Effects of sintering temperature and cristobalite content on the bending strength of spark plasma sintered fused silica ceramics

Fused silica ceramics have been extensively applied in the aerospace, optical, and telecommunication industries. In this study, spark plasma sintering (SPS) at 900-1300 degrees C was employed to fabricate transparent fused silica ceramics. The particle size of the primary powders was 8 mu m and 70 mu m according to particle size analyzer (PSA). The X-ray diffraction (XRD) analysis was also used to determine the crystalline phase and evaluate the crystallinity. Field Emission Electron Microscope (FE-SEM) images were taken to investigate the microstructure of the samples. The mechanical strength of the specimens was assessed by the three-point flexural strength technique. Results of XRD analyses showed that, the cristobalite was formed in the sintered samples at a temperature of 1300 degrees C. Semi-quantitative analyses showed that the sintered sample at 1300 degrees C with a particle size of 8 mu m contained cristobalite at about 15%, while the amount of the cristobalite in the 70-mu m sample was evaluated at about 4%. SEM images showed the presence of the microcracks developed as a result of the crystallization of the cristobalite in the sample P70S13. The acquired FTIR spectra indicated the presence of bonds of the cristobalites. Samples P70S11 exhibited bending strength of about 40 MPa, respectively. It was evident that the sample with an initial particle size of 8 mu m was of a lower bending strength than the sample with a particle size of 70 mu m.