B位复合铅基钙钛矿结构粉体煅烧合成过程中烧绿石相的形成机理研究

用X-射线衍射法(XRD)对B位复合铅基钙钛矿结构的铌镁酸铅Pb(Mg1/3Nb2/3)O3与铌铁酸铅Pb(Fe1/2Nb1/2)O3粉体"铌铁矿先驱体法"(即两步煅烧法)煅烧合成工艺过程中烧绿石相形成机理进行了研究.结果表明MgNb2O6/Pb3O4体系中烧绿石相的形成机理与FeNbO4/Pb3O4体系中的有所不同,前者主要通过从先驱体继承而来的残留Nb2O5与PbO反应而生成,而后者主要通过先驱体FeNbO4分解出来的Nb2O5与PbO反应而得到.     

液相合成铌酸钾粉体的研究

以Nb2O5、KECO3、HF和（NH4）2C2O4为原料，以柠檬酸为配位剂，乙二醇为酯化剂，用氨水调节溶液的pH值，首先将Nb2O5在水浴条件下溶于HF，加入（NH4）2C2O4和氨水获得沉淀物，而后用柠檬酸溶解获得Nb-柠檬酸溶液。K2CO3与Nb-柠檬酸溶液在乙二醇的交联作用下形成了K-Nb凝胶前驱体。用XRD和SEM研究了不同pH值、不同柠檬酸与金属离子的摩尔比条件下所形成的凝胶前驱体在不同温度下煅烧所得粉体的相组成和形貌。研究发现当柠檬酸与金属离子的摩尔比为3：1，柠檬酸和乙二醇的摩尔比为1：2时，可形成稳定的K-Nb前驱体溶液和凝胶。分析结果表明，K-Nb凝胶前驱体在加热过程中分解成K2CO3相，K2CO3与Nb-柠檬酸溶液发生反应生成KNbO3凝胶，凝胶经800℃煅烧3h或160℃水热反应8h可以制备出颗粒分布均匀的纯钙钛矿型KNbO3粉体。IR谱表明。800℃煅烧或160℃水热反应都出现了Nb-O的特征峰。     

碱熔Nb2O5湿化学法合成Pb（Mg1／3Nb2／3）O3纳米粉体

以Nb2O5作为反应的起始物，采用一种新型湿化学方法制备复合钙钛矿型Pb（Mg1／3Nb2／3）O3（简称PMN）纳米粉体。利用激光拉曼光谱、DSC／TG、TEM和XRD对制备的Nb-柠檬酸铵络合溶液、干凝胶粉末和PMN粉体进行了表征。研究了焙烧工艺对PMN粉体的物相组成、晶粒尺寸及相含量的影响。实验结果表明：在适宜的焙烧条件下，PMN粉体的平均粒径小于50nm，PMN相的含量大于70％。适当升高焙烧温度及延长保温时间或者采取二次焙烧均能提高钙钛矿相PMN的含量，其中采用二次焙烧的方法效果显著。     

纳米Ba_3Ti_4Nb_4O_(21)微波介质陶瓷粉体制备及表征

以铌柠檬酸盐、乙酸钡和钛酸正四丁酯为原料,采用溶胶-凝胶法,通过控制反应条件,在700℃的温度下获得Ba3Ti4Nb4O21纳米粉体,比采用普通固相法合成的温度低400℃左右。用红外光谱,差热-热重,X射线衍射以及透射电镜等手段表征Ba3Ti4Nb4O21柠檬酸盐前驱体以及煅烧后粉体的各项特性。结果表明:用柠檬酸盐溶胶-凝胶法制得的前驱体在700℃煅烧2h后,可获得纯Ba3Ti4Nb4O21纳米粉体,其平均粒径在30～50nm,适合于微波介质陶瓷的制备。     

La1-xSrxCo1-yFeyO3材料制备及结构分析

以溶胶-凝胶法制备La1-xSrxCo1-yFeyO3粉体，对粉体在不同温度热处理后的晶体结构进行XRD表征，详细研究粉体的成分组成以及发生的结构转变。结果表明，凝胶前驱体粉体颗粒比表面增大有利于钙钛矿结构晶相形成；合成粉体受前驱体比表面程度影响形成两种具有不同空间群钙钛矿结构晶相，并且各晶相元素化学计量比不相同，两相体系较稳定。     

