Abstract: Three typical ferroalloy slags, namely, silicon–manganese, nickel–iron, and chrome–iron slags, are produced in large quantities as by-products. This is because they are not efficiently utilized, which creates lots of pressure on environmental capacity and development of enterprises. At present, comprehensive utilization of ferroalloy slags is mainly concentrated on the traditional building materials such as cement and concrete. Although the construction industry consumes a large amount of ferroalloy slags, their high-energy consumption and relatively limited product value limit their maximum utilization. With the increasing market demand and improvement of energy and environmental awareness, the research on rational utilization of ferroalloy slags has been changing from its use as raw materials in traditional building materials to use as raw materials to produce new products with comparatively lower energy consumption and higher product value, which explores the possibility of slag reutilization in other fields. Based on the quality requirements of different ferroalloys, there are significant differences in the requirements of the raw materials and different smelting processes. As a result, different types of ferroalloy slags, having different physical and chemical properties, are produced. This study briefly presented the uses of the silicon–manganese, nickel–iron, and chrome–iron slags. It also showed how to classify these three typical ferroalloy slags. The differences of their chemical and mineral phase composition were also systematically analyzed in this study, which discussed different properties of different slags and provided the basic theoretical guidelines on how to efficiently utilize these slags. This study also emphatically summarized the latest domestic and foreign research advancements about their utilization in traditional building materials such as cement and concrete, and in new functional materials such as geopolymer, inorganic mineral fiber, microcrystalline glass, artificial light aggregate, and refractory materials required to build walls and as alternative raw materials to prepare functional ceramics. Based on the results of this study, we summarized the advantages and disadvantages of using the abovementioned ferroalloy slags as raw materials to generate different materials, and put forward the prospects for its future utilization direction and approach. The study also guided the key development areas for further studying and breaking through the bottleneck of the main utilization mode, formulating and improving the relevant application and pollution control standards, and developing and promoting high value-added products.
Abstract: Metal–organic frameworks (MOFs) are a class of organic–inorganic hybrid functional materials generally formed via self-assembly of metal ions or metal clusters and rigid organic ligands with nitrogen and oxygen atoms. The wide range of potential applications of MOF materials includes gas storage and separation, catalysis, sensing, and drug transportation and release, which can be attributed to their versatile designable structures, modifiable chemical functionality, low-density framework, large specific surface area, and functional and permanent pore space. MOF and its composite materials have also been employed to remove various contaminants from the environment in the recent decade. To present the remarkable research progress and outcomes of MOF materials in the removal of pollutants from the water environment, the related studies on the removal of heavy metals and organic pollutants from the water environment were reviewed in this paper. This was the second paper on the topic that mainly introduced the research progress of MOF materials in the removal of organic pollutants in aqueous solution. The previous studies have shown that MOF materials have open metal sites and Lewis acid–base sites; thus, they exhibit a high adsorption performance for dyes, antibiotics, pesticides, and persistent organic pollutants. Hydrogen bonding, π–π interaction, hydrophobic interaction, and electrostatic attraction are the main mechanisms for their adsorption of organic pollutants. In addition, the large pore structure of some MOF materials is conducive to the adsorption of macromolecular organic pollutants. Moreover, some MOF materials that can be used as catalysts for Fenton-like reactions, photocatalytic reactions, and persulfate activation to degrade organic pollutants, exhibit excellent catalytic performance. The degradation of pollutants in photocatalytic reactions can be mainly attributed to the contributions of ·O2?, ·OH, and h+. In the persulfate system, ·O2?, ·OH, SO4·?, and 1O2 are the main reactive oxide species that cause the decomposition of organic pollutants. Based on the review of previous studies, it is believed that future research will include but will not be limited to the following: (1) the improvement of the performance of MOF in removing organic pollutants and its recyclability; (2) the preparation of new MOF catalytic materials and investigation of catalytic reaction mechanisms; (3) the regulation of the defect structure of MOF to develop new MOF materials with high adsorption and catalytic efficiency; and (4) the analysis of new framework materials, e.g., covalent organic framework materials, and their applications in the field of pollutant purification.
