18 Search Results

Geologic carbon sequestration in mafic and ultramafic reservoirs is a scalable strategy for carbon dioxide removal, offering permanent storage via mineralization as stable carbonates. However, there is limited information on the structure and composition of key mineralization endpoints during sequestration. Here, we unravel the atomic structure, composition, and nanoscale morphology of carbonates recovered from a field-scale demonstration of CO₂ mineralization in basalt. Using transmission electron microscopy, we mapped mineralogical variations from the initial to later stages of subsurface carbonate growth and identified a previously unknown cation-ordered ankerite phase that exerts a primary control over carbonation processes. This study has providedmore » a new understanding of subsurface carbonation pathways which will impact the parameterization of predictive geochemical models for future sequestration efforts in basalt formations.« less

Herein, we examine the impact of Ga⁺ ion kinetic energy and the target material type on the extent of ion implantation and structural damage in atomic force microscopy probes made of Al₂O₃ and ZnO manufactured by focused ion beam (FIB) using scanning transmission electron microscopy and energy-dispersive X-ray mapping. Penetration of Ga into the Al₂O₃ lattice induced structural distortions and amorphization. For ZnO probes, Ga is uniformly dispersed across the surface, resulting in the formation of distinct clusters. Atom probe tomography further validates the Ga distributions in Al₂O₃ and ZnO nanoprobes. Complementary Monte Carlo simulations with the transport of ionsmore » in the matter program indicated that the introduction of Ga⁺ prompts the generation of cation and anion vacancies, an occurrence more pronounced in Al₂O₃ compared to ZnO. In conclusion, this study not only enriches the knowledge of ion-matter interactions, but also serves as a practical guide for the fabrication of nanoscale functionalized AFM probes.« less

A synthesis method for nanosized forsterite (Mg₂SiO₄) doped with varying concentrations of Ni and Co has been developed to support studies of carbonation-based extraction and separation of Ni and Co from mafic and ultramafic rocks. The protocol expands upon an existing sol–gel/surfactant method and is demonstrated for doping levels of 5% and 25% of Ni or Co. Variables such as metal reagents, surfactant ratios, and calcination procedures were optimized to achieve high specific surface areas and small particle sizes while minimizing secondary phase formation. Particle sizes ranged from 29 to 83 nm, and specific surface areas were between 11 andmore » 32 m² g⁻¹. Metal oxide impurities were minimal, appearing only in undoped and 25% Ni-doped samples at 0.6 wt% or less. Ni and Co were only detected in the +II oxidation state and partitioned predominantly in the M1 cation site of the forsterite crystal structure. Doped nanosized forsterites prepared with this method will enable in situ experiments that can track, at the molecular scale, the fate of Ni and Co during carbonation reactions and thus provide a knowledge base for improving metal extraction and separation technologies.« less

The ability to simultaneously monitor the flux of iron atoms within the solution and solid phases can provide considerable insight into mechanisms of iron oxide mineral transformations. The autocatalytic interaction between hematite and Fe(II)-oxalate has long been of interest for its environmental and industrial relevance. In this study we take advantage of iron isotopic labelling and mass-sensitive imaging at the single particle scale to determine how changes in solution composition correlate with the morphologic evolution of faceted, micrometer-sized hematite platelets. Net dissolution is confirmed through analyses of aqueous iron chemistry, as well as by quantitative atomic force microscopy. Isotopic mappingmore » techniques show that Fe(II) readily adsorbs to (001) and (012) surfaces in the absence of oxalate, but when oxalate is present selective dissolution of the (001) surface prevails and Fe deposition via recrystallization is not observed. Comparison between particle microtopographies following reaction with Fe(II), oxalate, and Fe(II)-oxalate show substantially different behaviors, consistent with distinct mechanisms of interaction with hematite surfaces. The extensive characterization conducted on the coupled solution/solid dynamics in this system provides new insight for distinguishing crystal growth, dissolution, and recrystallization processes.« less

