Thermal After-effect of a Lead Potash Soda Glass

Density Change of Glasses by Heating, Part IV

Abstract

The ice-point depression due to thermal after-effect of a thermometer glass reflects upon the fact that the density of a glass quenched from a certain holding temperature is always lower than that of the well annealed specimen even if the holding temperature lies in the region being considerably lower than the transition point.
From the results of the investigations made with lead glasses containing Na₂O, K₂O or both, which presumably show a strong thermal after-effect, the author concluded that the phenomenon is independent of the thermal history of glasses within the limits of experimental errors. Moreover it was found out that the appearance and disappea rance of the density change due to the thermal after-effect is reversible if the effects of compacting may be excluded.
The thermal expansion curves of rapidly cooled glasses showed hysteresis phenomena due to the release of the thermal after-effect. Hence the author was able to draw the curves showing the relations between the degree of the release of thermal after-effect and the reheating temperature.
The thermal expansion curves of the samples with various thermal histories, but free from both compaction and thermal after-effects were also obtained. Furthermore, the relation between the density change and the holding temperature were compared for many glasses having considerably different compositions and properties.