Abstract: The influence of freezing and thawing cycles on the physical and mechanical properties of granites with coarse and fine grains was studied by freezing and thawing cycle experiment and rock mechanic test. Rock samples were detected by nuclear magnetic resonance (NMR), their transverse relaxation time spectra and NMR images were got before and after freezing and thawing cycle experiment, and the porosity variation, pore structure and evolution laws were discussed. The macro phenomenological theory and the self-consistency theory were used to analyze the degradation principle of rock samples in macro and micro scales, respectively. It is found that the number of pores increases in the action of freezing and thawing cycles, which weakens the strength of rock samples. The theoretical values of damage models are in consistence with experimental data, but different damage theories show different results about the development of damage tendency. Granite with fine grains shows a better durability in the action of freezing and thawing cycles.
Abstract: XAD-2 resin and D101 resin were compared on adsorption separation of Microcystin-LR (MC-LR) in algae crude powder. Removal effects of impurities adsorbed on these resins with microcystins (MCs) by acetic acid, acetone and ethanol were discussed at different volume fractions. It is shown that XAD-2 resin has a better purification effect than D101 resin. When MC-LR purified by XAD-2 resin is leached by acetic acid, acetone and ethanol to remove the impurities, the optimum volume fraction is 40% for acetic acid, 10% for acetone and 20% for ethanol, respectively. When eluted with 60% methanol solution, MC-LR can reach its maximum mass fraction, and this purification method is well reproducible.
Abstract: The structure-activity of amine collectors, N-dodecyl-1,3-diaminopropanes (DN3) and N-lauryl ethylenediamine (DN2), was studied systematically with formulas derived by the authors. It is concluded that the collectors are characteristic of the smaller group electronegativity, the smaller absolute value of energy level difference of frontier molecular orbitals, the larger polar group diameter and the higher center atomic net charge. The collectors were used in reverse flotation of hematite for desilicication. The results show that the selectivity and collecting performance of DN3 and DN2 are better than those of dodecylamine (CH3(CH2)11NH2). The selectivity of DN3 is better than that of DN2, while the collecting performance of DN2 is better than that of DN3. These calculation results are in accordance with the flotation test ones.
Abstract: An original strain Bacillus mucilaginosus HJ07 was screened from bauxite sampled from Henan Province of China. It was induced mutagenesis by ultraviolet (UV) radiating and nitrosoguanidine (NTG) culturing, and then was used for bioleaching silicon from bauxite. After treated by 120 s UV radiating and 600 mg·L-1 NTG culturing, its kill rates are 89% and 90%, and its positive mutation rates are 16.5% and 18.7%, respectively. Two mutant strains UV-2 and NTG-5 were screened from a large number of mutant strains, and they have better bioactivity and de-silicon efficiency than HJ07 strain. In comparison with HJ07 strain, the time that UV-2 and NTG-5 strains reach stable growth in bauxite bioleaching systems shortens by 48 h and 24 h, respectively, and they have higher bacterial concentrations. After 12 d bioleaching, SiO2 mass concentrations in leachates of UV-2 and NTG-5 stains improve by about 25.6% and 12.5%, and the time that UV-2 and NTG-5 strains reach the leaching terminal point shortens by 3 d and 2 d, respectively. UV-2 and NTG-5 strains can produce much more organic acids and extracellular polymeric substances than HJ07 strain. Moreover, mineral particle surfaces leached by UV-2 strain are eroded much more obviously and covered with a thicker layer of zooglea.
Abstract: Aiming at serious fluorine pollution problems in current hydrofluoric acid treatment processes of niobium-tantalum ore, a new leaching process of niobium-tantalum ore with an alkaline hydrothermal system was proposed that KOH solution was used as a reaction medium to substitute highly toxic HF solution. The reaction rules of niobium-tantalum ore in the alkaline hydrothermal system were investigated. It is found that decomposition of niobium-tantalum ore into soluble potassium hexa-niobate (tantalate) is promoted by increasing the KOH mass fraction and reaction temperature when the KOH mass fraction range is less than 50%, but soluble potassium hexa-niobate (tantalate) will change to insoluble potassium niobate (tantalate) when the KOH mass fraction and reaction temperature are too high, then the leaching rates of niobium and tantalum decrease. The leaching rates of niobium and tantalum are merely 18.73% and 9.4% respectively under optimum leaching conditions that the KOH mass fraction is 35%, the reaction temperature is 200℃, the KOH-to-ore mass ratio is 4:1 and the reaction time is 2 h, but they will increase to 95% and 60% respectively when the ore is mechanically activated. The results indicate that mechanical activation can effectively enhance the leaching process of niobium-tantalum ore in the alkali hydrothermal system. And after the ore is activated, the particle size decreases, the specific surface area enlarges, the degree of lattice distortion increases, the amorphous level and the internal defect degree increase. As a result, the reaction activity of niobium-tantalum ore greatly improves and the leaching rates significantly increase.
