Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “MASKING”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,369 records · Page 76
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Automated Coupling of Nanodroplet Sample Preparation with Liquid Chromatography–Mass Spectrometry for High-Throughput Single-Cell Proteomics

Single-cell proteomics can provide critical biological insight into the cellular heterogeneity that is masked by bulk-scale analysis. Here, we have developed a nanoPOTS (nanodroplet processing in one pot for trace samples) platform and demonstrated its broad applicability for single-cell proteomics. However, because of nanoliter-scale sample volumes, the nanoPOTS platform is not compatible with automated LC-MS systems, which significantly limits sample throughput and robustness. To address this challenge, we have developed a nanoPOTS autosampler allowing fully automated sample injection from nanowells to LC-MS systems. We also developed a sample drying, extraction, and loading workflow to enable reproducible and reliable sample injection. The sequential analysis of 20 samples containing 10 ng tryptic peptides demonstrated high reproducibility with correlation coefficients of >0.995 between any two samples. The nanoPOTS autosampler can provide analysis throughput of 9.6, 16, and 24 single cells per day using 120, 60, and 30 min LC gradients, respectively. As a demonstration for single-cell proteomics, the autosampler was first applied to profiling protein expression in single MCF10A cells using a label-free approach. At a throughput of 24 single cells per day, an average of 256 proteins was identified from each cell and the number was increased to 731 when the Match Between Runs algorithm of MaxQuant was used. Using a multiplexed isobaric labeling approach (TMT-11plex), ~77 single cells could be analyzed per day. We analyzed 152 cells from three acute myeloid leukemia cell lines, resulting in a total of 2558 identified proteins with 1465 proteins quantifiable (70% valid values) across the 152 cells. These data showed quantitative single-cell proteomics can cluster cells to distinct groups and reveal functionally distinct differences.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Spatially Resolved Proteome Profiling of <200 Cells from Tomato Fruit Pericarp by Integrating Laser-Capture Microdissection with Nanodroplet Sample Preparation

Due to sensitivity limitations, global proteome measurements generally require large amounts of biological starting material, which masks heterogeneity within the samples and differential protein expression among constituent cell types. Methods for spatially-resolved proteomics are being developed to resolve protein expression for distinct single cell types among highly heterogeneous tissues, but have primarily been applied to mammalian systems. Here we evaluate the performance of cell-type-specific proteome analysis of tomato fruit pericarp tissues by a platform integrating laser capture microdissection (LCM) and a recently developed automated sample preparation system (nanoPOTS, Nanodroplet processing in One pot for Trace Samples). Tomato fruits were cryosectioned prior to LCM, and tissues were dissected and captured directly into nanoPOTS chips for processing. Following processing, samples were analyzed by nanoLC-MS/MS. Approximately 1900 unique peptides and 422 proteins were identified on average from ~0.04 mm2 tissues comprising ~ 8-15 parenchyma cells. Spatially-resolved proteome analyses were performed using cells of outer epidermis, collenchyma, and parenchyma. Using =200 cells, a total of 1,870 protein groups were identified and the various tissues were easily resolved. The results provide spatial and tissue-specific insights into key enzymes and pathways involved in carbohydrate transport and source-sink relationships in tomato fruit. Of note, at the time of fruit ripening studied here, we identified differentially abundant proteins throughout the pericarp related to chlorophyll biogenesis, photosynthesis, and especially transport.

Liang, Yiran↗
DOE OSTI2020

Kinetics and Optimization of the Lysine–Isopeptide Bond Forming Sortase Enzyme from Corynebacterium diphtheriae

