鉄超微粉のガス放出挙動と大気安定性

抄録

Temperature-programmed desorption (TPD) experiments of iron ultrafine powders (UFPs) prepared by the “hydrogen plasma-metal” reaction method, which had been subjected to a slow oxidation and exposure to air, was carried out, and compared with those of iron UFPs prepared by the vaporization method. These thermal desorption spectra were similar to each other. This means that the gas evolution spectra do not depend on the preparation methods of the powders, but depend on the surface conditions of the iron.
Surface compounds of iron UFPs after exposure to air and their role in the passivity in air were also investigated from the thermal desorption characteristics of the iron UFPs prepared by the vaporization method. After reduction, re-slow oxidation and followed by exposure to water vapour or mixture of water vapour and oxygen, thermal desorption experiments were carried out for the iron UFPs prepared by a vaporization method. The surface layers of iron UFPs consisted of Fe₃O₄, γ-Fe₂O₃ and iron oxyhydroxide. The formation of Fe₃O₄ or γ-Fe₂O₃ on the clean iron surface and followed by the formation of iron oxyhydroxide on these oxides were effective for the stabilization of the powder against atmospheric oxidation (corrosion). We demonstrate that iron UFPs, which have a large specific surface area, are excellent as a sample for the investigation of the gas adsorption and desorption characteristics of the iron surface.