Origin of Density Gradients in Sintered β-Silicon Carbide Parts

Sintered densities of β-silicon carbide compacts were observed to decrease as the thickness of the compact increased. The chemistry and density gradients of these compacts were analyzed, as well as the weight loss and the CO evolution during sintering. The sintering cycle was altered to include a vacuum hold between the temperatures of 1400° and 1700°C, which resulted in increased density. Depending on the temperature of the vacuum soak, densities of 98% could be achieved on tiles with a thickness greater than 2.5 cm. The density gradients within the compact were significantly reduced, but not totally eliminated. It is suggested that these gradients are due to the effect of microstructural coarsening which occurs simultaneously with CO evolution.