Site-specifically modified protein bioconjugates have important applications in biology, chemistry, and medicine. Functionalizing specific protein side chains with enzymes using mild reaction conditions is of significant interest, but remains challenging. Recently, the lysine–isopeptide bond forming activity of the sortase enzyme that builds surface pili in Corynebacterium diphtheriae ( Cd SrtA) has been reconstituted in vitro. A mutationally activated form of Cd SrtA was shown to be a promising bioconjugating enzyme that can attach Leu-Pro-Leu-Thr-Gly peptide fluorophores to a specific lysine residue within the N-terminal domain of the SpaA protein ( N SpaA), enabling the labeling of target proteins that are fused to N SpaA. Here we present a detailed analysis of the Cd SrtA catalyzed protein labeling reaction. We show that the first step in catalysis is rate limiting, which is the formation of the Cd SrtA-peptide thioacyl intermediate that subsequently reacts with a lysine ε-amine in N SpaA. This intermediate is surprisingly stable, limiting spurious proteolysis of the peptide substrate. We report the discovery of a new enzyme variant ( Cd SrtA Δ ) that has significantly improved transpeptidation activity, because it completely lacks an inhibitory polypeptide appendage (“lid”) that normally masks the active site. We show that the presence of the lid primarily impairs formation of the thioacyl intermediate and not the recognition of the N SpaA substrate. Quantitative measurements reveal that Cd SrtA Δ generates its cross-linked product with a catalytic turnover number of 1.4 ± 0.004 h –1 and that it has apparent K M values of 0.16 ± 0.04 and 1.6 ± 0.3 mM for its N SpaA and peptide substrates, respectively. Cd SrtA Δ is 7-fold more active than previously studied variants, labeling >90% of N SpaA with peptide within 6 h. The results of this study further improve the utility of Cd SrtA as a protein labeling tool and provide insight into the enzyme catalyzed reaction that underpins protein labeling and pilus biogenesis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Disorderly Conduct of Benzamide IV: Crystallographic and Computational Analysis of High Entropy Polymorphs of Small Molecules

Benzamide, a simple derivative of benzoic acid and a common intermediate of pharmaceutical compounds, was reported to form two polymorphs in 1832, but the single crystal structure of the more stable form was not solved until 1959. Nearly 50 years later, the second form was characterized by powder diffraction, followed shortly thereafter by characterization of a third form, a polytype of the most thermodynamically stable Form I. These two new forms, Forms II and III, are metastable. Herein, we describe a fourth polymorph, Form IV, discovered by melt crystallization concurrently with its crystallization under confinement at small length scales (<10 nm), where it is stable indefinitely. Form III exists under confinement in larger pores, and melting point data for different pore sizes corroborate the existence of Form IV below 10 nm. Form IV is highly disordered, precluding indexing of powder diffraction data other than hk0 reflections. Nonetheless, a combination of powder X-ray diffraction and computational crystal structure prediction reveals that Form IV contains a 2D motif resembling that of Form II, but with longrange order in the third dimension masked by ubiquitous stacking faults. This approach relies on distilling a large number of candidate structures to a few possible disorder models based on benzamide tetrads that organize in 2D parquet-like tiles, with organization along the third dimension, that can be modeled with various stacking fault configurations having distinct intermolecular interactions and translations in the dimension orthogonal to the tiling planes. These observations reveal a bewildering crystallographic complexity for such a simple molecule. Nonetheless, the approach described herein demonstrates that challenging structures that may be abandoned prematurely because of poor crystallinity, twinning, or disorder can be solved.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Phenazine-1-Carboxylic Acid-Producing Bacteria Enhance the Reactivity of Iron Minerals in Dryland and Irrigated Wheat Rhizospheres

Phenazine-1-carboxylic acid (PCA) is a broad-spectrum antibiotic produced by rhizobacteria in the dryland wheat fields of the Columbia Plateau. PCA and other phenazines reductively dissolve Fe and Mn oxyhydroxides in bacterial culture systems, but the impact of PCA upon Fe and Mn cycling in the rhizosphere is unknown. Here, concentrations of dithionite-extractable and poorly crystalline Fe were approximately 10% and 30–40% higher, respectively, in dryland and irrigated rhizospheres inoculated with the PCA-producing (PCA + ) strain Pseudomonas synxantha 2–79 than in rhizospheres inoculated with a PCA-deficient mutant. Yet, rhizosphere concentrations of Fe(II) and Mn did not differ significantly, indicating that PCA-mediated redox transformations of Fe and Mn were transient or were masked by competing processes. Total Fe and Mn uptake into wheat biomass also did not differ significantly, but the PCA + strain significantly altered Fe translocation into shoots. X-ray absorption near edge spectroscopy revealed an abundance of Fe-bearing oxyhydroxides and phyllosilicates in all rhizospheres. These findings indicate that the PCA + strain enhanced the reactivity and mobility of Fe derived from soil minerals without producing parallel changes in plant Fe uptake. This is the first report that directly links significant alterations of Fe-bearing minerals in the rhizosphere to a single bacterial trait.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Atomic Energy Accuracy of Neural Network Potentials: Harnessing Pretraining and Transfer Learning

