An ongoing challenge in geochemistry is accurately predicting rates of phase transformation in aqueous systems. We study phase transformations of oxides and sulfides, with particular attention to the roles that aggregation state, twinning and defects, primary particle size and shape, and composition play. Oriented aggregation can result in the incorporation of microstructural features, like defects and twin boundaries, that can serve as nucleation sites for phase transformation. We employ cryogenic transmission electron microscopy (TEM), in combination with dynamic light scattering, x-ray diffraction, and conventional TEM to elucidate the major control parameters that govern the kinetics of phase transformations of metal oxide nanoparticles. Rates of phase transformation, for example, increase substantially with decreasing particle size and increasing aggregation.

Phase transformations: Role of nanoparticle aggregation state

248th National Meeting (2014)

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