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Electrical Responses of Modified Mineral Surfaces as Observed With Spectral Induced Polarization and Atomic Force Microscopy
Atomic force microscopy (AFM) and spectral induced polarization (SIP) are widely used to investigate the electrical properties of mineral surfaces at vastly different scales of measurement. We compare AFM and SIP measurements made on two different materials (glass beads and silica gel) subjected to...
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Published in: | Journal of geophysical research. Solid earth 2024-02, Vol.129 (2), p.n/a |
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Main Authors: | , , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | Atomic force microscopy (AFM) and spectral induced polarization (SIP) are widely used to investigate the electrical properties of mineral surfaces at vastly different scales of measurement. We compare AFM and SIP measurements made on two different materials (glass beads and silica gel) subjected to etching, deposition of iron oxide particles, and inclusion of calcite grains. We found that the treatments produced qualitatively consistent behaviors in the AFM and SIP data. Direct AFM measurements of surface charge density for silica and calcite surfaces were quantitatively compared to values estimated from the SIP results using a grain polarization model. No statistically significant difference (at a 95% confidence level) was found between the surface charge density of silica estimated by AFM (2.3 ± 6.6 mC/m2 for glass beads and 1.6 ± 0.1 mC/m2 for silica gel) versus SIP (5.4 ± 4.4 mC/m2 for glass beads and 1.6 ± 0.5 mC/m2 for silica gel). The surface charge density for calcite determined by AFM (43.5 ± 12.9 mC/m2) was approximately 19 times higher than that found for silica. While the charge density of calcite surfaces determined by SIP was also generally higher than that found for silica, different treatments produced significantly different values between 4.7 and 258 mC/m2 (with a maximum 95% CI of ±8.7 mC/m2). Several possible explanations exist for the range of the observed SIP measurements, including aging of the calcite surfaces. Overall, this study suggests the potential for the complementary use of AFM and SIP measurements to constrain future investigations of polarization mechanisms in porous media.
Plain Language Summary
The electrical properties of rock and mineral surfaces are sensitive to their physical and chemical environment and are therefore important for earth applications ranging from detecting minerals to monitoring microbial growth. In most environmental settings, these properties are controlled by ions that move through the open pore spaces between grains and along mineral surfaces, where they are more tightly bound to charged surfaces. Atomic force microscopy (AFM) provides a way to directly measure the charge present on a mineral surface, but makes measurements at a microscopic scale and is not practical for field investigations or monitoring real‐time experiments in porous media. In contrast, spectral induced polarization (SIP) can measure electrical properties averaged over volumes of earth in the lab or field, but it is not always |
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ISSN: | 2169-9313 2169-9356 |
DOI: | 10.1029/2023JB028377 |