非均相法制备高浓碱溶液脱硅剂斜方水合碳铁酸钙的研究

提出以斜方水合碳铁酸钙为脱硅剂解决亚熔盐法处理一水硬铝石型铝土矿所得高浓碱溶出液的深度脱硅问题.采用非均相方法合成了碳铁酸钙(3CaO·Fe2O3·CaCO3·12H2O)脱硅剂,对影响合成过程的主要因素进行了考察.结果表明,适当提高合成温度、缩短合成时间可以提高水合碳铁酸钙的含量.最优合成工艺条件为:反应温度313 K,反应时间16 h,反应液固比25,搅拌速率500 r/min,氧化钙粒度0.104mm～0.120mm.脱硅过程中,斜方晶系的水合碳铁酸钙转变为立方晶型的钙铁石榴石,在此过程中二氧化硅和少量氧化铝进入晶体结构,形成钙铁硅石榴石和钙铁铝硅石榴石,脱硅产物的铝硅比小于0.5.     

六方水合铁酸钙的合成及其脱硅

通过正交实验对六方水合铁酸钙的合成温度、合成时间和合成体系中CaO与Fe2O3的摩尔比及合成体系的搅拌强度等因素对其脱硅效果的影响进行研究,并给出六方水合铁酸钙的最佳合成条件。结合X射线衍射分析讨论水合铁酸钙的脱硅机理,提出水合铁酸钙是一种高度分散的含钙化合物,其晶面间距较大,脱硅活性较高,并可大幅度降低铝损。在最佳条件下添加水合铁酸钙进行深度脱硅时,脱硅后铝酸钠溶液中的SiO2含量可降低到7 mg/L,硅量指数可达14 000,且脱硅产物中SiO2的饱和系数可达0.46。     

铝酸钠溶液深度脱硅

叙述了硅在铝酸钠溶液中的存在状态,指出了在烧结法生产氧化铝过程中铝酸钠溶液深度脱硅的重要性.介绍了铝酸钠溶液深度脱硅研究现状,讨论了Ca(OH)2、C3 AH6(立方水合铝酸钙)、C4 AHn(六方水合铝酸钙)、HCAC(水合碳铝酸钙)、HSAC(水合硫铝酸钙)、C4 FHn(六方水合铁酸钙)等含钙化合物深度脱硅机理及脱硅效果.     

水合碳铝酸钙深度脱硅的工业实践

详细地论述了水合碳铝酸钙合成的机理,利用水合碳铝酸钙深度脱硅的机理以及在工业生产中的应用,使烧结法精制铝酸钠溶液的硅量指数由400－480提高到600以上,同时产品氧化铝的质量有了明显的提高。     

水合硫铝酸钙的合成

通过正交实验对水合硫铝酸钙的合成温度、合成时间、合成体系中CaO与A12O3的摩尔比、合成体系中SO4^2-高于的浓度等因素对其脱硅效果的影响进行了研究，并给出了水合流铝酸钙的最佳合成条件。结合XRD分析和IR光谱分析讨论了水合硫铝酸钙合成机理和脱硅机理，提出水合流铝酸钙是一种高水合、高度分散的含钙化合物，其脱硅活性高。在最佳条件下添加水合硫铝酸钙进行深度脱硅，脱硅后的铝酸钠溶液中SiO2含量可降低到8mg／L，硅量指数可达12500。     

铝酸钠溶液预脱硅晶种活化技术

在烧结法氧化铝生产工艺中,为了保证产品质量,必须对粗液进行脱硅,而基于形成水合铝硅酸钠的脱硅路线,由于渣中硅含量高、铝损失少,是进行粗液第一步脱硅的必要步骤。烧结法氧化铝生产,采用粗液常压预脱硅—中压压煮脱硅—加石灰常压深度脱硅的三段脱硅工艺,对粗液一段常压预脱     

超细脱硅剂的制备与应用

采用液相沉淀法制备了超细水合铝酸钙(C3AHx),在单因素实验的基础上通过正交实验确定了合成超细水合铝酸钙的最佳工艺条件。采用XRD、SEM对脱硅剂进行物相和粒度形貌分析,探讨其脱硅机理。在最佳条件下添加超细水合铝酸钙进行深度脱硅,脱硅后的铝酸钠溶液中SiO2含量可降低到0.008g/L,硅量指数可达12500。     

改变拜耳法预脱硅工艺降低赤泥化学结合碱的研究

研究了拜耳法预脱硅工艺,目的在于降低赤泥化学结合碱。在预脱硅段使用低碱、高ak溶液(沉铝液)对铝土矿进行脱硅,然后补进浓缩的循环母液溶出铝土矿,使铝土矿中的含硅矿物更多地转化为水化石榴石形态,达到降低赤泥化学结合碱的目的。实验研究发现,当预脱硅温度为160℃,反应时间为120min,沉铝液碱含量为15%,ak为30.8,配矿C/S比为1.3,溶出温度为260℃,反应时间为60min时,采用本方法溶出河南某地铝土矿产生的赤泥N/S从常规溶出赤泥N/S的0.42降为0.23。     

