Effect of H-field or E-field on sintering and decrystallization of titanium oxides during 2.45 GHz microwave heating

The effect of an H-field or E-field on the sintering and decrystallization of titanium oxides during 2.45 GHz microwave heating was investigated. Titanium oxides (TiO₂-_x) were heated in a TE103 single-mode cavity, which was used to separate the maximum point of the H-field or E-field of the 2.45 GHz microwave radiation. Scanning electron microscopy (SEM) images taken after H-field heating showed that the sample was sintered well above 1400 °C. In the X-ray diffraction (XRD) patterns, the intensity of the diffraction peaks of TiO₂ decreased with increasing heating temperature between 1200°C and 1400 °C. After heating at 1500°C, however, the TiO₂ peak intensities increased and undefined peaks emerged. Decrystallization is the dominant reaction, driven by the nonthermal microwave effect, below 1400°C. As the effect of the thermal energy becomes larger than the nonthermal microwave effect above 1500°C, grain growth becomes the dominant reaction. During E-field heating, the surface structure changes to fiber-like and dot-like structures, while some areas are oxidized by plasma excited by the microwaves.