Factors affecting crystallization of bioactive glasses

The product range of bioactive glasses is restricted by their tendency to crystallize at working processes typically performed with high viscosity melts. In this work high-temperature properties viscosity, devitrification temperature and liquidus temperature of seven bioactive glasses are measured. Further, the parameters used to describe glass stability and crystallization tendency are discussed. The results indicate that bioactive glasses can be divided into two groups: (1) glasses which nucleate and crystallize within the whole viscosity range of interest for forming processes, such as sintering and fiber drawing, and (2) glasses with a viscosity range enabling high temperature processing without crystallization. The main difference between these groups is the primary crystalline phase in crystallization. Glasses showing sodium-calcium-silicate crystallization are sensitive to high temperature processing, while glasses showing wollastonite crystallization have better stability at working temperatures. Thus, by adjusting the composition special products, such as fibers and porous implants can be manufactured.