Diffusion Of Oxygen Species Research Articles

Kinetics of chromite ore reduction from MgO-CaO-SiO2-FeO-Cr2O3-Al2O3 slag system by carbon dissolved in high carbon ferrochromium alloy bath

Kinetic experiments were performed in an induction furnace to investigate the reduction of chromite ore by carbon dissolved in a high carbon ferrochromium alloy melt under conditions of varying Cr2O3 concentration, slag basicity, and temperature. The results obtained show that chromite reduction by dissolved carbon in slag systems of the type MgO-CaO-SiO2-FeO-Cr2O3- Al2O3 occurs principally by a stagewise process encompassing an intermediate reaction in which the divalent chromium oxide species is involved. During the fast period, Cr2O3 reduction is controlled by the diffusion of oxygen species in the slag for which a mass transfer coefficient of 0·003 cm s-1 was calculated. An activation energy value of 117 kJ mol -1 obtained for the reduction of Cr2O3 implies the rate controlling step is mass transfer of Cr2O3 from the slag to the slag/metal interface, since activation energies for metal phase control are typically <70 kJ mol -1. The second period represents a pseudo-equilibrium condition with respect to Cr2O3 reduction that is probably under thermodynamic control by a step or mechanism involving the reduction of divalent chromium oxide to chromium.

Deposition of Chromium Species at Sr‐Doped LaMnO3 Electrodes in Solid Oxide Fuel Cells II. Effect on O 2 Reduction Reaction

The reduction reactions on Sr‐doped (LSM) electrodes in solid‐oxide fuel cells in the absence and presence of a chromia‐forming alloy metallic interconnect have been investigated. Similar to those in the absence of the chromia‐forming alloy, the reduction reactions on LSM electrodes in the presence of chromia‐forming alloys are limited by two electrode processes, the diffusion of oxygen species on the LSM surface and the migration of oxygen ions into zirconia electrolyte. In the presence of chromia‐forming alloy, the dissociative adsorption and diffusion of oxygen on the LSM electrode surface are inhibited by the gaseous Cr species (e.g., ), and the migration processes of oxygen ions into zirconia electrolyte are inhibited by the solid Cr species [e.g., ] deposited on the electrolyte surface. The inhibiting effect of the solid Cr species becomes increasingly dominant on the reduction with the polarization time. The mechanism and kinetics of the reduction on the LSM electrodes in the absence and presence of chromia‐forming alloy are discussed. © 2000 The Electrochemical Society. All rights reserved.

Epitaxial growth of Naβ″-Al 2O 3 single crystal film on α-Al 2O 3

Epitaxial Naβ″-Al 2O 3 single crystal films have been grown into sapphire (0001)-substrates. The kinetic measurements and calculation indicate that the β″-Al 2O 3 crystal is formed via chemical reactions between the gaseous alkali-species and sapphire substrate which are controlled by diffusion of oxygen species in the solid phase. The mechanism and crystallographic translations of film-growth are discussed.

Kinetics and mechanism of oxide formation on titanium, vanadium and chromium thin films

Oxidation kinetics of thin films of titanium, vanadium and chromium in the temperature range 310–630 °C have been studied using backscattering spectrometry and X-ray diffraction. The growing oxides are Cr 2O 3 and TiO 2 for the oxidation of chromium and titanium films respectively. In the case of vanadium films the simultaneous growth of two oxides is assumed with compositions close to V 2O 5 and V 6O 13. In the region studied, the growth of the oxides has been found to obey various growth rate laws. Cr 2O 3 and the vanadium oxides grow parabolically with activation energies of 1.2 eV, whereas TiO 2 grows linearly with an activation energy of 2.0 eV. For chromium and titanium an initial fast oxidation is observed. Implanted xenon markers show that the oxide layer on vanadium films grows by diffusion of oxygen species in the oxide layer. The growth of the chromium oxide occurs almost entirely at the surface and is controlled by the motion of chromium species in the oxide. TiO 2 grows both at the surface and at the oxide-titanium interface.

A study of the stability of Co-rich TbFeCo thin films

The effect of cobalt-content on the stability of Tb(Fe/sub 1-x/Co/sub x/), (x varying from 40 to 100%) thin films (about 100 nm thick) was investigated in relation to structural, chemical, and magnetooptic (MO) properties. Unprotected and SiO-protected films were prepared by electron-beam coevaporation, MO hysteresis loops were obtained with a polar Kerr-effect measurement system. Low-energy X-ray microprobe analysis and induced coupled plasma techniques were used for chemical analysis and structural properties were studied by transmission electron microscopy. Incubation tests were performed to follow the aging of the samples. Static electrochemical tests were carried out to determine their resistance to corrosion. An explanation of the results is proposed based on both oxygen species diffusion and structural modifications. >