Lead titanate nanotubes synthesized via ion-exchange method: Characteristics and formation mechanism

A two-step method is presented for the synthesis of one dimensional lead titanate (PbTi₃O₇) nanotubes. Firstly, titanate nanotubes were prepared by an alkaline hydrothermal process with TiO₂ nanopowder as precursor, and then lead titanate nanotubes were formed through an ion-exchange reaction. We found that sodium titanate nanotubes have ion exchangeability with lead ions, while protonated titanate nanotubes have not. For the first time, we distinguished the difference between sodium titanate nanotubes and protonated titanate nanotubes in the ion-exchange process, which reveals a layer space effect of nanotubes in the ion-exchange reaction. In comparison with sodium titanate, the synthesized lead titanate nanotubes show a narrowed bandgap.     

Oxidation behavior of copper at high temperatures under two different modes of direct-current applications

Oxidation kinetics of copper in the temperature range of 973–1173 K atP _{O 2}=21.27 kPa exhibit enhancement and deceleration in the rates with changing polarity compared to normal oxidation under interrupted mode of directcurrent application. These conditions are achieved by connecting the oxidizing copper covered with an initially formed thin oxide film to the positive and negative terminal of a dc source, respectively. However, the influence of direction of the current is found to be opposite under uninterrupted mode of impressed current flow in the same temperature range. The effect of short-circuiting the metal to the outer oxide/air interface on the reaction kinetics is also reported. The rate of oxide-scale growth under normal condition, and two different modes of current applications as well as with shorting circuitry attachment conform to the parabolic growth law. The results pertaining to the two different modes of impressed current have been discussed considering both the phenomena of electrolysis of the oxide electrolyte and the polarization at the two phase boundaries. The enhancement and the reduction in rates under uninterrupted impressed current conditions are explained on the basis of increased and decreased average defect concentrations, respectively, within the oxide layer. The acceleration and deceleration in the rates under interrupted mode of current flow have been explained in the light of sustenance of a steeper and flatter electrochemical-potential gradient of defects, respectively, across the growing-oxide layer. The possible different responses of the metal/oxide and oxide/air interfaces to the impressed current brought into play by two different modes of current application, have enabled to display a better insight on the mechanistic aspects of scale growth under the influence of an externally applied current.     

海绵钛副产品氯化镁高温气相氧化反应器内流场的模拟研究

本文研究基于利用“原位热解—热法还原炼镁”海绵钛清洁生产新工艺,即还原蒸馏产生的气态氯化镁直接氧化热解制备高纯氧化镁及氯气,氧化镁经热法炼镁返回TiCl₄还原环节、氯气返回沸腾氯化环节作为原料,实现海绵钛生产中新的镁、氯循环。,并针对“海绵钛生产中新的镁、氯循环”中的关键步骤—气态氯化镁与氧气的均相热解反应的反应器进行研究。采用数值模拟和物理模拟方法研究了反应器模型内的浓度场和速度场,在氮气与二氧化碳流量比为6：1时,二氧化碳采用环向四口进气方式,气体混合不均匀度为0.02,气体混合程度最佳。     

High-Temperature Jet Spray Reactor for the Preparation of Rare Earth Oxides by Pyrolysis: Computer Simulation

