Abstract: Layered Mn-based series Li[Lix(MnM)1-x]O2 (M=Ni, Co, Cr, …) due to its much higher capacity is one of the very promising candidates of cathodes, which has become a research hotspot recently and attracted more and more attention. Especially, with the aid of advanced characterization techniques including in-situ analysis, studies on the complex structure and high-capacity delivering mechanism of the series have achieved significant progress. In the paper, the structural characterization and charge-discharge behavior of the high-energy density layered cathode were briefly introduced. Study progresses on the voltage degradation, interface/surface variation during cycling and performance improvements of Li[Lix(MnM)1-x]O2 were reviewed in detail particularly in view of its exiting issues. Furthermore, the challenges and prospects in the high-energy density layered cathode materials were also discussed herein.
Abstract: A new method for calculating the damage index was first proposed-point load strength method (PLSM), based on the scene point loading strength test results and the damage theory. In order to verify the reliability and accuracy of the method and demonstrate the relationship between the damage index and integrity index which has been computed using this method, a series of theoretical inferences, in-situ rock mass acoustic tests and the lab rock acoustic tests have been carried out. The results show that the damage index and rock mass integrity coefficient have good consistency. The damage index calculated by using this method is correspondent with the change trend of rock mass damage extent within the scope of the loose circle. The error value of measured and theoretical values is less than 7%. It shows that calculating the damage index through the method has high accuracy and reliability.
Abstract: FLAC3D strength reduction method had been adopted to research on the stability of 3D slopes with interbedding of soft and hard rocks, when the dip angle of stratum and the angle between the strike direction of slope and stratum changed, and the failure modes were identified and analyzed. The results show that:to identify the failure modes of slopes, the angle of the rock stratum, the angle between the strike direction of slope and stratum and the cut off condition on the slope surface should be considered. When β (the intersecting angle between the strike direction of slope and that of strata)<90°, with the increase of α (the strata inclination), the failure modes change from creeping-pressure induced ripping, plastic flowing-ripping, sliding-ripping to sliding-bending and bending-ripping; when β>90°, the failure modes change from plastic flowing-ripping to sliding-bending, and then become bending-ripping. With the increase of the angle between the strike direction of slope and stratum, the slope stability coefficient increases at first and then decreases, it reaches the maximum when β=90°, and the greater the α is, the greater the coefficient peak is. For the dip slope, with the increase of the angle of stratum, the trend of failure modes is:creeping-pressure induced ripping, sliding-ripping, sliding-bending, and bending-ripping. The stability coefficient decreases first and then increases, and there is a most unfavorable angle of the stratum, the corresponding stability coefficient is the least. As for the anti-dip slope, the trend of failure modes is creeping-pressure induced ripping and bending-ripping, and the stability coefficient increases gradually.
Abstract: First, the quantitative characterization of cement paste backfilling (CPB) material characteristics was studied, and a comprehensive index called solid filling rate was presented to describe the interaction of material characteristics, through analyzing the substance composition of CPB microstructure. Then, rheological experiments were made to get the corresponding rheological curves, which were fitted by the Bingham model to get the yield stress and plastic viscosity of CPB. The influence of material characteristics such as volume fraction, weighted average grain diameter, nonuniform coefficient, the mass fraction of fine particles and cement on CPB rheological parameters was analyzed, and its mechanism was explained from the view of microstructure. At last, a calculation model of rheological parameters including solid filling rate was constructed. The results indicate that under the same conditions, the yield stress and plastic viscosity increase exponentially along with the increase of volume fraction, decrease with the increase of nonuniform coefficient, and decrease first and increase soon with the increase of fine particles.
