The Influence of Precipitated Particles on the Grain Size in Cold-Rolled Al-Mn Alloy Foils upon Annealing at 100-550 °C.

The Al-Mn alloy heat exchanger fin production process includes a brazing treatment at s high temperature of 600 °C, in which coarse grains are preferred for their high resistance to deformation at elevated temperatures by decreasing the grain boundary sliding. In this study, Al-1.57Mn-1.57Zn-0.58Si-0.17Fe alloy foils cold rolled by 81.7% (1.1 mm in thickness) and 96.5% (0.21 mm in thickness) were annealed at 100-550 °C for 1 h to investigate their recrystallization behavior, grain sizes, and precipitates by increasing the annealing temperature, using micro-hardness measurement, electron back-scattered diffraction (EBSD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques. The micro-hardness results showed that the recrystallization finishing temperatures for the two samples were almost the same, 323 ± 2 °C. The EBSD results showed that when the annealing temperature decreased from 550 to 400 °C, the recrystallized grain sizes of the two samples were nearly identical-both increased slightly. Further decreasing the annealing temperature from 400 to 330 °C caused the grain sizes to increase more, with the thinner foil sample having a more significant increase. The SEM and TEM observations showed that the micron-sized primary-phase remained unchanged during the annealing process. The nano-sized secondary phase precipitates formed during the hot-rolling process experienced a coarsening and dissolving process upon annealing. The particle size of the secondary phase increased from 32 nm to 44 nm and the area fraction decreased from 4.2% to 3.8%. The nucleation analysis confirmed that the large primary-phase could act as a nucleation site through particle stimulated nucleation (PSN) mode. The relatively dense secondary phase precipitates with small sizes at lower temperatures could provide higher Zener drag to the grain boundaries, leading to fewer nuclei and thereafter coarser grains. The coarsening of the recrystallized grains in the foils could be implemented through thickness reduction and/or precipitation processes to form densely distributed nano-sized precipitates.

Simultaneous enhancement of strength and conductivity via self-assembled lamellar architecture.

Simultaneous improvement of strength and conductivity is urgently demanded but challenging for bimetallic materials. Here we show by creating a self-assembled lamellar (SAL) architecture in W-Cu system, enhancement in strength and electrical conductivity is able to be achieved at the same time. The SAL architecture features alternately stacked Cu layers and W lamellae containing high-density dislocations. This unique layout not only enables predominant stress partitioning in the W phase, but also promotes hetero-deformation induced strengthening. In addition, the SAL architecture possesses strong crack-buffering effect and damage tolerance. Meanwhile, it provides continuous conducting channels for electrons and reduces interface scattering. As a result, a yield strength that doubles the value of the counterpart, an increased electrical conductivity, and a large plasticity were achieved simultaneously in the SAL W-Cu composite. This study proposes a flexible strategy of architecture design and an effective method for manufacturing bimetallic composites with excellent integrated properties.

Efficient purification and high-quality regeneration of graphite from spent lithium-ion batteries by surfactant-assisted methanesulfonic acid.

With the vigorous development of the new energy industry, the use of lithium-ion batteries (LIBs) is growing exponentially, and the recycling of spent LIBs has gradually become a research hotspot. Currently, recycling both cathode and anode materials of LIBs is important to environmental protection and resource recycling. This research reportsa method ofefficient purification and high-quality regeneration of graphite from spent LIBs by surfactant-assisted methanesulfonic acid (MSA). Under the optimal conditions (0.006 mol/L sodium dodecyl sulfonate, 0.25 mol/L MSA, 10 vol% hydrogen peroxide, liquid-solid ratio of 30:1 mL/g, 60 °C, 1.5 h), the purity of the regenerated graphite was 99.7 %, and the recovery efficiency was 98.0 %. The regenerated graphite showed the characteristics of small interplanar spacing, high degree of graphitization, a small number of surface defects, and excellent pore structure, which was closer to commercial graphite. Furthermore, the regenerated graphite electrode exhibited superior rate performance and cycling stability with a high specific capacity of 397.03 mAh/g after 50 cycles at 0.1C and a charge-discharge efficiency of 99.33 %. The recovery of anode graphite beneficial for resource utilization, environmental protection, and cost control throughout the entire production chain.

