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Metal-silicate Partitioning at High Pressure and Temperature: Experimental Methods and a Protocol to Suppress Highly Siderophile Element Inclusions
Published on: June 13, 2015
Silicon coordination and speciation changes in a silicate liquid at high pressures.
Science (New York, N.Y.)
|September 1, 1989
Summary
High pressure transforms silicon (Si) in silicate liquids, changing its local geometry. This study detected pressure-induced changes in Si coordination using (29)Si NMR, revealing a shift towards octahedral Si in amorphous phases.
Area of Science:
- Geochemistry
- Materials Science
- Solid-State Chemistry
Background:
- The coordination and local geometry of silicon (Si) cations in silicate liquids are critical for magma properties.
- Understanding these structural changes under pressure is essential for geochemistry and materials science.
Purpose of the Study:
- To investigate pressure-induced changes in Si coordination in silicate glasses.
- To characterize the local atomic structure of Si in amorphous phases under high pressure.
Main Methods:
- Utilized (29)Si magic-angle spinning nuclear magnetic resonance (MAS NMR) spectrometry.
- Analyzed sodium disilicate (Na(2)Si(2)O(5)) glass samples quenched from high pressure (8 GPa) and temperature (1500 °C).
Main Results:
- Detected the presence of approximately 1.5% octahedral Si in glasses quenched from 8 GPa and 1500 °C.
- Confirmed that octahedral Si is part of a homogeneous, amorphous phase.
- Observed disproportionation of dominant tetrahedral Si speciation towards a more random distribution of bridging and nonbridging oxygens with increasing pressure.
Conclusions:
- High pressure induces a transition in Si coordination in silicate glasses.
- The observed structural changes influence the distribution of oxygen species around Si cations.
- These findings provide insights into the behavior of silicate liquids under extreme conditions.
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