A new type of high-temperature jet spray pyrolysis (SP) reactor is investigated in this article as part of studies on the preparation of rare earth oxides at Northeastern University (NEU), Shenyang, China. The jet spray reactor examined here is a horizontal, tubular reactor conveying the hot products of the combustion of methane and oxygen with a converging–diverging jet section in an arrangement that provides for inspiration of LaCl₃ solution to pyrolyze to La₂O₃ with the hot gas. The present article is concerned with a computer simulation using a computational fluid dynamic model to develop the velocity, temperature, and pressure profiles in the jet reactor since direct measurement is difficult. The article includes brief comments on a room-temperature model designed to examine the flow characteristics of the jet SP reactor. It was found that the velocity decreased at first, and then it increased near the jet throat. The highest velocity occurred at the throat of jet SP reactor where the LaCl₃ enters the unit. Along the reactor axis, the temperature decreases with distance from the gas inlet. The lowest temperature zone was near the wall before the throat of the reactor due to wall heat losses. The temperature was estimated to be close to 1700 K at the throat of the reactor, and it was about 1300 K toward the exit of the reactor. It was shown that a reaction would take place mainly in the throat and in the vicinity of first contact between gas and induced spray. A negative pressure was produced as gas passes through the converging–diverging throat of the jet SP reactor that causes the LaCl₃ solution to enter the throat of the reactor. While the investigations of this type of reactor are at an early stage, the results look promising. NEU continues to investigate this approach for the preparation of La₂O₃ based on high-temperature testwork and physical modeling techniques.     

多级复合流化床制备四氯化钛

为了解决四氯化钛制备过程中的粘结问题,采用复合流化床新工艺进行中试试验制备四氯化钛,可以有效利用镁钙含量大于2.5％的高钛渣原料.对氯气流量、流态化温度等参数的影响进行研究,并对反应产物的形貌进行分析,同时计算了反应效率.结果表明:TiO2的转化率达到90％,通过检测发现收尘渣表面富集MgCl2和CaCl2,而流化床中未出现粘结,说明该流化床具有一定的抗粘结能力.     

超重力反应结晶法制备纳米立方形CaCO_3颗粒Ⅰ.实验研究

以Ｃａ（ＯＨ）２悬浊液和ＣＯ２气体在超重力反应器（旋转填充床反应器）中进行碳化反应制备纳米立方形ＣａＣＯ３为研究对象,中试实验研究了超重力加速度ｇｒ、液体循环量Ｌ、气体流量Ｇ、Ｃａ（ＯＨ）２初始浓度等操作条件对产物粒度及其分布、碳化反应时间的影响。结果表明,利用超重力反应结晶法可以制备出平均粒度为１５－４０ｎｍ、分布较窄的立方形ＣａＣＯ３;碳化反应时间是传统方法的１／４－１／１０。     

贮氚老化对钯氢化物氢氘交换影响的色谱理论模拟

利用色谱分离的速率理论分析了贮氚老化影响钯氢化物中恒流速氢氘交换性能的原因,并利用塔板理论模拟了氢氘交换流出曲线,同时,实验对比了未贮氚老化与贮氚老化1.6年钯的氢氘交换流出曲线。理论模拟结果表明:贮氚老化后,钯氢化物氢氘交换反应的塔板数n减少,塔板高度H增加,交换反应的平衡时间增长,氢氘交换流出曲线趋于平缓,氢氘交换性能下降。而塔板高度的增加,是由于衰变3He滞留在钯材料中,导致氢同位素在老化钯中的扩散受阻,同时使得钯的氢同位素分离因子改变。实验对比结果表明:恒流速状态下,贮氚老化1.6年钯的氢氘交换流出曲线较之未贮氚老化钯变得平缓,氢氘交换性能下降。理论模拟与实验结果符合较好。     

Parameters affecting reaction rate and conversion of TiO2 chlorination in a fluidized bed reactor: Experimental and modeling approach

Pilot scale chlorination of TiO₂ was carried out with CO as reducing agent. The experimental analysis and modeling of chlorination process of TiO₂ in the presence of CO and Cl₂ in a semi-continuous fluidized bed reactor were aimed. Chlorination process was continuously monitored by measuring the amount of produced TiCl₄ with time. The effects of different operating parameters including chlorination temperature, feedstock particle size and size distribution, amount of feedstock and Cl₂ and CO flow rates on the conversion were systematically investigated. A gradual increase in chlorination temperature led to monotonous increase of conversion rate. Conversion decreased with increased particle size of feedstock. An increase in loaded feedstock led to a decrease in reaction conversion. A model was proposed to predict conversion, particle size distribution and mole fraction of components in gas phase as reaction proceeds. A good agreement between conversions predicted by the model and experimental data under various operating conditions was observed.     