Abstract: Basic characteristics of Indonesia laterite nickel ore were systematically studied in this paper. It is found that the nickel laterite mainly consists of lizardite and enstatine. Most of Mg located in lizardite is replaced by Ni in isomorphism. A series of experiments were performed to investigate Ni and Fe enrichment from the nickel laterite by calcination, hydrogen reduction and magnetic separation. The results show that the release of Ni and Fe oxides is achieved by calcination of nickel laterite and carbonate addictive. When the calcinate is reduced by hydrogen, Ni and Fe elements are found in metallic form in reduction products, and the metallization rate of Fe is more than 80~, which is much higher than that of the raw nickel laterite ore (from 4% to 8%). As the temperature rises, Ni is easy to bond with Fe in the form of Fe-Ni. The mass fractions of Ni and TFe in magnetic separation products reach 3% and 20%, and the yielding rates of Fe and Ni reach 80% and 90%, respectively, meaning that preliminary extraction of Fe and Ni is achieved.
Abstract: The effects of TiO2 content, Al2O3 content and binary basicity (CaO/SiO2) on the viscosity of a TiO2-Al2O3-CaO-SiO2 fully liquid slag with high TiO2 content and low mass ratio of CaO to SiO2 were studied in this paper. Experimental determinations of the viscosity were carried out in the temperature range from 1633 to 1873 K using the rotation cylinder method. When the TiO2 content is from 23% to 43%, the Al2O3 content is from 3% to 12%, and the binary basicity is from 0.3 to 0.7, the viscosity of the slag decreases with increasing TiO2 content and alkalinity, but increases with increasing Al2O3 content. TiO2 is classified as an acidic oxide by calculating the sulfur partition rate of the slag in the electric furnace melting process. Based on the data of viscosity measurement and the definition of TiO2 attributes, a new melt viscosity prediction model of the slag was proposed by modifying the Urbain model. Its prediction error is 11%, indicating that the model provides a reasonable prediction for fully liquid slags with high TiO2content and low mass ratio of CaO to SiO2.
Abstract: The flow field and surface characteristics in a continuous slab casting mold with four kinds of submerged entry nozzles (Type A:well-shaped bottom, 15° (upper port angle)-15° (lower port angle); Type B:mountain-shaped bottom, 15°-15°; Type C:well-shaped bottom, 40°-15°; Type D:mountain-shaped bottom, 40°-15°) were studied by using the dye tracer injection technique, a wave sensor and a propeller velocimeter within a full scale water model. It is found that the level fluctuation and surface velocity in the mold using a well-shaped bottom nozzle are less than those using a mountain-shaped bottom nozzle. The power of surface velocity fluctuations (frequencies ranging from 0.03 Hz to 0.1 Hz) using a well-shaped bottom nozzle is 50% less than that using a mountain-shaped bottom nozzle, so the molten slag entrapment may be reduced when using a well-shaped bottom nozzle in the mold. At a high casting speed of 1.8 m·min-1, a larger upper port angle of the nozzle outlet is in favor of depressing the swirling flow and vortexes at the nozzle outlet, and then the molten slag entrapment decreases. The surface velocity in the mold fed by a Type C nozzle is the lowest and its value is about 0.27 m·s-1 among the four investigated nozzles, so a Type C nozzle provides much allowance for increasing the casting speed. As a result, the optimal design for high speed casting is Type C nozzles.
Abstract: Hydrogen induced internal fatigue crack initiation and propagation in steel was studied by numerical simulation. First, finite element analysis (FEM) was used to analyze the process of hydrogen diffusion and accumulation at a defect in steel under fatigue load, and then the concentration of hydrogen was computed. According to the inclusion theory, the area where hydrogen accumulated was regarded as an elastic inclusion in the vicinity of the defect, and the concentration result of FEM analysis was used to calculate the stress intensity factor induced by the elastic inclusion. Thus a criterion of crack initiation and propagation was established. Hydrogen-induced fatigue crack initiation and propagation rules were studied under different load conditions. The FEM formula of transient diffusion deduced by Sofronis and McMeeking was adjusted with the trapezoidal rule. The trapezoidal rule reduces oscillations due to steep concentration and stress gradients after initial loading, this is very important to calculate the criterion of crack initiation and propagation. At the last, some methods of improving the simulation precision and refining model were discussed.
