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Abstract: Hematite nanoparticles were synthesized with U(VI) in circumneutral water through a coprecipitation and hydrothermal treatment process. XRD, TEM, and EXAFS analyses reveal that uranium may aggregate along grain boundaries and occupy Fe sites within hematite. The described synthesis method produces crystalline, single-phase iron oxide nanoparticles absent of surface-bound uranyl complexes. EXAFS data were comparable to spectra from existing studies whose syntheses were more representative of naturally occurring, extended aging processes. This work provides and validates an accelerated method of synthesizing uranium-immobilized iron oxide nanoparticles for further mechanistic studies. High temperature oxide melt solution calorimetry measurements were performed to calculate the thermodynamic stability of uranium-incorporated iron oxide nanoparticles. Increasing uranium content within hematite resulted in more positive formation enthalpies. Standard formation enthalpies of UxFe2–2xO3 were as high as 76.88 ± 2.83 kJ/mol relative to their binary oxides, or -764.04 ± 3.74 kJ/mol relative to their constituent elements, at x = 0.037. Data on the thermodynamic stability of uranium retention pathways may assist in predicting waste uranyl remobilization, as well as in developing more effective methods to retain uranium captured from aqueous environments.

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Abstract: The flexibility of the zeolite Rho framework offers great potential for tunable molecular sieving. The fully copper-exchanged form of Rho and mixed Cu,H- and Cu,Na-forms have been prepared. EPR spectroscopy reveals Cu 2+ cations are present in the dehydrated forms and Rietveld refinement shows these prefer S6R sites, away from the d8r windows that control diffusion. Fully exchanged Cu-Rho remains in an open form upon dehydration, the d8r windows remain nearly circular and the occupancy of window sites is low, so that it adsorbs CO 2 rapidly at room temperature. Breakthrough tests with 10% CO 2 /40% CH 4 mixtures show that Cu 4.9 -Rho is able to produce pure methane, albeit with a relatively low capacity at this p CO2 due to the weak interaction of CO 2 with Cu cations. This is in strong contrast with Na-Rho, where cations in narrow elliptical window sites enable CO 2 to be adsorbed with high selectivity and uptake but too slowly to enable the production of pure methane in similar breakthrough experiments. A series of Cu,Na-Rho materials was prepared to improve uptake and selectivity compared to Cu-Rho, and kinetics compared to Na-Rho. Remarkably, Cu,Na-Rho with >2 Cu cations per unit cell exhibited exsolution, due to the preference of Na cations for narrow S8R sites in distorted Rho and of Cu cations for S6R sites in the centric, open form of Rho. The exsolved Cu,Na-Rho showed improved performance in CO 2 /CH 4 breakthrough tests, producing pure CH 4 with improved uptake and CO 2 /CH 4 selectivity compared to that of Cu 4.9 -Rho.

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Abstract: The electron-ion collider (EIC) will be built at the Brookhaven National Laboratory over the next ten years, with the purpose of giving insight into nucleon structure, origins of nucleon mass and spin, and quark and gluon confinement. This thesis pertains to the silicon vertex tracker for an EIC experiment; the detector closest to the interaction point. The purpose of a silicon vertex tracker is to locate the origin vertex position of charged particles and measure the particle momentum, and the EIC physics goals require detector resolutions beyond current state-of-the-art silicon vertex trackers. The aim of this thesis is to find a suitable silicon sensor technology for further developments by tests performed in a lab and at a testbeam, and to find a silicon vertex tracker geometry with performance matching the EIC physics requirements using simulations. The baseline sensor for the studies comes from the ALICE inner tracker upgrade, and is called the ALPIDE sensor. A new monolithic silicon sensor development designed to increase depletion is tested and compared to the performance of an ALPIDE-like sensor, and found to improve charge collection performance while keeping the sensor capacitance low. This aids tracking performance, and the new development is thus considered a possible path for development of an EIC-specific sensor. Simulations of different silicon vertex tracker geometries and parameters are performed using GEANT4, and a high-performing layout consisting of inner and outer silicon sensor layers surrounded by a gaseous detector and silicon disks is developed. It is also found that if a more compact tracker is desired, an all-silicon concept outperforms a combination of silicon and gaseous detectors. Further simulations of the best-performing layouts with current projections of possible silicon sensor material thickness and pixel size show that they meet the requirements of the EIC physics goals in terms of momentum resolution if a 3 T solenoidal magnetic field is used, and pointing resolution regardless of magnetic field strength. The silicon vertex tracker developed in this work is one of two baseline tracker concepts used in the ongoing development of an EIC reference detector. The performance of different detector concepts is also studied using realistic electron-proton collision events generated using PYTHIA and propagated through the detector simulation, with a focus on charmed meson reconstruction. It is found that a compact all-silicon tracker can perform as well as an all-silicon concept with a larger radius in these studies, but a large-radius combination of silicon and gaseous detectors is always better than all-silicon concepts in the studied open charm case.

