Abstract: The influences of anionic polyacrylamide with low molecular weight(PAM A401) on coal and kaolinite were investigated by the flocs size distribution,FTIR spectra and wettability. Flotation kinetics tests were carried out to verify the effect of PAM A401. By using 12 mg·L-1 PAM A401 and conditioning for 11 min,at the cumulative particle size distributions of 10%,50% and 90%,the particle size of coal is 6.86,2.22 and 2.45 times that of kaolinite flocs,respectively,showing a better flocculation selectivity of coal. After PAM A401 adsorption,the peaks of hydrophilic functional groups of coal are strengthened and the coal particle surfaces become more hydrophilic. For kaolinite,both the hydrophilic and hydrophobic functional groups increase,and the kaolinite is slightly more hydrophobic. Compared with the conventional flotation,the flotation rate of selective flocculation flotation tests is higher,and 30% of collector is saved. The cumulative combustible recovery of selective flocculation flotation is 81.57%,which is 3.64% higher than the conventional flotation experiment,but the ash content of clean coal is similar. Although PAM A401 reduces the wettability of coal particle surfaces,the enlargement of apparent particle size of fine coal promotes efficient separation of fine coal.
Abstract: A dual-porosity medium with micro-fractured spherical matrix blocks was achieved on the basis of the structure characteristics of nano-micro pores and micro-fractures in shale gas reservoirs. The Laplace space solution of the dimensionless bottom hole pressure of fractured well production was obtained in consideration of the seepage,diffusion and desorption mechanism of shale gas and applying the Laplace transform and the Stehfest numerical inversion. Type curves of dimensionless production were plotted and the influencing factors of the type curves were identified. The results show that the matrix surface improves gas transfer from the matrix medium to the fracture network due to matrix micro fractures. Increasing the permeability and length of micro fractures accelerate the productivity significantly.
Abstract: This article aims at caving corner residual orebody by trench bottom structure in Xishimen Iron Mine. SURPAC software was used to calculate the ore volume,amount of metal and grade. A mathematical model of multi-objective optimization was established to maximize the amount of metal and grade. According to the special situation of corner residual orebody mining,the amount of metal was selected to be the main object. SURPAC software was developed to automatically calculate by using TCL script. With the help of the script software,all factors in the constraint were tested. The optimum position of trench bottom structure was obtained,which is on the 103.1 m level and 18.65 m to the orebody. Compared with the original design,the amount of metal is increased by 27.79% after this optimal design.
Abstract: To find the motion law and optimum size of floatation bubbles in a three-phase flow,the Eulerian model is used to simulate the motion process of bubbles with different initial diameters in pulps of different concentrations. The simulation results show that under the given initial condition,in the pulp with a certain concentration,bubbles of 4 mm catch the most mine grains; bubbles of any size above or below 4 mm cannot capture mine grains as many as those of 4 mm. When the pulp concentration is in the range of 20%-40%,the size of bubbles that capture the most mine grains does not change much. As the pulp concentration increases,the amount captured by a single bubble increases,so does the recovery rate of mine grains. In real production,bubbles of 3.5-4 mm have small deformation,moderate horizontal shift and lifting speed,and strong ability of capturing and carrying mine grains and lifting,which are benefit for improving the quality and quantity of floatation production.
The micropore structure and evolution of copper oxide ore particles before and after acid leaching were investigated by high resolution X-ray micro-computed tomography(micro-CT) and three-dimensional(3D) image analysis. The pore structure parameters,such as porosity,pore size distribution,pore connectivity and fractal dimension were statistically calculated. The results indicate that after acid leaching,the porosity increases obviously and the pore size distributes more widely. Some large pores appear and the mean pore diameter increases by 2 to 3 times. There is little pore connectivity before acid leaching,while the pore connectivity increases significantly after acid leaching,being inhomogeneous in three different directions. The fractal dimension of pores also increases after acid leaching,and the porosity and the mean pore diameter grows exponentially with the fractal dimension. 3-D image analysis is a powerful technique to quantitatively characterize the micro-scale pore structure of ore particles during acid leaching,so it facilitates to disclosure the evolution laws of pore structure.
