The effect of heat treatment on the microstructure of Li,OAl2O3-SiO2 glass-ceramics which contain crystals of either Li2Si03, Li2Si,05, or both was investigated quantitatively. Strength determinations for abraded rods were correlated with heat treatment on the basis of both size and distribution of crystals and the type and amount of crystal phases present. The presence of Li2Si205 crystals enhanced the strength, whereas the presence of Li2Si03 crystals did not change the strength of the abraded parent glass. The interrelation between strength and microstructure is discussed.

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The contrast between phases in pyrex glass was heightened for viewing in the electron microscope by exchanging silver ions for sodium ions in the glass. The scale of phase separation in pyrex was foud to be about 30 angstroms; sample of commercial soda-lime glass, prepared in the same way, showed no phase separtion.

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