Influence of microheterogeneities on the mechanical properties of high-viscous melts

Abstract

The influence of liquid-solid (Zerodur glass-ceramic melts) and liquid-liquid (PbO-B2O3 melts) two phase systems on the mechanical properties is investigated. The load-dependent mechanical properties which characterise the isothermal workability are: Newtonian and non-Newtonian flow behaviour, relaxation behaviour and therefore the stiffness as well as the high-temperature tensile strength of the melts. From the rheological point of view two systems (1 and 2) have to be regarded: 1) the liquid-solid and that part of the liquid-liquid system with the high-viscous inclusions within a low-viscous matrix on the one hand and 2) that part of the liquid-liquid system with the low-viscous inclusions within a high-viscous matrix on the other hand. These two systems show among various of the mentioned other special properties and relations a general decrease of high-temperature strength and isothermal workability with increasing portion of the distributed minor phase. System 1) shows with respect to constant equilibrium viscosities a constant non-Newtonian viscosity decrease, an increase of the relaxation modulus (stiffness) and a decrease of high-temperature tensile strength with increasing portion of solid and/or high-viscous inclusions. System 2) under the same aspect exhibits a strong increasing non-Newtonian viscosity decrease, a decrease of the relaxation modulus and a decrease of high-temperature tensile strength with increasing portion of the low-viscous inclusions.