Structure and Properties of Ceramics Based on Monetite and Nanodispersed Silica

Calcium-phosphate ceramics based on monetite and nanosized silica are produced by sintering at 500A degrees C. It is established that phase changes and solid-phase reactions occur during sintering to form ceramics that contain beta-calcium pyrophosphate (Ca2P2O7), calcium silicate (wollastonite, CaSiO3), and insignificant amount of beta-tricalcium phosphate (Ca-3(PO4)(2)). It is shown that the addition of silica inhibits re-crystallization of calcium pyrophosphate into tricalcium phosphate, if compared with ceramics prepared from monetite with no silica added. It is established that increasing the silica content in the starting composition leads to a decrease in the minimum pore size from 0.83 to 0.21 mu m. Highly pure nanosized silica (content of SiO2 > 99%) prepared by heat-treating of silicon carbide waste in a solar furnace is used in our research. The porosity of ceramics produced reaches 43.5-46.8% and the compressive strength is 16-24 MPa.