Effects of Adhesive Composition on Green Joining of CePO4-ZrO2 Ceramics

Green bodies of 25% CePO4/ZrO2 and ZrO2 ceramics were joined at 1450℃ for 120 min without applied pressure by using mixed powders slurries composed of CePO4 and ZrO2. The effects of CePO4/( CePO4 ZrO2 ) ratio of the adhesive on the bond strength of the joints were investigated. Maximum bond strength of 414 MPa was obtained by joining an adhesive with the ratio of 0. 5 Under the experimental conditions, the grain size of the particles grown in the joint was smaller than that in joined ceramics. The microstructure of the joint was more homogeneous than that of the matrix and without obvious crack, pores and other defects.     

Synthesis and characterization of CePO4 nanorods via solvothermal process

One-dimensional cerium phosphate(CePO4) nanorods were successfully synthesized by a facile and simple solvothermal method at 150 ℃ for 12 h, using Ce(NO3)3·6H2O and NaH2PO4·2H2O as the starting materials. Phase and morphologie of the as-synthesized CePO4 products, characterized by XRD, FESEM, and TEM, were proved to be perfect and uniform hexagonal CePO4 nanorods with aspect ratio of more than 100. The photoluminescence(PL) spectrometer was used to investigate the optical properties of the assynthesized hexagonal CePO4 nanorods.     

Overcharge performance of LiMn2O4/graphite battery with large capacity

The LiMn₂O₄/graphite battery was fabricated and its 3 C/10 V overcharge performance was studied. Spinel LiMn₂O₄ was synthesized by solid-state method and 325680-type size full battery was fabricated. The structure and morphology of the powders were characterized by XRD and SEM technique, respectively. The battery explodes after 3 C/10 V overcharged test, and surface temperature of the battery case arrives at 290 °C in 12 s after exploding. Black air is given out with blast. Carbon, MnO, and Li₂CO₃ are observed in the exploded powders. The cathode electrode remains spinel structure with 5.0 V charged. Cracks in the cathode electrode particles are detected with the increase of voltage by SEM technique. The 5.0 V charged electrode can decompose into Mn₃O₄ at 400 °C. It is demonstrated that the decomposition of 5.0 V charged electrode can be promoted and Mn⁴⁺ can be deoxidized to Mn²⁺ by carbon and electrolyte through the simulation of blast process.     

Effects of Nitrogen Doping on Microstructure and Photocatalytic Activity of Nanocrystalline TiO2 Powders

Nitrogen-doped TiO2 nanocrystalline powders were prepared by hydrolysis of tetrachloride titanium （TiCl4） in a mixed solution of ethanol and ammonium nitrate （NH4NO3） at ambient temperature and atmosphere followed by calcination at 400 ℃ for 2 h in air. FTIR spectra demonstrate that amine group in original gel is eliminated by calcination, and the TiO2 powder is liable to absorb water onto its surface and into its capillary pore. XRD and SEM results show that the average size of nanocrystalline TiO2 particles is no more than 60 nm and with increasing the calcination temperature, the size of particles increases. XPS studies indicate the nitrogen atom enters into the TiO2 lattice and occupies the position of oxygen atom. The nitrogen doping not only depresses the grain growth of TiO2 particles, but also reduces the phase transformation temperature of anatase to futile. The photocatalytic activity of the nitrogen-doped TiO2 powders has been evaluated by experiments of photocatalytic degradation aqueous methylene blue.     

Characteristic grain size: Part I description and definition

Characteristic grain size, G _c, is defined in the present paper. It indicates an intrinsic size of grain for a given system, and has the following advantages over the average grain size which is based on a statistical mean value of the linear intercept length of grains: (1) The characteristic grain size G _c has clear and determined geometric meaning, i. e. G _c refers to two times of the area-weighted average height of the surface elements to the centroid of grain or the average length of the chord through the centroid of grain; (2) The value of G _c can be directly obtained without introducing any correcting factors such as grain shape or grain size distribution factors. Generally, G _c is larger than the average grain size G when the Heyn intercept method is adopted for the grain size measurement. Project supported by the British Council Academic Link Scheme Synopsis of the first author Cao Shunhua, lecturer, born in Jan. 1965, strong interest in the following research areas: ceramic composites, FGMs, prototype design of WC-Co alloys, and preparation of β-SiC and sialon powders.     

