球磨石用量对钛酸钡介电性能的影响

通过改变料球水的比例以及采用沉降测试、水煮损耗测试、温度特性、电导率和化学分析等测试手段，研究了在制备钛酸钡的球磨工艺中球磨石的用量对钛酸钡粉体均匀性及钛酸钡介电性能的影响。研究结果表明，采用不同的料球水比例制得的电容器性能差别很大，当球：料：水=0．5：1：1时制得的钛酸钡性能最好。     

球磨工艺对钛酸钡陶瓷介电性能的影响

研究了固相法合成BaTjO3粉体时,在滚筒磨和搅拌磨中球磨BaCO3和TiO2粉体过程中,浆料的粒度、凝聚程度与球磨时间、筒容积的关系,分析了粉体均匀性对BaTiO3、陶瓷介电性能的影响.研究结果表明:TiO2粉体在球磨过程中,粒度大小没有显著变化,导致粉体凝聚的主要原因是BaCO3粉体;应先球磨BaCO3粉体10小时后再加入TjO2粉体继续球磨2小时所得的物料颗粒要比钡钛一起球磨所得的颗粒均匀,合成BaTiO3均匀性好;采用搅拌磨时,制备的BaTiO3陶瓷介电性能优于滚筒磨.     

高能球磨时间对MgNb2O6陶瓷显微结构和微波介电性能的影响

采用高能球磨法制备粉体,研究了粉体球磨时间对MgNb2O6陶瓷显微结构和微波介电性能的影响,结果表明,1180℃烧结陶瓷,随球磨时间增加,平均粒径减小,气孔率降低,相对密度增大,介电常数增大;升高烧结温度到1220℃以上,不同球磨时间制备陶瓷样品相对密度达到95.8％以上,平均晶粒尺寸3.5m,εr为19.7,而Qxf值随球磨时间先增大后减小.高能球磨制备粉体能有效促进MgNb2O6陶瓷在1220℃下中温烧结,且具有优良的微波介电性能(εr=19.7,Q×f=28 744 GHz),有望成为新一代中温烧结高频微波介质基板材料.     

聚酰亚胺/纳米钛酸钡复合薄膜的制备与表征

制备了一系列聚酰亚胺及其钛酸钡复合薄膜,并采用了XRD,IR等分析手段分析了复合薄膜的形貌和性能。主要研究内容如下:(1)采用水热法制备钛酸钡粉体;（2）分别用溶液混合法和原位聚合法制备PI/BT纳米复合薄膜。经分析可知,复合膜中钛酸钡粒子较为均匀地分散在聚酰亚胺基体中,并且复合膜的介电性能随钛酸钡粒子含量的增加而增加。在33%（钛酸钡的质量分数）1KHz频率时,制备的复合薄膜介电常数可达35,使其具有广泛的应用前景。     

粉体的球磨方式对Li1.0Nb0.6Ti0.5O3锂铌钛陶瓷烧结行为及微波介电性能的影响

通过X射线衍射、扫描电镜等分析手段结合介电性能测试结果,探讨了不同球磨方式(普通球磨及砂磨)制备的粉体对Li1.0Nb0.6Ti0.5O3(LNT)锂铌钛陶瓷的烧结行为、微观结构及微波介电性能的影响.用砂磨的方式粉碎粉体,获得了粒度分布均匀且分散性很好的粉体,在一定程度上降低了LNT陶瓷的烧结温度.另外,通过砂磨粉碎的粉体烧结而得到的陶瓷样品密度、相对介电常数(ετ)及机械品质因数与谐振频率的乘积(Q×f均高于普通球磨工艺制备的.结果表明:在1050℃烧结的陶瓷其具有相对优异的微波介电性能,ετ=9.9,Q×f=5 887 GHz,谐振频率温度系数τf=28.3×10-6/℃.     

