Functionalization of SiC-based materials by a selective YBa2Cu3O7-δ coating via sol–gel route in order to optimize their optical properties

SiC-based materials are good candidates for the application as solar receivers except concerning their optical properties. Indeed, considering the use at high temperature, materials used as solar receivers have to efficiently absorb the visible-near infrared waves (corresponding to solar spectral range) and simultaneously reflect the mid and far-infrared rays but SiC is absorbent in all the whole visible-infrared spectral domain. In this challenging work, a suitable YBa2Cu3O7-δ oxide which can present appropriate optical properties is studied. It was synthesized following a sol–gel route and it was obtained with a high level of purity. YBa2Cu3O7-δ pellets were realized and heat treated at different temperatures revealing that the higher the heat treatment is, the better the oxygen stoichiometry (7-δ) is and the smoothest the surface is. This directly acts on the YBa2Cu3O7-δ optical properties. Considering these results, an YBa2Cu3O7-δ coating was realized on SiC pellets by dip-coating. A homogenous and covering layer of about 10 μm was obtained presenting very promising optical properties which were predominant in the FIR-MIR range whereas absorptance was increased in NIR-visible range

Characterization and functionalization by sol–gel route of SiC foams

Ceramic foam materials are commonly used for various applications, including catalyst supports or solar receivers. SiC foams are good candidates for the latter application as solar receivers. Its efficiency is directly related to the geometry, which can be evidenced by X-ray microtomography, and optical properties of the receiver. A promising route to add functionalities with homogenous and adhering oxide coatings onto complex SiC foams in a single step process is proposed. This oxide synthetic process is derived from the Pechini method. Foams are fully impregnated by precursor sols with a controlled viscosity making a thin and totally covering coating

Advances in the deposition of ceramics by soft chemistry process : example of rare- earth silicate coatings

The dip-coating process consists in immersing a sample to be coated in the liquid medium and then removing it at a controlled speed in order to obtain a film of regular thickness, as shown in Figure 1a). Dip-coating technique is now used in many industrial fields (biomedical, transportation, optics…). It is a very simple, and easy process to implement for the deposition and shaping of different natures of coatings (ceramic, metallic and polymer). In the case of ceramic coatings, after the dip-coating operation, the layers undergo a sintering post-treatment leading to the consolidation and/or the densification of the deposit. The corresponding mechanisms need a rigorous control of many parameters. The parameters involved in the dip-coating process are related to the medium and to the process. Concerning the medium, the dispersion medium nature, the particles concentration, viscosity, and stability are the main ones. The stability of the suspension is a first-order parameter and a preliminary formulation work has been carried out to cope with it. Moreover, parameters relative to the fabrication process such as the number of layers and the thermal profile (intermediary and final temperatures), will also be key factors to be taken into account in the formation of homogeneous and reproducible coatings by dip-coating.This work highlights the influence of these various parameters in the case of rare earth silicates based coatings. The various experiments were carried out in correlation to the coatings quality and microstructure. Homogeneous and conformal ceramic coatings of few tens of micrometers thick, as shown in Figure 1b), were obtained. A multi-layers deposit in a sol loaded at 40% mass generally allows to reach the desired thickness. With these experiments relationship between dip-coating parameters and coatings microstructure and morphology can be established. Please click Additional Files below to see the full abstract

SiC substrates functionalization by impregnation of sols and-or suspensions in order to enhance the solar exchangers conversion efficiencies