Abstract: Zinc is a nonferrous metal necessary for modern industry and an important strategic resource. It ranks fourth among all metals in terms of world production after iron, aluminum, and copper. Zinc sulfide ore is the most important zinc-producing mineral in the world, followed by associated zinc oxide ore and zinc-containing secondary resources. China is rich in zinc resources. Most of China’s lead–zinc and copper–zinc deposits are mainly lead–zinc integrated deposits, lead–zinc sulfide deposits, and other associated components. These types of mineral resources lead to wastage of resources in the development and utilization processes and affect the subsequent smelting process, which places considerable pressure on the production efficiency and ecological environment. The current mining and metallurgical industry vigorously promotes industrial development and has shifted in the favor of recycling, low-carbon, and green technologies. The biological leaching technology, as a green and low-carbon wet metallurgy technology, meets the current environmental protection policy requirements. This technology uses microorganisms and their metabolites to soak valuable metals in ores and has many advantages such as simple process, environmental protection, and capability to process low-grade ores. With the development of hydrometallurgical technology, the biological leaching technology of zinc from various types of low-grade zinc resources has attracted researchers’ attention and shown considerable application potential. First, this study introduced the mineral characteristics of zinc resources and analyzed their bioleachability. Then, the bioleaching process of zinc was summarized, and the leaching bacteria, electrochemistry, thermodynamics, kinetics, and leaching mechanism were systemically introduced. Furthermore, the current situation and/or progress of zinc bioleaching technology were generalized. Finally, the development trend of zinc bioleaching process and future research hotspots were considered. This study shows that the breeding of highly efficient bioleaching bacteria and the corresponding technology and equipment inventions are the current research hotspots and can also be the development directions for zinc bioleaching in the future. This will help ensure rapid and effective development of the zinc bioleaching technology.
Abstract: Human skin is an extraordinary organ; it comprises an integrated, stretchable network of sensors that transmits information to the brain about tactile and thermal stimuli, enabling us to safely and efficiently operate in our environment. Researchers have become interested in large-scale electronic device networks inspired by human skin, motivated by the prospect of developing devices such as autonomous smart robots and bionic prostheses. Developing electronic networks consist of flexible, stretchable, and robust devices that are compliant with large-scale implementation and integrated with multiple functionalities is a testament to the progress in developing human-skin like electronic bodies. In the fields of human physiological parameter detection and robot tactile perception, electronic skin has been commonly used as a kind of flexible tactile biomimetic sensor. Conventional electronic skin tactile sensors based on metal and semiconductor materials do not meet the requirements for stretchability and portability during actual use because of poor flexibility and wearability. Attributed to the rapid development of flexible materials, and manufacturing and sensing technologies, new materials such as polydimethylsiloxane (PDMS), carbon nanotubes, and graphene have been used to prepare or support electronic skin sensors in recent years, thus enabling electronic skin to be more similar to human skin in terms of stretchability, compressibility, and spatial resolution of touch, and other properties. Now, multi-functional integrated electronic skin devices have realized interaction with smart devices to obtain further collection and processing of human body information. This study analyzed and discussed new electronic skin materials and sensing technologies used in electronic skin, including capacitive effects, piezoelectric effects, piezoresistive effects, optical effects, and wireless antenna sensing. We focused on the recent research progress in electronic skin in terms of stretch/compressibility, biocompatibility, biodegradability, self-power, self-healing, temperature sensitivity, and multi-functional integration. Moreover, we anticipate the future research directions of new electronic skin properties and possible ways to achieve large-area, low-cost, multi-function integrated electronic skin sensor arrays.
