Beneficial Effect of Pt and of Pre-Oxidation on the Oxidation Behaviour of an NiCoCrAlYTa Bond-Coating for Thermal Barrier Coating Systems

The oxidation behaviour of a thermal barrier coating (TBC) system is a major concern as the growth of the thermally grown oxide (TGO) layer on the bondcoating creates stresses that greatly favour the thermal barrier spallation. To delay the loss of the thermal protection provided, research has focused on the bondcoating composition and microstructure as well as on the parameters required for a suitable pre-oxidation treatment before the deposition of the ceramic top coat. Platinum is known to enhance the oxidation/corrosion resistance of MCrAlY coatings. The effect of Pt on the oxidation behaviour of a NiCoCrAlYTa coating was assessed in this study. In addition, pre-oxidation treatments were conducted to determine if the oxidation behaviour of the modified NiCoCrAlYTa coating could be further improved

New Insights on Gas Hydroquinone Clathrates Using in Situ Raman Spectroscopy: Formation/Dissociation Mechanisms, Kinetics, and Capture Selectivity

Hydroquinone (HQ) is known to form organic clathrates with different gaseous species over a wide range of pressures and temperatures. However, the enclathration reaction involving HQ is not fully understood. This work offers new elements of understanding HQ clathrate formation and dissociation mechanisms. The kinetics and selectivity of the enclathration reaction were also investigated. The focus was placed on HQ clathrates formed with CO2 and CH4 as guest molecules for potential use in practical applications for the separation of a CO2/CH4 gas mixture. The structural transition from the native form (α-HQ) to the clathrate form (β-HQ), as well as the reverse process, were tracked using in situ Raman spectroscopy. The clathrate formation was conducted at 323 K and 3.0 MPa, and the dissociation was conducted at 343 K and 1.0 kPa. The experiments with CH4 confirmed that a small amount of gas can fill the α-HQ before the phase transition from α- to β-HQ begins. The dissociation of the CO2–HQ clathrates highlighted the presence of a clathrate structure with no guest molecules. We can therefore conclude that HQ clathrate formation and dissociation are two-step reactions that pass through two distinct reaction intermediates: guest-loaded α-HQ and guest-free β-HQ. When an equimolar CO2/CH4 gas mixture is put in contact with either the α-HQ or the guest-free β-HQ, the CO2 is preferentially captured. Moreover, the guest-free β-HQ can retain the CO2 quicker and more selectively

Media réactif comprenant un support poreux imprégné d’un composé organique capable de former des clathrates de gaz, et son utilisation pour la séparation et le stockage de CO2

L'invention concerne un média réactif comprenant un support poreux sur lequel est déposé, sous forme solide, un composé organique capable de former des clathrates de gaz. L'invention concerne également un procédé de séparation du CO2, présent dans un mélange de gaz, dans lequel une capture du CO2 est réalisée par enclathration au moyen dudit média réactif. L'invention porte aussi sur des réacteurs permettant la mise en oeuvre dudit procédé

CO2 Capture and Storage by Hydroquinone Clathrate Formation: Thermodynamic and Kinetic Studies

Hydroquinone (HQ) can form a gas clathrate in specific pressure and temperature conditions in the presence of CO2 molecules. This study presents experimental data of clathrate phase equilibrium and storage capacity for the CO2-HQ system in the range of temperature from about 288 to 354 K. Intercalation enthalpy and entropy are determined using the obtained equilibrium data and the Langmuir adsorption model. On a kinetic point of view, CO2-HQ clathrate formation by solid/gas reaction revealed a non-negligible effect of textural parameters on enclathration rate

CO2–Hydroquinone Clathrate: Synthesis, Purification, Characterization and Crystal Structure

Organic clathrate compounds, particularly those formed between hydroquinone (HQ) and gases, are supramolecular entities recently highlighted as promising alternatives for applications such as gas storage and separation processes. This study provides new insights into CO2–HQ clathrate, which is a key structure in some of the proposed future applications of these compounds. We present a novel synthesis and purification of CO2–HQ clathrate monocrystals. Clathrate crystals obtained from a single synthesis and native HQ are characterized and compared using Raman/Fourier transform infrared/NMR spectroscopies, optical microscopy, and thermogravimetric analysis coupled to mass spectrometry. The molecular structure of the clathrate has been resolved by X-ray diffraction analysis, and detailed crystallographic information is presented for the first time

Characterization Study of CO2, CH4, and CO2/CH4 Hydroquinone Clathrates Formed by Gas–Solid Reaction

