Stripping Mechanism Research Articles

Stripping mechanism and Gaussian distribution model of a concave bionic comb for stripping prior to cutting

Stripping prior to cutting is a harvesting technique that only strips rice grains and obtains complete straws. This paper aims to solve the problems of high loss rate and short throwing distance for stripping prior to cutting. A concave bionic comb was developed based on the filiform papilla structure on the surface of a cattle tongue tip. The mechanism analysis and comparative research of the flat comb and the bionic comb were carried out. The results showed that when the arc radius was 5.0 mm, the magnification ratio of filiform papilla was 4.0, and the concave angle was 60°, the loss rate of falling grain was 4.3 %, and the loss rate of uncombed grain was 2.8 %. The diffusion angle of bionic comb was smaller than that of flat comb. The distribution characteristics of the thrown materials conformed to Gaussian distribution. Under the same working conditions, the falling grain loss rate and uncombed loss rate of the bionic comb were always lower than that of the flat comb. This study provides reference for the cross application of bionic technology and crop production field, promotes the harvesting way application of stripping prior to cutting in gramineous plants such as rice, wheat and sorghum, and provides a basis for harvesting the whole straws and expanding the way of comprehensive utilization of straws.

Removal Mechanisms and Microstructure Characteristics of Laser Paint Stripping on Aircraft Skin Surface

As a non-contact and non-destructive technology, laser cleaning provides an alternative method for the paint stripping of aircraft skins. Herein, the particular multi-layer paint on the aluminum alloy aircraft skin surface was stripped by adjusting laser parameters. Beyond expectation, multi-layer paint led to a highly complex surface as opposed to the ordinary single-layer paint after laser cleaning. The surface morphology, chemical compositions, and surface functional groups of the samples were analyzed, and the successful depaint parameters were found in this experiment with damage free of the aluminum substrate, i.e., laser energy density of 5.09 J/cm2 and scanning speed of 700 mm/s. More importantly, this paper revealed that the mechanisms of laser paint stripping from Al alloy aircraft skin are thermal decomposition, evaporation, and spallation. After laser cleaning, the surface nanoindentation hardness with paint completely stripped and undamaged was increased by 3.587% relative to that of the conventional mechanical lapping sample. The improvement of nanoindentation hardness was also confirmed by the microstructure characterized with electron backscatter diffraction (EBSD) in which plastic deformation led to strain hardening of the substrate surface. This study lays a solid foundation for large-scale, high-efficiency, and low-pollution removal of more complex paint layers on aircraft surfaces in the future.

New ultra-small design and high performance of an 8×8 massive MIMO antenna for future 6G wireless devices

The demand for the array antenna that consists of multiple ports has increased in recent years, because of its main importance in reducing noise and interference between users. In this paper, we propose a new method for designing an 8×8 (16-ports) multi-input and multi-output (MIMO) antenna. This method relied on the Micro Strip mechanism so that we presented a small antenna that operates at wide and multi-bands of millimeter waves (Mm-Waves). According to the information curves generated by the CST experimental software, it was observed that the proposed antenna operates well from 36 to 60 GHz. Therefore, the antenna achieved the best results in terms of many most important parameters, the reflection coefficient is <-10 dB, return loss is <-25 dB, and voltage standing wave ratio (VSWR) is < 2. In addition, the efficiency of the antenna for all frequencies from 70% to 97%, the envelope correlation coefficient (ECC) is <0.001, and the diversity gain (DG) is 10 dB for all frequencies, while the maximum gain achieved by the antenna is 9 dB at 46 GHz. All these good results achieved by the antenna make it the prominent and potential element in most of the future 6G wireless communication systems.

Ammonia recovery from anaerobic digestate: State of the art, challenges and prospects

Nitrogen-containing wastewater and organic wastes are inevitably produced during human activities. To reduce nitrogen pollution, much energy has been used to convert ammonia nitrogen into nitrogen gas through biological nitrogen removal method. However, it needs to consume high energy again during industrial nitrogen fixation, which give rise to massive greenhouse gas (GHG) emissions. Therefore, ammonia recovery from organic wastes has attracted much attention in recent years. In this review, the advantages and disadvantages of ammonia stripping, membrane separation and struvite precipitation are discussed firstly. The ammonia stripping mechanisms, influencing factors, mass transfer process, and the latest innovative ammonia stripping techniques from the anaerobic digestate of organic wastes are critically reviewed. Additionally, a comprehensive economic analysis of different ammonia removal or recovery processes is carried out. The challenges and prospects of ammonia recovery are suggested. Ammonia recovery is of great significance for promoting nitrogen cycle, energy saving and GHG emission reduction.