Abstract: For studying the collision and coalescence phenomena between liquid inclusions and solid inclusions in liquid steel, a water model experiment was conducted to simulate the process of solid inclusions captured by liquid inclusions. The results show that the main mechanisms on coalescence of droplet and inclusion collision are inertial impaction, intercept capture and wake flow trapping. This is similar to the mechanism of solid inclusions removed by liquid inclusions in molten steel. After the efficiency of capture by inertial impaction and the efficiency of capture by inertial impaction and intercept capture were calculated through the theoretical formula, it is found that the trend of the two is the same basically. The two curves of efficiency are roughly coincident, especially when the droplet diameter is larger. Therefore, it can be concluded that inertial impaction dominates in both approaches, which is consistent with the observed phenomena in the experiment that the most coalescence of droplet and inclusion collision is inertial impaction. The experimental data were analyzed and calculated. It is shown that the efficiency of droplet capturing solid particles is different from the calculated theoretical capture efficiency, but the trend is basically the same. This is because the fluid turbulence is low, the capture efficiency of different droplet diameters is relatively uniform, not as steep as the theoretical curve.
Abstract: The modified metering nozzles were fabricated by using sol-gel Al2O3-ZrO2 composite powder as additives in particle and ceramic type zirconia metering nozzles. The physical properties, mineral phase and microstructure of metering nozzles of particle and ceramic types before and after modification were studied and the damage mechanism of nozzles in continuous casting field test was analyzed. The results show that the ceramic type metering nozzle has lower apparent porosity, higher bulk density, higher compression strength and poorer thermal shock stability compared with the particle type metering nozzle. By adding Al2O3-ZrO2 composite powder, the apparent porosity of modified nozzles decreases, the bulk density and compression strength get higher, the thermal shock resistance of the particle type metering nozzle improves markedly, and the count of thermal shocks is about 1.5 times of that before modification. After the analysis of residual samples in continuous casting field test for 35 h, the damage of the ceramic type nozzle is mainly caused by the fracture in the service process for the poor thermal shock stability, cracks generating in the fracture process cause a certain degree of flaking and hole enlargement. Due to low strength and high apparent porosity, flaking and hole enlargement of the unmodified type particle metering nozzle is more serious. The thermal shock, scouring and erosion resistance of the particle type nozzle after being modified by Al2O3-ZrO2 composite powder improve remarkably because of the formation of MgAl2O4 spinel enhanced phase, but little hole enlargement occurs after casting test.
Abstract: The solid-state desilication kinetics of silicon manganese powder and Brazil manganese powder was investigated by microwave heating and conventional heating. During the two processes, Brazil manganese powder which reacted with silicon in silicon manganese was used as the desilication agent. The mixture was heated up to different temperatures and preserved heat for some time by microwave heating and conventional heating, respectively. The silicon content of desilication materials was measured and the apparent activation energy of desilication reaction was calculated. The results show that the single raw material and the mixture could be heated up in the microwave field in a short time. The desilication rate increases with the increase of heating temperature and holding time by both heating methods. The desilication rate and the reaction rate under the microwave field are significantly higher than those by conventional heating. Microwave heating can increase the rate of solid phase desilication. The restrictive step of solid-state desilication kinetics of silicon manganese powder and Brazil manganese powders by microwave heating is the diffusion step. The apparent activation energy of desilication reaction under the microwave field is 102.93 kJ·mol-1, but the apparent activation energy of desilication reaction by conventional heating is 180 kJ·mol-1. The microwave heating field can improve the kinetics condition of solid phase desilication, increase the reaction rate of solid phase desilication and reduce the activation energy of desilication reaction.
Abstract: The effects of MgO content on the viscosity and melting behaviors of CaO-Al2O3-MgO-FexO-SiO2-K2O slags were studied. The slag samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) to identify precipitated phases during the cooling process. Meanwhile, theoretical calculations on the viscosities, solidus/liquidus temperatures as well as quantities of various precipitated phases from the slag system were also carried out by using the FactSage software, which were compared with the experimental results. The results indicate that the addition of MgO in slag could cause the increase of melting temperature. The relation between viscosities and temperature presents a breakpoint where the viscosity has a rapid rise, and above this transition temperature, MgO content has little effect on the viscosity. The transition temperature increases with the increasing of MgO content. In the process of slag cooling, the crystalline phases are mainly composed of olivine and spinel. From the calculation results, it could be found that the addition of MgO enhances the precipitates of olivine, which makes the viscosity increase suddenly.
