Evolution of product phase assemblages during thermal decomposition of muscovite under strong disequilibrium conditions

http://www.minsocam.org/MSA/AmMin/TOC/Abstracts/2006_Abstracts/FM06_Abstracts/Devineau_p413_06.pdfWe investigated the thermal decomposition of muscovite in natural granite powders heated to 1175°C for durations from 5 min to 68 h, at 1 bar, paying special attention to the early stages of decomposition. This study shows that muscovite is completely transformed after 5 min. Muscovite pseudomorphs consist of glass, mullite, and Al-rich oxides. For short durations (5 and 40 min), the Al-rich phase was identiÞ ed by XRD, electron diffraction, and TEM microanalysis as γ-Al2O3 containing 4.8 wt% FeO (total Fe), probably a few weight percents of MgO, and possibly up to 10 wt% SiO2. Faint superstructure spots and diffuse streaks observed in electron-diffraction patterns suggest vacancy or trace elements ordering in the γ-Al2O3 defect spinel structure. γ-Al2O3 displays an unexpected acicular morphology, elongated along three directions at 120° in the basal (001)musc planes and parallel to lateral faces of the former muscovite. Mullite forms rods elongated in the basal (001)musc planes along a direction at 90° from one set of γ-Al2O3 needles. The γ-Al2O3 structure appears to be a metastable phase that is replaced by corundum for longer durations

Déstabilisation haute température de poudres granitiques : évolution des propriétés minéralogiques et physiques

Non disponible - Not availableL'objectif de ce travail est double : 1- Étudier les déstabilisations thermiques de poudres de granites altérés, 2- Valoriser leur utilisation dans la formulation de céramiques traditionnelles, les assemblages minéralogiques des granites altérés (argiles, quartz, feldspaths) étant les principales matières premières entrant dans la formulation de ces produits. A- Analyse statistique des relations entre propriétés élémentaires de granites altérés et propriétés d'usage des céramiques traditionnelles. Pour mener à bien cette étude, une trentaine de poudres de granites plus ou moins altérés sont compactées, séchées puis cuites à 1050 et 1175°C pendant 3h30, conditions se rapprochant de celles utilisées dans l'industrie céramique. De nombreux paramètres chimiques et physiques sont mesurés sur poudres et à chaque étape de l'élaboration du produit céramique. Les données obtenues sont traitées à l'aide de l'analyse statistique en composantes principales normées (ACP) afin de déterminer les paramètres clés qui interviennent dans les différentes étapes d'élaboration du produit céramique et qui contrôlent ses propriétés d'emploi. Cette étude statistique a démontré que : 1- la teneur en fer, la quantité de feldspaths et de micas sont les trois paramètres qui influencent la couleur et/ou les propriétés mécaniques des tessons ; 2- les conditions de mise en oeuvre des éprouvettes avant cuisson influencent la porosité avant et après cuisson ; 3- les argiles favorisent la cohésion des éprouvettes avant cuisson. De cette étude, il ressort qu'il serait possible de formuler des céramiques à partir de granites altérés. B- Déstabilisation thermique des minéraux granitiques. Applications au système quartzfeldspaths et à la muscovite La deuxième partie détailie les transformations texturales des poudres granitiques en liaison avec les déstabilisations minéralogiques induites par le traitement thermique. Des éprouvettes de poudre compactée sont chauffées à 1175°C pendant 5, 10, 40 minutes et 3, 24, 68 heures à pression atmosphérique puis trempées dans l'air. Les cinétiques de transformations sont analysées par des méthodes microscopiques, la microsonde électronique, la diffraction des rayons X, l'analyse d'images et la spectroscopie infra-rouge. A l'exception du quartz, les minéraux sont déstabilisés en moins de 3 heures. La fusion du matériel feldspathique entraîne une forte réduction de la porosité aussi bien à l'intérieur qu'entre les agrégats de particules. Une porosité occluse subsiste cependant au sein de la phase liquide continue : elle se présente sous la forme de pores sphériques et elle est engendrée par le piégeage de vapeur d'eau. La disparition de la muscovite est effective dès 5 minutes de chauffage et les produits néoformés sont des baguettes silice-alumineuses de type spinelle puis mullite associées à une phase liquide qui apparaît progressivement avec le mûrissement texturai des minéraux. L'orientation des baguettes est gouvernée par la cristallographie de la muscovite mère. Contrairement à la matrice quartzo-feldspathique, la déstabilisation de la muscovite provoque l'apparition d'une porosité occluse par la formation de pores piégeant une faible quantité d'eau issue de la déshydoxylation du phyllosilicate. L'augmentation de cette porosité avec la durée du chauffage est provoquée par l'arrondissement des pores dont la morphologie est initialement contrôlée par la cristallographie de la muscovite mère. Cette évolution texturale est rendue possible par le mûrissement texturai des baguettes néoformées qui induit une diminution de la rigidité du système et un relâchement des contraintes. Cependant, compte tenu de la faible teneur en muscovite dans les matériaux granitiques étudiés, la porosité issue de sa déstabilisation reste négligeable par rapport à la porosité totale des tessons

