AbstractsEngineering

Most of the high temperature resistant composites are made using ceramic matrices. Typically these composites are processed at temperatures higher than the operating temperatures. The results presented in this thesis focus on the development of an inorganic matrix composite that can be processed at temperatures ranging from 80 to 400° C and can withstand temperatures up to 1500° C. The composites can be fabricated using inexpensive mold-cast techniques or vacuum bagging techniques. Short discrete fibers can be incorporated in the matrix to improve mechanical properties. The composite is a two component system consisting of: potassium/sodium silicate solution and a powder component containing; silica, alumina, fillers, fibers, flow enhancing additives and activators. The major parameters evaluated in this dissertation are: (i) influence of fiber type and fiber content, (ii) matrix composition in terms of silica/alumina ratio, (iii) fabrication techniques, (iv) influence of curing temperature and (v) influence of exposure to temperatures varying from 200 to 1500° C. The response variables were: the integrity of the samples after high temperature exposure and the mechanical property of the composite. The fiber types consisted of: economical bulk alumina fibers, alumina fibers in paper form and uniform-short alumina fibers. The fiber content varied from 4 to 13 percent by weight of total matrix. Silica to alumina ratios were varied from 1 to 5. Fabrication techniques investigated include: compression molding using wetted alumina fiber papers and simple casting using a mold and vacuum bagging technique. The major findings are as follows: • Both mold-casting and vacuum bagging techniques can be effectively used for fabrication •Optimum curing temperature is 400° C •For composites with bulk-economical alumina fibers the maximum flexural strength is 65 Mpa and the maximum flexural modulus is 52 GPa •These values can be increased to 130 MPa and 85 GPa by using high quality fibers •The densities for composites with short fibers range from 2000 to 2800 kg/m3 •Typically higher density leads to higher strengths