Abstract: Due to various advantages such as outstanding light absorption coefficient, long charge carrier diffusion distance, simple synthesis method, and low cost, halide perovskite materials, which are light absorption materials, are widely considered as promising candidates for next-generation electronic and optoelectronic devices such as solar cell, light-emitting diode, photodetector, laser device, X-ray imaging, and information storage devices. Particularly, since the introduction of halide perovskite-based solar cells in 2009, their solar conversion efficiency has increased from 3.8% to 23%, which is almost equal to that of commercial silicon cells, in less than ten years. However, the low phase stability, ion migration-induced hysteresis phenomena, and performance degradation significantly impede the further commercial application development of halide perovskite-based materials. Most recently, more attention has been paid to the zero-dimensional (0D) halide perovskite quantum dots (QDs) as compared to polycrystalline perovskite films because of their unique optical and electrical properties such as high crystalline quality and defect tolerance, flexible composition, quantum confinement effect, and geometric anisotropy. This paper summarized the limitations of the polycrystalline perovskite films and reviewed the intrinsic optical properties and detailed synthesis methods of halide perovskite QDs as well as their applications in optoelectronic devices. Specifically, the recent breakthrough on 0D-2D mixed-dimensional van der Waals phototransistors was systematically introduced. In addition, some perspectives of mixed-dimensional van der Waals phototransistors, which include interfacial charge carrier behavior modulation and subsequent construction of high performance photosensing device, were highlighted, and the corresponding scientific issues and challenges were discussed as well. Such comprehensive review is expected to be helpful for understanding and solving current issues faced in this research field; thus, it will effectively guide the evolution of the halide perovskite quantum dot materials and the development of perovskite-based next-generation optoelectronic devices in future.
Abstract: As one of the most promising nanomaterials, metal-organic framework (MOF) thin films (also known as surfacesupported MOF thin films, SURMOFs) have attracted much attention in recent years. The development of various synthetic methods makes it possible to obtain MOF thin films with controlled thickness, uniformity, morphology, and even dimensions, providing tremendous opportunities for more applications. Different synthesis methods of MOF thin films based on liquid phase or vacuum range were first introduced, and one of the most effective ways to fabricate quality thin films was depositing self-assembled monolayers (SAMs) on the primary substrate to further induce the nucleation and growth of MOF thin films. Furthermore, some traditional applications of MOF thin films (e. g. separation, catalysis, sensing) were summarized, as well as some newly-developed applications in photocatalysis, energy storage, photovoltaics, and electronic devices, which meet the demands for environmental sustainability and cleaner energy. Although the future is promising, MOF thin films still face some challenges. Therefore, some key factors those limit the MOF films' practical application were discussed, for example, the unclear growth mechanism of thin films, the poor quality and low film thermoe lectric performance. Based on the review of recent developments, this article will provide references for the future research of MOF thin films.
Abstract: With the increasing demand for gold and the decreasing of easily treated gold resources, refractory gold ores, which are characterized by low gold recovery and high cyanide consumptions when subjected to direct cyanide leaching, have gradually become the main sources of gold. Thus, reasonable exploitation and utilization of refractory gold ores are of great significance to the sustainable development of the gold industry in China. To ensure a reasonable and efficient utilization of refractory gold ores, refractory gold ores were reviewed and classified in this paper, and the difficulties of handling were briefly reviewed. For over one hundred years, cyanidation has been the predominant process of extracting gold from mineral sources. The major reason for adopting cyanide rather than other lixiviants is its higher chemical stability and lower cost. But in recent years, the utilization of the traditional cyanide method to leach gold have been undesirable; this is mainly because the acute toxicity of cyanide can result in environmental pollution and human health hazard. Moreover, leaching of refractory gold ores by traditional cyanidation techniques also results in poor gold recovery. On this basis, non-cyanide lixiviants have attracted considerable attention in the metallurgical industry, and several non-cyanide leaching methods have been proposed for gold extraction because of their non-toxic nature, acceptable gold leaching rates, and high gold recovery. In this paper, the leaching mechanisms and the latest research progress of non-cyanide gold leaching techniques for refractory gold ores, such as leaching processes with thiosulfate, thiocyanate, thiourea, polysulfide, lime-sulfur-synthetic solution (LSSS) and chlorination, were discussed in detail. Then considering features of non-cyanide gold leaching such as a complex leaching system, unstable leaching agents, and large consumption of leaching agents, and development directions of non-cyanide gold leaching technology for refractory gold ores were proposed.
