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Crystallographic and crystal-chemical study of long period polytypes of micas
No full textDans cette thèse on a étudié par diffraction des rayons X des polytypes à longue période de micas, qui sont des cristaux naturels formés en condition hors équilibre dans un système magmatique. Leur séquence d'empilement peut être considérée comme une combinaison plus ou moins complexe de trois polytypes à courte période 1M, 2M1 et 3T, appelés « structures de base ». L'objectif est d'obtenir les premiers affinements structuraux des ces polytypes avec attention particulière à la distribution des cations dans chaque feuillet, car, d'après la littérature, il existe vraisemblablement une relation entre cette distribution et le mécanisme de formation de ces polytypes. Plus de 120 cristaux ont été analysés, parmi lesquels deux polytypes, dont la période est formée respectivement par 4 et 5 feuillets (indiqués comme 4M3 et 5M3 respectivement en notation de Ramsdell), ont été sélectionnés. Grâce aux résultats de l'affinement, deux interprétations de formation sont possible pour le polytype 4M3, qui prennent en considération le fait que la séquence d'empilement peut-être formée par l'inter-croissance de deux sous-structures : une 3T avec une 1M ou deux sous-structures 2M1 ; dans le dernier cas il s'agit d'un exemple de « cell-twin ». Les résultats de l'affinement structural du polytype 5M3 ont permis de prouver pour la première fois la coexistence des feuillets de type M1 et M2, qui diffèrent pour la distribution cationique dans la couche octaédrique, dans le même polytype. La formation de ces polytype peut-être due à la combinaison de deux sous-structures de base et plusieurs interprétations sont possibles : 3T+1M, 3T+2M1, 1M+2M1, ou deux 1M. Une étude géologique a été effectuée pour reconstruire l'histoire de la rhyodacite contenant les polytypes à longue période. Cette roche s'est formée suite à un mélange de magma, comme indiqué par la présence de textures de déséquilibre de plusieurs minéraux, phénomène qui semble avoir un rôle important dans la formation des ces polytypes, en incrémentant l'activation et les interactions des spirales de croissance, mais aussi les interactions spirale-cristal et cristal-cristal.We have studied by X-ray diffraction long period polytypes of micas, that are natural crystals formed far from the equilibrium condition in a magmatic system. Their stacking sequence can be considered as a more or less complex combination of three short polytypes 1M, 2M1 and 3T, called "basic structures". The aim was to obtain the first structural refinements of these polytypes, with special attention to the cationic distribution in the octahedral sheet, because, according to the literature, there seems to be a relation between this distribution and the formation of these polytypes. More than 120 crystals have been analysed, and two polytypes have been chosen, whose period is formed respectively by 4 and 5 layers (indicated as 4M3 and 5M3 respectively in Ramsdell notation). The refinement results suggest two interpretations for the formation of the 4M3 polytype, both indicating that the stacking sequence can be formed by the inter-growth of two sub-structures: a 3T with a 1M or two 2M1 sub-structures; the last case is an example of "cell twin". The results of the structural refinement of the 5M3 polytype show for the first time the coexistence of M1 and M2 types of layer, which differ for the cation distribution in the octahedral sheet, in the same polytype. The formation of this polytype can be due to the combination of two basic sub-structures and several interpretations are possible: 3T+1M, 3T+2M1, 1M+2M1, or two1M. A geological study has been done to reconstruct the history of the rhyodacite containing the long period polytypes. This rock is formed after a magma mixing, as showed by the presence of the disequilibrium textures of several minerals; this phenomenon seems to play a fundamental role for the formation of these polytypes, increasing the spiral?s activation and interactions, but also the spiral-crystal and crystal-crystal interactions
Experimental study of chemical evolution and isotope fractionation of Cl and Br in pore water expelled during strong clay compaction
Full text linkInternational audienceIn sedimentary basins, clay compaction by burial can lead to fluid overpressure and is suspected to also generate fresh waters, but few geochemical tracers are available to assess this process both qualitatively and quantitatively. Our objective was to carry out experiments on the chemical - and halogen (Cl, Br) isotope evolutions of pore water expelled during clay compaction. For this, the smectite-rich bentonite MX80 and an illite-rich marl (Sainte-Suzanne) were equilibrated with ocean water. During two compaction experiments under high fluid pressure (45 MPa), mechanical stress (up to 150 MPa) and temperature (up to 150 °C), it was found that the chemistry and isotope behavior is considerably different between the swelling clay and the non-swelling clay.We saw a general decrease of the cat- and anion concentrations in the expelled water, for swelling clay while its concentration slightly increases in the remaining pore fluid. This was not the case for non-swelling clay. More freshening of the expelled water occurred during the compaction at higher temperature.We also observed a larger range of isotopic variation for Br (δ81Br from 0.9‰ up to 1.5‰) than for Cl (δ37Cl from −0.5‰ to −0.1‰) in the compaction experiments. During the compaction of illite-rich marl, no significant variation of Cl isotope (δ37Cl close to 0‰) was observed while the δ81Br value of the expelled water showed the same general increase (from 0.9‰ up to 1.5‰) as during the compaction of smectite-rich bentonite.We observed limited mineralogical transformations in terms of dissolution/precipitation processes. Therefore the surface chemistry of the clay in combination with decreasing porosity, in part, drive the anion and isotope evolution. We propose that significant retention of Cl and Br in the pore water of the compacted smectite-rich bentonite is indicative of ultrafiltration and that Cl and Br isotopes are promising tracers to consider when tracking the origin of low-salinity formation waters in sedimentary basins
Cement encapsulation processes to mitigate the risks posed by different types of antimony-bearing mine waste