Effect of electric fields on tungsten distribution in Na2WO4-WO3 molten salt.

Tungsten coatings have unique properties such as high melting points and hardness and are widely used in the nuclear fusion and aviation fields. In experiments, compared to pure Na2WO4 molten salt, electrolysis with Na2WO4-WO3 molten salt results in a lower deposition voltage. Herein, an investigation combining experimental and computational approaches was conducted, involving molecular dynamics simulations with deep learning, high-temperature in situ Raman spectroscopy and activation strain model analysis. The results indicated that the molten salt system's behaviour, influenced by migration and polarization effects, led to increased formation of Na2W2O7 in the Na2WO4-WO3 molten salt, which has a lower decomposition voltage and subsequently accelerated the cathodic deposition of tungsten. We analyzed the mechanism of the effect of the electric field on the Na2W2O7 structure based on the bond strength and electron density. This research provides crucial theoretical support for the effect of electric field on tungsten in molten salt and demonstrates the feasibility of using machine learning-based DPMD methods in simulating tungsten-containing molten salt systems.

Effect of the Solid Solution and Aging Treatment on the Mechanical Properties and Microstructure of a Novel Al-Mg-Si Alloy.

A novel Al-Mg-Si aluminum alloy with the addition of the micro-alloying element Er and Zr that was promptly quenched after extrusion has been studied. The solid solution and aging treatment of the novel alloy are studied by observing the microstructure, mechanical properties, and strengthening mechanism. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques are employed to examine the changes in the microstructure resulting from various solid solution treatments and aging treatments. The best strengthening effect can be achieved when the solubility of the MgSi phase and precipitate ß″ (Mg2Si phase) is at their maximum. The addition of Er and Zr elements promotes the precipitation of the ß″ phase and makes the b″ phase more finely dispersed. The aging strengthening of alloys is a comprehensive effect of the dislocation cutting mechanism and bypass mechanism, the joint effect of diffusion strengthening of Al3(Er,Zr) particles and the addition of Er and Zr elements promoting the precipitation strengthening of ß″ phases. In this paper, by adding Er and Zr elements and exploring the optimal heat treatment system, the yield strength of the alloy reaches 437 MPa and the tensile strength reaches 453 MPa after solid solution treatment at 565 °C/30 min and aging at 175 °C/10 h.

Closed-loop recovery of molybdenum and value-added reuse of tungsten from alloy waste in additive manufacturing.

As metal additive manufacturing (MAM) technology is booming in the aerospace sector, alternatives to the traditional production methods of metals such as mining, processing, and refining with severe emissions are urgently needed. This study proposed a closed-loop route for efficient recovery of molybdenum (Mo) and value-added reuse of tungsten (W) from Cr-Co-Ni-Mo-W alloy waste in MAM. The results showed that the leaching efficiency of Mo and W reached 99.3% and 99.9%, respectively, using the dual chemical-physical means of mixed-alkali roasting and leaching by microwave heating, while the discharge of waste liquor containing Cr6+ was reduced. Leaching kinetic studies revealed that the metal leaching process was controlled by chemical reaction mechanism. Moreover, the 10%N1923 (primary amine)-5%TRPO (tri-alkyl phosphine oxide)-kerosene extraction system exhibited a synergistic extraction effect on Mo and W. After purification, Mo was recovered as Mo powder for MAM. Simultaneously, the recovered product of W, MnWO4, was applied as a photocatalytic material with excellent degradation of methylene blue dye. Ultimately, the proposed method obtained recovery efficiencies of 98.4% and 99.3% for Mo and W, respectively, achieving efficient and environmentally-friendly reuse of these key metals.

In Situ SEM, TEM, EBSD Characterization of Nucleation and Early Growth of Pure Fe/Pure Al Intermetallic Compounds.

