Microstructure and Electrical Properties of Er_2O_3-Doped ZnO-Based Varistor Ceramics Prepared by High-Energy Ball Milling

Zinc oxide (ZnO) varistors exhibit highly nonlin-ear voltage-current (V-I) properties and it is ex-pressed bythe relationI=KVα,whereKis a constantandαis a nonlinear coefficient .They are extensivelyused as surge arresters in electric power lines ,such a…     

Effects of Rare-Earth La2O3 Addition on Microstructures and Electrical Properties of SrTiO3 Varistor-Capacitor Dual Functional Ceramics

Generally, metal oxide varistors used for the pro tection of electrical circuits are based on ZnO andTiO2[1,2]. ZnO varistor, which is widely used due toits high non linearity coefficient, is composed of ZnOceramics with minor oxide additive…     

Preparation and Electrorheological Property of NaNO3-Doped Y2O3 Material

Theelectrorheological(ER)fluidisasuspension ofpolarizablesolidparticlesdispersedinanon con ductingliquid,exhibitingdrasticandreversible changeinrheologicalpropertieswhenanexternalelec tricfieldisappliedviaorderingofthemicrostructure intoparticulatecolumns[1].Thisrapidandreversibleresponsehaspotentialapplicationinmanyelectrically controlledmechanicaldeviceswhichtransformelectri calenergyintomechanicalenergy,suchasclutches,valves,dampingdevices,andsoon[2,3].However,ERfluidhasnotbeenutilizedlarg…     

Effect of La2O3 on Microstructure and Transmittance of Transparent Alumina Ceramics

Optically transparent alumina ceramics were fabricated by conventional process and sintered without pressure in H2 atmosphere. The results indicate that relative densities of alumina specimens increase to theoretical densities （T. D. ） with increasing content of La2O3. With increasing holding time during sintering, much less pores and larger grains were found in the sintered alumina samples. Higher transmittance was achieved in alumina codoped with MgO and La2O3 as compared with that doped with MgO only. The total-transmittance of alumina sample is up to 86% at twavelength range of 300 - 800 nm.     

Effect of CeO2 on Electrical Properties of （Nb, Mn）-Doped TiO2 Varistor Ceramics

Varistor ceramics are a class of semiconductor de-vices with high non-linearity in their current-voltage(V-I)characteristics.Among these,ZnO varistor isthe most typical material and is commercially used asvoltage suppressor to protect electronic componentsand power systems[1~4].However,ZnOis a kind ofpure resistance component and has low permittivity,high dielectric dissipation,lowresponse speed,andpoor ability to absorb high frequency noise and pulsesurge.Soits applicationis restrictedin el…     

球磨工艺对Al2O3/Mo复合材料组织的影响

针对原位自生Al2O3增强钼基复合材料晶粒较大的问题,采用溶胶-凝胶与高能球磨相结合的方法细化复合材料晶粒,并利用SEM、XRD对不同球磨工艺所制备Al2O3/Mo复合粉末及复合材料的组织进行了观察和分析。结果表明:随着球磨时间的延长,Al2O3/Mo复合粉末颗粒由球状变为层片状再成为细小的球状,颗粒大小由约1.5μm细化为约500nm,其中的钼晶粒不断细化;高球料比所得粉末的分散性和破碎细化程度较好;转速提高使得粉末颗粒的尺寸均匀程度降低,且伴有结块现象,不利于粉末的细化。在球料比5∶1、转速300r/min、球磨时间60h条件下获得的复合粉末,经压坯烧结可制备出Al2O3颗粒为纳米级的钼基复合材料。     

Effect of Rare Earths on Mechanical Properties and Microstructure of TiCN/Al2O3 Ceramics

The effects of Y on mechanical properties and microstructure of TiCN/Al2O3 ceramics were studied in details. The experimental results show that the mechanical properties and microstructure can be improved by adding rare earth in TiCN/Al2 O3 ceramics, flexural strength and fracture toughness of the composites increased when Y is doped by 18.99% and 18.58% than those of the matrix, respectively. Microstructure of cracks extension was observed through SEM and TEM. The mechanics of particles bridge, cracks branch and cracks deflection are enforced obviously during the processes of cracks extension because strong interfaces and weak interfaces coexist, so manifold mechanics of enforcement of toughness act upon together to increase fracture toughness of TiCN/Al2 O3 doped with Y.     