Removal of copper from nickel anode electrolyte through ion exchange

An novel method for removal of copper from nickel anodic electrolyte through ion exchange was studied after cupric deoxidization. Orthogonal design experiments show the optimum conditions of deoxidizing cupric into Cu+ in the nickel electrolyte are the reductive agent dosage is 4.5 times as the theoretic dosage and reaction time is 0.5 h at 40 ℃ and pH 2.0. Ion exchange experiments show that the breakthrough capacity(Y) decreases with the increase of the linear flow rate(X): Y=1.559-0.194X+ 0.006 7X2. Breakthrough capacity increases with the increase of the ratio of height to radius(RRH). The higher the initial copper concentration, the less the breakthrough capacity(BC). SO42- and nickel concentration have no obvious change during the process of sorption, so it is not necessary to worry about the loss of nickel during the sorption process. Desorption experiments show that copper desorption from the resin is made perfectly with NaCl solution added with 4% (volume fraction) H2O2 (30%) and more than 100 g/L CuCl2 solution is achieved.     

Computational simulation of fluid dynamics in a tubular stirred reactor

The flow and concentration fields in a new style tubular stirred reactor were simulated by simulating the fluids dynamics(CFD), in which FLUENT software was used and the standard k-ε model and multiple reference frame(MRF) were adopted. The various values of initial rotating speed and inlet flow rate were adopted. Simulations were validated with experimental residence time distribution(RTD) determination. It is shown that the fluid flow is very turbulent and the flow pattern approaches to the plug flow. The velocity increases from shaft to the end of impeller, and the gradient is enlarged by increasing the rotating speed. Comparison between RTD curves shows that agitation can improve the performance of reactor. As the flow rate increases, the mean residence time decreases proportionally, and the variance of RTD lessens as well. When rotating speed increases to a certain value, the variance of RTD is enlarged by increasing rotating speed, but the mean residence time has no obvious change.     

Room-temperature synthesis of crystallized LiCoO2 thin films by electrochemical technique

LiCoO₂ thin films have been directly synthesized on cobalt substrate in LiOH solution at room temperature by electrochemical method. The obtained LiCoO₂ thin films were characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The influence of electrochemical reaction time, current density and concentration of LiOH solution on the crystal structure and morphology of the obtained LiCoO₂ thin films was discussed emphatically. Our results show that the as-synthesized LiCoO₂ films all are pure hexagonal structure. The crystallinity, densification and uniformity of the films increase with increasing electrochemical reaction time, current density as well as concentration of LiOH solution and then decrease. The preferable electrochemical reaction conditions were optimized as: electrochemical reaction time is 50 h, current density is 1 mA cm⁻² and concentration of LiOH solution is 3 mol dm⁻³.     

高温气相反应合成金红石型纳米TiO2颗粒的研究

在高温气相反应器中,利用掺 ＡｌＣｌ３的 ＴｉＣｌ４氧化反应制备金红石型纳米 ＴｉＯ２颗粒研究了氧气预热温度、反应器尾部氮气流量、反应温度、停留时间等对 ＴｉＯ２颗粒大小的影响结果表明：提高氧气预热温度和加大反应器尾部氮气流量对控制产物粒径有利, ＴｉＯ２粒径随反应温度升高和停留时间延长而增大当反应温度为１３７３Ｋ, ＡＩＣｌ３与ＴｉＣｌ４摩尔比为 ０．２５、停留时间为１．７３ｓ时,纯金红石相纳米ＴｉＯ２颗粒的粒径分布为 ３０－５０ｎｍ．     

Efficient drilling of holes in Al2O3 armor ceramic using impregnated diamond bits

