Kinetics and mechanism of the formation of rare earth-transition metal compounds by calciothermic reduction

摘要

Rare earth transition metal compounds, such asSmCo_5, Nd_2Fe_14B, Sm_2Fe_17 are industrially importantpermanent magnet materials in view of their high magneto-crystalline anisotropy. The calciothermic process of reduction ofrare earth oxides in the presence of transition metals has beenfound to be economically attractive. This paper deals with thekinetics and mechanism of the formation of rare earth-transitionmetal compounds, viz, SmCo_5, Nd_2Fe_14B and Sm_2Fe_17by the calciothermic reduction process. In order to study thekinetics of the formation of the said intermetallics, Fe and Cowires were inserted in the pellets containing Sm_2O_3 orNd_2O_3, Fe or Co and Ca granules. The pellets were heatedunder argon atmosphere at different temperatures and for variousdurations. The wires were removed from the pellets and the depthsand compositions of the reaction zones were measured with thehelp of a scanning electron microscope . and energy dispersivespectrometer, respectively. X-ray diffraction of the reacted producthas been used to determine the formation of various phases atdifferent temperatures. The experimental results have beenanalysed to compare the kinetics and mechanism of the formationof three intermetallics.