19 research outputs found
Comprehensive Thermodynamic Study of the Calcium SulfateâWater Vapor System. Part 1: Experimental Measurements and Phase Equilibria
International audienceThe calcium sulfateâwater vapor system is of great scientific and technological importance due to its applications in several fields such as the construction materials industry, geology, and planetary sciences. While much effort has been concentrated during the past decades on characterizing the crystallographic structure of the different calcium sulfate polymorphs, some questions concerning their thermodynamic aspects as phase equilibria and their capability to increase their overall water content continuously beyond structural water content seem to have been left aside. Nevertheless, the comprehension of these aspects is of the utmost importance if we want to understand this chemical system fully. The present two-part work investigates these phenomena experimentally and by a thermodynamic modeling approach. In this first part, we develop a rigorous experimental protocol by thermogravimetric analysis under controlled temperature and water vapor partial pressure. We use this protocol to obtain thermodynamic equilibrium values for the overall water content of calcium sulfate hydrates. To ensure that the equilibrium was reached, we verified that these values could be obtained by distinct thermodynamic paths. With the equilibrium data, we were able to propose an updated equilibrium curve between soluble anhydrite AIII-CaSO4 and CaSO4·0.5H2O and estimate the thermodynamic parameters ÎrH° = (35.5 ± 1.0) kJ·molâ1 and ÎrS° = (80.0 ± 2.8) J·molâ1·Kâ1. After that, we were able to quantify the extent of water adsorption as a function of (T, PH2O), and we observed that it could represent a significant part of the overall water content of calcium sulfates
Comprehensive Thermodynamic Study of the Calcium SulfateâWater Vapor System. Part 2: Physical Modeling of Adsorption Phenomena
International audienceWe employ a rigorous thermodynamic modeling approach to investigate the water adsorption phenomena on two calcium sulfate compounds, AIII-CaSO4 and CaSO4·0.5H2O. In part 1 of this work ( Ind. Eng. Chem. Res., 2019, DOI: 10.1021/acs.iecr.9b00856), we prepared these two products by the dehydration of synthetic CaSO4·2H2O and obtained quantitative adsorption data as a function of the temperature and water vapor partial pressure. In this part, we develop macroscopic solution models (ideal and nonideal) to model monolayer adsorption on AIII-CaSO4. This allowed the calculation of the energies of adsorption for this phenomenon, evidencing a physisorption mechanism. For the CaSO4·0.5H2O, we interpreted the water adsorption using a multilayer adsorption model (BET model). For both materials, we showed that nitrogen adsorption data was not sufficient to represent their entire surface areas and porosity profiles compared to their water vapor sorption capacity
Photolithographic processing of silver loaded dielectric coatings based on preformed colloidal TiO2nanoparticles dispersed in a mesoporous silica binder
Titanium dioxide is a well known photocatalyst for reactions involving surface trapped photogenerated carriers. Noble metal photo-reduction may be used for the processing of silver/TiO 2 nanocomposite coatings that may exhibit interesting optical and electrical properties. We present here results of our investigations performed on an original system consisting of preformed colloidal TiO 2 nanoparticles homogeneously dispersed within a mesoporous silica host matrix. Light irradiation of samples immerged in an aqueous silver salt solution leads to the homogeneous deposition of silver islands in the vicinity of the TiO 2 particles and throughout the film thickness. The silver volume fraction is directly controlled by the irradiation dose up to a value of about 16Ă vol.%. Films exhibit tunable plasmonic properties that correspond to silver nanoparticles in interaction, and a percolation threshold is observed at 8ĂąâŹâ10Ă vol.%, leading to films with a conductivity of about 40Ă SĂ cm ĂąËâ1 . The major interest of this method lies in the high silver reduction quantum efficiency (about 50%) and the possibility to modulate optical and electronic properties by light irradiation while the low temperature of processing permits the photolithographic deposition of metallic patterns on organic flexible substrates
Modifications microstructurales en température de la phase hydrocalumite et des dérivés hydrocalumite-polymÚres
CLERMONT FD-BCIU Sci.et Tech. (630142101) / SudocTOULOUSE-ENSIACET (315552325) / SudocSudocFranceF
SynthĂšse et carbonatation dâun oxyde de magnĂ©sium mĂ©soporeux
