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This manuscript presents a benchmark problem for the simulation of single-phase flow, reactive transport, and solid geometry evolution at the pore scale. The problem is organized in three parts that focus on specific aspects: flow and reactive transport (part I), dissolution-driven geometry evolution in two dimensions (part II), and an experimental validation of three-dimensional dissolution-driven geometry evolution (part III). Five codes are used to obtain the solution to this benchmark problem, including Chombo-Crunch, OpenFOAM-DBS, a lattice Boltzman code, Vortex, and dissolFoam. These codes cover a good portion of the wide range of approaches typically employed for solving pore-scale problems in the literature, including discretization methods, characterization of the fluid-solid interfaces, and methods to move these interfaces as a result of fluid-solid reactions. A short review of these approaches is given in relation to selected published studies. Results from the simulations performed by the five codes show remarkable agreement both quantitatively—based on upscaled parameters such as surface area, solid volume, and effective reaction rate—and qualitatively—based on comparisons of shape evolution. This outcome is especially notable given the disparity of approaches used by the codes. Therefore, these results establish a strong benchmark for the validation and testing of pore-scale codes developed for the simulation of flow and reactive transport with evolving geometries. They also underscore the significant advances seen in the last decade in tools and approaches for simulating this type of problem.

The resistance of polymeric matrices to leaching of tritium water incorporated in oil microcapsules or in chemisorbent particles was studied. The phenol-formaldehyde matrix with tritium and cesium in oil microcapsules ensures highly reliable radionuclide immobilization: The half-decile leaching rate, g cm day, is 9 × 10 for H and 2 × 10 for Cs. A borate chemisorbent in combination with a polyurethane matrix was suggested for immobilization of highly radioactive tritium water vapor. [ABSTRACT FROM AUTHOR]

The specific character of forming nanosized structures on steel surface contacting with air and aqueous dispersion medium in the range of temperatures from 3 to 70 °C has been studied. The development of iron-oxygen structures leads to morphological g-row. As the initial structure the hydroxycarbonate Green Rust under the most conditions has been found. Two branches of phase transformation scheme under full and limited oxidation have been suggested. The optimum condition for forming lepidocrocite is low temperatures (25-35 °C) and for forming magnetite is middle ones (50 °C). The kinetic regularities of the XRD-pick amounts of lepidocrocite and magnetite from temperatures were calculated. [ABSTRACT FROM AUTHOR]

The technology of project modeling of probabilistic technological processes of production is given for the five problem areas: computation processes; modeling of assemble and disassemble operations; probabilistic network planning models; postal networks; processes with unreliable equipment. [ABSTRACT FROM AUTHOR]

It has been proposed to use magnesium oxide (MgO) to separate carbon dioxide directly from the atmosphere at the gigaton level. We show experimental results on MgO single crystals reacting with the atmosphere for longer (decades) and shorter (days to months) periods with the goal of gauging reaction rates. Here, we find a substantial slowdown of an initially fast reaction as a result of mineral armoring by reaction products (surface passivation). In short-term experiments, we observe fast hydroxylation, carbonation, and formation of amorphous hydrated magnesium carbonate at early stages, leading to the formation of crystalline hydrated Mg carbonates. The preferential location of Mg carbonates along the atomic steps on the crystal surface of MgO indicates the importance of the reactive site density for carbonation kinetics. The analysis of 27-year-old single-crystal MgO samples demonstrates that the thickness of the reacted layer is limited to ∼1.5 μm on average, which is thinner than expected and indicates surface passivation. Thus, if MgO is to be employed for direct air capture of CO 2 , surface passivation must be circumvented.

