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In-Situ Observation of the Alpha/beta Cristobalite Transition Using High Voltage Electron Microscopy

Published online by Cambridge University Press:  21 February 2011

A. Meike  and
W. E. Glassley
A. Meike
Affiliation:
Material and Chemical Sciences Division, Lawrence Berkeley Laboratory, Berkeley, CA 94720
W. E. Glassley
Affiliation:
Earth Sciences Division, Lawrence Livermore National Laboratory, Livermore, CA 94550
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Abstract

A high temperature water vapor phase is expected to persist in the vicinity of high level radioactive waste packages for several hundreds of years. We have begun an investigation of the structural and chemical effects of water on cristobalite because of its abundance in the near field environment. A high voltage transmission electron microscope (HVEM) investigation of bulk synthesized α-cristobalite to be used in single phase dissolution and precipitation kinetics experiments revealed the presence β cristobalite, quartz and amorphous silica, in addition to α-cristobalite. Consequently, this apparent metastable persistence of β-cristobalite and amorphous silica during the synthesis of α-cristobalite was investigated using a heating stage and an environmental cell installed in the HVEM that allowed the introduction of either dry CO2 or a CO2 + H2O vapor. Preliminary electron diffraction evidence suggests that the presence of water vapor affected the α-β transition temperature. Water vapor may also be responsible for the development of an amorphous silica phase at the transition that may persist over an interval of several tens of degrees. The amorphous phase was not documented during the dry heating experiments.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 176: Symposium U – Scientific Basis for Nuclear Waste Management XIII , 1989 , 631
Copyright
Copyright © Materials Research Society 1990

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