Face à la nécessité de trouver de nouvelles sources d'énergie, on assiste au développement des centrales solaires thermiques à concentration et plus particulièrement à tour. L'air est utilisé comme fluide caloporteur circulant dans un récepteur sur lequel sont concentrés les rayons solaires. L'absorbeur, situé dans le récepteur, est l'élément clé de ces dispositifs ; il doit absorber le rayonnement solaire tout en ayant une faible émissivité infrarouge pour limiter les pertes par rayonnement thermique observées. Le projet OPTISOL, dans lequel s'inscrivent ces travaux de thèse, a pour objectif d'optimiser les propriétés thermo-optiques d'un absorbeur volumique. Pour cela, une mousse en carbure de silicium a été choisie en tant que support mécanique de l'absorbeur, pour sa bonne tenue aux hautes températures, et pour sa capacité à absorber fortement le rayonnement solaire. Plusieurs laboratoires ont travaillé sur ce projet et le rôle du CIRIMAT fut, dans un premier temps, de caractériser ces mousses de carbure de silicium, par des techniques conventionnelles mais aussi par des techniques moins usuelles telles que la microtomographie X. Dans un second temps, les mousses de carbure de silicium ont été fonctionnalisées par un oxyde sélectif, YBaCuO, dans le but d'optimiser la sélectivité spectrale du système global. Pour cela, les techniques en voie liquide (sol-gel, suspensions, ...) ont été choisies et un procédé de fonctionnalisation a été développé, permettant de revêtir des substrats plans (pastille) et volumiques (mousse poreuse). La sélectivité spectrale du carbure de silicium ainsi fonctionnalisé a été étudiée par spectrométrie infrarouge-visible et les résultats obtenus sont prometteurs puisque une diminution de l'émissivité infrarouge a été observée tout en conservant une forte absorptivité du rayonnement solaire.The necessity of finding new energy sources leads to the development of concentrated solar thermal power plants and more particularly the one using towers. Air is used as a heat transfer fluid flowing in a receiver heated by concentrated sunlight. The absorber, located in the receiver, is the key element of these devices; it must both absorb solar radiation and have a low infrared emissivity to limit thermal radiation losses. This work is part of the OPTISOL project, which aim is to optimize the thermo-optical properties of a volumetric absorber. For this purpose, a silicon carbide foam was selected as the mechanical support of the absorber for its good resistance to high temperatures and for its ability to be efficient to absorb sunlight. Several laboratories have worked on this project and the role of CIRIMAT was, at first, to characterize these silicon carbide foams using conventional and less conventional techniques such as X microtomography. Secondly, silicon carbide foams have been functionalized by a selective oxide, YBaCuO, in order to optimize the spectral selectivity of the system. For this, liquid routes such as sol-gel or suspension techniques have been selected and a functionalization process was implemented for coating planar (pellet) and volumetric (porous foam) substrates. The spectral selectivity of the functionalized silicon carbide was studied by infrared-visible spectrometry and the results are promising since a decrease in the infrared emissivity was observed while maintaining a high absorptivity of solar radiation

Fonctionnalisation de supports de SiC par imprégnation de sols et-ou de suspensions en vue d'améliorer les rendements de conversion d'échangeurs solaires

The necessity of finding new energy sources leads to the development of concentrated solar thermal power plants and more particularly the one using towers. Air is used as a heat transfer fluid flowing in a receiver heated by concentrated sunlight. The absorber, located in the receiver, is the key element of these devices; it must both absorb solar radiation and have a low infrared emissivity to limit thermal radiation losses. This work is part of the OPTISOL project, which aim is to optimize the thermo-optical properties of a volumetric absorber. For this purpose, a silicon carbide foam was selected as the mechanical support of the absorber for its good resistance to high temperatures and for its ability to be efficient to absorb sunlight. Several laboratories have worked on this project and the role of CIRIMAT was, at first, to characterize these silicon carbide foams using conventional and less conventional techniques such as X microtomography. Secondly, silicon carbide foams have been functionalized by a selective oxide, YBaCuO, in order to optimize the spectral selectivity of the system. For this, liquid routes such as sol-gel or suspension techniques have been selected and a functionalization process was implemented for coating planar (pellet) and volumetric (porous foam) substrates. The spectral selectivity of the functionalized silicon carbide was studied by infrared-visible spectrometry and the results are promising since a decrease in the infrared emissivity was observed while maintaining a high absorptivity of solar radiation.Face à la nécessité de trouver de nouvelles sources d'énergie, on assiste au développement des centrales solaires thermiques à concentration et plus particulièrement à tour. L'air est utilisé comme fluide caloporteur circulant dans un récepteur sur lequel sont concentrés les rayons solaires. L'absorbeur, situé dans le récepteur, est l'élément clé de ces dispositifs ; il doit absorber le rayonnement solaire tout en ayant une faible émissivité infrarouge pour limiter les pertes par rayonnement thermique observées. Le projet OPTISOL, dans lequel s'inscrivent ces travaux de thèse, a pour objectif d'optimiser les propriétés thermo-optiques d'un absorbeur volumique. Pour cela, une mousse en carbure de silicium a été choisie en tant que support mécanique de l'absorbeur, pour sa bonne tenue aux hautes températures, et pour sa capacité à absorber fortement le rayonnement solaire. Plusieurs laboratoires ont travaillé sur ce projet et le rôle du CIRIMAT fut, dans un premier temps, de caractériser ces mousses de carbure de silicium, par des techniques conventionnelles mais aussi par des techniques moins usuelles telles que la microtomographie X. Dans un second temps, les mousses de carbure de silicium ont été fonctionnalisées par un oxyde sélectif, YBaCuO, dans le but d'optimiser la sélectivité spectrale du système global. Pour cela, les techniques en voie liquide (sol-gel, suspensions, ...) ont été choisies et un procédé de fonctionnalisation a été développé, permettant de revêtir des substrats plans (pastille) et volumiques (mousse poreuse). La sélectivité spectrale du carbure de silicium ainsi fonctionnalisé a été étudiée par spectrométrie infrarouge-visible et les résultats obtenus sont prometteurs puisque une diminution de l'émissivité infrarouge a été observée tout en conservant une forte absorptivité du rayonnement solaire

