Benefits of Microwave-Assisted Heat Treatment for Sintered Diopside Glass-Ceramics

Sinter-crystallization is a specific method of producing glass-ceramics that allows the manufacture of complexly shaped products, composites and solder. However, it usually is limited when the glass powders used are characterized by a high crystallization trend. This study proposes a new opportunity to improve the sinter-crystallization and demonstrates the benefits of microwave processing using diopside (CaMg(Si₂O₆)) glass-ceramics with an enhanced crystallinity of ~70%. The advantages of microwave processing are shown by comparing the results obtained with scanning electron microscopy, X-ray computed tomography and gas pycnometry for two glass-ceramic specimens. The first sample is obtained in the heat resistant furnace of an optical dilatometer, while the second is obtained by heating it with high-power microwave irradiation at 2.45 GHz, 1kW. Intense crystallization was observed in the sample sintered in an electric furnace, which blocked the sintering process and resulted in significant open porosity (7.1%). In addition, closed pores caused by the crystallization are observed in the centers of the sintered particles (5.2%). At the same time, the overall porosity of the microwave-sintered glass-ceramic is reduced by about two times, and the open porosity is practically eliminated (0.5%). In this sample, together with the crystallization-induced pores, some residual closed spherical pores, typical for a well-sintered sample, are also observed.