MICROWAVE-HEATING OF FUNCTIONAL CERAMICS WITH A HIGH PERMITTIVITY OR A SIGNIFICANT ELECTRICAL-CONDUCTIVITY

The use of microwaves for the sintering of ceramic is potentially an i nteresting technique : the fast heating due to the dissipation of ener gy inside the materials may lead, with limited damages for the environ ment, to new materials showing a structure and/or a microstructure dif ferent from the ones obtained in a classical furnace, that is to say t o unusual properties. Moreover, the possible existence (see paper of P . BOCH et al. in this volume) of a microwave effect, although highly q uestionable, corresponding to a decrease of the sintering temperature, makes this technique even more attractive. However, contrary to large domestic applications (for cooking), the use of microwave for industr ial sintering is not up to now very much developed. This paper tries t o point out the specificity of the microwave heating to show its limit s, and to give an overview of the work done in different laboratories, in the field of functional ceramics with a significant electrical con ductivity or a high permittivity.