Abstract: To study the anisotropy of gas seepage in coal seams with low permeability,coal samples were prepared respectively in the parallel bedding direction and the vertical stratification direction of the same coal rock. Tri-axial servo seepage tests on gascontained coal were detected by using a self-developed apparatus. It is found that the permeability of coal samples in the parallel is far greater than that of coal samples in the vertical. With the increase of axial pressure,the permeability of coal samples in the parallel reaches its minimum at the yield point before the peak failure,while the permeability of coal samples in the vertical gets its minimum at the initial period of the elastic stage. The permeability of both the parallel and the vertical nonlinearly increases after the peak failure.
Abstract: In order to research the impact of carbonate ions on water-rich filling materials,strength testing,scanning electron microscopy,X-ray diffraction analysis and IR spectrum testing were used to analyze the macro- and micro-structural change and the corrosion and deterioration mechanism of the materials in sodium carbonate solutions. It is found that the compressive strength of the materials in a sodium carbonate solution whose mass fraction is 10% decreases significantly with increasing soaking time. When the soak age is 90 d,the compressive strength of the materials decreases by 72.5% compared with standard curing for 28 d. After soaking for 28 d the specimen surface is muddy. XRD patterns show that after soaking in a sodium carbonate solution whose mass fraction is 10%,thaumasite generates in the materials. With increasing soaking time the amount of thaumasite increases. Infrared spectroscopy results show that there does not exist[AlO6]. This confirms that ettringite in the materials soaking in the sodium carbonate solution drastically reduces and transforms into pulpy thaumasite. As non-cemented materials,thaumasite will cause serious damage to the hardening body of the materials. This shows that the carbonate solution has corrosive action on water-rich filling materials.
Abstract: For the characteristics of weak ballability and inferior amenability of specularite concentrates, the granulating and sintering performances of imported specularite were investigated by two kinds of separated pre-agglomeration-sintering processes. Compared with the traditional granulation-sintering process, the separated micropelletizing-granulation-sintering process presents competitive results:decreasing the coke level from 4.85% to 4.20%, improving the productivity from 1.44 t·m-2·h-1 to 1.71 t·m-2·h-1, enhancing the tumble index from 57.60% to 63.80%, and cutting the solid fuel rate from 76.46 kg·t-1 to 65.24 kg·t-1. In the meantime, the separated pre-briquetting-granulation-sintering process also shows better results:decreasing the coke dosage from 4.85% to 4.70%, elevating the productivity from 1.44 t·m-2·h-1 to 1.64 t·m-2·h-1, and keeping the tumble index and the solid fuel rate steady. Overall, the separated pre-agglomeration-granulation-sintering process can significantly improve the sintering performance of specularite. The mechanism of action is that the separated pre-agglomeration-granulation-sintering process improves the permeability of the mixture markedly, decreases the coke dosage appropriately, results in a higher oxidation potential in the sintering bed, and produces more calcium ferrite and hematite finally. Meanwhile, mineral crystals in the product sinter grow perfectly and compactly, and the pores mainly develop into middle or small sized spheres from the irregular big ones, all of which contribute to the higher strength and better reducibility of the product sinter.
Abstract: Differential scanning calorimetric(DSC) data during non-free water removal in nickel laterite were determined with a NETZSCH STA 449 C thermal analyzer. Experiments were carried out at four heating rates of 10,15,20 and 25℃·min-1. According to these DSC curves at different heating rates,the activation energies were calculated by five different calculation methods of conversion rate,namely the Flynn-Wall-Ozawa(FWO),Hu-Gao-Zhang(Hu GZ),Boswell,Starink,and Friedman-Reich-Levi(Friedman)methods. The pre-exponential factor(A) and the most probable mechanism function were determined by the Malek method,then the relationship between reaction degree and time under an isothermal condition was derived and the energy consumptions at different temperatures were analyzed and compared. The average activation energy of non-free water removal in nickel laterite is 181.50 k J·mol-1. The average lnA is 21.95 min-1. The most probable mechanism function fits the Zhuralev-Lesokin-Tempelman(Z-L-T)equation well. The non-free water removal is controlled by three-dimensional diffusion. The average power decreases with increasing temperature.
