BaTiO3纳米粉体的制备和性能

采用溶胶-凝胶和溶胶-沉淀的方法合成了立方相纳米BaTiO3粉体．溶胶-凝胶法制备的粉体平均粒径为19nm，颗粒分布均匀、含少量BaCO3．溶胶-沉淀法得到了纯BaTiO3粉，平均粒径为42nm，存在部分团聚．两种方法相比，溶胶-凝胶法的粉体烧结密度较高，介电性能较好．讨论了两种合成方法的晶粒形成机理及对材料微观结构和介电性能的影响．     

PPy/BaTiO3纳米复合吸波材料的制备及性能研究

采用溶胶-凝胶法(Sol-gel)制备了钛酸钡纳米粉体,借助XRD、FT-IR、SEM及矢量网络分析仪等分析测试手段对试样晶相、颗粒粒径、表面形貌及吸波特性进行了研究。研究结果表明:BaTiO3粉体最佳的煅烧温度为900℃,BaTiO3颗粒大小均匀,呈单一晶相的四方型,粒径在40~70nm;PPy/BaTiO3复合材料呈现均匀的球形形状,且聚吡咯(PPy)在BaTiO3颗粒的表面包覆较好;PPy/BaTiO3复合材料的吸波特性,回损达到-17dB,其中小于-5dB频率范围为3200~5200 MHz,频宽达到了2000 MHz,具有较好的吸波性能。     

低温煅烧溶胶-凝胶法制备BaTiO3基纳米粉体

实验着重研究了凝胶煅烧工艺制度对通过柠檬酸盐溶胶-凝胶法制备复合掺杂的BaTiO3基粉体,制备纳米粉体的影响.最终确定了600℃为最佳煅烧温度,在此低温下煅烧干凝胶,并保温1h,再经二次掺杂混磨得到了晶粒细小、分散性好、低团聚的BaTiO3基纳米粉体.     

溶胶-凝胶法低温合成BaTiO3基纳米粉体

通过柠檬酸盐溶胶-凝胶法制备复合掺杂的BaTiO3基粉体,着重研究了凝胶煅烧工艺制度对制备纳米粉体的影响。最终确定了600℃为最佳煅烧温度,在此低温下煅烧干凝胶,并保温1h,再经二次掺杂混磨得到了晶粒20～70nm、分散性好的BaTiO3基纳米粉体。     

纳米BaTiO3的制备及其负载Ni基催化剂的应用研究

采用溶胶-凝胶法制备了纳米BaTiO3,用纳米BaTiO3粉体作载体通过浸渍法制备出Ni/BaTiO3催化剂,并将其用于CO2重整CH4制合成气反应.纳米BaTiO3粉体粒径为25～60nm,颗粒外貌近似球形,其最佳制备条件为水解用水量10mL,混合溶液pH=4～5,凝胶化温度343K,973K下煅烧处理.在反应温度为1073K,空速12000mL/(h.g.cat)下,Ni/BaTiO3催化剂可使重整反应的CH4和CO2转化率分别达到94.4%和93.3%.     

基于溶胶-凝胶法制备BaTiO3基PTCR纳米陶瓷粉体研究

以溶胶-凝胶法制备了BaTiO3基PTCR纳米陶瓷粉体，通过适当控制材料的掺杂量和烧成制度达到细化晶粒、降低烧结温度及降低室温率的目的。讨论了溶胶．凝胶过程中水的加入量、乙酸加入量、乙醇加入量、成胶温度对形成细晶粉体的影响，制备出的BaTiO3粉体具有纯度高、粒径小、均匀性好、活性高、热处理温度低等优点。R-T丁曲线表明1260℃较1240℃烧结具有高的升阻比、温度系数，低的电阻率、居里温度：XRD分析表明所得粉体与BaTiO3主峰相吻合；800℃预烧2h所得BaTiO3粉体的TEM图表明粉体分布较均匀、外形为近似球形，其平均晶粒尺寸约30nm左右，与XRD得到的晶粒相当，单个颗粒是单晶；1240℃下烧结所得样品的SEM图片看出样品的平均晶粒约1～2μm、晶粒较为均匀致密。     

