Physico-chemical studies on BELGARD EV and BELGARD EV2000 solutions Part I: Their densities and viscosities at various dilutions and temperatures

Abstract

The absolute densities of aqueous BELGARD EV and BELGARD EV2000 solutions of concentrations varying between 1 and 50 wt/vol% are determined in the temperature range 25–90°C. At any temperature the density, d, of the two substances varies with the concentration, C, according to d= a+ bC. The term a is the same for the two additives, being the density of pure water. By contrast, the term b is material-dependent. At comparable temperatures the b values of BELGARD EV are higher than those of BELGARD EV2000. Further, the b of BELGARD EV decreases linearly with rise of temperature, whereas that of BELGARD EV2000 follows an S-shape pattern. The density of solutions of constant additive concentration varies with temperature, t, according to d= d 25− ct. The temperature coefficient of density c varies with additive concentration in two distinct manners. For BELGARD EV c increases linearly up to 35 wt/vol% and remains constant thereafter. For BELGARD EV2000 c undergoes a sudden change at 38 wt/vol%; below and above this concentration c is concentration-independent. The disparity in behaviour of the b and c constants allows the differentiation between the two additives, which are otherwise identical in all respects. The linear dependence of density on solution concentration is made use of in controlling the solid content of BELGARD EV and BELGARD EV2000 preparations. The viscous flow of BELGARD EV and BELGARD EV2000 solutions of concentrations varying between 1–50 wt/vol% in the temperature range 25–90°C is measured. From this information the relative-, absolute-, specific-, kinematic-, reduced- and inherent viscosities are computed. The shape of the log η− C curves depends on the particular definition of η. Absolute, relative and kinematic viscosities give rise to well separated, almost parallel curves with slight concave curvature at low concentrations. Specific viscosity give rise to curves which inverse parabolic pattern at low concentrations, changing into straight lines above ca 15 wt/vol%. Inherent and reduced viscosities give rise to parallel straight lines over the entire concentration range. Rise in temperature brings about a decrease in viscosity. Plots of log η as a function of the reciprocal of absolute temperature are invariably straight lines, allowing the computation of the activation energy of viscous flow. The magnitude of this parameter depends on the type of viscosity examined. There is no significant difference between the activation energies of BELGARD EV and BELGARD EV2000. The variation of activation energy of the various viscosities with additive concentration is considered. No single relationship describes all viscosities. Measurement of the absolute and specific viscosities, complementary to density evaluation, is proposed for controlling the concentration of the two additives.