Abstract: Laboratory experiments were carried out by uniform design to investigate the effects of flocculant unit consumption,flocculant solution concentration and feed-slurry concentration on settling velocity and settling concentration in solid-liquid separation.According to the regression analysis of experimental data,the influence degrees of the three factors on settling velocity in descending order are feed-slurry concentration,flocculant unit consumption and flocculant solution concentration.Settling velocity shows a positive correlation with flocculant solution concentration and flocculant unit consumption,but a negative correlation with feed-slurry concentration.The influence degrees of the three factors on settling concentration in descending order are feed-slurry concentration,flocculant unit consumption and flocculant solution concentration.Settling concentration exhibits a positive correlation with flocculant solution concentration and feed-slurry concentration,but is independent of flocculant unit consumption.Nonlinear programme is used to find the optimal ratio,and the deviation of the predicted values and the measured ones from verification experiments is less than 8%.The recommended operating parameters for deep cone thickeners are the flocculant unit consumption of 5g·t-1,the flocculant solution concentration of 0.05% and feed-slurry concentration of 5.233%.
Abstract: Ferro-nickel granules were produced from nickel laterite ore/coal composite briquettes by high-temperature direct reduction.The effects of roasting temperature,roasting time,C/O(carbon/oxygen) molar ratio and flux amount on the grades and recovery rates of nickel and iron as well as on the quality of ferro-nickel granules were studied.The grades of nickel and total iron in the granules are 9.4% and 87.5% and the recovery rates of nickel and iron are 96.6% and 97.9%,respectively,when the roasting temperature is 1350℃,the C/O molar ratio is 1.4,the roasting time is 60min,and the limestone amount is 20%.The ferro-nickel granules were characterized by X-ray diffraction(XRD) and scanning electron microscopy(SEM) equipped with an energy dispersive spectrometer(EDS).The results show that nickel and iron basically exist in alloy state,and carbon is solid-soluted in the alloy.
Abstract: The number of Al type inclusions was analyzed by original position statistic distribution analysis(OPA) and the three-dimensional morphologies of inclusions were observed by a special depth erosion method.Total oxygen and nitrogen during the refining process were determined.Cleanness changes of the steel were evaluated by prolonging the RH pure circulation time.It is shown that the total oxygen can be reduced to 30×10-6 when the RH pure circulation time is 8 to 10min after alloying;the scrap steel should be adjusted before adding Al or titanium alloys,or it can influence the cleanness of the steel.The number of inclusions reaches the maximum value of 7.02mm-2 after adding Al within 5min,with the main inclusions of cluster Al2O3,and the size and number of inclusions decrease significantly during RH pure circulation after alloying.
Abstract: A new-type weathering steel 06CuPNi1Cr2 was developed by high-efficiently utilizing nickel and chromium in low nickel-chromium laterite ores.The influences of bath temperature and the partial pressure of carbon monoxide on decarburization and keeping chromium were studied and discussed to solve the problem of chromium oxidation in steelmaking.06CuPNi1Cr2 smelting experiments show that the effects of decarburization and keeping chromium are remarkable when the oxygen top-blowing is 3.0 to 3.3m3·min-1·t-1,the mass fraction of final carbon is 0.02% to 0.05% and the end-point smelting temperature is 1680 to 1700℃.
Abstract: Austenite grain growth phenomena of Q1030 steel at different heating temperatures were studied.In a certain heating temperature range,parts of austenite grains in Q1030 steel grow abnormally,leading to mixed grain phenomena.The inhibition effect of precipitated phase particles at different locations on grain growth was analyzed.The size and volume fraction of the particles at different heating temperatures were calculated by thermodynamic methods,and then the relationship between the pinning force of the particles and heating temperature was discussed.The result shows that the pinning force of the particles reduces sharply in a certain temperature range,resulting in the abnormal growth of partial austenite grains and producing the mixed grain phenomena.
Abstract: The continuous cooling transformation curves of under-cooled austenite in Nb-V microalloyed spring steel 60Si2CrVAT were measured by using a DIL805A quenching deformation dilatometer.The microstructure changes of under-cooled austenite in the tested steels at different cooling rates were studied by the metallographic method coupling with the microhardness method.The effect of Nb content on continuous cooling transformation of the tested steels was analyzed.The experimental results show that with the increase in Nb content,the high-temperature and medium-temperature phase transitions were promoted,the range of pearlitic transformation was widened,and the temperature of Ms point decreased from 284.2℃ to 258.3℃.The cooling rate for ferrite disappearance increased from 0.3℃·s-1 to 0.5℃·s-1,for pearlite disappearance from 2℃·s-1 to 3℃·s-1,and for bainite disappearance from 3℃·s-1 to 5℃·s-1.The cooling rate for bainite transformation occurrence increased from 0.4℃·s-1 to 0.6℃·s-1,while for martensite occurrence kept the same cooling rate of 1℃·s-1.