Abstract: With the development of the mining industry, a large number of accessible shallow mineral resources are being depleted, and some have now been completely exhausted. The exploitation of the Earth’s deep mineral resources has become the only way to meet the society’s growing demand for minerals. With the increase in mining depth, the geostress, temperature, and pore pressure of water increase significantly, and the nonlinear mechanical behavior of rock becomes prominent. To assess the damage and failure of surrounding rock in deep shaft under high osmotic pressure and asymmetric geostress, a coupled mechanical–hydraulic–damage model was proposed to examine the effective stress of surrounding rock in deep shaft. This approach took into account the maximum tensile stress criterion with shear failure based on the Mohr–Coulomb criterion and was applied to simulate damage evolution in heterogeneous rocks. On this basis, the mechanisms of pore pressure, rock permeability, and geostress and its effects on rock damage evolution and fracture propagation were further investigated. The results indicate that the larger the pore pressure and its gradient are, the larger the damage and failure areas of surrounding rock. With the decrease of permeability of country rock, the damage and failure areas of country rock gradually increase and tend to be stable. The geostress field plays an important role in controlling the failure morphology of surrounding rock. When the ratio between maximum and minimum horizontal principal stresses is small, the damage and failure zones of the surrounding rock are concentrated in the direction of the minimum horizontal principal stress, mainly shear damage. However, if the ratio is large enough, then the tensile damage zone may occur in the direction of the maximum horizontal principal stress. Notably, the ratio of the maximum horizontal principal effective stress to the minimum horizontal principal effective stress increases because of the presence of pore pressure. Therefore, a high pore pressure in the formation could increase the risk of tensile failure of surrounding rocks. The findings of this research can be applied to the optimization of the shaft design to avoid areas with high tectonic stress and high pore pressure and ensure the safety of shaft construction.
Abstract: Risetime/amplitude (RA) and average frequency (AF) have been usually used for qualitative analysis of fracture mechanism in acoustic emission (AE) monitoring. However, regardless whether fracture is shear or tensile in macroscopic view, it can be observed in laboratory experiments that the AE signals of shear increases when it is close to the failure stage of specimens. Therefore, RA and AF may also have the potential in indicating the violent reputure of rock. Furthermore, as the value of RA would increase with the distance within some limits, the observed RA and AF would be closer to the shear feature, which means the index is relatively safer under attenuation and is appropriate for in-situ monitoring. Based on the data monitoring of Huayingshan Tunnel, Yuguang Expressway during the construction process, the distributions of RA and AF on positions of different distances of the seismic source were compared. Results show that the maximum value of RA increases distinctly with the distance increase between the sensors and the seismic source, whereas the distribution of values of AF are nearly the same at different distances. To verify the validity of RA and AF in indicating the rupture of rock, parameter r of RA/AF ratio was set and the time history of r and coefficient of variation (CV) of r during the rupture process were studied and compared with other regular indexes, such as absolute energy and b value. The variation of CV could describe the intense rupture of rock properly and the analysis of CV could get a safer evaluation result especially when dealing with small-scale failure in rock mass. To find the best statistical method of CV, three statistical methods of CV were compared and results show that the CV of r can well illustrate the rock rupture, CV1 is more suitable for situations that the AE signals vary and are discrete, and CV3 is appropriate for monitoring of continuous AE signals.
Abstract: Spent cathode carbon block (SCCB) is considered to be a kind of hazardous waste, because it contains a large amount of soluble fluoride salts and toxic cyanides. The life of an aluminum electrolytic cell is generally 5?8 years, and the SCCB would be produced during the overhaul of the cell. Currently, most SCCBs are piled in landfills or stored for disposal in China. The unreasonable disposal of SCCBs will cause serious pollution and damage to the ecological environment, and wastage of valuable carbon material and fluoride salts. The key to the safe disposal and resource utilization of SCCBs is to separate the carbon and fluoride salts deeply. In this study, SCCB was treated by the pyrometallurgical process, and the characteristics of volatilization temperature of fluoride salts were firstly experimentally determined. For a laboratory-scale self-designed high temperature resistance furnace, a three-dimensional model was built and numerical calculation was performed. The heat transfer characteristics, temperature control law and effective volatilization region of fluoride salts were analyzed in detail. The experimental results demonstrate that the effective volatilization temperature of fluoride is higher than 1700 ℃, and the volatilization rate is higher than 93.1%. By simulating the evolution of the temperature field in the furnace under different power supply modes, it is obtained that under the power supply condition of heating at 12 V for 24 h and holding 9 V for 12 h, the maximum temperature in the furnace during the heating phase can reach 2250 ℃, and the theoretical volatilization volume of fluoride salts can reach 98%. After optimization, a step-by-step decreasing mode of power supply can improve the efficiency of treating SCCBs. Moreover, the treating temperature can be maintained for 20 h at 1700 ℃, which is beneficial to the deep separation of carbon material and fluoride salts in SCCB.
