The sol–gel route: A versatile process for up-scaling the fabrication of gas-tight thin electrolyte layers

Sol–gel routes are often investigated and adapted to prepare, by suitable chemical modifications, submicronic powders and derived materials with controlled morphology, which cannot be obtained by conventional solid state chemistry paths. Wet chemistry methods provide attractive alternative routes because mixing of species occurs at the atomic scale. In this paper, ultrafine powders were prepared by a novel synthesis method based on the sol–gel process and were dispersed into suspensions before processing. This paper presents new developments for the preparation of functional materials like yttria-stabilized-zirconia (YSZ, 8% Y2O3) used as electrolyte for solid oxide fuel cells. YSZ thick films were coated onto porous Ni-YSZ substrates using a suspension with an optimized formulation deposited by either a dip-coating or a spin-coating process. The suspension composition is based on YSZ particles encapsulated by a zirconium alkoxide which was added with an alkoxide derived colloidal sol. The in situ growth of these colloids increases significantly the layer density after an appropriated heat treatment. The derived films were continuous, homogeneous and around 20 μm thick. The possible up-scaling of this process has been also considered and the suitable processing parameters were defined in order to obtain, at an industrial scale, homogeneous, crack-free, thick and adherent films after heat treatment at 1400 °C

Potentialities of the sol-gel route to develop cathode and electrolyte thick layers Application to SOFC systems

In this work, we report the potential of sol–gel process to prepare cathode and electrolyte thin and thick layers on anodic NiO-YSZ supports which were also made from powders prepared by sol–gel route. YSZ and La2 − xNiO4 + δ, La4Ni3O10 were synthesized as electrolyte and cathode materials for SOFC applications. For electrolyte shaping, yttria stabilized zirconia (YSZ, 8% Y2O3) thick films were cast onto porous NiO-YSZ composite substrates by a dip-coating process using a new suspension formulation. Part of the YSZ precursor colloidal sol was added in the suspension to ensure both homogeneity and adhesion of the electrolyte on the anodic substrate after thermal treatment at 1400 °C for 2 h. By precisely controlling the synthesis parameters, dense and gas-tight layers with thicknesses in the range of 10–20 μm have been obtained. Gas-tightness was confirmed by He permeation measurements. Concerning cathode processing, a duplex microstructured cathode consisting of both La2 − xNiO4 + δ ultra-thin films (few nanometers) and La2 − xNiO4 + δ and/or La4Ni3O10 thick layers (few micrometers) was prepared on YSZ substrates by the dip-coating process, with the thickness being dependent on the nature of the dip-coated solution (polymeric sol or adequate suspension). The derived cathode microstructure, related to the number/thickness of layers and type of architecture, was correlated to the good cell electrochemical performances. Concerning cathode processing, a duplex microstructured cathode consisting of both La2 ? xNiO4 + ? ultra-thin films (few nanometers) and La2 ? xNiO4 + ? and/or La4Ni3O10 thick layers (few micrometers) was prepared on YSZ substrates by the dip-coating process, with the thickness being dependent on the nature of the dip-coated solution (polymeric sol or adequate suspension). The derived cathode microstructure, related to the number/thickness of layers and type of architecture, was correlated to the good cell electrochemical performances

SILICA MEMBRANES - BASIC PRINCIPLES

Basic principles on amorphous silica membranes are presented. The advantages and disadvantages of microporous amorphous silica are discussed to explain its use as separative membranes for specific applications. The synthesis methods are reported and examples of silica membrane designs are given

Salt storage and induced crystallisation in porous asymmetric inorganic membranes