Machine learning-based interatomic potentials (MLIPs) have transformed the prediction of potential energy surfaces (PESs), achieving accuracy comparable to ab initio calculations. However, atomic energy predictions, often assumed to lack physical meaning, remain underexplored. In this study, we demonstrate that inaccuracies in atomic energy predictions reduce the robustness and transferability of Neural Network Potentials (NNPs) and atomic energy error can be masked in total energy predictions due to error cancellation. Here, we validate this finding using challenging configurations involving deformation and failure under tensile loading. By pretraining atomic energy predictions using empirical potentials and applying transfer learning with density functional theory (DFT) data, we achieve notable improvements in the accuracy of total energy, forces, and stress predictions. Furthermore, this approach enhances the robustness and transferability of NNPs, emphasizing the importance of atomic energy predictions in developing high-quality and reliable MLIPs.

Active Learning↗
DOE OSTI2022

Time-Resolved Optical Pump-Resonant X-ray Probe Spectroscopy of 4-Thiouracil: A Simulation Study

We theoretically monitor the photoinduced ππ* → nπ* internal conversion process in 4-thiouracil (4TU), triggered by an optical pump. The element-sensitive spectroscopic signatures are recorded by a resonant X-ray probe tuned to the sulfur, oxygen, or nitrogen K-edge. We employ high-level electronic structure methods optimized for core-excited electronic structure calculation combined with quantum nuclear wavepacket dynamics computed on two relevant nuclear modes, fully accounting for their quantum nature of nuclear motions. We critically discuss the capabilities and limitations of the resonant technique. For sulfur and nitrogen, we document a pre-edge spectral window free from ground-state background and rich with ππ* and nπ* absorption features. The lowest sulfur K-edge shows strong absorption for both ππ* and nπ*. In the lowest nitrogen K-edge window, we resolve a state-specific fingerprint of the ππ* and an approximate timing of the conical intersection via its depletion. A spectral signature of the nπ* transition, not accessible by UV–vis spectroscopy, is identified. The oxygen K-edge is not sensitive to molecular deformations and gives steady transient absorption features without spectral dynamics. Here, the ππ*/nπ* coherence information is masked by more intense contributions from populations. Altogether, element-specific time-resolved resonant X-ray spectroscopy provides a detailed picture of the electronic excited-state dynamics and therefore a sensitive window into the photophysics of thiobases.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2020

Modern Approaches to Exact Diagonalization and Selected Configuration Interaction with the Adaptive Sampling CI Method

Recent advances in selected configuration interaction methods have made them competitive with the most accurate techniques available and, hence, creating an increasingly powerful tool for solving quantum Hamiltonians. In this work, we build on recent advances from the adaptive sampling configuration interaction (ASCI) algorithm. We show that a useful paradigm for generating efficient selected CI/exact diagonalization algorithms is driven by fast sorting algorithms, much in the same way iterative diagonalization is based on the paradigm of matrix vector multiplication. We present several new algorithms for all parts of performing a selected CI, which includes new ASCI search, dynamic bit masking, fast orbital rotations, fast diagonal matrix elements, and residue arrays. The ASCI search algorithm can be used in several different modes, which includes an integral driven search and a coefficient driven search. The algorithms presented here are fast and scalable, and we find that because they are built on fast sorting algorithms they are more efficient than all other approaches we considered. After introducing these techniques, we present ASCI results applied to a large range of systems and basis sets to demonstrate the types of simulations that can be practically treated at the full-CI level with modern methods and hardware, presenting double- and triple-ζ benchmark data for the G1 data set. The largest of these calculations is Si$_2$H$_6$ which is a simulation of 34 electrons in 152 orbitals. We also present some preliminary results for fast deterministic perturbation theory simulations that use hash functions to maintain high efficiency for treating large basis sets.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Selective Detection of Intermediate-Amplitude Motion by Solid-State NMR