Effect of Heat Treatment on Crystallization of Nd:YAG Ceramics

(Nd0.01 Y0.99 )3 Al5 O12 nano-sized powders were synthesized by low temperature combustion (LCS),using Nd2 O3 ,Y2 O3 ,Al(NO3)3 ·9H 2 O,ammonia water and citric acid as starting materials.The powders were characterized by TG-DTA,XRD,FT-IR,ICP and TEM,respectively.The grain sizes were calculated by the Scherrer’s formula using the full width at half maximum(FWHM)of YAG(420)crystal plane diffraction lines. The study focused on crystallization of ceramics at different heat treatment temperatures.The experimental results show that crystallizing temperature of YAG is 850℃,and the intermediate crystal phase YAP,appearing during heat treatment,transforms to YAG cubic crystal phase at the temperature of 1 050℃.The particle size of the powders synthesized by LCS is nano-sized.With the temperature increasing,the mean grain sizes raise,the stand deviations keep almost at the value of 2.0 and the lattice parameters decrease.The grains mainly grow by grain boundary diffusion.The lattice parameter expansion is caused by an increase of the repulsive dipolar interactions on surfaces of crystallites.     

Preparation and Characterization of Pb（Zr0.52Ti0.48）03 Ultrafine Powders by a Sol-gel Combined with Combustion Process

A simple and rapid process for synthesizing lead zirconate titanate,Pb（Zr0.52Ti0.48）O3（PZT）,ferroclectric powders was developed.This process,combining the sol-gel and combustion process.offers several advantages over conventional methods.including rapid solution synthesis,use of commercially available materials lower synthesis temperature and ease of obtaining ultrafine powders.The precursor solution for synthesizing powders was prepared from lead nitrate.zireonium nitrate.titanium oxynitrate,citric acid and deionized water.The precarsor was investigated by DSC-TG,and the PZT powders were investigated by powder-XRD,IR spectra and TEM.XRD analysis shous that the powders possess a single phase perovskite type structure,no pyrochlore phase exists.and TEM image shows that the grain size of the powders is about 40nm.     

XRD and HRTEM Analyses of the Ball Milled Nanocrystalline FeCo Alloy

The nanostractures of the ball milled FeCo particles were characterized as functions of the ball milling time （ t ） using quantitative X- ray diffraction （ XRD ）, high resolution transmission electron microscopy （HRTEM） analysis techniques. The results show that the nanocrystalliue bcc FeCo particles are available using carbonyl iron and cobalt powders as the start materials during the high-energy ball milling. At the early stage of ball milling, Co powders are easily mashed into nanocrystalllites, by which the surface of the larger Fe particles of about 80- 150 nm is coated. With t increasing, the refinement of grain size and the incorporation of defects including dislocations, disclinations and grain boundaries happen, and then FeCo alloy with a certain layered structure is formed, finally the layered stractare disappears with the formation of isotropic grains having a steadystate grain size in the nanometer regime after a certain period of t.     

Grain growth kinetics of SnO<Subscript>2</Subscript> nanocrystals synthesized by precipitation method