Abstract: The iron ore sintering process is the main source of NOx emissions and accounts for about 48% of the total NOx emissions in the iron and steel industry. The generated NOx is mainly from fuel consumption, and it usually exists in the form of quasi-particle in iron ore sintering bed. Therefore, it is important to deeply understand the combustion characteristics and NOx formation mechanism of quasi-particles in iron ore sintering process. Based on this, the effects of coke breeze particle size, presence of an adhering layer of quasi-particles, adhering ratio of quasi-particle, and coke breeze content on the mass conversion rate of different types of quasiparticles and conversion rate of fuel-N to NOx were investigated in a vertical quartz tube reactor in detail. The results show that the mass conversion rate decreases with increasing coke breeze particle size for S'- and S-type quasi-particles; the conversion rate of fuel-N to NOx decreases with increasing coke breeze particle size for S'-type quasi-particle and exhibits the opposite trend for S-type quasi-particle, which is because of the presence of an adhering layer consisting of fine iron ore and limestone. Considering the combustion characteristics of S-and S'-type quasi-particles, the presence of an adhering layer of quasi-particles favors the increase of mass conversion rate and conversion rate of fuel-N to NOx. The mass conversion rate and conversion rate of fuel-N to NOx both decrease with increasing adhering ratio for C-type quasi-particles whose adhering layer consists of fine limestone and coke breeze. For P-type quasi-particles comprising coke breeze, fine limestone, and fine iron ore, the mass conversion rate decreases with increasing coke breeze content. The conversion rate of fuel-N to NOx is not linear and reaches the lowest value when coke breeze content is 50%.
Abstract: Hot deformation is a way to effectively improve strength and plasticity of multiphase steels simultaneously, thereby, improving mechanical properties of multiphase steels. Hot deformation affects martensitic transformation mechanism, microstructure, and mechanical properties because it increases retained austenite content and improves stability of multiphase steels. Moreover, hot deformation plays a role in dislocation multiplication, and fine grain strengthening; it can reduce bainite transformation driving force, reduce bainite transformation point, and result in small multiphase organization after quenching-partitioning process. The result can significantly improve the properties of materials. The effects of high-temperature deformation on the stability of room-temperature microstructure, mechanical property, and retained austenite under treatment of IQ&PB (intercritical annealing-quenching and partitioning within the bainitic region) and DIQ&PB (intercritical deformation-intercritical annealing-quenching and partitioning within the bainitic region) processes were studied using scanning electron microscopy (SEM), transmission electron microscope (TEM), electron probe X-ray microanalyser (EPMA), X-ray diffraction (XRD), and tensile testing machine. The results show that dislocation density increases from 0.290×1014 to 1.286×1014 m-2 after 15% compression deformation, and the respective concentrations of C and Cu element enrichment in martensite (the original austenite) increases. Overall, dislocation multiplication produced by high-temperature deformation significantly promotes elemental distribution. After the deformation, the size of bainite lath shortenes and its width increases by 0.1 μm, the volume of the bainite transition increased by 14%, and the size of the polygonal ferrite significantly decreases under the DIQ&PB treatment. In terms of mechanical properties, the tensile strength increases by 132.85 MPa, and the elongation increases by 7%; the strength and ductility product reaches 25435 MPa·% after intercritical deformation heat treatment. The volume fraction of retained austenite increases from 7.8% to 8.99%, and the mass fraction of carbon in the retained austenite increases from 1.05% to 1.31% after compression deformation.