The coexistence of rigid and mobile molecules or molecular segments abounds in biomolecular assemblies. Examples include the carbohydrate-rich cell walls of plants and intrinsically disordered proteins that contain rigid β-sheet cores. In solid-state nuclear magnetic resonance (NMR) spectroscopy, dipolar polarization transfer experiments are well suited for detecting rigid components, whereas scalar-coupling experiments are well suited for detecting highly mobile components. However, few NMR methods are available to detect the segments that undergo intermediate-amplitude fast motion. Here, we introduce two NMR experiments, a two-dimensional T 2H -filtered CP-hCH correlation and a three-dimensional J-INADEQUATE CCH correlation, to observe this intermediate-amplitude motion. Both experiments involve 1 H detection under fast magic-angle spinning (MAS). By combining 1 H transverse relaxation (T 2H ) filters with dipolar polarization transfer, we suppress the signals of both highly rigid and highly mobile species, thus revealing the signals of intermediate mobile species. 1 H detection under fast MAS is crucial for distinguishing the different motional amplitudes. Here, we demonstrate these techniques on several plant cell wall samples and show that they allow the selective detection and resolution of certain hemicellulose and pectin signals, which are usually masked by the signals of the rigid cellulose and the highly dynamic pectins in purely dipolar and scalar NMR spectra.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2018

Role of Solute Attractive Forces in the Atomic-Scale Theory of Hydrophobic Effects

The role that van der Waals (vdW) attractive forces play in the hydration and association of atomic hydrophobic solutes such as argon (Ar) in water is reanalyzed using the local molecular field (LMF) theory of those interactions. In this problem, solute vdW attractive forces can reduce or mask hydrophobic interactions as measured by contact peak heights of the ArAr correlation function compared to reference results for purely repulsive core solutes. Nevertheless, both systems exhibit a characteristic hydrophobic inverse temperature behavior in which hydrophobic association becomes stronger with increasing temperature through a moderate temperature range. The new theoretical approximation obtained here is remarkably simple and faithful to the statistical mechanical LMF assessment of the necessary force balance. In conclusion, our results extend and significantly revise approximations made in a recent application of the LMF approach to this problem and, unexpectedly, support a theory of nearly 40 years ago.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Electronic Coherence and Coherent Dephasing in the Optical Control of Electrons in Graphene

Electronic coherence is of utmost importance for the access and control of quantum-mechanical solid-state properties. Using a purely electronic observable, the photocurrent, we measure a lower bound of the electronic coherence time of 22 ± 4 fs in graphene. The photocurrent is ideally suited to measure electronic coherence, as it is a direct result of coherent quantum-path interference, controlled by the delay between two ultrashort two-color laser pulses. The maximum delay for which interference between the population amplitude injected by the first pulse interferes with that generated by the second pulse determines the electronic coherence time. In particular, numerical simulations reveal that the experimental data yields a lower bound on the electronic coherence time, masked by coherent dephasing due to the broadband absorption in graphene. Overall, we expect that our results will significantly advance the understanding of coherent quantum control in solid-state systems ranging from excitation with weak fields to strongly driven systems.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2020

Generation of Tin-Vacancy Centers in Diamond via Shallow Ion Implantation and Subsequent Diamond Overgrowth

Group IV color centers in diamond have garnered great interest for their potential as optically active solid-state spin qubits. The future utilization of such emitters requires the development of precise site-controlled emitter generation techniques that are compatible with high-quality nanophotonic devices. This task is more challenging for color centers with large group IV impurity atoms, which are otherwise promising because of their predicted long spin coherence times without a dilution refrigerator. For example, when applied to the negatively charged tin-vacancy (SnV – ) center, conventional site-controlled color center generation methods either damage the diamond surface or yield bulk spectra with unexplained features. Here we demonstrate a novel method to generate site-controlled SnV – centers with clean bulk spectra. We shallowly implant Sn ions through a thin implantation mask and subsequently grow a layer of diamond via chemical vapor deposition. This method can be extended to other color centers and integrated with quantum nanophotonic device fabrication.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Prelithiated SiO x /Graphite-NMC811 Cells: Capacity Loss, Impedance Rise and Hidden Degradation Pathways Revealed Using Three-Electrode Diagnostics

