Diffusion Separation Research Articles

On thermophysical parameters of ion-thermal plasma technology for spent nuclear fuel processing

The paper describes the development of the Ion Sputtering – Thermal Separation (IS-TS) technology for closed nuclear fuel cycle and spent nuclear fuel (SNF) reprocessing. The atomization of the SNF pellet is performed by the plasma discharge in an inert gas or hydrogen medium, sputtered SNF atoms in the gas flow move along the separating diffusion tube and deposite separately on selected sections of the tube due to differentiation by saturated vapor temperatures. Based on the numerical calculation of the temperature field and the velocity field of the carrier gas, the values of the thermophysical parameters of the technology are obtained, which make it possible to design a prototype of a diffusion separation system with the optimal mode of sputtering and separate collection of SNF elemental components.

Cu(I) catalyzed ATRP for the preparation of high-performance poly (vinylidene fluoride)-g-poly 2-(dimethylamino)ethyl methacrylate crosslinked anion exchange membranes for enhanced acid recovery

The exclusive selectivity feature of an anion exchange membrane (AEM) makes it a core component of the diffusion dialysis (DD) process. Herein, we have developed a novel synthetic route for the preparation of AEMs with a controlled graft length and density by grafting 2-(dimethylamino)ethyl methacrylate (DMA) chains from the backbone of poly(vinylidene fluoride) (PVDF) by Cu(I) catalyzed atom transfer radical polymerization to produce PVDF-g-PDMA copolymer, which is converted to AEM by the reaction with α,α’-dichloro-p-xylene (XDC). XDC induces positive charge on the membrane surface and increases the hydrophilicity of the membrane. It also acts as a crosslinker and helps to create a network structure in the membrane, which increases overall membrane stability. The AEMs are used to separate hydrochloric acid from its mixture with metal salts by diffusion dialysis. A representative AEM containing 12% w/w PDMA, abbreviated as ATM-2, show diffusion coefficient (UH+) and separation factors (S) of 0.049 m/h and 117, respectively during the separation of HCl from 2 M HCl + 0.09 M FeCl2 solution. ATM-2 also shows higher UH+ and S values for the separation of HCl with its mixture of different metal salts, i.e., NaCl, CuCl2, and AlCl3. ATM-2 membrane endures a small loss of 1.5% and 3.2% in UH+ and S values, respectively, after submerging in a 2 M acid/salt mixture solution for 60 days. This confirms the good acid stability of the AEM. The results indicate the reasonable potency of the prepared AEMs to be a suitable candidate for DD applications.

Irradiation Effects on Stability of δ-UZr2 phase in U-50 wt% Zr Alloy

U-50wt%Zr is a candidate metallic nuclear fuel with potential application in light water reactors due to its excellent thermal properties and high radiation tolerance. The Zr-rich UZr fuels possess greater swelling resistance and fission gas release characteristics compared with U-rich UZr fuels. In this current study, the δ-phase U-50wt%Zr is proton irradiated at room temperature to 1 displacement per atom (dpa) to provide insights on phase stability under irradiation conditions. High resolution characterization of Transmission Electron Microscopy (TEM) and Atom Probe Tomography (APT) characterization techniques are used to elucidate microstructural changes due to irradiation. TEM and APT results show highly oriented bcc β-Zr-rich platelet precipitates nucleating adjacent to α-U phases inside the UZr2 matrix. Formation of this platelet morphology is characteristic of Widmänstatten structure which can be attributed to a variety of factors such as differences in thermal expansion coefficient between the phases, grain size, alloy composition, and cooling rate. The phases present are distinctly different than those observed through in situ annealing, but irradiation accelerates diffusion and phase separation kinetics. These microstructural changes in U-50wt%Zr are different from those achieved by pure thermodynamic or high temperature heavy ion irradiation experiments. Our work, together with previous ones, highlight the necessity to study the U-Zr phase diagram under non-equilibrium thermodynamics conditions to support this material's deployment as a viable nuclear fuel form.