Residual oil retention and stripping mechanism of hydrophilic pore surfaces during CO2 and N2 combined gas flooding

The mixed gas of CO2 and N2 can replace the great mass of the remaining oil in the center of the porous media channel, but the surface of the pore channels still retain more residual oil. Most of the previous studies focused on how to displace the residual oil in the center of the pore passages, while ignoring how to enhance the recovery degree of the residual oil on the pore surfaces. Moreover, there are few research results on the mechanism of residual oil retention and stripping on pore surfaces during CO2–N2 combined gas flooding, which need to be improved and supplemented. In this paper, the microscopic interaction process among gas phase, oil phase and pore surfaces were explored by molecular dynamics, the changes in microstructural between n-decane molecules and the spatial distribution of gas molecules and n-decane molecules in the system was clarified. The interaction energy between gas, n-decane and pore surfaces were analyzed to reveal the mechanism of remaining oil retention and stripping. The results indicated that when only CO2 in the gas phase, the oil films were easily divided by CO2 molecules, and the adsorption layer formed by CO2 molecules on the quartz surface could well detach the oil phase from the quartz surfaces. With the increase of the proportion of N2 in the mixed gas, the interaction energy between the gas and n-decane phase and between the gas phase and pore surfaces decreased, and the capacity of the gas phase to peel off the oil films from the pore surfaces was weakened. When the proportion of N2 in the gas phase exceeded 25%, the gas phase has no ability to peel off the oil films from the quartz surfaces. The research results have guiding significance for the CO2-N2 combined gas flooding to further tap the remaining oil.

A methodology for quantifying combustion efficiencies and species emission rates of flares subjected to crosswind

Despite strong indications that flares subjected to crosswinds can undergo fuel stripping mechanisms that reduce efficiency and lead to emission of unburned fuel, most published flare experiments have not considered the impact of a crosswind. Knowledge of flare performance in turbulent crosswinds representative of atmospheric wind is especially lacking. Accurate experiments to fill this gap can only be achieved in an environment where the wind conditions can be controlled. This work presents a methodology to determine the carbon conversion efficiency and species emission rates of a flare burning in a closed-loop wind tunnel. The developed methodology is based on solving an unsteady mass balance to relate measured accumulation rates in a closed-loop wind tunnel to emission rates, while extending the applicability and correcting errors of an earlier method. The developed methodology considers complicating factors such as infiltration and exfiltration of gases into and out of the wind tunnel, potential for reburning of products within the wind tunnel, and presence of inert species in the fuel stream. The methodology is assessed with a comprehensive Monte Carlo uncertainty and sensitivity analysis. Results suggest that carbon conversion efficiency can be measured with a systematic bias uncertainty of ≲ ±0.5%, ranging from 0.04% for a 99% efficient flare to 0.55% for a 70% efficient flare at 95% confidence, and methane emission rates can be measured within ±3.25% at 95% confidence. Demonstration experiments in a large closed-loop wind tunnel show that precision (repeatability) uncertainties will be larger but that overall (combined bias and precision) uncertainties of <10% are readily achievable.

Lithium metal stripping mechanisms revealed through electrochemical liquid cell electron microscopy

An understanding of lithium stripping is as important as that of lithium plating to achieve significant advances in using lithium metal anodes for high-energy rechargeable batteries. However, there have been limited studies on lithium stripping compared to lithium plating. Here we report the lithium stripping mechanisms revealed through in-situ electrochemical liquid cell transmission electron microscopy (TEM). We directly observe and compare the stripping behavior of the in-situ grown lithium dendrites and lithium nanograins covered by a lithium fluoride-rich solid-electrolyte interphase (SEI). We find the sporadic lithium stripping behavior and three important modes that can describe the stripping of individual lithium deposits, regardless of their morphology: (i) symmetric stripping, (ii) surface-preferred asymmetric stripping, and (iii) interface-preferred asymmetric stripping. In addition, SEI chemical mapping with high spatial resolution shows a remarkable SEI loss at the end of the lithium metal stripping, which illustrates the importance of SEI protection in the subsequent cycles.