纳米钛酸钡的掺杂对陶瓷性能的影响

采用掺杂纳米级钛酸钡和碳酸锰的方法,观察了掺杂不同量纳米级钛酸钡和碳酸锰后的钛酸钡坯片烧结所得陶瓷表面的显微组织形貌的变化,研究了单一掺杂纳米级钛酸钡、单一掺杂碳酸锰、复合掺杂碳酸锰+纳米级钛酸钡对陶瓷制品晶粒尺寸与介电性能的影响。结果表明：掺杂纳米级钛酸钡对钛酸钡陶瓷制品的介电性能有显著的提升,但是随着掺杂量的进一步增加,其介电性能的变化不大;掺杂碳酸锰对钛酸钡陶瓷晶粒的细化效果优于掺杂纳米级钛酸钡的效果;复合掺杂1%（质量分数,下同）碳酸锰+1%纳米级钛酸钡所得陶瓷的致密性高于单一掺杂1%碳酸锰的效果。     

粉体粒度对BaTiO_3陶瓷结构与电性能的影响

以采用共沉淀法制备的钛酸钡(BaTiO3)粉体为原料制备陶瓷。并利用XRD、DSC、SEM等分析手段对陶瓷材料的物相、相转变、显微结构进行表征,和利用电容测量仪、粒度分析仪等对陶瓷材料的电性能及粉体的粒度进行测试。研究了粒度对BaTiO3陶瓷微观结构和介电性能的影响。结果表明:随着预烧温度的提高,粉体的粒度增大,其陶瓷烧成温度也相应提高,并获得了优良的介温性能,粉体粒径为360nm的BaTiO3粉体经1290℃烧结后居里峰介电常数达到8119。     

新型碳-钛酸钡复合陶瓷膜的制备及介电性能研究

钛酸钡基陶瓷薄膜电容器以其高能量密度成为新能源领域独立动力电源和大容量储能电源的重要研究对象。本论文介绍了采用石墨纸作为电极材料、钛酸钡陶瓷作为介电材料制备陶瓷薄膜电容器的工艺,并利用石墨纸在高温环境下的渗碳来提高钛酸钡层的介电性能的方法,并研究了脱碳处理对复合材料介电性能的影响规律。制备了具有微观结构理想、介电性能优异的碳-钛酸钡复合陶瓷膜。结果表明陶瓷的晶粒大小为1μm左右,介电常数在100Hz 10V测试条件下达到3.9×105。     

退火温度对BaTiO_3薄膜的结构和介电性能的影响

采用溶胶-凝胶法制备Si（100）基片上的BaTi03陶瓷薄膜,并用红外光谱（IR）、x射线衍射（XRD）、扫描探针（SPM）等技术分析了钛酸钡凝胶的热解过程,以及不同退火温度下薄膜的晶粒、晶相、表面形貌、介电性能等指标。实验结果表明：高温有利于钛酸钡由立方相向四方相的转化;温度升高到1023K时,钛酸钡薄膜的表面形貌平整、均匀并具有良好的介电性能。     

球磨时间对ZnO压敏瓷电性能的影响

粉体是ZnO压敏瓷制备的起点,粉料的混合性直接影响其综合电性能。采用不同球磨球磨时间制备氧化锌压敏瓷粉体,通过扫描电镜和x射线衍射分析,探讨球磨时间对氧化锌压敏瓷电性能和微观组织的影响。研究结果表明,球磨5h制备的粉体烧结后综合电性能最好,其电位梯度为356V／mm;非线性系数为36．4,漏电流为1．38μA,致密度98．6％。     

原材料和制备工艺对硅酸锌陶瓷微波介电性能的影响

为了提高硅酸锌介质陶瓷的性能,研究了添加物、原材料和制备工艺对其微波介电性能的影响。采用固相法、并以去离子水代替乙醇作分散剂制备陶瓷粉料,闭腔法测量其无载Q值和频率温度系数。研究结果表明原材料的粒度、球磨工艺和烧结温度对Q.f值影响大,添加物TiO2不仅调节频率温度系数(τf),而且促进陶瓷烧结。当TiO2(wt%)12%,1240℃烧结时,获得优良的微波介电性能:介电常数(εr)为10.2,Q.f=91640GHz,τf=-5.78ppm/℃。并用该组成的材料制作了中心频率f0=5.4GHz,带宽Δf=96MHz,插损小于1.3dB的两级片式介质带通滤波器,可以用于通信系统。     