The nucleation and growth processes of pure Fe/pure Al intermetallic compounds (IMCs) during heat treatment at 380 °C and 520 °C were observed through in situ scanning electron microscopy (SEM). The size of the IMCs were statistically analyzed using image analysis software. The types and distribution of IMCs were characterized using transmission electron microscopy (TEM) and electron backscattering diffraction (EBSD). The results showed that: at 380 °C, the primary phase of the Fe/Al composite intermetallic compounds was Fe4Al13, formed on the Fe side and habituated with Fe. The IMC was completely transformed from the initial Fe4Al13 to the most stable Fe2Al5, and the Fe2Al5 was the habitus with Fe during the process of holding at 380 °C for 15 min to 60 min. At 380 °C, the initial growth rate of the IMC was controlled by reaction, and the growth rate of the thickness and horizontal dimensions was basically the same as 0.02-0.17 µm/min. When the IMC layer thickness reached 4.5 µm, the growth rate of the thickness changed from reaction control to diffusion control and decreased to 0.007 µm/min. After heat treatment at 520 °C (≤20 min), the growth of IMC was still controlled by the reaction, the horizontal growth rate was 0.53 µm/min, the thickness growth rate was 0.23 µm/min, and the main phase of the IMC was the Fe2Al5 phase at 520 °C/20 min.

Evolution of Grain Structure and Dynamic Precipitation during Hot Deformation in a Medium-Strength Al-Zn-Mg-Er-Zr Aluminum Alloy.

The hot deformation behavior of Al-Zn-Mg-Er-Zr alloy was investigated through an isothermal compression experiment at a strain rate ranging from 0.01 to 10 s-1 and temperature ranging from 350 to 500 °C. The constitutive equation of thermal deformation characteristics based on strain was established, and the microstructure (including grain, substructure and dynamic precipitation) under different deformation conditions was analyzed. It is shown that the steady-state flow stress can be described using the hyperbolic sinusoidal constitutive equation with a deformation activation energy of 160.03 kJ/mol. Two kinds of second phases exist in the deformed alloy; one is the η phase, whose size and quantity changes according to the deformation parameters, and the other is spherical Al3(Er, Zr) particles with good thermal stability. Both kinds of particles pin the dislocation. However, with a decrease in strain rate or increase in temperature, η phases coarsen and their density decreases, and their dislocation locking ability is weakened. However, the size of Al3(Er, Zr) particles does not change with the variation in deformation conditions. So, at higher deformation temperatures, Al3(Er, Zr) particles still pin dislocations and thus refine the subgrain and enhance the strength. Compared with the η phase, Al3(Er, Zr) particles are superior for dislocation locking during hot deformation. A strain rate ranging from 0.1 to 1 s-1 and a deformation temperature ranging from 450 to 500 °C form the safest hot working domain in the processing map.

Effect of Zr and Er Addition on the Microstructural Evolution of a Novel Al-Mg-Zn-Er-Zr Alloy during Hot Compression.

The hot compression experiment of homogenized Al-5.2Mg-0.6Mn-0.29Zn-0.16Er-0.12Zr alloy was carried out by the Gleeble-3500 thermal simulation testing system. The deformation behavior in temperatures of 350~500 ℃ and deformation rates of 0.01~10 s-1 was studied. The relationship between stress and strain rate and deformation temperature was analyzed. The constitutive equation of alloy high-temperature deformation was constructed by the Zener-Hollomon method, and the hot working diagram with the true strain of 0.2 and 0.5 was constructed according to the dynamic material model. The research results show that flow stress has a positive correlation with strain rate and a negative correlation with temperature. The steady flow stress during deformation can be described by a hyperbolic sinusoidal constitutive equation. Adding Er and Zr into Al-Mg alloy can not only refine grains and strengthen precipitation but also form a core-shell Al3(Er, Zr) phase. In the deformation process, Al3(Er, Zr) precipitates can pin dislocations and inhibit dynamic recrystallization (DRX). Dynamic recovery (DRV) is dominant during hot deformation. The mechanism of dynamic recovery is dislocation motion. At high temperatures, Al3(Er, Zr) can also inhibit grain coarsening. The average hot deformation activation energy of the alloy is 203.7 kJ/mol. This high activation energy can be due to the pinning effect of Er and Zr precipitates. The processing map of the alloy was analyzed and combined with the observation of microstructure, the hot deformation instability zone of the alloy was determined, and the suitable process parameters for hot deformation were obtained, which were 450~480 °C, and the strain rate is 0.01~0.09 s-1.

Comparison of Electric Vehicle Lithium-Ion Battery Recycling Allocation Methods.

