The Influence of Boric Oxide on Crystallisation of Soda-Potash-Lime-Silica Glass

JSGT 1945 V29 T038-T047

Substitution of boric oxide for silica in the series of glasses of percentage composition: (75·82−x)SiO₂, xB₂O₃, 8·56 CaO, 6·86 Na₂O, 7·90 K₂O, caused a reduction in the liquid us temperature from 1110° to a minimum of 875° at 5·44% boric oxide. Subsequent additions caused a slight rise in temperature to 890°, followed by a further drop to 830° at 22·54%. The maximum rate of crystal growth for the different glasses reflected quite closely the differences in liquidus temperature, values of 0·48, 0·05, 0·12 and 0·03 µper minute being found for the parent glass and those containing 5·44, 9·58 and 22·54% boric oxide, respectively. The minimum liquidus temperature and the rate of devitrification at about 5% boric oxide were associated with a change in the primary phase from tridymite to devitrite, and corresponded closely with a similar change found by G. W. Morey on adding varying amounts of boric oxide to a pure soda–lime–silica glass.

G. E. Walker