Temperature-Property Relationships: Their Bearing on the Constitution of Glass

JSGT 1937 V21 T123-T154From a consideration of the rate of change with temperature of such physical properties as viscosity and electrical resistivity, internal energy quantities may be derived the variation of which with temperature appears to be characteristic of glassy materials. The derivation of the fundamental formulae involved is indicated, and these relations substantiate the results obtained by empirical methods for a soda–lime–silica glass and two soda–silica glasses. A quantity β relating viscosity to electrical resistivity, varying according to the glass composition, appears to be an index of the complexity of the glass and is independent of temperature over the range 15–1400° and thus independent of the physical condition of the glass. For vitreous silica β has the value 6·2, which was confirmed from existing experimental data. A relationship between viscosity, electrical resistivity, and vapour pressure has been established for a soda–silica glass containing approximately 49% Na₂O. Above the liquidus temperatures the glasses appear to be associated to a constant degree, and to behave in the manner of simple liquids, for a linear relation existed between log viscosity and 1/T_Abs for a series of soda–silica glasses ranging from 12·6 to 60·0%  Na₂O. A molten soda–lime–silica glass appears to have an average effective molecular weight of approximately 1000, and in the condition of maximum association, about 3000. The molecular energies of the soda–silica glasses at the compositions Na₂O.2SiO₂ and Na₂O.SiO₂ are found to be very nearly in the ratio of the corresponding molecular weights. The variation of thermal expansion coefficient could be related to the energy content of the glasses at temperatures below the softening point. This comparatively simple inter-relationship of physical properties has led the authors to construct an ideal (internal) energy curve the form of which is probably a characteristic of all glasses.

Eric Preston & Eric Seddon