Onset Temperature Of Reduction Research Articles

Analysis of surface oxides on an Fe-12Cr alloy by reduction in a hydrogen flow

I have previously used a temperature-programmed reduction in hydrogen to identify surface oxides on nickel base alloys [1]. The reduction onset temperature of oxides depends on the cation-oxygen bond strength [2-6]. Sufficiently large differences in the reduction onset temperatures make identification of oxides possible [7-9]. The amount of water vapour produced as a result of the reduction is directly proportional to the amount of the oxide reduced. The high sensitivity of the thermal conductivity detectors (TCDs) used in gas chromatography allows detection of the minute amounts of water vapour evolved during the reduction of surface oxide on samples with small surface area [1]. The quantity of the oxides is determined by measuring the area under the peak of the detector signal curve, which is directly proportional to the water vapour content. Thin films, consisting of iron oxide and chromium oxide mixtures, their solid solutions or iron-chromium spinel form during oxidation of Fe-Cr alloys below 500°C [10-12]. In this work surface oxides were identified on an Fe-12Cr alloy oxidized in air at 400 and 500 ° C, the composition of the oxide films were calculated and the oxidation rates of the alloy components were compared. Samples of a commercial (Middelburg Steel and Alloys, South Africa) 3CR12 alloy (11.5% Cr, 0.6% Ni, 0.25% Ti, 0.4% Si, 0.9% Mn, 0.02% C and 0.015% N) were oxidized at 400 and 500°C in air. The 10 mmx 10 mm x 7 mm samples were polished before oxidation with 1/~m diamond paste. In the experiments the following were used: 99.9% pure electrolytic iron (Metallurg Co., South Africa), 99.5% pure electrolytic 2 to 3 mm chromium particles (BDH Chemical Co., UK), 99% pure ferric oxide (Cerac Co., USA), 410L water-atomized stainless steel (0.071% C, 0.86% Si, 0.49% Mn, 0.024% S, 12.3% Cr and 0.012% O; Glidden Metals, USA), and 99.99% pure hydrogen, containing < lp.p.m, oxygen and having a dew point below - 72 ° C. The analysis technique was described in detail in [1]. A specimen was placed in a quartz reactor with a hydrogen stream of 4dm3h ~ The reactor temperature increased at a rate of 15°Cmin ~. A

Color of 8wt% Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;-Containing Glaze Fired in Various Atmospheres

A glaze containing 8wt% Fe2O3 was fired in various atmospheres with the same firing schedule. The effect of firing atmosphere on the color of the iron glaze was studied with a color analyzer, and by ESR, X-ray diffraction, and EPMA.(1) The glaze fired in oxidizing atmospheres was black irrespective of the firing conditions, but the color of glaze fired in reducing atmospheres varied with the onset temperature of reduction.(2) The color of the glazes which were reduced at 900° or 1000°C was black with red spots. The glazes which were reduced at 1100° and 1200°C were red and black, respectively.(3) The results of ESR, X-ray diffraction and EPMA suggested that the black color of the glaze fired in oxidizing atmospheres was caused by the coexisting Fe3+ and Fe2+ ions. The black and the red colors in the glaze fired in reducing atmospheres were due to aggregated metallic iron and aggregated Hematite, respectively.

Energy storage using the reversible oxidation of barium oxide

Co-based oxides have been considered as one of the most promising materials for thermochemical energy storage (TCES) systems, however, the high operation temperature limits their applications. Specially, when Co3O4-based materials are used in concentrated solar power (CSP) system, a large mirror field area is required to meet the high endothermic temperature, which significantly increases the cost of a CSP system. In addition, the high cost of Co-based materials also limits its application. Improving the energy density can effectively reduce the use of the materials. Thus, in this work, to reduce the reduction onset temperature and increase the energy density of Co-based oxides, the TCES performance of Co3-xMgxO4 oxides is investigated. Co2.8Mg0.2O4 shows the best TCES performance. The reduction onset temperature of Co2.8Mg0.2O4 is ∼775.6 °C, which is 133.7 °C lower than that of the pure Co3O4 (∼909.3 °C). Mg-decoration can also improve the energy density of Co3O4 by 8.02 %. Furthermore, the in situ XRD spectra of the oxides indicate that precipitation of MgO from the Co3O4 lattice during the reduction reaction result in a metastable structure of the oxide, which is conducive to its reduction reaction. Density functional theory calculations indicate that Co2.8Mg0.2O4 possessed a higher defect formation energy and shorter chemical bonds than the pure cobalt oxide, which result in its lower reduction onset temperature and higher energy density. The cost-benefit analysis results showed that Mg-decoration could significantly reduce the area of mirror field and the use of energy storage material for a CSP system.