(Invited) Zeolite-Templated Carbon As a Model Material for Electrochemical Energy Storage in Nanometre-Spaced Carbon Channels

Beyond lithium-ion battery (LIB) chemistries demand new electrode materials exhibiting unique features to accommodate the larger and/or multivalent active ions. Zeolite-templated carbon (ZTC) is an ordered microporous carbon scaffold that is molecularly thin, electrically conductive, and covalently connected in three dimensions. Its narrow pore size distribution is centered at 1.2 nm, permitting the introduction and ultrafast conduction of large molecular guests. In this work, we demonstrate the serviceability of ZTC as a stable cathode material across wide voltage ranges for both bulky, polyatomic anions (as in dual-ion batteries, DIBs, and/or hybrid capacitors, HCs) and multivalent cations (e.g., magnesium-ion batteries, MIBs) in high energy density and high power density electrochemical cells. Charge storage proceeds by a purely capacitive mechanism at the surface of ZTC, mated with the faradaic mechanism of metal plating and stripping at the anode. A suite of techniques including solid-state NMR spectroscopy sheds insight into the role of the solvent, anion, and cation in electrochemical insertion/deinsertion of the active ions within the microporous framework of ZTC. Figure 1

Stepwise separation and recovery of molybdenum, vanadium, and nickel from spent hydrogenation catalyst

Recovering metal values in hazardous spent hydrogenation catalysts is of vital economic and environmental importance. Herein, the selective recovery of valuable molybdenum (Mo), vanadium (V), and nickel (Ni) from spent hydroprocessing catalysts are achieved by using a sulfuric acid leaching-stepwise extraction process. After roasting in the air at 400 °C, the valuable metals are effectively leached within 20 min by 1 mol/L sulfuric acid at 75 °C. The leaching efficiency of Al, Ni, Mo, and V is 22.16%, 99.44%, 98.59%, and 100%, respectively. Based on the species analysis of the leachate, a stepwise extraction separation route was established for selective recovery of Mo, Ni, and V from the acidic leachate. Mo and V are preferentially co-extracted by the mixed TOA/Cyanex272 with a molar ratio of 7:3, which exhibits an excellent extraction selectivity over Ni and Al. Increasing the concentration of Cyanex272 in the mixed system can effectively improve the selective stripping of vanadium but slightly inhibit its extraction. Residual Ni in the raffinate can be selectively separated by 50%(V/V) commercial HBL110 with an extraction efficiency of 98.5%. Especially, the reductive sodium sulfite can greatly enhance the selective stripping of vanadium from the loaded organic phase. Residual Mo in the organic phase can be well stripped with an alkaline solution. The selective stripping mechanism of vanadium is revealed by the FT-IR and Raman spectra. This work proposes a sustainable stepwise separation route for recovering valuable metals in the spent hydroprocessing catalyst.

Design and evaluation of coconut fiber bionic‐stripping device based on Lucanidae palate frictional characteristics

AbstractManual stripping of coconut fiber has low processing efficiency coupled with difficulty in operation. To overcome these problems, a coconut fiber bionic‐stripping device based on Lucanidae palate frictional characteristics was designed. The device relied on the torsion spring edge hook and brush working principle to strip the coconut fiber. The coconut shell was not damaged during the stripping operation owing to the elasticity and toughness of the bionic torsional spring. The test parameter optimization was carried out using the coconut fiber bionic‐stripping device and analyzed using Design‐Expert.V8.0.6 Software. The results showed that the planting distance between torsion springs had significant effect on stripping coconut fiber (p &lt; .001), but the diameter of torsion spring had the least effect on stripping coconut fiber. Regression analysis of the test data showed that the device had higher processing efficiency at coconut rotation speed of 1200 rad/min, coupled with bionic torsion springs diameter and planting distance of 2.0 and 17 mm, respectively. Under optimal combination of parameters, coconut fiber removal thickness was found to be R△ = 30.9 mm. The data obtained showed high repeatability, thereby indicating that the coconut fiber bionic‐stripping device can meet the technological requirements for coconut fiber removal.Practical ApplicationsThis study focuses on coconut characteristics as well as the process requirements for coconut fiber removal. A mechanism to strip the fiber using bionic torsion springs was proposed, which was designed based on the characteristics of the Lucanidae palate. Including a device for peeling coconut fiber using bionic torsion springs. Furthermore, the structural stress analysis of the device was carried out so as to explore the feasibility of using the bionic torsion spring group to peel coconut fiber. Parameter optimization test, performance analysis, and comparative performance analysis were carried out using the device to analyze the influence of different bionic torsion spring group parameters on the thickness of stripped coconut fiber. This can provide a theoretical and experimental basis for the study of coconut fiber stripping mechanism, and can broaden the existing research methods of coconut fiber stripping.

