International audienceIn support of the selection of structural materials for heat exchangers in helium-cooled high temperature reactors, the oxidation behaviour of the Ni-base chromia-former alloy 230 was investigated at 850 A degrees C in diluted helium atmosphere with a low water vapour content. In such a media, the equivalent partial pressure of oxygen (imposed by the 850 degrees C in diluted helium atmosphere with a low water vapour content. In such a media, the equivalent partial pressure of oxygen (imposed by the P(H2O)/PH(2) ratio) is very low (P(O2)(eq) around 10(-16) Pa). The equivalent partial pressure of oxygen has no straight influence on the parabolic rate constant (k(p)); on the other hand, P(H2) and P(H2O) demonstrate a complex influence on k(p). Photoelectrochemistry analyses revealed that this oxide could simultaneously contain two types of cationic defects. Specific oxidation tests with D(2)O showed that the oxide scale also contains hydrogen. A mechanist model is proposed in order to describe the scale growth using both cationic defects. Those theoretical results show, at least qualitatively, how PH(2) and PH2O may concurrently influence the oxidation rate

No abstract

No abstract

Alloy 230 (also named Haynes® 230) was tested as interconnect for production of hydrogen via High Temperature Vapor Electrolysis (HTVE). Samples were oxidized at 800°C in the both atmospheres representative of the HTVE operating conditions: Ar-1%H2-9%H2O (for cathode side) and air (for anode side). The high temperature oxidation behaviour was studied in both atmospheres together with the electrical conductivity of the thermally grown oxide scales. Oxidation kinetics indicated lower oxidation rate in H2/H2O compared to air (kp = 3.8 .10-15 g2.cm-4.s-1 in H2/H2O and kp = 1.6 .10-14 g2.cm-4.s-1 in air). The corrosion products were characterized by scanning electron microscopy associated with X-ray diffraction analyses and energy dispersive X-ray analyses. The sample electrical behaviour was evaluated by determining the Area Specific Resistance (ASR). The ASR was higher in H2/H2O (ASR = 1 ohm.cm2) than in air (ASR = 0.04 ohm.cm2). The diffusion of proton or hydrogen containing species through the oxide scale is proposed to be responsible for the increase of the electrical conductivity in cathode side.