Mössbauer studies of ferrihydrite for Fischer-Tropsch catalysts

The 6-line ferrihydrite sample for Ficher-Tropsch catalysts was prepared by using a combination of a co-precipitation technique and a spraydrying method. The crystallographic and magnetic properties of 6-line ferrihydrite sample were investigated by using x-ray diffractometer (XRD), vibrating sample magnetometer (VSM), and Mössbauer spectrometer. The XRD patterns of the ferrihydrite sample, measured at 295 K, showed 6-lines peak and its structure was found to be a single-phased hexagonal with space group of P3m1 according to JCPDS card. The temperaturedependent magnetization curves were measured under 1000 Oe between 4.2 and 300 K, and showed blocking temperature (TB) around 110 K. Also, Mössbauer spectra of the 6-line ferrihydrite sample were taken at various temperatures ranging from 4.2 to 295 K. At temperature below TB, the obtained spectra were analyzed as two-sextets for Fe sites, while At temperature above TB, the obtained spectra showed a doublet due to relaxation, resulting from the spin dynamic effect.