Abstract: China has large regions that freeze seasonally or multiple times a year. Special geological and climatic conditions must be considered for the engineering construction and mining of mineral resources in these regions, and slope stability in cold regions merits study. Taking the Yulong Copper Mine in the Tibet Autonomous Region as an example, the average altitude of this mining area is approximately 4000 m, the average daily minimum temperature in the coldest month is approximately ?20 ℃, and the freezing period is long. Slope stability is considerably affected by freezing and thawing, and frozen rock creates several challenges to blasting and excavation, thereby restricting mine production efficiency. To study the dynamic mechanical characteristics of slope rock under low-temperature conditions, marble samples are drilled from the slope of the Yulong Copper Mine. With the help of the SHPB experimental system with a low-temperature control system, dynamic compression and tensile mechanics experiments are performed on rock samples under normal temperature and dry conditions, normal temperature and adequate water conditions, and low-temperature freezing conditions to explore the influence of temperature and water content on rock dynamic mechanical properties. The experimental results show that (1) the average uniaxial dynamic compression and tensile strength of frozen rock samples at ?20 ℃ are increased compared with those at room temperature under the joint influence of water/ice phase transformation at low temperature and rock matrix cold shrinkage. Among these phenomena, the latter is the main reason that the strength of frozen rock increases substantially. Under four strain rates, the compressive stress increased by 1.30, 1.62, 1.41, and 1.43 times, and the tensile stress increased by 1.36, 1.28, 1.22, and 1.29 times, respectively. (2) Under the influence of pore water softening, a saturated rock sample has less dynamic strength than a dry rock sample. Therefore, the experimental data under the same strain rate show that the strength of a rock sample follows the order of frozen > dry > saturated. (3) For a given strain rate, the dynamic impact crushing time of saturated marble is the longest, and the decrease with increasing strain rate is the fastest. For a given strain rate, the crushing energy consumption is larger for a rock sample at freezing temperature than at normal temperature and increases greatly with increasing strain rate.
Abstract: In rocky road drilling and blasting in coal mines, the key to work efficiency is cutting. Although blast hole depth has steadily increased with increasing rocky road excavation activities, the cut hole depth is still ordinarily shallow, which is normally kept at 200 mm or less. Using an intelligent design system, a key technology, and equipment matching research of a drilling and blasting method in the Huainan mining area as the engineering background, this paper conducts research on the overdepth coefficient of cutting holes and the optimization of cutting-blasting parameters, aiming at the excessive number of full section blast holes in the mining area and the randomness and irrationality of blast hole layout. The overdepth coefficient, η, was obtained by theoretical derivation, numerical modeling, field testing, and monitoring. Based on this, the coincidence degree of fracture area, φ, is also introduced. This paper analyzes the rock stress state and stress wave attenuation phenomenon during blasting with different overdepths, establishes the relationship between the overdepth and stress between cut holes, determines the calculation formula and value range of the key parameters of the cut cavity, and investigates whether there is an optimal cut hole overdepth coefficient. The coincidence degree with fracture area increases the explosive blasting energy utilization rate and provides a theoretical basis for decreasing the charge and number of holes while retaining the blasting impact. The propagation law of explosion stress wave and the distribution and evolution law of effective stress in rock mass during overdepth blasting of cutting holes at different depths are explored using LS-DYNA numerical simulation, and the variation characteristics of stress wave intensity at different overdepth stress measuring points are compared, based on the geomechanical parameters of surrounding rock in Gubei Coal Mine. The effect of varying cut hole depths on the free surface after blasting and the blasting effect is revealed; overdepth blasting schemes of 200, 300, 400, and 500 mm are applied to the rocky road excavation site. The blasting effect indicators such as single cycle footage, blast hole utilization rate, explosive unit consumption, block rate of each overdepth blasting scheme, and ordinary blasting scheme are compared, and the effect of different overdepths on the quality and effect of cutting-blasting is compared and analyzed. On this premise, the blast hole layout is refined further, the number of blast holes is reduced, and the optimal blasting scheme is determined. The results show that the coincidence degree of fracture area increases as the overdepth coefficient increases, and the blast hole utilization rate initially increases and then decreases as the overdepth coefficient increases, between 0.17 and 0.22, causing the blast hole utilization rate to the peak. This theory proposes a novel approach to increasing the blast hole utilization rate. When the depth of the overdepth is 400 mm, The blasting energy is primarily used to create a crack area around the cut hole, which provides enough free surface for the subsequent central hole and auxiliary hole blasting, reduces the difficulty of rock breaking, increases the volume of the blasting chamber, and facilitates subsequent rock throwing. Simultaneously, the effective stress of each measuring point decays slowly with time, the average stress is higher, and the tensile fracture effect of the stress wave on the surrounding rocks increases and prolongs, creating a complete and even rock mass fracture. The blast hole utilization rate reaches the maximum of 95.2%, the bulk rate and explosive unit consumption are significantly reduced, the rate of half-hole mark rate is significantly increased, and the road construction quality is good. It demonstrates that ultra-deep blasting can enhance not only the blast hole utilization rate but also the blasting impact and road construction quality, which has some guiding significance for the parameter optimization of rocky road drilling and blasting construction.