MULTIFRACTAL MODELING OF GAS–WATER RELATIVE PERMEABILITY CONSIDERING MULTISCALE AND MULTIEFFECTS: INVESTIGATION OF UNCONVENTIONAL GAS DEVELOPMENT

Unconventional gas is a momentous energy source due to its considerable reserves and eco-friendly properties, where relative permeability is a key evaluative parameter of unconventional gas extraction. However, the geo-complexity, multiscale and multieffect of the unconventional gas reservoir challenge the relative permeability evaluation and production enhancement. Here, we establish a gas–water flow model by integrating multifractal theory, covering from nanoscale to macroscale and regarding the effects of slip, gas desorption–diffusion and water film separation, to reliably evaluate the relative permeability evolution during unconventional gas development. Based on our model, we describe the permeability of the unconventional reservoir with an 88% less evaluation error compared to the single fractal Darcy with the literature benchmark. Moreover, we characterize the gas–water relative permeability with a no more than 10% evaluation error based on the experimental data. The slip effect plays the most crucial role in the evaluation precision of relative permeability. We reveal that the permeability of the unconventional gas reservoir is decreased by the increase of generalized fractal dimension which enhances the heterogeneity and tortuosity of pores. We uncover that the slip effect facilitates the relative permeability of gas and water. Besides, the gas desorption–diffusion boosts gas relative permeability while limiting water relative permeability, whereas water film separation enhances water relative permeability but hinders gas relative permeability. This work brings insights into the precise description of multiscale and multieffect gas–water porous flow in unconventional gas development.

Diffusive separation in rarefied plume interaction

In the present study, we propose the use of a light, inert carrier gas to support deposition uniformity and rate in continuous physical vapor deposition, in which closely spaced slots or nozzles are required to achieve a sufficiently high deposition rate. Interaction shocks between the emerging rarefied plumes cause undesired nonuniformities in the deposited coating. The present work evaluates the effect of adding a carrier gas on the interaction shock. We study the interaction between two sonic plumes consisting of a binary mixture, i.e., silver as coating material and helium as a light inert carrier gas, by direct simulation Monte Carlo. While the inlet Mach and Knudsen numbers were kept constant, the fraction of carrier gas was varied to single out the effect of species separation. The influence of rarefaction on species separation was also studied. Species separation produces a high carrier-gas fraction in the periphery and an accumulation of the heavier species in the jet core. The resulting change in the speed of sound alters the local expansion characteristics and, thus, shifts the shock location and weakens the shock. These phenomena intensify with the degree of rarefaction. It is shown that adding a light carrier gas increases deposition rate may enhance uniformity and reduce stray deposition.

Thermoacoustic Soret separation.

In a fluid mixture in a channel with an axial time-averaged temperature gradient, high-amplitude oscillating flow can greatly increase the axial flux of thermal diffusion (Soret) separation of the components of the mixture. The enhancement occurs when the oscillating lateral temperature gradient greatly exceeds the axial gradient, causing a large oscillating concentration that can be favorably time-phased with the oscillating flow. This process can occur even with a negligible pressure oscillation or with a negligible temperature response to pressure, as is the case in most liquid solutions. The thermal boundary condition imposed by realistic solids on thermoacoustic liquids is imperfect, adding mathematical complications that are absent for typical gases, for which the solid surface is temporally isothermal. Compared with gas mixtures, the high Lewis number in typical liquid solutions reduces the separation flux associated with the time-averaged temperature gradient, but it also reduces the remixing associated with the time-averaged mole-fraction gradient. For large enough channels, the second-law separation efficiency is only slightly reduced from that of steady liquid Soret separation.

Protein drift-diffusion dynamics and phase separation in curved cell membranes and dendritic spines: Hybrid discrete-continuum methods.

