Most natural (geologic/geophysic) and technical/industrial processes do involve dehydration/dehydroxylation/deprotonation processes, chemical transformations and phase-transitions which need to be properly characterized by using combinations of analytical techniques such as TG/DTA, HT-XRD and HT spectroscopies. Dehydroxylation/deprotonation in minerals are associated to oxidation processes of multi-valence elements, such as Fe or Mn, and may affect the physical properties of the rock where they occur. For instance, the increase in electrical conductivity in subduction zones has been related to transformations in OH-bearing phases such as amphiboles or micas (Wang et al., 2012). The thermal stability and HT behavior of amphiboles have been widely studied in the last few years, and crystal-chemical details controlling HT behavior have now been identified (Tribaudino et al., 2008; Zema et al., 2012). Important issues still need to be studied, including the way protons diffuse throughout the mineral matrix, and the role of multiple-valence elements in this process. In this work we describe the HT-FTIR analysis of a sample close to the boundary between potassic-ferro-richterite and potassic-arfvedsonite, synthesized by Redhammer & Roth (2002) and recently re-examined by SC-XRD. Both in situ and ex-situ (quenched) absorbance data were collected on doubly-polished single-crystal sections using a Linkam HT heating stage, able to work up to 1200°C. A significant absorbance increase in the OH-stretching region was observed in situ, which was explained by a strong increase with T in the absorption coefficient. In contrast, data collected after quenching show that the complete deprotonation occurs in a limited T range (~100°). Combination of FTIR and SC-XRD refinement (Oberti et al., in prep) shows that H loss is paralleled by Fe oxidation at the M(1) site. Attempts to constrain the kinetics of H loss under isothermal annealing at different T are underway.
Synthetic potassic-ferro-richterite: HT behavior and deprotonation process by single-crystal FTIR spectroscopy and structure refinement
2015
Abstract
Most natural (geologic/geophysic) and technical/industrial processes do involve dehydration/dehydroxylation/deprotonation processes, chemical transformations and phase-transitions which need to be properly characterized by using combinations of analytical techniques such as TG/DTA, HT-XRD and HT spectroscopies. Dehydroxylation/deprotonation in minerals are associated to oxidation processes of multi-valence elements, such as Fe or Mn, and may affect the physical properties of the rock where they occur. For instance, the increase in electrical conductivity in subduction zones has been related to transformations in OH-bearing phases such as amphiboles or micas (Wang et al., 2012). The thermal stability and HT behavior of amphiboles have been widely studied in the last few years, and crystal-chemical details controlling HT behavior have now been identified (Tribaudino et al., 2008; Zema et al., 2012). Important issues still need to be studied, including the way protons diffuse throughout the mineral matrix, and the role of multiple-valence elements in this process. In this work we describe the HT-FTIR analysis of a sample close to the boundary between potassic-ferro-richterite and potassic-arfvedsonite, synthesized by Redhammer & Roth (2002) and recently re-examined by SC-XRD. Both in situ and ex-situ (quenched) absorbance data were collected on doubly-polished single-crystal sections using a Linkam HT heating stage, able to work up to 1200°C. A significant absorbance increase in the OH-stretching region was observed in situ, which was explained by a strong increase with T in the absorption coefficient. In contrast, data collected after quenching show that the complete deprotonation occurs in a limited T range (~100°). Combination of FTIR and SC-XRD refinement (Oberti et al., in prep) shows that H loss is paralleled by Fe oxidation at the M(1) site. Attempts to constrain the kinetics of H loss under isothermal annealing at different T are underway.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