Abstract: To study the effect of fatty acid unsaturation on low-rank coal flotation, oleic acid, linoleic acid, and linolenic acid with the same number of carbon atoms but an increasing number of double bonds were selected as flotation collectors and compared with conventional nonpolar collector diesel oil. Adhesion force measurements between particles and bubbles and molecular dynamics simulation of reagent adsorption were used to reveal the mechanism of unsaturated fatty acids enhancing low-rank coal flotation. The flotation results show that unsaturated fatty acid collectors surpass nonpolar diesel oil in flotation performance, and the flotation yield of low-rank coal increases with fatty acid unsaturation. Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) were used to analyze the surface morphology and surface functional groups of low-rank coal. SEM results show that the surface of low-rank coal is loose and contains many pores and cracks, which is not conducive to the spreading of chemicals on coal surfaces and the mineralization of bubbles and particles. The results of FTIR and XPS show that the surface of low-rank coal contains several oxygen-containing functional groups and has poor hydrophobicity, resulting in low flotation recovery. The adhesion force between bubbles and coal surfaces was measured in different collector solutions. The maximum adhesion between bubbles and coal surfaces increased with collector unsaturation in diesel oil, oleic acid, linoleic acid, and linolenic acid systems, indicating an increase in the floatability of coal particles with collector unsaturation. Furthermore, the molecular dynamics simulation of unsaturated fatty acid adsorption showed that unsaturated fatty acids spread on coal surfaces through hydrogen bonding between the polar groups of these molecules and surfaces. With an increasing number of double bonds, unsaturated fatty acids become more polar, and the spread of unsaturated fatty acids on coal surfaces gradually becomes more extensive, which leads to increasing particle floatability. This is the main reason for the increase in flotation recovery of low-rank coal with unsaturated fatty acids.
Abstract: Manganese is one of the important strategic resources in China, and there is a saying that “no manganese, no steel”. In 2020, China’s output of electrolytic metal manganese was 1501300 tons, accounting for 96.5% of the global output. At present, manganese metal is mainly obtained using the electrodeposition process. Electrolytic manganese anode slime (EMAS) is a kind of solid waste generated during the production of electrolytic metal manganese, which contains a significant amount of manganese, lead, and other resources. Every year, 60000?180000 tons of EMAS will be discharged in China, and direct discharge will cause severe environmental pollution. Cleaning and efficiently leaching Mn from EMAS is the key to realizing its resource utilization. A large number of studies have achieved efficient leaching of manganese from EMAS. Still, there are a number of issues, such as complicated processes, high leaching cost, a large amount of reducing agent, and residual organic matter in the leaching solution. Therefore, it is urgent to find a new method for efficient clean leaching of manganese from EMAS. This study proposed a new method of enhancing manganese leaching from EMAS with an H2SO4–H2O2 leaching system. The effects of the dosage of H2SO4 and H2O2, reaction temperature, reaction time, and solid–liquid ratio on the leaching efficiency of manganese from EMAS were studied. The results show that the leaching efficiency of manganese was 97.23%, and the content of Pb in the leaching residue was 53.71%, when the mass ratio of EMAS to H2O2 was 1∶0.8, the mass ratio of EMAS to H2SO4 was 1∶0.9, the leaching temperature was 45 ℃, the solid–liquid mass ratio was 1∶10 and the leaching time was 15 min. Leaching mechanism analysis showed that manganese oxide leaching in EMAS was reduced by H2O2 under acidic conditions, and Mn mainly exists in the leaching solution as MnSO4, as well as Pb in leaching residue is mainly enriched with PbSO4. This study offers a new idea for resource utilization of EMAS.