The authors acknowledge the financial support from the Australian Research Council ( DP1901002502 ) and ( DP190101734 ) grants. Publisher Copyright: © 2021Processing brines to recover strategic mineral salts using evaporation ponds requires large surface areas and are slow, even in arid climates. Here we show a novel membrane macropore storage mechanism that induces fast salt crystallisation in mesoporous top-layers in inorganic asymmetric membranes, stemming from 789 million nucleation points per metre square of surface area. During membrane pervaporation, dissolved salts are retained mainly in the macropores of the substrate which subsequently provide ideal conditions for crystal nucleation and growth on the membrane surface upon drying. This novel pore storage mechanism is attained owing to the solution flow modulation of the mesoporous titania and gamma-alumina layers that is counterbalanced by the flow of water during pervaporation. Therefore, pore size control is imperative to avoid flooding in the macroporous substrate. This work further shows the fundamental properties of the salt storage mechanism described by a single salt production coefficient, and a global salt production coefficient for metal chloride salts. This technology could potentially be considered for unlocking and process strategic global minerals from brines.publishersversionpublishe

Binary iron cobalt oxide silica membrane for gas separation

This work investigates the preparation, characterisation and performance of binary iron/cobalt oxide silica membranes by sol-gel synthesis using tetraethyl orthosilicate as the silica precursor, and cobalt and iron nitrates. It was found that cobalt and iron oxides were generally dispersed homogeneously in the silica structure, with the exception of a few minor patches rich in cobalt oxide. The ml-gel synthesis affected the micro-structural formation of binary metal oxide silica matrices. Increasing the iron content favoured condensation reactions and the formation of siloxane bridges, and consequently larger average pore sizes which lead to low He/N-2 permselectivity values below 20. In the case of high cobalt content, a higher silanol to siloxane ratio was observed with tighter pore size tailoring, as evidenced by higher He/N-2 permselectivities reaching 170. The binary metal oxide and silica interfaces proved to follow a molecular sieving mechanism characterised by activated transport where the permeance of the smaller gas molecules (He and H-2) increased with temperature up to 500 degrees C, whilst the permeance of larger gas molecules (CO2 and N-2) decreased. (C) 2014 Elsevier B.V. All rights reserved

Novel membrane percrystallisation process for nickel sulphate production

This research reports on an investigation of the performance of inorganic membranes for use in the percrystallisation of nickel sulphate hydrate. In this novel process, the separation of the solvent (water) and the crystallised solute (nickel sulphate hydrate) occurs continuously in a single-step, avoiding further downstream processing (crystal filtering and drying). The inorganic membranes were synthesised with sucrose solution followed by a post vacuum-assisted impregnation of the coated film on a α-alumina substrate and carbonisation under nitrogen atmosphere. The highest fluxes measured were 22 L m h and 1 kg m h (40 g L ) for water and nickel respectively. Interestingly, the transport of solution through the membrane also affected the hydration state of the nickel sulphate, as well as the crystal type and shape. High water fluxes delivered pure nickel sulphate heptahydrate with elongated and laminar crystal particles (~200 μm). Lower water fluxes produced both heptahydrate and hexahydrate salts with approximately spherical particles (also ~200 μm). There a number of factors that influence the crystallisation reaction such as the rate of evaporation which affects water availability and the resultant temperature at the permeate side of the membrane. Finally, the activation energy for nickel sulphate crystallisation was estimated to be approximately 16 kJ mol based on feed solution temperatures

Novel inorganic membrane for the percrystallization of mineral, food and pharmaceutical compounds

This work demonstrates for the first time the phenomenon of continuous percrystallization using a carbon membrane derived from the pyrolysis of food grade sugar. In addition, it is also the first demonstration of membranes separating solute from solvent and delivering dry crystals in a single step. This is contrary to membrane crystallization, which requires two further processing steps to filter crystals from a solution followed by drying the wet crystal particles. The results indicate that carbonised sugar membranes can confer ideal conditions of super-saturation, leading to instantaneous and continuous percrystallization of compounds at the permeate side of the membrane. As a result, very high percrystallization production rates of up to 55,000 kg m per year are achieved. It is proposed that the percrystallization occurs in a wet thin-film modulated by solution permeation via the mesopores of the membrane, where vapour and crystals are separated at the membrane's solid-liquid-vapour interface. The potential deployment of this novel technology is further demonstrated for a wide range of crystallization applications in chemical, hydrometallurgy, food and pharmaceutical industries

