The Amorphization of Ln-Si (Ln=Rare Earth Metal) Alloy Powders by Mechanical Alloying

Abstract

Crystalline powders of Si and Ln (Ln=Sm, Nd, Gd, Tb, Dy, Er) in the composition ratio Si : Ln=2 : 1 were mechanically alloyed in an inert atmosphere using a laboratory ball mill. The progress of the mechanical alloying was identified by X-ray diffraction. The amorphization reaction between Si and Ln proceeded according to a second-order formula. The sequence of the rate of amorphization reaction for the Si-Ln system was Sm>Gd>Tb>Nd≥Dy>Er. The reaction rate was affected by the crystal structure of Ln. In the case of Gd, Tb, Dy and Er having the same structure (hexagonal closed packed), the reaction rate was correlated to the volume ratio (V_Ln⁄V_Si). In the Sm-Si system, which had the fastest MA rate, Sm has a unique structure in which triangular planes of Sm atoms overlap fourfold and would be easily attacked by Si atoms. In Nd-Si system, the rate would be affected by the structure of double hexagonal closed packed of Nd. The crystallization of Si-Ln was studied by means of X-ray diffraction, differential thermal analysis and electrical resistivity measurement.