Multi-frequency microwave sintering of ceramics

Summary form only given, as follows. The potential advantages of using microwaves for processing of materials is related to the volumetric character of microwave absorption in many non-metallic materials. However, the volumetric heating raises the temperature of the sample as a whole, but the interior often becomes hotter than exterior due to heat losses from the surface. This may lead to non-uniform mechanical properties and even cracking. Our objective is to eliminate this difficulty by processing materials simultaneously with two microwave sources at widely separated frequencies. Under these conditions the temperature profile in the material can be electronically controlled by dynamically varying the power of the sources. This approach allows to control not only the rate of energy deposition within the material being processed, but also the region in which the energy is dissipated, because the depth of penetration into material depends on microwave frequency. A microwave furnace driven simultaneously by a 3 kW magnetron operating at 2.45 GHz and a 1 kW klystron operating at 28 GHz is currently under construction. We hope to be able to report on the operation of this system. In addition, to get a better insight into microwave heating of ceramic materials and into the optimization of this process we developed a computer code capable of modeling of the heat propagation in the sample. We plan to use this code to study the feasibility of controlling the heating process when two frequency microwave system is used. The computations will be carried out at frequencies 2.45 GHz and 28 GHz for two ceramic materials: Al/sub 2/O/sub 3/ and SiC.