Bridging heterogeneous and homogeneous catalysts by ultrathin metal-polyphthalocyanine-based nanosheets from electron-coupled transalkylation delamination

Homogeneous and heterogeneous materials are attractive electrochemical reaction catalysts, specifically metal-nitrogen-carbon (M-Nx-C) organic-based molecular materials are emerged as the most promising candidates. However, efficiently producing M-Nx-C organic-based nanosheets for solving the poor activity of bulk-phase catalysts remains a significant challenge. Herein, we put forward a first concept of semi-homogeneous molecular catalysts, through producing 2D metal-polyphthalocyanine (M-PPc) nanosheet with the superiority of hetero/homogeneous via an electrochemical delamination to achieve bridging from hetero to homogeneous. Multi-step ex-situ characterizations and theoretical simulations reveal a novel mechanism of electrochemical stripping, named as electron-coupled transalkylation, where occurs transalkylation, site-to-site transalkylation, and hydrocarbon evolution reactions accompanied by the transformation of intermediates from B-Ni1.0Fe0.3 PPc, (TBA+)x·B-Ni1.0Fe0.3 PPc, x*(C4H9)x·B-Ni1.0Fe0.3 PPc, to final product of Ni1.0Fe0.3 PPc NSs, realizing the eventual delamination. The semi-homogeneous Ni1.0Fe0.3 PPc NSs delivers a lower overpotential of 269 mV to reach 10 mA cm-2 than benchmark RuO2 and maintains superior stability for oxygen evolution. DFT calculations unveil that the NiN4 double sites of Ni1.0Fe0.3 PPc NSs acted as real catalytic centres not only reduce the energy barrier of reaction process, but also accelerate adsorption of intermediates and desorption of oxygen molecules, thus boosting the oxygen evolution kinetics.

Direct dynamics simulation of the thermal O(3P) + dimethylamine reaction in the triplet surface. I. Rate constant and product branching

AbstractIn order to provide atomistic details for the mechanism of the collisional dynamics of O(3P) and dimethylamine (DMA) in the triplet electronic surface, direct dynamics simulations are reported herein. The simulations are performed at the U‐HSE06/aug‐cc‐pVDZ level of theory. The results are reported for the relative collision energy of 7.8 kcal/mol. For the vibrational and rotational excitations, following temperature regimes have been considered: 200 and 10 K, respectively. Simulations reveal that the reaction can lead to two product channels in the considered energy regime: (1) 2OH + 2CH3NHCH2 and (2) 2OH + 2CH3NCH3. The computed reaction cross section for pathways 1 and 2 are as follows: 17.89 0.20 Å2 and 3.28 0.03 Å2, whereas the computed microcanonical reaction rate constants for pathways 1 and 2 are as follows: (4.21 0.05)*10−10 and (7.72 0.07)*10−11 cm3/(molecule sec). Both pathways follow direct and indirect H abstraction processes. Among the direct pathways, stripping and rebound mechanisms have been observed, whereas the indirect pathway involves formation of a post‐reaction complex having lifetime ~0.4–0.5 ps. The velocity scattering angle distribution for the reaction is dominated by scattering in the sideways (60–120 ) and backward (120–180 ) directions with some contribution from the scattering in the forward direction (0–60 ).

