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Pool combustion experiments have been conducted for three alkali metals, namely, lithium (Li), sodium (Na) and potassium (K). Lithium and sodium are found to show a two-stage combustion behaviour which has been reported for a number of other metals. Here, the combustion is characterized by a sporadic rise in the flame temperature accompanied by a bright glow. Potassium is found to burn in vapour phase combustion in all cases without sporadic temperature excursions. In the present study, this different burning behaviour is attributed to the formation of thick oxide agglomerates in the case of Li and Na through the pores of which oxygen/metal vapour has to diffuse for combustion to occur. In such cases, a second stage of vapour phase combustion occurs when the oxide agglomerate is heated sufficiently so that the vapour of the liquid metal trapped in the pores breaks through to the surface. In the case of potassium, a self-cleaning mechanism, attributable to the high solubility of the metal oxides in liquid potassium and the relatively low melting point of the potassium oxides, enables a clear liquid surface to be exposed throughout for vapour phase combustion to prevail always. Recorded temperature profiles, SEM analysis of the oxide agglomerates as well as calculations of the metal-oxygen equilibrium thermo-chemistry for the three metals confirm this scenario. � 2011 The Combustion Institute.

El presente trabajo aborda el estudio de la composición mineralógica y petrológica de un afloramiento de andesitas alteradas en la región volcánica de Cabo de Gata (Los Escullos), mediante Difracción de rayos X, Microscopía Óptica (MO) y Electrónica (MEB) con Energía Dispersiva. El objetivo es determinar los procesos de alteración que fueron capaces de formar gran proporción de cristobalita, independientemente de los procesos de silicificación que generaron venas y diques silíceos en este afloramiento. La microscopía óptica revela que la alteración afectó solo a la matriz de la andesita, quedando los fenocristales (anfíbol, biotita, plagioclasa y opacos) preservados. La matriz está constituida mayoritariamente por cristobalita y pequeñas cantidades de zeolitas y esmectitas, que se formaron posteriormente a la cristobalita. Las maclas de cristales de cristobalita con hábitos cuadrangulares y tetragonales, identificados en MEB, sugieren que pudo haber una precipitación en fase de vapor. Se considera que la cristobalita se constituye por un proceso de desvitrificación, planteando la hipótesis de que también pudo existir cristalización de cristobalita en fase de vapor, durante la percolación de gases en el comienzo del enfriamiento del vidrio volcánico, This paper studies the mineralogical and petrological composition of an outcrop of altered andesite in the volcanic region of Cabo de Gata (Los Escullos), using X-ray diffraction, optical microscopy and scanning electron microscopy (SEM) with energy dispersive analyses. The aim is to determine the alteration processes that were able to develop a large amount of cristobalite in the andesites. This cristobalite grew independent of the silicification that generated siliceous veins and dikes in this outcrop. Optical microscopy reveals that the alteration affected only the andesite groundmass, leaving the phenocrysts (amphibole, biotite, plagioclase and opaques) preserved. The paste is mainly composed of cristobalite and small amounts of zeolites and smectites, which were formed in a later stage. The twinnings of cubic and tetragonal cristobalite crystals, identified in SEM, suggest that they might be formed as a vapour-phase. It is considered the cristobalite was formed by devitrification and perhaps by vapour-phase mineralization and that may be necessary a cristobalite precursor formation, in order to provide the nuclei. This process would occur during the percolation of gas at the start of cooling of the glass in the andesitic flow

[EN] This paper studies the mineralogical and petrological composition of an outcrop of altered andesite in the volcanic region of Cabo de Gata (Los Escullos), using X-ray diffraction, optical microscopy and scanning electron microscopy (SEM) with energy dispersive analyses. The aim is to determine the alteration processes that were able to develop a large amount of cristobalite in the andesites. This cristobalite grew independent of the silicification that generated siliceous veins and dikes in this outcrop. Optical microscopy reveals that the alteration affected only the andesite groundmass, leaving the phenocrysts (amphibole, biotite, plagioclase and opaques) preserved. The paste is mainly composed of cristobalite and small amounts of zeolites and smectites, which were formed in a later stage. The twinnings of cubic and tetragonal cristobalite crystals, identified in SEM, suggest that they might be formed as a vapour-phase. It is considered the cristobalite was formed by devitrification and perhaps by vapour-phase mineralization and that may be necessary a cristobalite precursor formation, in order to provide the nuclei. This process would occur during the percolation of gas at the start of cooling of the glass in the andesitic flow., [ES] El presente trabajo aborda el estudio de la composición mineralógica y petrológica de un afloramiento de andesitas alteradas en la región volcánica de Cabo de Gata (Los Escullos), mediante Difracción de rayos X, Microscopía Óptica (MO) y Electrónica (MEB) con Energía Dispersiva. El objetivo es determinar los procesos de alteración que fueron capaces de formar gran proporción de cristobalita, independientemente de los procesos de silicificación que generaron venas y diques silíceos en este afloramiento. La microscopía óptica revela que la alteración afectó solo a la matriz de la andesita, quedando los fenocristales (anfíbol, biotita, plagioclasa y opacos) preservados. La matriz está constituida mayoritariamente por cristobalita y pequeñas cantidades de zeolitas y esmectitas, que se formaron posteriormente a la cristobalita. Las maclas de cristales de cristobalita con hábitos cuadrangulares y tetragonales, identificados en MEB, sugieren que pudo haber una precipitación en fase de vapor. Se considera que la cristobalita se constituye por un proceso de desvitrificación, planteando la hipótesis de que también pudo existir cristalización de cristobalita en fase de vapor, durante la percolación de gases en el comienzo del enfriamiento del vidrio volcánico., Este trabajo ha sido financiado a través del proyecto MINECO CGL2011-27826-02.

