摘要:

IntroductionNanoscale phenomena are ubiquitous and important to geoscience. The realization is growing that many outcomes and rates of geochemical processes are governed by phenomena at the nanometer scale, often in or at the surface of small particles. Surface interactions probably exert a disproportionate influence on the structure, chemistry, and movement of natural and anthropogenic nanomaterials in the Earth. In many cases, traditional distinctions between solutes, colloids and solids become vague. Nanoparticles, with sizes in the 1–100 nm range, lie in the realm between dissolved molecular clusters and crystalline macroscopic solids. Their properties are different from those of either.Fine grained oxides precipitated from aqueous solution often crystallize in structures different from those of coarsely crystalline materials: γ-alumina instead of corundum, anatase and brookite instead of rutile, maghemite instead of hematite, and a host of complex hydrous iron oxyhydroxides. It has been suspected that differences in surface energy stabilize, as nanoparticles, polymorphs that are metastable in the bulk.1,2Oxide melt solution calorimetry has recently been used to measure enthalpies of phase transformation and surface enthalpies of different oxide polymorphs.3Calorimetric measurements are generally confirming this hypothesis of energy crossover between polymorphs at the nanoscale. This review summarizes recent work in the UC Davis Thermochemistry Facility on the energetics of nanophase oxides. For a broader overview of nanoparticles and Earth processes, the recent review volume on nanoparticles in the environment4should be consulted.

ISSN:1467-4866    

DOI:10.1039/b308711e

出版商:RSC    

年代:2003

数据来源: RSC