Abstract: Uniform and pitting corrosion behaviors of fine-grained rebar and low-carbon rebar in simulated concrete pore(SCP) solutions were investigated by means of corrosion potential,linear polarization resistance(LPR) and cyclic polarization.The influence of two different rebar surface conditions,i.e.,sandblasted and as-received,on the corrosion behavior of the rebar was taken into consideration.The results indicate that fine-grained rebar and low-carbon rebar show almost the same uniform corrosion behavior,and the passivation effects are better for sandblasted rebar than as-received rebar.In the latter period of corrosion,sandblasted rebar shows a higher uniform corrosion resistance than as-received rebar.Cyclic polarization measurements reveal that sandblasted rebar performs better in delaying pitting corrosion due to the relatively homogeneous surface than as-received rebar.Since more impurity-containing grain boundaries in fine-grained rebar facilitate the occurrence of pitting corrosion,the probability of pitting corrosion for as-received fine-grained rebar is slightly higher than that of as-received low-carbon rebar.
Abstract: With a high-temperature and high-pressure condensation autoclave simulating the circumstance of CO2 corrosion in wet gas pipelines,the variation in corrosion behavior and morphology of X70 pipeline steel was studied by changing the wet gas temperature and the temperature difference between the wet gas and the pipe wall.Scanning electron microscopy(SEM) and energy dispersive spectrometry(EDS) were employed to analyze the morphologies and characteristics of corrosion scales on the steel.The results were compared with those under solution-immersed conditions in a high-temperature and high-pressure autoclave.Using a corrosion prediction model,the influence of some important parameters on corrosion at the top of wet gas pipelines were preliminary studied,such as wet gas and pipe wall temperatures,temperature difference,condensed liquid film temperature and condensation rate.The results show that at the same temperature of the pipe wall(5℃),the corrosion rate increases with the wet gas temperature rising;while at the same temperature of wet gas(25℃ and 45℃),the corrosion rate decreases slightly with the pipe wall temperature rising.In the temperature range of 20 to 45℃,corrosion scales are easily peeled off from the substrate,and uniform corrosion is the predominant morphology.
Abstract: Fe-40Cr-5Al alloy anodes were prepared by vacuum induction melting for aluminum electrolysis.The electrolysis corrosion behaviors of the alloy anodes at 800℃ and 900℃ were investigated.Aluminum electrolysis tests were conducted in a cryolite-alumina low-temperature electrolyte system,at an anodic current density of 0.5A·cm-2 for 10h.The results indicated that the corrosion rate of the alloy anodes reduced with decreasing electrolysis temperature.After electrolysis at 900℃,there was a porous corrosion layer on the anode surface,while a protective oxide scale formed after electrolysis at 800℃.The oxide scale was divided into two layers,in which the outer layer was a Fe(Al,Cr)2O4 spinel and the inner layer was a composite oxide consisting of Fe,Cr and O.The purity of the collected aluminium products after electrolysis at 800℃ was 98.552% and the corrosion rate of the alloy anodes was 5.51cm·a-1.
Abstract: The corrosion resistance of BFe10-1-1 alloy with continuous columnar-grained microstructure in a 3.5% NaCl solution was investigated by means of polarization tests and electrochemical impedance spectroscopy(EIS),and compared with that of BFe10-1-1 alloy with conventional polycrystalline microstructure fabricated by conventional casting.Polarization test results show that both BFe10-1-1 alloys have similar electrochemical behavior,and their polarization curves include three distinct regions,that is,the active dissolution region,the active-passive transition region and the limiting current region.However the corrosion rate of BFe10-1-1 alloy with continuous columnar-grained microstructure is lower than that of the one with conventional polycrystalline microstructure,as less microsegregation in BFe10-1-1 alloy with continuous columnar-grained microstructure can effectively avoid interdendritic corrosion.EIS spectra indicate that BFe10-1-1 alloy with continuous columnar-grained microstructure has a higher charge transfer resistance and a higher corrosion product film resistance compared with BFe10-1-1 alloy with conventional polycrystalline microstructure.The results further demonstrate that BFe10-1-1 alloy with continuous columnar-grained microstructure has a better corrosion resistance.
