DECAY OF (FE1-XNIX)(0.96)S - DSC INVESTIGATION

The decay of a monosulphide solid solution (mss) with the composition (Fe1-xNix)(0.96)S was investigated by means of differential scanning c alorimetry in the temperature range, from 20 to 305 degrees C. Thermal effects of various natures were detected: i) Ordering-disordering in the Fe-Ni sublattice near 100 degrees C. ii) Pentlandite exsolution (e xothermal peak); the peak temperature varies from 180 to 240 degrees C and depends on the initial composition; the higher the Ni content, th e lower the exsolution temperature. iii) Magnetic-paramagnetic transit ion. The transition temperature decreases down to 220 degrees C as the Fe:Ni ratio is decreased from 10:0 to 4:6. Ni atoms are the defects i n the magnetic ordering of the mss generated by the Fe atoms in the me tal sublattice. Thus, the driving force for pentlandite exsolution is the removal of Ni atoms from the magnetic mss into the nonmagnetic pen tlandite. This is the reason why the Fe:Ni ratio in the generated pent landite is much higher than that in the initial mss.