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Transiciones estructurales en el hielo de agua amorfo e implicaciones astrofísicas
1NASA/Ames Research Center, Moffett Field, CA 94035, USA.
Science (New York, N.Y.)
|August 5, 1994
Resumen
El hielo de agua sufre cambios estructurales, transformándose a través de tres formas amorfas (Iah, Ial, Iar) durante el calentamiento. Estas transformaciones explican las propiedades inusuales observadas en los hielos astrofísicos.
Área de la Ciencia:
- Ciencia de los materiales Ciencia de los materiales.
- La astroquímica es astroquímica.
- Química Física es la química física.
Sus antecedentes:
- El hielo de agua amorfo es frecuente en entornos astrofísicos.
- Comprender sus transiciones estructurales es crucial para interpretar las observaciones de hielo interestelar.
Objetivo del estudio:
- Para investigar las transformaciones estructurales del hielo de agua depositado en vapor bajo el vacío durante el calentamiento.
- Identificar y caracterizar las diferentes fases amorfas del hielo de agua y sus temperaturas de transición.
Principales métodos:
- Se empleó la difracción de electrones de área seleccionada (SAED, por sus siglas en inglés) para controlar los cambios estructurales.
- El hielo de agua depositado en el vapor se calentó de 15 K a 188 K bajo vacío.
Principales resultados:
- Se identificaron tres formas distintas de hielo de agua amorfo: hielo amorfo de alta densidad (Iah), hielo amorfo de baja densidad (Ial) y una tercera forma (Iar).
- Las transiciones ocurrieron en rangos de temperatura específicos: Iah a Ial (3868 K), y la formación de Iar a 131 K.
- Y coexiste con hielo cúbico (Ic) de 148 K a por lo menos 188 K.
Conclusiones:
- Las transformaciones de hielo amorfo identificadas proporcionan explicaciones para las propiedades anómalas de los hielos astrofísicos.
- La transición de Iah a Ial está vinculada a la difusión radical y la recombinación en los hielos interestelares.
- La fase Iar explica la retención y liberación anómalas de gas en hielos ricos en agua a temperaturas elevadas.
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