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 × 10⁴) (1/T) - 22.15 and for temperatures above 775°C, E_vis= (1.121 × 10⁴) (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.