查看更多>>摘要：Accumulative roll bonding(ARB)is a severe plastic deformation method to prepare the metallic composite material by physical method at room to elevate temperature,without the generation of additional waste solid or gas.With the physical characteristicsmulti-material and hybrid structure,the mechanical and function properties of the ARB composite material,like Al/steel,Al/Mg,Al/Cu,etc.,shall have the"1+1＞2"effect on the mechanical and functional properties,including the remarkable properties that include lightweight,high strength,thermal/electrical conductivity,electromagnetic shielding,and other functions.To deeply investigate the preparation method and microstructural evolution of various metal laminates by ARB,as well as the mechanical and functional properties of the laminate,an overview of the history of ARB technique,the breakthrough of ARB sheet properties,as well as the relative products in industries is provided.Addi-tionally,the future development of ARB technology and the utilization of composite materials in different areas will be discussed.
查看更多>>摘要：Utilizing ultrafine iron ore concentrate for pellet production can expand domestic iron ore resources in China and promote the utilization of low-grade ores.However,a challenge arises with the low decrepitation temperature and reducibility in the preparation process of ultrafine iron ore concentrate pellets.To address the challenge,a novel approach was proposed,which incorporated straw powder as an additive to enhance pellet porosity,thereby improving the decrepitation temper-ature and reducibility of ultrafine iron ore concentrate pellets.The effect of varying proportions of straw powder(0.0-2.0％)on the characteristics of ultrafine iron ore concentrate pellets was examined.Results indicate that at a 2.0％straw powder ratio,pellet decrepitation temperature notably rises from 380 to 540 ℃,while the reducibility index escalates from 25.7％to 48.1％.Nevertheless,the addition of straw powder results in diminished drop strength,compressive strength of green pellets,and cold crushing strength of fired pellets.In addition,enhanced pellet reducibility leads to exacerbated reduction swelling index and reduction degradation index.Despite these effects,all parameters remain within an acceptable range.
查看更多>>摘要：The thick layer and graded feeding technology of a belt roasting machine is an effective method for improving the production efficiency and quality index of pellet production,and a reasonable design of the mechanical structure of the layer is the basis for optimizing the heat and mass transfer performance of the layer.Janssen effect and von Mises yield criterion were used to establish a simplified mathematical model describing the elastic and plastic deformation of the green pellet under the action of an external force.The mechanical characteristics of extrusion,contact,and elastic-plastic deformation between green pellet particles in the material layer of the belt roasting machine were modeled using EDEM software.For a green pellet size of 12 mm,as the layer height increases from 300 to 1000 mm,the maximum vertical pressure on the pellets increases from 11.64 to 24.01 N,and the porosity decreases from 27.04％to 22.01％.As the layer height increases,the contact between the green pellets becomes more intense,and the force chain structure of the layer becomes more stable;the Janssen effect is observed when the layer reaches 700 mm.The compressive strength of the green pellets is linearly related to the particle size,and the compressive strength increases with an increase in particle size.At a layer height of 600 mm,as the particle size of the green pellets increases from 8 to 20 mm,the maximum vertical pressure increases from 7.54 to 44.16 N,and the porosity increases from 23.20％to 31.47％,while the yield per unit of the layer decreased by 12.1％.Small particles have a more stable force chain structure,larger comparative area,and higher production efficiency;however,their compressive strength is lower.Large particles have higher compressive strength and good permeability in the layer,but the production efficiency is relatively low.In actual production,a variety of factors should be integrated to optimize the feeding,and a multi-granularity graded feeding is the most ideal feeding.