Abstract: In the secondary cooling zone of continuous casting, the cooling uniformity of the billet largely depends on water flux distribution and is closely related to crack formation. Nozzle spray distance is the main influencing factor of water flux distribution in continuous casting billet. Therefore, the investigation of the effect of nozzle spray distance on secondary cooling uniformity is of considerable importance in the design and optimization of the secondary cooling system of the billet. In the present study, the water flux distributions of the nozzles used in the secondary cooling zone of continuous casting of the billet were measured under different spray distances. A heat transfer and solidification model was established to analyze the thermal behavior of 82B steel billet. The model specifically considered the distribution of secondary cooling water along the transverse direction and was calibrated via comparing the measured and simulated surface temperatures. The effect of nozzle spray distance on the secondary cooling uniformity of the billet was investigated using the model. Results show that the increase in nozzle spray distance helps to improve the uniformity of secondary cooling water along the transverse direction, resulting in the decreased transverse uniformity and increased longitudinal uniformity of surface temperature. These effects are beneficial for the internal cracks but harmful for the corner cracks of the billet. Increasing the nozzle spray distance in the first segment of the secondary cooling zone and decreasing the nozzle spray distance in the second segment of the secondary cooling zone can decrease the maximum reheating rate and increase the corner temperature, thereby achieving the purpose of simultaneously improving the internal and corner cracks of the billet. On this basis, a nozzle arrangement method, i.e., gradually increasing the nozzle spray distance along the casting direction of each segment in the secondary cooling zone was proposed. This method contributes to the improvement of “longitudinal–transverse” cooling uniformity of the continuous casting billet.
Abstract: In recently years, high-speed and heavy-haul railway technology has been rapidly developed and widely used in China. Pearlite steel is usually used in railway wheels, and its structure is composed of pearlite and ferrite. Pearlite has properties, including mechanical properties, that combine those of ferrite and cementite, and it also has acceptable strength and toughness. The comprehensive mechanical properties of pearlite are better than those of ferrite or cementite alone. When upper bainite is produced after the heat-treatment of ER8 wheel steel, the upper bainite may become the channel of crack development because of the large carbide particles and the weak strengthening effect and especially because of the presence of flake ferrites. In this study, the influence of different contents of upper bainite on the crack propagation behavior of ER8 wheel steel was investigated. The microstructure and crack growth path of ER8 wheel steel were studied by laser scanning confocal microscopy (LSCM) and scanning electron microscopy (SEM). The experimental results show that ER8 wheel steels not only have ferrite and pearlite but also upper bainite. The crack propagates through the upper bainite and pearlite and finally stops in the pearlite region. Compared with the pearlite microstructure, the crack propagation path in the upper bainite is more tortuous. The crack propagation and deformation of ER8 wheel steels were observed in situ by scanning electron microscopy. The experimental results show that when ER8 iron wheel steel containing 80% upper bainite is stretched, the microstructure deformation process is mainly ferrite and upper bainite. The crack in the upper bainite and the pearlite continues to expand with the pearlite deformation. However, when ER8 iron wheel steel containing 50% upper bainite is stretched, the deformation process mainly involves ferrite and pearlite, and the upper bainite retards the ferrite and pearlite deformation. The upper bainite can effectively prevent crack growth and plays an important role in deflecting crack path and delaying crack growth. Moreover, it hinders the deformation of ferrite and pearlite.
