Fabrication of transparent SiO2 glass by pressureless sintering and spark plasma sintering

Transparent SiO2 bodies were prepared by pressureless sintering (PLS) and spark plasma sintering (SPS). The effects of sintering and annealing temperature on the transmittance of the SiO2 bodies were investigated. The SiO2 bodies sintered by SPS and PLS at 1073–1573 K were amorphous. With increasing the sintering temperature to 1673 K, the SiO2 bodies sintered by PLS were crystallized while those sintered by SPS were still amorphous. The relative density of the SiO2 bodies sintered by SPS was 98.5% at 1373 K and 100% at 1573 K, whereas that sintered by PLS was 92.6% at 1373 K and 98.9% at 1573 K. The transmittance was 91.0% and 81.5% at a wavelength (λ) of 2 μm for the SiO2 sintered bodies by SPS and PLS, respectively. In the ultraviolet range, the transmittance of the SiO2 bodies sintered by SPS at 1573 K was about 40% at λ = 200 nm and increased to 75% after annealing at 1073 K for 1 h, which was about three times of the transmittance of the SiO2 bodies sintered by PLS (24.8%).