Improving glass-forming ability and crystallization behavior of porous glass-ceramics in CaO–Al2O3–TiO2–P2O5 system

Glass-forming ability and crystallization behavior of various compositions in the CaO–Al2O3–TiO2–P2O5 system were investigated, using differential thermal analyzer (DTA), X-ray diffractometry (XRD) and scanning electron microscopy (SEM) methods. According to our experiments, the precipitated crystalline phases were altered and the glass-forming and crystallization behaviors improved simultaneously, by addition of Al2O3 to the system. In the most promising composition, calcium pyrophosphate (Ca2P2O7) and calcium titanium phosphate (CaTi4(PO4)6) were formed during an ordinary short time heat treatment around the first DTA crystallization peak temperature of it. However, long-term heat treatment led to crystallization of calcium pyrophosphate (Ca2P2O7) and titanium pyrophosphate (TiP2O7) phases. Chemical leaching of the optimum resulted glass-ceramic with HCl, caused that calcium pyrophosphate was selectively dissolved out and a porous skeleton of titanium pyrophosphate remained. Porous structure of final products seems to be conceivable for applications as filters, membranes, catalyst supports, etc.