Abstract: Rhodium-containing homogeneous catalysts are the most active catalysts for homogeneous hydrogenation. Spent homogeneous catalysts contain 100–2000 g?t–1 of rhodium (Rh) and plenty of hazardous organic components, making them an essential resource of Rh. The recovery of Rh from homogeneous catalysts has excellent economic and environmental benefits. Based on Rh in the spent homogeneous catalysts, a new technology for green dissociation of the Rh–P chemical bond and complexation leaching of Rh was developed, allowing the green and efficient recovery of Rh. Compared with traditional incineration-fragmentation and acid leaching methods, the proposed technology eliminated issues such as long process times, severe environmental pollution, and a low recovery rate of Rh. In this study, first, the low-melting-point organics were removed using distillation. Then, the Rh+ in the homogeneous rhodium–phosphine complex was oxidized as Rh3+ through H2O2, which reduced the binding of organic ligands to Rh. Meanwhile, the RhCl63? formed by Rh3+ and Cl– dissolved into the aqueous solution. The effects of distillation temperature, the concentration of Cl–, the dosage of H2O2, the concentration of H+, and reaction time on the recovery efficiency of Rh were studied. The parameters listed above were optimized using response surface methodology. The results showed that the influence of each parameter on the recovery efficiency of Rh was as follows: H2O2 dosage > Cl– concentration > reaction time. The recovery efficiency of Rh reached 98.22% after 4 h of distillation at 260 °C, leaching Rh in the mixture solution of 3.0 mol?L–1 Cl–, 37% (volume fraction) of the spent homogeneous catalyst dosage of H2O2, 1.0 mol?L–1 H+, and at 90 °C for 4.5 h. Finally, the oxidation–complexation kinetic behavior of Rh was studied using spectrophotometry. The activation energy of the leaching reaction was 39.24 kJ?mol–1, indicating that the rate-controlling step of this process was a surface chemical reaction.
Abstract: Much waste copper clad laminate sorting residue is generated from the flotation process of recovering copper resources from waste printed circuit boards. The improper treatment and disposal of waste copper clad laminate sorting residue harms the environment and human health. According to the National Hazardous Waste List (2021 edition) of China, this waste belongs to HW13 (900-451-13) hazardous waste. The sorting residue contains approximately 1% copper, which is similar to the average copper grade of 0.8% in China. Therefore, this residue is an important copper renewable resource and has a high potential for copper recycling. To optimize the effective factors, including the Fe2+ concentration, initial solution pH value, and pulp density, and clarify the mechanism during the bioleaching process of waste copper clad laminate sorting residue, a Box–Behnken design of response surface methodology was first used, and a scheme consisting of 17 experiments was designed in the present study. Through the multiple regression fitting analysis of experimental results, a quadratic polynomial regression model was established. The regression model showed high reliability and simulation accuracy and was then used to optimize the bioleaching process. Under the optimal conditions (6.13 g·L?1 Fe2+, initial leaching solution pH value of 1.65, and pulp density of 30%), 92.2% maximum Cu extraction was obtained. Then, a modified scale-up bioleaching experiment in a 100-L stirred tank was performed. The results indicated that the maximum copper recovery reached 98%, and less than 0.02% of copper was detected in the bioleaching residue after 6 h of bioleaching because of the improved bioleaching operating conditions in the 100-L stirred tank, including slowly adding the sorting residue, additional stirring (200 r·min?1), aerating (20 L·h?1), and controlling the bulk pH value (solution pH value <2.5 adjusted with 50% (v/v) H2SO4). Leaching kinetic data described by a modi?ed shrinking core model indicated that interfacial transfer and diffusion across the solid ?lm layer controlled the copper dissolution kinetics. In conclusion, copper in the sorting residue was dissolved primarily by Fe3+ oxidation and secondarily by H+ attack throughout the bioleaching process. Notably, the continuous regeneration of Fe3+ by an iron-oxidation microbial consortium led to more Fe3+ distributed across the solid film layer of residual iron/calcium compounds and accumulated on the reacted core, which not only reduced total iron consumption (particularly Fe3+) but also substantially improved copper extraction from waste copper clad laminate sorting residue. These findings should have important implications for the green recycling and reuse of waste printed circuit boards and other waste electronic appliances.
