Chain-of-cubes iron nanoparticles prepared by borohydride reduction of acicular akaganeite particles

Ellipsoid shaped akaganeite (beta-FeOOH) particles, 70 nm long and 10 nm in diameter, were prepared by forced hydrolysis of ferric chloride. The beta-FeOOH particles were suspended in a lamellar liquid crystal phase at 0 degrees C and reduced with dilute sodium borohydride solution to iron particles. These conditions allowed us to slow the reduction reaction and isolate partially reduced iron particles. Transmission electron microscopy images showed that the particles were being reduced from the outside and there were nanometer-sized spherical iron clusters on the surface. Fully reduced iron particles were chains of cubes, with the cubes about 20 to 25 nm in size. The cubes were connected either corner to corner, edge to edge, or face to face. The face to face chains of cubes had the desired acicular shape, with aspect ratios exceeding five. This face to face chain of cubes microstructure was also observed in commercial iron particles. (C) 1999 American Institute of Physics. [S0021-8979(99)66308-3].