This article reviews the current status on the dynamic behavior of highly stressed rocks under disturbances. Firstly, the experimental apparatus, methods, and theories related to the disturbance dynamics of deep, high-stress rock are reviewed, followed by the introduction of scholars’ research on deep rock deformation and failure from an energy perspective. Subsequently, with a backdrop of high-stress phenomena in deep hard rock, such as rock bursts and core disking, we delve into the current state of research on rock microstructure analysis and residual stresses from the perspective of studying the energy storage mechanisms in rocks. Thereafter, the current state of research on the mechanical response and the energy dissipation of highly stressed rock formations is briefly retrospected. Finally, the insufficient aspects in the current research on the disturbance and failure mechanisms in deep, highly stressed rock formations are summarized, and prospects for future research are provided. This work provides new avenues for the research on the mechanical response and damage-fracture mechanisms of rocks under high-stress conditions.
Cobalt has excellent electrochemical, magnetic, and heat properties. As a strategic resource, it has been applied in many high-tech products. However, the recent rapid growth of the battery industry has substantially depleted cobalt resources, leading to a crisis of cobalt resource supply. The paper examines cobalt ore reserves and distribution, and the recent development and consumption of cobalt resources are summarized as well. In addition, the principles, advantages and disadvantages, and research status of various methods are discussed comprehensively. It can be concluded that the use of diverse sources (Cu-Co ores, Ni-Co ores, zinc plant residues, and waste cobalt products) for cobalt production should be enhanced to meet developmental requirements. Furthermore, in recovery technology, the pyro-hydrometallurgical process employs pyrometallurgy as the pretreatment to modify the phase structure of cobalt minerals, enhancing its recovery in the hydrometallurgical stage and facilitating high-purity cobalt production. Consequently, it represents a promising technology for future cobalt recovery. Lastly, based on the above conclusions, the prospects for cobalt are assessed regarding cobalt ore processing and sustainable cobalt recycling, for which further study should be conducted.
Polypropylene (PP) fiber-reinforced cement-based tailings backfill (FRCTB) is a green compound material with superior crack resistance and has good prospects for application in underground mining. However, FRCTB exhibits susceptibility to dynamic events, such as impact ground pressure and blast vibrations. This paper investigates the energy and crack distribution behavior of FRCTB under dynamic impact, considering the height/diameter (H/D) effect. Split Hopkinson pressure bar, industrial computed tomography scan, and scanning electron microscopy (SEM) experiments were carried out on six types of FRCTB. Laboratory outcomes confirmed fiber aggregation at the bottom of specimens. When H/D was less than 0.8, the proportion of PP fibers distributed along the θ angle direction of 80°–90° increased. For the total energy, all samples presented similar energy absorption, reflectance, and transmittance. However, a rise in H/D may cause a rise in the energy absorption rate of FRCTB during the peak phase. A positive correlation existed between the average strain rate and absorbed energy per unit volume. The increase in H/D resulted in a decreased crack volume fraction of FRCTB. When the H/D was greater than or equal to 0.7, the maximum crack volume fraction of FRCTB was observed close to the incidence plane. Radial cracks were present only in the FRCTB with an H/D ratio of 0.5. Samples with H/D ratios of 0.5 and 0.6 showed similar distributions of weakly and heavily damaged areas. PP fibers can limit the emergence and expansion of cracks by influencing their path. SEM observations revealed considerable differences in the bonding strengths between fibers and the FRCTB. Fibers that adhered particularly well to the substrate were attracted together with the hydration products adhering to surfaces. These results show that FRCTB is promising as a sustainable and green backfill for determining the design properties of mining with backfill.