熔融盐法制备BaTiO_3粉体及Rietveld全谱拟合物相表征

通过熔融盐法以BaC2O4、TiO2为前驱体,NaCl为熔盐制备了BaTiO3粉体。SEM分析所得样品为立方状颗粒,粒径为50～300nm。采用Rietveld全谱拟合法对其物相组成进行了分析,并通过变温XRD对BaTiO3相变进行了表征。Rietveld全谱拟合结果表明,该方法制备的BaTiO3粉体在室温下是一种四方、立方混合相,质量分数分别为73.9%、26.1%。精修结果的数值判据分别为:加权剩余方差因子Rwp=5.93%、剩余方差因子Rp=4.78%、拟合优值S(Goodnessoffit)=1.53。变温XRD研究表明所制备的BaTiO3粉体具有四方到立方相的相变。     

溶胶-凝胶法在纳米粉体制备中的应用

溶胶-凝胶法是制备纳米粉体的一种低温工艺,具有制品纯度高、化学均匀性好、颗粒细、可容纳不容性组分和不沉淀组分、掺杂分布均匀、合成温度低、成分容易控制、工艺设备简单等优点。本文介绍了溶胶-凝胶法的概念、工艺原理及其在TiO2、ZrO2、BaTiO3、Al2O3等纳米粉体制备方面的应用,提出了溶胶-凝胶法制备纳米粉体的局限性及发展方向。     

利用无机盐制备γ-Al2O3粉体与薄膜的工艺技术研究

发明了γ-A12O3基陶瓷气敏传感器材料体系,并正研究其薄膜型传感器件.本文以廉价的无机盐Al(NO3)3·9H2O为原料,通过溶胶-凝胶法制备了勃姆石(γ-A1OOH)溶胶,然后经干燥、煅烧制备了γ-Al2O3的粉体,并通过旋转涂覆工艺制备了γ-A12O3的薄膜,应用X射线衍射(XRD)、X射线光电子能谱(XPS)、原子力显微镜(AFM)等现代分析技术对粉体的物相和薄膜的组分及表面形貌进行了表征,对γ-A1OOH溶胶制备过程中的一些影响因素进行了探讨,得出了比较好的制备γ-Al2O3基陶瓷粉体和薄膜型气敏传感器的工艺技术条件.     

溶胶凝胶法制备超细负热膨胀性ZrW2O8粉体

以溶胶凝胶法制备负热膨胀材料ZrW2O8粉体并与固相法制备的粉体相比较.对其前驱体进行热重-差热分析(TG-DSC)、以X射线粉末衍射(XRD)、透射电镜(TEM)、扫描电子显微镜(SEM)分别对粉体进行物相分析和形貌观测.结果表明溶胶凝胶法比固相法合成温度低,于610℃合成单一立方结构ZrW2O8粉体,并且粉体颗粒比固相法小,为100nm;ZrW2O8粉体有很好的负热膨胀特性,以高温X射线衍射分析,在室温约500℃范围内,溶胶凝胶法制备的粉体的热膨胀系数为-5.93×10-6/K;比固相法(-6.31×10-6/K)的略低.     

Use of coupling agents as a route to improvement of the compressibility of fine zirconia and alumina powders

In order to improve the compressibility of fine zirconia and alumina powders, powders were surface-treated with aluminate, silane and titanate coupling agents. The surface modification reduced both powder/powder friction and powder/die-wall friction, which increased the density of the compacts. At 2% additions, the effectiveness of the coupling agents on density increase was in the order, silane > titanate > aluminate. In zirconia systems with different titanate concentrations it was found the optimum amount of coupling agent could be approximated by the amount required for monolayer coverage on the powder surface.     

