Rheological Behaviour of Textured Glass-Ceramic Melts Produced by the Cylinder Compression Method

摘要

The rheological behaviour of glass-ceramic Li-disilicate melts is characterized by the Newtonian and non-Newtonian viscosity. These quantities are determined from the thermally corrected rate-dependent flow curves of the cylinder compression experiments on the basis of equal (Newtonian) equilibrium viscosities (isochomal conditions). Certain crystalline volume fractions in the glass samples are produced by primary nucleation and crystallization treatments. The flow parameters show a characteristic non-linear decrease with increasing compression rates. This two step shear thinning behaviour is determined, within the range of small deformation rates, by the suspension effect of the initial crystals and at larger deformation rates by the non-Newtonian flow behaviour of glass melt matrix. The suspension effect is based on a flow orientation mechanism of the crystals, building up a certain texture. The alignment depends on the size, shape and concentration of the specimens. Based on a recently developed flow equation for stress induced changes of viscosity in single-phase glass melts, a qualitative and quantitative description of the non-Newtonian flow behaviour of glass melts with suspended crystals is presented.