Abstract: Aluminum oxide is a common component in mold powder and is a kind of amphoteric oxide. It shows the characteristics of acid oxide under high-alkalinity conditions and of alkaline oxide under low-alkalinity conditions. In general, adding Al2O3 to the traditional CaO–SiO2-based mold flux will increase the viscosity and melting point of the mold flux, which will consequently reduce the mold flux’s ability to adsorb inclusions. In addition, as the content of Al2O3 in the slag increases, the solidification temperature of the slag can be reduced, thereby improving the lubricating ability of the mold flux. At present, the research on the crystallization performance of Al2O3 on mold fluxes mainly focuses on low-reactivity or non-reactive mold fluxes for high-aluminum steel and high-titanium steel. Relevant studies have shown that Al2O3 in low-reactivity or non-reactive mold fluxes can increase the crystallization incubation time of the mold flux, reduce the critical cooling rate of the flux, and inhibit the crystallization process of the flux. In mold powder with low to medium alkalinity content (R = 1.2–1.5) or new CaO–Al2O3-based low-reactivity mold powder, the addition of Al2O3 will increase the viscosity of the slag and melting point and decrease (or increase) the solidification temperature and crystallization performance. In recent years, ultrahigh-alkalinity mold powder (R = 1.65–1.85) has been successfully applied in peritectic steel continuous casting mold powder, effectively coordinating the contradiction between the mold powder heat transfer and lubrication function. However, there is no relevant report on the influence of Al2O3 on the performance of mold flux under ultrahigh-alkalinity conditions. In this study, an ultra-high-alkalinity mold flux (comprehensive alkalinity R = 1.75) is taken as the research object, and the influence of Al2O3 on the flow, melting, and solidification characteristics of the mold flux is analyzed. The research results show that as Al2O3 increases, the viscosity and melting temperature increase, and the transition temperature decreases. Particularly, with an average increase of 1% Al2O3, the melting temperature of the mold flux will increase by approximately 5 ℃, and the turning temperature will decrease by approximately 12 ℃. In addition, as the Al2O3 content in the slag increases by 1%, the starting crystallization temperature drops by approximately 11 °C on average. The average crystallization rate decreases with the increase in Al2O3 in the slag, and Al2O3 has a significant effect on the crystallization rate. Moreover, with the increase in the content of Al2O3 in the slag, the proportion of crystals in the crystalline phase of the mold slag gradually decreases, but the type of crystals remains unchanged.
Abstract: γ-Al2O3 is an enormously important industrial material, especially used as catalysts, catalyst supports, and adsorbents due to its attractive structural, surface, and dielectric properties. Particularly, catalytic reduction of pollutants such as nitric oxide, as well as oxidation of hydrocarbons, is accomplished with precious metals such as platinum or palladium dispersed on the γ-Al2O3 surface. γ-Al2O3 loaded with precious metals has an excellent catalytic degradation ability of organic matter and is widely used to treat exhaust gas from stationary and mobile sources. High-temperature sintering is a major cause of catalyst deactivation. For example, at higher treatment temperatures (>800 ℃), γ-Al2O3 transforms into δ-Al2O3 and θ-Al2O3, decreasing in surface area and a change in dielectric properties. Additionally, in the reaction environment, supported metal nanoparticles grow in size, leading to the loss of catalyst activity. How to improve the anti-sintering performance of catalysts is a particular concern of this field. This review analyzes the reason and mechanism of the high-temperature sintering of γ-Al2O3 loaded with precious metal. A high temperature leads to Ostwald ripening and particle migration, coalescence of precious metals, and phase transformation of γ-Al2O3, reducing the specific surface area and activity of the catalyst. On this basis, the approaches for improving the high-temperature thermal stability of catalysts were reviewed and sorted out from three aspects, namely, precious metals, supports, and the interaction between them. First, the focus is on precious metal modification, carrier modification, and changing the interaction between them to improve thermal stability. Additionally, other methods, such as the confinement method and crystal plane control, are thoroughly examined and explained. These strategies provide new insights into catalyst design. Finally, the developmental trends of γ-Al2O3-based oxidation catalysts are broadly forecasted.