煤系硫铁矿浮选尾矿热化学活化脱硅制备铝精矿

提出热活化脱硅技术处理某煤系硫铁矿浮选尾矿制备铝精矿,对制备氧化铝精矿的工艺制度及脱硅机理进行研究。结果表明:该尾矿适宜的热化学活化脱硅制度为活化焙烧温度1 150℃、焙烧时间15～20 min、碱浸溶硅温度125～140℃、溶出时间30 min、NaOH浓度140 g/L。在此条件下,对Al2O3和SiO2含量分别为46.22%和28.33%(质量分数)的硫铁矿浮选尾矿,焙砂SiO2溶出率达到71.91%,所得铝精矿中Al2O3含量达69.29%,铝硅比5.59。XRD结果表明:硫铁矿尾矿中伊利蒙脱石、高岭石和叶腊石等铝硅酸矿物在焙烧过程中活化分解生成无定形SiO2和少量莫来石,与此同时,一水硬铝石转变成α-Al2O3。在焙砂的碱浸过程中,无定形SiO2溶解于NaOH溶液被脱除,而α-Al2O3和莫来石不能溶解,同时生成的水合铝硅酸钠(Na8Al6Si6O24(OH)2(H2O)2)将导致SiO2溶出率降低。焙烧过程中尾矿中的黄铁矿转化为赤铁矿、锐钛矿部分转化成金红石,在碱浸过程中它们均不会溶解而进入铝精矿中。     

高铝粉煤灰生料配比对熟料烧成温度及溶出性能的影响研究

本文以高铝粉煤灰预脱硅后脱硅灰为原料,研究了不同钙比(1.90、2.10)、铁铝比(0.032、0.050)对熟料烧成温度范围及溶出性能的影响;试验结果表明:铝硅比1.6、铁铝比0.032、碱比0.93、0.95、1.00的条件下高钙熟料相对于低钙熟料氧化铝溶出率提高1.6%~2.3%,氧化钠溶出率提高0.98%~1.4%;铝硅比1.6、铁铝比0.050、碱比0.93、0.95、1.00的条件下高钙熟料相对于低钙熟料氧化铝溶出率提高1.5%~2.25%,氧化钠溶出率提高0.22%~1.75%;高钙熟料相对于低钙熟料可扩宽熟料烧结温度范围10℃,生料铁铝比由0.032提高至0.050可降低熟料烧成温度20℃,可扩宽熟料烧成温度范围10℃。     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

Thermodynamics Study on the Decomposition of Chromite with KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

Influence of Heat Treatment on Damping Behaviour of the Magnesium Wrought Alloy AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(Bi LaxFe1-xO3)–0.5(Pb Ti O3)(x = 0.05,0.10,0.15,0.20)(BLxF1-x-PT) were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range(102–106Hz) at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures(200–300 °C).     

Quantitative Analysis of the Crystallographic Orientation Relationship Between the Martensite and Austenite in Quenching–Partitioning–Tempering Steels

The orientation relationships(ORs)between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction(SAED)as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_(bcc).A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.     

Growth Kinetics of Single Inclusion Particle in Molten Melts

On the basis of the single-particle framework, a new theory on inclusion growth in metallurgical melts is developed to study the kinetics of inclusion growth on account of reaction and collision. The studies show that the early growth of inclusion depends on reaction growth and Brawnian motion collision, and where the former is decisive, the late growth depends on turbulence collision and Stokes＇ collision, and where the former is dominant; collision growth is very quick during the smelting process, lessened in the refining process, but nearly negligible in the continuous casting process.     

Theoretical Analysis for the Motion and Temperature of Melt Droplets in Spray Degassing Process

The motion of melt droplets in spray degassing process was analyzed theoretically. The height of the treatment tank in spray degassing process could be determined by the results of theoretical calculation of motion of melt droplets. To know whether the melt droplets would solidify during spraying process, the balance temperature of melt droplets was also theoretically analyzed. Then proof experiments for theoretical results about temperature of melt droplets were carried. In comparison, the experimental results were nearly similar to the calculation results.     

Using Finite Element and Contour Method to Evaluate Residual Stress in Thick Ti-6Al-4V Alloy Welded by Electron Beam Welding

This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates(50 mm thick) by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.     

Microstructures and Tensile Properties of Ultrafine-Grained Ni–(1–3.5) wt% SiC_(NP) Composites Prepared by a Powder Metallurgy Route

Silicon carbide nanoparticle-reinforced nickel-based composites(Ni–Si CNP),with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pure nickel samples were also prepared for comparative purposes.To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–Si CNPcomposites transmission electron microscopy(TEM) was used,while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests.TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample,whereas,for the Ni–Si CNPcomposites,the presence of nano-dispersed Si CNPand twinning crystals was observed.These homogeneously distributed Si CNPwere found located either within the matrix,between twins or on grain boundaries.For the Ni–Si CNPcomposites,coerced coarsening of the Si CNPassembly occurred with increasing Si CNPcontent.Furthermore,the grain sizes of the Ni–Si CNPcomposites were much finer than that of the unreinforced pure nickel,which was considered to be due to the composite ball milling process.In all cases,the Ni–Si CNPcomposites showed higher strengths and hardness values than the unreinforced pure nickel,likely due to a combination of dispersion strengthening(Orowan effects) and particle strengthening(Hall–Petch effects).For the Ni–Si CNPcomposites,the strength increased initially and then decreased as a function of Si CNPcontent,whereas their elongation percentages decreased linearly.Compared to all materials tested,the Ni–Si CNPcomposite containing 1.5% Si C was found more superior considering both their strength and plastic properties.