Browsing by Author "Pye, L. David"

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    Crystallization kinetics of fluorosilicate glasses
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1989) Mathur, Akshay; Pye, L. David
    Crystallization kinetics and properties of fluorosilicate glasses containing 0 to 8 wt% fluorine have been studied. The effect of isothermal and non-isothermal heat treatments on the fraction crystallized has been investigated by the use of quantitative X-ray diffraction analysis and differential scanning calorimetry. A time-temperature-transformation diagram was constructed which shows a maximum rate of crystallization at about 650 °C. Activation energies of crystallization are found to be close to those for viscous flow which indicate similar mechanisms for both processes. The Avrami coefficients and other crystallization parameters have also been evaluated.
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    Glass formation and structure of glasses in the Y2O3-Fe2O3-B2O3 system
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1991) Padture, Nitin P.; Pye, L. David
    An extensive region of glass formation and liquid immiscibility have been found in the Y2O3—Fe2O3—B2O3 system. The glass transition and crystallization temperatures were determined for selected single phase glasses in this system. The glass transition temperature and the stability of the glass were found to decrease with increasing concentration of Fe2O3 . Mössbauer spectroscopy, infrared spectroscopy and transmission electron microscopy were used to obtain an insight into the structure of these glasses. Infrared and Mössbauer spectra indicate that, similar to the Y2O3—Al2O3—B2O3 system, glasses in the above system contain (FeB2O6)∞ chains composed of FeO4-tetrahedral and BO3-triangular structural units. Hyperfine splitting phenomena were observed in the Mössbauer spectra of glasses containing high Fe2O3 concentrations. The appearance of such hyperfine lines, and the decrease in the isomer shift with increasing Fe2O3 content, suggest formation of iron-rich microclusters, which is supported by the presence of microstructure at a very fine scale. Glasses with increasing Y2O3 concentration showed a decrease in the isomer shift and quadrupole spliting. Glases containing TiO2 yielded A-Fe2O3 when crystallized.
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    Nitridation of phosphate glass melts with ammonia
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1989) Heuberger, Martin; Pye, L. David
    A sodium metaphosphate glass melt was nitrided with ammonia in a newly designed tilted tube furnace with a rotating crucible. An optimum nitridation temperature of 780 °C led to 7.2 wt% of nitrogen in a clear glass in only 10 h. Crystallization of this glass was greatly reduced by incorporation of nitrogen. From the present results a reaction mechanism and structural model is developed for this incorporation. This model provides a better understanding of the nitridation process and may lead to successful nitridation of compositions with a P/Na ratio > 1. Based on thermodynamic considerations, the use of a graphite crucible is thought to play a role in the development of brown glasses at temperatures greater than 780 °C via reduction to phosphorus.
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    Statistical analysis of viscosity-composition data in glassmaking
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1994) Öksoy, Dolun; Pye, L. David; Boulos, Edward N.
    The objective of this work is to revisit and expand the methods for calculating viscosities of glass with changes in composition that was pioneered by Lakatos, Johansson, and Simmingsköld. Using the data provided by these authors, an empirical statistical model will be presented. This will illustrate the effect of composition change on viscosity that can be expected in a typical glassmaking process.
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    Was Libyan Desert Glass formed by a sol-gel process?
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1989) McPherson, Donald M.; Pye, L. David; Fréchette, Van Derck; Mortsea, Mary
    Despite extensive research for nearly five decades, the origin of Libyan Desert Glass remains a puzzle. It is suggested that this glass was made by a low-temperature, chemical process known to have produced other natural glasses, such as opal. This new genesis is based upon a periodic void spacing observed in this material and irreversible changes that occur upon heating, especiahy crystallization and consolidation. These features are seemingly irreconcilable with a melt-derived origin for Libyan Desert Glass, but are consistent with a low-temperature chemical mode of formation.