Sintering of advanced ceramics using a 30-GHz, 10-kW, CW industrial gyrotron

At the Forschungszentrum Karlsruhe, Germany, a compact gyrotron system was established in 1994 to investigate technological applications in the field of high-temperature materials processing by means of millimeter-wave (mm-wave) radiation. Besides the improvement of the system design, research activities are mainly engaged in studies on debindering and sintering of various types of advanced structural and functional ceramics. Due to volumetric heating and enhanced sintering kinetics, the application of microwaves allows one to shorten the processing time and therefore reduce energy consumption. Besides these effects, microwave technology gives the unique possibility of influencing the microstructure and physical properties of the ceramic materials. This paper will discuss the benefits of the mm-wave technology with respect to sintering of structural ceramics, such as TiO ₂-ZrO₂-MgO multicomponent ceramics, nanocrystalline oxide ceramics, and Si₃N₄, as well as lead-zirconate-titanate piezoceramics as one of the most interesting classes of functional ceramics