National audienceGreenhouse gas emissions, in particular carbon dioxide, are considered as the main causes of the global warming. So, capture and storage of C02 coming from industrial installation are major environmental objectives. One way of C02 separation and capture is to use carbonation/decarbonation cycles on various capture masses. Among numerous candidates, magnesium oxide presents the advantage to form a thermodynamically stable carbonate, to be regenerable by simple heating, and to be available in large quantifies and at low-cost. If magnesium oxide has been largely studied for applications in catalysis, its use as C02 capture mass remains misunderstood. Thus the reaction of MgO carbonation made the object of few studies, and the main ones deal with utilization at high temperatures (300-350°C) and high C02 pressures (10-20 bar). In this work, we are interested in both the synthesis of magnesium oxide with high specific surface area, and its carbonation properties at atmospheric pressure. The way of synthesis of a mesoporous magnesium oxide is described, as well as the physicoÂŹchemical characterizations of such an oxide. The reaction of carbonation is followed by means of thermogravimetric experiments. The influences of temperature, C02 partial pressure and water vapor partial pressure are investigated. These results are completed by the characterizations of texture and morphological properties of the solid and their change during the reaction.Les Ă©missions de gaz Ă effet de serre, et notamment de dioxyde de carbone, sont considĂ©rĂ©es comme les principales causes du rĂ©chauffement climatique. Ainsi, le captage et le stockage du CO2 issu des rejets industriels sont des objectifs environnementaux capitaux. Une voie de sĂ©paration et de captage du CO2 est lâutilisation de cycles de carbonatation/dĂ©carbonatation par diverses masses de captage. Parmi les nombreux oxydes candidats, lâoxyde de magnĂ©sium prĂ©sente lâavantage de former un carbonate stable thermodynamiquement, dâĂȘtre rĂ©gĂ©nĂ©rable par simple chauffage, et dâĂȘtre disponible en grande quantitĂ© et Ă faible coĂ»t. Si lâoxyde de magnĂ©sium a Ă©tĂ© trĂšs Ă©tudiĂ© pour des applications en catalyse, son utilisation en tant que masse de captage de CO2 reste assez mĂ©connue. Ainsi, la rĂ©action de carbonatation de lâoxyde de magnĂ©sium a fait lâobjet dâun nombre peu important dâĂ©tudes, et les principales concernent des utilisations Ă haute tempĂ©rature (300-350°C) et forte pression de CO2 (10-20 bar). Dans ce travail, nous nous intĂ©ressons Ă la prĂ©paration dâun oxyde de magnĂ©sium Ă forte surface spĂ©cifique ainsi quâaux propriĂ©tĂ©s de carbonatation de ce solide Ă pression atmosphĂ©rique. La voie de synthĂšse dâun oxyde de magnĂ©sium mĂ©soporeux est dĂ©crite, ainsi que les caractĂ©risations physico-chimiques de cet oxyde. La rĂ©action de carbonatation est suivie par le biais dâexpĂ©riences de thermogravimĂ©trie. Les influences de la tempĂ©rature, de la pression partielle de CO2 et de la pression partielle de vapeur dâeau sont notamment investiguĂ©es. Ces rĂ©sultats sont complĂ©tĂ©s par le suivi de lâĂ©volution des caractĂ©ristiques texturales et morphologiques du solide au cours de la rĂ©action de carbonatation
Approfondissement des aspects thermodynamiques du systĂšme CaSO<sub>4</sub>-H<sub>2</sub>O
National audienceLe terme gypse est employĂ© pour dĂ©signer les minĂ©raux principalement constituĂ©s de sulfate de calcium dihydratĂ©, CaSO4·2H2O. Ce matĂ©riau a une grande importance industrielle puisque sa calcination (ou dĂ©shydratation partielle) est le principal procĂ©dĂ© de fabrication du plĂątre, qui est le produit inorganique avec la plus grande production industrielle au monde. Ce produit est majoritairement constituĂ© de sulfate de calcium hĂ©mi-hydratĂ©, CaSO4·0,5H2O. MalgrĂ© cette importance et le fait que ces matĂ©riaux soient utilisĂ©s depuis lâantiquitĂ©, le systĂšme minĂ©ral CaSO4-2H2O reste mal connu. Surtout concernant les teneurs en eau des produits de calcination du gypse. Cette absence dâune comprĂ©hension complĂšte des transformations de ce systĂšme est due Ă plusieurs phĂ©nomĂšnes qui contribuent Ă sa complexitĂ©. Dâabord, celui-ci possĂšde plusieurs polymorphes : lors de la dĂ©shydratation du sulfate de calcium dihydratĂ©, diffĂ©rents hydrates du type CaSO4·εH2O peuvent ĂȘtre obtenus, oĂč ε peut valoir 0,625, 0,5, ou 0 selon les conditions de tempĂ©rature T et pression partielle de vapeur dâeau P. De plus, ces composĂ©s peuvent aussi prĂ©senter des zones de divariance, i.e., des domaines oĂč la teneur globale en eau ε peut changer continument selon T et P. La connaissance fine des domaines de stabilitĂ© de chaque espĂšce et des mĂ©canismes rĂ©actionnels mis en jeu au cours des transformations