Comportement d'îlots de silicium épitaxié sur corindon (01.2)

Before coalescence from observations of silicon islands on sapphire (01.2), versus growth time and impingement rate on substrate, we analyse distribution of mean diameters. From the radial distribution function of the islands it is possible to suppose around each island a domain of influence larger than the mean diameter. This zone decreases, as the growth time increases, and the islands near the coalescence, behave as hard spheres. An activation energy of surface diffusion of silicon was calculated.L'examen d'îlots silicium sur corindon (01.2), avant coalescence, en fonction du temps, et de la vitesse de croissance, nous a permis de tracer la distribution des diamètres des îlots. Nous avons pu mettre en évidence à partir de la fonction de distribution radiale des îlots, une zone d'influence autour des cristallites. Cette zone décroît lorsque le dépôt augmente jusqu'à transformer à la coalescence les îlots en sphère dure. Un coefficient de diffusion superficiel du silicium a été calculé

Nickel divided catalysts in the NiMo system : correlation between parent alloy-catalyst

The structure of Mo-doped Raney catalysts prepared from Mo- doped Ni2Al3 alloys was investigated essentially by transmission electron microscopy and fine-scale microanalysis. The structure of the catalyst is directly related to the microstructure of the precursor alloy and can be correlated with the physicochemical characteristics and the activity of the catalyst for hydrogenation of acetophenone in the liquid phase

Contribution to the study of the Fe-Nb-C ternary system

In the present paper, solidification sequences are proposed in relation to the observed microstructures for Fe-Nb-C iron based ternary alloys. These alloys are arc melted and characterised by means of differential thermal analysis, scanning electronic microscopy and by quantitative electron probe microanalysis. Thus, an invariant eutectic ternary reaction L $\leftrightarrow$ $\gamma$ + NbC$_{\rm 1-x}$ + Fe$_3$C is proposed at 1140°C.Dans cet article, les séquences de solidification sont proposes en relation avec les microstructures observées pour une famille d’alliages ternaires base fer Fe-Nb-C. Ces alliages ont été élaborés dans un four à arc et caractérisés par Analyse Thermique Différentielle, Microscopie Electronique à Balayage et Microsonde Electronique. Ainsi, une réaction invariante ternaire L $\leftrightarrow$ $\gamma$ + NbC$_{\rm 1-x}$ + Fe$_3$C est proposée à 1140 °C

Synthesis and Characterization of Ni-B Binary Alloys Incorporating Vanadium

The microstructure of a series of binary Ni-B alloys containing various amounts of vanadium additions were investigated by Differential Thermal Analysis (DTA), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Energy Dispersive X-ray Analysis (EDXA). Due to the vanadium addition in the alloys quenched from the liquidus, the formation of the Ni3B phase was enhanced even when the nominal composition was hypoeutectic. The addition of vanadium led to the formation of phase τ (Ni20.4V2.6B6) during the present investigation. In addition the crystallographic orientation relationship of this ternary phase with the nickel matrix was reported. The solid-state eutectoid transformation of the Ni3B phase during cooling was also reported and discussed. KEY WORDS: alloy, solidification, microstructure, adduct, transformation. Global Journal of Pure and Applied Sciences Vol.11(2) 2005: 277-28