Optical Properties and the Constitution of Glass

JSGT 1949 V33 T239-T254

The classification of constituents as network-formers, modifiers or intermediates must be revised in certain glass-forming systems. The function of constituents is influenced not only by their charge and apparent radius, but also by the packing and the electron distribution in the structure. The concentration, the species of other constituents, the temperature and the thermal history affect both packing and electron distribution, and the function of the constituents will become different as these factors vary. The molar refraction is evaluated as an indicator of electron distribution. High refractions indicate loose electronic systems. Classical network-formers are characterised by low, modifiers by high apparent molar refraction of oxygen in a continuous series. The asymmetry of electrons in non-noble gas configurations, such as those of Tl⁺, Pb²⁺, Bi³⁺, is thought of as a supplementary condition of glass formation, for example, in Pb₂SiO₄• The molar refraction of borosilicate glasses was found to decrease significantly during the initial stages of fine annealing. The expected increase of the refractive index then occurs as the result of stronger factors favouring an increase in density. These phenomena are correlated with continuous ordering tendencies of glass in the transformation range.

Frank L. Jones & Norbert J. Kreidl