Abstract: High-silicon electrical steel is an excellent soft magnetic material with high permeability, low coercive force, and nearzero magnetostriction coefficient. Compared with other preparation methods of high-silicon electrical steel sheet, the rolling method has the advantages of short process and high efficiency. Among the rolling methods, hot rolling is one of the most important part in the formation of high-silicon electrical steel sheet. Therefore, it is very important to study the hot deformation and dynamic recrystallization behaviors of high-silicon electrical steels. In this study, hot deformation and dynamic recrystallization behaviors of Fe-(5.5%, 6.0%, 6.5%) Si high-silicon electrical steel were studied using a Gleeble-3800D thermal-mechanical simulator with a deformation temperature of 750-1050℃ and strain rate of 0.01-1 s-1. The constitutive equations of Fe-(5.5%, 6.0%, 6.5%) Si high-silicon electrical steels were established by linear regression analysis. The thermal deformation activation energies of Fe-5.5% Si, Fe-6.0% Si, and Fe-6.5% Si high-silicon electrical steel are 310.425, 363.831, and 422.162 kJ·mol-1, respectively. It is observed that the thermal deformation activation energies of Fe-(5.5%, 6.0%, 6.5%) Si high-silicon electrical steel improve with the increase of Si content, which makes the deformation resistance of Fe-(5.5%, 6.0%, 6.5%) Si high-silicon electrical steel improve with the increase of Si content. Moreover, the dynamic recrystallization percentage was calculated using the intercept method of metallographic examination, and the statistical results show that the dynamic recrystallization percentage of Fe-(5.5%, 6.0%, 6.5%) Si high-silicon electrical steel decreases with the increase of Si content under the same deformation condition. Meanwhile, at the temperature of 750-850℃, the softening mechanism of Fe-(5.5%, 6.0%, 6.5%) Si high-silicon electrical steel is mainly dynamic recovery, while at the temperature of 950-1050℃, the softening mechanism is mainly dynamic recrystallization.
Abstract: Single-crystal silicon is widely used in optoelectronics and micro-electromechanical systems because of its unique physical and chemical properties. Ductile-mode removal of single-crystal silicon can be realized by strictly controlling the cutting parameters, which significantly affect the machining efficiency. To improve the surface quality without reducing the machining efficiency, nanometric cutting experiments were performed using high-resolution scanning electron microscopy (SEM) with online observation. First, the samples were prepared, and the nanometric cutting edge of a diamond cutting tool was fabricated by focused ion beam (FIB) technology. Then, the initiation and propagation of the micro cracks were observed online by scanning electron microscopy to analyze the machining behavior of single-crystal silicon in brittle mode. Finally, using diamond cutting tools with edge radii of 40, 50, and 60 nm, respectively, the effects of crystal orientation and tool edge radius on the critical thickness of brittle-ductile transition of single-crystal silicon were studied. The experimental results show that in the presently studied crystal orientations, single-crystal silicon is most easily removed in the ductile mode along the[111] direction on the (111) plane, where the critical thickness of brittle-ductile transition is about 80 nm. In addition, the smaller the tool edge radius is, the more prone is the single-crystal silicon to brittle fracture in the nanocutting process. When the tool edge radius is 40 nm, the critical thickness of brittle-ductile transition is about 40 nm. However, the machined surface quality increases with decrease of the tool edge radius. This indicates that the sharper the cutting tool, the easier it is to obtain a high-quality surface.