La1-xSrxCo1-yFeyO3材料制备及结构分析

以溶胶-凝胶法制备La1-xSrxCo1-yFeyO3粉体,对粉体在不同温度热处理后的晶体结构进行XRD表征,详细研究粉体的成分组成以及发生的结构转变.结果表明,凝胶前驱体粉体颗粒比表面增大有利于钙钛矿结构晶相形成;合成粉体受前驱体比表面程度影响形成两种具有不同空间群钙钛矿结构晶相,并且各晶相元素化学计量比不相同,两相体系较稳定.     

过氧化氢络合共沉淀法制备PZT陶瓷粉体

以ZrOC12·8H2O、TiCl4、Pb(Ac)2·3H2O为原料,H2O2为络合剂,通过络合共沉淀法制备了Pb(zr0.53Ti0.47)O3粉体.研究了沉淀过程中沉淀剂种类对前驱体沉淀的洗涤-过滤特性及收率的影响.结果表明,以预先溶解有硫酸铵的氨水为沉淀剂制备的前驱体的洗涤-过滤特性得到显著改善,所用的过滤时间缩短近一个数量级,同时收率也得到明显的提高;XRD结果表明前驱体经过600℃煅烧处理后里单一钙钛矿结构,且结晶性能良好;EPMA电子能谱表明粉体组成与拟定配比相同,且粉体的组成均匀性良好.     

共沉淀法合成PbZrO3粉体

锆酸铅(PbZrO3,PZ)作为典型的ABO3型钙钛矿材料,在500 K附近发生从顺电相到反铁电相的相转变.以硝酸铅、氧氯化锆为原料,氨水为沉淀剂,采用共沉淀方法成功合成了PbZrO3粉体.利用差热分析(DTA)和热失重分析(TG)研究了共沉淀前驱体的热行为,利用XRD跟踪粉体的相演化,研究了煅烧温度对钙钛矿相锆钛酸铅形成的影响.发现共沉淀加强了Pb、Zr离子的混合,促进了钙钛矿相锆钛酸铅的形成,经600℃低温煅烧便可获得结晶良好的钙钛矿相PbZrO3粉体.     

两步沉淀法合成Bi3.25La0.75Ti3O12(BLT)粉体及其表征

以五水硝酸铋(Bi(NO3)3·5H2O)、水合硝酸镧(La(NO3)3·nH2O)和钛酸四丁酯((C4H9O)4Ti)为原料,氨水为沉淀剂,分两步沉淀Ti离子和Bi、La离子,利用沉淀法合成了Bi3.25La0.75Ti3O12(BLT)粉体.利用差热分析(DTA)和热失重(TG)对两步沉淀法制备的前驱体粉体的热行为进行了分析,用X射线衍射(XRD)研究了其晶相演化过程,利用场发射扫描电子显微镜(FESEM)对BLT粉体粒度和形貌进行了观察.结果显示两步法制备的前驱体粉体经低温煅烧直接转化为单一的铋层状钙钛矿相BLT粉体,在700℃煅烧2 h合成的BLT粉体颗粒不大于100nm,颗粒间结合疏松,具有良好的分散性.     

低热固相法合成镁铝尖晶石

以分析纯碱式乙酸铝、硝酸镁为原料,柠檬酸为配合剂,采用低热固相反应制备前驱体,然后通过煅烧的方式获得了MgAl_2O_4粉体.研究了煅烧温度、柠檬酸用量对MgAl_2O_4粉体性能的影响.结果表明,可在全固相条件下通过低热固相反应得到Mg和Al分子级混合的前驱体,该前驱体煅烧到700 ℃保温3 h形成含有部分阳离子缺陷的尖晶石晶相,随温度升高,逐渐转化为结晶完整的尖晶石.柠檬酸使用量符合化学计量比n(C_6H_8O_7):n(Mg+Al)为1:1时能够获得比表面积达到166 m~2/g的MgAl_2O_4粉体.     

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.