硼化物和硼化物-钢阴极导电棒

硼化物的性质广泛研究了作为阴极材料的二硼化钛和二硼化锆。并对这些材料进行了烧结、热压,亦用改进的热压技术进行了制造。表1和表2分别列出了二硼化钛和二硼化锆的性质。     

燃烧剂对二硼化钛晶体形态的影响

以(Mg+Al)+B_2O_3+TiO_2为基础配系,通过改变燃烧剂中Mg和Al相对比例,研究不同燃烧剂对二硼化钛晶体形态的影响,探讨二硼化钛的晶体特征及其生长机理。研究表明,采用自蔓延高温合成法所获得的二硼化钛粉末,其晶体形态除了呈不规则颗粒状外,还存在着片状、柱状和晶须阵列等形态,典型的二硼化钛晶体形态呈六棱柱状。以Al粉部分取代Mg粉,可以有效增加柱状二硼化钛晶体的相对量。二硼化钛晶体的生长倾向一方面取决于其晶体结构本身,同时也取决于二硼化钛晶体生长时周围的成分起伏、能量起伏等环境条件。一维二硼化钛的形成对于增强硼化钛基陶瓷材料的韧性具有重要的意义。     

硼化钛工业性试制与生产

硼化钛是制造硼化钛阴极的主要原料。以前我国没有硼化钛工业生产、实验室生产的少量硼化钛粉成本高，难地推广应用。兰江冶炼厂与中南工业大学合作进行了用高温电阻炉直接合成硼化钛的工业性试验，并建成了月产５００ｋｇ硼化钛的生产线，为铝电解工业推广应用硼化钛阴极创造了良好条件。本文具体介绍了硼化钛的试制方法和产品的质量分析结果。     

新槽衬材料的开发

1　二硼化钛试验槽美国西弗吉尼亚世纪铝公司与EMEC咨询公司、SGL碳公司、肯特基世纪铝公司以及果尔登西北铝公司合作 ,在美国能源部的支持下联合攻关 ,旨在降低铝电解槽阴极碳和铝界面处的电阻 ,该项科研课题的作法是要在阴极中提供一个可补充的硼源 ,使硼与铝水中掺有的钛发生反应 ,在阴极处生成一层二硼化钛。该课题的目标是要建立起这样一种二硼化钛表层以实现降低电耗、提高产量、延长电解槽使用寿命的目的。该项课题可分为三个研究阶段。第二阶段已于 2 0 0 2年完成。其内容是用三块浸渍有二氧化硼的碳块来更换三块标准碳块。第三…     

机械化学置换反应合成碳化钛和二硼化钛

碳化钛和二硼化钛的熔点、硬度和强度都很高,而且具有很高的化学稳定性,生成热的绝对值也高。通常在高温下采用置换反应、碳热反应、直接反应、自扩散高温合成方法制备。近来,采用机械化学合成法通过钛粉分别与碳粉和硼粉的燃烧反应成功制得了碳化钛和二硼化钛。然而,这些传统的制备方法要求在高温下和(或)以昂贵的钛粉末为原材料来实现。 利用还原金属来实现机械化学置换反应(MDR)的方法已可用来制备WC,但是,还未能用于制备过渡金属的碳化物与硼化物。对碳化钛和二硼化钛来说,TiO2+2Ca=Ti+2CaO、Ti+C=TiC和Ti+2B=TiB2的反应焓分别…     

放电等离子烧结法制备二硼化钛多孔陶瓷

以二硼化钛微粉为原料，采用放电等离子烧结技术，通过控制烧结温度、保温时间、施加压力等工艺参数，成功的制备出具有高强度和高气孔率的二硼化钛多孔陶瓷。采用浸泡介质法，三点弯曲法测试了材料的气孔率，开口气孔率及强度；用扫描电镜对材料断口进行了观察。实验结果表明：在1300-1500℃的烧结温度下，获得了气孔率33％～45％，最大抗弯强度〉60MPa的二硼化钛多孔陶瓷。扫描电镜结果显示，二硼化钛颗粒间有明显的颈部烧结。     

铝电解槽惰性阴极材料的研究进展

介绍了铝电解槽惰性阴极的发展概况。新近国外报道的惰性阴极材料共有T_1B_2碳胶涂层、T_1B_2等离子喷镀层、T_1B_2电镀层和T_1B_2烧结体四种。同时简述了硼化钛的制造方法和硼化钛—碳胶涂层阴极的国内试验情况。     

广西分公司160kA电解槽硼化钛阴极涂层试验

简要介绍了硼化钛阴极涂层的理论依据和现场实施效果,认为硼化钛涂层可以延长槽寿命,延缓炉底压降的上升,具有明显的节能效果。     

硼化钛结构稳定性、力学和热力学性能理论研究

采用基于第一性原理的密度泛函理论计算了硼化钛的稳定性、电子结构、弹性模量、各项异性参数和低温热容等。计算结果表明,硼化钛的成键包含金属、共价和离子键,Ti2B的金属性最强,而TiB2的共价性最明显;其中TiB_Pm3m与TiB_F43m分别为热力学与力学失稳结构,而TiB2的稳定性最佳,TiB2的体模量、剪切模量和杨氏模量分别为251.4,260.1和564.6 GPa,显著高于其他硼化钛。B/G值表明,TiB2的韧性差,从而限制了其作为切削工具或耐磨部件的应用。因此,认为要获得良好的韧性与耐磨性,应设计制备TiB2基复合材料。     

脉冲加热库仑滴定法测定二硼化钛中的氧

采用脉冲加热库仑滴定法测定二硼化钛中的氧,研究了二硼化钛中氧量的测定条件,建立了分析方法,能准确、快速地测定二硼化钛中的氧含量,并能推广应用于金属陶瓷材料中氧含量的测定。与日本EMGA-620W氧氮分析仪红外法比较,证明本方法简便、可靠。     

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.     

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.     

Directional Growth of Tin Crystals Controlled by Combined Solute Concentration Gradient Field and Static Magnetic Field

A new method was introduced to achieve directional growth of Sn crystals. Microstructures in liquid(Pb)/liquid(Sn) diffusion couples were investigated under various static magnetic fields. Results show that the β-Sn crystals mainly reveal an irregular dendritic morphology without or with a relatively low static magnetic field(B0.3 T). When the magnetic field is increased to 0.5 T, the β-Sn dendrites close to the final stage of growth begin to show some directional character. With a further increase in the magnetic field to a higher level(0.8–5 T), the β-Sn dendrites have an enhanced directional growth character, but the dendrites show a certain deflection. As the magnetic field is increased to 12 T, the directional growth of the β-Sn dendrites in the center of the couple is severely destroyed. The mechanism of the directional growth of the β-Sn crystals and the deflection of the β-Sn crystals with the application of static magnetic field was tentatively discussed.     

电化学噪声数据处理方法概述

综述了常见的电化学噪声数据处理方法,介绍了直流趋势剔除、统计分析、快速傅立叶变换(FFT)法计算功率谱密度(PSD)以及小波变换处理电化学噪声信号的基本过程,并阐释了各种数学处理及所得参数的物理意义。