Effect of phosphate compound on physical and mechanical properties of SiO2 ceramic

This paper reports on the addition of Al(H2PO4)(3) binder solution with different vol% ratio and its effects on the mechanical behavior of the formed silicon dioxide ceramic. The starting material, commercial phosphate-bonded investment material, was analyzed by X-ray fluorescence (XRF) spectrometry. After silicon dioxide powder was mixed with a binder, the thick liquid was poured into a rubber mold and allowed to dry at room temperature. Then, the green bodies formed were sintered at 1200 degrees C for 5 h in a furnace in air atmosphere. Phase and impurities of all the ceramic samples were characterized by X-ray diffraction (XRD) and Raman spectroscopy. The morphology was revealed by scanning electron microscopy (SEM). The local atomic structures of some ceramic samples were investigated by extended X-ray absorption fine structure (EXAFS) to better understand the formation of phosphate compound. Compression test was carried out on the ceramic samples at room temperature. Results showed that quartz-cristobalite transformation in the silicon dioxide structure did not significantly affect the mechanical property of the ceramic samples prepared in this work. Porosity was decreased with Al(H2PO4)(3) diluted binder ratio. The presence of pores act as stress concentration points in SiO2-based ceramics in which crack could initiate under loading. We strongly believe that a sharp increase in the compressive strength is due to phosphate compound and its unique morphology.