Abstract: Thick-section Al-Zn-Mg aluminum alloy extrusions are key materials for manufacturing rail transit vehicles, and stress corrosion cracking (SCC) is an important engineering application problem during the service life of these materials. The effect of sampling direction on the stress corrosion cracking behavior of Al-Zn-Mg alloys was investigated through constant load tensile stress corrosion and electrochemical tests. The microstructures of specimens were analyzed in different sampling directions both before and after stress corrosion via optical microscopy, scanning electron microscopy, and electron backscatter diffraction. Specimens with their tensile axes parallel or perpendicular to the extrusion direction of the extruded profiles were labeled as longitudinal specimens and transverse specimens, respectively. The specimens were completely immersed in a corrosive solution, a mixture of 35 g Na Cl and 1 L deionized water, with a constant unidirectional loading of 225 MPa for 360 h at 50 ± 2 ℃. The experimental results show that the transverse specimen is fractured at 315 h, whereas the longitudinal specimen does not break during the entire loading process. Thus, the transverse specimens have poor resistance to stress corrosion cracking. The corrosion current density of the longitudinal section (L-S) is0. 980 m A·cm-2, which is approximately 5 times that of the transverse section (T-S). Thus, corrosion tends to propagate along the longitudinal direction. The L-S is more susceptible to corrosion than the T-S owing to the larger misorientation difference and higher energy of the grain boundary. During the stress corrosion loading process, anodic dissolution occurs and forms corrosion pits. Then, the cooperation of the wedge force produced by the accumulation of corrosion products and constant load causes the crack to propagate along the grain boundary. Intergranular corrosion of the two types of samples is obvious under all immersion corrosion conditions. Different specimens exhibit the tendency to undergo stress corrosion cracking.
Abstract: The dendritic morphology, elements segregation index, precipitates morphology, and precipitates types in GH5605 ingot produced by vacuum induction melting and electroslag remelting were investigated by using optical microscopy (OM), field-emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS) spectrum analysis and the results of thermodynamic and kinetic calculations by Thermal-Calc and JMatPro sofeware. To study the effects of high-temperature diffusion annealing on GH5605 ingot, the annealing system was investigated and the microstructure and macrostructure characteristics of GH5605 ingot were analyzed before and after the diffusion annealing by differential scanning calorimetry (DSC) and thermal compression simulation tests in Gleeble 3800 test machine. In the OM results, dendrites are not obvious, and secondary dendritic arms cannot be distinguished in the GH5605 surface but they are gradually clearer toward the center area. The EDS results show that element segregation index is comparably small in GH5605 ingot; every element segregation index is in the range of 0. 9-1. 4 which is not as large as those of nickelbased superalloy. The main segregating elements during solidification are Cr and W which mainly segregate in the dendritic regions.According to the FESEM results, the precipitate phases include austenite and grain boundary carbide M23C6 and because of the Cr and W segregation at dendritic arms, an unexpected eutectic phase comprising austenite and M23C6 appears, and the alternating lamellae of austentite and M23C6 develop a lathlike morphology. Different macrostructure and microstructure characteristics including the morphology of dendritic, elements segregation index, grain size, morphology and the amount of eutectic phase were analyzed and compared in different annealing times. The high-temperature diffusion annealing system is optimal at 1210 ℃/8 h, at which the dendrites and elemental segregation are substantially eliminated, and the eutectic phase is almost dissolved.
Abstract: In the process of CO2 capture by chemical absorption, regeneration energy consumption accounts for 70%-80% of the total energy consumption. Currently, the most critical issue is how to reduce the energy consumption of regeneration. Equipment such as micro-reaction calorimeter (Thermal Hazard Technology provides), differential reaction calorimeter and Setaram C80 thermal differential calorimeter is used to compare the reference and sample solutions, which are simultaneously heated to compensate for heat loss of the sample solution during the measurement, but the heat of reaction cannot be directly measured. In this study, the reaction heats of MEA (ethanolamine) and MDEA (N-methyldiethanolamine) with CO2 at 10%, 20%, 30%, 40%, and 50% mass fraction were measured by synchronous thermal tracing technique. By synchronously controlling the temperature of the shell of the container and the internal solution, the temperature gradient was reduced to form a "thermal barrier"to prevent the solution from exchanging heat with the external environment in the form of conduction, convection, or radiation. A dynamic adiabatic environment was obtained without thermal compensation. The accuracy of direct measurement of the trace gas-liquid reaction heat was improved to save the sample amount. The experimental results show that the simultaneous thermal tracking method is more accurate. With the increase of solution concentration, the reaction heat of MEA first decreases and then increases, and the reaction heat of MDEA decreases gradually. When the mass concentration of MEA and MDEA is between 20% and 40%, the mass concentration has no significant effect on the reaction heat. The curve of temperature rise formed by exothermic reaction appears to be concave.
