STRENGTHENING OF GLASS THROUGH SURFACE CRYSTALLIZATION OF BETA-SPODUMENE SS

Compositions close to spodumene with additional flux were investigated regarding surface crystallization for strengthening of glass articles . The influence of Au, TiO2, P2O5 and ZnO was determined. After a gene ral characterization, nucleation and crystallization rates and the act ivation energies for viscosity of the starting glasses were determined . Further, the activation energy for crystallization and the Avrami ex ponents were calculated from the results of differential thermal analy sis. Transformation with time and temperature was investigated, showin g that crystallization of the beta-eucryptite solid solution starts at temperatures around T-g. At higher temperatures, the beta-spodumene s olid solution is the predominant crystalline phase. The base compositi on was chosen for further investigation of crystalline growth. Glass r ods were drawn under industrial conditions. Due to a crystallized surf ace layer with an extremely low expansion coefficient, the flexural st rength of the initial glass increased fourfold to a maximum fo 800 MPa .