James E. Shelby

Protonic species in vitreous silica

Abstract Protons can exist in vitreous silica as molecular hydrogen, hydroxyl and hydride species. Examples of each species are discussed. The molecular extinction coefficient for molecular hydrogen dissolved in vitreous silica has been measured (0.26 1/mol cm). Formation and removal of hydroxyl and hydride in vitreous silica by thermally- and radiation-induced reactions is discussed. It is shown that the stability of hydroxyl in vitreous silica is a strong function of the mode of production of the hydroxyl. New data regarding the effect of radiation on the infrared bands due to hydroxyl in vitreous are also presented.

Crystallization of glasses in the system BaOTiO2B2O3

Abstract Glass formation by rapid quenching was studied for the system BaOTiO 2 B 2 O 3 . Compositions on the periphery of the glass forming region either phase separate or crystallize. Crystalline phases are identified by X-ray diffraction. Differential thermal analysis was used to study the crystallization behavior of the glasses. The glasses generally show two crystallization temperatures. The effect of composition on the first crystallization temperature is studied for increasing BaO and TiO 2 contents. Anomalous behavior, similar to that for properties of the parent glass, is observed for various series of glasses in the system. Glasses were heat treated at the onset temperature of their first crystallization. X-ray diffraction was employed to determine the phases which occur in the glass-ceramic.

Calcium fluoroaluminate glasses

Binary calcium aluminate glasses containing 59–70 mol % CaO have been formed, as have a series of glasses in which CaF2 replaces CaO. The transformation range viscosity and glass transformation temperature of the binary glasses decreases as the CaO concentration increases, whereas the thermal expansion coefficient, refractive index, and infrared cutoff wavelength increase. The substitution of CaF2 for CaO results in a decrease in the refractive index, viscosity, and glass transformation temperature, an increase in the thermal expansion coefficient and electrical conductivity, and no detectable change in the infrared cutoff wavelength. Magic angle spinning nuclear magnetic resonance indicates that the aluminum ions in these glasses are in tetrahedral coordination. These results will be discussed in terms of the structures of these glasses.

Properties and structure of PbO‐PbF2‐B2O3 glasses

Glasses containing as little as 5 mol % B2O3 have been made in the ternary system PbO‐PbF2‐B2O3. Glass transformation and crystallization temperatures, thermal expansion behavior, and electrical conductivity of these glasses have been measured. The lead fluoroborate glasses appear to be anion conductors, with conductivities among the highest ever reported for fluorine‐conducting glasses. A model for the structural role of fluorine in these glasses is proposed.

Properties of alkali–alkaline earth metaphosphate glasses

Abstract Several properties of alkali–alkaline earth metaphosphate glasses have been measured. These properties include density, transformation range viscosity and dc electrical conductivity, with emphasis on the conductivity measurements. Glasses studied include series in which Li 2 O or Na 2 O is replaced by MgO, CaO or BaO, mixed alkali glasses containing a constant concentration of BaO and a series in which ZnO replaces BaO. The conductivity decreases by orders of magnitude as an alkaline earth oxide replaces either Na 2 O or Li 2 O. Replacement of one alkaline earth by another while maintaining the identity of the alkali ion has a much smaller effect on the conductivity of these glasses. The mixed alkali effect is evident in the conductivities of the Li–Na and Na–K glasses.

Effects of water content on aluminosilicate glasses and the relation to strong/fragile liquid theory☆

The effect of variations in water content on the transformation range properties of 25Na2O25Al2O350SiO2, 10Na2O10CaO20Al2o360SiO2, 20CaO20Al2O360SiO2, and 20Y2O320Al2O360SiO2 glasses are presented. Samples of these glasses were prepared with a range of water of hydroxyl contents by melting under various partial pressures of water. With an increase in water content of each glass, a decrease in both the glass transformation temperature, Tg, and the transformation range viscosity are observed. The magnitude of these effects of water depends strongly on composition and is correlated with the activation energy for viscous flow. The data from this study are combined with the known effects of water on the properties of phosphate, borate, heavy metal fluoride, and other silicate glasses to show that the flow properties of ‘strong’ liquids are affected much more dramatically than those of ‘fragile’ liquids. These data are used to determine a quantitative empirical relationship between the magnitude of the effect of water on flow properties and the fragility of the glass-forming liquid.

Lead fluoroborate glasses

Glasses containing up to 60‐mol % PbF2 have been made in the binary system PbF2‐B2O3. The glass transformation and crystallization temperatures, thermal expansion behavior, and electrical conductivity of these glasses have been measured. A corresponding series of lead borate glasses were also studied to provide a basis for comparison of the effects of fluorine and oxygen on the properties of these glasses. The lead fluoroborate glasses appear to be anion conductors, with conductivities approaching the highest ever reported for fluorine conducting glasses.

The mixed alkali effect in lithium-sodium aluminosilicate glasses

The electrical conductivity of several series of lithium-sodium aluminosilicate glasses has been measured. The results indicate that the mixed alkali effect increases in magnitude with increasing alumina concentration, even though the total alkali oxide content of all glasses considered is identical. These results further indicate that the non-bridging oxygen content of the glass has no significant role in the mechanism responsible for the mixed alkali effect. Results of this study are discussed in terms of current theories proposed to explain this anomalous behavior.

Electron spin resonance: A potential diagnostic for oxide impurities in ZrF4-based glasses

Abstract Two ZrF 4 -based glasses (ZBLALi and ZBLAN) were analyzed for total oxygen both before and after remeltings at 775° C in pure O 2 at 700 Torr for various lengths of time. All of these samples were studied by electron spin resonance (ESR) both before and after exposure to a range of 60 Co γ-ray doses. Prior to irradiation, a resonance centered on g = 2.0 was observed in the O 2 -treated samples but not the unremelted base glasses. The origin of this preirradiation signal is demonstrated to be a trace Fe 3+ impurity (≤ 50 ppm) resulting from oxidation of Fe 0 present in the furnace environment during remelting. A radiation-induced signal which appeared in all samples (but with greater intensities in the remelted glasses exhibiting the largest Fe 3+ contaminations) is identified as an O 2 − molecular ion on the basis of its g values ( g 1 = 2.0042, g 2 = 2.0085, g 3 = 2.0274) and, particularly, its 17 O hyperfine structure ( A ∥ = 7.75 mT) as obtained for a sample which had been remelted in an 17 O-enriched oxygen atmosphere. This O 2 − ion is easily detected at levels ∼ 0.01 per million zirconium atoms.

Stability and crystallization of lead halosilicate glasses

Abstract Lead fluoro- and chlorosilicate systems show large regions of glass formation with significant areas of stable glasses as indicated by values T x − T g . Crystallizing highly conductive β-PbF 2 crystals from lead fluorosilicate glasses produced interesting conductivity results. Enhanced conductivity was noted for some devitrified samples, but interpretation of the data was difficult. Volatization of fluorine from fluorosilicate melts appears to be minimal as is shown by melt history effects on physical properties.