El presente trabajo aborda el estudio de la composición mineralógica y petrológica de un afloramiento de andesitas alteradas en la región volcánica de Cabo de Gata (Los Escullos), mediante Difracción de rayos X, Microscopía Óptica (MO) y Electrónica (MEB) con Energía Dispersiva. El objetivo es determinar los procesos de alteración que fueron capaces de formar gran proporción de cristobalita, independientemente de los procesos de silicificación que generaron venas y diques silíceos en este afloramiento. La microscopía óptica revela que la alteración afectó solo a la matriz de la andesita, quedando los fenocristales (anfíbol, biotita, plagioclasa y opacos) preservados. La matriz está constituida mayoritariamente por cristobalita y pequeñas cantidades de zeolitas y esmectitas, que se formaron posteriormente a la cristobalita. Las maclas de cristales de cristobalita con hábitos cuadrangulares y tetragonales, identificados en MEB, sugieren que pudo haber una precipitación en fase de vapor. Se considera que la cristobalita se constituye por un proceso de desvitrificación, planteando la hipótesis de que también pudo existir cristalización de cristobalita en fase de vapor, durante la percolación de gases en el comienzo del enfriamiento del vidrio volcánico This paper studies the mineralogical and petrological composition of an outcrop of altered andesite in the volcanic region of Cabo de Gata (Los Escullos), using X-ray diffraction, optical microscopy and scanning electron microscopy (SEM) with energy dispersive analyses. The aim is to determine the alteration processes that were able to develop a large amount of cristobalite in the andesites. This cristobalite grew independent of the silicification that generated siliceous veins and dikes in this outcrop. Optical microscopy reveals that the alteration affected only the andesite groundmass, leaving the phenocrysts (amphibole, biotite, plagioclase and opaques) preserved. The paste is mainly composed of cristobalite and small amounts of zeolites and smectites, which were formed in a later stage. The twinnings of cubic and tetragonal cristobalite crystals, identified in SEM, suggest that they might be formed as a vapour-phase. It is considered the cristobalite was formed by devitrification and perhaps by vapour-phase mineralization and that may be necessary a cristobalite precursor formation, in order to provide the nuclei. This process would occur during the percolation of gas at the start of cooling of the glass in the andesitic flow

The ignimbrites of the northeast Niğde area, which are subdivided into the Lower, Middle and Upper ignimbrites on the basis of their compositional and stratigraphical characteristics, display textural variations from the base to the top. A large proportion of these ignimbrites have been altered and recrystallized by the processes of compaction, welding and devitrification, and as a result of volatile movement. The alteration and recrystallization processes include four stages: hydration, glassy and spherulitic stages accompanied by vapour-phase crystallisation. In the early phases of devitrification, detailed shard shapes are easily recognisable with the scanning electron microscope, but as alteration proceeds clarity of detail disappears because compaction results in collapse of the structure of the rock. Spherulitic and vapour-phase crystallisation usually involves the growth of alkali feldspar and cristobalite. These later stages are more common in the Upper Ignimbrite than the Middle and Lower ignimbrites.

The ASTEC/Sophaeros computer code has been developed to model transport of reactive gases and aerosols in pipe flows with extensive coverage of chemical and physical phenomena. As part of the ASTEC severe-accident code co-developed by IRSN in France and GRS (Gesellschaft für Anlagen- und Reaktorsicherheit) in Germany, it is principally used to evaluate so-called radioactive source terms released to the environment in the event of potential accidents affecting water-cooled nuclear reactors. A major uncertainty in the past concerned the impact of chemistry on radioactivity transfer where the treatment of chemical phenomena was recognized as inadequate. Work described here, involving mainly systematic identification of relevant species and thermodynamic- data verification, has vastly improved this situation leading in particular to creation of a comprehensive database with fully-referenced sources of information. Further prospective improvements in this area are described.

This research work investigates the biodegradation of 2-chlorophenol vapours in a trickling biofilter packed with a ceramic material, and seeded with a pure strain of Pseudomonas pickettii . The process was tested at laboratory scale over 260 days of operation under varying loading conditions. More than 98% degradation efficiencies were achieved for loading rates up to 82.5 g m −3 h −1 . Process analysis, performed using data on 2-chlorophenol concentration profiles along the biofilter bed, shows that best biofilter performance (i.e. maximum degradation capacity and efficiency) can be obtained for a narrow range of operating conditions, which can be ensured by proper sizing of biofilter diameter and height.