Nanocrystals as Model Systems for Pressure-Induced Structural Phase Transitions

COVER: Colorized, high-resolution transmission electron microscope lattice-fringe image of seven nanoparticles of UO 2 produced by the activity of sulfate-reducing bacteria. Note that the largest uraninite particle is <3 nm in diameter (Suzuki and Banfield, in preparation). Example: Predominantly inorganic nanoparticle formation in acid drainage 3 Other inorganic pathways for formation of nanoparticles 5 NANOPARTICLE FORMATION VIA BIOLOGICAL PATHWAYS 6 Example: Iron-oxidizing microbes and nanoparticle formation in AMD systems 6 Example: Nanoparticles formed by microbes in anoxic regions of AMD systems 10 Other examples of biological pathways that lead to nanoparticles in the environment 14 MICROBES, NANOPARTICES, AND MINERALOGICAL BIOSIGNATURES 16 NANOPARTICLES: HOW AND WHY ARE THEY DIFFERENT? 16 Introduction 16 Surface free energy and surface stress 19 Surface energy and particle size 20 Surface "pressure" and structural responses in nanoparticles 21 THERMODYNAMICS OF NANOPARTICLE SYSTEMS. 22 Minimization of the total free energy by phase transformation 23 Examples of phase stability in nanoparticle systems 29 Particle size and surface adsorption 35 Nanoparticles and organics 36 KINETICS IN NANOPARTICLE SYSTEMS 37 Brief review of kinetic models for macroscopic solids 37 Kinetics of amorphous-to-nanocrystalline transformations 38 Kinetics of crystalline transformations involving nanoparticles 39 Crystal growth of nanocrystalline particles 41 Aggregation and nucleation 44 Possible galvanic interactions in nanoparticle mixtures .: 46 Microstructure development in nanocrystals 47 SOME RESEARCH OPPORTUNITIES AND CHALLENGES 48 ACKNOWLEDGMENTS ".:..-51 REFERENCES 51