Some Phenomena Related to the Hydrophobicity of Silicate Glasses and Adsorbed Oxygen

A number of silicate glasses have been melted which can be made to support a drop of water with a contact angle near 90°. It is demonstrated that the hydrophobicity is caused by a layer of semi-chemisorbed oxygen. The oxygen is adsorbed at active centers which are related to the presence of octahedrally coordinated metal ions.     

Nucleation and Growth of Sodium Disilicate Crystals in Sodium Disilicate Glass

A high-temperature microscope for use with transmitted or reflected light up to × 400 magnification and up to 1400°C. was constructed. Nucleation and crystal growth in sodium disilicate glass was studied with this microscope. Heterogeneous nucleation occurred at the interface between the glass and the platinum heating element from 450° to 870° C. with a maximum at 600° C. Heterogeneous nucleation also occurred at the glass-atmosphere interface from 25° to 375° C. as a result of surface reactions with water vapor. No homogeneous nucleation was observed. Linear growth rates of α and β sodium disilicate crystals were measured from 600° to 870° C. in two sodium disilicate glasses. Metastable growth of both α and β was observed, and growth rates of α and β were the same at a given temperature for a given glass. An equation relating fluidity and undercooling to growth rate was applied.     

Determination of Stoichiometry Variations in LiNbO3 and LiTaO3 by Raman Powder Spectroscopy

Raman spectroscopy of powders is shown to be a sensitive technique for detecting stoichiometry variations. The method makes use of the broadening of the Raman-active modes which occurs when the translational symmetry of the lattice is reduced on deviation from simple, fixed cation ratios in the structure. Application of the technique to the LiNbO₃( ss ) system shows that the room-temperature solid-solution range does not exceed 50±0.5 mol% Nb₂O₅ and that congruent LiNbO₃( ss ) at 51.4 mol% Nb₂O₅ is thermodynamically unstable below ≅800°C. Similarly, application of the Raman method to the LiTaO₃( ss ) system indicates that congruent LiTaO₃( ss ) at 51.0 mol% Ta₂O₅ is unstable at temperatures <1000°C.     

Functional Properties of a Food Colorant Prepared from Red Cabbage

Spectral, colorant, and stability properties of colorants based on red cabbage, grape, cranberry, beet, and Red No. 40 were compared in buffer and in a simulated beverage. At pH 3, red cabbage imparted a red color similar to that of beet juice and less orange than that of the other colorants. Increasing the pH of red cabbage extracts to 4 produced a bathochromic shift and decreased color strength. Tristimulus parameters displayed maxima when L was varied. Red cabbage pigments were more stable during heating and storage than were the other colorants tested. pH had little effect on color stability; exposure to light greatly increased color loss during storage.