Band 19, Heft 6

Experimental and numerical studies have been undertaken to check the influence of a magnetic field on the viscosity of liquid GaInSn with suspended solid particles. The rheological investigations show a significant change of the slope of the measured flow curves between the situation B = 0 and 0.02 T. By means of numerical simulations of the flow in the presence of Lorentz forces it could be shown that the influence of magnetohydrodynamic damping of the flow reduces the measured changes but does not annihilate them. As conclusion a 15 % change of viscosity of the melt in a magnetic field with B = 0.02 T could be fixed.

The rheological behavior of emulsions has been extensively investigated through experiments made at atmospheric pressure. This study presents a new experimental characterization of these fluids with measurements performed under pressure and in a large range of temperature. The results show that viscosities obey Barus model that predicts an exponential increase with pressure. The extent of the increase is governed by a unique piezoviscous coefficient. This coefficient exhibits a non monotonous variation with temperature. It has been shown that its thermal dependence and its value can be related to the viscoelastic properties of the fluid. The coefficient is an increasing function of temperature for a solid-like behaviour and a decreasing function of temperature for a liquid-like behaviour. This approach has been applied to heavy crude oils. It has been demonstrated that water droplets and oil composition modify the elastic character of heavy crude oils and as a consequence they modify their piezoviscosity.

The viscoelastic performance indicators of a commercial roofing membrane and an ecological bituminous membrane, which contains EVA copolymer from disused greenhouses and filler from landfill, are investigated. Rheological methods reveal as a useful tool to investigate basic and technical aspects of these materials. It is shown that using an extrusion rheometer adapted to measure the flexibility at low temperatures and measuring the tackiness by means of a plate-plate rheometer, constitute basic experiments that help to develop new membranes. Under these premises, it is demonstrated that the ecological membrane is a performing material, whose sole shortcoming is a slightly higher application temperature.

The rheological behavior of ceramic oxide hydroxide alumina pastes with high solid loading is investigated. In order to enable an adequate and experimentally rheological characterization, the measurements are carried out with a Rheostress viscometer under isothermal conditions. Various compositions of a commercial AlOOH powder and binder mixture are investigated. We discuss the variation of loss modulus G′ , storage modulus G″ , apparent and complex viscosities η , η * as function of frequency and shear rate. The solid phase used here is the boehmite; the most important precursor for the γ -Al 2 O 3 phase for several applications such as catalysts or functional layers of ceramics. Solid phase compositions used are justified by the applications of boehmite in the manufacturing of catalytic materials. A transition zone that appears at a concentration of 55 %wt of the solid phase (Pural) and at which the rheological behavior changes from viscoelastic to elastic is observed. This transition is of a importance as far as ceramic manufacturing is concerned.