Abstract: A laser tailor welding experiment of 1800 MPa press hardening steel and low-alloy high-strength steel CR340LA was carried out using an optical fiber laser. The microstructure evolution and hot stamping formability of tailor-welded blanks were investigated under different laser welding powers and welding speeds, and the mechanical properties and distribution of the microhardness of the welding joints were analyzed and studied. Results show that the comprehensive mechanical properties of the laser tailor-welded blanks have little difference under three welding processes. The loss of elongation and tensile strength caused by welding joints is within 28.3% and 9.1% of the base metal. After laser welding, the fusion zone of the tailor-welded blanks is a martensite structure, which is bulky and has high hardness. The microstructure in the heat-affected zone on both sides is mainly ferrite and martensite, and there is no obvious softening zone in the joint under the welding processes. The tensile specimens of the tailor-welded blanks are all broken in the CR340LA base metal zone, approximately 12 mm away from the weld center, and a weld heave phenomenon occurs, which may be due to the uneven distribution of material properties after welding. Hot stamping of the tailor-welded blanks with a welding power and welding speed of 4000 W and 0.18 m·s?1, respectively, was carried out at high temperature, and no weld cracks were found during the experiment. Thus, these tailor-welded blanks have good performance and meet the requirements of automobile laser tailor-welded blanks. The tensile test results show that the fracture location of the specimens is the same as that before hot stamping, both of which are located in the CR340LA base metal area. During the stretching process, the fusion zone shifts to the side of the high-strength base metal, which results in a stress concentration and necking fracture on the side of the weak-strength base metal.
Abstract: The welding of 8-mm thick Q235 low-carbon steel plates by keyhole tungsten inter gas welding (K-TIG), a deep penetration argon arc welding technique with tungsten electrode, is associated with many problems, including an unstable welding process and a small welding current window. To solve these prominent problems, the method of adding shielding flux on the back of the welding workpieces was proposed for the first time in this paper. This method can improve the stability of the welding process. The butt welding method was used to achieve the result of single-sided welding and double-sided forming without adding welding wire or prefabricating groove during the welding process. The results show that direct current (DC) in the range of 430–480 A is successfully used to weld the 8-mm thick Q235 low-carbon steel. The welding current window is expanded to 50 A, and the welding process stability is significantly improved. After expanding the welding current window, the microstructures and properties of welded joints obtained under different welding currents were systematically studied. The results show that the distribution of microstructures and the mechanical properties of the welded joints under different welding currents present the same states. The microstructures of the weld zone are composed of ferrite + pearlite + widmanstatten structure; the microstructures of the fusion zone are composed of Widmanstatten structure; the structures of the heat-affected zones are composed of ferrite + a small amount of pearlite. In addition, with the increase in the welding current, the fusion width of the back of the workpiece increased slightly. In the welding joint, the hardness value of the fusion zone is the highest, followed by the weld zone, and the heat-affected zone. The base material has the least hardness, and the final tensile fracture position of the welded joint is in the heat affected zone.
Abstract: Metal pipes are the important components of structural load-bearing and conveying gas or liquid in the industrial field. However, the final forming profile obtained with the traditional bending process highly depends on the forming mold; the forming profile is simple, but the mold cost is relatively expensive. Thus, it is difficult for wide promotion on the bent pipe with a complex profile, especially for small batch production. The free bending process as a method of solving this problem is attracting a lot of attention. This process can achieve precision forming of the pipe without a forming mold. The pipe can be bent into different radii by adjusting the relative positions of the fixed die and mobile die. This process not only reduces the manufacturing cost but also improves the forming quality. The development of the free bending process will help to achieve high precision, high performance, high efficiency, and digitization of the industrial production of the metal pipes. In this study, an aluminum alloy 6061 pipe with a diameter of 30 mm and wall thickness of 2.0 mm was chosen. Its mechanical parameters were obtained by a tensile test of the axial and circumferential specimens of the pipe, and the obtained parameters were used for the parameter characterization of the chosen constitutive model. Meanwhile, a press bending test was carried out to validate the chosen model. Afterward, the pipe space free bending process was simulated by the finite element method, and the results were analyzed. Finally, the optimal values of the process parameters, including the shape of the mobile die, the size of the clearance of the mobile die and pipe, the frictional coefficient, and the feed speed of the pipe, were determined. This study has a great significance in the application of pipe space free bending forming process.