Properties of barium titanate powders in relation to the heat treatment of the barium titanyl oxalate precursor

Barium titanate powders have been prepared by calcining barium titanyl oxalate precipitated by the Clabaugh and Merker processes, and their crystallization kinetics, morphology, and phase composition have been assessed. The results demonstrate that the Clabaugh process allows one to obtain powders with a low content of residual phases and tune the grain size (68–1935 nm) and crystal structure of barium titanate in wide ranges. The powders prepared through the Merker process have a narrower range of crystallite sizes (110–740 nm) and higher content of residual phases.     

Preparation and characterisation of ultrafine lead titanate (PbTiO3) powders

Ultrafine lead titanate (PbTiO₃) powders in tetragonal form have been successfully prepared via three processing routes, namely, conventional co-precipitation, microemulsion-refined freeze drying, and microemulsion-refined co-precipitation. The formation process of lead titanate from the resulting precursors was monitored using techniques such as thermal analyses and X-ray diffraction for phase identification. It was found that the two microemulsion-refined processing routes led to a lower formation temperature for lead titanate than that observed in the conventional co-precipitation route. The three lead titanate powders have also been compared for particle and agglomerate size distributions and specific surface area. It appears that the microemulsion-refined co-precipitation is the technique which results in the formation of the finest lead titanate powder amongst the three processing routes investigated in the present work. This revised version was published online in September 2006 with corrections to the Cover Date.     

Effect of Ultrasonic Processing on the Synthesis of Barium Titanyl Oxalate and the Characteristics of the BaTiO<Subscript>3</Subscript> Powder Prepared from It

Barium titanyl oxalate (BTO) with small deviations from stoichiometry has been synthesized by a chemical and a sonochemical method (under ultrasonication). Ultrasonic processing has been shown to reduce the particle size of the resultant BTO powder by about ten times and ensure a nearly spherical shape of the particles. The morphology of barium titanate powders prepared by decomposing the BTO at a temperature of 900°C is similar to that of the parent BTO and independent of stoichiometry. The powders have a barium to titanium ratio Ba/Ti = 1.002 and 0.987. The barium titanate powders synthesized using the sonochemical method contain a smaller amount of residual phases and have a larger specific surface area, smaller crystallite size (~100 nm), and smaller unit-cell parameters than do the powders prepared without ultrasonication.     

The effect of high energy mechanochemical processing on the microstructure, piezoelectric, ferroelectric and mechanical properties of PLZT ceramics

Lead lanthanum zirconate titanate (PLZT) ceramics were synthesized using a high energy mechanochemical processing technique, using tungsten carbide grinding vials and balls. The ceramic powders were prepared using the constituent oxide powders, which were subjected to high energy milling, without the use of any excess PbO in the starting composition. TEM studies revealed the formation of very fine particles of the order of 30?nm, due to the milling effect. Highly dense ceramics could be prepared via sintering which resulted in ultra-high strains in these piezoelectric samples of up to 0.25%, a value which has not been reported hitherto by any other known process. The effect of the reduction in particle size on the microstructure, mechanical and electrical properties of PLZT ceramics were studied and are discussed herein.     

莫来石溶胶的制备及对钛酸铝粉体的包裹

以硝酸铝和正硅酸乙酯为主要原料制备稳定莫来石溶胶, 用浸渍包膜的工艺方法对钛酸铝(Al₂TiO₅, AT) 粉体进行包裹, 研究了溶胶性能及含量对钛酸铝粉体包裹效果及性能改善的影响。结果表明: 溶胶的浓度为0.18~0.30mol/L、 黏度在56~93mPa · s之间、 pH=3.0、 包膜厚为0.15~0.20μm时, 可得到包裹效果良好的莫来石-钛酸铝粉体, 制备出性能优良的莫来石-钛酸铝复合材料。复合材料的抗折强度为36~50MPa, 为钛酸铝材料强度的10~15倍, 复合材料的热膨胀系数为1.89~2.25×10-6/℃(室温至1000℃), 复合材料中的钛酸铝在1100℃/300h的热处理未发生分解。应用TG-DSC、 XRD、 SEM、 EPMA等对包膜前后莫来石粉体和复合材料粉体的热学行为、 形貌和成分进行研究, 探讨了性能与结构之间的关系。      

Investigations on surface composition and microstructure of sintered barium titanate