Abstract: Al-22Si-2Fe-xMn alloys were prepared by conventional casting and a segment-based inclined cooling plates. It is shown that inclined cooling preparation technology can improve the morphology and size of primary Si, but has limited effect on the needle-shaped Fe-rich phase. The effect of Mn addition on the crystal structure of Fe-rich phase under the condition of inclined cooling was analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The hardness and wear resistance of hypereutectic Al-Si alloys with different Mn/Fe mass ratios were also researched by friction and wear test. Results indicate that long needle-shaped Fe-rich phase of tetragonal structure decreases gradually and disappears basically in alloys as the Mn/Fe mass ratio increases by inclined cooling casting hypereutectic Al-Si alloys. When the Mn/Fe mass ratio is 0.7, Fe-rich phase is mainly hexagonal structure block-shaped or fishbone-shaped α-Al15(Fe, Mn)3Si2 phase. By the time, the wear resistance is enhanced compared with no Mn element addition. The wear mechanism gives priority to abrasive wear manner.
Abstract: Breaking through the conventional P/M processing, a new process for preparing high density Fe-Cu-C alloys was designed. Through sulfuring treatments on the surface of iron powder, Fe reacts with moderate S to generate FeS, which is uniformly coated on the surface of iron powder particles and formed a thin-layered FeS lubrication film. The FeS lubrication film is useful for reducing the friction of compaction. The phase, element distribution and microstructure were characterized by X-ray diffraction, scanning electron microscopy and field emission scanning electron microscopy. The results show that the FeS lubrication film coating on the surface of iron powder is significant to improve the green density and activate sintering. After sulfuring treatments, Fe-2Cu-0.8C alloys with 0.5% S exhibit higher mechanical properties:the green density reaches 7.31 g·cm-3, the hardness 78.6 HRB, and the tensile strength 485 MPa. When the mass fraction of S is 0.8%, redundant FeS accounts for pressing volume fraction, resulting in the decreasing of green density and mechanical properties.
Abstract: SiCp/7085 composites with 10% particle volume fraction was prepared by a semi-solid mixture-mechanical stirring-ultrasound vibrations method. The particle distribution and interface bonding were studied through optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD), and the effect of ultrasonic field on the particle agglomeration and interfacial bonding of the composites was studied emphatically. The experimental results indicate that the effect of mechanical stirring on the agglomeration and interfacial bonding of 400 mesh particles is not significant. Under ultrasonic field, the coating of particles agglomeration can be effectively get rid of by instantaneous high pressure and temperature and micro jet induced by cavitation. That ultrasonic gets rid of the oxide film on the particle surface, removes the gas layer and makes magnesium in melt contact with particles directly is a very important factor in improving wettability between melt and particles. Finally, the MgAl2O4 strengthening phase is formed at the interface and a better interface bonding is got.
Abstract: The effect of Y-base rare earth on the inclusions modification, microstructure and impact toughness of E36 steel was investigated by using scanning electron microscopy and energy spectrum analysis. The results indicate that Y-base rare earth improves the microstructure and reduces the interlamellar spacing and content of pearlite. The typical cleavage fracture of E36 steel is quasi-cleavage and dimple fracture when adding Y-base rare earth. Fine and spherical rare earth inclusions are the main reason for the fracture transformation. The impact toughness of E36 steel is improved obviously by Y-base rare earth, especially at the low temperature. In comparison with E36 steel without Y-base rare earth, the longitudinal impact energy of E36 steel containing Y-base rare earth is increased by 33.5%, and the transverse impact energy is increased by 113.7% at -60℃. Moreover, the difference of longitudinal and transverse impact toughness is decreased by Y-base rare earth significantly. To E36 steel without Y-base rare earth, the proportion of longitudinal and transverse impact values is greater than 1.70 and it reaches 2.77 at -60℃. And the proportion of longitudinal and transverse impact values is 1.51-1.73 for E36 steel plate containing Y-base rare earth.
