BORON-NITRIDE OBTAINED FROM MOLECULAR PRECURSORS - AMINOBORANES USED AS A BN SOURCE FOR COATINGS, MATRIX, AND SI3N4BN COMPOSITE CERAMIC PREPARATION

Aminoboranes, pure or partially converted into aminoborazines using th ermal or aminolysis polymerization, have been used as boron nitride pr ecursors. An amorphous BN preceramic is obtained when pyrolysed up to 1000 degrees C that can be stabilized using further annealing up to 14 00 degrees C or crystallized into h-BN above 1700 degrees C. These mol ecular precursors have been used to prepare carbon fiber/BN matrix mic rocomposites to get an efficient BN coating on graphite and as a BN so urce in Si3N4/BN composite ceramic. The properties of these new types of samples have been compared with those obtained by classical process es. The boron nitride obtained from these precursors is a good sinteri ng agent during the hot-pressing of the samples. However, the crystall inity of BN, even sintered up to 1800 degrees C, remains poor. In fact , most of the mechanical properties of the composite ceramic (density, porosity, hardness) are clearly improved and the aminoboranes san be considered as convenient boron nitride sources and helpful sintering a gents in hot-pressing technology. (C) 1997 Academic Press.