Comparative experiments and theoretical analysis of the surface chemistry changes of goethite (GT) and goethite containing Ni (GTN) in the lattice in the presence of salicylhydroxamic acid (SA) were performed. It was revealed that in the presence of 100 g·t−1 of SA, the flotation recovery of GTN and GT increased with increasing pH, achieving a maximum recovery of 98.9% for both minerals at pH 8.3 and decreasing beyond that pH, with GTN having a slightly higher recovery than GT, except at pH 8.3. This was further confirmed by the higher complexation energies of GTN⋯SA (−883.87 kJ·mol−1) compared with GT⋯SA (−604.23 kJ·mol−1) resulting from covalent, closed-shell, and conventional hydrogen bonding. The higher adsorption of SA onto GTN relative to GT was due to the formation of a π-hole in GTN, thereby promoting a higher interaction of the collector with the mineral. Thus, the presence of Ni in the GT lattice improves and decreases the adsorption and desorption of SA onto and from the mineral, respectively, compared with those onto and from GT.
Electrochemical lithium extraction from salt lakes is an effective strategy for obtaining lithium at a low cost. Nevertheless, the elevated Mg : Li ratio and the presence of numerous coexisting ions in salt lake brines give rise to challenges, such as prolonged lithium extraction periods, diminished lithium extraction efficiency, and considerable environmental pollution. In this work, LiFePO4 (LFP) served as the electrode material for electrochemical lithium extraction. The conductive network in the LFP electrode was optimized by adjusting the type of conductive agent. This approach resulted in high lithium extraction efficiency and extended cycle life. When the single conductive agent of acetylene black (AB) or multiwalled carbon nanotubes (MWCNTs) was replaced with the mixed conductive agent of AB/MWCNTs, the average diffusion coefficient of Li+ in the electrode increased from 2.35 × 10−9 or 1.77 × 10−9 to 4.21 × 10−9 cm2·s−1. At the current density of 20 mA·g−1, the average lithium extraction capacity per gram of LFP electrode increased from 30.36 mg with the single conductive agent (AB) to 35.62 mg with the mixed conductive agent (AB/MWCNTs). When the mixed conductive agent was used, the capacity retention of the electrode after 30 cycles reached 82.9%, which was considerably higher than the capacity retention of 65.8% obtained when the single AB was utilized. Meanwhile, the electrode with mixed conductive agent of AB/MWCNTs provided good cycling performance. When the conductive agent content decreased or the loading capacity increased, the electrode containing the mixed conductive agent continued to show excellent electrochemical performance. Furthermore, a self-designed, highly efficient, continuous lithium extraction device was constructed. The electrode utilizing the AB/MWCNT mixed conductive agent maintained excellent adsorption capacity and cycling performance in this device. This work provides a new perspective for the electrochemical extraction of lithium using LFP electrodes.
Traditional hydrometallurgical methods for recovering spent lithium-ion batteries (LIBs) involve acid leaching to simultaneously extract all valuable metals into the leachate. These methods usually are followed by a series of separation steps such as precipitation, extraction, and stripping to separate the individual valuable metals. In this study, we present a process for selectively leaching lithium through the synergistic effect of sulfuric and oxalic acids. Under optimal leaching conditions (leaching time of 1.5 h, leaching temperature of 70°C, liquid-solid ratio of 4 mL/g, oxalic acid ratio of 1.3, and sulfuric acid ratio of 1.3), the lithium leaching efficiency reached 89.6%, and the leaching efficiencies of Ni, Co, and Mn were 12.8%, 6.5%, and 21.7%. X-ray diffraction (XRD) and inductively coupled plasma optical emission spectrometer (ICP-OES) analyses showed that most of the Ni, Co, and Mn in the raw material remained as solid residue oxides and oxalates. This study offers a new approach to enriching the relevant theory for selectively recovering lithium from spent LIBs.
Mg-6Zn-2X(Fe/Cu/Ni) alloys were prepared through semi-continuous casting, with the aim of identifying a degradable magnesium (Mg) alloy suitable for use in fracturing balls. A comparative analysis was conducted to assess the impacts of adding Cu and Ni, which result in finer grains and the formation of galvanic corrosion sites. Scanner electronic microscopy examination revealed that precipitated phases concentrated at grain boundaries, forming a semi-continuous network structure that facilitated corrosion penetration in Mg-6Zn-2Cu and Mg-6Zn-2Ni alloys. Pitting corrosion was observed in Mg-6Zn-2Fe, while galvanic corrosion was identified as the primary mechanism in Mg-6Zn-2Cu and Mg-6Zn-2Ni alloys. Among the tests, the Mg-6Zn-2Ni alloy exhibited the highest corrosion rate (approximately 932.9 mm/a) due to its significant potential difference. Mechanical testing showed that Mg-6Zn-2Ni alloy possessed suitable ultimate compressive strength, making it a potential candidate material for degradable fracturing balls, effectively addressing the challenges of balancing strength and degradation rate in fracturing applications.