Monodispersed spheroidal SnO₂ nanocrystals with the grain size of 8–30 nm were synthesized by the precipitation method using SnCl₄·5H₂O (stannic chloride hydrate) as raw materials. Differential scanning calorimetry/thermogravimetry (DSC/TG), X-ray diffraction (XRD) and transmission electron microscope (TEM) were used to characterize the structure of SnO₂ nanocrystals. The influences of the calcination temperature and time on the lattice constant, the lattice distortion and the grain size of SnO₂ nanocrystals were discussed based on the XRD results. The grain growth kinetics of SnO₂ nanocrystals during calcination process was simulated with a conventional grain growth model which only took into account of diffusion and with a new isothermal model proposed by our group, which took into account of both diffusion and surface reactions. Using conventional model, the grain growth rate constant of SnO₂ crystals is 1.55×10⁴ nm⁵/min with a pre-exponential factor of 5 and an activation energy of 108.62 kJ/mol. Compared with the convention model, the new isothermal model is more realistic in reflecting the grain growth behavior of SnO₂ nanocrystals during the calcination process. This indicates that the grain growth of SnO₂ nanocrystals is controlled by both diffusion and reaction factors, and the effect of surface reactivity on the grain growth of SnO₂ nanocrystals could not be ignored. A combined activation energy estimated with the new isothermal model is 53.46 kJ/mol.     

Low-temperature Rapid Synthesis of Ultrafine Hafnium Carbide Ceramic Powders

Nano hafnium carbide(HfC) powders were synthesized by sol-gel combining hightemperature rapid heat treatment process using citric acid and hafnium tetrachloride as the raw materials. The effects of ball milling treatment on the phase and morphology of pyrolysis products(HfO_2-C) and final HfC product were investigated and the influences of heat treatment temperature and holding time on the structure and properties of the synthesized hafnium carbide powders were also studied. The experimental results showed that the HfO_2-C powders with good uniformity and small particle size were prepared by controlling the milling time. Pure HfC powders with an average particle size of 500 nm were obtained at 1 700 ℃ with a holding time of 3 min, and the oxygen content was about 0.69 wt%, lower than that of the hafnium carbide powders prepared by SPS(0.97%).     

Characteristic grain size: Part II measuring principles

The principles for measuring characteristic grain sizes of materials, such as fully-dense single phase materials, porous materials and materials with isolated second phase particles, are developed on the basis of its definition associated closely with the surface area per unit volume, Sv, of grain. The focus of the measuring principles of the characteristic grain size is put on determining Sv of grains. Unlike the measurement of average grain size commonly used, G, correcting factors such as grain shape and grain size distribution factors, will not be applied to the determination of the characteristic grain size, G _c, due to its unique geometric meaning and the measure precision of S _v being guaranteed by quantitative stereological technique and gas adsorption method. The measurement of G _c can be directly carried out on the polished and etched cross section of materials, similar to the measurement of the average grain size using the Heyn intercept method. Project supported by the British Council Academic Link Scheme Synopsis of the first author Cao Shunhua, lecturer, born in Jan. 1965, strong interest in the following research areas: warm compaction, FGMs, prototype design of WC-Co alloys, preparation of β-SiC and sialon powders.     

基于LBM-DEM耦合计算模型的含水层内悬浮颗粒运动特性

基于格子Boltzmann法(LBM)与离散单元法(DEM)的基本理论,通过对格子单松弛模型演化方程进行修正,建立LBM-DEM耦合计算模型。引入浸没移动边界方法(IMB),利用MATLAB开发LBM-IMB-DEM耦合求解程序,对悬浮颗粒在含水介质中的运动过程进行模拟计算。通过开展层析柱强制渗流试验,验证计算模型与求解方法的正确性,从孔隙尺度分析地下水动力、颗粒形貌和尺寸效应对含水层渗透性能的影响。结果表明,进口流速为5×10_^-5m/s时,含水层各区域的渗流速度均呈现下降、回升、稳定的三个连续阶段。将悬浮颗粒由球形硅微粉替换为非球形硅微粉后,各断面的平均流速最大降幅升高,恢复率降低。基于颗粒受力平衡分析,由于球形硅微粉转动惯量较低,易于脱离含水介质表面;非球形硅微粉多絮凝成团,迁移过程中出现沉积或被孔喉捕获的机率提高,并且沉积后难以发生再释放过程。随着渗流速度的降低与含水介质计算区域的增加,悬浮颗粒形貌的变化对于含水层水动力场演化过程的影响程度增强。     

Synthesis and characterization of Li1.05Co0.3Ni0.35Mn0.3M0.05O2 (M=Ge,Sn)cathode materials for lithium ion battery