The paper describes studies on surface atomic composition, microstructure and microarea elemental distribution in sintered undoped as well as donor or acceptor doped polycrystalline barium titanate ceramics. The specimens examined are derived from barium titanate powders synthesized by two different wet chemical procedures namely oxalate precursor route and gel-to-crystallite conversion. The compositional analysis is carried out by backscattering spectrometry (BS) involving 3.05 MeV ¹⁶O(α,α)¹⁶O resonant scattering while investigations on microstructure and microarea elemental distribution are performed using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), respectively. The specimens prepared by either method are monophasic; however, their surface atomic composition, microstructural features as well as electrical characteristics are significantly different. The specimens obtained by oxalate precursor route generally have Ti rich surfaces and exhibit coarse to fine grained microstructure depending on the nature and extent of doping. The Mn-doped specimens exhibit appreciable O deficiency. The specimens prepared by gel to crystallite conversion, in contrast, usually have Ba enriched surfaces and exhibit fine-grained microstructure. EDS measurements show the segregation of acceptors such as Mn, Cu and Zn in the grain boundaries of oxalate precursor derived ceramics. Further, the relative atomic ratio of Ti to Ba at the sites of segregations is higher compared to other locations.     

Role of particle size of alumina on the formation of aluminium titanate as well as on sintering and microstructure development in sol–gel alumina–aluminium titanate composites

With a view to develop low temperature fine grained alumina–aluminium titanate composite, influence of alumina particle size on the temperature of formation of the aluminium titanate, sintering behaviour and microstructure development of alumina–aluminium titanate composite prepared through a sol–gel core shell approach is reported. The alumina matrix composite containing 20 wt% aluminium titanate has been prepared from alumina powders having different average particle size in the range 300–600 nm. The alumina particle size appears to have no significant influence on the formation temperature of in situ formed aluminium titanate. However, the microstructural analysis of the dense ceramic showed that the average grain size of the alumina–aluminium titanate composite increases with increase in the alumina particle size. XRD analysis indicated the absence of rutile titania in the sintered composite ensuring complete formation of aluminium titanate. Smaller starting alumina particle size led to finer grain size composites. The present study therefore shows that although the starting particle size of alumina has no significant role on the lowering of formation temperature of aluminium titanate, it does influence the microstructure of the composite.     

Synthesis and sintering of barium titanate fine powders by ultrasonic spray pyrolysis

Crystalline, spherical barium titanate fine powders with a narrow particle size distribution were prepared by ultrasonic spray pyrolysis. The stability of the starting solution was influenced by type of barium source and peptizer. The particle structure was influenced by the pyrolysis temperature of the barium source. The particle structure derived from barium acetate was dense, while powders derived from barium nitrate involved a lot of hollow particles. As-prepared powders were crystallized to a perovskite structure. Inductively coupled plasma analysis showed that the BaO/TiO₂ molar ratio of as-prepared powders was 50.5:49.5. The effects of the concentration of the starting fluid, pyrolysis temperature and flow rate of carrier air through the furnace on powder characteristics such as particle size, size distribution and crystal phase were investigated. The particle size depended on the concentration of starting solution and the flow rate of carrier air, but the particle size distribution was independent of these variables. Single-phase BaTiO₃ was obtained at more than 700°C. The relative density of barium titanate sintered at 1200°C was 98%. The hollow particles in the powders resulted in a low sintering density and a large grain size. The dielectric constant and tan δ of barium titanate at 25°C were 4500 and 0.02, respectively.     

Synthesis of barium titanate nanopowder by a soft chemical process

A simple soft chemical method of synthesizing barium titanate nanopowders and nanorods is described here, where titanium dioxide/titanium isopropoxide was taken as a source of titanium, tartaric acid was taken as a template material, nitric acid as an oxidizing agent. The synthesized powders and rods were characterized by XRD, TG and DTA, SEM and IR spectroscopy. In this process phase pure barium titanate nanopowders and nanorods can be prepared at a temperature of 900 °C and the process is simple and cost-effective.