Abstract: The atmospheric corrosion of a metal under a thin electrolyte layer is caused due to the adsorption of the thin electrolyte layer on metal surfaces. As the electrolyte layer is considerably thin, the application of a traditional three-electrode system is considerably difficult; therefore, localized electrochemical technologies are of great use in this field. Herein, different localized electrochemical techniques for atmospheric corrosion under a thin liquid film were discussed. In particular, the applications of scanning Kelvin probe microscopy, wire-beam electrodes, and micro-droplet electrodes were introduced and comprehensively explained. In addition, the key parameters of the tests, which show the relation between thin film/droplet size and corrosion kinetics, were summarized. Furthermore, the issues that currently exist in this field and the potential for improvement was proposed in this research.
Abstract: Diopside[CaMg(SiO3)2] is a common mineral form of calcium magnesium silicate. Apart from dioside quarries, diopside also appears in skarn tailings. Diopside is a novel energy-saving raw material, mainly used in the ceramics industry. Glazed tiles prepared with diopside have the characteristics of low-temperature fast curing, which offers significant advantages to the building materials industry. The results reported in this paper show that the silicate and quartz composition in skarn lead and zinc tailings are likely to participate in the generation of ettringite and C-S-H gel in hydration reactions, respectively. Therefore, lead/zinc tailings can be used as concrete admixtures. As an important component of skarn tailings, the study of the ash reactivity of this type of tailings has great significance for comprehensive utilization in industry, but the relevant literature is incomplete. Paste samples were prepared with diopside, gypsum, and calcium hydroxide in this paper. The ash reactivity of fine-ground diopside was studied and hydration products were investigated using X-ray diffraction, scanning electron microscopy, fourier transform infrared spectroscopy, differential scanning calorimeter and nuclear magnetic resonance. The results show that the compressive strength of the paste prepared from fine-ground diopside can reach 9.83, 12.79, and 18.87 MPa at curing ages of 3, 7, and 28 d, suggesting that fine-ground diopside has good ash reactivity. The hydration products of cement prepared with fine-ground diopside are mainly accounted for by the C-S-H gel. Nuclear magnetic resonance results show that with the deepening of the hydration reaction, the percentage of silicon atoms in the Q2 structure state reduces and the Al/Si ratio in the C-S-H gel is lower than that in the original diopside material. With an increasing curing age, a small amount of gypsum and a large amount of Ca(OH)2 participate in the reaction. The amount of C-S-H gel hydration products increases gradually. The filling effect of the gypsum particles promotes the growth of the tructure's strength with an increasing curing time, although this effect does not alter the chemical reactions. These results will provide sufficient evidence for preliminary judgments of whether skarn tailings possess ash reactivity.
Abstract: Block caving mining has the advantages of large production capacity, safe operation, low mining cost, and easy organization and management. Therefore, it is considered as one of the natural alternatives to the current open cut mining. The migration law of ore-rock and the design of ore drawing parameters during ore drawing are the key to block caving mining. The caving rocks usually contain pore water between the fine particles, therefore, the caving rock in an unsaturated state is a solid-liquid-gas three-phase coupling field. The electric double layer force as well as the ionic hydration force, electrostatic force, and Van der Waals force result in the interaction between adjacent particles on a molecular scale. However, the interaction is also resulted in the force of the liquid bridge. To explore the influence of moisture content on the shape of an isolated movement zone in block caving method under ore drawing in mesoscale, the stress between unsaturated ore particles was analyzed. The fine particles flow and discrete bulks of ore-rocks were investigated using lattice Boltzmann method (LBM) and discrete element method (DEM), respectively. Based on the LBM-DEM coupling algorithm, the ore-drawing models of the block caving method were constructed, and the relationship between the moisture content and the shape of the isolated movement zone was obtained. The accuracy and reliability of the ore-drawing models based on the LBM——DEM coupling algorithm were verified by comparing the simulation results with the existing research results. The results indicate that the moisture content of ore-rock has significant effects on the shape of the isolated movement zone. When the same ore-rock mass fraction is discharged, with an increase of moisture content, the height of isolated movement zone increases and then decreases, and the shape of isolated movement zone becomes slender and then is restored gradually. The critical value of moisture content during the change of isolated movement zone shape is about 10%.