We develop methods for investigating protein drift-diffusion dynamics in heterogeneous cell membranes and the roles played by geometry, diffusion, chemical kinetics, and phase separation. Our hybrid stochastic numerical methods combine discrete particle descriptions with continuum-level models for tracking the individual protein drift-diffusion dynamics when coupled to continuum fields. We show how our approaches can be used to investigate phenomena motivated by protein kinetics within dendritic spines. The spine geometry is hypothesized to play an important biological role regulating synaptic strength, protein kinetics, and self-assembly of clusters. We perform simulation studies for model spine geometries varying the neck size to investigate how phase-separation and protein organization is influenced by different shapes. We also show how our methods can be used to study the roles of geometry in reaction-diffusion systems including Turing instabilities. Our methods provide general approaches for investigating protein kinetics and drift-diffusion dynamics within curved membrane structures.

Cell-Size Space Regulates the Behavior of Confined Polymers: From Nano- and Micromaterials Science to Biology.

Polymer micromaterials in a liquid or gel phase covered with a surfactant membrane are widely used materials in pharmaceuticals, cosmetics, and foods. In particular, cell-sized micromaterials of biopolymer solutions covered with a lipid membrane have been studied as artificial cells to understand cells from a physicochemical perspective. The characteristics and phase transitions of polymers confined to a microscopic space often differ from those in bulk systems. The effect that causes this difference is referred to as the cell-size space effect (CSE), but the specific physicochemical factors remain unclear. This study introduces the analysis of CSE on molecular diffusion, nanostructure transition, and phase separation and presents their main factors, i.e., short- and long-range interactions with the membrane surface and small volume (finite element nature). This serves as a guide for determining the dominant factors of CSE. Furthermore, we also introduce other factors of CSE such as spatial closure and the relationships among space size, the characteristic length of periodicity, the structure size, and many others produced by biomolecular assemblies through the analysis of protein reaction-diffusion systems and biochemical reactions.

Parameter Sensitivity Study on Inflow Distortion of Boundary Layer Ingested Turbofans

The inflow distortion to the fan introduced by the ingestion of the fuselage boundary layer is the most critical challenge in realizing the benefits of boundary later ingesting (BLI) concepts. Minimizing the level of distortion while maintaining the desired amount of ingested boundary layer and free stream flow is crucial in minimizing the penalties to fan efficiency and noise emissions. In this paper, a parametric sensitivity study is performed to examine the integration of two semi-buried BLI turbofans at the rear end of a typical tube-and-wing body (TWB) fuselage. The key parameters influencing BLI, such as the nacelle installation positions, wing position, fuselage length, rear fuselage shape, intake shape and operating conditions were evaluated by computational fluid dynamics (CFD). Among the investigated parameters, increasing the nacelle spanwise installation spacing improved inflow distortion by reducing the diffusion separation, but this needs to be offset against the added weight and nacelle drag. A high wing position variant showed strong interference between the wing and the nacelle, which must be avoided as this significantly increases the complexity of the inflow distortion. A moderate angle of attack (AOA) variation did not affect the fan inflow distortion but there was a tendency for interference from the wing to increase when the AOA was increased. The general conclusions from this study will be useful in the conceptual design of a similar type of BLI configuration, as well as a more comprehensive optimization of this type of aircraft–engine integration.

Boosting light harvesting and charge separation in 3D porous WS2@C@ZnIn2S4 skeleton heterojunction for efficient solar fuels production

Construction of photocatalysts with efficient light-harvesting and charge separation properties for boosting photocatalytic hydrogen (H2) evolution is still a challenge. Herein, a three-dimensional (3D) porous WS2@C@ZnIn2S4 skeleton heterojunction is successfully synthesized by epitaxial growth of ZnIn2S4 nanosheets on the WS2@C skeleton. The optimal WS2@C@ZnIn2S4 photocatalyst exhibits considerable photocatalytic H2 evolution rate (11.15 mmol·g−1·h−1) and CO2-to-CH4 production performance (43.29 μmol·g−1), respectively. The high photocatalytic performance can be ascribed to the fact that multiple light reflection and scattering behaviors originated from 3D architecture facilitates to prolong the interaction length between photons and catalyst, which significantly enlarging the light-harvesting ability and utilization efficiency. Importantly, highly conductive WS2@C skeleton can drive photo-induced charge transportation from ZnIn2S4 to WS2 co-catalyst via the interfacial charge-transfer pathways. The DFT calculations further demonstrate the promotional effects of multiple diffuse reflection and separation of photo-generated carriers in photocatalytic H2 evolution.

