High-temperature sup 29 Si NMR investigation of solid and molten silicates
- Stanford Univ., CA (USA)
High-temperature (up to 1250{degree}C) {sup 29}Si NMR T{sub 1} and line-shape measurements were made on silicate samples with varying SiO{sub 2} contents. The sample represented a range of bridging and nonbridging oxygen distributions from Q{sup 4} in albite (NaAlSi{sub 3}O{sub 8}) to Q{sup 2} and Q{sup 0} in a mixture of lithium orthosilicate and metasilicate (Li{sub 4}SiO{sub 4}/Li{sub 2}SiO{sub 3}). T{sub 1} relaxation data as a function of temperature for glassy samples showed a dramatic increase in efficiency at the glass transition. This was ascribed to relaxation by paramagnetic impurities becoming more efficient as silicon atoms and impurity ions begin to diffuse through the material at temperatures above T{sub g}. In each sample chemical exchange was observed at high temperature, indicating that the lifetime of a silicate tetrahedron in the melt is short on the NMR time scale, i.e., a few microseconds. Variable-temperature line-shape data for potassium tetrasilicate (K{sub 2}Si{sub 4}O{sub 9}) allowed the exchange process to be modelled and spectra to be simulated, yielding an activation energy for the process. This was in good agreement with the activation energy for viscous flow derived from viscosity measurements. It appears that {sup 29}Si NMR is coming close to detecting the fundamental step in viscous flow in silicates with good agreement between the time constant of the exchange process determined by NMR and the shear relaxation time of the potassium tetrasilicate liquid.
- OSTI ID:
- 6619566
- Journal Information:
- Journal of the American Chemical Society; (USA), Journal Name: Journal of the American Chemical Society; (USA) Vol. 112:1; ISSN 0002-7863; ISSN JACSA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360602 -- Other Materials-- Structure & Phase Studies
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
CHALCOGENIDES
DATA
DATA ANALYSIS
EVEN-ODD NUCLEI
EXPERIMENTAL DATA
FLUID FLOW
INFORMATION
ISOTOPES
LIGHT NUCLEI
MEASURING INSTRUMENTS
MEASURING METHODS
NMR SPECTRA
NUCLEI
NUMERICAL DATA
OXIDES
OXYGEN COMPOUNDS
SILICATES
SILICON 29
SILICON COMPOUNDS
SILICON ISOTOPES
SILICON OXIDES
SPECTRA
STABLE ISOTOPES
VERY HIGH TEMPERATURE
VISCOUS FLOW