The coercive force of fine particles of monoclinic pyrrhotite (Fe7S8), between 77 K and 600 K

Abstract

The temperature dependence of coercive force (Hc) between 77 K and 600 K has been investigated for fine particles of monoclinic pyrrhotite (Fe7S8) of < 1 mm and 1- 30 mm particle sizes. The study has shown that Hc is strongly dependent on temperature, as temperature rises above room temperature (293 K) to near the Curie point (Tc = 593 K). On the other hand, Hc was observed to be weakly dependent on temperature, between liquid Nitrogen temperature (77 K) and room temperature. For the entire temperature range, the data can be expressed satisfactorily as a second order polynomial, Hc (T) = aT 2 + bT + g where a, b and g are numerical constants for a given particle size fraction. The form of this analytic expression is different from that obtained by the authors for the coercive force dependence on temperature which they plausibly expressed in the form Hc (T) µ (1 - T/Tc)q where q < 1, for the temperature range 293-573 K, but which breaks down below 293 K. By considering the variation of the coefficient g with particle size, within the size range 1 and 30 mm it is shown that g(L) = 75.6 L-0.33 kA m-1.



JOURNAL OF THE GHANA SCIENCE ASSOCIATION Volume 1 Number 2, January (1999) pp. 90-99