Interfacial Reactions between Si and SiO2 with Ceramic Additives

Abstract

In this study, 10 wt.% ceramics—Al2 O3, La2 O3, Y2 O3, MgO, and TiO2 —were employed as additives for amorphous SiO2 after pressing and annealing at 1300◦ C. The amorphous SiO2 changed to cristobalite SiO2. Through X-ray diffraction, scanning electron microscopy, and transmission electron microscopy with energy-dispersive spectrometry, the reaction phases of La2 Si2 O7, Y2 Si2 O7, and MgSiO3 (Mg2 SiO4) were found in the SiO2 with 10 wt.% La2 O3, Y2 O3, and MgO additives. Cracks formed in the Si and SiO2 –ceramic additive sites because of the difference in the coefficients of thermal expansion among the Si, SiO2, ceramic additives, and reaction phases. After Si came into contact with the SiO2 –ceramics, two types of microstructures were found: those with and those without an amorphous SiO2 reaction layer at the interface. Amorphous SiO2 layer formation is due to the replacement of the Si position in SiO2 by Al3+ and Ti4+ impurities, which can break the bonds between Si atoms. The O content in the Si decreased from 6–9 × 1017 atoms/cm3 for SiO2 to less than ~1016 for SiO2 –Al2 O3 and SiO2 –MgO. The average resistivity of the Si was 3 Ω·cm for SiO2 and decreased to 0.12–0.36 Ω·cm for the SiO2 with ceramic additives.