Influence of aluminium and boron ions on the crystallization of silicate–phosphate glasses from the NaCaPO4− SiO2 system

Abstract

Silicate–phosphate glasses belong to a group of bioactive materials. But they are characterized by low fracture toughness. One of the best ways to improve the mechanical parameters of glasses is to change their chemical composition (for example, the introduction of Al3+ or B3+ ions) or to carry out their partial devitrification.Conducted DSC investigations allowed to state that crystallization of glasses from the NaCaPO4–SiO2 system with phase separation phenomenon is a multistep process. Two exothermic peaks on DSC curves meaning crystallization of two different phases separately crystallize matrix and droplets. The addition of aluminium or boron ions into the structure of silicate–phosphate glasses causes the devitrification which runs in one stage (presence of only one peak on DSC curves). This effect is the consequence of the homogenizing influence of B3+ and Al3+ ions on the structure and microstructure of tested glasses.The direct crystallization of glasses from: NaCaPO4–SiO2, NaCaPO4–SiO2–AlPO4 and NaCaPO4–SiO2–BPO4 systems, has been made in a gradient furnace (based on DSC examinations). Obtained glass-crystalline materials have been studied by the MIR and XRD methods, which have confirmed the results of thermal examinations.