Search results for "Fine powder"
showing 3 items of 3 documents
Caractérisation de poudres de zircone synthétisées par voie hydrothermale
1998
La synthese hydrothermale permet la realisation de poudres fines cristallisees et desagglomerees Ces qualites sont appropriees a l'elaboration de composites fins oxyde/oxyde par synthese simultanee des deux phases. Nous avons developpe ce protocole pour la realisation de nanocomposites ahrmine/zircone (Q). Nous presentons ici plus particulierement le travail effectue sur la zircone, Les conditions de traitement hydrothermal et d'un traitement thermique modere supplementaire sont analysees en relation avec les caracteristiques des poudres synthetisees. Differentes techniques complementaires sont utilisees pour ces poudres de zircone: diffraction des rayons X (% de la phase quadratique, taill…
Mixed-Valence Defect Ferrites : a New Family of Fine Powders and Thin Films of Spinel Ferrites
1997
When highly divided spinel ferrites become reactive enough with oxygen, to allow the oxidation of the Fe 2+ ions at low temperature and of substitute cations too, when these cations are capable of different valence states. We prepared fine particles of spinel ferrites substituted by Mn, Mo, Cu, by chimie douce, especially from oxalate precursors and used them to reveal and to study the oxido-reduction phenomena occurring in these finely divided materials. It was shown that the oxidation created a new family of spinel ferrites : the mixed-valence defect ferrites, having specific characteristics and properties. The ferrites of this type can be fine powders prepared at low temperature, or grou…
Valence states of copper in copper ferrite spinels CuxFe3−xO4 (0 < x ≤ 1) fine powders: Evidence of copper insertion
1997
Abstract The oxidation in cation deficient spinels of copper iron spinels Cu x Fe 3− x O 4 (0 x ≤ 1) synthesized by soft chemistry with a grain size x per mole of ferrite, three oxidation phenomena corresponding to Cu + at B-sites (130°C), Fe 2+ at B-sites (180°C) and Cu + at A-sites (240°C) have been found in close relation with the cation-oxygen distance of each oxidizable cation. For nonstoichiometric synthesized spinels Cu x Fe 3− x O 4+ δ with δ x , the presence of additional interstitial Cu + ions has been envisaged. The oxidation temperature of these interstitial ions (> 300°C) is higher than that for Cu + ions at Asites suggesting that interstitial copper ions also essentially resid…