thermiques successives du sulfate de calcium dihydratĂ© reste Ă ce jour sujet Ă discussion. Les mĂ©canismes de dĂ©shydratation et hydratation en voie solide-gaz ne sont que partiellement dĂ©crits dans la littĂ©rature scientifique. Dans ce contexte, lâun des objectifs de ce travail est donc la connaissance des phases et des transformations impliquĂ©es, lors de la dĂ©shydratation de poudres de sulfate de calcium dihydratĂ©. De plus, la nature de la divariance pour ce systĂšme est Ă©galement investiguĂ©e. Des expĂ©riences de thermogravimĂ©trie en conditions isothermes et isobares, selon diffĂ©rents protocoles, ont Ă©tĂ© rĂ©alisĂ©es dans une gamme de tempĂ©rature allant de 30ÂșC Ă 250ÂșC pour des pressions partielles de vapeur dâeau comprises entre 5 et 60 hPa. Les rĂ©sultats obtenus permettent lâidentification de deux domaines de divariance et dâun domaine de monovariance. Les variations des teneurs en eau par rapport Ă la stĆchiomĂ©trie de chaque polymorphe sont interprĂ©tĂ©es Ă travers des modĂšles adaptĂ©s Ă chaque domaine de divariance. Des valeurs de variation dâenthalpie et dâentropie sont ainsi obtenues pour les diffĂ©rentes transformations. Enfin, un diagramme de phase « tempĂ©rature-pression de vapeur dâeau » est proposĂ© en se basant sur la stabilitĂ© des diffĂ©rentes phases obtenues dans les gammes de tempĂ©rature et pression de vapeur dâeau investiguĂ©es
Synthesis, characterization and low temperature carbonation of mesoporous magnesium oxide
International audienceA sample of MgO was successfully synthesized using thermal decomposition of hydromagnesite and compared to commercial material. The characterization of materials using XRD, SEM, BET and BJH methods showed that the thermal decomposition way led to rectangular mesoporous microsheets with high specific surface area of 100 m2 gâ1. This porous magnesium oxide has been shown to be a potential candidate for CO2 capture at low temperatures range (30 and 50 °C), low pressures of CO2 (PCO2=600mbar) and in the presence of water vapor (PH2O=15mbar). In these conditions, our results show that 11% of MgO was converted to hydrated magnesium carbonate MgCO3·3H2O after 8 h of carbonation in a thermobalance and reached 54% after 24 h of carbonation using tube furnace. After carbonation, hydration reaction pore size and surface area have noticeably changed
Approfondissement des aspects thermodynamiques et cinétiques des transformations solide-gaz du systéme CaSO<sub>4</sub>-H<sub>2</sub>O
Le prix Jean Besson a Ă©tĂ© dĂ©cernĂ© Ă JoĂŁo Preturlan.Le prix « Jean BESSON » vient rĂ©compenser lâexposĂ© jugĂ© scientifiquement et pĂ©dagogiquement le meilleur Ă lâissue de cette premiĂšre journĂ©e.National audienceLe terme gypse est employĂ© pour dĂ©signer les minĂ©raux principalement constituĂ©s de sulfate de calcium dihydratĂ©, CaSO4·2H2O. Ce matĂ©riau a une grande importance industrielle puisque sa calcination (ou dĂ©shydratation partielle) est le principal procĂ©dĂ© de fabrication du plĂątre, qui est le produit inorganique avec la plus grande production industrielle au monde. Ce produit est majoritairement constituĂ© de sulfate de calcium hĂ©mi-hydratĂ©, CaSO4·0,5H2O. MalgrĂ© cette importance et le fait que ces matĂ©riaux soient utilisĂ©s depuis lâantiquitĂ©, le systĂšme minĂ©ral CaSO4-H2O reste mal connu. Dâabord, celui-ci possĂšde plusieurs polymorphes : lors de la dĂ©shydratation du sulfate de calcium dihydratĂ©, diffĂ©rents hydrates du type CaSO4·εH2O peuvent ĂȘtre obtenus, oĂč ε peut valoir 0,625, 0,5, ou 0 selon les conditions de tempĂ©rature T et pression partielle de vapeur dâeau P. De plus, ces composĂ©s peuvent aussi prĂ©senter des domaines de divariance, i.e., la teneur globale en eau Δ peut changer continument selon T et P. La connaissance fine des domaines de stabilitĂ© de chaque espĂšce et des mĂ©canismes rĂ©actionnels mis en jeu au cours des transformations thermiques successives du sulfate de calcium dihydratĂ© reste Ă ce jour sujet Ă discussion. Les mĂ©canismes de dĂ©shydratation et hydratation en voie solide-gaz ne sont que partiellement dĂ©crits dans la littĂ©rature scientifique. Dans ce contexte, lâun des objectifs de ce travail est donc la connaissance des phases et des transformations impliquĂ©es, lors de la dĂ©shydratation de poudres de sulfate de calcium dihydratĂ©, et la dĂ©termination des Ă©tapes Ă©lĂ©mentaires mises en jeu ainsi que les lois cinĂ©tiques associĂ©es. Des expĂ©riences en thermobalance en conditions isothermes et isobares ont Ă©tĂ© rĂ©alisĂ©es dans une gamme de tempĂ©rature allant de 30 Ă 250°C pour des pressions partielles de vapeur dâeau comprises entre 5 et 60 hPa. Des caractĂ©risations physico-chimiques des solides obtenus ont aussi Ă©tĂ© rĂ©alisĂ©es. Les rĂ©sultats permettent de dĂ©terminer prĂ©cisĂ©ment les zones de divariance et de monovariance. Un modĂšle cinĂ©tique de germination-croissance a pu ĂȘtre proposĂ© et appliquĂ© aux donnĂ©es expĂ©rimentales