Electrodes containing SiO x /graphite (Gr) materials are attractive as anodes for high-energy lithium-ion batteries. However, their mechanical deformation, electrochemical response, and impedance evolution during long-term cycling are strongly coupled, complicating accurate diagnosis of performance fade mechanisms. In this work, the behavior of electrochemically prelithiated SiO x /Gr anodes paired with NMC811 cathodes is systematically investigated using techniques that include in-situ dilatometry, three-electrode electrochemistry, and multiscale post-cycling microscopy. The SiO x /Gr electrode exhibits a maximum expansion of 49% upon lithiation to 10 mV vs Li + /Li, with 84% of the expansion and 91% of the capacity being reversible. In full cells, relatively stable cycling with only 12% capacity fade over 500 cycles is observed. Three-electrode experiments reveal cell-level impedance growth, which is dominated by the NMC811 cathode: the SiO x /Gr anode exhibits minimal net impedance rise and an initial impedance decrease at low potentials. Despite this apparent electrochemical stability, cross-sectional SEM, PFIB tomography, and cryo-STEM reveal irreversible anode thickening caused by the accumulation of an inorganic-rich solid electrolyte interphase (SEI) permeating the anode bulk. Electrode potential-shift analysis further demonstrates that Li + ions released from lithium reservoirs in the prelithiated anode mask true lithium inventory loss during aging. These results demonstrate that low-expansion SiO x /Gr anodes can simultaneously exhibit favorable cycling and impedance metrics while undergoing substantial, hidden degradation, underscoring the importance of electrode-resolved diagnostics for evaluating prelithiated silicon-based anodes.

25 ENERGY STORAGE↗
DOE OSTI2020

Genesis and Propagation of Fractal Structures During Photoelectrochemical Etching of n-Silicon

The genesis, propagation, and dimensions of fractal-etch patterns that form anodically on front- or back-illuminated n-Si(100) photoelectrodes in contact with 11.9 M NH 4 F (aqueous) have been investigated during either a linear potential sweep or a constant potential hold ( E = +6.0 V versus Ag/AgCl). Optical images collected in situ during electrochemical experiments reflected the location and underlying mechanism of initiation and propagation of the structures on the surface. X-ray photoelectron spectroscopic (XPS) data collected for samples emersed from the electrolyte at varied times provided detailed information about the chemistry of the surface during fractal etching. The fractal structure was strongly influenced by the orientation of the crystalline Si sample. Furthermore, the etch patterns were initially generated at points along the circumference of bubbles that formed upon immersion of n-Si(100) samples in the electrolyte, most likely due to the electrochemical and electronic isolation of areas beneath bubbles. XPS data showed the presence of a tensile-stressed silicon surface throughout the etching process as well as the presence of SiO x F y on the surface. The two-dimensional fractal dimension, D f,2D , of the patterns increased with etching time to a maximum observed value of D f,2D = 1.82. Promotion of fractal etching near etch masks that electrochemically and electronically isolated areas of the photoelectrode surface enabled the selective placement of highly branched structures at desired locations on an electrode surface.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Polymer, Additives, and Processing Effects on N95 Filter Performance

The current severe acute respiratory syndrome coronavirus 2 (SARS-COV-2) pandemic has highlighted the need for personal protective equipment, specifically filtering facepiece respirators like N95 masks. While it is common knowledge that polypropylene (PP) is the industry standard material for filtration media, trial and error is often required to identify suitable commercial precursors for filtration media production. This work aims to identify differences between several commercial grades of PP and demonstrate the development of N95 filtration media with the intent that the industry partners can pivot and help address N95 shortages. Three commercial grades of high melt flow index PP were melt blown at Oak Ridge National Laboratory and broadly characterized by several methods including differential scanning calorimetry (DSC), X-ray diffraction (XRD), and neutron scattering. Despite the apparent similarities (high melt flow and isotacticity) between PP feedstocks, the application of corona charging and charge enhancing additives improve each material to widely varying degrees. From the analysis performed here, the most differentiating factor appears to be related to crystallization of the polymer and the resulting electret formation. Materials with higher crystallization onset temperatures, slower crystallization rates, and larger number of crystallites form a stronger electret and are more effective at filtration.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Adsorption and Destruction of the G-Series Nerve Agent Simulant Dimethyl Methylphosphonate on Zinc Oxide