Abstract: MXenes are a class of two-dimensional inorganic materials comprising transition-metal carbides, nitrides, or carbonitrides of several atomic layers thick. Their general formula is (Mn+1XnTx), where M is a transition metal, such as Ti, n is the number of atomic layers, X is carbon and/or nitrogen, and Tx is the functional group introduced in the reaction process, such as OH, H, or F. They are obtained from the MAX precursor (Mn+1AXn, where A is a group of 13 or 14 elements, such as Al and Si). In 2011, Gogotsi, Barsoum, et al. first reported the synthesis of Ti3C2Tx by selective etching of the Al layer using a Ti3AlC2 MAX phase precursor impregnated with HF solution. The advantageous properties of MXenes, such as large specific surface area, fast charge–discharge performance, and small volume change, have made them attractive for lithium-ion battery anode materials, as first reported by the group Simon and Gogotsi in 2012. Since then, much attention has been paid to MXenes. Researchers hope to use MXenes for lithium-ion battery anode materials with high capacity, high safety, and improved energy density and battery life. However, a multilayer MXene material will collapse or accumulate during the preparation process, resulting in a large reduction in the contact area, thus reducing the electron and ion transport capacity of the MXene material perpendicular to the layer structure. Hence, MXenes are usually combined with other materials to improve the obtained structure, expand the layer spacing, and help enhance their electrochemical properties. This paper reviews the approaches to improving the electrochemical properties of MXenes by doping with transition-metal oxides, transition-metal sulfides, and silicon, as well as the scheme to achieve a stable and dendrite-free metal anode by using MXenes and high-capacity anode materials. Last, future challenges faced by MXenes as anode materials for lithium-ion batteries are analyzed and prospected.
Abstract: Over the past decade, the power conversion efficiency of perovskite solar cells has increased from 3.8% to the current 25.5%, which is expected to become the next generation of commercial thin-film solar cells. However, the widely used TiO2 electron transport layer has low electron mobility, requires a high annealing temperature, and has poor UV light stability, limiting the performance of TiO2-based perovskite solar cells, especially long-term stability. SnO2 is expected to be the first choice to replace TiO2 electron transport layers because of its high electron mobility, suitable band structure, low-temperature solution synthesis, and stable chemical structure. Although the certified maximum efficiency of state-of-the-art SnO2-based perovskite solar cells had exceeded 25%, it was still below its theoretical efficiency. Therefore, component engineering, interface engineering, solvent engineering, and other methods to improve the efficiency and stability of SnO2-based perovskite solar cells have become a major research focus. Currently, regulating the SnO2/perovskite and perovskite/hole transport layer interface is key to optimizing the performance of SnO2-based perovskite solar cells. Most studies focused on improving the charge transport performance of SnO2 and modifying the SnO2/perovskite interface, while few studies have addressed defect passivation of the perovskite layer and the modification of the perovskite/SnO2 interface. Therefore, it is essential to summarize the research progress of interface modification and performance optimization of SnO2-based perovskite solar cells. This paper introduces the types and characteristics of defects in the bulk and surface of the SnO2 electron transport layer, as well as defects in the bulk, grain boundaries, and surface of the perovskite film. The research progress of the interface modification (bulk and surface defect passivation) and performance improvement for the SnO2 electron transport layer/perovskite and perovskite/hole transport layer are reviewed. Finally, the research directions of SnO2-based perovskite solar cells on interface modification and performance optimization are presented.
Abstract: TiO2 has been widely studied because of its excellent photocatalytic properties but still has defects, such as the short lifetime of the photogenerated carrier. To solve these problems, a novel NaF–TiO2/rGO composite has been successfully synthesized using the hydrothermal method. The photocatalyst complexes were characterized using transmission electron microscope (TEM), energy dispersive spectrometer (EDS), diffraction of X-rays (XRD), photoluminescence spectroscopy (PL), and ultraviolet–visible spectroscopy (UV–Vis). This paper investigates the effects of hydrothermal temperature, hydrothermal time, rGO content, and NaF content on the photocatalytic activity of the NaF–TiO2/rGO composite, and the photocatalytic activity is evaluated using the photocatalytic degradation of RhB under fluorescent lamp illumination for approximately 80 min. The TEM analysis and identification results indicate that rGO can be incorporated into TiO2 to form a heterogeneous structure. The XRD results show that no heterophase formation occurs in the prepared NaF – TiO2/rGO composite, and the NaF – TiO2/rGO composite on the rGO surface does not cause the crystal shape change of the anatase phase. The PL results indicate that the main products are TiO2 with {001} and {101} facet synergy, and adding rGO effectively reduces the electron–hole pair recombination rate. The UV–Vis results show that the band gap energy of TiO2 is reduced by introducing NaF and further reduced after rGO is combined, thereby enhancing the photocatalytic activity and efficiency of TiO2. Compare and analyze RhB degradation using different factor systems and determine the best synthesis process for preparing composite materials at a hydrothermal temperature of 100 ℃, a hydrothermal time of 10 h, an rGO content of 0.3%, and a NaF content of 30%. The composite material had the best photocatalytic activity. The photocatalytic test results indicate that NaF–TiO2/rGO synthesized using the hydrothermal method has a better light absorption efficiency. The samples have a better RhB degradation rate under simulated solar irradiation. The RhB degradation followed pseudo-first-order reaction kinetics with a rate constant of 0.0448 min?1, which is 1.67 times that of NaF–TiO2. The RhB degradation rate over 80 min reached 99.8%, increasing first and then remaining constant with increasing NaF–TiO2/rGO dosage. Additionally, NaF–TiO2/rGO has good catalytic activity in the pH range of 3?11. The results of free radical capture showed that all three kinds of free radicals participated in RhB photocatalytic degradation, and the main active species in the reaction system should be ·OH and h+.
