The rates of extraction of Li 2 0 and Si0 2 from silicate glasses containing up to 34 mole per cent Li 2 0 were studied. From the composition containing 7 mole per cent Li 2 0 hardly any Li 2 0 could be extracted, apparently due to entrapment of the lithium silicate phase in a matrix of silica. On raising the Li 2 0 content to 10 mole per cent and above, the separated phase became progressively continuous and the rate of extraction increased sharply. Boro-silicate glasses containing 10 and 12 mole per cent of Li 2 0 and B 2 0 3 respectively, were readily attacked by water due to the presence of a more readily soluble phase. The soluble phase having a probable composition around 1.5 Li 2 0, 1 B 2 0 3 , 1 Si0 2 , could be selectively extracted from one of the glasses leaving a skeleton containing over 92 per cent Si0 2 and hardly any Li 2 0. Compositions comparatively richer in Li 2 0 and B 2 0 3 , disintegrated in water presumbly due to the presence of the insoluble phase as islets in a matrix of soluble boro-silicate phase. Replacing B 2 0 3 by Al 2 0 3 in one of the glass compositions, the resistance to water attack increased by over t1-ro orders of magnitude. The mechanism of water attack has been discussed in relation to the structure and phase separation phenomena.
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