Organophosphorus chemical warfare agents (CWAs) are extremely toxic compounds that are nominally mitigated with gas mask filtration employing metal oxide impregnated activated carbon filtration material. To develop more effective sorbents, it is important to understand the surface chemistry between these organophosphorus compounds and the individual components that make up these filtration materials. In this study, density functional theory (DFT) and Fourier transform infrared spectroscopy (FTIR) were employed to investigate the adsorption and decomposition mechanisms between a sarin simulant molecule, dimethyl methylphosphonate (DMMP), and zinc oxide, which is a component found in current filtration materials. Theoretical calculations show that DMMP readily adsorbs to a pristine and hydroxylated ZnO ($101\bar 0$) surface with average adsorption energies of 132 and 65 kJ mol –1 , respectively. Experimental diffuse reflectance fourier transform infrared spectroscopy (DRIFTS) reveals that ZnO adsorbs water and readily hydroxylates under ambient conditions, which can facilitate adsorption through hydrogen bonding of the P$=$O to ZnO surface hydroxyls. FTIR gas phase analysis also reveals that DMMP decomposes in the presence of ZnO nanoparticles (NPs) to produce methanol at room temperature. Assuming a fully hydroxylated surface of ZnO, DFT calculations reveal several plausible mechanisms for DMMP decomposition to form methanol with an activation energy barrier of 99.6 kJ mol –1 . Finally, on the basis of this energy barrier to decompose DMMP, a turnover frequency (TOF) of only 3.5 × 10 –7 s –1 is calculated assuming full coverage of DMMP on the ZnO nanoparticles tested. This value is qualitatively consistent with experimental results.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Geochemical Evidence for Rare-Earth Element Mobilization during Kaolin Diagenesis

This study investigates how saprolization influences inherent rare-earth element (REE) source rock signatures and how depositional environment(s) and diagenetic reactions ultimately impact the REE signature within sedimentary kaolin bodies. Rare-earth element geochemistry signatures are particularly useful for tracking element sources and mobility and are, therefore, powerful tools in the investigation of clay mineral formation and diagenesis. Rare-earth element and bulk chemical compositions were determined using discrete chemical analyses and chemical imaging. Saprolitic materials show an enrichment in the light and heavy REEs, compared with the parent material, with enhanced Ce/Eu anomalies. Light REEs within sedimentary kaolins are associated with phosphate mineralogy and have experienced variable degrees of diagenetic fractionation and mobilization. Cretaceous kaolins display more light REE mobility compared with Tertiary kaolins, which show very little REE fractionation. Degrees of REE fractionation are driven primarily by differences in sedimentary kaolin physical properties and the presence of organic acids in groundwater. Unfortunately, the provenance of the Georgia kaolins could not be determined based solely on the trace-element and REE compositions because fractionations during saprolization and diagenesis mask much of the inherent provenance signatures. Lastly, implications for the REEs as an economic deposit and their beneficiation are discussed.

58 GEOSCIENCES↗
DOE OSTI2019

Controls of Microstructure and Chemical Reactivity on the Replacement of Limestone by Fluorite Studied Using Spatially Resolved Small Angle X-ray and Neutron Scattering

Fluid-mineral interactions can alter the pore structure and mineral composition of earth materials, sometimes leading to complete replacement of one mineral phase by another. A quantitative understanding of these processes is needed for the prediction of contaminant transport in nuclear waste management, oil and gas exploration, geothermal energy production and in many geological processes. Currently, a detailed understanding of how the original microstructure and chemical reactivity is affecting the replacement rate and porosity development is lacking which would enable the prediction of contaminant transport. Here, we present a systematic experimental study of limestone replacement in the model system calcite-fluorite varying both the texture and chemical reactivity of the parent rock. By combining X-ray ((U)SAXS) and neutron (ultra) small-angle scattering ((U)SANS) we quantified changes in the porosity as a function of depth within the sample and time. By shielding the samples with a set of annular Cd-masks during neutron scattering, we obtained spatially-resolved porosity information. Microstructural changes were investigated using scanning electron microscopy (SEM), and composition changes were accessed using chemical imaging by Time-of-Flight Secondary Ion Mass Spectrometry (ToF—SIMS) and SEM-Energy-Dispersive X-Ray Spectroscopy (SEM-EDX). The replacement of limestone via fluorite takes place via advantageous pathways enhancing the available reactive surface area, e.g. fractures, accessible, interconnected porosity, non-connected porosity grain boundaries and twin boundaries. The results presented in this paper emphasize the importance of a detailed structural and textural assessment of the starting material both in experimental studies and in nature to make accurate predictions about reaction rates.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