Diffusion separation of submicron particles by using magnetized spheres

The diffusion capture of submicron-sized particles in the gradient field formed by the magnetized ferromagnetic spheres in the external homogeneous magnetic field has been theoretically investigated. Magnetic field measurements were made with a specially designed prototype magnetometer. The simple semi-empirical formula of the magnetic force acting on the submicron particle was determined. The analytical solution of the diffusion equation for steady states was obtained. The concentration distribution of the particles in capturing regions was determined. A formula was obtained to evaluate the critical size of the submicron particles captured in this area. The effects of magnetic, hydrodynamic and geometric parameters of the investigated system on the critical size of the particles in the diffusion event were evaluated. The critical size of the particles decreased with the increase of the external magnetic field and was found to be independent of the dimensions of the spheres. As a result; the diffusion separation phenomenon in the gradient field formed by the magnetized ferromagnetic spheres is more effective than in the gradient magnetic field formed by the wires. The results obtained contribute to the development of the theory of magnetic separators using ferromagnetic matrix elements.

The variability and seasonality in the ratio of photosynthetically active radiation to solar radiation: A simple empirical model of the ratio

A constant ratio of photosynthetically active radiation (PAR) to solar radiation (SR) (about 0.45–0.46) has been used in many ecological studies to convert SR into PAR by multiplication. The constant ratio is useful and convenient. However, there is no general agreement on whether the ratio is 0.45 or 0.46 and how distributed globally. Accordingly, many local empirical ratios have been reported. This study aims to demonstrate a global distribution of the ratio and its changing range. Thus, we created two simple empirical models to estimate the ratio based on the in-situ climatic data to achieve the aim. The models were created based on accurate data of SR and PAR observed using a direct and diffuse separation method at Tateno in Tsukuba, Japan. At three validation sites in Japan, the ratio could be estimated with an error within 3%, a considerable reduction from 15% in using a constant. The numerical model also produced the ratio within approximately 3% errors. Using the proposed model, we demonstrated that the annual mean of the ratio had a range from 0.409 to 0.477. The results will contribute to the uncertainty estimation when using a constant ratio.

Recent Advances in Porous Materials for Photocatalytic CO2 Reduction.

Photocatalytic CO2 reduction into solar fuels is a promising technology for addressing energy and CO2 emission issues. Because of the superior properties in CO2 adsorption and activation, molecular diffusion, light absorption, and charge separation and transfer, porous materials have been developed into a multifunctional platform for photocatalytic CO2 reduction. In this Perspective, we first discuss the emerging trends of CO2 reduction in major inorganic porous materials-based photocatalysts, such as mesoporous materials, macroporous materials, hollow materials, hierarchically porous materials, and zeolites. Prospects and challenges in the development of porous materials-based photocatalysts are then outlined. Finally, we envision feasible solutions for the deployment of porous materials to enhance photocatalytic CO2 reduction performance.

Insight into the influence of morphology and structure of Fe3O4 nanoparticles on demulsification efficiencies