Bi基微波介质材料研究进展

低温烧结微波介质陶瓷是近年来电介质材料方面的一个重要研究方向,也是发展片式多层微波器件的基础材料.Bi基材料具有较低的烧结温度和优良的介电性能,因而受到了广泛的关注.据此,对不同介电常数Bi基微波介质材料体系的研究进展及应用作了综合介绍,并分析了低熔点氧化物掺杂、离子取代对不同体系微波介质材料结构、介电性能的影响.     

DIELECTRIC PROPERTIES OF MATERIALS AND MEASUREMENT TECHNIQUES

The dielectric properties of materials are defined, and the nature of their dependence on moisture content, frequency of the applied electric field, temperature of the material, and density of particulate materials is discussed. Dielectric properties of liquid water are summarized. The influence of moisture content, frequency, temperature, and density on the values of the dielectric constant and loss factor, real and imaginary parts of the relative complex permittivity, respectively, are illustrated for several different kinds of materials. Examples include dielectric properties for the cereal grains corn and wheat, pecans, and pulverized coal. Techniques for the measurement of dielectric properties of materials at high frequencies and microwave frequencies useful for dielectric heating and drying applications are discussed briefly, and numerous publications describing these methods in greater detail are cited for reference.     

DIELECTRIC PROPERTIES OF MATERIALS AND MEASUREMENT TECHNIQUES

The dielectric properties of materials are defined, and the nature of their dependence on moisture content, frequency of the applied electric field, temperature of the material, and density of particulate materials is discussed. Dielectric properties of liquid water are summarized. The influence of moisture content, frequency, temperature, and density on the values of the dielectric constant and loss factor, real and imaginary parts of the relative complex permittivity, respectively, are illustrated for several different kinds of materials. Examples include dielectric properties for the cereal grains corn and wheat, pecans, and pulverized coal. Techniques for the measurement of dielectric properties of materials at high frequencies and microwave frequencies useful for dielectric heating and drying applications are discussed briefly, and numerous publications describing these methods in greater detail are cited for reference.     

机械球磨时间对液相烧结Ba2Ti3Nb4O18陶瓷材料结构和性能的影响

Ba2Ti3Nb4O18是BaO-TiO2-Nb2O5体系中一种新型的介质材料,具有优良的微波介电性能.为满足低温共烧陶瓷技术(low temperature cofired ceramics,LTCC)对微波介质陶瓷材料的低温烧结要求,实现在900℃与银电极共烧,添加了质量分数为5%的ZnO-B2O3玻璃作助融剂,并研究了机械球磨时间对粉料粒径、陶瓷样品的烧结密度、显微结构和介电性能的影响.机械球磨6h的粉体粒径适中(约90nm),用该粉料制备的陶瓷样品可以在900℃致密烧结(大于理论密度的95%).且高频介电性能为(1MHz下测试):介电常数εt≈36,介电损耗tanδ≈2× 10-4,电容温度系数αc≈2.5×10-6/℃.同时微波介电性能良好:εt=33.3,品质因数和频率的乘积Qf=14274GHz.可与银电极共烧结作为LTCC介质瓷料.     

Influence of process parameters on the morphology,rheological and dielectric properties of three-roll-milled multiwalled carbon nanotube/epoxy suspensions

