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Neutron Scattering and Diffraction Studies of Fluids and Fluid-Solid Interactions

Chemical Sciences Division Oak Ridge National Laboratory Oak Ridge, Tennessee 37831-6110, U.S.A., e-mail: coledr@ornl.gov

Kenneth W. Herwig and Eugene Mamontov

Spallation Neutron Source Oak Ridge National Laboratory Oak Ridge, Tennessee 37831-6475, U.S.A.

John Z. Larese

Department of Chemistry University of Tennessee Knoxville, Tennessee, 37996, U.S.A.

The first 20% of the full text of this article appears below.

	INTRODUCTION

 
Role of fluids in earth systems with the focus on H₂O
Geologic fluids (defined liberally as gases, liquids, and supercritical solutions) act as reaction media, reactants, and carriers of energy and matter in the natural environment. Among the many different types of geologic fluids, those containing volatile C-O-H-N-S species and those enriched in chloride salts (brines) are of particular interest. They occur widely in varied geochemical settings, commonly contain significant quantities of dissolved and suspended compounds (complex hydrocarbons, organic macromolecules, colloids/nanoparticles), play a crucial role as primary reaction media, and are important sources and sinks of greenhouse gases. The consequences of coupled reactive-transport processes common to most geological environments depend on the properties and reactivities of these fluids over broad ranges of temperature, pressure and fluid composition. The relative strengths of complex molecular-scale interactions in geologic fluids, and the changes in those interactions with temperature, pressure, and fluid composition, are the fundamental basis for observed fluid properties. Understanding these solvent-mediated interactions for broad classes of solutes and suspensions in natural systems over the range of conditions typical of geologic fluids will greatly improve our capability to model and predict fluid behavior, reactivity, and the partitioning of elements and isotopes between coexisting species and phases.

Complex intermolecular interactions of C-O-H-N-S fluids (H₂O, CO₂, H_2, H₂S, N₂, CH₄) result in their unique thermophysical properties, including large deviations in the volumetric properties from ideality, vapor-liquid equilibria, and critical phenomena. Water is one of the best general solvents for inorganic materials due to its molecular structure and the distribution of electric charge (Neilson et al. 2002). In aqueous fluids containing various solutes (electrolytes, metals, organic/bio-molecules), numerous solute-solute and solute-solvent reactions lead to specific interactions, including complexation, binding, local ordering, and clustering. Indeed, a key goal in geochemistry is to develop a comprehensive understanding of the thermophysical properties, structures, . . . [Full Text of this Article]

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