This work proposed a strategy of indirectly inducing uniform microarc discharge by controlling the content and distribution of β-Mg17Al12 phase in AZ91D Mg alloy. Two kinds of nano-particles (ZrO2 and TiO2) were designed to be added into the substrate of Mg alloy by friction stir processing (FSP). Then, Mg alloy sample designed with different precipitated morphology of β-Mg17Al12 phase was treated by microarc oxidation (MAO) in Na3PO4/Na2SiO3 electrolyte. The characteristics and performance of the MAO coating was analyzed using scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), contact angle meter, and potentiodynamic polarization. It was found that the coarse α-Mg grains in extruded AZ91D Mg alloy were refined by FSP, and the β-Mg17Al12 phase with reticular structure was broken and dispersed. The nano-ZrO2 particles were pinned at the grain boundary by FSP, which refined the α-Mg grain and promoted the precipitation of β-Mg17Al12 phase in grains. It effectively inhibited the “cascade” phenomenon of microarcs, which induced the uniform distribution of discharge pores. The MAO coating on Zr-FSP sample had good wettability and corrosion resistance. However, TiO2 particles were hardly detected in the coating on Ti-FSP sample.
Additive friction stir deposition (AFSD) is a novel structural repair and manufacturing technology has become a research hotspot at home and abroad in the past five years. In this work, the microstructural evolution and mechanical performance of the Al-Mg-Si alloy plate repaired by the preheating-assisted AFSD process were investigated. To evaluate the tool rotation speed and substrate preheating for repair quality, the AFSD technique was used to additively repair 5 mm depth blind holes on 6061 aluminum alloy substrates. The results showed that preheat-assisted AFSD repair significantly improved joint bonding and joint strength compared to the control non-preheat substrate condition. Moreover, increasing rotation speed was also beneficial to improve the metallurgical bonding of the interface and avoid volume defects. Under preheating conditions, the UTS and elongation were positively correlated with rotation speed. Under the process parameters of preheated substrate and tool rotation speed of 1000 r/min, defect-free specimens could be obtained accompanied by tensile fracture occurring in the substrate rather than the repaired zone. The UTS and elongation reached the maximum values of 164.2 MPa and 13.4%, which are equivalent to 99.4% and 140% of the heated substrate, respectively.
AlSi10Mg porous protective structure often produces different damage forms under compressive loading, and these damage modes affect its protective function. In order to well meet the service requirements, there is an urgent need to comprehensively understand the mechanical behavior and response mechanism of AlSi10Mg porous structures under compressive loading. In this paper, AlSi10Mg porous structures with three kinds of volume fractions are designed and optimized to meet the requirements of high-impact, strong-energy absorption, and lightweight characteristics. The mechanical behaviors of AlSi10Mg porous structures, including the stress–strain relationship, structural bearing state, deformation and damage modes, and energy absorption characteristics, were obtained through experimental studies at different loading rates. The damage pattern of the damage section indicates that AlSi10Mg porous structures have both ductile and brittle mechanical properties. Numerical simulation studies show that the AlSi10Mg porous structure undergoes shear damage due to relative misalignment along the diagonal cross-section, and the damage location is almost at 45° to the load direction, which is the most direct cause of its structural damage, revealing the damage mechanism of AlSi10Mg porous structures under the compressive load. The normalized energy absorption model constructed in the paper well interprets the energy absorption state of AlSi10Mg porous structures and gives the sensitive location of the structures, and the results of this paper provide important references for peers in structural design and optimization.