Abstract: To improve the coiling temperature control accuracy for change-over strip or the first coil of batch hot-rolling, data mining technology was adopted to infer the water cooling learning coefficient which is used in coiling temperature model preset for actual rolling strip from massive production data. Firstly, cooling feature parameters were recognized and defined respectively as absolute, relative, equal and tactical type. Then, the similar distance of each feature parameter between actual rolling strip and each historical rolled strip was calculated and summed. When the total similar distance of each rolled strip met the requirement, the produced strip was clustered as similar with actual rolling strip. Meanwhile, the weight value of the similar strip was calculated by considering its time effect. Secondly, based on the cooling information of the head and tail ends of each similar rolled strip, three object functions which are respectively composed of temperature predictive error and related penalty items such as a penalty deviated from regression learning coefficient and a penalty departed from the default learning coefficient were created and the corresponding constraints were also given. Gradient descent method was utilized to solve the quadratic programming problem. After three mathematical optimization calculations, a referenced learning coefficient and two parameters reflecting the relationship between the learning coefficient with rolling speed and target coiling temperature were obtained and then used to compute the learning coefficient needed in the cooling schedule calculation according to thread speed and target coiling temperature of the actual rolling strip. Application results show that the presented model’s adaptive parameter setting algorithm, based on the cooling data of 100,000 rolled strips can enhance the pre-setup ability of the coiling temperature model for strip head end. The adaptive setting ability of the learning coefficient will increase with the diversity of the strip cooling data stored in the memory and the number of similar strips retrieved.
Abstract: The health condition of hot-rolling back-up rolls plays a key role in controlling the strip profile quality and rolling stability. The characteristics of nonlinearity, strong coupling, and the use of limited samples complicate the prediction of the back-up roll health state. The current back-up roll replacement strategy of each steel mill is generally determined according to a certain rolling time or rolling kilometer, and such a maintenance mode is based on experience. In actual experience, due to different strip specifications in each rolling cycle, the degrees of wear on the back-up rolls are different. Regular maintenance methods may easily lead to excessive wear of the back-up rolls and reduce the quality of the strip shape at the end of the unit, or premature roll replacement wastes the back-up roll performance. This paper proposed a construction method for the back-up roll virtual health index and a Copula function–based model for predicting the health condition of complex working conditions. The health condition of a pair of back-up rolls was characterized by combining roll bending and shifting data, and the back-up roll condition was divided by the K-means clustering method. The Copula prediction model was constructed using the process data under each working condition, and finally, according to the actual rolling schedule, the arrangement order combines the prediction results of the working conditions. The production performance data of a 1780-mm hot rolling line were used to verify the results. The results show that the proposed Copula-based prediction model can accurately and effectively predict the health condition of the back-up roll according to the rolling schedule; thus, it can serve as the basis of a more scientific strategy to guide the replacement and maintenance of the back-up roll.
Abstract: The depletion and environmental pollution associated with traditional fossil energy sources has generated great interest in the development of new energy. Among the kinds of new-energy batteries, lithium-ion batteries have the advantages of small size, high energy density, a long life cycle, zero emissions, and no pollution. These batteries are widely used in many industries and fields, including vehicles. Currently, assessments of the health status of lithium-ion batteries have become a hot research topic. The lithium-ion battery has complex electrochemical characteristics and its capacity tends to degrade with cyclic charges and discharges. When its capacity degrades to the failure threshold (usually 70%–80% of rated capacity), the life of lithium ion battery is considered to have reached an end. Therefore, investigations to better predict the remaining useful life of a lithium-ion battery can help to improve system reliability and prevent accidents. Battery-system health evaluations have important research and application value. In this study, the voltage change curves of the lithium-ion battery were investigated with discharge time under equivalent cycle conditions and different cycle times. By analyzing the slope change rule of the derivative function at an equivalent characteristic point for different cycle times, the life degradation curves of the lithium-ion battery under equivalent cycle conditions were established. Using the NASA and self-test JZ equivalent cycle batteries, the intersection point of the specific-slope straight line and curve at early and late stages of discharge was taken as the equivalent feature points for predicting the equivalent cycle life. Based on these two groups of feature points, Mini and Mlat degradation models were established, respectively. To verify this method, other batteries in the equivalent-cycle battery pack were tested. The results of the test data set validate the prediction accuracy and stability, which has strong application value.
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