Functional Fe3O4 nanoparticle (Fe3O4 NP) is one of the most attractive candidates in the demulsification field because of its outstanding recycling ability, low cytotoxicity, and good biocompatibility. However, the lack of research on their interfacial properties greatly inhibits further development in the industrial demulsification process. The main aim of this work is to explore interfacial properties of functional Fe3O4 NPs from their intrinsic natures, namely morphologies and structures. Three Fe3O4 NPs with different morphologies, including triangle-shaped Fe3O4 NPs (TF NPs), octahedron-shaped Fe3O4 NPs (OF NPs) and truncated octahedron-shaped Fe3O4 NPs (TOF NPs), were prepared by using the solvothermal reaction. Their demulsification capacities of water-in-cyclohexane (W/C) emulsion were evaluated and the TOF NPs had best performance. The demulsification process including diffusion, adsorption and phase separation stages of these Fe3O4 NPs were investigated in detail by interfacial experiments and mathematical models for explain the demulsification result. The diffusion coefficient was calculated at both the early and late stages of the demulsification process, along with their adsorption energy and the elastic modulus of oil-water interfaces. TOF NPs had the largest diffusion coefficient of 1.777 × 10−6 and 2.443 × 10−6 m2/s at the early and late stages, respectively. The W/C interface adsorption energy of TOF NPs were much lower than that of the others and the elastic modulus of W/C interface reduced by TOF NPs was also more effective than that by the others.

The origin of fast‐charging lithium iron phosphate for batteries

AbstractSince the report of electrochemical activity of LiFePO4 from Goodenough's group in 1997, it has attracted considerable attention as cathode material of choice for lithium‐ion batteries. It shows excellent performance such as the high‐rate capability, long cyclability, and improved safety. Furthermore, the raw materials cost of LiFePO4 are lower and abundant compared with conventional Li‐ion battery oxides compounds. The lithium extraction from LiFePO4 operates as biphase mechanism accompanied by a relatively large volume change of ∼6.8%, even though, nanosized LiFePO4 shows exceptionally high‐rate capability during cycling. In the aim to explain this remarkable feature, recent reports using cutting‐edge techniques, such as in situ high‐resolution synchrotron X‐ray diffraction, explained that the origin of the observed high‐rate performance in nanosized LiFePO4 is the absence of phase separation during battery operation at high current densities. In this review, the importance of understanding lithium insertion mechanisms towards explaining the significantly fast‐charging performance of LiFePO4 electrode is highlighted. In particular, phase separation mechanisms, are unclear and deserve considerable attention. Several proposed models for Li diffusion and phase separation in LiFePO4 are summarized. In addition, the crystallographic aspects, defect structures of LiFePO4 are also reviewed. Finally, the status of development of other olivine‐type LiMPO4 (M = Co, Mn, and Ni) are summarized.

Design of Gas Diffusion Cascade for Production of Carbon Isotope Using Ethylene as Processing Gas

Carbon-13 isotope has a wide range of applications in medical diagnosis, scientific research, food safety and other fields, and the market demand for carbon-13 isotope is also showing an upward trend. In order to explore the separation and production methods of carbon-13 isotope, the gas diffusion separation experiment with ethylene as the processing gas was carried out, and the cascade was designed on this basis. Through the single-stage separation experiment, it can be obtained that the overall separation factor of the gas diffusion method for separating ethylene under the existing experimental conditions is 1.014. The gas diffusion cascade enrichment of carbon-13 isotope involves two steps. The first step is to separate ethylene using a squared-off cascade to obtain the heavy fraction with the carbon-13 isotope abundance reaching 49%. The second step is to convert ethylene into carbon dioxide, and then use a squared-off cascade to separate the carbon dioxide to obtain the heavy fraction with the carbon-13 isotope abundance reaching 95%.

Isotopic Composition of CO2 in the Atmosphere of Mars: Fractionation by Diffusive Separation Observed by the ExoMars Trace Gas Orbiter

AbstractIsotopic ratios in atmospheric CO2 are shaped by various processes throughout Mars' history, and can help understand what the atmosphere of early Mars was like to sustain liquid water on its surface. In this study, we monitor the O and C isotopic composition of CO2 between 70 and 130 km for more than half a Martian year using solar occultation observations by the Atmospheric Chemistry Suite onboard the ExoMars Trace Gas Orbiter. We find the vertical trends of the isotopic ratios to be consistent with the expectations from diffusive separation above the homopause, with average values below this altitude being consistent with Earth‐like fractionation (δ13C = −3 ± 37‰; δ18O = −29 ± 38‰; and δ17O = −11 ± 41‰). Using these measurements, we estimate that at least 20%–40% of primordial C on Mars has escaped to space throughout history. The total amount of C lost from the atmosphere is likely to be well in excess of this lower limit, due to carbonate formation and further sink processes. In addition, we propose a photochemical transfer of light O from H2O to CO2 to explain the larger enrichment in the ratio in H2O than in CO2.