Power lithium-ion batteries (LIBs) are an important component of carbon neutrality in the transportation sector. The rapid growth of the LIB recycling industry is driven by various factors, such as resource scarcity. As a process interacting upstream and downstream, LIB recycling must consider the impact of the application of modeling approaches on the allocation of environmental benefits and burdens, especially at a time when carbon emissions are highly correlated with profit. In this study, seven allocation methods were chosen and applied to the production and multiple recycling process of typical LIB on the same data basis. The application of different allocation methods produced very disparate allocation results, and the conclusions of previous studies comparing the environmental performance of battery types need to be revisited. The life-cycle assessment (LCA) results should be interpreted with caution due to the impact of the allocation methods. Furthermore, a multi-indicator qualitative analysis based on product and process characteristics compares the applicability of the allocation methods to different aspects of LIB recycling. Relevant product standards for batteries should consider the characteristics of different methods and recommend a specific allocation method for the LCA community to employ in time to ensure that relevant studies are representative and comparable.

Effect of Aging Treatment on the Precipitation Behavior of a Novel Al-Cu-Zr Cast Alloy.

A novel Al-Cu-Zr alloy is designed in this paper, which provides a method for further improving the strength of Al-Cu alloys. In this paper, the addition of the micro-alloying element Zr in Al-Cu alloy was studied. The effect of aging treatment on the mechanical properties and precipitation behavior of the alloy was studied. With the addition of Zr, Al3Zr phases were formed in the alloy, which acts as obstacles to dislocation motion. In addition, Al3Zr phases can be used as the nucleation site of θ' phases to promote precipitation. All this can improve the strength of Al-Cu alloys. After one-step aging, corresponding to the highest hardness, the largest amount of θ' phases were observed in the alloy matrix. By contrast, after two-step aging, the θ' phases were finer, and a large amount of Guinier-Preston (GP) zones formed during the pre-aging step, which were transformed into denser and finer θ' phases in the secondary aging step. After the same solution treatment (540 °C/12 h), undergoing 120 °C/4 h + 175 °C/10 h two-step aging, the ultimate tensile strength, yield strength, and elongation of the Al-Cu-Zr alloy were 398.7 MPa, 313.3 MPa, and 7.9%, respectively.

Valence and coordination form transition of tungsten ions in molten alkali chlorides.

This study examined the possibility of deep significance for the reduction of low-valence tungsten to inhibit disproportionation reactions in various molten alkali chlorides. Electrolysis and electrochemical tests of tungsten carbide were carried out in molten LiCl, LiCl-KCl, NaCl-KCl, NaCl-CsCl, and KCl-CsCl. One finding was that the reduction valence of tungsten ions decreased as the radius of the solvent alkali ion increased. This phenomenon may be viewed from the dissolution of tungsten carbide and the existence and deposition of tungsten ions. The mechanism of tungsten ion reduction and the stable configuration of tungsten ion groups were confirmed via a detailed study of the computational calculation. The increase in the radius of the solvent alkali ion was conducive to the dissolution of tungsten from tungsten carbide in the form of low valence state. Other results also indicated that W(II) ion groups first deposited on the cathode. They had the advantages of smaller coordination numbers and faster diffusion combined. Morphological and composition analysis results of the products are also presented.

Novel Styrene-Based Polyamine Sorbent for Efficient Selective Separation of Molybdenum.

Tungsten (W) and molybdenum (Mo) are important strategic resources but the two coexist in both primary ore and waste. Before a single metal product is obtained, it is often necessary to separate the two. In this work, we reported two new polyamine resins (D301@PA and D301@TA), which can be obtained by an assembled amine (primary amine or tertiary amine) and traditional D301 resin by the dipping method. Then, the sorption experiments with the amine resins were carried out, and the selectivity and sorption capacity of the two new polyamine resins for MoS4 2- have been significantly improved. Among them, D301@TA showed the highest sorption capacity of 414 mg·g-1 and a separation factor of 108. Finally, the sorption mechanism can be inferred through scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) analysis, and X-ray photoemission spectroscopy (XPS); the Cl- ions in the amine resin and the MoS4 2- ions were subjected to ion exchange. This work provides a green and efficient approach for separating tungsten and molybdenum.