Abstract: In view of serious environmental pollution in the traditional roasting-cyanide leaching process,a roasting and selfleaching process was adopted to treat gold-bearing sulfides. The transformation rate of elemental sulfur and the gold leaching rate were tested at different roasting temperatures,roasting times and sample masses. The phase transformation of sulfur in the sulfides was analyzed by X-ray diffraction analysis,scanning electron microscopy and energy dispersive spectrometry. It is found that pyrite in the sulfides transforms to elemental sulfur and pyrrhotite because of a thermal decomposition reaction. Along with the increasing of roasting temperature and roasting time,the characteristic diffraction peaks of pyrite gradually weaken and finally disappear. Meanwhile,the characteristic diffraction peaks of pyrrhotite generate and heighten. The initial dense pyrite particles become porous. Under the conditions of the roasting temperature of 800℃,roasting time of 60 min,nitrogen flow of 1 L·min-1 and sample mass of 50 g,the transformation rate of elemental sulfur and the gold leaching rate reach 42.53% and 88.7%,respectively. Gold from the sulfides is effectively extracted by this non-cyanide leaching.
Abstract: The solidification process of NH4Cl-70% H2O ingots was simulated and experimentally investigated based on the solidification theory and a volume-averaged multiphase solidification method. Although the solidification process of NH4Cl-70% H2O ingots has been investigated previously,but these researches are mainly focused on the single phenomenon of the process such as the formation of channel segregation,convection or the formation of grains. On the basis of fore-researches,combining numerical simulation with experiment,nearly all the phenomena occurring in the solidification process of the ingot were investigated in this paper,especially the equiaxed crystals' floating and settling down on the bottom of the ingot,and the convection induced by such floating of equiaxed crystals which was reproduced by the simulation. Finally,the mechanism of the forming of macro-segregation was deeply discussed.The calculation showed that equiaxed grains floated down from the mold wall and tended to settle down on the bottom of the ingot.When the volume fraction of equiaxed grains accumulated up to a critical value,columnar grains would stop their growth,and so the columnar-to-equiaxed transition(CET) process was to the end. Owing to solute partitioning and the sedimentation of equiaxed grains,there was negative macro-segregation in triangle shape on the bottom of the ingot,while a wide range of positive macro-segregation was constructed on the upper part of the ingot. The calculated results are relatively conformed to the experimental ones in aspects of the sedimentation of equiaxed grains and the induced fluid convection,indicating that the key factors leading to macro-segregation are crystal sedimentation and fluid convection.
Abstract: The high-temperature mechanical properties of Al-TRIP steel with 0.16% C,1.49% Mn and 1.35% Al,which is applied to automobiles,were investigated by using a Gleeble 3500 machine. The phase transition temperature interval was measured by differential scanning calorimetry(DSC). The fractographs and microstructures near the tensile fracture of the steel at different tensile temperatures were analyzed by means of a scanning electron microscope and an optical microscope. The zero ductility temperature(ZDT) and the zero strength temperature(ZST) of the steel were measured to be 1425℃ and 1430℃,respectively. The brittleness temperature interval Ⅰ is from 1400℃ to the melting point,and the brittleness temperature interval Ⅲ is from 800℃ to 925℃.Ferrite precipitation from austenite grain boundaries is the main cause of the presence of the brittleness temperature interval Ⅲ. With specimens cooling from 975℃ to 700℃,the proportion of ferrite increases continuously,while the reduction of area(ψ) decreases firstly and then increases. When the proportion of ferrite reaches to 8.1%(at 850℃),the value of ψ decreases to 28.9%; but when being stretched at 800℃,the proportion of ferrite is greater than 16.7%,and the value of ψ is more than 38.5%. A small number of Al N particles precipitate in the steel at 1275.6℃. These Al N particles are coarse,but they have no influence on the ductility of the steel.