查看更多>>摘要：Ultrafine iron powder is widely used due to its excellent performance.Hydrogen reduction of fine-grained high-purity iron concentrate to prepare ultrafine iron powder has the advantages of low energy consumption,pollution-free,and low cost.The hydrogen reduction of high-purity iron concentrates,characterized by the maximum particle size of 6.43 pm when the cumulative distribution is 50％and the maximum particle size of 11.85 pm when the cumulative distribution is 90％while the total iron content of 72.10％,was performed.The hydrogen reduction could be completed at 425 ℃,and the purity of ultrafine iron powders was more than 99 wt.％in the range of 425-650 ℃.Subsequently,the effect of reduction tem-perature on various properties of ultrafine iron powder was investigated,including particle morphology,particle size,specific surface area,lattice parameters,bulk density,and reaction activity.It was found that the reaction activity of the iron powders prepared by hydrogen reduction was much higher than that of the products of carbonyl and liquid phase synthesis.Below 500 ℃,the reduced iron powders were nearly unbound,with a small particle size and a low bulk density.The particles had a porous surface,with a specific surface area as high as 11.31 m2 g-1.The crystallization of reduced iron powders was imperfect at this time,the amorphization degree was prominent,and the interior contained a high mechanical storage energy,which had shown high reaction reactivity.It was suitable for catalysts,metal fuels,and other functionalized applications.
查看更多>>摘要：The municipal solid waste incineration fly ash(MSWI-FA)contains a large amount of heavy metals,and the process of iron ore sintering and treating fly ash needs to pay attention to the migration characteristics of heavy metals.The impact of the application of MSWI-FA in the sintering process on the emission law of heavy metals in the collaborative treatment process was studied,and corresponding control technologies were proposed.The results showed that the direct addition of water washing fly ash(WM-FA)powder resulted in varying degrees of increase in heavy metal elements in the sinter.As the amount of WM-FA added increases,the content of heavy metal elements correspondingly increases,and an appropriate amount of WM-FA added is 0.5％-1.0％.The migration mechanism of heavy metals during the sintering treatment of WM-FA was clarified.Heavy metals are mainly removed through direct and indirect chlorination reactions,and Cu and Cr can react with SiO2 and Fe2O3 in the sintered material to solidify in the sinter.Corresponding control techniques have been proposed to reduce the heavy metal elements in WM-FA through the pre-treatment of WM-FA.When the WM-FA was fed in the middle and lower layers of the sintered material,the high temperature of the lower layer was utilized to promote the removal of heavy metals.The Ni element content has decreased from 130 to 90 mg kg-1,and the Cd removal rate has increased by 23％.The removal rates of Cd and Cr elements increase by 2.4 and 5.5 times,respectively.There is no significant change in sintering indexes.
查看更多>>摘要：The sulphate is an important factor restricting the efficient and stable operation of the activated coke(AC)flue gas purification system.The simulation experiments and in situ infrared tests of AC taken from desorption tower of the AC flue gas purification system were carried out to first calibrate the thermal desorption characteristics of adsorbed NH3 and sulphate and explore the reaction behaviour of NH3 with SO2 and H2SO4.On this basis,some advice for optimising the sulphate generation was put forward to improve the purification efficiency of the AC system.The results show that the temperatures of the desorption of adsorbed NH3,the decomposition of(NH4)2SO4 and NH4HSO4 are 224,276 and 319 ℃,respectively,which lays the foundation for the quantitative analysis of sulphate on AC.Regardless of the NH3 amount,only a small portion of H2SO4 is converted to sulphate,as the H2SO4 deposited in AC pores or agglomerated together could not come into contact with NH3.The final reaction product of NH3 and SO2 is mainly(NH4)2SO4 which is continuously generated because the newly generated H2SO4 is continually exposed to NH3,if NH3 is enough.The reaction of NH3 with H2SO4 takes precedence over with NH4HSO4.In the initial stages in which H2SO4 is exposed to NH3,the product is essentially all NH4HSO4 as intermediate.Then,it is further converted to(NH4)2SO4 whose amount reaches equilibrium when the accessible H2SO4 is exhausted.All the NH3 adsorbed on AC entering the desulphurisation tower generates NH4HSO4,but the amount is limited.The remaining SO2 entering the denitrification tower mainly generates(NH4)2SO4;thus,limiting the remaining SO2 amount is necessary to guarantee denitrification efficiency.When the NH3 injection is changed to the desulphurisation tower,the initial NH3 injection rate can be increased to complete the conversion of accessible H2SO4 as soon as possible in order to obtain higher denitrification efficiency.
