TEM study of the reaction mechanisms involved in the carbothermal reduction of hafnia - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue RSC Advances Année : 2015

TEM study of the reaction mechanisms involved in the carbothermal reduction of hafnia

(1) , (1) , (1) , (1)
1

Résumé

The synthesis of HfCxOy oxycarbides through the carbothermal reaction of hafnia with carbon black was undertaken. The obtained powders at different rates of advancement were studied by TEM and XRD in order to investigate the reaction mechanisms involved during such a transformation. The contact between the two starting reactants is shown to be non-reactive, attesting to the transformation operating through solid–gas reactions. The hafnia phase is destabilized by the CO(g) rich atmosphere and is consumed by the migration of ledges at the surface of the crystals acting as a zipper mechanism that liberates HfO(g) and CO2(g) species. The carbon dioxide thus released is used in return to oxidize the carbon black forming carbon monoxide through the Boudouard equilibrium. The liberated HfO(g) then reacts with the ambient CO(g) to form the oxycarbide phase which is shown to nucleate in the carbon black areas. The oxycarbide nuclei display a core–shell microstructure which is formed by a single crystal core embedded in an oxygen rich amorphous phase. During the final stage of the reaction, the atmosphere, which, saturated in CO(g), progressively reduces the oxygen rich gangue until it finally disappears. The accurate determination of the cell parameter of the oxycarbide phase during the reaction indicates that the first formed compound is nearly saturated in carbon, comparable to the metallic carbide. The small change in the lattice parameter indicates that the chemical composition is very restricted, so the solid solution of oxygen within the hafnium oxycarbide seems to be very limited.
Fichier non déposé

Dates et versions

hal-01153968 , version 1 (20-05-2015)

Identifiants

Citer

Florian Réjasse, Gilles Trolliard, Olivier Rapaud, Alexandre Maitre. TEM study of the reaction mechanisms involved in the carbothermal reduction of hafnia. RSC Advances, 2015, 5, pp.45341-45350. ⟨10.1039/C5RA02190A⟩. ⟨hal-01153968⟩
58 Consultations
0 Téléchargements

Altmetric

Partager

Gmail Facebook Twitter LinkedIn More