Etude morphologique des poudres. Applications au titanate de baryum et à l'alumine

In this paper, we specially looked to the study of shape of particles and aggregates of BaTiO$_3$ and AI$_2$O$_3$ powders with very different physico-chemical features in order to characterize morphologically pulverulent media. Although the analysis of the shape may be carried out on two different scales, providing access either to the silhouette or to the roughness of particles or aggregates, only the investigation of the silhouette has been approached as a first step. For that purpose a number of shape factors was selected and correlations were looked for by statistical analysis.Dans cet article, nous nous sommes penchés plus particulièrement sur l'étude de la forme de particules et d'agrégats de poudres BaTiO$_3$ et AI$_2$O$_3$, présentant des caractéristiques physico-chimiques très différentes, dans le but de caractériser morphologiquement des milieux pulvérulents. Bien que l'analyse de la forme puisse s'effectuer à deux échelles différentes permettant d'accéder, soit à la silhouette, soit à la rugosité des particules ou des agrégats, nous n'avons abordé ici, dans un premier temps, que l'étude de la silhouette. Nous avons pour cela sélectionné un certain nombre d'indices de forme et recherché des corrélations par analyse statistique

Solidification of polycrystalline silicon ingots : simulation and characterization of the microstructure

Polycrystalline silicon prepared by directional solidification exhibits a very heterogeneous morphology. Consequently the global methods of quantitative image analysis are not applicable. On the contrary, the P(l) function gives access to the size distribution in number F(l) and in weight G(l). For a given stage of the growth, the effect of new grains was simulated and was seen to modify markedly the slope of the size distributions at the origin.La morphologie du silicium polycristallin obtenu par solidification dirigée est très hétérogène et ne peut pas être analysée par les méthodes globales d'analyse quantitative d'images. Par contre il est possible d'utiliser la fonction P(l) qui donne accès aux distributions de tailles en nombre, F(l), et en mesure, G(l). Les résultats obtenus sur une simulation d'apparition de nouveaux grains à un stade donné de la croissance, ont permis de montrer que la pente à l'origine de la distribution en nombre, F (l), est très sensible à une germination secondaire

Glass: A prehistoric material for the future

International audienceno abstrac

Steady state creep behavior of two ceramic composites SiCf-SiC and SiCf -MLAS

Creep were performed by three-point bending under vacuum on SICf -SiC and SiCf-MLAS composites. The results are compared and discussed according to criteria based on the values of both temperature and stress and on the damaging features observed

Morphological investigation of ceramics for capacitors

To control and to improve the homogeneity of a dielectric based on baryum titanate, we have investigated the different stages of the process - ceramic powder, slurry and sintered materials - by automatic image analysis methods. The influence of many parameters has been considered : formulation parameters ; grinding conditions ; particle size and shape ; binder, dispersant and plastification agents; temperature and time of sintering ; ..

Microstructure and morphology of SiC

This paper deals with the study of a new generation of ceramic matrix composites, SiCf-SiBC, which consists of a 2.5D perform of SiC fibers and of a self sealing multilayered matrix. Three different batches of these CMCs have been investigated in a morphological point of view thanks to the observations performed at the mesoscopic scale by scanning electron microscopy and automatic image analysis, and also at a microscopic scale by transmission electron microscopy. Through this study, a lot of care was taken about the description of the pyrocarbon interphase and of the different matrix interfaces, which play a key role in the damage features, and more specially in the deflection of the matrix microcracks developed through tested mechanical composites

Advantages of SiC Hi-Nicalon or NLM 202 fibers in SiCf-SiBC composites

International audienceSiCf-SiBC composites were produced using NLM 202 and Hi-Nicalon SiCf fibers. Tensile creep tests were performed under a reduced pressure of argon. These composites show a good creep resistance at 1473 K with a strain rate ranging from 10(-9) to 10(-7) s(-1), depending on the stress level. The creep strength was improved by using Hi-Nicalon instead of NLM 202 SiCf fibers, to the extent of increasing the loadability by 50 MPa at the same operating temperature or increasing the temperature by 50 K for the same load. The damage observed in SEM micrographs and the use of the damage mechanics provide evidence that creep is governed by a damage-creep mechanism in two steps