Kinetic and mechanistic aspects of the dehydration of CaSO<sub>4</sub>·2H<sub>2</sub>O
Marc Aurousseau, président du Codegepra, a remis le prix du meilleur poster à Joao Dal-Bo-Preturlan, doctorant centre SPIN (encadré par Laetitia Vieille et Loïc Favergeon).National audienceGypsum is the mineralogical term used to describe materials that are mainly constituted of calcium sulfate dihydrate (CaSO<sub>4</sub>·2H<sub>2</sub>O). These materials can be obtained either from natural or synthetic sources and are of paramount importance for modern construction material industry because they represent the main raw materials to produce plaster. This product is widely employed to manufacture gypsum wallboards and serves as an additive for other construction materials (<i>e.g.</i> cements). The production process of plaster consists in partially dehydrate gypsum in calcination furnaces, large-scale heterogeneous industrial reactors, to obtain calcium sulfate hemihydrate (CaSO<sub>4</sub>·0.5H<sub>2</sub>O), which is the main constituent of plaster. (<i>Kuntze</i>, 2015) In order to better understand the functioning of these industrial reactors and to be able to propose improvements in this matter, it is mandatory to better understand the thermodynamics of the CaSO<sub>4</sub>-H<sub>2</sub>O system and the reaction mechanism for each chemical transformation taking place during the calcination process. In this context, one of the objectives of the present work is to increase the current understanding about the reactivity of calcium sulfate dihydrate, clarify remaining questions on reaction kinetics, and propose a kinetic-geometric model of the transformation of this material. In order to perform this, the dehydration of a highly pure calcium sulfate dihydrate powder was monitored using thermogravimetric analysis under isotherm and isobaric conditions. This was performed in order to obtain kinetic and reaction rate curves. Temperature ranging from 86°C to 110°C and water vapor partial pressure ranging from of 10 hPa to 60 hPa were investigated. Morphological and textural characterizations of the solids were also employed to understand the way of transformation. Based on this knowledge, a kinetic nucleation-growth model was then proposed and applied to the experimental data in order to obtain kinetic parameters for nucleation and growth. A growth mechanism was written and the change of kinetic parameters with temperature and water vapor partial pressure was explained. (<i>Mampel</i>, 1940; <i>Helbert</i> et <i>al.</i>, 2004; <i>Pijolat</i> et <i>al</i>., 2011
Kinetics and mechanism of the dehydration of calcium sulfate dehydrate: a comprehensive approach for the dehydration of ionic hydrates under controlled temperature and water vapor pressure
International audienceWe studied the kinetics and mechanism of the dehydration reaction of calcium sulfate dihydrate to hemihydrate under controlled temperature and water vapor partial pressure. From kinetic and reaction rate curves obtained using thermogravimetric analysis (TGA) under isothermal and isobaric conditions, we determined the overall behavior of this dehydration reaction and the effects of the systemâs intensive variables on its kinetics. We observed that the reactions take place with an initial induction period that decreases with increasing temperature, followed by a sigmoidal mass loss controlled by both nucleation and growth processes. Characterization of our samples at different points of the reaction allowed us to observe and confirm a surface nucleation process followed by isotropic growth of the nuclei with inward development of the solid product. We then employed the Mampel kinetic model based on the observed experimental results considering the physical nature of the investigated transformation and the real geometry of the particles. From this model, we obtained sets of kinetic parameters for the nucleation and growth processes and their evolution with temperature. We then proposed physicochemical mechanisms for both processes, and they were considered to interpret the kinetic parameters obtained previously. The mechanistic analysis of the system allowed determination of the effects of both temperature and water vapor pressure on the kinetic behavior of the reaction, which corresponds to a novel approach for the dehydration reaction of calcium sulfate dihydrate. The universal kinetic approach used to treat this chemical system in this work can be applied for studying the dehydration of other ionic hydrates