Viscosity and Electrical Resistivity and their Bearing on the Nature of Glass*

Abstract

AbstractThe mechanisms of viscous flow and of electrolytic conduction in liquids have been examined to show the significance of the activation energy which is evaluated from the temperature coefficients of viscosity and electrical resistivity. It is shown that the high numerical values characteristic of silicate glasses arise from the ionic character of the liquid, the small coordination number (4) for silicon, and the high electric charge on the ions (Si, 4; 0,2; etc.). Below the softening range, a glass is not necessarily stabilized (i.e., in equilibrium with respect to molecular association or dissociation processes) and its properties depend on its history, mechanical, thermal, etc. In stabilized glasses, the activation energies for viscosity and electric resistivity rise continually with falling temperatures, showing no maximum, in contrast to the views of Preston and Seddon.The oxygen, to silicon ratio has a dominating rôle in the structure of silicate crystals, as shown by W. L. Bragg. Similar concepts are applied to glass, and it is shown that the Preston‐Seddon proposal of definite compounds in soda‐silica glasses may be replaced by an alternate explanation.The quantity, β, in the equation, η=arβ, which relates viscosity to resistivity, has a value of 4 to 6 for certain soda‐containing glasses. The suggestion is made that viscous shear requires the breaking of four to six times as many sodium‐oxygen bonds as does electrical conduction.Finally, an internal energy‐temperature curve, based on specific‐heat data for fused silica, has been constructed. The curve shows a. steady rise with increasing temperature. It is typical of several glasses.