Fonctionnalisation de supports de SiC par imprégnation de sols et-ou de suspensions en vue d'améliorer les rendements de conversion d'échangeurs solaires

The necessity of finding new energy sources leads to the development of concentrated solar thermal power plants and more particularly the one using towers. Air is used as a heat transfer fluid flowing in a receiver heated by concentrated sunlight. The absorber, located in the receiver, is the key element of these devices; it must both absorb solar radiation and have a low infrared emissivity to limit thermal radiation losses. This work is part of the OPTISOL project, which aim is to optimize the thermo-optical properties of a volumetric absorber. For this purpose, a silicon carbide foam was selected as the mechanical support of the absorber for its good resistance to high temperatures and for its ability to be efficient to absorb sunlight. Several laboratories have worked on this project and the role of CIRIMAT was, at first, to characterize these silicon carbide foams using conventional and less conventional techniques such as X microtomography. Secondly, silicon carbide foams have been functionalized by a selective oxide, YBaCuO, in order to optimize the spectral selectivity of the system. For this, liquid routes such as sol-gel or suspension techniques have been selected and a functionalization process was implemented for coating planar (pellet) and volumetric (porous foam) substrates. The spectral selectivity of the functionalized silicon carbide was studied by infrared-visible spectrometry and the results are promising since a decrease in the infrared emissivity was observed while maintaining a high absorptivity of solar radiation.Face à la nécessité de trouver de nouvelles sources d'énergie, on assiste au développement des centrales solaires thermiques à concentration et plus particulièrement à tour. L'air est utilisé comme fluide caloporteur circulant dans un récepteur sur lequel sont concentrés les rayons solaires. L'absorbeur, situé dans le récepteur, est l'élément clé de ces dispositifs ; il doit absorber le rayonnement solaire tout en ayant une faible émissivité infrarouge pour limiter les pertes par rayonnement thermique observées. Le projet OPTISOL, dans lequel s'inscrivent ces travaux de thèse, a pour objectif d'optimiser les propriétés thermo-optiques d'un absorbeur volumique. Pour cela, une mousse en carbure de silicium a été choisie en tant que support mécanique de l'absorbeur, pour sa bonne tenue aux hautes températures, et pour sa capacité à absorber fortement le rayonnement solaire. Plusieurs laboratoires ont travaillé sur ce projet et le rôle du CIRIMAT fut, dans un premier temps, de caractériser ces mousses de carbure de silicium, par des techniques conventionnelles mais aussi par des techniques moins usuelles telles que la microtomographie X. Dans un second temps, les mousses de carbure de silicium ont été fonctionnalisées par un oxyde sélectif, YBaCuO, dans le but d'optimiser la sélectivité spectrale du système global. Pour cela, les techniques en voie liquide (sol-gel, suspensions, ...) ont été choisies et un procédé de fonctionnalisation a été développé, permettant de revêtir des substrats plans (pastille) et volumiques (mousse poreuse). La sélectivité spectrale du carbure de silicium ainsi fonctionnalisé a été étudiée par spectrométrie infrarouge-visible et les résultats obtenus sont prometteurs puisque une diminution de l'émissivité infrarouge a été observée tout en conservant une forte absorptivité du rayonnement solaire

Functionalization of SiC-based materials by a selective YBa2Cu3O7-δ coating via sol–gel route in order to optimize their optical properties

International audienceSiC-based materials are good candidates for the application as solar receivers except concerning their optical properties. Indeed, considering the use at high temperature, materials used as solar receivers have to efficiently absorb the visible-near infrared waves (corresponding to solar spectral range) and simultaneously reflect the mid and far-infrared rays but SiC is absorbent in all the whole visible-infrared spectral domain. In this challenging work, a suitable YBa2Cu3O7-δ oxide which can present appropriate optical properties is studied. It was synthesized following a sol–gel route and it was obtained with a high level of purity. YBa2Cu3O7-δ pellets were realized and heat treated at different temperatures revealing that the higher the heat treatment is, the better the oxygen stoichiometry (7-δ) is and the smoothest the surface is. This directly acts on the YBa2Cu3O7-δ optical properties. Considering these results, an YBa2Cu3O7-δ coating was realized on SiC pellets by dip-coating. A homogenous and covering layer of about 10 μm was obtained presenting very promising optical properties which were predominant in the FIR-MIR range whereas absorptance was increased in NIR-visible range