This research will explore how crystals of nanometer dimensions (nanocrystals) grow, and how rates and mechanisms of subsequent reactions are affected by particle size. Nanocrystalline materials are products of chemical weathering and microbial biomineralization and account for much of the reactive surface area in weathered rocks, soils, and sediments. The modified stability and reactivity of nanocrystals is also of significance to materials science. Recent experimental work on coarsening of nanocrystalline materials has revealed that under a subset of conditions, particles grow by crystallographically oriented attachment. This largely unrecognized mechanism involves reduction in surface energy by direct elimination of surfaces. Research will examine the importance of coarsening by oriented attachment in nature and will quantify the effects of this mechanism on reaction kinetics. Experimental work will continue to use the convenient and important TiO2 system and characterization studies will primarily involve high-resolution transmission electron microscopy and X-ray diffraction. The product of this work will be new understanding of kinetics in the nanocrystalline size domain.