合金粉末预氧化法制备Ag-SnO2-Y2O3电接触材料的研究

Ag-SnO2是各国电接触材料研究人员近年来新开发的一种无镉新型触头材料,它具有较好的导电导热性,优良的耐热性、抗电弧烧蚀性和抗熔焊性,是目前代替Ag-CdO的最理想材料。本文通过合金粉末预氧化法、复合粉体改性处理技术来制备Ag-SnO2-Y2O3电接触材料,添加稀土后合金粉末容易氧化,氧化粉体经改性处理后可有效改善氧化物颗粒与银基体间的润湿性、改善材料的后续加工性能,并且所制备的Ag-SnO2-Y2O3材料密度高、组织均匀、不存在宏观偏析,SnO2和Y2O3颗粒在材料中弥散均匀分布。     

Synthesis of Al2O3/TiCN-0.2%Y2O3 Composite by Hot Pressing

Al2O3/TiCN composites were synthesized by hot pressing.The influences of components and HP temperature on mechanical properties,such as bending strength,breaking tenacity and Vickers hardness were investigated.The results showed that the mechanical properties of Al2O3/TiCN composite increased with temperature when hot pressing temperature is below 1650 ℃.The mechanical properties reached their maximums when the composites were sintered at 1650 ℃ for 30 min under hot pressing pressure of 35 MPa,the value of bending strength,breaking tenacity and Vickers hardness was 1015 MPa,6.89 MPa·m1/2,and 20.82 MPa,respectively.When hot pressing temperature was above 1650 ℃,density decreased because of decomposition with increased temperature,and mechanical properties dropped because of rapid growth of grains in size at high temperature.Microstructure analysis showed that the addition of Y2O3 led to the formation of YAG phase so as to inhibit the growth of crystals.This helped to improve breaking tenacity of the composites.TiCN particles with diameters of 1 μm dispersed at Al2O3 grain boundaries,inhibited grain growth and enhanced mechanical properties of the composites.SEM study of the propagation of indentation cracks showed that the bridge linking behavior between matrix and strengthening phase might lead to the formation of the coexisted field of crack deflection,branching and bridge linking.The mechanism of this phenomenon was that the addition of Y2O3 improved the dispersion of TiCN particles so as to enhance the tenacity of the composites.The breaking tenacity was changed from 5.94 to 6.89 MPa·m1/2.     

高能球磨对La_(2/3)Ca_(1/3)MnO_3晶体结构和磁性的影响

通过在传统的烧结工艺上加上球磨工艺制备了单相 L a2 / 3Ca1 / 3Mn O3氧化物 ,研究了球磨对氧化物的结构和磁性能的影响 ,发现晶格常数和晶胞体积增大 ,但晶体结构类型基本不变 ,仍为钙钛矿四方相结构 ,而交流磁化率、磁化强度、居里温度减小。球磨引起氧的欠缺、无序效应 ,对电阻有一定的影响     

Study on BaO-Sm2O3-TiO2 Microwave Dielectric Ceramics Doped with Bismuth and Zinc

BaO-Sm2O3-TiO2 microwave dielectric ceramics doped with Bi and Zn was studied. The experiment was based on BST microwave dielectric ceramics doped with Bi2O3, which is shown by Ba4(Sm1-yBiy)28/3Ti18O54. When y=0.15, ZnO was added and the effects of ZnO on this system were studied. The result shows that the dielectric characteristics of BST microwave dielectric ceramics are the most excellent when the content of ZnO is 3%, and the optimal sintering temperature is 1200 ℃.     

