Observations of the formation of multiple-mist regions on the fracture surfaces of soda-lime-silicate and fused silica glasses are reported. These regions occur only in high-strength specimens. The same empirical equation that is applicable to the basic fracture mirror-primary mist also describes secondary and tertiary mist regions, although the proportionality constants increase as the order of the mist region increases. Results suggest that these mist radii constants may be related in specific ratios, which decrease with successive mist regions. Criteria of mist-region formation are reviewed with respect to additional restrictions imposed by the consideration of multiple mists. The authors suggest that an energy criterion is most applicable, and a schematic diagram is proposed.

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Fibers of Li,O.A1,O32Si0, glass were ion-exchanged for 1 to 300 min in a n NaN03 bath at 366°C. The internal friCtiQn and the Li and Na concentration profiles were measured. As Na progressively replaced Li, the alkali internal friction peak became smaller while a new peak (mixed-alkali peak) appeared and increased in magnitude. These changes in internal friction are similar to those that occur when a second alkali is added to glasses prepared by conventional melting. The magnitudes of both internal friction peaks in the ion-exchanged glass depended on the overall composition of the glass; that of the alkali peak depended on the composition of the unexchanged glass core, whereas that of the mixed-alkali peak depended on the composition of the exchanged layer on the glass surface. When the exchanged surface layer was dissolved, the original alkali peak was restored, and the mixed-alkali peak disappeared. Changing the alkali distribution did not affect the mixed-alkali peak much; however, it caused the alkali peak to shift to higher temperatures and become smaller. The height of the alkali peak can be used to determine the maximum depth of penetration of the second alkali.

Protons were introduced into the surface of an Li2O·Al2O3·2SiO2 glass fiber (0.5 mm in diameter) by ion exchange in NH4HSO4 at 366°C for 21 h. Infrared absorption measurements established that the protons were associated with bridging oxygen ions. After ion exchange, the magnitude of the alkali internal friction peak decreased and a new peak appeared at ∼220°C. This new peak is attributed to the interaction of alkali and hydrogen ions, independent of the presence of nonbridging oxygen ions.