Abstract: The machining process is generally accompanied by intense friction and heat generation. Excessive heat flux subsequently leads to thermal damage and shape defects on the workpiece, which will greatly reduce the service life of the tool. As a novel coolant, nanofluids can effectively improve the lubrication and cooling conditions in precision machining. This paper uses the ionic liquid 1-ethyl-3-methylimidazole tetrafluoroborate ([EMIm]BF4) to disperse multi-walled carbon nanotubes (MWCNTs) and molybdenum disulfide (MoS2). The nanofluid with excellent tribological properties was prepared. The crystal structure of nanoparticles was analyzed by an X-ray diffractometer (XRD). The wettability and particle dispersibility of nanofluids were characterized by a Raman spectrometer, nanoparticle size potential analyzer and contact angle measuring instrument. Thermophysical properties were tested by a thermal conductivity measuring instrument and rheometer. Finally, a friction and wear tester and an ultra-depth-of-field microscope were used to analyze the friction properties of the prepared nanofluids. The following results are obtained. (1) After the MWCNTs or MoS2 nanoparticles are modified by the adsorption of [EMIm]+ cations, the Zeta potential of the nanofluids is greatly increased, and the laminated structure formed by the adsorption of two nanoparticles increases the particle size distribution range. By this time, an electrostatic equilibrium area is formed around the nanoparticles, whereby the particles are effectively dispersed due to the steric hindrance effect. (2) MWCNTs, MoS2, and their composite nanofluids are determined as pseudoplastic fluids, which are easy to spread and form films on metal (superalloy GH4169) surfaces with a minimum contact angle of 59.33°. After testing, the addition of nanoparticles and dispersants in the nanofluids did not cause a sharp increase in the viscosity, and the average viscosity was found to be as low as 1.49 mPa·s (25 °C), thus maintaining the flow advantages of water-based coolants while obtaining a higher thermal conductivity [up to 1.02 W·(m·K)?1 (25 °C)]. This is suitable for machining fields that require efficient flow heat transfer. (3) MWCNTs, MoS2, and their composite nanofluids greatly enhance the anti-friction and anti-wear properties of the base fluid (deionized water), especially composite nanofluids containing two nanoparticles, which form a “bearing-like” effect by stacking the layered and tubular combined structures. Thus, the lubrication performance is optimal. Compared with the traditional water-based coolant, the average friction coefficient of the composite nanofluid is small (0.083). At the same time, the adhesive wear or abrasive wear on the surface of the workpiece is further reduced, the wear scar is narrow and shallow, and the volume wear rate is reduced by 72.33%.