Abstract: Continuous circulating smelting experiments based on multi-refining converter melting technology were performed to research the recycling of decarburized slag in the dephosphorization period. The results show that under the condition of low Fe O content,strong mixing,blowing for about 5 min and[C] ≥ 2.8% in the dephosphorization stage,the content of phosphorus in molten metal is less than 0.025%. With the continuous circulating smelting,the consumption of lime decreases from 65 kg·t-1 to 31 kg·t-1,the[P] content drops from 0.018% to 0.005%,and the smelting reaches equilibrium after 2-4 furnaces. During the smelting process,60-80 kg slag per ton steel is poured out at the end of the dephosphorization period,while 120-130 kg remaining slag per ton steel is poured out at the end of the loop. The average mass of slag is about 83 kg per ton steel,more less than 120 kg per ton steel in the ordinary process.
Abstract: Inclusions in the surface of low carbon aluminum killed steel slabs cast at high casting speed were analyzed by Aspex automated scanning electron microscopy in a large area. The changes in number and size of inclusions were tested at different casting speeds,and the influence of flow fields and sulfur content on the distribution of inclusions was explained in detail. It is found that when the casting speed increases,the depth and length of hooks decrease. Hooks in the slab subsurface is not obvious when the casting speed larger than 2 m·min-1,so inclusions larger than 200 μm cannot be found in the slab surface. Inclusions with the size of 50-200 μm in the slab surface are mainly entrapped by the solidified shell,and the entrapment of inclusions is influenced by forces acting on inclusions at the solidifying front. The flow velocity of molten steel increases due to increasing casting speed,then the washing force becomes large and the entrapping force becomes small,and therefore the number of entrapped inclusions decreases. If the sulfur content in the steel is high at high casting speed,inclusions will be easily entrapped by the solidified shell due to the thermal Marangoni force acting on inclusions obviously.
Abstract: The crack morphology and element segregation in continuous casting slabs were studied to solve the problem of internal cracks. The stress of the solidification front was analyzed by a finite element model at a series of reduction parameters and compared with the critical value. It is found that C,P and S enrich in dendrites and exist in grain boundaries,these are just the internal causes,but the true cause for internal cracks is the tensile stress of the solidification front. When the slab passes through the straightening segment,the reduction effect of rollers results in the stress of the solidification front exceeding the critical value,however,the corresponding stresses in the arc and horizontal segments do not exceed the critical value,so the solidification front in the straightening segment would be much easy to crack. Statistics analysis shows that when soft reduction and straightening are separately carried out,the occurrence rate of internal cracks reduces by about 41.3%.
The microstructure,martensite/austenite(M/A) islands,precipitated phases,high-angle grain boundaries and effective grain size of hot rolled and tempered low carbon bainitic steel AH80 DB were studied by scanning electron microscopy(SEM),transmission electron microscopy(TEM) and electron back-scattered diffraction(EBSD). The reason for the improvement in impact toughness of the low carbon bainitic steel after tempering was discovered. The results show that the microstructures of both the samples mainly consist of lath bainite,granular bainite and acicular ferrite. There is more acicular ferrite in the tempered steel. Coarse M/A islands are found in the hot rolled steel and its distribution is directional,the ratio of large-angle grain boundaries is 17.33%,and the average effective grain size is 3.57 μm. Nevertheless,the size of M/A islands decreases after tempering. Besides,the ratio of largeangle grain boundaries increases by 3.43% and the average effective grain size decreases by 0.56 μm after tempering. The precipitated phase of the hot rolled steel is(Nb,Ti) C with the size of 50-150 nm,while much small and spherical precipitates with the size of about 10 nm appear after tempering.
Abstract: The precipitation behavior of σ phases in W-containing S32760 super duplex stainless steel was studied by aging treatment experiments. The morphology and chemical composition of the σ phases were investigated by scanning electron microscopy and transmission electron microscopy. The effects of the σ phases on the mechanical properties and corrosion resistance of the stainless steel were analyzed additionally. The σ phases composed of Fe-Cr-Mo-W have a tetragonal structure and abundantly precipitate at 850-1000℃ in the stainless steel with quite high strength and hardness and extremely poor plasticity,for example,the elongation is lower than 4.0%. There are still a few of σ phases at 1050℃,though the elongation increases to 31.1%,the values of impact toughness are discrete,and the average impact energy is low. Until 1080℃,the σ phases completely dissolve to the matrix. The tensile strength and the elongation are 640 MPa and 35.5%,and the longitudinal and the transverse impact energies averagely reached to 217 J and 110 J,respectively. As the treatment temperature increasing,the pitting potential(Eb) improves,and the mass loss rate of pitting corrosion decreases. The pitting potential of the stainless steel treated at 1080℃ is up to 1246 m V,while the mass loss rate decreases only to 0.005-0.007 g·m-2·h-1 when being soaked in a 3.5% Na Cl solution at 50℃.