Abstract: In mining, cement paste backfill technology uses the high concentration tailings that remain after mineral processing to backfill underground stopes. These tailings are prepared by dewatering, mixed with a proportion of cement or other binder, then, after sufficient mixing, the saturated homogenized slurry is pumped or gravity-transported. Therefore, high concentration tailings are a prerequisite for cement paste backfill preparation and high quality backfill. The paste thickener is a key component that shows high efficiency dewatering, and rake shearing greatly affects tailings dewatering performance; therefore, appropriate rake torque design is crucial for efficient paste thickener operation. Rake torque is a key factor in determining the dewatering extent and the rate of flocculation in the networked structure bed in the thickener compression zone. In some industry processes, the problems of rake bogging, rat holing, swirl motion, and insufficient underflow concentration can affect production or seriously damage equipment. All these problems can be attributed to poor rake design or operation. Based on the non-Newtonian characteristics of a mud bed and the correlation of slurry initial shear stress with solids concentration, a torque mathematical model was proposed. The model predicted a rake torque increase with an increase in underflow concentration during thickener operation; the percentage of rake torque variation reached 4.67%. Regression analysis indicates that the percentage of rake torque presents as a polynomial function of the underflow concentration. At the same time, bed height affected rake torque slightly and the rake torque percentage varied within 0.27% when the bed height fluctuated. The predicted effects of underflow concentration and bed height on rake torque are confirmed and compared with 64 h of operational data on thickener operations in a lead-zinc mine.
Abstract: To ease the imbalance between the supply and demand for iron ore in the ferrous industry of China, a low-temperature reduction process via an ore-coal composite method was developed to recover iron from low-grade iron-ore resources (about 30%). In addition, industrial tests on this new reduction process were performed using a rotary kiln (φ1.5 m×15 m). However, rings were formed in the rotary kiln after some days of operation, and these rings affected normal operation. Ring formation during rotary kiln reduction has become a restraining factor for development of coal direct reduction processes using rotary kilns. Previous studies have mainly focused on the reduction process of high-grade ore (> 60%) for direct-reduced iron production. The manner in which highgrade ore reduction differs from low-grade ore reduction is unclear. So, the characteristics of the ring samples need to be studied primarily. Then, the characteristics that affect the formation mechanisms of the rings need to be investigated. Accordingly, relative operation may be developed and ring formation may be prevented. In this paper, ring samples formed in a rotary kiln during a low-grade iron-ore reduction process were studied. The characteristics and formation mechanisms of the ring samples were investigated in detail. The characteristics for ring samples collected from different positions in the rotary kiln were analyzed from the aspects of macro morphological, physical, and chemical compositions, softening and melting properties, and microstructural properties. Thermodynamic phase diagrams, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, X-ray diffraction, and chemical phase analyses were applied to reveal the ring formation mechanism during the rotary kiln reduction process. Results show that rings mainly comprise pellets and molten wrappage surroundings. The amount of molten wrappages and the proportions of MFe and CaO increase in the ring samples that are next to the kiln wall. The results also show that the ring samples exhibit lower softening and melting temperatures at this location. The main reason of ring formation is found to be the low melting phases including fayalite formed by FeO and SiO2 in pelletizing powder and hedenbergite compounded by CaO (brought about by coal ash). Moreover, the existence of low melting point phases promotes the diffusion and migration of newly formed iron grains between metallized pellets, which exacerbates ring formation.
Abstract: The currently used low carbon operation in blast furnaces (BFs) leads to a thin coke layer and deterioration in gas and liquid permeability. Previous studies have reported that coke breeze, formed by the graphitization of coke, is one of the main influences on gas and liquid permeability in the high-temperature zone of a BF. To investigate the influence of the graphitization of BF coke on its metallurgical properties, the degree of coke graphitization under different heating temperatures from 1100 to 1500℃ was investigated. The dependence of the degree of graphitization on coke reactivity index (CRI) and coke strength after reaction (CSR) was also studied. The relationship between different degrees of graphitization in coke and alkali metals was clarified. Finally, the micro-morphology of coke was inspected and analyzed. Results show that with increasing temperature, the degree of coke graphitization intensifies. With every 100℃ rise in heating temperature, the degree of coke graphitization increases 1.8 times, the value of the spacing of layers (d002) decreases by 2%, and the values of the layers diameter of microcrystalline structure (La) and the stack height (Lc) are improved by 3% and 15%, respectively. In addition, it is observed that the surface stomata of the coke decreases particularly the large pores, the mosaic structure decreases, the isotropic structure increases, and the degree of structural ordering increases. When the degree of graphitization intensifies, the CRI of the coke gradually decreases, the CSR gradually increases, the degree of coke degradation weakens, the formed large pores reduced, and the trend for pore wall damage is reduced. Moreover, the alkali metal plays a catalytic role in improving the CRI and decreasing the CSR. It is considered that the graphitized coke resists the destruction of the alkali metal and thus decreases the degree of coke degradation.
