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.