Abstract: The effects of deformation degree and thermal aging on the tensile properties,phase boundaries,local strain distribution,coincidence site lattice(CSL) boundaries and orientation distribution of duplex stainless steels were investigated by electron backscattered diffraction(EBSD). It is found that after thermal aging,the strength of duplex stainless steels enhances and the ductility decreases. The number and density of small-angle boundaries in ferrite grains increase slightly under large deformation conditions.The plastic deformation ability and local strain in ferrite phases of the thermal aged materials decline. Large deformation destroys the original distribution of austenite and ferrite grains,as well as Σ3 twinning boundaries.
Abstract: The initial corrosion behavior of the acrylic polyurethane coating/carbon steel interface in a 3.5% NaCl solution was in-situ investigated by electronic speckle pattern interferometry(ESPI),electrochemical impedance spectroscopy(EIS) and scanning electrochemical microscopy(SECM). The effect of nano-TiO2 on the interfacial behavior was examined. At the beginning stage without macroscopic defects,a tiny change at the interface was successfully detected by ESPI. EIS results could reflect the change of low frequency impendence moduli,which were agreed with the electrochemical morphology obtained by SECM. In other words,the interfacial changing velocity(corrosion initiation rate) of the coating without nano-TiO2 is faster than that of the coating with nano-TiO2,indicating that the addition of nano-TiO2 slows down the corrosion of the acrylic-based polyurethane/carbon steel interface.
Abstract: According to the principles of simultaneous equilibria and mass equilibria, CuInSe2 (CIS) were prepared by total aqueous process at normal pressure and room temperature. A series of thermodynamic equilibrium equations were deduced for the complex system of Cu+-In3+-Se2--NH3-L2--Cl--H2O (T=298 K), and the equilibrium curves of lgc-pH were drawn. It was found from these equilibrium diagrams that[NH3]T primarily affected the[Cu+]T concentration,[L2-]T influenced the[In3+]T concentration, and[Cl-]T had impact on both. The highest precipitation coefficient was obtained at pH 7.0-8.5. As a result, based on the principles of simultaneous equilibria and mass equilibria of the Cu+-In3+-Se2--NH3-L2--Cl--H2O system (T=298 K) and used total aqueous process at normal pressure and room temperature, CIS nanoparticles can be synthesized by adjusting the pH value to 7.0-8.5, and their size is about 20 to 50 nm.
Abstract: Silicon/carbon composites as anode materials for lithium batteries with high power capacity were synthesized by a high temperature pyrolysis method. The performances of the silicon/carbon composites were investigated by X-ray diffraction,thermogravimetric analysis,scanning electron microscopy,transmission electron microscopy,galvanostatic cell cycling,and cyclic voltammetry. It is found that the silicon/carbon composites consist of silicon,carbon and few silicon dioxide phases,and the carbon content is about 39%. Electrochemical cycling tests of button cells show that the specific capacity is far more than that of carbon materials. The initial charge capacity of the silicon/carbon composites is 768 m Ah·g-1 at a current of 0.2 m A and the initial coulombic efficiency is 75.6%.After 70 cycles the reversible specific capacity is 529.0 m Ah·g-1 and the average capacity deterioration rate of each cycle is 0.44%.These improvements can be attributed to the introduction of carbon in the Si/C composites and carbon coatings on the Si surface,which provide a rapid lithium transport pathway,reduce the cell impedance and stabilize the electrode structure during charge/discharge cycles.
Abstract: Using a sol-gel prepared TiO2-ZrO2 carrier,Cr-MnOx/TiO2-ZrO2composite catalysts were synthesized by a critic acid solution impregnation method. The physical and chemical properties of the catalysts were characterized by X-ray diffraction,specific surface area determination(BET),scanning electron microscopy and X-ray photoelectron spectroscopy. Meanwhile,the lowtemperature catalytic activity and the sulfur and water resistance were evaluated with selective catalytic reduction(SCR) of NO by NH3. The introduction of Cr element to MnOxyields a new CrMn1.5O4 active phase,in which Mn primarily exists as Mn3+ and Mn4+.The Cr5+ valence state facilitates the transformation of Mn3+ to high oxidation state Mn4+,which is beneficial to the low temperature SCR reaction. Because of lower first ionization energy and electronegativity,Cr preferentially reacts with SO42- and SO32- than Mn,thus protecting MnOx not to be sulphatized and resulting in the enhanced antitoxic performance of Cr-MnOx/TiO2-ZrO2. Among the prepared five catalysts with different molar ratios of Cr/(Cr + Mn),Cr(0.4)-MnOx/TiO2-ZrO2 demonstrates the best performance owing to the largest surface area and the best particle dispersion,and a 95.8% denitrification efficiency can be achieved at 180℃.When 5% H2O and 10-4 SO2 are simultaneously added,the denitrification efficiency decreases slowly and stabilizes at 73% after 8h reaction.
