Observation of fine particle aggregating behavior induced by high intensity conditioning using high speed CCD

1 Introduction Flotation is a dominant separation technique employed by the mineral industry, especially in metal recovery. However, this technology only well responds to mineral particle in a narrow size range, out of which flotation efficiency falls sub…     

Kinetic study on pressure leaching of high iron sphalerite concentrate

The kinetics of pressure leaching high iron sphalerite concentrate was studied.The effects of agitation rate,temperature, oxygen partial pressure,initial acid concentration,particle size,iron content in the concentrate and concentration of Fe2 added into the solution on the leaching rate of zinc were examined.The experiment results indicate that if the agitation rate is greater than 600 r/min,its influence on Zn leaching rate is not substantial.A suitable rise in temperature can facilitate the leaching reaction,and the temperature should be controlled at 140-150℃.The increase trend of Zn leaching rate becomes slow when pressure is greater than 1.2 MPa,so the pressure is controlled at 1.2-1.4 MPa.Under the conditions of this study,Zn leaching rate decreases with a rise in the initial sulfuric acid concentration;and Zn leaching rate increases with a rise of iron content in the concentrate and Fe 2 concentration in the solution.Moreover,the experiment demonstrates that the leaching process follows the surface chemical reaction control kinetic law of“shrinking of unreacted core”.The activation energy for pressure leaching high iron sphalerite concentrate is calculated,and a mathematical model for this pressure leaching is obtained.The model is promising to guide the practical operation of pressure leaching high iron sphalerite concentrate.     

高能超声对原位合成Al_3Ti/6070复合材料凝固组织的影响及机制

以Al-K_2TiF_6为反应体系,采用熔体反应法,在高能超声场下原位合成Al_3Ti/6070复合材料.采用XRD、SEM、EDS等手段研究不同超声参数如超声时间和超声强度对Al_3Ti/6070复合材料增强体形貌及尺寸的影响.建立了超声作用下熔体中颗粒行为模型,并对其机制进行了探讨.结果表明:在一定的超声强度下(0.66 kW/cm~2),颗粒尺寸随超声作用时间的延长(1～7 min)先减小后增大,当作用时间为3 min时,颗粒最细小,尺寸为1～2 μm,形貌主要为小块状或短棒状;当超声作用时间大于3 min时,颗粒数量随时间增加而急剧减少;在相同的超声作用时间(3 min)下,颗粒尺寸随超声强度的增加而减小,当超声强度为0.82 kW/cm~2时,颗粒尺寸为0.5～1 μm,颗粒形貌主要为小块状或粒状,当超声功率大于0.82 kW/cm~2时,颗粒数量随超声功率增加而急剧减少.高能超声作用下Al_3Ti/6070复合材料的最佳制备工艺为:超声强度0.66～0.82 kW/cm~2,超声作用时间3 min.     

焊接热输入对低合金高强钢力学性能及组织的影响

通过立向上焊接B780CF钢板试验,改变焊条电弧焊的焊接热输入,考察其对熔敷金属力学性能及组织的影响。结果发现,随着焊接热输入的增加,抗拉强度逐渐递减,冲击吸收能量先增加后减小,在30kJ/cm时达到最佳,强韧性达到优良的匹配。     

Effect of quenching temperature on structure and properties of centrifugal casting high speed steel roll

The critical points and time-temperature-transformation (TTT) curves of the isothermal transformation diagrams for a high-speed steel casting on a horizontal centrifugal casting machine had been determined experimentally in the study. The effects of quenching temperature on the microstructures and properties of centrifugal casting high speed steel (HSS) roll has been investigated using scanning electron microscopy (SEM), light optical microscopy (LOM) and X-ray diffraction (XRD) as well as using tensile, impact, and hardness tests. The results show that the HSS roll has excellent hardenability and its matrix structure can be transformed into the martensite after being quenched in the sodium silicate solution. The retained austenite in the quenching structure increases and the hardness decreases when the quenching temperature exceeds 1,040℃. The tensile strength and impact toughness of HSS roll increase once the quenching temperature is raised from 980℃ to 1,040℃. However, the tensile strength and impact toughness have no significant change when the quenching temperature exceeds 1,040℃. The HSS roll quenched at 1,040℃ exhibits excellent comprehensive mechanical properties.     

热处理对高速钢W6Mo5Cr4V3Co8组织和性能的影响

采用OM,SEM,EDS,TEM以及力学性能试验,研究了热处理工艺对不同尺寸规格的粉末冶金高速钢W6Mo5Cr4V3Co8微观组织和力学性能的影响。结果表明,区别于普通高速钢,粉末冶金高速钢微观组织中没有大颗粒尺寸共晶碳化物,退火组织中碳化物均匀、细小,颗粒尺寸小于3μm。因此,不同尺寸规格钢材以及不同截面方向的组织都保持着高度的一致性;试验钢在1080～1180℃较宽的温度范围内淬火都能够获得67 HRC以上的硬度。淬火后的组织为马氏体+残留奥氏体+未溶碳化物,淬火奥氏体晶粒尺寸非常细小;经过高温回火后,试验钢存在明显的二次硬化效应,二次硬化峰出现在520℃。二次硬化现象是由残留奥氏体转变和合金碳化物析出共同作用的结果,TEM分析显示,试验钢经高温回火析出的二次硬化碳化物包含VC;冲击韧性试验结果表明,不同截面尺寸粉末高速钢的冲击韧性基本相当,同一钢材其横向和纵向的冲击韧性相差不大。     

高能喷丸处理对Al-Zn-Mg合金的组织和力学性能的影响

采用透射电镜(TEM)、光学显微镜(OM)、显微硬度计和微力材料试验机等研究了 Al-Zn-Mg合金高能喷丸处理后的表层显微组织和力学性能.结果表明:经高能喷丸处理后,在距离Al-Zn-Mg合金表面约20 μm深度范围内形成了随机取向的等轴纳米晶层,表面层的结构特征尺寸随层深的增大呈梯度变化,无明显界面;由于细晶强化作...     

Effect of partial remelting time on the initial carbide in semisolid structure of hypereutectic high Cr cast iron

1 .Introduction High chromium white cast iron is one of the wear-resistant materials widely used at present. With an increase of carbon content, the volume fractions of carbides increase. As a result, its wear resistance is enhanced and impact toughness declines co}espondingly If the carbon