Synthèse hydrothermale et réalisation de céramiques de titanozirconate de plomb dopé pour des applications électroniques et électrotechniques

Le frittage à basse température de compositions complexes avec ou sans ajout de nickel est étudié pour des applications actionneurs. Ce travail est basé sur la comparaison de 2 voies de préparation de ces matériaux. Le chamottage de précurseurs oxydes permet de préparer des matériaux de référence à haute température mais également à basse température grâce à un ajout d'excès de plomb. Un nouveau protocole de synthèse hydrothermale de poudres PZT multidopées est mis au point à partir de précurseurs liquides. L'incorporation des dopants est particulièrement étudiée. Les différentes poudres et céramiques sont caractérisées. Leurs caractéristiques structurales, microstructurales et électriques sont comparées. Une méthode originale de diffraction X en température a été mise au point. Elle permet d'estimer la dispersion chimique du PZT morphotropique pour les poudres et pour les céramiques frittées. Le comportement au frittage est déterminé à partir de suivis dilatométriques. Les poudres chamottées frittent à 1150ʿC. L'utilisation d'un excès de plomb permet de fritter ces poudres dès 850ʿC mais s'avère désastreuse pour leurs propriétés. Les poudres hydrothermales sont réalisées sans excès de plomb et permettent la fabrication de céramiques PZT denses dès 950ʿC. Ces céramiques hydrothermales sont plus homogènes que les céramiques chamottées et ce malgré leur température de frittage moins élevée. Leurs propriétés électriques sont comparables à celles obtenues pour les céramiques de référence frittées à 1150ʿC. La structuration en domaine dans ces matériaux et l'analyse des relations microstructures propriétés sont abordées à partir d'une première observation en microscopie électronique en transmission.MAUBEUGE-BU (593922101) / SudocVALENCIENNES-BU Sciences Lettres (596062101) / SudocSudocFranceF

Alkali-Activated Materials based on Callovo-Oxfordian Argillite: Formation, Structure and Mechanical Properties

International audienc

Thermal resistance of argillite-based alkali-activated materials. Part 1: Effect of calcination processes and alkali cation

International audienc

Adaptation of the geopolymer composite formulation binder to the shaping process

International audienceThis work aims to adapt a formulation of a geopolymer composite to elaborate complex shapes. Here a hollow cylinder is chosen to investigate different possible solutions: building process according to the formulation. To this end, different content of metakaolin, wollastonite, and glass fibers was used to identify the feasibility of shaping of the geopolymer composites. Hollow cylinder shape was elaborated from different formulations by casting and additive manufacturing (robocasting or Direct Ink Writing) regarding their feasibility. The mechanical properties of the formulations were then analyzed with thermal analysis, compressive and flexural tests, and compared with their way of shaping. The results showed that the viscosity can be mainly controlled by the wollastonite content. The formulations adapted to the robocasting present an optimal mechanical resistance due to a higher amount of reinforcement elements. A formulation that can be cast and robocast has been obtained and presents a compressive strength of 89 MPa and bending strength of 15 MPa. Thus, here some keys are 2 given to design a formulation of geopolymer composite adapted to a shaping process by modifying the metakaolin, wollastonite, and glass fiber content

Shaping of geopolymer composites by 3D printing

International audienceThis work aims to shape a hollow cylinder with a geopolymer and an additive manufacturing process (3D printing) without organic additives. The formulation of a geopolymer composite using only mineral parts is proposed and the parameters of the 3D printing process were optimized. The mechanical properties, the microstructure, and the adhesion of the layers of the printing material were analysed and compared with the literature. The results showed that the geopolymer composite could be printed with the addition of small ratios of wollastonite, glass fibers, or non-reactive aluminosilicate and by modifying the printing speed. The stacking layers exhibited a good adhesion between them, avoiding the socalled "cold joints" effect, and the fibers are flow-oriented during the process. Some hollow cylinders are successfully printed with a flexural strength of 15 MPa

INFLUENCE OF THE WOLLASTONITE AND GLASS FIBERS ON GEOPOLYMER COMPOSITES WORKABILITY AND MECHANICAL PROPERTIES

International audienceThis work aims to synthetize geopolymer composites and study the influence of the aluminum concentration, wollastonite and glass fibers on the properties of the fresh and hardened material. To this end, different metakaolin, wollastonite and glass fibers contents were used to synthesize geopolymer composites. The effect of reinforcement elements on the geopolymerization reaction has then been studied with FTIR spectroscopy and thermal analysis (DTA-TGA). Moreover, the viscosity and the setting time of the reactive mixture, as well as the compressive strength of the hardened material, have been measured for the different compositions. The results showed that the nature of the reinforcement added induces different polycondensation reactions. The wollastonite improves the viscosity and the mechanical properties by ensuring a better dissolution of the metakaolin, whereas the glass fibers act as an anchoring site during the geopolymerization reaction, leading to a ductile failure of the material. Finally, the aluminum concentration enables to monitor the viscosity and setting time of the reactive mixture and has a significant influence on the microstructure and the compressive strength. Thus, the initial formulation of the geopolymer composites allows controlling the properties of the fresh and hardened geopolymer composites

Composites à matrice céramique industriels et commerciaux pour le chemisage d’alvéole de stockage de déchets radioactifs

International audienc

Corrosion Behavior and Sacrificial Properties of Zn and Zn-Al Coatings in Conditions Simulating Deep Geological Disposal of Radioactive Waste at 80 °C

In France, it is planned to manage high-level radioactive waste via deep geological disposal. The carbon steel overpacks containing the waste will face corrosion processes specific to the unusual environment of the disposal. To protect these overpacks against corrosion, the use of metallic sacrificial coatings was considered as a possible solution. Therefore, the corrosion behavior of thermally sprayed Zn and Zn-15wt.%Al coatings (500 µm thick) was studied in a solution simulating the specific environment of the disposal. Galvanic corrosion experiments were performed with a coated steel electrode connected to a bare steel one, which simulated a coating defect. First, it was observed that the Zn coating had lost its sacrificial properties after ~2 months of coupling. XRD and µ-Raman analysis carried out after the experiment demonstrated that the coating was covered with a protective hemimorphite (Zn4Si2O7(OH)2·H2O)-rich layer. In contrast, the Zn-15wt.%Al coating kept its sacrificial properties all along the 6-month experiment. It proved to be covered with a layer mainly composed of Zn and Zn-Al hydroxysulfates, which did not contain hemimorphite. However, SEM cross-sectional observations showed that the electrolyte had seeped into the coating and had even reached the steel surface. This infiltration led to the oxidation of the splats inside the coating, even close to the steel surface, and induced a large swelling of the coating. Its thickness was increased by 50%

Influence of the nature and amount of carbonate additions on the thermal behaviour of geopolymers: A model for prediction of shrinkage

International audienc