Effect of Pressures (up to 4 kbar) on the Polymerization of Liquid Selenium from Measurements of Viscosity

Abstract

The viscosity of liquid selenium was measured between 220°—350°C and up to pressures of 4 kbar, using a rolling‐ball viscometer. An extrapolation of the viscosity data to the freezing point at various pressures gave the viscosity along the melting curve of hexagonal selenium. This extrapolation showed that the viscosity along the melting curve decreased to 1/5 its initial value at 6.0 kbar, then rose with further increase in pressure. The data revealed that the slope of the log₁₀ viscosity vs 1/T² (°K) curve was independent of pressure up to at least 4.5 kbar. Analysis of the effect of pressure on the degree of polymerization in terms of the ring‐chain equilibrium theory of Eisenberg and Tobolsky indicated that pressure has only a slight effect on the average chain length. Thus, the minimum in viscosity along the melting curve appears to be a balance between the effects of shorter chain length toward decreasing the viscosity and that of diminished free volume toward increasing the viscosity.