In order to improve the electrochemical performance and thermal stability of Li_1.05Co_1/3Ni_1/3Mn_1/3O₂ materials,Li_1.05Co_0.3Ni_0.35Mn_0.3M_0.05O₂（M=Ge,Sn）cathode materials were synthesized via co-precipitation method.The structure,electrochemical performance and thermal stability were characterized by X-ray diffraction（XRD）,charge/discharge cycling,cyclic voltammetry（CV）,electrochemical impedance spectroscopy（EIS）and differential scanning calorimetry（DSC）.ESEM showed that Sn-doped and Ge-doped slightly increased the size of grains.XRD and CV showed that Sn-doped and Ge-doped powders were homogeneous and had the better layered structure than the bare one.Sn-doped and Ge-doped improved high rate discharge capacity and cycle-life performance.The reason of the better cycling performance of the doped one was the increasing of lithium-ion diffusion rate and charge transfer rate.Sn-doped and Ge-doped also improved the mateials thermal stability.     

Microstructures and properties of WC-2OCo-1Y2O3 cemented carbide by hot-press and liquid phase sintering

Ultrafine tungsten carbide and fine cobalt as well as nano yttrium oxide powders were used as the raw materials. The effects of hot-press below the eutectic temperature and conventional liquid phase sintering on the structures and properties of WC-20Co-1Y2O3 cemented carbide were studied. It is shown that hot-pressed alloy has the character of isotropic properties and microstructure with homogeneous and ultrafine WC grains. However, the ultrafine and fully-densified structure is developed at the cost of the presence of large amount of cobalt-lake (uneven-ly distributed binder phase), and thus lower strength. Yttrium oxide in the alloy cannot play the role of grain growth inhibitor fully when cemented carbide with high content of cobalt and ultrafine raw materials is sintered at high liquid phase sintering temperature. Peculiar platelet-enhanced bi-model structure is formed in WC-20Co-1Y2 O3 cemented carbide by conventional liquid phase sintering, which points out that yttrium oxide in the alloy facilitates the formation of plate-like WC grain.     

Fabrication and microstructure of C<Subscript>a</Subscript>TiO<Subscript>3</Subscript> coating by laser cladding

In order to explore the way to improve the adhesion of the calcium phosphate bioceramic coating to Ti substrate, the CaTiO3 coating was fabricated on Ti substrate by laser cladding (LC) using powders of CaCO3 and CaHPO4, and then the composition and microstructure of the coatings were investigated. During LC, CaCO3 can hardly react with Ti, and the coating fabricated using CaCO3 powder is mainly composed of the process of CaO, the decomposition product of CaCO3. Moreover, the coating has a loosened structure and part of it has peeled off from the substrate. CaHPO4 reacts vigorously with Ti, and the coating fabricated using CaHPO4 mainly consists of CaTiO3 which is one of the reaction products between Ti and CaHPO4. Chemical bonding is formed at the interface between coating and substrate, which may enhance the adhesion of the CaTiO3 coating to Ti substrate. Furthermore, CaTiO3 dendrite and eutectic of CaTiO3 and Ca2P2O7 are found on the surface of the coating, implying that a transition can be formed between CaTiO3 and some calcium phosphate bioceramic. So CaTiO3 coating fabricated using CaHPO4 can be a potential candidate to improve the adhesion between calcium phosphate coating and Ti substrate. However, there are also pores and cracks existing in the coating, which may degrade the mechanical properties of the coating.     

