Microwave processing of ceramics

Summary form only given. We have investigated sintering, both with and without a plasma, reaction bonding of silicon nitride (RBSN), and chemical vapor infiltration (CVI) synthesis of ceramic matrix composites using microwave heating. The sintering rate of alumina in a plasma excited either by microwaves or induction coupling (5 MHz) is significantly greater than with conventional heating. The enhancement is believed to be caused by the creation of excess point defects by the plasma. Both microwave CVI and RBSN seek to take advantage of the temperature gradients inherent in volumetric heating so the reaction or deposition of matrix can take place from the center to the surface, thus enabling a greater degree of reaction than can be obtained by isothermal processing. Experimental and modeling results of these two processes are presented.