DESTABILISATION HAUTE TEMPERATURE DE POUDRES GRANITIQUES : EVOLUTION DES PROPRIETES MINERALOGIQUES ET PHYSIQUES

This work has two main objectives : 1- studying melting reactions of powders of weathered granites during heat-treatment, 2- developing their use in traditional ceramic industries as the minerals contained in these granites (quartz, feldspars, clays) correspond to the main raw materials used in the manufacture of ceramic products. A- Statistical relationships between the basic properties of weathered granites and the properties of traditional ceramics Thirty powders obtained from more or less altered granites were compacted, dried, and fired at 1050°C and 1175°C during 3h30 ; these conditions are similar to those used in the ceramics industry. Chemical and physical measurements were conducted on the raw materials and on various processed powders after compaction, drying and heating. Data were treated using Principal Component Analysis (P.C.A.) to determine the main parameters that control the properties of end-products. This statistical study proved that : 1- iron, feldspar and mica contents influences the colour and/or mechanical properties of potsherds ; 2- experimental conditions used in the elaboration of green proofs influence porosity before and after firing ; 3- the presence of clay minerals promotes the cohesion of green proofs. This study clearly confirms that weathered granites can be used as raw materials for producing traditional ceramics. B- Breakdown of granitic minerals during heat-treatment. Applications on quartz-feldspars system and on muscovite. This work details the textural transformations of granitic powders that depend on mineralogical transformations induced by heat-treatment. Pressed powders were heated at 1175°C during 5, 10, 40 minutes and 3, 24, 68 hours under atmospheric pressure, then quenched in air. Transformation kinetics are controlled by different microscopic methods (petrographical microscope, S.E.M., T.E.M.), electron microprobe, X-ray diffraction, image analysis and Infra-Red spectroscopy. Except quartz, granitic minerals are decomposed in the first 3 hours of heating. Feldspars melting leads to a strong decrease of porosity inside and between particle aggregates. Trapped pores remain spherical in the homogeneous silicate melt, due to the trapping of water vapour. Muscovite disappears after 5 minutes of heating. Reaction products in pseudomorphed muscovite are needle-shaped and are identified as Al-Si with a spinel structure that will be transformed later to mullite. The silicate melt resulting from muscovite breakdown develops upon textural ripening of minerals. The orientation of needles is controlled by the crystallography of the initial muscovite. In contrast with what was observed for quartzo-feldspathic matrix, muscovite breakdown leads to the appearance of pores that enclose small water vapour amounts resulting from phyllosilicate dehydroxylation. This porosity increases with heating time. Initially, pore shape is controlled by the crystallography of the initial muscovite whereas for long run durations, the pores become spherical. Changes in pore shape and pore volume can be assigned to a decrease of the rigidity of breakdown products allowed by textural ripening of needles. However, as the granitic materials studied have a low muscovite content, porosity induced by muscovite breakdown remains marginal with regard to the total porosity of potsherds.L'objectif de ce travail est double : 1- Etudier les déstabilisations thermiques de poudres de granites altérés, 2- Valoriser leur utilisation dans la formulation de céramiques traditionnelles, les assemblages minéralogiques des granites altérés (argiles, quartz, feldspaths) étant les principales matières premières entrant dans la formulation de ces produits. A- Analyse statistique des relations entre propriétés élémentaires de granites altérés et propriétés d'usage des céramiques traditionnelles Pour mener à bien cette étude, une trentaine de poudres de granites plus ou moins altérés sont compactées, séchées puis cuites à 1050 et 1175°C pendant 3h30, conditions se rapprochant de celles utilisées dans l'industrie céramique. De nombreux paramètres chimiques et physiques sont mesurés sur poudres et à chaque étape de l'élaboration du produit céramique. Les données obtenues sont traitées à l'aide de l'analyse statistique en composantes principales normées (ACP) afin de déterminer les paramètres clés qui interviennent dans les différentes étapes d'élaboration du produit céramique et qui contrôlent ses propriétés d'emploi. Cette étude statistique a démontré que : 1- la teneur en fer, la quantité de feldspaths et de micas sont les trois paramètres qui influencent la couleur et/ou les propriétés mécaniques des tessons ; 2- les conditions de mise en œuvre des éprouvettes avant cuisson influencent la porosité avant et après cuisson ; 3- les argiles favorisent la cohésion des éprouvettes avant cuisson. De cette étude, il ressort qu'il serait possible de formuler des céramiques à partir de granites altérés. B- Déstabilisation thermique des minéraux granitiques. Applications au système quartz-feldspaths et à la muscovite La deuxième partie détaille les transformations texturales des poudres granitiques en liaison avec les déstabilisations minéralogiques induites par le traitement thermique. Des éprouvettes de poudre compactée sont chauffées à 1175°C pendant 5, 10, 40 minutes et 3, 24, 68 heures à pression atmosphérique puis trempées dans l'air. Les cinétiques de transformations sont analysées par des méthodes microscopiques, la microsonde électronique, la diffraction des rayons X, l'analyse d'images et la spectroscopie infra-rouge. A l'exception du quartz, les minéraux sont déstabilisés en moins de 3 heures. La fusion du matériel feldspathique entraîne une forte réduction de la porosité aussi bien à l'intérieur qu'entre les agrégats de particules. Une porosité occluse subsiste cependant au sein de la phase liquide continue : elle se présente sous la forme de pores sphériques et elle est engendrée par le piégeage de vapeur d'eau. La disparition de la muscovite est effective dès 5 minutes de chauffage et les produits néoformés sont des baguettes silico-alumineuses de type spinelle puis mullite associées à une phase liquide qui apparaît progressivement avec le mûrissement textural des minéraux. L'orientation des baguettes est gouvernée par la cristallographie de la muscovite mère. Contrairement à la matrice quartzo-feldspathique, la déstabilisation de la muscovite provoque l'apparition d'une porosité occluse par la formation de pores piégeant une faible quantité d'eau issue de la déshydoxylation du phyllosilicate. L'augmentation de cette porosité avec la durée du chauffage est provoquée par l'arrondissement des pores dont la morphologie est initialement contrôlée par la cristallographie de la muscovite mère. Cette évolution texturale est rendue possible par le mûrissement textural des baguettes néoformées qui induit une diminution de la rigidité du système et un relâchement des contraintes. Cependant, compte tenu de la faible teneur en muscovite dans les matériaux granitiques étudiés, la porosité issue de sa déstabilisation reste négligeable par rapport à la porosité totale des tessons

