Characterization of the Surface Oxide Layer of Iron Ultrafine Particles

Abstract

The surface oxide layer of spherical iron ultrafine particles preapred by the gas vaporization method was investigated by X-ray photoelectron spectroscopy (XPS), MOssbauer spectroscopy and infrared (IR) absorption measurement. Fe 2 p XPS spectra showed the existence of iron hydroxide oxide on the surface of the oxide layer of iron ultrafine particles. It seemed that the surface of the oxide layer was not completely covered with iron hydroxide oxide, considering from the lowness of the value of C ls surface charging. The existence of FeO at the metal/oxide interface was not confirmed by depth profiling of the particles. The iron hydroxide oxide on the surface of the oxide layer was identified as amorphous iron hydroxide oxide by IR absorption measurement. Besides the iron(10 (Fe+) oxidation state, relatively large amount of iron(M) (Fe) oxidation state was observed in the MOssbauer spectra, and this implied the existence of both Fed: ), and r-Fe203 in the oxide layer. From the results of these experiments, the component of the surface oxide layer from the outside to the inner core of iron ultrafine particles was concluded as follows. amorphous Fe0(OH) and r-Fe20, I 7-Fe203 and F e s, / Fe The surface component of iron ultrafine parricles examined b y this, study are in good agreement with the surface component suggested by temperature programmed desorption (TPD) method in the previous studies. We have demonstrated the excellence of TPD method as a means for surface analysis of such small particles as ultrafine particles.