Abstract: The fluid flow pattern and free surface fluctuation in a mold profoundly influence both molten steel solidification and molten slag thermodynamics behavior in the continuous casting process. In addition, the fluid flow and surface fluctuation behaviors are important factors of inclusions floatation, meniscus hook formation, and shear layer instability that affect the slab quality. In this work, a 0.6-scale water model of slab mold was built according to a 220 mm×1800 mm actual mold from a Chinese steel plant to investigate the fluid field and free surface fluctuation during the continuous casting process. The characters of fluid flow were studied with particle image velocimetry (PIV) in different submerged entry nozzle (SEN) conditions, including SEN outlet angle, SEN bottom structure, and SEN submerged depth. Simultaneously, the fluctuation behaviors of the mold free surface were monitored using wave-amplitude sensors and analyzed using the F value. The findings show that there are shear flow with tilt down velocity vectors appearing near the one-fourth wide face position of the mold free surface, and some irregular vortexes are detected near the SEN position. In addition, the results show that increasing the SEN outlet angle and submerged depth can expend the up-recirculation flow domain and intensify its buffer action; therefore, the velocity of mold liquid surface decreases. However, changing the SEN bottom structure has negligible effect on fluid flow velocity at the position of one-fourth wide face of the mold free surface, although it can reduce the turbulent kinetic energy of the steel jet. Besides, the variation of surface fluctuate amplitude corresponds to the F value well, and the optimal F, which helps to reduce and avoid the possibility of mold slag entrapment can be obtained in the conditions of SEN outlet angles of 15° and 20° and submerged depths of 135 and 145 mm, respectively.
Abstract: Owing to martensitic transformation during deformation, high-manganese transformation-induced plasticity (TRIP) steels show an excellent combination of strength and ductility. They are considered as second-generation automobile steels. Because of the influence of strain rate, the TRIP behaviors of high-manganese steels may be different during dynamic and static compressions. Therefore, it is necessary to study the TRIP behaviors during dynamic deformation. Based on the research on the TRIP behaviors of high-manganese steel at low strain rates, in this study, the TRIP behaviors were evaluated at high strain rates. Given the special shape of hat-shaped specimen and fixed position of shear zone, the grains present in the shear zone of high-manganese steel before and after dynamic compression were quasi-in-situ characterized using the electron backscattering diffraction (EBSD) technique. Besides, the phase distribution of grains in different locations of shear zone was analyzed. In addition, finite-element simulations and stress calculations were conducted using the ANSYS/LS-DYNA and MATLAB softwares, respectively, to further analyze the differences in the phase transformation of each grain. The results show that the combined action of stress and strain, orientation of austenite, and the interactions among grains influences the TRIP behaviors. The higher the stress and strain the easier the phase transformation. Because of the existence of shear stress in hat-shaped specimens, phase transformation is more likely to occur in austenite with orientation along〈100〉 and〈110〉than austenite with orientation along〈111〉, and phase transformation is most likely to occur in austenite with orientation along〈110〉. Moreover, the phase transformation behavior of austenite with a favorable orientation and large grain size will be less affected by neighboring grains and easier to achieve a complete phase transformation. However, the phase transformation of striped grains with a beneficial orientation will be constrained when the phase transformation of neighboring grains is difficult. Grains with sharp corners easily undergo phase transformation because of stress concentration. If the shear stress of twinning is larger than that of slip, but the largest and second largest stresses are almost equal, both the twin systems may compete with each other and phase transformation becomes difficult. Martensitic transformation often occurs near the grain boundary where the stress concentration is severe during dynamic compression but rarely in grains. α'-M has a shape of thin sheet, and its variant selection is obvious.
Abstract: As carbon nanotube buckypaper composites have a good interfacial properties, conductivity, and thermal conductivity, they can be used for whole-life health monitoring of composite materials. In this paper, carbon nanotube buckypaper and its sensors have been prepared. Meanwhile, composites samples with the buckypaper sensors at different positions were obtained. Tensile loading and unloading tests were performed. By analyzing changes in the buckypaper resistance change rate and composite strain, a strain-sensing coefficient was obtained to clarify the synergistic deformation of composite materials. The results of this study demonstrate that buckypaper sensor can be used to monitor the tensile fatigue damage of composites.
