Dehydration and rehydration of a tuff vitrophyre
The basal vitrophyre of the Topopah Spring Member of the Paintbrush Tuff at Yucca Mountain, Nevada, is a perlitic glass with 2.8 to 4.6% water. The dehydration of this vitrophyre was studied by thermogravimetric analysis (TGA) and by isothermal heating at 50{degrees}, 100{degrees}, 200{degrees}, and 400{degrees}C for 3.4 years followed by 1.1 years of rehydration at high controlled humidity ({approximately}79% relative humidity). No crystallization of the glass was observed in long-term dehydration or rehydration; the only observed chemical alteration was loss of up to 60% of original fluorine. TGA studies show a characteristic two-stage dehydration of the vitrophyre, with two-thirds to three-fourths weight loss occurring most rapidly at temperatures ranging from 278{degrees} to 346{degrees}C in 10{degrees}C/min heating experiments. The remaining water, about 1% in all of the vitrophyre samples studied regardless of total water content, is lost only on second-stage heating to temperatures above 650{degrees}C. Long-term isothermal heating at {le}400{degrees}C releases only the first-stage water. Loss of essentially all first-stage water occurred in less than 1 hour at 400{degrees}C; proportionately lower losses were obtained at 200{degrees} and 100{degrees}C. Small (0.2%) water loss occurred in the 50{degrees}C experiment. A time-temperature-dehydration diagram generated from the isothermal heating data shows a clustering of dehydration contours that are the equilibrium equivalent of the rapid first-stage water loss in dynamic TGA experiments. These dry-heating experiments provide an end-member characterization of glass transformations for comparison with water-saturated heating experiments in which glass alteration is prominent. 29 figs., 7 figs., 7 tabs.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 159857
- Journal Information:
- Journal of Geophysical Research, Journal Name: Journal of Geophysical Research Journal Issue: B12 Vol. 98; ISSN JGREA2; ISSN 0148-0227
- Country of Publication:
- United States
- Language:
- English
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