This study aims at achieving a high efficient mode of hole-drilling in Al₂O₃ armor ceramic by using impregnated diamond bits. First, the most suitable diamond segment for the armor ceramic is selected by using higher quality diamonds and varying the composition of the metal matrix, as well as combining to the drilling test and SEM examination. Bit structure parameters such as grain size, diamond concentration, number of slots and wall thickness are optimized then by an orthogonal test. Experiments for analyzing the influence of the axial force and spindle speed to the efficiency are also carried out. Then hole quality is discussed. Finally, the ground surface integrity of Al₂O₃ armor ceramic is analyzed under SEM examination. The results show: (1) the bit with diamond type of SMD40 and metal matrix of Cu50Co25Sn18Ti7 (wt%) presents the best self-dressing capability among the four kind of different matrix bits; (2) the bit with wall thickness of 2.5 mm, grain size of 35/40 US mesh, diamond concentration of 100% and number of slots of 2 achieves a higher efficient mode; (3) the increased axial force and spindle speed could increase the drilling efficiency but overlarge axial force and too high spindle speed also lower the efficiency; (4) hole quality can be improved by using an prepress exerted device; (5) the ground surface of Al₂O₃ armor ceramic is composed of fractured area and ductile streak area which indicate that the material removal mode is contributed by both brittle fracture and ductile cutting, and the brittle fracture removal is dominant.     

微生物固定化吸附剂吸附Pd(II)的研究

微生物法在吸附处理重金属污染和回收贵金属方面具有广阔的发展前景。利用载体A固定化大肠杆菌开发了一种高效微生物固定化吸附剂,研究其对Pd(II)的吸附特性,构建其对Pd(II)的动态吸附模型,并开展了循环再生实验。结果表明,吸附柱的穿透时间和耗竭时间与大肠杆菌的浓度、微生物固定化吸附剂的填充量成正相关,与溶液流速成负相关;载体A:粘结剂:大肠杆菌的质量比为4:1:3,固定化吸附剂添加量为15 g、溶液流速3 mL/min时,吸附柱对Pd(II)有较好的吸附效率,穿透时间和耗竭时间分别为60 min和360 min;使用2 mol/L的HCl对负载Pd(II)后吸附剂进行解吸处理,解吸率达到99.32%;吸附-解吸循环5次后,固定化吸附剂对Pd(II)的吸附量基本保持不变。     

Mathematical Simulation on Oxidation of Ilmenite in Fluidized Bed

ＭａｔｈｅｍａｔｉｃａｌＳｉｍｕｌａｔｉｏｎｏｎＯｘｉｄａｔｉｏｎｏｆＩｌｍｅｎｉｔｅｉｎＦｌｕｉｄｉｚｅｄＢｅｄＳｕｎＫａｎｇ（孙康）（ＤｅｐａｒｔｍｅｎｔｏｆＮｏｎｆｅｒｒｏｕｓＭｅｔａｌｓ，ＮｏｒｔｈｅａｓｅｒｎＵｎｉｖｅｒｓｉｔｙ，Ｓｈｅｎｙ...     

Behavior of Ni‐base alloy 625 in methanol‐supercritical water systems

Methanol reacts with water under supercritical conditions to form a hydrogen rich gas. This reforming reaction can be performed without the addition of a catalyst. Typical reaction conditions are 25 MPa pressure and 600°C temperature and short residence times. The tubular flow reactor used was made of the nickel base alloy 625. The reactor was operated continuously for more than 1000 hours without problems. The feed concentration was 5 weight‐% methanol. The major component of the product gas was hydrogen (up to more than 70 vol‐%). Methanol conversion was higher than 99% and the liquid effluent was clear and free of soot. After exposure, the reactor has been sectioned and each section has been analyzed. No major corrosion phenomena were observed. Severe ductility loss of the material could be measured in the higher temperature section of the reactor.     