Abstract: BiVO4/TiO2-graphene(BiVO4/TiO2-GR) photocatalysts were prepared by a facile solvothermal method. The composite photocatalysts were characterized by X-ray diffraction,transmission electron microscopy,UV-Vis diffuse reflectance spectrometry,and photoluminescence spectrometry. The photocatalytic activity was evaluated by degradation of methylene blue(MB)under simulated sunlight irradiation. It is found that the composite photocatalysts have a strong absorption peak in the 530-800 nm range of visible light. The introduction of graphene not only enlarges the absorption range of visible light,but also makes BiVO4 and TiO2 particles disperse uniformly in graphene sheets,and can capture and transfer the photogenerated charges,leading to an efficient improvement in photocatalytic activity.
Abstract: A mesoporous silica substrate consists of uniformly distributed and unconnected spherical pores. Since the pore diameter is less than the characteristic wavelength of thermal radiation,near-field radiative heat transfer cannot be ignored. In this paper,near-field radiation across a spherical pore in mesoporous silica was simulated by employing the fluctuation dissipation theorem and the Green function. The calculated equivalent thermal conductivity of radiation was further developed to modify the thermal conductivity of mesoporous silica. The combined thermal conductivity of mesoporous silica was obtained by using the porosity weighted dilute medium(PWDM) model to combine the equivalent thermal conductivity of radiation across the pore,the thermal conductivity of confined air in the pore and the thermal conductivity of the silica substrate. Such factors as the pore diameter and the material temperature were further analyzed. Research results show that the radiative heat transfer at the mesoscale is 2-7 orders higher than that at the macroscale.The heat flux and equivalent thermal conductivity of radiation across a spherical pore decrease exponentially with increasing pore diameter,but increase with increasing temperature. The combined thermal conductivity of mesoporous silica decreases gradually with increasing pore diameter,while increases smoothly with increasing temperature. The smaller the pore diameter,the more significant the near-field effect,which cannot be ignored. When the pore diameter is greater than 50 nm,the size effect gradually disappeared.
Abstract: In a blast furnace raceway with many mediums,two-dimensional temperature radiant images are obtained with a CCD camera installed in the blowpipe peephole. After the blast furnace raceway is divided into many small pieces,the radiation heat transfer process in the blast furnace raceway is simulated and a matrix equation is established by using a mathematical model. Then the three-dimensional temperature field of the blast furnace raceway is derived from solving the equation. In simulating the radiation heat transfer process,a new method,which is more effective and accordant with actual production,is introduced that a distance-based Gaussian function model is used to simulate radiation energy propagation in the blast furnace raceway,and thus a better threedimensional temperature field is got by this method. Due to the existence of fluctuation error,CCD camera measurement error and so on,random error is added in the measurement data to demonstrate the effectiveness and stability of the reconstructed temperature field.The results show that the three-dimensional temperature field is very close to the actual temperature field,and the error is within 5%that is allowed in the blast furnace industry.
