Formation of nanosized particles encapsulated in boron nitride during low-temperature annealing of mechanochemically treated Fe-BN mixtures

Electron microscopic investigations and X-ray studies of mechanically activated mixtures of iron and boron nitride provide evidence of the transformation of hexagonal boron nitride into the amorphous state, which is shows up as a halo with maximum at d = 3.35 Angstrom in the electron diffraction patterns. According to the obtained electron microscopic data, the particles of iron and boron nitride after mechanical activation form aggregates with a size of 300-1000 nm. The iron particles exhibit a rather broad size distribution (from 3-7 nm to 100 nm), while the minimal size of the boron nitride particles is several tens of nanometers. Annealing of iron samples with boron nitride after preliminary mechanical activation, at a temperature of 860degreesC, caused the formation of nanosized encapsulated particles of iron boride Fe2B. The surface of the Fe2B nanoparticles were coated with a shell composed of hexagonal boron nitride, 5-15 nm thick. The size of the encapsulated particles varies within a rather broad range from 30 to 50 nm to several hundred nanometers. (C) 2003 Elsevier B.V. All rights reserved.