Low temperature reduction of SmCl3 during mechanical milling

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Rare earth metals with the exception of Sm, Eu and Yb can be refined by the calciothermic reduction of the oxide or halide [1,2]. With Sm, a metallothermic reduction is only possible if one uses more electronegative and costly reductants such as La or mischmetal. For example, the calciothermic reduction of SmCl[sub 3] results in the formation of SmCl[sub 2] due to the high stability of the divalent chloride. Examination of reaction free energies indicates that it should be possible to refine Sm from SmCl[sub 3] at low temperatures using Na as the reductant. The free energy curves for Sm and SmCl[sub 2] reactions cross at [approximately]400K, with the Sm reaction having the more negative free energy change at low temperatures. Recent studies have shown the mechanical alloying process provides a highly effective method for inducing chemical reactions at low temperatures. The refining of a number of metals, including Ti, Ta, Er and Gd from chloride precursors, has been demonstrated. In this paper the authors report the synthesis of Sm at low temperatures during the mechanical milling of SmCl[sub 3] and Na.