The Ti-5Al-2Sn-4Zr-4Mo-2Cr-1Fe (β-CEZ) alloy is considered as a potential structural material in the aviation industry due to its outstanding strength and corrosion resistance. Electrochemical machining (ECM) is an efficient and low-cost technology for manufacturing the β-CEZ alloy. In ECM, the machining parameter selection and tool design are based on the electrochemical dissolution behavior of the materials. In this study, the electrochemical dissolution behaviors of the β-CEZ and Ti-6Al-4V (TC4) alloys in NaNO3 solution are discussed. The open circuit potential (OCP), Tafel polarization, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and current efficiency curves of the β-CEZ and TC4 alloys are analyzed. The results show that, compared to the TC4 alloy, the passivation film structure is denser and the charge transfer resistance in the dissolution process is greater for the β-CEZ alloy. Moreover, the dissolved surface morphology of the two titanium-based alloys under different current densities are analyzed. Under low current densities, the β-CEZ alloy surface comprises dissolution pits and dissolved products, while the TC4 alloy surface comprises a porous honeycomb structure. Under high current densities, the surface waviness of both the alloys improves and the TC4 alloy surface is flatter and smoother than the β-CEZ alloy surface. Finally, the electrochemical dissolution models of β-CEZ and TC4 alloys are proposed.
Porous intermetallics show potential in the field of filtration and separation as well as in the field of catalysis. Herein, porous TiFe2 intermetallics were fabricated by the reactive synthesis of elemental powders. The phase transformation and pore formation of porous TiFe2 intermetallics were investigated, and its corrosion behavior and hydrogen evolution reaction (HER) performance in alkali solution were studied. Porous TiFe2 intermetallics with porosity in the range of 34.4%–56.4% were synthesized by the diffusion reaction of Ti and Fe elements, and the pore formation of porous TiFe2 intermetallic compound is the result of a combination of the bridging effect and the Kirkendall effect. The porous TiFe2 samples exhibit better corrosion resistance compared with porous 316L stainless steel, which is related to the formation of uniform nanosheets on the surface that hinder further corrosion, and porous TiFe2 electrode shows the overpotential of 220.6 and 295.6 mV at 10 and 100 mA·cm−2, suggesting a good catalytic performance. The synthesized porous Fe-based intermetallic has a controllable pore structure as well as excellent corrosion resistance, showing its potential in the field of filtration and separation.
The martensitic transformation temperature is the basis for the application of shape memory alloys (SMAs), and the ability to quickly and accurately predict the transformation temperature of SMAs has very important practical significance. In this work, machine learning (ML) methods were utilized to accelerate the search for shape memory alloys with targeted properties (phase transition temperature). A group of component data was selected to design shape memory alloys using reverse design method from numerous unexplored data. Component modeling and feature modeling were used to predict the phase transition temperature of the shape memory alloys. The experimental results of the shape memory alloys were obtained to verify the effectiveness of the support vector regression (SVR) model. The results show that the machine learning model can obtain target materials more efficiently and pertinently, and realize the accurate and rapid design of shape memory alloys with specific target phase transition temperature. On this basis, the relationship between phase transition temperature and material descriptors is analyzed, and it is proved that the key factors affecting the phase transition temperature of shape memory alloys are based on the strength of the bond energy between atoms. This work provides new ideas for the controllable design and performance optimization of Cu-based shape memory alloys.
CsPbX3-based (X = I, Br, Cl) inorganic perovskite solar cells (PSCs) prepared by low-temperature process have attracted much attention because of their low cost and excellent thermal stability. However, the high trap state density and serious charge recombination between low-temperature processed TiO2 film and inorganic perovskite layer interface seriously restrict the performance of all-inorganic PSCs. Here a thin polyethylene oxide (PEO) layer is employed to modify TiO2 film to passivate traps and promote carrier collection. The impacts of PEO layer on microstructure and photoelectric characteristics of TiO2 film and related devices are systematically studied. Characterization results suggest that PEO modification can reduce the surface roughness of TiO2 film, decrease its average surface potential, and passivate trap states. At optimal conditions, the champion efficiency of CsPbI2Br PSCs with PEO-modified TiO2 (PEO-PSCs) has been improved to 11.24% from 9.03% of reference PSCs. Moreover, the hysteresis behavior and charge recombination have been suppressed in PEO-PSCs.
