abstract
High-energy ball milling is a relatively new process for the synthesis of technologically useful compounds that require high temperatures in the conventional solid-state reaction method. It is thought that high-impact energy transferred to microscopic amounts of powder momentarily trapped between two colliding balls leads to a local transient of high pressure and temperature that drives the reaction at the surface of the trapped particles. The technique of ball milling has been successfully used to produce nanocrystals of the sillenite phase of bismuth silicate (BSO), and its titanate (BTO) and germanate (BGO) homologues. Our aim in this paper is to see, experimentally, whether passage through an intermediate phase occurs en route to the final product. The results of our study using various analytical techniques show that indeed, in the case of BSO and BTO, an intermediate phase is formed temporarily along the grinding route. The SEM pictures of the powders in the various stages of the grinding process also indicate that a process of phase transformation takes place at the surface of the crystals. We have not been able to identify the precise structure of the intermediate phase, but show that it is an unstable phase that transforms with heat treatment preferentially into the desired sillenite phase in the case of BTO and to the reactants in the case of BSO.
subject category
Materials Science; Physics
authors
Carrasco, MF; Mendiratta, SK; Marques, L
our authors
