Preceramic polymer derived cellular ceramics

Ceramic foams were prepared by a self-blowing process of a poly(silsesquioxane) melt at 270 °C. The cell size, the interconnectivity density and the shape of the foam cells were adjusted by a thermal pre-curing procedure of the polymer at 200 °C. Inorganic fillers were used to modify processing behaviour and properties of the pyrolysed ceramic foam. After pyrolysis in inert atmosphere at 1200 °C ceramic composite foams with a total porosity up to 87% were obtained. The open cell ceramic foams had a mean cell diameter of 1.2 mm and a mean strut thickness of 0.2 mm. Interpenetrating phase composites (IPCs) were fabricated by infiltrating the open cellular ceramic preform with Mg alloy melt at 680 °C and a pressure of 86 MPa. The mechanical properties were found to depend on the reactions between the metal and the ceramic forming MgO, Mg₂Si and Al₁₂Mg₁₇ as the major reaction products. The IPCs showed a significantly higher creep resistance at 135 °C, compression strength and elastic modulus compared to the unreinforced magnesium alloys.