Kinetics of silica-phase transitions

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Description

In addition to the stable silica polymorph quartz, several metastable silica phases are present in Yucca Mountain. The conversion of these phases to quartz is accompanied by volume reduction and a decrease in the aqueous silica activity, which may destabilize clinoptilolite and mordenite. The primary reaction sequence for the silica phases is from opal or glass to disordered opal-CT, followed by ordering of the opal-CT and finally by the crystallization of quartz. The ordering of opal-CT takes place in the solid state, whereas the conversion of opal-CT takes place through dissolution-reprecipitation involving the aqueous phase. It is proposed that the ... continued below

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23 p.

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Duffy, C.J. July 1, 1993.

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Description

In addition to the stable silica polymorph quartz, several metastable silica phases are present in Yucca Mountain. The conversion of these phases to quartz is accompanied by volume reduction and a decrease in the aqueous silica activity, which may destabilize clinoptilolite and mordenite. The primary reaction sequence for the silica phases is from opal or glass to disordered opal-CT, followed by ordering of the opal-CT and finally by the crystallization of quartz. The ordering of opal-CT takes place in the solid state, whereas the conversion of opal-CT takes place through dissolution-reprecipitation involving the aqueous phase. It is proposed that the rate of conversion of opal-CT to quartz is controlled by diffusion of defects out of a disordered surface layer formed on the crystallizing quartz. The reaction rates are observed to be dependent on temperature, pressure, degree of supersaturation, and pH. Rate equations selected from the literature appear to be consistent with observations at Yucca Mountain.

Physical Description

23 p.

Notes

INIS; OSTI as DE93016231

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  • Other Information: PBD: Jul 1993

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  • Other: DE93016231
  • Report No.: LA--12564-MS
  • Grant Number: W-7405-ENG-36
  • DOI: 10.2172/138671 | External Link
  • Office of Scientific & Technical Information Report Number: 138671
  • Archival Resource Key: ark:/67531/metadc620577

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Office of Scientific & Technical Information Technical Reports

Reports, articles and other documents harvested from the Office of Scientific and Technical Information.

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Creation Date

  • July 1, 1993

Added to The UNT Digital Library

  • June 16, 2015, 7:43 a.m.

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  • Feb. 29, 2016, 9:30 p.m.

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Duffy, C.J. Kinetics of silica-phase transitions, report, July 1, 1993; New Mexico. (digital.library.unt.edu/ark:/67531/metadc620577/: accessed December 9, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.