The influence of process parameters on the morphology, rheological and dielectric properties of multiwalled carbon nanotubes (MWCNT)/epoxy suspensions processed by three-roll milling has been investigated. Two apron roll speeds, 180 rpm (low) and 270 rpm (high); two different number of passes, 1 (low) and 5 (high); and two MWCNT loadings 0.01 (low) and 0.1 wt.% (high) were examined. Results obtained from rheological and dielectric measurements indicate that milling at the lower roll speed of 180 rpm leads to better enhancement of rheological and dielectric properties compared to milling at 270 rpm. The results also indicate that a higher number of passes is more favorable for improved rheological and dielectric properties. The relationship between the microstructure and the properties of the suspensions has been explained using the exfoliation-rupture MWCNT agglomerate dispersion mechanism. Milling at 180 rpm was observed to promote exfoliation of MWCNT agglomerates, whereas milling at 270 rpm promoted rupture. Agglomerate statistics carried out on micrographs of the suspensions provided circumstantial evidence that milling at the lower speed indeed promoted exfoliation over rupture, while milling at the higher speed promoted rupture. This technique of combining rheological and dielectric measurements could be an invaluable tool for monitoring MWCNT agglomerate dispersion changes, and hence tuning nanocomposite properties.     

PARTICLE-SIZE DISTRIBUTION OF GLAZES*

The particle-size distributions of experimental and commercial stains and glazes and glaze materials were determined by using the Andreasen pipette method. The variation in particle size of two porcelain glazes, raw and fritted, was correlated with the glaze working properties and certain physical properties of the glaze film, such as fluidity, microtexture, scratch-hardness, and glaze stress. The relation of grinding efficiency to length of milling time and different ball size was studied for these two glazes and also for a stain, and the color imparted by the stain at different grain sizes was noted.     

Self-propagating high-temperature synthesis of barium titanate and subsequent densification by spark plasma sintering (SPS)

This paper describes the self-propagating high-temperature synthesis (SHS) of perovskitic oxides, specifically BaTiO₃, and their subsequent densification by spark plasma sintering. With the final goal of obtaining dense nanostructured materials, SHS products were mechanically treated at different milling time conditions, before densification. It was found that the grain size of ball milled powders decreases with increasing milling time, this effect being more evident at early stages of milling. Depending upon the ball milling (BM) conditions adopted, crystallite size in the range 15–70 nm was obtained. After milling for 5 h, the resulting powders (20–30 nm) were sintered by SPS, at 700 A, for different periods of time. By properly varying sintering time in the interval 70–140 s, it is possible to obtain products with relative density in the range 66–99%, respectively. In particular, grain growth during sintering was found to be limited (below 50 nm) if the electric current is applied for time intervals equal to or less than 100 s. The observed dielectric properties are typical of a nanocrystalline BaTiO₃ ceramic.     

Impedance spectroscopy analysis of BaFe12O19 M-type hexaferrite obtained by ceramic method

The impedance spectroscopy analysis for M-type BaFe₁₂O₁₉ (BaM) ceramics prepared by ceramic route is reported. The main aim is to investigate the electric properties in function of the synthesis parameters (milling time and milling power). It was shown that milling parameters strongly influence the electrical properties such as dielectric constant, whose magnitude increases with the milling power. Moreover the relaxation frequency is fully dependent on the milling parameters and it shifts to high frequencies when milling power decreases. Finally, impedance and dielectric loss tangent also change with milling parameters.     

Dielectric properties of epoxy/graphite flakes composites: Influence of loading and surface treatment

Epoxy-rich carbon-based composites are well recognized materials in industries owing to their good mechanical properties and thermal stability. Here, dielectric properties of composites based on bisphenol-A-epoxy resin loaded with 5, 6, 10, and 15 wt% of graphite flakes (GF) have been studied. The frequency and temperature dependence of the dielectric permittivity, dielectric loss, and ac conductivity have been examined in temperature (−103 to 97°C) and frequency (20 Hz–200 kHz) range. Influence of the filler surface chemistry have been studied for composites loaded with 5 wt% GF obtained: (i) under wet milling, without or with adding Triton-100x as a surfactant, or (ii) under dry milling in the presence of KOH. The composite made of epoxy loaded with 5 wt% exfoliated expanded graphite flakes (EEG), was also prepared. The surface treatment with KOH notably increased dielectric constant of the composite, keeping low dielectric loss, while treatment with Triton-100x significantly increased tanδ. The composite loaded with exfoliated expanded graphite shows higher ac conductivity than those obtained with flaky graphite, GF. Possibility to change dielectric properties of the composites without changing the loading content can be used as an approach in tailoring one with desired dielectric properties.