Abstract: The Cu–Ti alloy has similar mechanical properties and electrical conductivity to the Cu–Be alloy. It also exhibits excellent high-temperature properties and stress relaxation resistance. Therefore, it has emerged as a promising material to replace the toxic Cu–Be alloy. With the technological advances, the new generation of connector materials put forward higher requirements for performance, such as strength over 1000 MPa and conductivity over 15%IACS. However, it is difficult to obtain Cu–Ti alloys with such high strength and conductivity. An effective way is to increase the aging temperature or prolong the holding time of the alloy. When the strength of the alloy is reduced, the increase in cost is inevitable. The refining of grains or the regulation of size and distribution of precipitates has proved more effective, which is also true for Cu–Ti alloys. Currently, the refined grain size is still 10–50 μm achieved through a series of common processing methods, including hot rolling, solid solution, and cold rolling. Therefore, the improvement of strength and conductivity is limited for the Cu–Ti alloy. This paper provides a preparation method for synchronously improving the strength and conductivity of the Cu–Ti alloy. The Cu–3Ti–0.1Mg–0.05B–0.05La alloy with an ultra-fine grain structure is obtained via the vacuum casting and cold billet opening. The secondary aging process is used to adjust the size and distribution of the second phase to obtain a Cu–Ti alloy strip with high strength and good conductivity. The results show that the Cu–3Ti–0.1Mg–0.05B–0.05La alloy displays the maximum microhardness of 356 HV and a conductivity of 14.5%IACS after aging at 400 ℃/2 h. The relationship between the second phase precipitation and properties of the Cu–3Ti–0.1Mg–0.05B–0.05La alloy was analyzed using TEM (Transmission electron microscope). The evolution of the second phase is the Ti-rich phase → the granular phase β′-Cu4Ti phase → the granular β′-Cu4Ti phase + lamellar β-Cu4Ti phase → the lamellar β-Cu4Ti phase. The granular β′-Cu4Ti phase is the most important strengthening phase; the lamellar β-Cu4Ti phase can decrease the strength of the alloy but increase the conductivity. The comprehensive properties of Cu–3Ti–0.1Mg–0.05B–0.05La alloy can be further optimized by the secondary aging process. The microhardness and electrical conductivity of the Cu–3Ti–0.1Mg–0.05B–0.05La alloy reach 341 HV and 20.5%IACS after the primary aging at 450 ℃/8 h + 50% cold rolling + secondary aging at 400 ℃/1 h.
Abstract: GH4169, a precipitation-strengthened nickel-based superalloy, has been extensively used in structural applications in temperatures up to 650 ℃ because of its high-temperature strength, long-term stability, thermal fatigue, creep resistance, corrosion resistance, weldability, oxidation resistance, and easiness to forging. Although GH4169 has been introduced for many years, it is still widely used in many applications, especially under a high-temperature environment such as the turbine engine and the turbine disk part of advanced aero-engines, spacecraft, and gas turbines. Its microstructure mainly contains five phases: γ, γ″ (Ni3Nb), γ′ (Ni3AlTi), δ (Ni3Nb), and MC carbides. The main strengthening phase of the GH4169 alloy is the γ″ phase, which is metastable, and its phase transformation to the δ phase occurs when exposed at temperatures above 650 ℃. This paper studied the effect of temperature on the creep behavior and mechanism of the nickel-based superalloy GH4169 and analyzed its fracture morphology and creep rupture mechanism. Experimental results showed that the steady creep rate of the GH4169 alloy increased, and the creep life of the GH4169 alloy decreased significantly with the increase of the creep temperature, i.e., the alloy had strong temperature sensitivity. During the creep process, the γ" phase grew, aggregated, and transformed to the δ phase. With the increase of the creep temperature, the transition of the γ″ phase to the δ phase was faster, the amount of γ″ phases in the crystal decreased, the size and volume of the δ phase increased, and the number and size of secondary cracks decreased. When the creep temperature was 650 ℃, more bright white tearing edges in the fracture appeared, the dimple size was different, and there were a small amount of precipitates and carbonization. When the temperature increased to 670 ℃, the dimple size decreased, with mainly shallow dimples and cleavage surfaces appearing. When the temperature increased to 690 ℃, there were only a few dimples and cleavage steps, and the number of δ phases increased significantly, which meant that the fracture mode was cleavage fracture or quasi-cleavage fracture.
Abstract: Welding robot is widely used in many kinds and working conditions of welding production in the current machinery manufacturing industry. It plays an essential role in the machinery manufacturing industry. At the moment, in most industries, welding robots still work by teaching and payback. When the welding object or conditions change, the robot cannot make corresponding adjustments in time, which makes the welding gun deviate from the weld center, resulting in the decline of welding quality. The realization of automatic and intelligent welding is the inevitable development trend in the future. The application of machine vision in the welding field will promote the transformation of welding technology from rigid welding automation to flexible welding intelligence. Welding automation and intelligence are intended to improve the working conditions and environment, reduce labor costs, and improve product quality. Robotic welding technology is known for its great efficiency and consistent quality. A four-step welding seam tracking system is suggested based on segmented scanning, filtering, feature points extraction, and path planning. Through the laser sensor installed at the end of the welding robot, the welding seam data is continuously collected in multiple segments in a segmented scanning manner. To improve the tracking accuracy, a combined filtering method is used to correct the data to reduce the effects of burrs, data distortion, and noise on the surface of the weldment. Then the feature points are collected, and the coordinate system is calibrated in order to identify the welding points. Finally, the spatial welding path is obtained by path planning. Two-dimensional type S and three-dimensional complex welding experimental investigations are carried out. The results show that the proposed method can form a complete welding path. The average errors of the two weldments are about 0.296 mm and 0.292 mm, respectively, which are close enough to fulfill the required accuracy of 0.5 mm. It shows that the proposed tracking method is effective and can provide a reference for the research of high-precision tracking and automatic welding.
