Viscosity and Density of Boron Trioxide

Extensive and accurate viscosity values for molten B2O3 are reported over the continuous range from 20 poises (at 1400°C) to 1010 poises (at 318°C). The measurements were made with a wide-range rotating-cylinder viscometer. The melts were pretreated by bubbling superdry nitrogen through them to ensure a minimum water content. Above 800°C the temperature dependence of the viscosity curve obeyed the Arrhenius equation; below 800°C the curvature was smooth showing no breaks. At the low temperatures, although its curvature decreased, the viscosity curve did not obey the Arrhenius equation. Densities were determined between 411° and 1400°C. Over this range the volume expansion coefficient changed by 1 order of magnitude from 3.35 × 10−4/°C to 3.34 × 10−5/°C. The liquid volume expansion coefficient above 1200°C was smaller than that of the glass below the glass transition temperature, indicating some type of structural rearrangement in B2O3.