Documents disponibles écrits par cet auteur

Oxygen grain-boundary transport in polycrystalline alumina using wedge-geometry bilayer samples / H. Cheng in Acta materialia, Vol. 58 N° 7 (Avril 2010) 

Public ISBD [article]  in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2442–2451 Titre : Oxygen grain-boundary transport in polycrystalline alumina using wedge-geometry bilayer samples : Effect of Y-doping Type de document : texte imprimé Auteurs : H. Cheng, Auteur ; H.S. Caram, Auteur ; W.E. Schiesser, Auteur Année de publication : 2011 Article en page(s) : pp. 2442–2451 Note générale : Métallurgie Langues : Anglais (eng) Mots-clés : Oxidation  Grain-boundary  diffusion  Ceramics  Grain  boundaries  Dopants Résumé : Novel wedge-geometry, dual-layer alumina samples, both undoped and 500 ppm Y3+-doped, were studied in the temperature regime 1250–1400 °C to determine the effect of Y3+ on oxygen grain-boundary transport in alumina. The samples consisted of a wedge-shaped, single-phase alumina top layer, diffusion bonded to an alumina/Ni substrate containing a fine, uniform dispersion of Ni marker particles (0.5 vol.%). The extent of the alumina spinel oxidation layer was measured as a function of the wedge thickness for a series of heat-treatment conditions. Models of the transport behavior were used to derive values for the rate constants (k) in both the alumina top layer and the alumina/Ni substrate. It was found that the presence of yttrium slows oxygen grain-boundary diffusion in alumina by a factor of ∼5 (at 1300 °C), and increases the corresponding activation enthalpy for oxidation from 407 ± 20 to 486 ± 34 kJ mol−1. Microstructural observations suggested that yttrium also slows Ni outward diffusion. A comparison of the different k values revealed that, at 1300 °C, the presence of Ni alone enhances transport by a factor of ∼2 relative to undoped alumina. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008763 [article] Oxygen grain-boundary transport in polycrystalline alumina using wedge-geometry bilayer samples : Effect of Y-doping [texte imprimé] / H. Cheng, Auteur ; H.S. Caram, Auteur ; W.E. Schiesser, Auteur . - 2011 . - pp. 2442–2451. Métallurgie Langues : Anglais (eng) in Acta materialia > Vol. 58 N° 7 (Avril 2010) . - pp. 2442–2451 Mots-clés : Oxidation  Grain-boundary  diffusion  Ceramics  Grain  boundaries  Dopants Résumé : Novel wedge-geometry, dual-layer alumina samples, both undoped and 500 ppm Y3+-doped, were studied in the temperature regime 1250–1400 °C to determine the effect of Y3+ on oxygen grain-boundary transport in alumina. The samples consisted of a wedge-shaped, single-phase alumina top layer, diffusion bonded to an alumina/Ni substrate containing a fine, uniform dispersion of Ni marker particles (0.5 vol.%). The extent of the alumina spinel oxidation layer was measured as a function of the wedge thickness for a series of heat-treatment conditions. Models of the transport behavior were used to derive values for the rate constants (k) in both the alumina top layer and the alumina/Ni substrate. It was found that the presence of yttrium slows oxygen grain-boundary diffusion in alumina by a factor of ∼5 (at 1300 °C), and increases the corresponding activation enthalpy for oxidation from 407 ± 20 to 486 ± 34 kJ mol−1. Microstructural observations suggested that yttrium also slows Ni outward diffusion. A comparison of the different k values revealed that, at 1300 °C, the presence of Ni alone enhances transport by a factor of ∼2 relative to undoped alumina. DEWEY : 669 ISSN : 1359-6454 En ligne : http://www.sciencedirect.com/science/article/pii/S1359645409008763