Abstract: To improve lubrication during the hot extrusion of titanium alloys, a new type of glass lubricant based on phosphate glass, SiO2, and NaCl was prepared. The viscosity-temperature curve of the lubricant with different composition ratios was determined from an extrusion experiment. Corrosion by the lubricant of a titanium alloy under high temperature was analyzed via scanning electron microscope. The heat transfer characteristics between the titanium alloy and die steel was studied using heat transfer coefficient measurement equipment. The results show that the viscosity of the glass lubricant, with a mass ratio of phosphate, SiO2, and NaCl of 70:20:10, varies slightly between 600℃ and 900℃, ranging from 1.3×105 to 9.4×105 Pa·s. This is beneficial to improvements in the extrusion and lubrication of titanium alloys. When the contact time between the new glass lubricant and the titanium alloy is not more than 3 min at 950℃, the new glass lubricant shows little corrosion on the surface of the titanium alloy, and serves the function of removing the original oxide layer on the alloy surface. High-temperature corrosion of the titanium alloy surface increases gradually with an increase in contact time. When the initial temperatures of the TA15 titanium alloy and H13 die steel are 900 and 400℃ respectively and the final thickness of the new glass lubricant is approximately 0.1 mm, the heat transfer coefficient between the titanium alloy and die steel increases from 185 to 1714 W·m-2·s-1 with an increase in contact time. In a traditional silicate glass lubricant, used in the hot extrusion of titanium alloys, the heat transfer coefficient increases from 286 to 2025 W·m-2·s-1. This demonstrates that the proposed glass lubricant exhibits better thermal barrier properties at high temperatures than the traditional one.
Abstract: In the design and development of electric vehicles (EVs), the variation in lithium ion cells (LICs) is one of the most important safety issues as it can cause a decrease in the life of the battery systems and shorten the mileage range. This problem is rooted in the design accuracy and rationality of the process values for the battery electrodes, and defining the effects of temperature and state of charge (SOC) on the electrodes is a critical step toward improving the variation in LICs. In this paper, the electrochemical impedance spectroscopy (EIS) method was adopted to study the 2.8 A·h 18650 cell. Firstly, the cells was dissembled and then attached the positive/negative electrodes separately to coin cells with an Li plate as the count electrode. Secondly, the impedance changes at different temperatures (25, 10 and-5℃) and the SOCs for these coin cells were studied using EIS. The results show that for 20% -100% state of charge at different temperatures, the negative electrode is the control electrode; electrochemical impedance is several times that of the positive electrode, especially, at-5℃, it reaches 4 times. Therefore, the negative electrode is the control factor in the kinetic variation process. For 0-20% SOC at 25 and 10℃, the electrochemical impedance of the positive electrode is larger than that of the negative electrode and it becomes the control electrode. Regarding EVs:1) the normal SOC usage range is 20% -95%; and 2) the working temperature range is above 0℃ to satisfy cell variations in the pack and benefit the life of the cells. Combined with the above results, it can be concluded that improving the variation in the negative electrodes is most useful to the variation in the 2.8 A·h 18650 cell. Above all, in the design process for LICs, the variation of electrodes should be improved as a target for improving costs and yields.
Abstract: Many solid particles in industrial processes require heating or cooling, such as calcinated petroleum coke, blast furnace slag, and steel slag. A moving bed with tubes is a viable design for facilitating such complex heat transfer processes. As particles are the primary heat carriers in this flow, the flow pattern of particles across the tubes in a moving bed is the main determinant of the heattransfer mechanism. The characteristics of particle flows across a tube structure are vastly different from those of a continuous-medium flow. Therefore, the flow pattern of particles moving across a bed of tubes must be studied prior to the heat-transfer mechanism. A simple pseudo-funnel flow model that can calculate parameters such as velocity field and residence time was established in this study for particle-flow modeling, and the range of parameters required to describe particles flowing across tubes was discussed. Using a movingbed test device made of transparent PMMA material, the flow of particles across aligned tubes banks was measured and a set of experimental results were obtained. Simultaneously, the discrete element method (DEM) was used for numerical simulations of the particleflow distribution in the system, and the obtained results were compared and verified by experimental results. Computational results from the quasi-funnel flow model were then compared with the DEM numerical simulation results to find the set of parameters required to describe particles flowing across aligned tube banks in the pseudo-funnel flow model. By setting appropriate values of the abovementioned parameters, the relative error between the two models could be reduced to 3%. This study provides a foundation for future studies on heat transfer processes in moving granular beds and the design and optimization of similar heat exchange devices.
