Chapter (Book)
Electronic Resource
English
Metal Foam , Silicon Carbonitride , Organosilicon Polymer , Conventional Powder Processing , Amorphous Ceramic Engineering , Industrial and Production Engineering , Materials Science, general , Ceramics, Glass, Composites, Natural Methods , Characterization and Evaluation of Materials , Inorganic Chemistry
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