AN EXPERIMENTAL-STUDY ON THE INFLUENCE OF SHEAR ON THE FLOW BEHAVIOR,SPONTANEOUS CRYSTALLIZATION, MICROSTRUCTURE AND MECHANICAL-PROPERTIESOF A FLUOROPHLOGOPITE GLASS-CERAMIC

The influence of a shear field acting in the molten state during the c rystallization of a sodium fluorophlogopite glass-ceramic on the theol ogical behavior of the melt, the resulting microstructure, and the com pressive strength of the solidified glass-ceramic, was investigated. F low curves of the molten glass-ceramic show slightly non-newtonian beh avior except in the vicinity of the crystallization temperature, where the crystallization starts. The temperature-dependent viscosity of th e melt shows an untypical z-shaped behavior. The temperature of the tu rning point corresponds to the temperature of newtonian flow behavior of the melt. The microstructure of the solidified glass-ceramic sample s treated under various thermomechanical conditions was analyzed with regard to the crystal sizes, shapes and corresponding distribution fun ctions. The compressive strength of the solid is affected by the total deformation realized in the melt state during shearing and depends on the temperature at which the melt was sheared. Different correlations between the compressive strength and the crystal fraction, dependent on the shear conditions of the melt, were found.