Improving the Oxidation Resistance of Fe-Cr-Mn Interconnector of Solid Oxide Electrolyte Fuel Cell with the Addition of Trace Elements

Fe-Cr-Mn alloy is a common material used for the metallic interconnector of solid oxide electrolyte fuel cells (SOFC). However, its high temperature oxidation resistance needs to be strengthened to improve the performance of SOFC. In this study, the effect of trace additions of Ti, Mo, Co and La on the high-temperature behavior of Fe-Cr-Mn alloy was investigated. The composition of Fe-22Cr-2Mn-X (X = Ti, Mo, Co, La) alloys was designed to maintain a bcc structure with the aid of the thermal-calc software. These alloys tended to form Cr-rich oxide in the inner layer and Mn-rich oxide in the outer layer of the specimens after oxidative tests at 850°C, thus reducing the likelihood of chromium oxide evaporation. The experimental results indicated that the addition of Co and La produced better oxidation resistance at high temperatures than Ti and Mo. In addition, the influence of trace elements on electrical resistance of the interconnector material was examined as well.

Gas and liquid phase interactions at the chromium oxide cathode of a direct current arc discharge

The behaviour of a chromium oxide liquid sample has been studied in the presence of an argon arc discharge, the oxide being contained in a cathode crucible. The arc current was maintained at 24 and 44 A, at 21 V. The arc temperature distribution range was between 7 000 and 8 500 K, while the liquid oxide temperature stabilized at 2 420 or 2 620 K, depending on the arc current used. The reduced metal was obtained in the molten bath as a mixture with its oxide and was identified by X-ray diffraction.Using the Cr(I) 434.4-nm and Cr(I) 396.3-nm, as well as the Cr(II) 321.7-nm spectral data, it could be shown that a considerable part of the reduced chromium found at the cathode may originate from the arc discharge, migration of the Cr(II) species occurring under the effect of the electric field. The thermodynamic conditions in the cathode bath cannot explain the formation of Cr from the oxide decomposition in the bath. Also, in view of the low chromium oxide vapor pressure at the prevailing bath temperature, the mass transfer rate from the cathode bath to the arc should be increased by liquid oxide projection into the arc gas, under the effect of arc impact on the cathode. This should be followed by oxide evaporation and decomposition at high temperatures. This study confirms that the arc–cathode interaction may substantially increase the amount of oxide reduction at the cathode.

Oxydation von Wolfram und Molybdän in Sauerstoff-Atmosphäre bei niederen Drucken und hoher Temperatur ** ** / Oxidation of Tungsten and Molybdenum in Oxygen-Atmosphere at Low Pressures and High Temperature

The oxide evaporation of Mo and W (polycrystalline and 110-oriented) in oxygen (2·10-6 to 6·10-6 Torr) at 1900 K is investigated. Two parallel discs are operated in an oxygen atmosphere. One of these discs ("emitter", Mo or W) is kept at 1900 K, the other one ("collector") at 1000 K. During operation, oxides of the emitter material are formed on the emitter surface, evaporated, and condensed on the collector. The oxide profile on the collector is measured by microprobe. The profile allows the determination of WM=jM/jE and Wtot = j(O2 in oxides)/jE. jM: evaporation density of W or Mo atoms bound in oxides; j (O2 in oxides) : evaporation density of oxides of emitter metal and impurities (in O2-units) ; jE : impingement density of O2-molecules. Calculations used to determine WM and Wtot are described. The measurements gave the following values for WM and Wtot:tungsten, polycrystalline: WM=(7±1)%; Wtot= (8,5 ± 1)%; tungsten, 110-oriented: WM= (2±0.5)%; Wtot≈2%; molybdenum, polycryst.: WM=(37±2)%; Wtot= (42 ±4)% .