Abstract: The self-resonating waterjet has the characteristics of high-frequency pressure oscillation and strong cavitation. Accurately grasping the jet characteristics is a prerequisite for the application research of self-resonating waterjets. The characteristics of the self-resonating waterjet are typically acquired through a test. Traditional test methods primarily include the striking test and signal detection in the nozzle chamber. However, these methods both have the disadvantage of low detection accuracy and the inability to overcome the impact of high ambient pressure. In this article, a detection method for self-resonating waterjet characteristics based on the flow signal in a pipeline was proposed. The pressure sensors were transferred from within the high pressure tank to the outside of the tank and were arranged in the front pipeline outside the tank to avoid the influence of high ambient pressure. Dual-pressure sensors were used to acquire the flow pressure pulse signal, and signal-processing technology was used to effectively suppress noise interference for enhancing the intensity of useful signals and accurately obtaining the pressure fluctuation information of the self-resonating waterjet.The test results show that the spectral characteristics acquired from the flow pressure signal in the pipeline agree with the results obtained from the signal in the chamber and are also consistent with the theoretical calculations. Thus, the pressure oscillation characteristics of the waterjet are fully characterized. Moreover, the acoustic power spectrum obtained from the flow pressure signal in the pipeline is in accordance with the result obtained from the hydrophone in the high pressure tank. Consequently, the cavitation characteristic of the waterjet is well characterized. Therefore, the detection method based on the flow signal in the pipeline is entirely feasible and advanced and provides a new means for the study of the self-resonating waterjet under high ambient pressure.
Abstract: It is important for mechanical structures to be lightweight, and this is mainly realized by using hollow parts in structures. Presently, hollow shaft parts are used in vehicles, machine tools, and other equipment. Traditional hollow shaft parts are mainly manufactured by cutting, die forging, which have low production efficiency and low material utilization. With the increasing demand for hollow shafts, it is necessary to replace traditional processes with an efficient and advanced technology. Cross wedge rolling (CWR) has been widely used to produce shafts because of its advantages of higher productivity, better product quality, and lower material and energy consumption. Manufacturing of hollow shafts using cross wedge rolling with mandrel has received much attention. Phenomenon of roundness error often occurs in the formation of thick-walled hollow shafts using cross wedge rolling. Hot compression tests were conducted to investigate hot deformation behavior of alloy steel 25 CrMo4 in cross wedge rolling forming conditions, and true stress-strain curves were obtained. Based on the results, a finite element (FE) simulation model of cross wedge rolling for thick-walled hollow shafts was established using Deform-3 D, and formation mechanism and effects of area reduction, forming angle, and stretch angle on roundness error were analyzed. The simulation results indicate that the greater the area reduction, the smaller the roundness error; the greater the forming angle, the smaller the roundness error (where decrease in roundness error is facilitated by increasing rolling temperature); and the greater the stretch angle, the greater the roundness error (which is restrained by increasing the rolling temperature).Some process parameters were investigated by verifying the cross wedge rolling experiment, and the experimental results and simulation results were compared. The results show that the prediction accuracy of the FE model is high.
