DETERMINATION OF POROSITY OF REDUCED HEMATITE BY STEREOLOGIC METHODS

The stereologic analysis of a solid grain has been applied for determi nation of its porosity. The investigations were carried out on a natur al hematite grain reduced to magnetite at 723K. Stereologic analysis e nabled the porosity of this material to be determined on the basis of independently measured grain contours and volume fractions of grain co mponents: hematite, magnetite and pores. A conformity criterion has be en formulated, regarding determination of grain volume on the basis of known densities of components and their measured volume fractions in the grain, and on the basis of weight and apparent grain density measu rements. The volume increase accompanying reduction of hematite to mag netite, determined from these independent measurements, was in the ran ge 7-19%. By measuring Feret's diameter, the volume of the convex enve lope of the grain increased as a result of phase transformation by abo ut 11%. Simultaneously, the volume of the solid phase was found to dec rease by 1.5%. The total porosity of the reduced grain, determined by stereologic analysis amounted to 17.5%; 7.7% of which was related to c racks and large pores, and 9.8% to small pores in the magnetite phase. The porosity value determined by the classical mercury method was app roximately the same.