A Methyl-Modified Silica Layer Supported on Porous Ceramic Membranes for the Enhanced Separation of Methyl Tert-Butyl Ether from Aqueous Solution.

As a kind of volatile organic compound (VOC), methyl tert-butyl ether (MTBE) is hazardous to human health and destructive to the environment if not handled properly. MTBE should be removed before the release of wastewater. The present work supported the methyl-modified silica layer (MSL) on porous α-Al2O3 ceramic membranes with methyltrimethoxysilane (MTMS) as a precursor and pre-synthesized mesoporous silica microspheres as dopants by the sol-gel reaction and dip-coating method. MTMS is an environmentally friendly agent compared to fluorinated alkylsilane. The MSL-supported Al2O3 ceramic membranes were used for MTBE/water separation by pervaporation. The NMR spectra revealed that MTMS evolves gradually from an oligomer to a highly cross-linked methyl-modified silica species. Methyl-modified silica species and pre-synthesized mesoporous silica microspheres combine into hydrophobic mesoporous MSL. MSL makes the α-Al2O3 ceramic membranes transfer from amphiphilic to hydrophobic and oleophilic. The MSL-supported α-Al2O3 ceramic membranes (MSL-10) exhibit an MTBE/water separation factor of 27.1 and a total flux of 0.448 kg m-2 h-1, which are considerably higher than those of previously reported membranes that are modified by other alkylsilanes via the post-grafting method. The mesopores within the MSL provide a pathway for the transport of MTBE molecules across the membranes. The presence of methyl groups on the external and inner surface is responsible for the favorable separation performance and the outstanding long-term stability of the MSL-supported porous α-Al2O3 ceramic membranes.

Trace removal of benzene vapour using double-walled metal-dipyrazolate frameworks.

In principle, porous physisorbents are attractive candidates for the removal of volatile organic compounds such as benzene by virtue of their low energy for the capture and release of this pollutant. Unfortunately, many physisorbents exhibit weak sorbate-sorbent interactions, resulting in poor selectivity and low uptake when volatile organic compounds are present at trace concentrations. Herein, we report that a family of double-walled metal-dipyrazolate frameworks, BUT-53 to BUT-58, exhibit benzene uptakes at 298 K of 2.47-3.28 mmol g-1 at <10 Pa. Breakthrough experiments revealed that BUT-55, a supramolecular isomer of the metal-organic framework Co(BDP) (H2BDP = 1,4-di(1H-pyrazol-4-yl)benzene), captures trace levels of benzene, producing an air stream with benzene content below acceptable limits. Furthermore, BUT-55 can be regenerated with mild heating. Insight into the performance of BUT-55 comes from the crystal structure of the benzene-loaded phase (C6H6@BUT-55) and density functional theory calculations, which reveal that C-H···X interactions drive the tight binding of benzene. Our results demonstrate that BUT-55 is a recyclable physisorbent that exhibits high affinity and adsorption capacity towards benzene, making it a candidate for environmental remediation of benzene-contaminated gas mixtures.

A Practice of Reticular Chemistry: Construction of a Robust Mesoporous Palladium Metal-Organic Framework via Metal Metathesis.

Constructing stable palladium(II)-based metal-organic frameworks (MOFs) would unlock more opportunities for MOF chemistry, particularly toward applications in catalysis. However, their availability is limited by synthetic challenges due to the inertness of the Pd-ligand coordination bond, as well as the strong tendency of the Pd(II) source to be reduced under typical solvothermal conditions. Under the guidance of reticular chemistry, herein, we present the first example of an azolate Pd-MOF, BUT-33(Pd), obtained via a deuterated solvent-assisted metal metathesis. BUT-33(Pd) retains the underlying sodalite network and mesoporosity of the template BUT-33(Ni) and shows excellent chemical stability (resistance to an 8 M NaOH aqueous solution). With rich Pd(II) sites in the atomically precise distribution, it also demonstrates good performances as a heterogeneous Pd(II) catalyst in a wide application scope, including Suzuki/Heck coupling reactions and photocatalytic CO2 reduction to CH4. This work highlights a feasible approach to reticularly construct noble metal based MOFs via metal metathesis, in which various merits, including high chemical stability, large pores, and tunable functions, have been integrated for addressing challenging tasks.

