High‐Temperature Density Determination of Boron Oxide and Binary Rubidium and Cesium Borates

Density determinations of pure B 2 O 3 and binary rubidium and cesium borates have been made in the temperature ranges 450° to 1300°C and 500° to 1100°C respectively. The density of B 2 O 3 can be represented between 600° and 1000°C as d = 1.3388 + 228 (1/T) and for temperatures above 1000°C as d = 1.3947 + 157.9 (1/T), where d is in grams per milliliter and T is in °K. The volume expansion (dV/dT) in the alkali borate systems at 800°C increases with an increase of alkali oxide when the alkali concentration is more than 18 mole %. This increase in the volume expansion follows the order Cs > Rb > K > Na > Li. In the range 15 to 20 mole % alkali oxide a break in the volume expansion was observed. This break suggests a possible change in the structural configuration of the alkali borates.