The effect of ionic and metallic silver on the crystalline phases developed in CaO-Al2O3-TiO2-P 2O5 glasses

Development of crystallization in the CaO-Al2O3-TiO2-P 2O5 system glasses was investigated in the presence of ionic and metallic silver. Differential thermal analysis, X-ray diffractometry, ultra violet-visible spectrophotometry, atomic force microscopy and scanning electron microscopy were used to evaluate the resulted glasses and glass-ceramics. It was found that silver ions facilitated crystallization by decreasing the viscosity of the glasses. However, metallic silver, which was formed through heat treatment in hydrogen atmosphere, improved heterogeneous crystallization of the reduced glasses in the subsequent heat treatment. The preformed metallic silver led to effective crystallization of calcium titanium phosphate (CaTi4(PO4)6), calcium metaphosphate (Ca(PO3)2) and calcium pyrophosphate (Ca2P2O7) phases at significantly decreased temperatures. The two latter phases were partially dissolved out by leaching in acidic solution and left out a porous structure of calcium titanium phosphate glass-ceramic.