Abstract: Development of context-aware technologies and rapid advancement in communication are essential parts of most industries, such as underground mining, pervasive medical care, smart space, and wireless sensor network surveillance. On occasions that require positioning services, location techniques offer convenience and may even save lives. In underground mining, not only do the miners work in a hostile environment but the environment itself threatens their lives. Thus, determining the precise location of people and objects in underground environments is essential. However, GPS cannot be used for practical application underground and underground localization seems to be the most feasible way to provide positional information to mining vehicles. The localization of underground vehicles has been a critical obstacle in the development of intelligent mining vehicles. Faced with the bad environment, interference, and multipaths among other effects, it is difficult to obtain high-precision positioning results using conventional algorithms. In addition, the underground environment is mostly made up of long narrow tunnels, which is not conducive to an arrangement of anchor nodes, and the layout of underground anchor nodes usually has great influence on the positioning results. Therefore, ordinary positioning methods do not meet the high-precision positioning requirements of intelligent mining. In this paper, traditional trilateration was analyze, the reasons for error was summarized, and an improved algorithm was proposed. Simulation results showed the effectiveness of the improved algorithm. In addition, the principle of topology optimization was proposed by theoretically analyzing the error band and using the maximum absolute positioning error to simulate the influence of topology on positioning accuracy. According to the characteristics of the environment, minimizing the average maximum absolute positioning error was the principle of topology optimization. Here, simulation and field experiments were carried out to verify the improved algorithm and topology optimization method. The experimental results show that the improved algorithm can reduce the error by 15% -43% under the same topology, the optimized topology can reduce the error by 17% -65%, and a combination of the two can reduce the error by 74%. The results show that under the same localization conditions, the proposed algorithm can significantly improve the accuracy of the localization results. In addition, there is a close relationship between localization result and topology structure. Based on the actual environment, choosing a flexible topology layout can further improve positioning accuracy, and combining the improved algorithm with the topology optimization method can achieve a higher positioning accuracy.
Abstract: In the current construction industry, exterior wall external insulation systems are widely used but suffer some obvious weathering problems such as deformation, drop in thermal insulation, and fracture of the surface layers. To investigate the weathering performance of an exterior wall external insulation system from the perspective of wall temperature stability, ABAQUS finite element software was used to establish a three-dimensional transient thermal-structural coupling model of the effect of paint finishes, with added adhesive powder polystyrene particle insulation slurries, on exterior wall external insulation. Numerical simulation analysis was carried out to calculate the real-time temperature field, thermal stress, and displacement distribution of different functional layers under heating-cooling cycles. Results show that during the heating-cooling cycles, the temperature difference in the coating layer is the greatest, that in the interior layer is the smallest, and the daily change is within 2℃. The rate of temperature change in the insulation slurry layer in the thickness direction is higher than that in the other materials. The coating layer is subjected to tension-compression cycles with tension at low temperatures and compression at high temperatures. The inner surface of the primary wall is always under compression throughout these cycles and the stress variation in the primary wall is small. By comparison, the stress in the interfacial mortar layer is large and that in the insulation slurry layer is almost zero. The maximum displacement in the thickness direction occurs in the insulation slurry layer.
Abstract: The safety situation in the construction industry across the world has been complicated for a long time, and the high incidence of accidents poses great challenges to this situation. Research on occupational safety and health indicates that people are prone to misconduct or unsafe behavior when they are tired. A large number of accident analyses show that fatigue is one of the most important reasons for accidents. When the human body enters into a fatigue state, the physiological parameters change accordingly. The aim of this study was to investigate the effects of heart rate and heart rate variability (HRV) on physiological fatigue in a sustained bricklaying task. A mathematical model was proposed for evaluating physiological fatigue. Five male healthy participants were selected to imitate construction by engaging in bricklaying on an 86 cm platform. HRV data were collected every 30 min during the sustained task, and heart rate was measured every minute. Analysis of variance, one-sample t-test, and nonlinear curve fitting were adopted in this study. Physiological fatigue shows a significant change with heart rate fluctuation (significant level α=0.05, P<0.05). With an increase in physiological fatigue, the heart rate needs a longer time to decrease to the normal level. No significant difference is observed in HRV between the subjects (α=0.05, P>0.05). The trend of the physiological fatigue curve follows a cubic function. The nonlinear curve fitting results (R2=0.8892) show that the development trend of physiological fatigue shows an "S" trend, which can be divided into the following three stages:fatigue adjustment period, fatigue stability period, and fatigue instability period. Proper rest in the fatigue failure period (In this experiment, it was about 90 min.) can slow or delay physiological fatigue.
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