The monomolecular surface layer of acceptor doped CeO2 may become neutral and metallic or charged and semiconducting. This is revealed in the theoretical analysis of the oxygen pressure dependence of the surface defects concentration in acceptor doped ceria with two different dopant types and operated under different oxygen pressures. Recently published experimental data for highly reduced Sm0.2Ce0.8O1.9−x (SDC) containing a fixed valence dopant Sm3+ are very different from those published for Pr0.1Ce0.9O2−x (PCO) with the variable valence dopant Pr4+/Pr3+ being reduced under milder conditions. The theoretical analysis of these experimental results fits very well the experimental results of SDC and PCO. It leads to the following predictions: the highly reduced surface of SDC is metallic and neutral, the metallic surface electron density of state is g s = 0.9 × 1038 J−1·m−2 (1.4 × 1015 eV−1·cm−2), the electron effective mass is m eff,s = 3.3m e, and the phase diagram of the reduced surface has the α (fcc) structure as in the bulk. In PCO a double layer is predicted to be formed between the surface and the bulk with the surface being negatively charged and semiconducting. The surface of PCO maintains high Pr3+ defect concentration as well as relative high oxygen vacancy concentration at oxygen pressures higher than in the bulk. The reasons for the difference between a metallic and semiconducting surface layer of acceptor doped CeO2 are reviewed, as well as the key theoretical considerations applied in coping with this problem. For that we make use of the experimental data and theoretical analysis available for acceptor doped ceria.
CO2 electrochemical reduction (CO2ER) is an important research area for carbon neutralization. However, available catalysts for CO2 reduction are still characterized by limited stability and activity. Recently, metallic bismuth (Bi) has emerged as a promising catalyst for CO2ER. Herein, we report the solid cathode electroreduction of commercial micronized Bi2O3 as a straightforward approach for the preparation of nanostructured Bi. At −1.1 V versus reversible hydrogen electrode in a KHCO3 aqueous electrolyte, the resulting nano-structure Bi delivers a formate current density of ∼40 mA·cm−2 with a current efficiency of ∼86%, and the formate selectivity reaches 97.6% at −0.78 V. Using nanosized Bi2O3 as the precursor can further reduce the primary particle sizes of the resulting Bi, leading to a significantly increased formate selectivity at relatively low overpotentials. The high catalytic activity of nanostructured Bi is attributable to the ultrafine and interconnected Bi nanoparticles in the nanoporous structure, which exposes abundant active sites for CO2 electrocatalytic reduction.
Electromagnetic wave (EMW)-absorbing materials have considerable capacity in the military field and the prevention of EMW radiation from harming human health. However, obtaining lightweight, high-performance, and broadband EMW-absorbing material remains an overwhelming challenge. Creating dielectric/magnetic composites with customized structures is a strategy with great promise for the development of high-performance EMW-absorbing materials. Using layered double hydroxides as the precursors of bimetallic alloys and combining them with porous biomass-derived carbon materials is a potential way for constructing multi-interface heterostructures as efficient EMW-absorbing materials because they have synergistic losses, low costs, abundant resources, and light weights. Here, FeNi alloy nanosheet array/Lycopodium spore-derived carbon (FeNi/LSC) was prepared through a simple hydrothermal and carbonization method. FeNi/LSC presents ideal EMW-absorbing performance by benefiting from the FeNi alloy nanosheet array, sponge-like structure, capability for impedance matching, and improved dielectric/magnetic losses. As expected, FeNi/LSC exhibited the minimum reflection loss of −58.3 dB at 1.5 mm with 20wt% filler content and a widely effective absorption bandwidth of 4.92 GHz. FeNi/LSC composites with effective EMW-absorbing performance provide new insights into the customization of biomass-derived composites as high-performance and lightweight broadband EMW-absorbing materials.