Full text link15 páginas, 3 tablas, 6 figurasIn this study cement encapsulation processes of different types of mine waste generated from the exploitation of Sb ore deposits were evaluated as a way to manage them and avoid further environmental pollution and the negative impact on surrounding ecosystems. For this purpose, Sb-bearing mine waste rocks, mine tailings, and smelting waste were subjected to cementation processes using Portland cement/calcium hydroxide as binder and different binder:mine waste ratios (10:90–80:20 wt%). The encapsulated materials were characterized for their mechanical behavior (compressive strength test), leaching properties (batch shaking and tank leaching tests), and mineralogical and chemical composition by X-ray powder diffraction, scanning electron microscopy, and electron microprobe analysis. A binder:mine waste ratio of 40:60 wt% was found appropriate to decrease the leachable Sb concentrations at levels below the limit for acceptance at non-hazardous waste landfills. Diffusion was the main mechanism controlling Sb leaching. The obtained effective diffusion coefficients and developed compressive strengths indicate that the encapsulated materials were suitable for disposal. Therefore, according to their leaching and strength characteristics, the encapsulated mine wastes derived using the indicated conditions could be deposited at landfills for non-hazardous waste, thus minimizing the environmental hazards caused by their accumulation in the mine surrounding areas. Additionally, according to the Dutch legislation on the use of waste materials in the built sector, some formulations of encapsulated mine tailings already met the Sb leaching requirement for open (un-insulated) construction applications. Therefore, Sb-bearing mine wastes, especially mine tailings, also present a great potential to be recycled as substitutes for natural aggregates in concrete in construction applications. Antimony was mostly preserved in the original Sb-bearing phases [Fe and Sb (oxyhydr)oxides and tripuhyite] after the encapsulation processes. Of compounds resulting from the hydration of Portland cement, C-(A)-S-H phases predominated, having an important role in attenuating the Sb release from the different types of mine waste; average Sb2O5 contents of 0.12–0.31 wt% were found in C-(A)-S-H phases.The present study was carried out under the project TERMET (Grant number: RTI 2018-095433-B-I00) funded by Ministerio de Ciencia e Innovacion ´ (MCIN), Spain/Agencia Estatal de Investigacion (AEI), Spain and by Fondo Europeo de Desarrollo Regional (FEDER) "A way of making Europe", European Union, and the project “CLU-2019-05–IRNASA/CSIC Unit of Excellence”, funded by the Junta de Castilla y Leon ´ (Spain) and cofinanced by the European Union (European Regional Development Fund (ERDF) “Europe drives our growth”).Peer reviewe
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Oxidation of mudstone in a tunnel (Tournemire, France): consequences for the mineralogy and crystal chemistry of clay minerals
No full textInternational audienceThe excavation of a tunnel through a mudstone formation provides an opportunity to examine the effects of the modification of the physical and chemical environment on the rock. The mineralogical and chemical consequences of hydration-dehydration cycles and of oxidation have been evaluated in the case of the Toarcian mudstone formation at the Tournemire experimental site (France). Studies by X-ray diffraction and tansmission electron microscopy of both altered and preserved samples show that the introduction of air and condensed water causes the oxidation of pyrite and the subsequent generation of acid and sulphate-rich waters at the micron scale, in the local environment of pyrites. The fluid-clay particle interactions around the oxidized pyrites induce: (1) a statistical enrichment in Si of the IS clay minerals; (2) an increase in the Fe(III)/Fe total ratio in some of the IS particles; and (3) the dissolution of illite layers in mixed-layer IS. These evolutions are consistent with the results of numerical modelling which reproduced the interaction between the clay particles and the acid water
Characterization of smectite and illite by FTIR spectroscopy of interlayer NH4 + cations
No full textInternational audienceFTIR spectroscopy has been applied to NH + 4-exchanged dioctahedral clay minerals to determine the molecular environment of NH + 4 and to quantify N concentration. FTIR under vapour-pressure control, coupled with heating and freezing treatments has shown that NH + 4 ion symmetry varies with the nature of clay minerals. NH + 4 has a perfect tetrahedral symmetry in hydrated or dehydrated smectites and belongs to the T d symmetry group. The NH + 4-bending vibration is centred at 1450 and 1425 cm-1. The Si 4+-Al 3+ substitution in dioctahedral clay minerals induces the loss of symmetry elements of the NH + 4 tetrahedron which acquires a C 2v symmetry. As a consequence, the T d-C 2v transition can be used to characterize the smectite-illite transition. Quantification of NH + 4 content per half unit cell is provided by n NH 4 = k[NH 4 ]/[OH] where [NH 4 ]/[OH] is the band area ratio of the NH + 4-bending vibration to the OH-stretching vibration. k = 1.1 for hydrated smectite, 0.9 for dehydrated smectite and 0.8 for illite or tobelite. The bending vibration of NH + 4 is chosen for the calculation because it is not affected by superimposed contributions
Hydrothermal reactivity of K-smectite at 300°C and 100 bar: dissolution-crystallization process and non-expandable dehydrated smectite formation
No full textInternational audienceThe hydrothermal reactivity of a smectite saturated with K was studied experimentally at 300~ and 100 bar in (Na,K) chloride solutions (Na/K = 0, 50 and 100, liquid/ solid ratio = 10/1). X-ray diffraction, TEM and microprobe results show: (1) a partial to total dissolution of the initial smectite layers; and (2) tbe crystallization of newly-formed euhedral t-S. Random IS is formed after 7 days, but an ordered mixed-layer IS containing <30% expandable layers formed in the longest runs (112 days). The IS is characterized by non-expandable layers of two distinct types: dehydrated smectite and illite. The Si content is lower in the IS than in the initial smectite, thus creating a charge deficit, mostly compensated by the introduction of Na to the interlayer space, and yielding a silica release to the solution and subsequent crystallization of quartz and cristobalite
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