A Mossbauer study of chromite-magnesia refractories.

A range of natural chrome ores, containing iron in two valence states, have been investigated using the technique of Mossbauer spectroscopy. The instrumentation required to cry out the technique was studied and an additional item of equipment was designed and constructed to extend the temperature range over which the effect could be observed. All the chrome ores yielded a complex spectra which could be attributed to a combination of octahedrally and tetrahedrally co-ordinated Fe2+ and Fe3+ quadrupole doublets. A model for fitting the spectra was devised assuming the presence of octahedrally co-ordinated Fe3+ and tetrahedrally co-ordinated Fe2+. The inhomogeneous nature of the samples caused a broadening of the tetrahedral Fe2+ contribution which was fitted as a distribution of three doublets. The Mossbauer parameters obtained were compared with those of pure compounds of a similar structure. Spectra recorded from 12K to 600K enabled effective Debye temperatures to be calculated. Second order Doppler shift (S.O.D.S.) calculations gave values for theta[D] of 385K and 658K for the Fe2+ and Fe3+ contributions respectively. Absorption area data gave similar values. An examination of the temperature dependence of the quadrupole splitting of the Fe2+ contributions appeared to confirm the validity of the proposed fitting model. Estimations of the Fe2+ / Fe3+ ratio were made using the data obtained and yielded values of 1.6 - 3.6.