Observing Ram Pressure at Work in Intermediate Redshift Clusters with MUSE: The Case of Abell 2744 and Abell 370

Abstract Ram pressure stripping has been proven to be effective in shaping galaxy properties in dense environments at low redshift. The availability of Multi Unit Spectroscopic Explorer (MUSE) observations of a sample of distant (z ∼ 0.3–0.5) clusters has allowed one to search for galaxies subject to this phenomenon at significant lookback times. In this paper we describe how we discovered and characterized 13 ram-pressure-stripped galaxies in the central regions of two intermediate redshift (z ∼ 0.3–0.4) clusters, A2744 and A370, using the MUSE spectrograph. Emission-line properties as well as stellar features have been analyzed to infer the presence of this gas-only stripping mechanism, that produces spectacular ionized gas tails (Hα and even more astonishing [O ii](3727, 3729)) departing from the main galaxy body. The inner regions of these two clusters reveal the predominance of such galaxies among blue star-forming cluster members, suggesting that ram pressure stripping was even more effective at intermediate redshift than in today’s universe. Interestingly, the resolved [O ii]/Hα line ratio in the stripped tails is exceptionally high compared to that in the disks of these galaxies, (which is comparable to that in normal low-z galaxies), suggesting lower gas densities and/or an interaction with the hot surrounding intracluster medium.

Adsorption behavior of n-hexane and its mixtures with CO2, CH4, H2O and SDBS in hydrophobic silica nanopores

Different solvents including CO2, CH4, H2O and chemical agents are used to enhance oil recovery (EOR) in shale oil reservoirs. However, due to the complex pore structure and multi-phase fluids, the adsorption behavior of hydrocarbons in nanopores becomes an important effect for the shale oil stripping. A comprehensive comparison of n-hexane (n-C6H14) and its mixtures of CO2, CH4, H2O and sodium dodecyl benzene (SDBS) in hydrophobic silica nanopores is studied using molecular dynamics (MD) simulation in this paper, and the adsorption configuration, the adsorption density and the adsorption energy are discussed successively to reveal the adsorption mechanism of different injection solvents. The configuration results show that n-hexane forms a relatively denser adsorption structure on the hydrophobic silica surface. After solvents of CO2, CH4 or SDBS is injected with the same injection volume, CO2 or CH4 will be scattered around the system, H2O will be aggregated on surface as a group, while SDBS will be aggregated in the adsorbed oil layer. Six symmetrical adsorption layers of n-hexane are formed in nanopores with different solvent/n-hexane, and the density increases gradually from center to surface. The density peak of the first n-hexane adsorption layer (near the surface) is in the order of CO2/n-hexane system > CH4/n-hexane system > H2O/n-hexane system > SDBS/n-hexane system. The van der Waals interaction is the main interaction between fluids (n-hexane and different solvents) and the silica surface. SDBS has the strongest ability to reduce binding energy, followed by H2O, CH4 and CO2. The density distribution and the calculation of C atoms show that n-hexane molecules can be effectively desorbed from the silica surface. With the same injection volume, SDBS has the best ability of stripping shale oil, followed by H2O, CH4 and CO2. The results obtained in this paper provide important insights into the mechanism of oil adsorption and stripping using different solvents in shale oil reservoirs.

Allostery and molecular stripping mechanism in profilin regulated actin filament growth

Profilin is an actin-sequestering protein and plays key role in regulating the polarized growth of actin filament. Binding of profilin to monomeric actin (G-actin) allows continuous elongation at the barbed end (BE), but not the pointed end, of filament. How G-actin exchanges between the profilin-sequestered state and the filament state (F-actin) to support the BE elongation is not well understood. Here, we investigate the involved molecular mechanism by constructing a multi-basin energy landscape model and performing molecular simulations. We showed that the actin exchanging occurs by forming a ternary complex. The interactions arising from the BE binding drive the conformational change of the attached G-actin in the ternary complex from twist conformation to more flatten conformation without involving the change of nucleotide state, which in turn destabilizes the actin–profilin interface and promotes the profilin stripping event through allosteric coupling. We also showed that attachment of free profilin to the BE induces conformational change of the BE actin and facilitates its stripping from the filament. These results suggest a molecular stripping mechanism of the polarized actin filament growth dynamics controlled by the concentrations of the actin–profilin dimer and the free profilin, in which the allosteric feature of the monomeric actin plays crucial role.