Liquid-phase water isotope separation using graphene-oxide membranes

We report pressure-driven liquid-phase isotope separation (dead-end filtration) to enrich D and 18O in natural water using graphene oxide (G-O) and UV-reduced graphene oxide (UV-rG-O) membranes. The isotope diffusivity (molecular diffusion and adsorption separation) was found to be responsible for isotope separation. Adsorption separation is the dominant mechanism for improvements in D and 18O enrichment via increased G-O loading that leads to the increased number of adsorption sites (epoxy and hydroxyl groups on G-O), and higher degrees of reduction of G-O that result in the narrowing of the nanochannels which decreases the portion of water molecules experiencing molecular diffusion. The best performing membrane was “UV-rG-O” made by exposing a G-O membrane to 24 h UV irradiation from one side, showing enrichment of D of 0.5% for D/H and 18O of 0.08% for 18O/16O in a single-stage experiment, without contribution from the vapor pressure isotope effect. This work improves the understanding of the mechanisms for graphene-based membrane separation of D and 18O enriched water.

Nonequilibrium Processes in Polymer Membrane Formation: Theory and Experiment.

Porous polymer and copolymer membranes are useful for ultrafiltration of functional macromolecules, colloids, and water purification. In particular, block copolymer membranes offer a bottom-up approach to form isoporous membranes. To optimize permeability, selectivity, longevity, and cost, and to rationally design fabrication processes, direct insights into the spatiotemporal structure evolution are necessary. Because of a multitude of nonequilibrium processes in polymer membrane formation, theoretical predictions via continuum models and particle simulations remain a challenge. We compiled experimental observations and theoretical approaches for homo- and block copolymer membranes prepared by nonsolvent-induced phase separation and highlight the interplay of multiple nonequilibrium processes─evaporation, solvent-nonsolvent exchange, diffusion, hydrodynamic flow, viscoelasticity, macro- and microphase separation, and dynamic arrest─that dictates the complex structure of the membrane on different scales.

Characterizations on phase reconstruction, microstructure evolution and separation of magnetic ferrite ceramics from low-grade manganese ores by novel uphill reaction diffusion and magnetic separation

Traditional utilization of ferruginous manganese ore has mainly concentrated on the separation of Mn and Fe. However, an alternative process of novel uphill reaction diffusion followed by magnetic separation was developed for the synchronous recovery of manganese and iron as the form of ferrite ceramics from the ferruginous manganese ore in this work. The phase reconstruction, interfacial uphill reaction diffusion, ferrite size quantification and separation behavior were characterized via various means of XRD, XPS, TEM, VSM, SEM-EDS, optical microscopy, microhardness and thermodynamic analyses. In the phase reconstruction course, manganese and iron oxides reacted to form ferrites, whereas the impurities were enriched in liquid silicate phases due to the uphill reaction diffusion. Meanwhile, the ferrite particles grew and the liquid silicates aggregated owing to the intensified reaction diffusion by CaO addition. During the water quenching process, microcracks at the cleavage plane between the silicate and ferrites are preferentially generated due to fast cooling shrinkage of liquid silicates. Huge differences in hardness, magnetism, fusibility and cooling shrinkage of ferrites and silicates provided excellent mineralogical conditions for the successful grinding and magnetic separation of ferrites. Eventually, a soft magnetic manganese ferrite precursor with recoveries of 89.2 wt% iron and 85.6 wt% manganese was obtained. The interfacial reaction mechanisms for the formation of ferrites and silicates were also discussed in this work.