Search results for "Metallurgy"

Mechanical Stresses: Inhibitor of Catalyst of High Temperature Oxidation?

2001

Oxidation of metals is a complex reaction in which mechanical and chemical phenomena occur. A dynamic and macroscopic model is developed in order to simulate oxidation kinetics of a metal. It includes the stress/diffusion coupling in the bulk and the interfacial phenomena at metal/oxide interface. Its application to the Zr/ZrO 2 system shows the important role of stress field distribution in oxide on kinetic behavior. According to the sign of stress gradient in the oxide scale, the oxidation rate can speed up or slow down. The calculated kinetic curves could he fitted using a k p .t 1/n law where n and kp vary all over the process, like for the experimental kinetic curves.

MOCVD deposition of YSZ on stainless steels

2003

Abstract Yttria stabilized zirconia was deposited on stainless steel using the metal–organic chemical vapor deposition (MOCVD) technique, from β-diketonate precursors. The variation of the evaporation temperatures of yttrium and zirconium precursor allowed to control the level of Y within the film. Over the temperature range 125–150 °C, the Y content increased from 2.5 to 17.6 at.%. X-ray diffraction (XRD) analyses evidenced tetragonal phase of zirconia when the Y content was below 8 at.%, and cubic phase for higher concentration. Sputtered neutral mass spectrometry (SNMS) profiles confirmed that the control and stability of Y precursor temperature were of major importance to guarantee the …

Mechanical properties of aluminum, zirconium, hafnium and tantalum oxides and their nanolaminates grown by atomic layer deposition

2015

ABSTRACT The mechanical properties of two different metal oxide nanolaminates comprised of Ta 2 O 5 and Al 2 O 3 , HfO 2 or ZrO 2 , grown on soda–lime glass substrate by atomic layer deposition, were investigated. Ta 2 O 5 and Al 2 O 3 layers were amorphous, whereas ZrO 2 and HfO 2 possessed crystalline structure. Thickness of single oxide layers was varied between 2.5 and 15 nm. The total thickness of the laminate structures was in the range of 160–170 nm. The hardness values of single layer oxides on glass ranged from 6.7 GPa (Ta 2 O 5 ) to 9.5 GPa (Al 2 O 3 ). Corresponding elastic moduli were 96 GPa and 101 GPa. The hardnesses of laminates were in the range of 6.8–7.8 GPa and elastic mo…

Microchemical Model for High Temperature Oxidation of Zirconium

1997

Micromechanical Approach of the High Temperature Oxidation of Zirconium

1996

LFZ growth of (Bi, Pb)–Sr–Ca–Cu–O superconducting fibers

1991

Powder x-ray diffraction, d.c. and a.c. susceptibilities, and SEM have been used to study (Bi1−xPbx)2Sr2Ca2Cu3O10−δ fibers grown by the Laser Floating Zone method. The well-oriented, long-grained superconductor fiber properties are shown to be highly dependent on the partial pressure of oxygen in the growth atmosphere, as well as on fiber pulling rate. Slowly grown fibers contain initially the 2212 (80 K) phase; the 2223 (110 K) phase also appears upon annealing in air. Faster growth rates result in fibers that contain a mixture of the 2212 and 2201 phases and, in this case, long annealing procedures are necessary to observe the 2223 phase.

On the Effect of Surface Treatment to Improve Oxidation Resistance and Conductivity of Metallic Interconnects for SOFC in Operating Conditions

2008

International audience; Due to the reduction of operating temperature from 1000°C to 800°C, chromia forming alloys are the best candidates for interconnects in Solid Oxide Fuel Cells (SOFCs). These interconnects have to be operational in service conditions, at 800°C in air (cathode side) and in humidified hydrogen (anode side). The performance of the interconnect stainless steels is limited by the oxide scale formation (chromia), the low electronic conductivity of this scale and the possible volatility of chromium oxides. In the field of high temperature oxidation of metals, it is well known that the addition of a nanometric layer made of reactive element oxide such as, La2O3, Nd2O3 and Y2O…

Inhomogeneous speed effects on H-2 vibrational line profiles in ternary mixtures

2000

International audience; A study of speed inhomogeneous broadening of the hydrogen vibrational line profiles in the collisional regime for ternary mixtures is reported. The Q(1) line of H-2 in H-2-Ar-N-2, H-2-He-Ar, and H-2-He-N-2 mixtures is investigated by high resolution stimulated Raman spectroscopy for various concentrations and temperatures. A model, successfully used for binary mixtures, is extended to ternary mixtures. An excellent agreement is obtained between theory and experiment for H-2-Ar-N-2, by using the collisional parameters previously obtained from binary mixtures study. For H-2-He-Ar and H-2-He-N-2, H-2-He collisions play a "hardening" effect in the H-2 soft speed memory m…

Global sea-to-air flux climatology for bromoform, dibromomethane and methyl iodide

2013

Volatile halogenated organic compounds containing bromine and iodine, which are naturally produced in the ocean, are involved in ozone depletion in both the troposphere and stratosphere. Three prominent compounds transporting large amounts of marine halogens into the atmosphere are bromoform (CHBr3), dibromomethane (CH2Br2) and methyl iodide (CH3I). The input of marine halogens to the stratosphere has been estimated from observations and modelling studies using low-resolution oceanic emission scenarios derived from top-down approaches. In order to improve emission inventory estimates, we calculate data-based high resolution global sea-to-air flux estimates of these compounds from surface ob…

L'évolution des premières métallurgies extractives du cuivre

2003

International audience; L'histoire de la métallurgie extractive débute avec le cuivre. Malgré la rareté, des témoignages archéologiques, l'étude des sites d'extraction et notamment des déchets permet depuis peu de caractériser, au moins partiellement, les premiers procédés. Ainsi, on arrive aujourd'hui à documenter ce qui fut une véritable révolution au tout début de cette métallurgie, quand, d'une activité à faible production durant le Chalcolithique et le début de l'âge du Bronze, on passe progressivement à une véritable production de masse vers le milieu et la fin de l'âge du Bronze. Les premiers procédés sont non scorifiants, ils séparent mal le stérile du métal, et conduisent à des per…