Decomposition of Fe2B by mechanical grinding

RODRÍGUEZ TORRES, C.E.; SÁNCHEZ, F.H.; MENDOZA ZÉLIS, L. A.

PHYSICAL REVIEW B - CONDENSED MATTER AND MATERIALS PHYSICS

Año: 1995 vol. 51 p. 12142 - 12148

0163-1829

The decomposition of the intermetallic compound Fe2B into its elemental constituents has been observed by Mössbauer-effect spectroscopy and x-ray diffraction after mechanical grinding in a horizontal vibratory mill for different times. The system evolution can be described in two stages. During the first one the rms strain increases up to about 6% and the Fe2B mean grain size reduces to approximately 50 nm. By the end of this step the energy accumulated by the compound becomes of the order of its formation enthalpy. During the second stage segregation of iron is observed at almost constant rate while some of the Fe2B stress is released and its mean crystallite size continues to diminish up to about 4 nm. A simple calculation indicates that for this degree of fragmentation, decomposition becomes energetically favorable. The occurrence of decomposition instead of amorphization is justified on the basis of kinetic arguments. The influence of air contamination of milling atmosphere has been investigated.