Abstract: The effect of test temperature on the stress corrosion cracking (SCC) behavior of Z3CN20-09M stainless steel was studied in high temperature water containing Cl-. It is shown that the changing tendency of sensitivity to SCC is not consistent with test temperature. The sensitivity to SCC achieves maximum at 320℃ and minimum at 290℃, and it is in the middle at 250℃. Bi-layer oxidation films with a compact inner layer and a loose outer layer form on the sample surface when the temperature is 250℃ and 320℃; but when the temperature is 290℃, there is only a single compact layer oxidation film. Most of corrosion pits form in ferrite. SCC cracks usually initiate preferentially at the bottom of corrosion pits or along austenite/ferrite phase boundaries, and they are inclined to propagate along the phase boundaries or within ferrite. The effect of austenite/ferrite phase boundaries on SCC cracks strongly depends on the relative orientation of SCC cracks to the phase boundaries. When the SCC crack propagates parallel to the phase boundary, it is inclined to propagate along the phase boundary; but when the SCC crack propagates perpendicularly to the phase boundary, the phase boundary hinders its propagation.
Abstract: The potential and corrosion current of pure zinc, pure copper and zinc/copper coupling structures with different distances to the stray current source in northern Shaanxi soil simulation solution were studied with a self-made stray current simulating instrument. Electrochemical impedance spectroscopy (EIS) was used to analyze the corrosion behavior of these grounded materials. It is found that there exists an obvious transition from the cathode to anode in the surface of pure zinc as a grounding material, and samples are seriously corroded in the anodic zone. The electrochemical reaction resistance of pure copper is much higher than that of zinc, revealing that copper has a better corrosion resistance in stray current containing media. When zinc is used as a sacrificial anode material and coupled with Cu, the potential of Cu is shifted to the more cathodic part. Previous Cu which located at the exit zone of stray current steps to the cathodic zone and then it is protected.
Abstract: The hot deformation behavior of 6111 aluminum alloy was investigated by high-temperature tensile testing on a Gleeble-1500 thermal-mechanical simulator at deformation temperatures of 350, 450, 550℃ and strain rate of 0.1, 1, 10 s-1. It is shown that the flow stress of the aluminum alloy decreases when the temperature rises but increases when the strain rate increases, and the hot deformation behavior transfers from a strain-hardening deformation stage to a steady-state deformation stage. A unified viscoplastic constitutive model coupled with dislocation density was established in consideration of the effects of strain, temperature and strain rate on the flow stress. Material constants in the constitutive model were solved through a genetic algorithm. Predicted true stress-true strain curves calculated by this model are in good agreement with experimental data.
Abstract: Cu nanopowders were used to improve the performance of iron based alloy products formed by high velocity compaction. Under the condition that Cu powders were remain unchanged as a constant of 1.5%, part or all of Cu micropowders were replaced by Cu nanopowders. Seven kinds of iron-based alloy product samples in which the mass fractions of Cu nanopowders were 0-0.25%, 0.50%-0.75%, 1.00%, 1.25% and 1.50% respectively were prepared by high velocity compaction. The green compacts were sintered at 1150℃ for 2 h subsequently. It is found that the microstructure and performance of the iron base P/M parts is improved and the dimensional accuracy is also effectively controlled with the addition of Cu nanopowders. The tensile strength and hardness of the sintered alloy which contains 0.75% of Cu nanopowders are 720.6 MPa and 94.7 HRB, respectively. The axial and radial shrinkages of the obtained samples are in the ranges of 0.4% to 0.7% and -0.09% to -0.23% respectively when the mass fraction of Cu nanopowders is from 0.25% to 1.50%.
Abstract: Aiming at performance failure of non-oxide materials under high temperature water vapor conditions, the reaction behavior of hexagonal BN powder with the average particle size of 1.2 μm at a temperature range of 1273 K to 1373 K in water vapor (the volume ratio of H20/air was 3:7) was investigated by thermogravimetric analysis, X-ray diffraction and scanning electron microscopy, together with a comparison with the reaction behavior of BN powder in dry air. The reaction process of BN powder in aqueous conditions has the following characteristics:the weight gain rate increases quickly in the initial stage of reaction, but it becomes slow at the later stage of reaction. The reaction mechanism was discussed together with thermodynamic calculation. It is shown that the weight gaining is attributed to oxidation of BN powder to form B2O3. A reaction of B2O3 with H2O forming volatile products causes the weight gaining rate become slowly. In both stages, the weight gain rate all increases when the temperature rises. The reaction kinetics of BN powder in high-temperature water vapor is fitted precisely and quantitatively by Chou's model, and the results get a good agreement with experimental data.
