CEE Seminar: Lawrence Anovitz and Juliane Weber
Applications of Neutron Scattering in Geochemistry
Neutron scattering experiments provide to study a wide range of materials properties, including those of interest in geochemistry, providing advantages in sample penetration, and hydrogen, magnetism, and isotopic sensitivity. This talk will begin with an overview of neutron scattering studies, their applications and limitations and comparisons with X-ray approaches, then continue to an analysis of several examples where neutron analyses, coupled with outer approaches, played a critical role in understanding geological processes.
The nature of porosity changes during dissolution/reprecipitation reactions is one such problem critical to a wide range or geological problems including oil and gas recovery, aquifer evolution, nuclear waste storage and CO2 sequestration. We will first present a systematic experimental study of volume-reducing limestone dissolution and reprecipitation reactions in the model systems calcite-dolomite (CaCO3 - CaMg(CO3)2 and calcite-fluorite (CaCO3-CaF2). By varying the porosity and permeability of the parent rock, we tested the effect on the replacement reaction. Through the combination of X-ray and neutron (ultra) small angle scattering ((U)SAXS & (U)SANS), we quantified changes in the porosity as a function of depth within the sample and time. Porosity characterization was coupled with chemical mapping by scanning electron microscopy with energy-dispersive X-ray spectroscopy and time-of-flight secondary ion mass spectrometry. Our results demonstrate that the microstructure primarily controls replacement speed and the size regime of porosity development. Abundance of features that enhance the reactive surface area, such as porosity, grain boundaries or twinning within minerals, leads to a faster replacement via these pathways. We identified grain boundaries as reactive pathways via transmission electron microscopy analyses of a cross-section perpendicular to the grain boundary. Our results demonstrate the importance of the initial microstructure for the replacement reaction speed and mechanism.
(U)(SAXS/(U)SANS analysis such as those used in the first study have shown that geometerials (as well as metals and ceramics) tend to contain large numbers of sub-micron pores. Whereas these may contribute minimally to the overall porosity in many materials, they tend to dominate the reactive surface area. In addition, neutron and other studies have shown that the properties of fluids in many of the smallest of these pores deviate significantly from those expected for bulk fluids. At the extreme this leads to “ultraconfimenement,” where only a single fluid molecule can fit in a given space. We will conclude our talk by showing how this understanding lead to the discovery of a new material – “quantum water.”
Join this seminar on Zoom
Thursday, March 23 at 4:05pm to 5:00pm
John D. Tickle Engineering Building, 405
851 Neyland Dr, Knoxville, TN 37996
- Event Type
- Civil and Environmental Engineering
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