Highly efficient sorption of molybdenum from tungstate solution with modified D301 resin.

The separation of molybdenum (Mo) from tungstate solution is a bottleneck problem in tungsten (W) metallurgy, and it hinders the development of high-purity tungsten materials. In this research, a modified D301 resin was used to adsorb and separate molybdenum from tungstate solution. The maximum sorption capacity (Q e) of modified D301 for MoS4 2- was found to be 428 mg g-1 and the separation coefficient (ß) was 108.9 when the contact time was 4 h and the reaction temperature was 25 °C and the pH value of the tungstate solution was 7.2. The sorption process conforms to Langmuir isotherm models and the quasi-second-order kinetic model. The sorption mechanism was also discussed, which was a single layered spontaneous sorption process. Theoretical calculations infer bonding behavior between the N atom on the resin and the S atom on the MoS4 2- molecule. The sorption energy is -7.67 eV, which indicated that the sorption process is stable chemical sorption. The desorption experiment showed that more than 90% molybdenum could be desorbed from the loaded resin when the concentration of sodium hydroxide solution was 5 w%. Finally, after three-stage sorption-desorption, almost all molybdenum in the solution was adsorbed, achieving better separation of tungsten and molybdenum.

Preparation of Small-Particle and High-Density Cobalt Carbonate Using a Continuous Carbonate Precipitation Method and Evaluation of Its Growth Mechanism.

Spherical CoCO3 powder with a small particle size and high density was successfully prepared using a continuous carbonate liquid precipitation method with a raw material of cobalt chloride solution, a precipitant of NH4HCO3, and without a template. The effects of the concentration of ammonium carbonate, process pH, and feeding rate on the tap density and apparent density of cobalt carbonate were investigated. It was found that the apparent and tap density values of 4.4 µm of cobalt carbonate were 1.27 g/cm3 and 1.86 g/cm3, respectively, when the initial concentration of NH4HCO3 solution was 60 g/L, the pH was 7.15-7.20, and the feeding rate of cobalt chloride was 2 L/h. The anisotropic growth process of the crystal lattice plane of CoCO3 under the aforementioned optimal conditions were studied. The results demonstrated that the crystal grew fastest along the (110) facet orientation, which was the dominant growth surface, determining the final morphology of the primary particles. The scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HR-TEM) results demonstrated that the primary particle morphology of the cobalt carbonate was a nanosheet. The unit cell of cobalt carbonate, of a hexagonal structure in the horizontal direction, grew horizontally along the (110) facet orientation, while 20-35 unit cells of the carbon carbonate were stacked along the c-axis in the thickness direction. Finally, the sheet-shaped particles were agglomerated into dense spherical secondary particles, as presented through the crystal re-crystallization model.

Regeneration and characterization of LiNi0.8Co0.15Al0.05O2 cathode material from spent power lithium-ion batteries.

The use and scrap of lithium ion batteries, especially power lithium ion batteries in China, are increasing every year. Regeneration of spent battery materials is not only important for environmental protection and resource saving, but also for the production of high value-added materials. In this research, spent power lithium-ion battery cathode material LiNi1-xCoxO2 was acid-leached and a polymetallic leaching solution containing Li, Ni, Co, Al and Cu was obtained. Cu was extracted from the leachate by using CP-150 (2-hydroxy-5-nonyl salicylaldehyde oxime). The optimal conditions were found to be organic: aqueous phase ratio (O/A) = 2:1, extraction agent concentration of 30%, and pH = 3. The precursor was prepared by coprecipitation of the leachate after Cu removal. Then, cathode material of lithium nickel cobalt aluminate LiNi0.8Co0.15Al0.05O2 was synthesized under the optimal conditions of n (precursor): n (lithium carbonate) = 1:1.1, calcination temperature of 800 °C for 15 h. The regenerated LiNi0.8Co0.15Al0.05O2 product prepared under the optimized conditions was in a pure phase with a layered structure and a smooth surface morphology. The first charge specific capacity was 248.7 mAh/g, and the discharge specific capacity was 162 mAh/g. The interfacial impedance was 119 Ω. The 50th-cycle discharge specific capacity was 149.1 mAh/g, and the capacity retention rate was high as 92%. Therefore, the regenerated cathode material exhibited good performance.