Abstract: The evolution of three different initial microstructures of GH864 alloy after heat treatment was studied by optical microscopy(OM) and field emission scanning electron microscopy(FESEM).The impact toughness at room temperature and crack propagation rate at 650℃ were analyzed after heat treatment.The results indicate that the grain microstructural evolution of GH864 alloy is hereditary between initial forging state and heat treatment state after 1020℃,4h/air cooling→845℃,4h/air cooling→760℃,16h/air cooling,while carbides in grain boundaries and γ' phases are not significantly different.The larger the grain size,the better crack propagation behavior the alloy has,and the worse the impact toughness is.It is highlighting that the necklace microstructure has a better effect to improve the impact toughness and crack propagation behavior of GH864 alloy.
Abstract: The fracture characteristics of precipitates in cast eutectic Al-Si alloys were studied during tensile processes by observing the fracture and precipitates.It is shown that the primary/eutectic Si cracks mainly through transcrystalline fracture owing to structural defects.Primary Si with a diameter size less than 2.0μm can block the propagation of secondary cracks.The blocky iron-rich phases crack through transcrystalline fracture,while cracks within the Chinese script iron-rich phases propagate along their primary dendrites.The copper-rich phases deflect the crack propagation and inhibit the nucleation of microcracks within the iron-rich phases.Increasing the Cu content neutralizes the harmful effects of the iron-rich phases to some extent and is of benefit to the mechanical properties.
Abstract: Some factors influencing silicon productivity were studied for producing polycrystalline silicon by zinc reduction.When the reaction reached equilibrium,the relation between gas phase compositions and temperature was analyzed at the Zn/SiCl4 molar ratio of 2,4 and 8 under the pressure of 0.1,0.3 and 0.6MPa,respectively.The changes of silicon productivity with gas pressure,temperature and Zn/SiCl4 molar ratio were discussed.The results show that lower temperatures,suitable pressures and higher Zn/SiCl4 molar ratios have a positive effect on the zinc reduction process.The major side-reactions which affect the silicon productivity were then determined.Finally the optimum operating conditions for the zinc reduction process were presented as 1200K,0.2MPa and the Zn/SiCl4 molar ratio of 4.Under the optimum operating conditions,the theoretical silicon productivity can be 90.3%.
Abstract: The crystallization behavior of mineral wool was investigated by means of differential thermal analysis(DTA) and X-ray diffraction(XRD).DTA curves reveal the presence of two overlap exothermic peaks and XRD results shows that two crystalline phases are separated out:one is akermanite-gehlenite(AlCa2Mg0.5O7Si1.5),which was crystallized between 850℃ and 920℃;the other is anorthite(CaAl2Si2O8),which was crystallized between 880℃ and 1010℃.The Ozawa method and the modified Kissinger method were used to analyze the crystallization mechanism and the activation energy of crystallization.For the crystalline of akermanite-gehlenite,the activation energy of crystallization and the Avrami exponent are 248kJ·mol-1 and 0.682 respectively,indicating surface crystallization;whereas for anorthite,the activation energy of crystallization is 347kJ·mol-1,revealing three-dimensionality of crystal growth according to the results of scanning electron microscopy(SEM).
Abstract: The sealing properties and structure of Bi2O3-BaO-SiO2-RxOy(Bi-Ba-Si-O) glass were studied for fabricating solid oxide fuel cells(SOFC).The density functional theories(DFT) were employed for the structure optimization of Bi2O3 into SiO2 glass networks,and was theoretically determined to be the most possible structure of bismuth as interconnections in the Bi-Ba-Si-O glass.The functions and possible existence structures of Ba2+ and Al3+ were also discussed.According to experimental investigations,the coefficient of thermal expansion(CTE) of the Bi-Ba-Si-O glass is 11×10-6K-1(50 to 530℃) which can be matched with the YSZ electrolyte(CTE:10.2×10-6K-1) and the SUS430 steel metallic interconnect(CTE:11.3×10-6K-1).Data form XRD analysis show that the Bi-Ba-Si-O glass is amorphous and consistent with the theoretical analysis.When the Bi-Ba-Si-O glass is used as sealing materials for SOFC,the glass,the SUS430 metallic interconnect and the YSZ electrolyte adhere well with good air-tightness.It is concluded that the Bi-Ba-Si-O glass can meet the requirements of SOFC sealing materials.
Abstract: Radio-frequency(RF) plasma reactors are well suitable to high-rate generation of high pure nanoparticles in vapor synthesis methods.In the synthesis system of TiO2 nanoparticles with little gas flow which concludes titanium tetrachloride and oxygen,the temperature distribution was computed by solving a second-order partial differential equation by the finite difference method in Matlab.By coupling the temperature distribution with kinetic equations of particle growth,the final average size and the size distribution of TiO2 nanoparticles were obtained by calculating along each gas streamline.The simulation results computed at different input concentrations agree with experimental data,on the whole.As the assumptions of the gas flow and concentration distribution in the system are sample and without considering the effect of mass transportation on the final particle size in the growth process,the proposed model deserves to be further improved.
