Morphological control of particles

The objective of this review is to highlight the theoretical and practical aspects of particle morphological control. Materials with directional prope rties are opening new horizons in material science. structural, optical, an d electrical properties can be greatly augmented by the fabrication of comp osite materials with anisotropic microstructures or with anisotropic partic les uniformly dispersed in an isotropic matrix. Examples include structural composites, magnetic and optical recording media, photographic film, and c ertain metal and ceramic alloys. The new applications and the need for mode l particles in scientific investigations are rapidly outdistancing the abil ity to synthesize anisotropic particles with specific chemistries and narro wly distributed physical characteristics (e.g. size distribution, shape, an d aspect ratio). Anisotropic particles of many compositions have been produ ced but only a few (gamma-Fe2O3 and AgI) are produced with any degree of ch emical and physical control. These two examples are the result of Literally decades of study. Unfortunately, the science and technology (mainly the te chnology) that have evolved are maintained as proprietary information. Thus , while we generally know what systems yield single crystal, anisotropic-sh aped particles, we do not know how to make powders of these crystals with t he desired control of shape uniformity, aspect ratio and phase composition. Particle shape control is a complex process requiring a fundamental unders tanding of the interactions between solid state chemistry, interfacial reac tions and kinetics, and solution (or vapor) chemistry. During synthesis of Ether than a large single crystal the parameters controlling crystal growth must be balanced with the requirements for anisotropic powder nucleation a nd growth. Although there has been considerable progress in large single cr ystal growth and the synthesis of powders composed of monodispersed, spheri cal particles, these efforts have not often been transferred to the synthes is of anisotropic particles. (C) 2000 Elsevier Science Ltd. All rights rese rved.