Viscosity Determination of Boron Oxide and Binary Borates

The anomalous behavior of rubidium and cesium borate glass and the boron coordination in alkali borate liquids are discussed. The viscosity‐composition isotherms of rubidium and cesium borates have been found to follow the same trend as those of other alkali borates. For boron oxide at temperatures between 500° and 775°C, the activation energy for viscous flow, E vis = (4.213 × 10 4 ) (1/T) ‐ 22.15 and for temperatures above 775°C, E vis = (1.121 × 10 4 ) (1/T) + 7.40, in which T is in °K. The activation energies for viscous flow, E vis , in kcal per mole, increase with all molten alkali borates in the order Li > Na > K > Rb > Cs to about 20 mole % of akali oxide. This phenomenon is explained on the basis of Douglas's hole theory.