The heterogeneous nature, local presence, and dynamic evolution of defects typically govern the ionic and electronic properties of a wide variety of functional materials. While the last 50 years have seen considerable efforts into development of new methods to identify the nature of defects in complex materials, such as the perovskite oxides, very little is known about defect dynamics and their influence on the functionality of a material. Here, the discovery of the intermittent behavior of point defects (oxygen vacancies) in oxide heterostructures employing X-ray photon correlation spectroscopy is reported. Local fluctuations between two ordered phases in strained SrCoO x with different degrees of stability of the oxygen vacancies are observed. Ab-initio-informed phase-field modeling reveals that fluctuations between the competing ordered phases are modulated by the oxygen ion/vacancy interaction energy and epitaxial strain. The results demonstrate how defect dynamics, evidenced by measurement and modeling of their temporal fluctuations, give rise to stochastic properties that now can be fully characterized using coherent X-rays, coupled for the first time to multiscale modeling in functional complex oxide heterostructures. The study and its findings open new avenues for engineering the dynamical response of functional materials used in neuromorphic and electrochemical applications., (© 2023 UChicago Argonne, LLC and Oak Ridge National Laboratory. Advanced Materials published by Wiley-VCH GmbH.)

Nucleation and growth of minerals has broad implications in the geological, environmental and materials sciences. Recent developments in fast X-ray nanotomography have enabled imaging of crystal growth in solutions in situ with a resolution of tens of nanometres, far surpassing optical microscopy. Here, a low-cost, custom-designed aqueous flow cell dedicated to the study of heterogeneous nucleation and growth of minerals in aqueous environments is shown. To gauge the effects of radiation damage from the imaging process on growth reactions, radiation-induced morphological changes of barite crystals (hundreds of nanometres to ∼1 µm) that were pre-deposited on the wall of the flow cell were investigated. Under flowing solution, minor to major crystal dissolution was observed when the tomography scan frequency was increased from every 30 min to every 5 min (with a 1 min scan duration). The production of reactive radicals from X-ray induced water radiolysis and decrease of pH close to the surface of barite are likely responsible for the observed dissolution. The flow cell shown here can possibly be adopted to study a wide range of other chemical reactions in solutions beyond crystal nucleation and growth where the combination of fast flow and fast scan can be used to mitigate the radiation effects., (open access.)

The microstructure of minerals and rocks can significantly alter reaction rates. This study focuses on identifying transport paths in low porosity rocks based on the hypothesis that grain boundary widening accelerates reactions in which one mineral is replaced by another (replacement reaction). We conducted a time series of replacement experiments of three limestones (CaCO 3 ) of different microstructures and solid impurity contents using FeCl 2 . Reacted solids were analyzed using chemical imaging, small angle X-ray and neutron scattering and Raman spectroscopy. In high porosity limestones replacement is reaction controlled and complete replacement was observed within 2 days. In low porosity limestones that contain 1-2% dolomite impurities and are dominated by grain boundaries, a reaction rim was observed whose width did not change with reaction time. Siderite (FeCO 3 ) nucleation was observed in all parts of the rock cores indicating the percolation of the solution throughout the complete core. Dolomite impurities were identified to act as nucleation sites leading to growth of crystals that exert force on the CaCO 3 grains. Widening of grain boundaries beyond what is expected based on dissolution and thermal grain expansion was observed in the low porosity marble containing dolomite impurities. This leads to a self-perpetuating cycle of grain boundary widening and reaction acceleration instead of reaction front propagation., (© 2023. UT-Battelle, LLC.)

Understanding the behavior of defects in the complex oxides is key to controlling myriad ionic and electronic properties in these multifunctional materials. The observation of defect dynamics, however, requires a unique probe-one sensitive to the configuration of defects as well as its time evolution. Here, we present measurements of oxygen vacancy ordering in epitaxial thin films of SrCoO_{x} and the brownmillerite-perovskite phase transition employing x-ray photon correlation spectroscopy. These and associated synchrotron measurements and theory calculations reveal the close interaction between the kinetics and the dynamics of the phase transition, showing how spatial and temporal fluctuations of heterointerface evolve during the transformation process. The energetics of the transition are correlated with the behavior of oxygen vacancies, and the dimensionality of the transformation is shown to depend strongly on whether the phase is undergoing oxidation or reduction. The experimental and theoretical methods described here are broadly applicable to in situ measurements of dynamic phase behavior and demonstrate how coherence may be employed for novel studies of the complex oxides as enabled by the arrival of fourth-generation hard x-ray coherent light sources.

