Raw Material Heating and Optical Glass Synthesis Using Microwaves

Microwaves have been used as a heat source in various chemical processes, and their application range is expanding to include high-temperature processes. Existing microwave-based methods for glass syntheses predominantly involve coating and drying. Moreover, microwaves have rarely been applied to glass melting, which consumes a large amount of energy. In this study, the raw materials required for preparing optical glass were heated using microwaves to reduce the energy consumption of the glass-melting process. Microwaves were applied to the raw materials of a typical optical glass, i.e., borosilicate crown glass (BK7). The results indicated that the raw materials rapidly reached the target temperature of 1000 °C and were heated particularly well at temperatures above 500 °C. This was reflected in the high microwave absorption of BK7 above 500 °C, as confirmed by dielectric-constant measurements in the high-temperature range using resonance perturbation. Additionally, BK7 was heated on a 100 g scale in a large microwave-concentrated hexagonal furnace. The obtained glass exhibited a refractive index of 1.5155 (d-line of helium: λ = 587.56 nm), which is comparable to that obtained via conventional heating. Our findings are expected to help reduce the time needed for glass melting considerably and conserve energy, thus contributing to a sustainable society.