Research on Y2O3：Eu Phosphor Coated with In2O3

Y2O3：Eu red phosphor for FED application was prepared by high temperature solid-state reaction. The In2O3 coating by precipitation method to the phosphor was applied and the analyses of XRD, Zeta potential, SEM, EDS and low voltage cathodoluminescence （CL） were conducted for investigating the coating effect. The results showed that In2O3 coating promoted the low voltage CL of the phosphor efficiently. The promotion was possibly due to the enhancement of the surface conductivity of the phosphor grains.     

Synthesis of ZrO2-HfO2-Y2O3-Sc2O3 Nano-Particles by Sol-Gel Technique in Aqueous Solution of Alcohol

Zirconium dioxide is a significant material withgood physicochemical characteristics . It is used inmanyfields such as energysources ,material and envi-ronment . Cubic phase zirconium dioxide doped withyttria (YSZ) is alreadyin wide use in solid oxygenfu-…     

Structural and Electrochemical Characteristics of Mg0.94 La0.06 Ni AlloyPrepared by Ball Milling

The amorphous Mg0.94Lao.o6Ni alloy was synthesized by ball milling for different time at 400 r min^-1. Electrochemical performances of the alloy electrodes were investigated and the results show that the specimens would reach their maximum electrochemical discharge capacities at the first charge/discharge cycle. The cyclic tests and X-ray diffraction(XRD) results show that discharge capacities would decrease rapidly due to the crystallization of the amorphous and the oxidization of magnesium on the particle surface during the electrochemical charge/discharge cycling. In addition, the DTA and SEM results reveal that the thermal stabilities will be improved and the size of the alloy will be decreased with the ball-milling time. The amorphous Mgo.96Lao.04Ni alloy prepared by ball milling for 40 h at 400 r min^-1 shows the bestelectrochemical properties.     

Preparation and Characterization of Gd3Sc2Ga3O12 Polycrystalline Material by Co-Precipitation Method

Gd3Sc2Ga3O12 polycrystalline material for single crystal growth was prepared with Ga, Gd2O3 and Sc2O3 as starting materials and aqueous ammonia as the precipitator by co-precipitation method. The precursors sintered at various temperatures were characterized by infrared spectra （IR）, X-ray diffractometry （XRD） and transmitted electron microscopy （TEM）. The results showed that pure GSGG phase could be obtained at 900 ℃. The sintered powders were well-dispersed and less-aggregated in the sintered temperature range of 900 - 1000 ℃. XRD and TEM show that the polycrystalline particle sizes of the polycrystalline powders were about 20 - 50 nm. Compared with the method that Ga2O3, Gd2O3 and Sc2O3 were mixed directly and sintered to get polycrystalline materials, the synthesized temperature was lower and sintered time was shorter. Thus co-precipitation was a good method to synthesize GSGG polycrystalline material.     

Al2O3含量对放电等离子烧结Al2O3/Cu复合材料组织与性能的影响

以微米级Cu粉为基体相,纳米Al₂O₃颗粒为绝缘相,采用机械球磨和放电等离子烧结工艺相结合的方法制备Al₂O₃/Cu复合材料,研究Al₂O₃含量对复合材料微观结构、电阻率和热导率的影响。结果表明,Al₂O₃/Cu复合材料为核?壳结构,随Al₂O₃含量增加,Al₂O₃包覆层对Cu基体的包覆效果逐渐提升;当w(Al₂O₃)为5%时,Al₂O₃/Cu复合材料的热导率较高,为85.92 W/(m·K),但电阻率偏低,仅为12.6 mΩ·cm。当w(Al₂O₃)增加至15%时,虽然Al₂O₃/Cu复合材料的密度降至6.69 g/cm³,孔隙率较高,但电阻率显著提高至2.09×10⁸ mΩ·cm,约为Cu电阻率的10¹¹倍,且热导率为7.6 W/(m·K),明显高于传统金属基板的热导率。     

Influence of B2O3 on Spectroscopic Properties of Er^3＋/Yb^3＋ Co-Doped Tungsten-Tellurite Glasses