Abstract: MnO2 powders with micro/nano spheres simple, quick and low-temperature hydrothermal method and microrods for supercapacitors were synthesized via a Their preparation process was optimized by orthorhombic test and single factor experiment. The crystalline structure, surface morphology and supercapacitive properties of the as-prepared MnO2 powders were studied by X-ray diffraction, scanning electron microscopy and electrochemical measurement. Experimental results show that the optimal reaction conditions are the reaction temperature of 150℃, the KMnO4/MnCl2 molar ratio of 2.5:1.0, the reaction time of 3 h, and the filling factor of 40%. Under the optimal conditions, the as-prepared MnO2 powders have typical α-MnO2 structure with hollow and porous micro/nano spheres and microrods. The α-MnO2 micro/nano sphere diameter is about from 0.2 to 0.8 μm, while the α-MnO2 microrods have the diameter of 30 nm and the length of 5 μm. The discharge specific capacitance of products at the 5th discharge cycle retains 255, 170, 133, 105 and 88 F·g-1 at current densities of 100, 150,200,250 and 300 mA·g-1, respectively. Moreover, the values of equivalent series resistance and charge transfer resistance decrease to 0.37 Ω and 0.40 Ω, respectively.
Abstract: The kinematic characteristics of rotary blanking without press rollers was researched, and then a design scheme of dies was put forward for sheet metal rotary blanking. Finite element simulation of 45# steel sheet rotary blanking processes was performed by ABAQUS software based on shear failure criterion and arbitrary Lagrangian Eulerian adaptive meshing method, and the influence of technical parameters on machining quality was analyzed according to this simulation result. It is found that the front and rear cutting edges of square holes undergo five stages during rotary blanking:metal sheet bending, punch indentation, crack initiation and propagation, material fracture and separation, and punch pullout. Quality defects in rotary blanking processes appear as perpendicularity, burr, corner collapse, indentation, etc. The main factors which influence cutting quality perspicuously include nominal clearance, punch height, roller radius, and so on. Decreasing the nominal clearance, lessening the punch height and enlarging the roller can improve cutting quality, especially are good to cutting perpendicularity and burr height. For carbon steel such as 45# steel, the nominal clearance of the rear cutting edge should be 5% to 10% of metal sheet thickness and this value of the front cutting edge can be smaller. The roller radius should be 100 to 150 times greater than metal sheet thickness. On the condition that the metal sheet could be fully separated, the punch height should be as small as possible.
Abstract: Aiming at the multiple working conditions of steering knuckle arms in mining dump truck steering systems during operation, this paper established a load mathematical model and obtained the dangerous load working conditions. In consideration with primary and secondary relations among these working conditions, an optimization design model of steering knuckle arms under multiple working conditions was elicited after the weight of each working condition was valued by fuzzy evaluation as well as the objective function and constraint function were response surface modeled by response surface method. Then Matlab software was used to program and solve the design model, and finally optimization design of steering knuckle arms under multiple working conditions was realized. The rationality of practical application and the value of optimization under multiple working conditions were further confirmed in comparison with the optimal results under a single working condition.
Abstract: In order to research the combustion characteristics of low concentration coal mine gas containing aqueous vapor in porous media, numerical analysis was carried out by the computational fluid dynamics (CFD) method. The temperature distribution law and pollutant discharge were studied when the gases with different aqueous vapor contents burnt in a porous media burner. It is shown that the axial temperature and combustion efficiency of the burner decrease with the increase of moisture content in the gas. Temperature distributions at each location in the burner under different working conditions are visualized through two-dimensional temperature contours and they provide guidance for burner design. The NOx discharge amount decreases when the aqueous vapor content increases at appropriate thermal efficiency; this not only contributes to protect the environment, but also is useful to make CO change into CO2 for controlling toxic gas production.
Abstract: Based on an actual wind turbine tower on land with the hub height of 50.41 m, the seismic dynamic response of the structure under different seismic loads was studied by a finite element model and time history analysis method. Then the horizontal displacement and stress critical values of the structure were discussed under serviceable limit state, plastic limit state and residual displacement limit state, and the critical response peak values of ground motion were calculated. Based on the above work, the seismic behavior of the structure was evaluated. It is shown that plate boundary type ground motion has a greater influence on this kind of structure. It takes the main place on critical value evaluation and performance evaluation. The serviceable limit state of the tower is the first limit state.
Abstract: Aiming at the order acceptance problem of nmlti-node and multi-process routes with the characteristics of earliness/tardiness, a mixed intelligent tuned harmony search algorithm (HITHS) with improved NEH heuristic algorithm, local search and intelligent tuned harmony search was proposed for resolving the problem. In this algorithm, some initial solutions in the initial solution space were generated by improved NEH heuristic algorithm. Then these initial solutions were updated with intelligent tuned harmony search. In the updating process, a series of operations such as interchange, exchange and reverse of local search were used to avoid falling into a local optimal solution, and thus the problem's approximate optimum solution was got. At last, a case of the problem was tested by the mixed algorithm. The effectiveness and efficiencies of the mixed algorithm was proved by the case's analysis and compared with harmony search.
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