Selective separation of lithium from the high magnesium brine by the extraction system containing phosphate-based ionic liquids

The new extraction system containing phosphate-based ionic liquid ([N 1888 ][P 507 ] + TBP+FeCl 3 ) could significantly reduce the striping acidity from 6–9 mol·L −1 to 1~1.5 mol·L –1 . At the same time, the Li + extraction efficiency and separation factor were 63.8% and 190.7, respectively. • For the new system, Li + could be effectively stripped by HCl (1~1.5 mol·L −1 ). • The optimal results of E (Li) and β (Li/Mg) were 63.8% and 190.7, respectively. • The E (Li) remained above 70% by six extraction-stripping-extraction cycles. The high acidity of stripping is one of the major problems that hinder the industrialization of the tributyl phosphate (TBP) + FeCl 3 system for lithium extraction from the salt lake brines with high Mg/Li ratio. In this study, a novel solvent extraction system, trialkylmethylammonium di(2-ethylhexyl)orthophosphinate ([N 1888 ][P 507 ]) + TBP + FeCl 3 , was developed to significantly reduce the difficulty of stripping and simplify the extraction process. The conditions of extraction and stripping were systematically studied in the present work. The results showed that Li + extraction efficiency could reach 61% under the optimal extraction parameters and Li + stripping ratio was 90% with a relative mild conditions of O/A = 10:1, [HCl] aq = 1.5 mol·L –1 . Also, combined with experimental results, FT-IR analysis, and UV analysis, the possible mechanisms of lithium extraction and stripping were put forward. Li + was extracted from the aqueous phase through the formation of [Li·2TBP][FeCl 4 ] adduct, meanwhile [N 1888 ][P 507 ] was just slightly involved in the extraction step. In the stripping procedure, the interaction between [FeCl 4 ] − and [Li·2TBP] + might be destroyed, and new possible complexes, [Li·2TBP] + , and [FeCl 4 ·TBP·P 507 ] 2− /[FeCl 4 ·P 507 ] 2− were formed in the organic phase. Additionally, the extraction efficiency of Li + remained above 70% while the organic phase was reused for six cycles. Compared with the traditional system, the addition of [N 1888 ][P 507 ] resulted in a slight decrease of Li + extraction efficiency (about 5%), the stripping acidity significantly reduced from 6 mol·L –1 HCl to 1.5 mol·L –1 HCl. This new extraction system showed a promising performance in selective extracting and easy stripping in lithium separation from the salt lake brines with high Mg/Li ratio.

Visualizing Heterogeneous Lithium Plating and Stripping during Fast Charging

Lithium plating is an obstacle for the development of fast-charge batteries and enabling of widescale electric vehicle adoption. Synchrotron high-energy X-ray diffraction was used to directly identify and track lithium plating in a full LiNi0.5Mn0.3Co0.2O2 / graphite pouch cell operated with a 6C charge rate for greater than 1200 cycles. The magnitude and spatial distribution of lithium plating, lithium stripping, and the effect of plating on lithium intercalation into graphite were quantified. For discharged cell maps, irreversible and fully lithiated graphite (LiC6) was closely correlated with lithium plating and can be considered a highly reliable indicator of lithium plating in cases where plated lithium is below the detection sensitivity. Isolated regions of slight plating initially stripped to below the detection limit, but over time the coverage and amount of plated lithium increased while the stripping efficiency decreased. Long term monitoring of lithium formation in a fast-charge battery provides important information for a better understanding of lithium plating and stripping mechanisms in practical cells.

