Hydrogen Reactions with Germanium Silicate Glasses
Date
2006-09
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Publisher
New York State College of Ceramics at Alfred University. Kazuo Inamori School of Engineering.
Abstract
The effect of processing technique and the presence of striations in glasses on the properties and behavior of binary GeO2-SiO2 is reported. Optical images of the as-received binary GeO2-SiO2 glasses prepared by OVD show concentric circular striations observed as a refractive index pattern resulting from the layer-by-layer deposition processing technique. The composition of two different binary GeO2-SiO2 glasses was examined using electron microprobe analysis. The environmental scanning electron microscope (ESEM) was used to characterize the striations after etching. The density, refractive index, and thermal expansion coefficient of binary GeO2-SiO2 glasses have been measured and found to be relatively insensitive to the presence of striations.
Treatment of 100 mol% SiO2, 6 mol% GeO2-94 mol% SiO2 and 14.6 mol% GeO2-85.4 mol% SiO2 glasses was monitored using infrared spectroscopy and optical spectrometry as a function of time under a H2 atmosphere (700 Torr) at 500ºC, 600ºC, 700ºC and 800ºC. Hydrogen reactions with binary GeO2-SiO2 glasses to form hydroxyl species, monitored using infrared spectroscopy, are a function of time, temperature and germanium content. The effect of GeO2 concentration on hydroxyl formation is evident as induced hydroxyl formation increases with increasing GeO2 concentration. The rate of hydroxyl formation increases with increasing temperature for both binary GeO2-SiO2 glasses. Hydroxyl concentration is uniform throughout the thickness of the sample at saturation. Hydride species do not form during heat treatment in hydrogen at any of the temperatures in either of the binary GeO2-SiO2 glasses, as indicated in the lack of change in their infrared spectra.
The change in concentration of reduced germanium species in the glass caused by hydrogen diffusion is monitored using optical spectroscopy and is a function of time, temperature and germanium content. This reaction is associated with an intense change in color of the glass from colorless to brown. The effect of GeO2 concentration on color formation is evident, as induced color formation increases with increasing GeO2 concentration. The rate of color formation increases with increasing temperature for both binary GeO2-SiO2 glasses. A detailed analysis of the changes in the optical spectra resulting from hydrogen reactions is provided. Color formation is confined to the exposed surface of each sample. Color concentration is not uniform across the surface of the sample, but varies systematically with areas of non-uniform concentration in the samples. This reaction is associated with an induced crystallization. A detailed analysis of the induced crystallization resulting from hydrogen reactions, using X-ray diffraction and Raman spectroscopy, is provided. Induced crystal formation is confined to the exposed surface of each sample and is not uniform across the surface of the sample, but it varies systematically with areas of non-uniform concentration in the samples, similar to the results observed with color formation.
Hydrogen treatment of pure GeO2 glasses was monitored as a function of time under a hydrogen atmosphere (700 Torr) at 400°C, 450°C and 500°C. Pure GeO2 glasses heat treated in the presence of hydrogen readily react to form reduced germanium species confined to the surface of each sample, including crystals of pure germanium.
Description
Advisory committee members: Thomas Seward, Matthew Hall, Alexis Clare. Dissertation completed in partial fulfillment of the requirements for the degree of Doctorate of Philosophy in Glass Science at the Kazuo Inamori School of Engineering, New York State College of Ceramics at Alfred University
Type
Thesis