Abstract: In the 21st century, with the rapid development of computing and sensing technology, autonomous driving has become a hot and important research topic. The vast market for bicycles has created numerous opportunities for driverless bikes. An unmanned bicycle robot has the characteristics of flexible movement and narrow body, thus it can be widely used in disaster area-rescue operations, entertainment performances, and transportation scenes. Therefore, several scholars have studied and focused on this type of bicycle. For the lateral self-balancing problem of bicycle robots, a new balance control method has been studied for a class of bicycle robots that are equipped with an angular momentum wheel. The kinematics constraint of the robot balance control is constructed based on the lateral balance condition of the bicycle robot, and the balance constraint is regarded as the control target. Based on the Udwadia–Kalaba (U–K) theory, a torque analytical model satisfying the lateral balance of the robot was established, and a balance constraint following the controller based on the model was designed. The findings show that the proposed control method can achieve the lateral balance of the bicycle robot and overcome the disturbance caused by the initial deviation of the lateral roll angle θ. Through the calculation of the balance torque model, the bicycle robot is actively balanced. Compared with the traditional PD feedback control method, the control method based on the model design has the characteristics and advantages of fast system response, low overshoot, and ease of optimization of the control torque. The proposed control method is simulated and confirmed using MATLAB, and lateral self-balancing control of the bicycle robot is achieved at the initial roll angular velocities of 0, 1, 2, and 5°·s?1. The simulation results confirm the stability and effectiveness of the control system. This study proposes a novel idea for the balance control of unmanned bicycle robots.
Abstract: Blasting is widely used in national infrastructure construction as a paramount means of excavating hard rock and soil bodies. Blasting operations frequently occur in densely populated areas, endangering human physical and mental health. To reasonably evaluate the impact of blasting disturbance on personnel in adjacent areas and ensure the safety of the physical and mental health of personnel, constructing a human comfort evaluation system under the influence of blasting vibration is essential. Because of the uncertainty of human subjective feelings in the existing human comfort evaluation system under the influence of blasting vibration, the human vibration response test was performed by simulating blasting vibration using a vibrating table. Subjective sensations and electrocardiogram (ECG) changes were collected from 16 volunteers under the influence of blast vibration in different directions and at different levels. Subjective human sensations were quantified using the root mean square of successive differences (RMSSD) of adjacent RR interval values, a time-domain indicator of heart rate variability. The quantitative relationships among blasting vibration parameters, ECG index, and human subjective feelings were analyzed. A human comfort evaluation system under the influence of blasting vibration was constructed. The results show that the vertical direction is the main vibration direction affecting human comfort, and the influence of vibration on the human body is related to the main vibration-sensitive parts of the human body. When the main vibration-sensitive parts move up from the foot to the head, the influence is gradually increased. There is a link between the ST segment in the human ECG and human comfort. When the human body is subjected to vertical vibration, there is a drop in the ST segment in human ECG and human comfort is reduced, whereas there is no significant change under horizontal vibration. With an increase in vibration frequency and velocity, the human ECG index RMSSD shows a trend of first decreasing and then increasing under the vertical vibration; meanwhile, it decreased under the horizontal vibration, but the decreasing amplitude is limited. There is a quantitative relationship between the decline ratio of RMSSD and blasting vibration parameters and human subjective feelings. The quantitative relationships among blasting vibration parameters, ECG index, and human subjective feelings can realize the quantitative evaluation of human comfort under the influence of blasting vibration. In the blasting construction, a vibration velocity of 0.7 cm·s?1 and a vibration frequency of 80 Hz in the vertical direction of the surface can be used as the control threshold of blasting engineering in the adjacent densely populated area.
Monthly, started in 1955 Supervising institution：Ministry of Education Sponsoring Institution：University of Science and Technology Beijing Editorial office：Editorial Department of Chinese Journal of Engineering Publisher：Science Press Chairperson：Ren-shu Yang Editor-in-Chief：Ai-xiang Wu ISSN 2095-9389CN 2095-9389