Surface self-diffusion studies on metals under elevated reaction conditions are limited, as it is inherently challenging to unambiguously follow atomic transport across highly-reactive surfaces. Here, quantitative and mechanistic insight into thermally induced atomic transport processes in bcc α-iron at the sub-nanometer level was achieved using isotopic tracer techniques coupled with in situ atom probe tomography (APT) capabilities. Specifically, using a reactor directly connected to the APT, needle-shaped specimens fabricated from epitaxial thin films with an embedded ⁵⁷Fe tracer layer were annealed in Ar at 500 °C and 350 °C for 1 hour. Furthermore, the tracer was positioned at various depthsmore » in the APT specimen by field evaporation, enabling targeted and simultaneous analysis of lattice and surface diffusion. ⁵⁷Fe concentration profiles reveal lattice self-diffusion occurs at 500 °C on the order of ~7 – 9 monolayers, while lattice diffusion is not resolvable at 350 °C. Considerable surface transport was, however, observed at both conditions, where atomic transport over the specimen surface led to the formation of a thin (≤1 nm), isotopically-intermixed layer at the surface. Further, the observed isotopic redistributions at 500 °C were convoluted by additional processes occurring in the subsurface, such as atomic intermixing in correlation with lattice diffusion. However, surface diffusion was determined to be the primary transport process at 350 °C and was thereby quantified. Ultimately, these results demonstrate the significance of surface self-diffusion as a short circuit pathway. More broadly, this approach has the potential to provide detailed insight into (self-)diffusion mechanisms across various materials while targeting site-specific reactions under elevated reaction conditions.« less

Organic macromolecules exert remarkable control over the nucleation and growth of inorganic crystallites during (bio)mineralization, as exemplified during enamel formation where the protein amelogenin regulates the formation of hydroxyapatite (HAP). However, it is poorly understood how fundamental processes at the organic-inorganic interface, such as protein adsorption and/or incorporation into minerals, regulates nucleation and crystal growth due to technical challenges in observing and characterizing mineral-bound organics at high-resolution. Here, atom probe tomography techniques were developed and applied to characterize amelogenin-mineralized HAP particles in vitro, revealing distinct organic-inorganic interfacial structures and processes at the nanoscale. Specifically, visualization of amelogenin across the mineralizedmore » particulate demonstrates protein can become entrapped during HAP crystal aggregation and fusion. Identification of protein signatures and structural interpretations were further supported by standards analyses, i.e., defined HAP surfaces with and without amelogenin adsorbed. These findings represent a significant advance in the characterization of interfacial structures and, more so, interpretation of fundamental organic-inorganic processes and mechanisms influencing crystal growth. Ultimately, this approach can be broadly applied to inform how potentially unique and diverse organic-inorganic interactions at different stages regulates the growth and evolution of various biominerals.« less

Perovskite structured transition metal oxides are important technological materials for catalysis and solid oxide fuel cell applications. Their functionality often depends on oxygen diffusivity and mobility through complex oxide heterostructures, which can be significantly impacted by structural and chemical modifications, such as doping. Further, when utilized within electrochemical cells, interfacial reactions with other components (e.g., Ni- and Cr-based alloy electrodes and interconnects) can influence the perovskite's reactivity and ion transport, leading to complex dependencies that are difficult to control in real-world environments. Here, this work uses isotopic tracers and atom probe tomography to directly visualize oxygen diffusion and transport pathwaysmore » across perovskite and metal-perovskite heterostructures, that is, (Ni-Cr coated) Sr-doped lanthanum ferrite (La_0.5Sr_0.5FeO₃; LSFO). Annealing in ¹⁸O_2(g) results in elemental and isotopic redistributions through oxygen exchange (OE) in the LSFO while Ni-Cr undergoes oxidation via multiple mechanisms and transport pathways. Complementary density functional theory calculations at experimental conditions provide rationale for OE reaction mechanisms and reveal a complex interplay of different thermodynamic and kinetic drivers. These results shed light on the fundamental coupling of defects and oxygen transport in an important class of catalytic materials.« less

Irradiation induced non-equilibrium point defect populations influence mass transport in oxides, which in turn affects their stability and performance in hostile environments. In this study a strong dose rate dependence is observed.

New insight into the geochemistry of ancient environments can be gained through structural and chemical analyses of nanometer-scale features within minerals. Here, we present recent developments using atom probe tomography (APT) enabling direct visualization of nanoscale fluid inclusions trapped within pyrite (FeS₂) and thereby chemical characterization of remnant seawater. Pyrite framboids (spherical clusters of nanocrystals) were sampled from the Middle Devonian Leicester Pyrite Member (New York). Scanning transmission electron microscopy shows low density regions distributed within the pyrite consistent with nanoscale pores (<4 nm in size). APT 3D visualization and compositional mapping reveals that the nanopores are filled with water.more » The inclusions appear to preserve the elemental signature of the water column in which the framboids formed, specifically seawater components including Na, K, Mg, and Ca. Mg/Ca ratios within the pyrite were generally measured to be within 0.6±0.2 – consistent with calcite-dominated seawater conditions existing in the Middle Devonian. Furthermore, this study demonstrates the potential for a novel approach to reconstruct paleoenvironmental conditions from coupled elemental and structural analyses of nanoscale fluid inclusions.« less