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Estudio XAS a alta temperatura de Fe2SiO4 líquido: Coordinación reducida del hierro ferroso
Science (New York, N.Y.)
|October 8, 1993
Resumen
La espectroscopia de absorción de rayos X revela que la coordinación Fe2+) disminuye de seis en la fayalita cristalina a cuatro en el líquido Fe2SiO4. Este cambio estructural impacta las propiedades de fusión y la partición de elementos en la Tierra.
Área de la Ciencia:
- La geoquímica es la geoquímica.
- Ciencia de los materiales Ciencia de los materiales.
- Física de los minerales Física de los minerales
Sus antecedentes:
- Comprender la estructura de los fundidos de silicato es crucial para interpretar las observaciones geofísicas y los procesos geoquímicos dentro de la Tierra.
- El hierro (Fe) es un componente clave en muchos materiales geológicos, y su estado de coordinación influye significativamente en las propiedades del fundido.
- Los modelos anteriores de Fe ((2+) en líquidos de silicato carecían de información estructural detallada a las temperaturas y presiones relevantes.
Objetivo del estudio:
- Para determinar el entorno estructural local de Fe2+) en Fe2SiO4 (fayalita) fundida utilizando espectroscopia de absorción de rayos X.
- Para investigar el número de coordinación y los cambios en la longitud del enlace Fe2+) -O durante la fusión.
- Desarrollar un modelo estructural para el Fe ((2+) en fundiciones de composición olivina y sus implicaciones para los sistemas geológicos.
Principales métodos:
- Se realizó una espectroscopia de absorción de rayos X (XAS) sobre el líquido Fe(2) SiO(4) a 1575 K y 10−4 GPa.
- El análisis implicó la contabilización de una armonía en la estructura líquida.
- Comparación de datos espectroscópicos con la fayalita cristalina en su punto de fusión.
Principales resultados:
- La longitud del enlace Fe2+-O en el líquido Fe2SiO4 es de 1,98 ± 0,02 Å, significativamente más corta que en la fayalita cristalina (aprox. 2.22 Å). es decir.
- El número promedio de coordinación Fe2+) disminuye de seis en la fayalita cristalina a cuatro en el líquido.
- Este cambio de coordinación es análogo a los cambios inducidos por la fusión en algunas sales iónicas.
Conclusiones:
- Se desarrolló un modelo para el entorno estructural de rango medio de Fe ((2+) en fundidos de composición olivina basado en la disminución de coordinación observada.
- Los hallazgos explican las propiedades clave del líquido Fe(2) SiO(4), incluida la densidad, la viscosidad y la partición Fe-Ni.
- El modelo tiene implicaciones para la comprensión de la fusión de silicatos en la corteza y el manto de la Tierra.
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