Poudres et trichites de carbure de silicium derivees de gels : synthese et caracterisation

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Développement d'un nouveau procédé de synthèse de membranes inorganiques ou composites par voie CO2 supercritique pour la séparation de gaz

L'utilisation de membranes pour la séparation/purification de mélanges de gaz permet d'envisager la mise en œuvre de procédés continus et faiblement énergivores. Les performances des membranes étant directement reliées à la méthode utilisée pour leur synthèse/modification, une nouvelle génération de membranes est attendue à partir de la méthode originale de dépôt dynamique développée et mise au point dans ce travail, en milieu CO2 supercritique (CO2SC). Les propriétés des fluides supercritiques, intermédiaires entre celles d'un liquide et d'un gaz (densité et diffusivité élevées, viscosité faible), laissent en effet présager la formation de microstructures originales. Les précurseurs sont solubilisés dans le CO2 sous pression puis transportés jusqu'au support membranaire. Cette méthode a été explorée pour : i) la synthèse directe de membranes à base de silice sur des supports macroporeux et ii) la modification de membranes zéolithiques MFI par des alcoxydes (MDES, TEOS) ou par des oligomères fluorés. Dans le premier cas, l'étude des paramètres de dépôt montre que la maîtrise des phénomènes chimiques de la transition sol-gel (contrôlés principalement par la température) dicte la microstructure du matériau final, au travers du degré de condensation/réticulation des clusters déposés. La modification des membranes zéolithiques MFI par un alcoxyde permet de doubler la permsélectivité He/SF6 initiale, sans forte baisse de perméance ( (He)~10-6 mol.Pa-1.s-1.m-2). Dans ce cas, la force, la nature et la disponibilité des sites acides de la charpente MFI sont des critères clés pour la fixation de l'alcoxyde. Les membranes MFI modifiées par un oligomère fluoré sont imperméables au SF6 et la permsélectivé He/N2 peut atteindre une valeur de 136 à 25C ( (He)~10-8 mol.Pa-1.s-1.m-2). Cette nouvelle méthode dynamique de dépôt/modification développée dans ce travail apparaît comme une approche très versatile qui permet de contrôler la structure du matériau déposé en ajustant les paramètres du procédé.Using membranes for the separation/purification of gas mixtures makes possible the implementation of continuous processes with low energy consumption. Membrane performance being directly related to their synthesis/modification method, a new membrane generation is expected from the original "dynamic" deposition method which has been designed and developed in this work, in supercritical CO2 (scCO2) media. Indeed, the properties of supercritical fluids are intermediate between those of liquids and gases (high density and diffusivity, low viscosity), original membrane microstructures are expected to be derived from this process. The selected precursors are solubilized in compressed CO2 and then transported to the membrane support. This method has been explored for both: i) the synthesis of silica-based membranes on macroporous supports and ii) the modification of MFI zeolite membranes by either alkoxides (MDES, TEOS) or fluorinated oligomers. In the first case, an investigation of the deposition parameters demonstates that the sol-gel chemistry (controlled mainly by temperature) masters the final material microstructure, through the degree of condensation/crosslinking of the deposited clusters. Modification of MFI zeolite membranes with alkoxides can double their initial He/SF6 permselectivity without lowering too much their permeance ( (He)~10-6 mol.Pa-1.s-1.m-2). In this case, the alkoxide fixation is monitored by the strength, nature and availability of acid sites in the MFI network. MFI membranes modified with fluorinated oligomers are SF6-tight and their He/N2 permselectivity can reach 136 at 25C ( (He)~10-8 mol.Pa-1.s-1.m-2). This new dynamic deposition/modification method developed in this work appears as a versatile approach in which the final material structure can be controlled by adjusting the process parameters.MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

A short overview on purification and conditioning of syngas produced by biomass gasification: Catalytic strategies, process intensification and new concepts

International audienc