Hydroquinone (HQ) is known to form organic clathrates with some gaseous species such as CO2 and CH4. This work presents spectroscopic data, surface and internal morphologies, gas storage capacities, guest release temperatures, and structural transition temperatures for HQ clathrates obtained from pure CO2, pure CH4, and an equimolar CO2/CH4 mixture. All analyses are performed on clathrates formed by direct gas–solid reaction after 1 month’s reaction at ambient temperature conditions and under a pressure of 3.0 MPa. A collection of spectroscopic data (Raman, FT-IR, and 13C NMR) is presented, and the results confirm total conversion of the native HQ (α-HQ) into HQ clathrates (β-HQ) at the end of the reaction. Optical microscopy and SEM analyses reveal morphology changes after the enclathration reaction, such as the presence of surface asperities. Gas porosimetry measurements show that HQ clathrates and native HQ are neither micro- nor mesoporous materials. However, as highlighted by TEM analyses and X-ray tomography, α- and β-HQ contain unsuspected macroscopic voids and channels, which create a macroporosity inside the crystals that decreases due to the enclathration reaction. TGA and in situ Raman spectroscopy give the guest release temperatures as well as the structural transition temperatures from β-HQ to α-HQ. The gas storage capacity of the clathrates is also quantified by means of different types of gravimetric analyses (mass balance and TGA). After having been formed under pressure, the characterized clathrates exhibit exceptional metastability: the gases remain in the clathrate structure at ambient conditions over time scales of more than 1 month. Consequently, HQ gas clathrates display very interesting properties for gas storage and sequestration applications

CATHY : une plateforme expérimentale multi-échelles pour l'étude et la CAracTérisation d'HYdrates de gaz

Les hydrates de gaz sont des structures cristallines, composées d’un réseau tridimensionnel de molécules d’eau pouvant emprisonner sous certaines conditions de pression et température des molécules de gaz comme par exemple le méthane ou le dioxyde de carbone (CO2). Les recherches menées sur ces composés ont de nombreuses applications pratiques à fort impact économique dans les domaines du flow-assurance (prévention de la formation d'hydrates de gaz pour assurer la production de gaz ou de pétrole), du captage/stockage du CO2 (traitement et/ou stockage de gaz sous pression), de l’environnement (production d'énergie propre, transport et stockage de gaz), de l’énergie (exploitation des dépôts naturels d’hydrates représentant une source colossale de gaz naturel), et de l’industrie du froid (utilisation en tant que nouveaux Matériaux à Changement de Phase (MCP)). La plateforme CATHY met en synergie trois laboratoires (le LFC-R, le LaTEP et l’IPREM-ECP) de l’Université de Pau et des Pays de l’Adour (UPPA) pour l’étude et la caractérisation expérimentale des hydrates de gaz par plusieurs techniques complémentaires, mises en œuvre à différentes échelles, dans les domaines suivants : - micro et macro spectroscopie RAMAN pour l’analyse cinétique et structurale in-situ; - synthèse d’hydrates à échelle pilote et à l’échelle de la goutte ; - micro et macro calorimétrie (un brevet déposé) sous pression pour la détermination de propriétés thermodynamiques (diagrammes d’équilibre de phases, enthalpies, etc). Les différents équipements de la plateforme ainsi que des résultats expérimentaux caractéristiques de chaque technique seront illustrés et présentés pour l’hydrate de CO2

Double beam FT-IR reflection spectroscopy on monolayers

For in situ infrared studies of ultrathin films deposited on solid substrates or spread at an air/liquid interface, we have developed a new FT-IR double beam approach basedondifferential reflectivity by polarization modulation. Beca use only the s-component (perpendicula r to the plane of incidence) of th e electromagnetic tield is inciden t o n the studied surface. the spectral fea tures a reeasy to interpret in terms of molccular orientation. Spectra of a cadmium a rachidate La ngmuir- Blodgett film deposited on a goldmirrar and a DMPC Langmuir film spread at the air/water interfac

Double beam FT-IR reflection spectroscopy on monolayers

For in situ infrared studies of ultrathin films deposited on solid substrates or spread at an air/liquid interface, we have developed a new FT-IR double beam approach basedondifferential reflectivity by polarization modulation. Beca use only the s-component (perpendicula r to the plane of incidence) of th e electromagnetic tield is inciden t o n the studied surface. the spectral fea tures a reeasy to interpret in terms of molccular orientation. Spectra of a cadmium a rachidate La ngmuir- Blodgett film deposited on a goldmirrar and a DMPC Langmuir film spread at the air/water interfac