Loading effect at air plasma etching of fabric of polyethylene terephthalate fibers

The results of studying the loading effect at low temperature air plasma action on the surface of fabric of polyethylene terephthalate filament yarns are presented. Gravimetric and mass-spectrum techniques were used in this work. Gas evolution changes plasma properties and, as a consequence, the target process kinetics. Due to the mutual influence of heterogeneous and volumetric processes not only flows of active oxygen particles on the material surface reduce but also the correlations of these flows change. The NO molecule concentration is closely connected with the atom oxygen balance. Even when the fraction of the reactor surface occupied by the fabric is relatively low, the NO molecules’ concentration drops appreciably. For a wide interval of discharge parameters, the specific rates of etching, the oxygen absorption from the gas phase, the gaseous product formation, and the NO molecule concentration decrease extensively when the reactor load ratio is increased from 6% to 50%. The interconnected influence of the parameters and the loading is shown in the behavior of the reaction product formation. In the case of the load ratio rising, the correlation of the degradation channels changes to a channel with a yield of CO and H₂ stronger at higher initial gas pressure.     

ZX5—400晶闸管整流弧焊电源的改进

通过对美国林肯电气公司 Ｄ Ｃ－ ４００ 晶闸管整流弧焊电源的试验分析,找出了 Ｚ Ｘ５ － ４００ 晶闸管整流弧焊电源在采用高纤维素焊条进行小电流焊接中,产生断弧、熄弧粘条、电弧不稳定的原因,并对 Ｚ Ｘ５ － ４００ 晶闸管整流电源进行改进,使其不但适应采用高纤维素焊条进行的下向焊,而且也适应普通焊条的焊接。     

Precursor-based synthesis and electrochemical performance of LiMnPO4

Olivine-like LiMnPO₄ was prepared from the NH₄MnPO₄·H₂O precursor precipitated from the aqueous solution. Different morphologies of the LiMnPO₄ were obtained by the solid-state reaction of the precursor with LiOH (granular, 100–300 nm) and by ion-exchange reaction with eutectic mixture LiCl–LiNO₃ (flake-like crystallites up to 10 μm). The morphology and size distribution of the precursor NH₄MnPO₄·H₂O is preserved during ion-exchange, establishing a new preparation route for nanosized LiMnPO₄. After ball-milling with carbon black the granular material delivers 30% of the theoretical capacity at C/5. The rate capabilities of the obtained materials are compared with the results from sol–gel synthesis in the light of particle size effect.     

Solar Carboreduction of Alumina Under Vacuum

A preliminary study on carboreduction of alumina under vacuum, which was necessary before the solar reactor design, has been performed using an induction heater equipped with a graphite susceptor as the sample holder surrounded by a ceramic tube serving as the metal vapor deposit site. The primary objective was to study the forward and backward reactions as a function of temperature and CO partial pressure. It was concluded that at reaction temperatures above 1600°C and at an average CO partial pressure below 0.2 mbar, the amount of residual by-products in the graphite crucible was negligible, whereas tests with an average CO partial pressure of 2.6 mbar required temperatures above 1800°C to convert the stoichiometric reactants pellets fully. It was concluded that pure aluminum can be found only at deposit sites with temperatures below 600–700°C in tests with temperature and pressure suitable to prevent the volatile suboxide formation in the forward reaction. Based on these results, the solar reactor was designed with a sharp temperature drop from the hot to the cold area. The results of solar tests with different levels of CO partial pressure and temperature conditions reveal that the alumina to aluminum conversion is about 90% for reaction temperatures above the minimum temperature required for full conversion as predicted by the thermodynamic calculations at the appropriate pressure. However, at lower temperatures, a significant amount of solid Al₄C₃, Al₄CO₄, and volatile Al₂O can be formed in the forward reaction, leading to an increase of the residual by-product in the reactant holder as well as lower purity of the aluminum product and an increase of the alumina content in the deposits at the cold reactor’s zone. The observed nanocrystalline and amorphous morphology of the deposits caused by fast cooling in the cold zone will also be discussed.