Rates and extents of mineral precipitation in porous media are difficult to predict, in part because laboratory experiments are problematic. It is similarly challenging to implement numerical methods that model this process due to the need to dynamically evolve the interface of solid material. We developed a multiphase solver that implements a micro-continuum simulation approach based on the Darcy-Brinkman-Stokes equation to study mineral precipitation. We used the volume-of-fluid technique in sharp interface implementation to capture the propagation of the solid mineral surface. Additionally, we utilize an adaptive mesh refinement method to improve the resolution of near interface simulation domain dynamically. The developed solver was validated against both analytical solution and Arbitrary Lagrangian-Eulerian approach to ensure its accuracy on simulating the propagation of the solid interface. The precipitation of barite (BaSO 4 ) was chosen as a model system to test the solver using variety of simulation parameters: different geometrical constraints, flow conditions, reaction rate and ion diffusion. The growth of a single barite crystal was simulated to demonstrate the solver's capability to capture the crystal face specific directional growth.

Unlabelled: Spine disorders are a highly relevant problem in neurosurgical pathology. The development of diagnostic imaging methods makes it possible to perform intraoperative computed tomography. A special intraoperative cone beam computed tomography scanner "O-arm" has been designed; it combines a function of a C-arm machine and computer tomography scanner. The O-arm system can be used along with navigation system and robotic assistance device. Availability of these devices in an operating room allowed us to study the effectiveness and features of intraoperative CT imaging., Objective: To evaluate the intraoperative use a cone beam computed tomography scanner "O-arm" and the navigation system in surgical treatment of spine disorders., Material and Methods: In August-November 2013, 43 patients with degenerative spine disorders, spine and spinal canal tumors underwent surgeries at the N.N. Burdenko Neurosurgical Institute using an intraoperative computed tomography scanner "O-arm" and the navigation system., Results: It is reasonable to use intraoperative CT "O-arm" device with the navigation system when surgical treatment is performed under complex anatomical conditions (a thin root of the vertebral arch, scoliotic or post-traumatic spinal deformity) and the surgery zone cannot be visualized using 2D imaging methods. Intraoperative CT control and navigation system can be employed by neurosurgeons in clinics where the standard stabilizing surgeries and percutaneous methods either are employed rarely or have just started to be used., Conclusions: The use of an intraoperative CT device "O-arm" with the modern navigation system for surgical treatment of spine and spinal cord disorders allows one to perform surgical interventions under complex anatomical conditions, reduces the absorbed radiation dose, and is safe for patients.

Herein we report on the influence of salt and polyelectrolyte (PEL) concentration, molecular weight, and mixing ratio on the size and size distribution of polyelectrolyte complex (PEC) particles composed of cationic poly(diallyldimethylammonium chloride) and anionic poly(styrene sulfonic acid). The unusual salt concentration dependence of PEC particle sizes was observed. This behavior was explained by competition of two processes both related to the charge screening: swelling/shrinking of the outer shell formed by the excess PEL molecules and increasing/decreasing of the aggregation rate of colloidal PEC particles. The results on the size regulation of PEC particles by varying PEL concentration reflect both competitive processes as well. The regulation of the mixing ratio of PEL allows producing PEC particles with different charges, and it does not affect significantly the PEC particle size regulation by salt concentration. The PEC size dependence on the molecular weight of polymer was shown to be power and an exponent value of α ≈ 0.13 was obtained for the spherical PEC particles. This value is lower than one for polymer particles with a compact globular structure with exponent values of α = 0.33. However, the molecular weight of only one polymer component of a two-component PEC particle was varied.