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 general characterization, nucleation and crystallization rates and the activation energies for viscosity of the starting glasses were determined. Further, the activation energy for crystallization and the Avrami exponents were calculated from the results of differential thermal analysis. Transformation with time and temperature was investigated, showing that crystallization of the beta-eucryptite solid solution starts at temperatures around T-g. At higher temperatures, the beta-spodumene solid solution is the predominant crystalline phase. The base composition was chosen for further investigation of crystalline growth. Glass rods were drawn under industrial conditions. Due to a crystallized surface layer with an extremely low expansion coefficient, the flexural strength of the initial glass increased fourfold to a maximum fo 800 MPa.