Abstract: Hook characteristics in continuous casting slabs of low-carbon steel under different casting conditions were investigated. According to hook morphology, hooks were classified into different types. Distributions of bubbles and inclusions near hooks were analyzed, and the influence of casting parameters on hook depth was discussed. Bikerman's equations and theory of meniscus solidification were used to explain the various hook morphology. Results show that on the basis of morphology hooks can be classified into four types, including whole-leaf type, double-hook type, truncated type and re-solidified type. The percentage of re-solidified type is the highest (46.8%), and the percentages of whole-leaf type, truncated type and double-hook type are respectively 25.3%, 7.6% and 6.3%. Studies demonstrate that the inclusion number near hooks is obviously higher than that in other zone, indicating floating inclusions in the mold can be captured by hooks. Comparing different casting parameters, the use of FC-Mold, the decrease of the submerged depth of the submerged entry nozzle (SEN) and the increase of casting speed can reduce the hook depth. Calculated results of Bikerman's equation and theory of meniscus solidification can explain the formation mechanisms of different hook morphologies.
Abstract: A forming experiment of 40Cr steel was conducted by using a warm extrusion technology, and the friction-wear behavior of the samples at different extrusion temperatures were observed. The wear morphologies, distributions of chemical elements and phase compositions were analyzed by scanning electronic microscopy (SEM), energy diffusive spectrometry (EDS), and X-ray diffraction (XRD), respectively, and the wear mechanism of warm extrusion on 40Cr steel was discussed. The results show that the grains are samll by warm extrusion at 550℃, the content of retained austenite is higher, and the hardness is the highest, showing that the wear resistance is the best. The size of grains is bigger and the contents of retained austenite decrease at the extrusion temperature of 650℃ and 750℃. The coefficient of friction is 0.7667 at the extrusion temperature of 550℃ under the load of 5 N, while that is 0.8587 at the extrusion temperatures of 650℃, which increases by 12.01%, and the wear performance decreases. At the extrusion temperature of 750℃, the coefficient of friction is 0.8764, which increases by 14.31% compared with 550℃, and the wear performance is worse. The wear forms of the samples at 550, 650 and 750℃ are common abrasive wear.
Abstract: Wall thickness asymmetry is a common problem for cross wedge rolling (CWR) hollow shafts, which is especially usual in the CWR process of hollow shafts of small diameter and large height-diameter ratio. In this paper, the constitutive equation of hot deformation of 5Cr21Mn9Ni4N heat resistant steel was investigated by the thermocompression experiment on the Gleeble-1500D thermo-simulation machine. The law for the variation of wall thickness during forming 5Cr21Mn9Ni4 hollow valve with CWR was presented, which is obtained via changing mandrel diameter and by means of finite element method (FEM) and experiment. The results confirm that when hollow valve with mandrel is formed with the CWR process, there is a critical diameter of mandrel. It makes wall thickness of hollow valve optimal. On the basis of FEM, it is stated that uniform flow of material along the axial direction is necessary for wall thickness uniformity of hollow valve, and circumferential stretching strain near zero, increase of radial compression strain with decrease of axial tension strain permit to improve wall thickness uniformity of hollow valve.
Abstract: In order to improve the accuracy of burden surface prediction in a blast furnace with bell-less top, a mathematical model of burden distribution considering burden motion was established. Based on the analysis of burden motion in the furnace, the burden motion was pointed as an important factor affecting the burden formation, and a 1:10 dimension scale bell-less top distributor model was used to analyze the effect of different burden components' velocity on heap formation. Then a heap formation prediction model considering burden motion was established, the numerical method was employed to determine the heap position and the heap shape, and at last the model was applied to predict the burden surface. Results show that the burden motion is the main reason causing the difference between the heaping angles in both sides of the heap, the variations of area of the heap cross section and heap profile. The heap profile is constructed by lines and curves in the heap formation prediction model, and the important model parameters, including the heaping angles and the length of curved transition area, all take burden motion into account. Thus the profile constructed is close to the actual heap, and the accurate predicted burden surface is achieved after applying this model to burden distribution prediction.
