Survey of conditions to produce metal-boron amorphous and nanocrystalline alloys by chemical reduction

Chemical reduction synthesis (CRS) has been employed to produce binary and ternary M-B (M = Fe, Co, Ni and Mn) alloys of different structural arrangements: amorphous and amorphous/nanocrystalline alloys, the latter comprising nanometric crystalline particles embedded in an amorphous matrix. The optimum concentrations to obtain amorphous alloys are 0.1 M (100 ml, metallic salt) and 0.2 M (250 ml, reductor: NaBH(4)) as deduced from X-ray diffraction and room temperature Mossbauer spectroscopy. If equal concentrations and aerosol droplets are used, the amorphous/nanocrystalline structure is the largest fraction produced. From the variation of pH we predict the feasibility and optimisation of the reduction process, in particular, reaction mass yields. In some cases, the alloys have one or two peaks in the AC susceptibility at temperatures < 200 K. (C) 2001 Elsevier Science B.V. All rights reserved.