Some Properties of Mixed Alkali–Lime–Silica Glasses containing Lithia, Soda, Potash and Rubidia

JSGT 1934 V18 T268-T285

The densities, thermal expansions and values of M_gand T_gwere studied of four series of glasses of general formula 75% SiO₂,10CaO, 15(R₂’O+R₂”O), in which (R₂’O and R₂”O) represented, respectively (Li₂O+Na₂O), (Li₂O+K₂O), (Na₂O+K₂O) and (K₂O+Rb₂O), and in which each oxide varied in amount from 0 to 15%. In the first three series the curves relating the composition to the density and the thermal expansion respectively, consist of two straight or nearly straight intersecting lines, the change of direction being most marked in the series containing the oxides (Li₂O+Na₂O) of lightest molecular weight. The corresponding curves for the (K₂O+Rb₂O) glasses are continuous straight lines. The breaks occur at simple molecular ratios, namely K₂O:2Na₂O, Li₂O:2K₂O, and Na₂O:K₂O. The thermal expansion coefficients are highest for the lithia glasses, diminishing in the order Li₂O, Na₂O, K₂O, Rb₂O. Three transition points appear in the thermal expansion–composition curves of all the glasses containing Li₂O, Na₂O, and K₂O, except the 15% K₂O glass, and two transition points in the 15% K₂O glass and the (K₂O+Rb₂O) series. The softening point or upper annealing temperature rises in the order Li₂O, Na₂O, K₂O and Rb₂O, the value of M_gfor the 75% SiO₂ 10CaO, 15Rb₂O being 740°. The corresponding caesium oxide glass could not be melted at 1650°.

 S. C. Waterton & W. E. s. Turner