Study of relaxation effects in the 57Fe Mössbauer spectra of carbon-supported iron carbide particles

A modified model of relaxation for systems containing both a magnetic field and an electric field gradient is presented. This model is used to explain the 57Fe Mössbauer spectra of small iron χ-carbide particles supported on two types of high surface area carbon. On the basis of this model, it is concluded that χ-carbide particles interact weakly with graphitic carbon, but very strongly with nearly amorphous carbon. On the nearly amorphous carbon, the particles may, in fact, have an unusually high surface-to-volume ratio.