The Influence of Thermal Treatment on the Opacity of Fluoride Opal Glasses

JSGT_1932_V16_T210_T218

The paper records experiments on the effect of heat treatment in developing opacity in a glass of percentage composition SiO₂ 67·52, Al₂O₃ 3·81, CaO 5·86, Na₂O 18·54, F₂ 4·00, and in two other glasses of similar composition varying from it mainly in respect of small amounts (1–3%) of SiO₂, CaO, and Na₂O. Prepared slabs of the glasses were heated at 700° for periods varying from 1 minute up to 4 hours and at varying temperatures from 450–900° for a constant period of 20 minutes. The general transmission, unscattered transmission, reflection, and absorption were measured for each specimen. The conclusions were drawn that the relation between heat treatment and optical properties of opal fluoride glasses is in accordance with Tammann's theory of crystallisation from supercooled solutions and each glass has its own maximum opacifying temperature. For the glass the precise composition of which is given above this temperature lies between 650° and 700°.

I. Kitaigorodsky & S. I. Kurovskaja