Abstract: The effect of grain refinement by TiN particles in the simulated coarse-grained heat-affected zone of a high-strength low-alloy steel was investigated by means of analytical characterization techniques such as in-situ microscopy and electron back scattered diffraction analysis. Abundant finely dispersed nanoscale TiN particles form in the specimen and effectively retard the grain boundary migration during simulated high heat input welding,which results in refined austenite grains. TiN precipitates on the surface of aluminum oxide,which is the effective nucleation site for acicular ferrite during the cooling process and induces the austenite transform to the fine-grained mixed microstructure of a small proportion of acicular ferrite embedded in predominantly bainite.
Abstract: The fracture toughness of a nearly lamellar Ti-45Al-8Nb-0.2W-0.2B-0.1Y alloy and a fully lamellar Ti-45Al-7Nb-0.2W-0.2Hf-0.3B-0.15 C alloy at 750℃ was investigated by prefabricating a fatigue crack in the compact tension(CT) specimen,and the corresponding fracture morphologies were observed by optical microscopy and scanning electron microscopy. It is found that the fracture toughness of the nearly lamellar high Nb-containing Ti Al alloy is 19.54 MPa·m1/2 at 750℃,obviously lower than the value of 31.58 MPa·m1/2 for the fully lamellar alloy. The maximum cyclic load at which the fatigue crack initiates in the nearly lamellar alloy is noticeably less than that in the fully lamellar alloy. Fracture images show that for the nearly lamellar alloy,cracks initiate mainly in equiaxed γ grains and propagate in different ways,intergranularly or transgranularly in γ grains or lamellar colonies. But for the fully lamellar alloy,cracks initiate mainly at lamellar interfaces perpendicular to the load direction and propagate in both interlamellar and translamellar ways,in accompanying with secondary crack initiation.
Abstract: The microstructure evolution of V-4Cr,V-4Ti and V-4Cr-4Ti alloys was studied before and after hydrogen implantation at 500℃. Before hydrogen implantation the matrix of V-4Cr alloy is clean,while parallel and vertical needle-like precipitates exist in the matrix of the other two alloys,and there are a lot of dislocations around the precipitates. After hydrogen implantation at 500℃ a large amount of uneven-distributed black dot defects and defect clusters appear in V-4Cr alloy. Besides the black dot defects,a lot of bubbles are found in V-4Ti and V-4Cr-4Ti alloys,and the average size of bubbles in V-4Cr-4Ti alloy is smaller than that in V-4Ti alloy. In addition,the dissolution phenomena of the precipitates happen in the both alloys. There are very few bubbles found near the grain boundary in the range of 25 nm in V-4Cr-4Ti alloy,which probably indicate that the defects,such as bubbles,caused by irradiation can be restrained by the existing of grain boundaries in this material.
Abstract: The effects of the reaction molar ratio of ammonium sulfate and the content of sodium chloride on the purity and yield of potassium sulfate were investigated in this article. The growth rate of single crystal potassium sulfate was in-situ observed with a stereo microscope in a flow system to find desirable conditions for the rapid growth of potassium sulfate crystals. The results indicate that the recovery of potassium sulfate is about 80% when the molar ratio of 2KCl to (NH4)2SO4 is 1:1. Na Cl has significant influence on the purity and recovery of potassium sulfate,and reduces the quality of the product. To accelerate the growth of potassium sulfate crystals,the saturation of potassium sulfate and the solution flow rate should be increased.
Abstract: Based on the GTN model,a modified GTN model applicable to compressive stress conditions was established by considering the effect of microvoid shear deformation on the loss of load-carrying capacity. The elastic-plastic constitutive model with the damage model was implemented in finite element software Abaqus/Explicit with ALE description through user subroutine VUMAT.Parameter values of the modified GTN model in simulation were determined by fitting the load-displacement curve in tensile and pure shear tests. Then,the modified GTN model was employed in finite element simulation of rotary blanking processes to predict the sheared edge quality and the simulation results were experimentally verified. The results show that for the leading cutting edge where the clearance is small,the roll-over depth is small and the burnish depth tilting at an angle is large. For the tailing cutting edge where the clearance is large,the roll-over and fracture depths are large and the burnish depth is small. Microcracks will simultaneously initiate near the flanks of the punch and die for the leading cutting edge,while for the tailing cutting edge they will occur firstly near the flank of the die.
