Papers by Author: Philippe Blanchart

Abstract: This work is devoted to the study of the geometrical stability in time of UyAm1-yO2-x pellet due to self-irradiation at room temperature. Dense and tailored porosity U1-yAmyO2-x (y=0.10; 0.15) compounds were fabricated by a powder metallurgy process. Up to 3.4.1017 α particles/g, an increase in the diameter of 0.9% was observed for the dense compounds while for the tailored porosity material a diameter increase of 0.4% was observed. Swelling laws have been established from the experimental data.

Abstract: We illustrate the x-ray Combined Analysis approach capabilities in characterizing silicates and phyllosilicates for samples exhibiting crystallographic textures. Two mullite composite ceramics, one elaborated under uniaxial pressure the other under centrifugation, and one uniaxially pressed montmorillonite aggregate, are studied in terms of texture, cell parameters and phase contents. Several weak texture components are present in the mullite samples, combinations of planar- and fibre-like textures. The methodology is able to take account of the amorphous silica-like matrix of the composite, and cell parameters and structure of mullite correspond to the commonly modelled used for this phase. The montmorillonite turbostratic phase is correctly reproduced with its fibre texture, eventhough minor phases are also present and modelled in the aggregate.

Abstract: Silicate ceramics with clays are some of the most complicated ceramic systems because of the very complex relationship between the behavior of mineral materials during the ceramic processing and the transformations during heating. A major challenge is to predict the phase transformations in silicate ceramics, since complex relationship occur between the microstructural and structural characteristics of fired product and the physical properties. Clay minerals undergo strong structural transformations during heating, simultaneously to a complex path of thermal transformations. Individual reactions cannot simply identify since they are closely related and overlapped. At temperature above 800°C, new phases are recrystallized and many of the reactions are strongly topotactic. Mullite is the most important phase, which recrystallizes with a range of morphology and stoichiometry. Variables affecting the mullite formation include the clay mineral type and behavior during heating, the possible occurrence of liquid and impurities as Fe. It results in large variations of the stoichiometry and shape of mullite crystals, which are embedded in a low ordered phase to form a micro-composite microstructure. This presentation will review recent research, looking at structural transformations in some typically used phyllosilicate systems : (i) structural transformation of kaolinite and mica phases were identified at temperature up to 1100°C. They evidence a residual structural order of high temperature phases which is favorable to the topotactic recrystallization of mullite; (ii) from the high temperature form of phyllosilicates, an organized network of mullite can be obtained; (iii) the composition of a local and transient liquid and the presence of minor elements as Fe has a significant influence on the mullite morphology; (iv) mechanical properties are closely related to size and organization degree of the mullite network; (v) the process itself influence the kinetic of structural transformation and particularly the powder compact density and the thermal cycle. These research in silicate ceramics evidence multiple and complex challenges, providing opportunities for future development.