Abstract: A crystal plasticity model exhibiting deformation twinning is introduced based on the classical crystal plasticity theory,and its numerical implementation is conducted in which a fully implicit integration procedure is employed. In this constitutive model,the saturation-type hardening law is adopted and the direct proportion relationship between twin resistance and slip hardening is used to describe the effect of twinning on slip hardening and twin hardening. By considering the physical meaning of all the 13 parameters in this model,the classification methodology is presented for these parameters. Taking Fe-22Mn-0.6C twinning induced plasticity(TWIP) steel as an example,a local sensitivity analysis of hardening parameters is investigated emphatically. The effects of hardening parameters on the macro-mechanical response,the activation and evolution of twinning and the strategy for determining the hardening parameters are discussed. According to the difference of deformation mechanisms,the macroscopic deformation are divided into a twin hardening stage and a twin hardening failure stage. And then the determination method and the suggestive ranges for the hardening parameters are given. It is found that the initial slip resistance is linearly associated with the yield limit,and the value of initial resistance stress ranges from 80 MPa to 160 MPa. The twin hardening stage weakens when the twin hardening index increases,the range of values allowed for the twin hardening index is 0 to 3. When the ratio between twinning resistance and slip resistance increases,thegrowth rate of twinning decreases and the turning point of the hardening stage moves backward until it is disappeared. The range of values for the ratio between twinning resistance and slip resistance will be 1 to 1.3.
Abstract: In order to research the ridge-buckle control method in the coiling process of steel strips with local high points,elastoplastic stress and ridge-buckle models are established by using the theory of three-dimensional elastoplastic deformation and introducing a plastic flow factor. Then a stress distribution model of ridge-buckle strips and an online setting model of buckling critical coiling tension are derived from the hypothesis of stress functions,the S. Timoshenko principle of least work,and the theory of Galerkin virtual displacement. Simulation results show that the uneven distribution of strip tension and axial compressive stress caused by radial accumulation of local high points is the main cause of strip ridge-buckles. The ridge-buckle quantity increases when the local high point's height,coiling diameter and coiling tension increase; the ridge-buckle of a thin strip is more obvious than that of a thick one.The critical coiling tension decreases with the increase of strip thickness,the local high point's height and coiling radius.
Abstract: A coupled heat transfer model of work rolls and an aluminum strip is established to obtain the multi-parameter coupled subsection cooling regulation characteristics of work rolls in aluminum cold rolling. This coupled model includes building the thermal conduction differential equation of the work rolls and strip,solving the strip deformation heat and friction heat,establishing the heat transfer boundary conditions,calculating the work roll thermal crown,and solving the differential equations by using a two-dimensional alternating difference method. Simulation results show that the positive and negative adjustment domains are approximately equal at the same rolling parameters,but each domain is affected by rolling parameters. The increase of rolled length,header pressure and friction coefficient has positive effect on the subsection cooling control ability,while the rolling speed is on the contrary.
Abstract: A power allocation algorithm supporting delay constrains which maximizes the channel effective capacity of secondary users for satellite "Underlay"cognitive radio networks is proposed to improve the spectrum utilization of a satellite communication system. A power interference model is established based on the topology of satellite cognitive radio networks first,and then the object functions of effective capacity are derived both in perfect and imperfect channel state information environments. The Lagrange method is used to obtain the optimized transmitting power of secondary users by introducing the time-domain channel correlation coefficient.Optimized power adjusting strategies under different scenes are discussed while the power allocating and optimizing process is simplified. Factors which affect the effective capacity of secondary users are analyzed by simulation. The results indicate that the proposed power allocation algorithm can adjust the transmitting power of secondary users according to delay constrains with channel fading characteristics,and the channel effective capacity of secondary users is improved obviously compared to the traditional equal power allocation policy.
Abstract: A Chlamydomonas reinhardtii immobile mutant named ift81 was screened by insertional mutagenesis. The mutant was bald or with two short flagella. Gene sequencing confirmed that fifty-two base pairs in the fifth extron of IFT81 gene were replaced by the exogenous gene aphⅧ in the mutant. After a recombinant plasmid containing full IFT81 gene was imported into the mutant ift81,the phenotype of the mutant was rescued and the expression of IFT81-HA could be detected,which confirmed that the defect in IFT81 gene led to the abnormal flagella directly. Electron microscopy images exhibited the abnormal flagella of the mutant. An immunofluorescence assay revealed that IFT81 protein was localized to the basal body and flagella. This work shows that loss of protein IFT81 will directly lead to the defects of flagellar assembly,and IFT81 protein is indispensable for flagellar assembly in Chlamydomonas reinhardtii.
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