Déstabilisation haute température de poudres granitiques (évolution des propriétés minéralogiques et physiques)

ORLEANS-ISTO (452342307) / SudocNANCY/VANDOEUVRE-INPL (545472102) / SudocSTRASBOURG-Géologie (674822251) / SudocSudocFranceF

Melting kinetics of granitic powder aggregates at 1175°C, 1 atm.

Melting experiments of pressed granitic powders (10% < 3.23 m, 50% < 31.63 m, 90% < 169.85 m) have been performed at 1175°C, 1 atm for different run durations (5, 10, 40 mn and 3, 24, 68 h). During partial melting, quartz and feldspars progressively decrease in abundance, the amount of melt produced increases sharply after 40 mn and leads to a strong decrease of the porosity of the powder (from 42% before heat-treatment to 10% after 68 h). In the 5 mn charge, thin glass films (1-2 m) appear cementing small particles grains and narrow glass channels are formed and trapped within both albite and K-feldspar. Newly-formed K-feldspars appear in the 10 and 40 mn charges. They are both texturally and compositionally distinctive from the original feldspars. All feldspars have totally disappeared after 3 h and quartz (up to 330 m) persists in the longest experiment (68 h). For durations longer than 40 mn, glass compositions are chemically zoned. They vary mainly between two end-members, one rich in normative feldspar components and poor in normative quartz and the other rich in normative quartz corresponding to areas close to the quartz interface. The melting reaction is governed by disequilibrium melting. Two melting regimes were identified: (1) a low melt fraction regime corresponding to heterogeneous nucleation of melt at the surface and within interiors of both albite and K-feldspar and (2) a high melt fraction regime kinetically controlled by diffusive mass transport within the melt layer. The lack of leucite implies that the melting relations of K-feldspar observed in this study are congruent. About 50 days are needed for the melting reaction to approach chemical equilibrium at 1175°C