Quasiclassical Trajectory Study of the O(3P) + CO2(1Σg+) Reaction at Hyperthermal Energies

This paper presents the reaction mechanism, cross sections, and product energy partitioning for the O + CO2 reaction, calculated using Born-Oppenheimer molecular dynamics simulations with the quasiclassical trajectory (BOMD-QCT) method. At collision energies up to 9.5 eV, three reactions, oxygen exchange (above ∼1.5 eV), abstraction (above ∼5.5 eV), and dissociation (above ∼7.5 eV) occur, with abstraction and dissociation involving either an insertion-elimination mechanism or a stripping mechanism. The insertion-elimination mechanism involves the formation of a planar CO3 intermediate which lies 0.52 eV above the ground-state CO2; the energetic barrier for oxygen abstraction via this mechanism is 3.52 eV. Interestingly, the insertion-elimination mechanism predominately contributes to the cross sections at collision energies just above the effective energetic threshold for the abstraction and dissociation reactions; at higher collision energies, the contribution from the stripping mechanism increases and eventually dominates. At a collision energy of 9.5 eV, the cross sections for oxygen exchange, abstraction, and dissociation are 4.17 a02, 1.58 a02, and 0.68 a02, respectively. The lower reaction cross sections, higher effective reaction barrier, and product energy distribution of the stripping mechanism were attributed to the short lifetime (28 fs) of the OCOO species compared with that of the CO3 species (45 fs) that arises in the insertion-elimination mechanism. For the exchange reaction, it is found that roughly 40% of the reactant translational energy ends up in CO2 vibration, which provides a single-collision mechanism to produce highly excited CO2. We also studied intersystem crossing effects using trajectory surface hopping calculations and find no changes compared to single surface (triplet) calculations at energies below 7.5 eV; however, at 7.5 eV and higher the abstraction cross sections are changed by as much as 20%, and the (very small) dissociation cross sections are changed by factors of four or more.

A novel method for the separation of niobium and titanium from sulfuric acid-oxalate solutions using N235 and MIBK

Niobium consumption has burgeoned owing to the increasing application of niobium in critical industries, including the aerospace and oil and gas industries. Conventional metallurgical technologies and separation methods for niobium extraction use highly concentrated HF, which is hazardous to both humans and the environment. A solvent extraction system comprising trioctyl tertiary amine (N235) and 4-methyl-2-pentanone (MIBK) that can extract and separate niobium from an oxalate-containing H2SO4 solution is proposed in this paper. Niobium solutions tend to contain titanium and iron impurities; therefore, the effects of various conditions on the separation of the three elements were investigated. The extraction mechanism and thermodynamics of the process were also examined. Over 82% niobium was extracted at an organic-to-aqueous phase ratio of 1:1 and the H+ concentration of 8.29 mol/L using an organic phase with 50 vol% N235 and 50 vol% MIBK as the extractants at 20 °C. Only 18.4% titanium and 3.35% iron were co-extracted. Two stripping processes, both of which further separated niobium and titanium, are also proposed herein. The possible composition of the niobium-containing extraction complex was [(R3NH)·NbO(C2O4)2(H2O)2], as supported by a Fourier transform infrared spectroscopy (FT-IR) analysis and ultraviolet–visible (UV–vis) spectrophotometry. The extraction mechanism was inferred to be the association of R3NH+ in N235 with the [NbO(C2O4)2(H2O)2]− from the acidic niobium-containing solution, and the stripping mechanism was concluded to be anion exchange. The enthalpy change (∆Ho) of the extraction system was −11.0 kJ/mol at 288.15–313.15 K, which indicated that niobium extraction from the H2SO4 solution with oxalate using N235 and MIBK was an irreversible exothermic process.

Stripping mechanisms and remediation for H− beams

Negative hydrogen ions are often used for injecting protons from linacs to storage rings via charge-exchange injection. In this process, the two electrons are stripped by a foil or laser to produce protons which can be merged with an existing beam without significantly affecting its dynamics, allowing high intensities of protons to be accumulated. However, this capability comes with the drawback that the outer electron of an H$^-$ ion has a low binding energy and can easily be stripped away prior to injection. This paper addresses the following stripping mechanisms: interactions with residual gas in the beam pipe, blackbody radiation from accelerator components, and electromagnetic fields from accelerator optics (Lorentz-force stripping) and particles within the bunch itself (intrabeam stripping); with a discussion on how to avoid excessive activation from stripped H$^0$ particles and protons. We also demonstrate that the proportion of stripped H$^0$ colliding with a nearby beam pipe or machine-element walls presents only roughly 10\% of those lost in stripping; the remaining stripped particles traverse to the end of a linac or local straight section, which may relax the limits for allowable stripping-based beam loss in H$^-$ accelerators.