Abstract: In order to reveal the formation mechanism of the manifested waves of cold rolled strips,the distributed dislocation was calculated by using measured residual stress,and a distributed dislocation-residual stress model was proposed. The stress field of an elastic plane with a typically distributed dislocation in the straight boundary was analyzed using the complex variable function method of plane elasticity,and the interaction was studied between the stress fields due to several straight lines with the distributed dislocation.In combination with measured data,the actual distributed dislocation which corresponds to a small relative error of residual stress was calculated in a general way. The form of the deflection function was shown by analyzing the distributed dislocation,which coincides with the actual buckling mode.
Abstract: To shorten the residence time of the H2/O2 interface and restrict the start-up voltage of the stack during the start-up process of a proton exchange membrane fuel cell(PEMFC),the effect differences of direct start-up,hydrogen purging time and auxiliary load current on the performance of PEMFC were studied by experiment. A fuel system start-up control strategy was proposed which combines hydrogen-purging the anode with starting the auxiliary load current. Experimental results prove that the start-up control strategy limits the start-up voltage of the fuel cell,shortens the residence time of the H2/O2 interface during the start-up process of the stack,and is conducive to improve the single-battery voltage balance. So it is a kind of effective PEMFC start-up control strategy.
Abstract: From the viewpoint of the attribute measurement of rough sets,a new attribute measurement based on the hybrid metric mechanism was provided to accurately evaluate the significance of attributes. This proposed attribute measurement analyzes the significance of attributes from different levels of information granularity. In addition,a parameter weighting factor was introduced to the attribute measurement according to the characteristics of data distribution. On this basis,an ensemble classifier was constructed based on the proposed attribute measurement mechanism in rough sets. Experimental results and comparative analysis show that the proposed method can effectively reduce the attribute dimension of data. Compared with the single attribute measurement,the proposed method has a better classification performance.
Abstract: In order to study the ability of lees to adsorb heavy metals,this article was focused on the effects of wastewater p H values,Pb2+ and Zn2+ mass concentrations,and adsorption time on the adsorption quantity of Pb2+ and Zn2+ from simulated acid mine drainage using lees. Test results show that the maximum removal rate appears when the p H value is 4. The adsorption of Pb2+ by lees accords with the Langmuir equation,but the adsorption of Zn2+ is followed by the Freundlich equation. Under the optimal conditions,the maximum adsorption capacity of Pb2+ and Zn2+ by lees is 8.29 mg·g-1 and 15.31 mg·g-1,respectively. The adsorption process reaches equilibrium after 4 h,in agreement with the second-order kinetics model. The contents of cellulose,hemicelluloses and lignine in the lees is 23.3%,65.5% and 0.5%,while become 19.6%,42.3% and 2.6% after adsorption of Pb2+ and Zn2+,respectively. The electro-negativity of lees increases while the p H value raises,and it reduces after adsorption of Pb2+ and Zn2+. Fourier transform infrared spectra indicate that the main functional groups are amide and ester reacting in the adsorption process.
Abstract: A kind of novel modified organobentonite composite owning good adsorption effect and high recovery efficiency was made to improve the adsorption property of organobentonite. Graphene was chosen to modify organobentonite. The modifying process was conducted by microwave irradiation. The structure and adsorption properties of the adsorption material were studied and the mechanism of action was discussed. Organobentonite and the modified organobentonite were used to adsorb humic acid from water after being characterized by scanning electron microscopy,Fourier transform infrared spectrometry and X-ray diffraction analysis. It is found that graphene and organobentonite composite uniformly and the basal spacing increases from 1.37 to 2.68 nm. The humic acid removal rate reaches 95.52% under the conditions of the temperature of 25℃,the p H value of 6,the composite dosage of 5 g·L-1and the adsorption time of 1 h. The adsorption data fits well the Langmuir isotherm model and the pseudo-second-order model,the maximum theoretical adsorption capacity of the composite is 52.08 mg·g-1,and the adsorption is an exothermic process. The graphene modified organobentonite can be regenerated with Na OH,and the regeneration efficiency reaches 86% after the fifth regeneration when the Na OH concentration is 0.1 mol·L-1.
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