查看更多>>摘要：In order to increase the utilization rate of vanadium-titanium magnetite in blast furnace smelting,the viscosity and potassium removal capacity of CaO-SiO2-Al2O3-MgO-BaO-TiO2 slag(CaO/SiO2=1.05,1-5 wt.％BaO,2-20 wt.％TiO2)were studied for slag optimization using the cylinder method and slag-metal equilibrium technique,respectively.Also,the structural properties of the slag were characterized by Fourier transform infrared spectroscopy.The concept of"a ring structure of Ti-O-Si"was proposed to express the change in the viscosity of the blast furnace slag.The results showed that the viscosity of slag increased with the increase in BaO content while the potassium removal capacity decreased.Furthermore,an increase in TiO2 content from 2 to 20 wt.％resulted in a decrease in viscosity and an increase in potassium removal capacity.The Fourier transform infrared spectroscopy results showed that the charge compensation of Ba2+can form complex aluminosilicate structure and increase the viscosity of slag.Meanwhile,with the increase in TiO2 content,Ti4+ions replace Si4+in the silicon-oxygen tetrahedral structure,thereby reducing the degree of polymerization of the silicate network and decreasing the viscosity.
查看更多>>摘要：The value-added utilization of converter steel slag is crucial,with China's annual production having reached 100 million tons.The utilization of converter slag in the construction materials sector is limited as it undergoes volume expansion during the aging process,mainly caused by the hydration reaction of free calcium oxide present in the slag.The influence of alumina addition on the mineral transformation of typical industrial converter slag was investigated.Different quantities of alumina were introduced into the slag,and the original and modified slags were remelted under argon atmosphere,followed by quenching.The experimental results were compared with thermodynamic simulation calculations for further analysis.As the alumina content increases,it reacts with the free calcium oxide in slag,leading to the formation of low-melting-point calcium aluminoferrite.Additionally,alumina addition effectively reduces slag viscosity.Finally,an assessment of the energy consumption for alumina-modified and silica-modified converter slags was presented.
查看更多>>摘要：A three-dimensional mathematical model has been established for a novel metallurgy process coupling an annular gas curtain with swirling flow at tundish upper nozzle.The discrete phase model and volume of fluid model were applied to simulate the gas-liquid multiphase flow behavior in tundish and nozzle.The effect of argon flow rate on the migration behavior of bubbles and interface behavior between steel and slag was also investigated.The presented results indicate that the novel coupling process can significantly change the flow pattern in the stream zone of a tundish,prolong the average residence time of liquid steel,and reduce the dead fraction.A complete annular gas curtain is formed around the stopper rod of tundish.Under the action of drag force of liquid steel,a part of small bubbles enter the nozzle through the swirling grooves and gather toward the center of the nozzle by centripetal force.As the argon flow rate increases,the volume fraction of argon gas entering the nozzle increases,which enhances the swirl intensity and increases the concentration of bubbles in the nozzle.To avoid the formation of slag open eye in tundish,the argon flow rate should not exceed 8 L min-1.
查看更多>>摘要：Obtaining a reasonable mold flow field for casting slabs with different sections is challenging by solely modifying the nozzle structure and continuous casting process.Research was conducted on small-sectioned(1000 mm × 220 mm)and large-sectioned(3250 mm × 220 mm)slab continuous casting molds with a fixed nozzle form(concave bottom nozzle,side port inclination angle of 0°).A three-dimensional electromagnetic model is established to analyze the current frequency,installation position,and rotation angle under the active deceleration mode and acceleration mode.The results indicate that,regardless of the deceleration mode for small-sectioned slabs or the acceleration mode for large-sectioned slabs,the magnetic flux density in the mold decreases with increasing current frequency.However,the maximum elec-tromagnetic force initially increases and then decreases,suggesting that both electromagnetic modes have the same optimal current frequency(3 Hz).The optimal mechanical design parameters for the deceleration mode of electromagnetic variable flow device(EM-VFD)with the small-sectioned slab are as follows:installation position Z=115 mm and rotation angle of 15°,ensuring that the maximum electromagnetic force is applied to the nozzle jet area.For the acceleration mode of the large-sectioned slab EM-VFD,the optimal mechanical design parameters are as follows:Z=115 mm and rotation angle of 10°,ensuring that the maximum electromagnetic force is applied to 1/4 and 3/4 areas of the wide face.These findings indicate that the new electromagnetic variable flow device,which can actively adjust the flow rate and angle of the steel even under given working conditions,provides the possibility for reasonable control of the mold's flow field.
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