Volumetric Microwave Heating of Mullite Ceramic Using a 28 GHz Gyrotron

In this paper, we present and discuss experimental results from a microwave sintering of a mullite ceramic, produced from a mixture of alumina and silica xerogel extracted from a sago waste ash. The composition has been prepared by adding 60 %wt amount of alumina into the silica xerogel. As a radiation source for the microwave heating, a 28 GHz wave gyrotron has been used. The influence of the sintering temperature on the structural properties was studied in detail. It has been found that the mixture crystallizes completely as a single mullite phase at a temperature of 1600°C after heating for 10 min at a temperature rate of 45oC/min. Most importantly, such result cannot be achieved by conventional heating. The results that have been obtained in this study allow one to conclude that the microwave sintering of using a 28 GHz gyrotron is an appropriate technological process for the production of mullite ceramics and is characterized by several advantages such as shorter times of the thermal cycle, lower sintering temperatures and higher quality of the final product.