Open Access

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Abstract: Injection of CO2 into shale reservoirs to enhance gas recovery and simultaneously sequester greenhouse gases is a potential contributor towards the carbon-neutral target. It offers a low-carbon, low-cost, low-waste and large-scale solution during the energy transition period. A precondition to efficient gas storage and flow is a sound understanding of how the shale's micro-scale impacts on these phenomena. However, the heterogeneous and complex nature of shales limits the understanding of microstructure and pore systems, making feasibility analysis challenging. This study qualitatively and quantitatively investigates the Bowland shale microstructure in 3D at five length scales: artificial fractures at 10–100 μm scale, matrix fabric at 1–10 μm-scale, individual mineral grains and organic matter particles at 100 nm–1 μm scale, macropores and micro-cracks at 10–100 nm scale and organic matter and mineral pores at 1–10 nm-scale. For each feature, the volume fraction variations along the bedding normal orientation, the fractal dimensions and the degrees of anisotropy were analysed at all corresponding scales for a multi-scale heterogeneity analysis. The results are combined with other bulk laboratory measurements, including supercritical CO2 and CH4 adsorption at reservoir conditions, pressure-dependent permeability and nitrogen adsorption pore size distribution, to perform a comprehensive analysis on the storage space and flow pathways. A cross-scale pore size distribution, ranging from 2 nm to 3 μm, was calculated with quantified microstructure. The cumulative porosity is calculated to be 8%. The cumulative surface area is 17.6 m2 g−1. A model of CH4 and CO2 flow pathways and storage with quantified microstructure is presented and discussed. The feasibility of simultaneously enhanced gas recovery and subsurface CO2 storage in Bowland shale, the largest shale gas potential formation in the UK, was assessed based using multi-scale microstructure analysis. The potential is estimated to store 19.0–21.2 Gt CO2 as free molecules, together with 18.3–28.5 Gt CO2 adsorbed onto pore surfaces, implying a theoretical maximum of 47.5–49.5 Gt carbon storage in the current estimate of 38 trillion cubic metres (∼1300 trillion cubic feet) of Bowland shale. Simple estimates suggest 6.0–15.8 Gt CO2 may be stored in practice.

Open Access

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Abstract: The effects of vacuum induction melting (VIM) vacuum (<1 Pa to 100Pa) on gas content, oxide inclusions and mechanical properties of Ni-based superalloy K4648 has been investigated by electron beam (EB) button experiment under high vacuum (10-3 Pa) and high resolution synchrotron X-ray powder diffraction (SXPD). The results indicated that VIM remelting vacuum drop has obvious effect on the existing form of trace oxygen. The total amount of oxygen did not increase significantly but a dramatic increase in the amount of oxide inclusions by 1-2 orders of magnitude was found. The inclusions are mainly oxides including Al2O3, Cr2O3, Ni(Al,Cr)2O4 and complex oxides or sulfides. Remelting under 100-110Pa has no significant effect on mechanical properties such as stress rupture life and tensile strength but decreased ductility obviously. In comparison to the normal vacuum counterpart, the tensile elongation and impact ductility of the alloy remelted under lower vacuum level decreased by 67% and 40%, respectively. This study reveals the relationship between the vacuum level and mechanical properties of superalloys and highlights the trace amount of oxide inclusions which should be considered as one of the key issues for the cleanliness of superalloys apart from the typical measurement of the gas content only.