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Void formation in a duplex scale formed on Fe-5Cr alloy at 773 K has been elucidated by oxygen chemical potential distribution, the flux of oxide ion and its divergence. The calculation predicts that voids preferentially form at the interface between inner and outer scales in the low oxygen partial pressure in which the predominant defect of iron is interstitial ion. The flux of oxide ion changes discontinuously at this interface and the divergence of the flux gives voids. Calculated volume fraction of voids at this interface is in good agreement with that has been measured.

New apparatus for direct heating of alloy specimen in the gas stream has been developed in order to analyze not only reforming reaction but also carbon deposition on the alloy surface in low S/C environment. A foil of iron can be heated directly to 1073 K by the Joule heat from the specimen. Temperature of the foil can be kept at 1073 plus-minus 10 K by using AC power regulator connected with temperature controller. Temperature of the foil is not influenced by the thermal radiation from the oxide scale during the oxidation. One experiment has been carried out to check carbon deposition on the ferritic alloys at 1073 K in the CH4-H2O gas mixture. Oxidation and carbon deposition simultaneously occur on the alloy surface and no carbon deposition is observed in the chamber. Developed apparatus is suitable for investigation of carbon deposition and carburization of alloys in low S/C environment.

Voids are frequently generated and dispersed in oxide scales formed in high temperature oxidation of metals. The divergence of ionic flux may play an important role in the void formation in a growing scale. Kinetic equations were derived for describing chemical potential distribution, ionic fluxes and their divergence in the scale. The divergence was found to be the measure of void formation. Defect chemistry in scales is directly related to the sign of divergence and gives an indication of the void formation behavior. The quantitative estimation on the void formation was successfully applied to a growing magnetite scale in high temperature oxidation of iron at 823 K.

A quantitative elucidation of the void formation in a growing scale with Schottky defects and p-type conduction during high temperature oxidation of metals. The evaluation of the divergence of ionic fluxes indicates that (1) Voids form in the scale preferentially in the vicinity of the metal/scale interface, (2) The volume of voids increases in a parabolic manner, (3) The volume fraction of voids and the scale is independent of time. The comparison between the calculation and the experimentally observed scale microstructure of NiO and CoO confirmed well the validity of the prediction.

Fe-Cr ferritic alloy is one of the candidates of interconnects. This alloy has a good oxidation resistance by formation of a protective Cr2O3 scale, which also protects from carburization. Using hydrocarbon gas as fuel, Cr concentration near the alloy surface may decrease by the formation of Cr carbides. The formation of the protective Cr2O3 scale is failed. It is expected that Nb addition to Fe- Cr alloy prevents from carburization because Nb has stronger affinity to carbon than Cr. Fe-16 mass%Cr and Fe-16 mass%Cr- 1.0 mass%Nb alloys were exposed to the atmosphere with S/C=1.1 at 1073 K up to 604.8 ks. In the case of Fe-16Cr alloy, carburization occurred extensively and internal Cr oxides and carbides were formed inside of the alloy. No Cr carbides were observed in all parts of the Nb added alloy. This indicates that carburization resistance is improved by the addition of Nb.

Estimation of void formation in oxide scale is important for predicting exfoliation of the oxide scale. Void formation in magnetite scale formed on iron at 823 K has been elucidated by chemical potential distribution, flux of oxide ion and its divergence. This calculation also estimates a effective diffusion coefficient, which includes both lattice diffusion and grain boundary diffusion in magnetite scale. The resulting effective diffusion coefficients give the quantitative elucidation of the morphology of the magnetite scale. The divergence of oxide ion explains well a position and an amount of void in magnetite scale.

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New apparatus for direct heating of alloy specimen in the gas stream has been developed in order to analyze not only reforming reaction but also carbon deposition on the alloy surface in low S/C environment. A foil of iron can be heated directly to 1073 K by the Joule heat from the specimen. Temperature of the foil can be kept at 1073 plus-minus 10 K by using AC power regulator connected with temperature controller. Temperature of the foil is not influenced by the thermal radiation from the oxide scale during the oxidation. One experiment has been carried out to check carbon deposition on the ferritic alloys at 1073 K in the CH4-H2O gas mixture. Oxidation and carbon deposition simultaneously occur on the alloy surface and no carbon deposition is observed in the chamber. Developed apparatus is suitable for investigation of carbon deposition and carburization of alloys in low S/C environment.

Fe-Cr ferritic alloy is one of the candidates of interconnects. This alloy has a good oxidation resistance by formation of a protective Cr2O3 scale, which also protects from carburization. Using hydrocarbon gas as fuel, Cr concentration near the alloy surface may decrease by the formation of Cr carbides. The formation of the protective Cr2O3 scale is failed. It is expected that Nb addition to Fe- Cr alloy prevents from carburization because Nb has stronger affinity to carbon than Cr. Fe-16 mass%Cr and Fe-16 mass%Cr- 1.0 mass%Nb alloys were exposed to the atmosphere with S/C=1.1 at 1073 K up to 604.8 ks. In the case of Fe-16Cr alloy, carburization occurred extensively and internal Cr oxides and carbides were formed inside of the alloy. No Cr carbides were observed in all parts of the Nb added alloy. This indicates that carburization resistance is improved by the addition of Nb.