Abstract: The forming process of valve roughcasts by single cross wedge rolling was simulated with finite element software DEFORM-3D 6.0,focusing on the stress and strain fields and alternating times of rolled pieces at the center point under different stretching angles.Rolling experiments at different stretching angles were done on an H500 rolling mill,and the area of the centre hole was calculated for each rolled piece.The influence of stretching angle on internal defects in rolled pieces was analyzed on the basis of simulation and experimental results.It is shown that a relatively larger stretching angle can improve the internal defects.Experimental results show that the area of the centre hole decreases with the stretching angle increasing.The stretching angle of 8°40' is propitious to improve internal defects in valve roughcasts produced single cross wedge rolling when the other parameters are invariable.
Abstract: Combining the theory of wedge cross rolling(WCR) with forming gears by rolling,a method was proposed to form teeth simultaneously when rolling gear shafts.The method can not only realize the near net forming of gear shafts,but also improve the mechanical properties and service life of teeth.In the process of forming teeth by rolling,the feed was not continuous but intermittent,and workpieces were compelled to roll in free graduation under the rotation of dies.The calculation method and change law of die tooth pitch,the design of die tooth forms,the calculation method of the minimum feed at the first half circle and the law of feed change in each stage of rolling were presented on the basis of mathematical models and experiments.The rolling process was simulated by numerical software Deform-3D,with which the dies can be correctly designed.A toothed shaft with the module of the gear m=2,the number of teeth z=20 and the pressure angle a'=20° has been successfully formed with the H630 rolling tool.It is proved that forming teeth on gear shafts by wedge cross rolling is feasible.
Abstract: For the bottleneck of improving the accuracy of minority class samples within the paradigm of imbalanced datasets,a novel under-sampling method based on the cooperative co-evolutionary mechanism was presented in this paper.During the employment of the method,the majority and the minority samples were divided into two populations,which adopted the cooperative co-evolutionary mechanism,dynamically adaptive crossovers and mutation operators to automatically adjust the evolution process within populations.Simulation results prove that the method enhances the capacity of local search,improves the distribution characteristics of populations and strengthens the capacity of global convergence.Moreover,the method notably improves the accuracy of the minority samples without degrading that of the majority ones.Compared to other classical resampling methods,the method shows good noise immunity with more powerful robustness.
Abstract: With slag,fly ash,desulfurized gypsum,lime and aluminium sulphate as soil stabilizers,the compressive strength of consolidated soil first increased and then decreased with the amount of added NaCl increasing.The compressive strength of consolidated soil in every curing age reached its maximum value when the content of added NaCl was 2%.The consolidation rates of Na+ and Cl- increased very fast when the curing age prolonged from 3d to 7d,then slowed down from 7d to 28d,and finally kept stable in the range of 60% to 80% after 28d.The results of nuclear magnetic resonance(NMR) of 29Si and 27Al showed that there were amounts of 4-coordinated and 6-coordinated Al in the C-S-H net.The NMR analysis also indicated that in the C-S-H net some of Si4+ was substituted by Al3+.The substitution provided a condition for Na+ solidification.NaCl can promote the transformation of Al coordination from 4-coordinated one to 6-coordinated one,and improve the polymerization degree of the cementitious system.
Abstract: A calculation method of horizontal displacement was studied for the dual structure consisting of flexural-shear substructures and flexural substructures.The flexural substructures are regarded as flexural cantilever walls which exhibit a predominantly flexural behavior,and the flexural-shear substructures are regarded as Timoshenko cantilever walls which exhibit a mixed flexural/shear behavior.On the basis of the above assumptions,a differential equation was established for calculating the displacement of the dual structure.With boundary conditions,the analytical solutions of the displacement,including the flexural deformation,the shear deformation and the total horizontal displacement,were derived when the dual structure was subjected to uniform loads.The relation between the dual structure consisting of flexural-shear substructures flexural substructures and that consisting of shear substructures flexural substructures was discussed,and the result shows that the later can be viewed as a special form of the former where the flexural stiffness of the flexural-shear substructures tends to infinity.
Abstract: Initial imperfections in actual plate structures have impact on the structural stability and safety.Considering actual steel structures as a research background,with emphasis on the effect of initial imperfections,the nonlinear stability of stiffened plates was analyzed under the condition of different initial imperfection sizes,stiffener types,loading ways and boundaries.As for a simply supported plate,the thinner the plate,the more remarkable the influence of initial imperfections is.Considering the same initial imperfections,the nonlinear buckling value of flat steel is the largest.The influence of initial imperfections on the nonlinear stability of plates is large under uniaxial loading.Initial imperfections impact on a simply supported plate or a consolidated plate stable.
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
