Studies of strength mechanism in newly developed chemically bonded ceramics in the system CaOSiO 2P 2O 5H 2O

Abstract

Strength data are presented on totally new room temperature setting cements in CaO-SiO 2-P 2O 5-H 2O system. These compositions lie in the range of CaO:45–65, P 2O 5:29–50, SiO 2:4–20 (wt.%) and were prepared by sol-gel techniques using calcium nitrate and lactate, phosphoric acid and Ludox as precursors. Pressed pellets of the calcined powders were hydrated for times ranging from 1 day to 90 days at room temperature, 85° and 100°C. Typical values of splitting tensile strength near 15 MPa were common at room temperature, and 28 MPa at 100°C; maximum strengths of 31 MPA were achieved at 100°C for 1 day of hydration in some compositions. Microstructural analysis by SEM, XRD and EDAX showed the presence of unusually well crystallized CSH-1, Ca-hydroxy apatite and a well crystallized hydrated silicocarnotite phase together with gels of CSH and/or CSPH. The high strengths are attributed to the ultrafine powders used and the formation of well developed gels of CSH and CSPH which serve as the bond interlinking with crysalline grains of Ca(OH) 2, Ca-hydroxy apatite, CSH and CSPH.