Dynamic Crystallization of a Haplogranitic Melt - Application to Pegmatites

International audienceBoth equilibrium and dynamic crystallization experiments have been performed on a hydrous haplogranitic melt at 200 MPa to model nucleation and growth mechanisms and simulate pegmatite textures. The equilibrium results provide a reference frame (phase assemblages and compositions, liquidus and solidus temperatures and dependence with the melt H2O concentration) to parametrize the kinetic experiments. The seven H2O-saturated dynamic crystallization experiments followed a specific time-temperature path. After a pre-conditioning step at 800 °C, charges were cooled between 3.5 and 7 °C/min to 700, 660 and 600 °C corresponding to ΔT of 20, 60 and 120 °C. Dwell times ranged from 42 up to 1440h. Variable mineral assemblages and textures, and two types of polymineralic assemblages were obtained depending on ΔT and t. For ΔT = 120 °C, crystallization is sequential and includes graphic quartz-alkali feldspar intergrowths characteristic of pegmatite textures. The crystallization sequence reflects nucleation and growth of kinetically-favored metastable phases and solid solution compositions from the supercooled melt. Early alkali feldspars are more K-rich than expected at equilibrium and late albites more Na-rich. The K-rich graphic texture progressively evolves to a Na-rich intergrowth texture. Melts also follow a progressive though limited sodic evolution with time. At the interface of growing alkali feldspars, melts are enriched in SiO2 and depleted in Al2O3, Na2O and, to a lesser extent, K2O. H2O accumulates at the interface reaching concentration levels higher (by 1-2 wt%) than the saturation. Rejection of SiO2 and H2O at the interface controls the effective undercooling in the local melt and promotes rapid textural changes toward larger grain sizes at the front of graphic zones. Textural ripening takes place contemporaneously to sequential crystallization. Growth rates for quartz and alkali feldspar are tightly grouped, between 7.3 x 10-11 and 1.6 x 10-12 m s-1. Textures from the dynamic crystallization experiments closely resemble natural pegmatites but layered aplite units have not been reproduced. Our results confirm and strengthen the importance of liquidus undercooling to generate pegmatite textures

Incorporation of Zn in the destabilization products of muscovite at 1175 degrees C under disequilibrium conditions, and implications for heavy metal sequestration

International audienceThis work reports on the thermal decomposition of muscovite within a granite powder doped with 8.5 wt% ZnO and heated during 10 min to 68 h at 1175°C, and the implications for the sequestration of Zn, and other heavy metalts in such decomposition products. Samples were characterized using analytical scanning and transmission electron microscopy. After 10 min, muscovite is completely pseudomorphosed by Si-rich glass, spinel structure phases, and minor mullite. Spinel phases incorpo-rate Zn, but their compositions depend on their position within the muscovite pseudomorphs. Al-rich oxides crystallize at the core of the pseudomorphs while Zn-Al spinels are located at the rims. The most Al-rich spinels have compositions close to γ-Al2O3, a metastable transition alumina, with up to 5 wt% MgO, 2 wt% Fe2O3, 4 wt% ZnO, and 9 wt% SiO2. The most Zn-rich spinels show compositions intermediate between Al2O3 and gahnite (ZnAl2O4), with up to 31 wt% ZnO and significant contents of MgO (3 wt%), Fe2O3 (5 wt%), and SiO2 (10 wt%). After 68 h, stable spinels are gahnite close to the end-member composition with MgO and Fe2O3 contents below ca. 5 wt%, and SiO2 contents ca. 1 wt%. These results support the existence of a metastable solid solution between γ-Al2O3and gahnite. This experimental work shows that Zn can be incorporated in spinel structures after heating at 1175°C during short durations and Zn is preferentially incorporated in the muscovite pseudomorphs as opposed to the Qtz-Fds glass. Consequently, the thermal breakdown of phyllosilicates can be a viable process to immobilize heavy metals such as Zn