A series of novel Er^3＋/Yb^3＋ co-doped （85- x ） TeO2-15WO3-xB2O3 （TWB;x=2%,5%,8%（mole fraction） ） glasses were prepared. Influence of B203 on the spectroscopic properties of Er^3＋/Yb^3＋ co-doped tungsten-tellurite glasses were investigated. It is found that the intensity of 1.5μm fluorescence, lifetime of the ^4I13/2 level and upconversion fluorescence all decrease with the increase of B2O3 content. The product of full width at half maximum （FWHM） and stimulated emission cross-section （σe^peak） of Er^3＋ ：^4I13/2→^4I15/2 transition has an optimum when B203 is 5% （mole fraction）. The emission spectra of Er^3＋ ： ^4I13/2→^4I15/2 transition was analyzed using peak-fit routine, and an equivalent four-level system was proposed to estimate the stark splitting for the 411512 and ^4I13/2 levels of Er^3＋ ions in TWB glasses at room temperature.     

Preparation and Upconversion Luminescence of Y3Al5O12 ： Yb^3＋ , Er^3＋ Trapsparent Ceramics

YAG： 1% （atom fraction） Yb^3＋ , 0.5% （atom fraction） Er3＋ transparent ceramics were fabricated by the solid state reaction method using high-purity Y2O3, Al2O3, Yb2O3, and Er2O3 powders as starting materials. The mixed powder compact was sintered at 1760 ℃ for 6 h in vacuum and annealed at 1500 ℃ for 10 h in an air atmosphere. The ceramics consisted of about 10μm grains and exhibited a pore-free structure. The optical transmittance of the ceramics at 1064 nm was nearly 80%. Upconversion emissions were investigated on the ceramics pumped by a 980 nm continuous wave diode laser, and strong green emission centered at 523 and 559 nm and red emission centered at 669 nm were observed, which originated from the radiative transitions of ^2H11/2→^4I15/2, ^4S3/2→^4I15/2, and ^4F9/2→^4I15/2 of Er^3＋ ions, respectively.     

Band gap and structure characterization of Tm2O3 films

Single crystalline Tm2O3 films were grown on Si (001) substrates by molecular beam epitaxy using metallic Tm source and atomic oxygen source. X-ray photoelectron spectroscopy, atomic force microscopy and high-resolution transmission electron microscopy were employed to investigate the compositions, surface morphology and microstructure of the sample. A very flat surface with a root mean square roughness of 0.3 nm could be reached, and a sharp interface between the film and the Si substrate was achieved. The result of optical spectrum at ultraviolet and visible wavelengths showed that the band gap of the Tm2O3 film was 5.76 eV.     

A comparative study on nano La2O3 suspension treated by ultrasonic and ball milling

This paper presented a scientific study of the effects of four dispersion methods on the dispersion capability of nano La2O3 suspensions, which are ball milling, ultrasonic, ultrasonic followed by ball milling and ball milling followed by ultrasonic. For the purposes of comparing their dispersion capability, sedimentation test, Zeta-potential measurement test, particles size measurement test and transmission electron microscopy (TEM) test were carried out. Suspension ability coefficient was also defined with expectation to estimate the stability of nano La2O3 suspension through granularity size, and their relationship curve was worked out. The results showed that ultrasonic followed by ball milling enjoyed an excellent capability of dispersion for nano La2O3 suspension. Its mechanism was discussed, and breakage models of nano La2O3 particles were developed. The study results indicated that ultrasonic followed by ball milling could break through both the limits of ultrasonic dispersion size range and thermo-effect, and thus was able to overcome the problem of the secondary aggregation of nanoparticles. Moreover, aggregations could be further de-agglomerated. As a result, dispersion capability of nano La2O3 suspension could be improved more greatly by ultrasonic followed by ball milling. And its suspension stability was the best with the highest suspension ability coefficient of the nanoparticles. It was found in the experiment that there was almost no obvious phenomenon of stratification for the suspension with a little sediment after being deposited for 8 d.