Coprecipitation preparation and voltage sensitive characteristics of doped ZnO varistor

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Solvothermal preparation and characteristics of Sn-doped In2O3

Sn-doped In2O3 （ITO） nanopowders were prepared in ethanol solvent by solvothermal process. The effects of the solvothermal temperature, coprecipitation pH value and SnO2 content on the products phase and microwave absorption were investigated by X-ray diffractometry and microwave reflectance. ITO nanopowders with cubic structure can be respectively prepared at 250 and 270 ℃ for 6 h. The prepared product is InOOH or the mixture of InOOH and In3Sn4O12 when the solvothermal temperature is below 250℃. With rising solvothermal temperature and prolonging time, the absorption of the ITO powders gradually decreases. The products are ITO nanopowders by coprecipitating at pH=9 or 11, but ITO powders with Sn3O4 at pH=6. The absorption of powders prepared at pH=6 is better than that at any other pH value. The products are all ITO nanopowders and crystal size reduces with increasing SnO2 content. The microwave absorption of ITO nanopowders with SnO2 content of 8% （mass fraction） is the best among samples with different SnO2 contents.     

煅烧温度对Ca1-xPrxMnO3粉体结构与导电性能的影响

为改善CaMnO₃粉体的导电性能,采用溶胶-凝胶自蔓延法在不同温度下合成Ca1-xPr_xMnO₃(0≤x≤0.3)粉体,并研究煅烧温度对Ca1-xPr_xMnO₃粉体结构及导电性能的影响．结果表明,随着煅烧温度的升高,电阻率呈现先降低后升高的变化趋势,且在1 000 ℃时电阻率最低．XRD分析结果表明,Ca1-xPr_xMnO₃粉体的特征衍射峰均向小角度方向偏移,且强度随着煅烧温度的升高而增强．XRD计算结果表明,Ca1-xPr_xMnO₃粉体的晶胞参数受烧结温度影响,是导致电阻率变化的原因之一,煅烧温度为1 000 ℃时,粉体的晶格畸变程度相对较大．SEM分析结果表明,Ca0.75Pr0.25MnO₃粉体的晶粒尺寸随温度的升高不断增大,合适的粒度有利于粉体电阻率的降低．在煅烧温度为1 000 ℃的Ca1-xPr_xMnO₃粉体中Mn的平均价态最低．晶界效应、粒度和Mn的价态3个因素共同作用导致了Ca1-xPr_xMnO₃粉体的电阻率随温度升高而呈现先减小后增大的变化趋势．     

Effect of Grain Size of CaCO3 and SiO2 on the Formation of C3S Under Different Conditions

The effect of grain size of CaCO3 and SiO2 on the formation of C3S under various conditions, such as rapid heating rate（800 ℃/min）, normal heating rate（30 ℃/min） and in the presence or absence of ZnO, was studied. The results show that the decomposition temperature of CaCO3, the temperature of appearance of liquid phase and the f-CaO content descend when the grain size of CaCO3 and SiO2 becomes smaller, which attributes to the reactive activity enhancement of powders due to the decrease of the particle size. When the grain size of CaCO3 and SiO2 is below 1 μm, the rate of the formation of C3S is greatly raised. A rapid sintering rate and the presence of ZnO have an important effect on the formation of C3S and can lower the temperature of the formation of C3S by about 50 ℃.     

Synthesis and characterization of bismuth-doped tin dioxide nanometer powders

Bismuth-doped tin dioxide nanometer powders were prepared by co-precipitation method using SnCl4 and Bi（NO3）3 as raw materials. The effects of calcining temperature and doping ratio on the particle size, composition, spectrum selectivity of bismuth-doped tin dioxide and the phase transition of Bi-Sn precursor at different temperatures were studied by means of X-ray diffraction, transmission electron microscopy, ultraviolet-visual-near infrared diffuse reflection spectrum and the thermogravimetric-differential scanning calorimetry. The results show that prepared bismuth-doped tin dioxide powders have excellent characteristics with a single-phase tetragonal structure, good dispersibility, good absorbency for ultraviolet ray and average particle size less than 10 nm. The optimum conditions for preparing bismuth-doped tin dioxide nanometer powders are as follows： calcining temperature of 600℃, ratio of bismuth-doped in a range of 0. 10 - 0.30, and Bi-Sn precursor being dispersed by ultrasonic wave and refluxed azeotropic and distillated with mixture of n-butanol and benzene. The mechanism of phase transition of Bi-Sn precursor is that Bi^3＋ enters Sn-vacancy and then forms Sn-O-Bi bond.