Abstract: To study the scheduling problem in the captive oxygen plant of a large-scale integrated steel mill, a mixed integer linear program (MILP) model was developed to minimize the oxygen emission. On the basic of the model, the oxygen production scheduling during blast furnace (BF) blow-down was studied as a case, and the effect of initial pipe network pressure (at the beginning of the BF blow down) on the oxygen emission ratio was analyzed. The system presents the oxygen emission when the initial pipe network pressure is larger than a critical value. The oxygen emission ratio increases with the increase of initial pressure in an approximately linear relationship, and the larger the buffer capacity of the high-pressure pipe network, the bigger the slope of this linear relationship. When there is the oxygen emission and for the same initial pressure of high-pressure pipe network, the bigger the buffer capacity of high-pressure pipe network, the smaller the oxygen emission ratio. This relationship tends to become inconspicuous as the initial pressure increasing, when the initial pressure is equal to the maximum allowed pressure, the oxygen emission ratio is unaffected by the buffer capacity of the high-pressure pipe network.
Abstract: Aimed at the frequently occurred problem of slab camber in rough rolling of hot strip mills, the main factors causing slab camber, including the difference in longitudinal stiffness of the mill on both sides, incoming wedge and running deviation of rolled pieces, were analyzed by combining with the spring equations and analytical method in this paper, and the corresponding adjustment values were respectively calculated. Based on rolling force difference on both sides, the tilting control model of slab camber was established. This model could reflect the quantitative relationship between the main factors and camber, such as the difference in longitudinal stiffness of the mill on both sides, incoming wedge and running deviation of rolled pieces, etc., and then the tilting values of roll gap for controlling camber were calculated in each pass of the rough rolling mill. Comparing with the real values by off-line verification, the averaged ratio of measured and calculated values is 0.977. The results show that the tilting values of roll gap can be estimated by the tilting control model of slab camber in each pass. Since putting the model into a 2250 mm hot strip mill, the camber values not complying with tolerance declined from 24.88% to 6.62%. By improving the control effect of camber, the slab camber problem has been greatly eased.
Abstract: In the preparation process of novel polymer quartz piezoelectric sensors using AT-cut quartz substrates and polymer materials, the roughness and the chemical characteristics of the substrate surface have a great influence on the production of the sensors. It could result in thickness-varied or defective films of the sensors, which make the sensor's frequency signals unstable. In this paper, a mechanical model of the sensor is presented, which takes into account the conditions that the film is thickness-varied and defective. The ANSYS software was used to obtain the vibration characteristics of the mechanical model under complex conditions by modal analysis. Results show that the natural frequency values of the sensor change from a stable state to a divergence state with the increase of the film defect in the radius, and the natural frequency values of the sensor increase linearly with increase of the thickness for the film. It indicates that the thickness of the film should be kept uniform and the defect radius should be limited within 0.5 mm during producing the sensors. The results provide an important basis for producing the qualified polymer quartz piezoelectric sensors.
Abstract: Cellular networks in 5G are tending to be heterogeneous and ultra-dense. Simulation methods used in a traditional hexagonal grid model are too idealized and inaccurate, and they are no more adaptive to heterogeneous cellular networks today. To settle optimal deployment of base stations, a popular approach for analyzing heterogeneous cellular networks is Poisson point process (PPP) based on stochastic geometry, which assumes that the locations of base stations are completely space random. According to the model of PPP, a lower bound of the probability of coverage is gotten. However, the base stations or users may be clustered at specific areas (e.g. cell edge and hot spot areas) so that the space distribution based on PPP will be inaccurate. In order to settle this problem, Poisson clustered process (PCP) is used to model deployment and planning of the base stations in three-layer heterogeneous cellular networks including macrocells, picocells and femtocells. First of all, a model of the locations of base stations based on PCP was proposed and the formation of clusters of the base stations was discussed. Second, based on the analysis of aggregated interference received by users, the cell-association mechanism of instantaneous signal to interference plus noise ratio (SINR) was adopted, the model of outage probability using SINR was derived and three special cases of the model were given. Finally, according to the model, the difference of outage probability between using PCP and PPP was compared by simulation, and the curve of outage probability is changing as the SINR threshold changes. It shows that using PCP can get a lower outage probability than using PPP.
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
