Chemical, structural and magnetic studies of natural chromites.
Author
Al-Shihiyah, Maryam Hamdan Abdullah.
English abstract
Thirteen specimens of natural chromite from the Oman ophiolite separated by magnetic separation, density separation and hand picking were characterized by X ray diffraction and scanning electron microscopy. The X-ray diffraction patterns obtained at room temperature showed that all the specimens studied have a face centered cubic spinel structure. Nine of the samples were studied by Mössbauer spectroscopy in the paramagnetic region between 80 K and 300 K. The measured Mössbauer spectra decomposed into three doublets; two attributed to Feat at the tetrahedral (A1, A2) sites and the third attributed to Fe** at the octahedral (B) site. The ferrous/ferric ratio obtained from the Mössbauer analysis together with the atomic concentration derived from the microprobe data were used to derive the chemical formulae for the nine specimens. The data indicate an essentially ordered arrangement of iron atoms in the crystal structure of natural chromite. The magnetic behavior of six specimens was investigated by means of dc magnetic susceptibility measurements in the paramagnetic region. The measured magnetic susceptibility showed a kink at about 160 K in the curve of inverse magnetic susceptibility and temperature that was proposed to the reorientation of the spins of some cations at the octahedral site due to a distortion in the crystal symmetry.
