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As part of a general contribution to the study of accelerator driven system (ADS) nuclear reactor feasibility, a study of the five-component system Bi-Fe-Hg-O-Pb was undertaken. New results about the quasi-binary Bi 2 O 3 -Fe 2 O 3 are presented in this paper. The phase diagram was reinvestigated by differential scanning calorimetry, x-ray diffraction, and electron probe microanalysis. A new compound was discovered and characterized: Bi 25 FeO 40 . Its crystallographic structure was refined. Invariant and transition temperatures are given, as well as phase compositions.

International audienceThe ZrCxOy oxycarbides are well-known relevant ceramic materials for ultra-high temperature applications. The intrinsic macroscopic properties of ZrCxOy being closely related to the C/O ratio, a detailed analysis of the C–O–Zr system has been undertaken experimentally in order to accurately determine the extent of the solid solution of oxygen within the oxycarbide phase at different synthesis temperatures. The obtained results were then used as diagrammatic data to extrapolate the ternary C–O–Zr phase equilibria diagram by the CALPHAD method, providing a predictive tool for the oxycarbide synthesis. The model proposed in the temperature range 1650–2000 °C is in fair agreement with results obtained in the literature. The chemical determination of the relative ratio between light elements (oxygen (O) and carbon (C)) being a difficult issue for most of the general applications, an accurate determination of the cell parameters of the different oxycarbide compositions has been performed to propose an abacus reporting the evolution of the cell parameter against the C/O amount. The chemical composition of the oxycarbide is shown to be determined with an accuracy better that a few percent. It is also shown that the evolution of the cell parameter is not linear, indicative of a possible change of the ionocovalent character of the chemical bonds with the composition of ZrCxOy

In the present work, the role of silica as sintering aids in the densification and the grain growth of yttrium aluminum garnet doped by neodymium (Nd:YAG) ceramics has been investigated. The samples were prepared by ball milling of pure oxides (Al2O3, Y2O3, Nd2O3, SiO2), shaped by cold uniaxial pressing, and sintered in vacuum between 1473 and 1973 K. After cooling, the specimens were annealed under air or vacuum. Their microstructure and the chemical composition of the secondary phases were examined using electron probe microanalysis, scanning electron microscopy, or transmission electron microscopy techniques. From these results, silica addition proved to be efficient on the densification kinetics between 1673 and 1873 K, especially when SiO2 content exceeds 0.05 wt%. Indeed, the solid‐state reaction between SiO2 and Nd:YAG particles in the vicinity of 1660 K leads to a liquid phase that adopts a eutectic composition in the Al2O3–Y2O3–SiO2 system. This phase enhances the densification by improving rearrangement of particles and mass transport at the grain boundaries. At a high temperature, liquid phase and silica were partially removed and some intergranular and intragranular inclusions of residual silica remained after cooling. The most promising thermal treatment consists of sintering Nd:YAG ceramics under vacuum at a high temperature (T≥1973 K) to reach fully dense pieces and to decrease the volume fraction of secondary phases (i.e., liquid phase or silica‐based phases). Finally, these conditions would allow to produce transparent YAG pieces due to their good homogeneity with regard to their microstructural properties (grain size, volume fraction of secondary phases).

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