Abstract: Time-triggered Ethernet (TTE) is a new high-speed, real-time and fault-tolerant communications technology that combines high real-time services and traditional best-effort services. TTE is highly valuable in the application of transmission technology in the aerospace field. To ensure the security requirements of important information, the TTE network adopts a dual redundant network structure. Traditional links execute switching operation at the occurrence of failure, and the physical link switching causes some overhead and delays. When using dual-network transmission, the protocol is complicated, and the discard windows discard redundant packets, which will also cause the increase of network delay. In this paper, an adaptive dual redundant network structure was proposed.This structure did not only meet the real-time performance requirements of the TTE network services, but also met the security requirements of the TTE network service. Time labels for redundant messages were designed in this structure, and using time labels could restore transmissions adaptively. A scheduling scheme of mixed traffic—time-triggered (TT) traffic, rate-constrained (RC) traffic, and best-effort (BE) traffic—in TTE network was designed. Based on the importance of the packet, the sender adaptively classified the network packet. Among the mixed traffic scheduling transmission, the TT traffic through the terminal redundancy was processed and backed ups, and it was transmitted in dual networks. RC and BE traffics were not important information; therefore, they did not need backup; they were transmitted dispersedly in dual networks. In addition, based on deterministic network analysis method, the closed delay bound of RC traffic under adaptive double redundant scheduling method was deduced. Furthermore, several simulation result under extreme network, determined network, and queuing theory simulation model show that the scheduling method based on adaptive dual redundancy can reduce the network delay. This design does not only satisfy the security requirements of the TTE network, but also meets the real-time requirements of the service.
Abstract: In recent years, the air quality in China has become a matter of serious concern. Among the available indicators for evaluating air quality, PM2.5 is one of the most important. It comprises a complex mixture of extremely small particles and liquid droplets emitted into the air, whose diameters are no more than 2.5 μm. Environments with a high PM2.5 index are extremely harmful to human health. Once inhaled, these particles can affect the heart and lungs and cause serious health problems. Air pollution is closely related to meteorological conditions such as wind speed, wind direction, atmospheric stability, temperature, and air humidity. With the development of various machine learning methods, deep learning models based on neural networks are increasingly applied in air pollution research. In this study, the temperature, humidity, wind velocity data at different pressure altitudes from 8 locations around Beijing and average of PM2.5 data in Beijing were analyzed and normalized. Multi-dimensional data was ideal for research applications using machine learning methods. and three neural network models were built, including the back propagation (BP), convolutional neural network (CNN), and long short-term memory (LSTM) models, and trained them using the meteorological and PM2.5 data.The results indicate that the accuracies of the back propagation and convolutional neural network models in predicting the PM2.5 pollution level in the next hour is much lower than that of the long short-term memory model. The PM2.5 pollution index predicted for the next hour by the long short-term memory model is very close to the actual value. This result reveals the strong relationship between the PM2.5 pollution index of Beijing and the local meteorological conditions. The long short-term memory model is trained using meteorological data from different pressure altitudes, and found it to be more accurate in predicting pollution levels when using near-surface meteorological data than that obtained from multiple altitudes.
Abstract: Anti-impact design is a very important aspect to ensure the safety of reinforced concrete (RC) bridges against extreme loads, such as explosions from terrorists attacks and accidental collisions of rockfalls and vehicles. The impact behavior of the pier columns, which is the most important vertical components in the bridge structures, have attracted much attention in recent years, and experimental studies on the impact behavior of scaled pier columns have been conducted by many researchers. It has been acknowledged that the size effect has a significant influence on the dynamic response of structural elements. Therefore, in this study, the performance of the prototype reinforced concrete pier columns under lateral impact loads was investigated. Using a numerical simulation technique, three-dimensional finite element models of a prototype pier column under impact loading were established and validated through comparisons with impact tests in the literature. A new damage assessment method based on the sectional damage factor was presented to determine the damage level of reinforced concrete pier columns. The effects of impact parameters such as impact mass, impact velocity, and impact stiffness on the failure mode and damage mechanism of reinforced concrete pier columns were also identified in detail. The simulation results show that the energy dissipation of reinforced concrete pier columns under impact loading can be divided into local energy dissipation in the contact area and overall energy dissipation in the whole component. When the initial kinetic energy of the impact body remains constant, different combinations of the impact mass and velocity can lead to a significant discrepancy in the damage mechanism of reinforced concrete pier columns. The proposed damage assessment method based on sectional damage factors can be utilized to accurately describe the failure state of the reinforced concrete pier columns. In addition, the contribution of the axial load to the impact capacity of reinforced concrete pier columns is limited, and the columns are more likely to suffer shear failure with the increasing axial force. The impact stiffness has a significant effect on the impact force and the dynamic response of reinforced concrete pier columns.
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