EFFECTS OF ETHYLENE GLYCOL SATURATION PROTOCOLS ON XRD PATTERNS: A CRITICAL REVIEW AND DISCUSSION

International audienceThe study of the transformation of smectite to illite, chlorite or vermiculite via interstratified clay minerals needs precise qualitative and quantitative determinations of the different layers in the mixed- layer clays and is generally based on X-ray diffraction (XRD) patterns after specific treatments of the clay samples. Saturation with K or Mg followed by ethylene glycol (EG) solvation are classical methods used to identify high-charge smectite and vermiculite. These procedures have been applied to two experimental clays, one composed of smectite layers and the second, a mixture of vermiculite and smectite layers. Different methods of glycolation (EG vapor or liquid EG) produce significant differences in the XRD patterns. Comparison with literature data indicates that K-saturated, high-charge smectite (~0.8 < total charge <1/unit-cell) and Mg-vermiculite (whatever its charge) do not expand in ethylene glycol vapor (d values ~14ÿ15 A Ê ). Expansion to 17 A Ê in liquid ethylene glycol occurs for Mg-vermiculite with a total charge of <~1.2/unit-cell and for K-saturated, high-charge smectite, when the tetrahedral charge is <~0.7/unit-cell. This study shows that: (1) procedures of glycolation need to be standardized; (2) the use of saturation protocols using both liquid ethylene glycol and ethylene glycol vapor yields useful additional information about the distribution of charges in clay minerals

In situ neutron diffraction analysis of the influence of geometric confinement on crystalline swelling of montmorillonite

The swelling properties of a bentonite MX-80 and a Na montmorillonite obtained from MX-80 purification were analyzed as a function of relative humidity in free and constrained conditions. Gravimetric and XRD techniques were used to study the hydration of powder and compacted pellets in non confined conditions whereas hydration under constrained conditions was investigated in situ by neutron diffraction using a cell specifically designed for the present study. MX-80 bentonite and purified montmorillonite were compacted to an apparent density of 1.7 and equilibrated at various relative humidities using P2O5 and solutions saturated with different salts allowing to work in a wide range of relative humidity between 0 and 0.98. At low relative humidity, the hydration of montmorillonite is similar in free and constrained conditions. For relative pressures higher than 50%, swelling in constrained pellets deviates from that observed for free pellets. Reorientation phenomena of clay layers were also observed for bentonite and montmorillonite starting at 65%RH. At 98% RH, two well-defined basal spacings were obtained in the case of confined bentonite. The major peak corresponds to three-layer hydrates (18.6 Å) and the second one to two-layer hydrates (16 Å). In contrast, only the latter peak is observed when hydration is realized in free geometrical conditions. In the case of Na mont ..

Experimental Constraints on the Crystallization of Silica Phases in Silicic Magmas

International audienceLow-pressure silica polymorphs, e.g. quartz (Qtz), tridymite (Trd), and cristobalite (Crs), are common in silicic magmas, but the conditions of their formation are still unclear. The stability fields of these polymorphs have been determined in the SiO2, SiO2–H2O, and haplogranite systems, but these simple systems are not directly applicable to silica polymorph crystallization in natural silicic magmas. The present study compiles an experimental database of new and previously-published data documenting the crystallization of silica phases in natural silicic magmas and simple synthetic systems. Silica polymorphs are identified using Raman spectroscopy and their pressure-temperature domains of occurrence and chemical compositions are determined at pressures between 0·1 and 200 MPa, temperatures between 685 to 1200° C, and under H2O-saturated and H2O-undersaturated conditions. Qtz is the stable silica polymorph at pressures higher than 25–30 MPa, temperatures between ∼700 and 950° C, and occurs for a narrow range of melt SiO2 contents (∼79–81 wt %). Constraints on Qtz stability derived from simple systems are mutually compatible with, and thus applicable to natural compositions. This is consistent with Qtz compositions being close to ‘pure’ SiO2, both in experiments and nature. In volcanic systems, Qtz crystallization may occur in magmatic reservoirs and deep volcanic conduits. Trd did not crystallize in the experiments conducted as part of this study despite several experiments having been performed in the Trd stability field. This is consistent with results from the literature which show that Trd crystallization is kinetically inhibited in particular relative to Crs. Natural Trd have compositions deviating substantially from ‘pure’ SiO2, so that stability limits determined in simple systems should not be applied directly to natural cases. Crs was encountered at pressures below 20–30 MPa (or H2O contents < ∼1·5 wt %), from sub-solidus (∼800° C) to near-liquidus (up to 1040° C), and coexisting with melts having a large range of SiO2 contents (70–81 wt %). The Crs stability field is much larger in natural magmas compared to pure SiO2 systems. Crs is a metastable phase stabilized by components (Al, Na, K; about 3 wt %) present in the silicic melt. In volcanic systems, Crs crystallization may thus be restricted to subsurface manifestations such as lava domes