Y2O3, La2O3, Sm2O3对氧化铝瓷烧结及力学性能的影响

研究了3种稀土氧化物对氧化铝陶瓷烧结性能和力学性能的影响.结果表明 含Y2O3,La2O3,Sm2O3的添加剂促进了氧化铝瓷的烧结,提高了氧化铝瓷的力学性能.Y2O3和Sm2O3掺量为0.50%,La2O3掺量为0.75%时氧化铝瓷在1600或1620 ℃保温2 h烧结,相对密度达98.9%以上,强度超过439 MPa,断裂韧性达5.15 MPa·m1/2以上.微观结构分析表明,Y2O3,La2O3,Sm2O3抑止氧化铝晶粒生长,细化晶粒,使晶粒尺寸较均匀形成致密化结构.     

La2O3对Cu/Al2O3甲醇水蒸气重整制氢催化剂性能的影响

采用并流共沉淀法制备了系列Cu/La2O3/Al2O3甲醇水蒸汽重整制氢催化剂, 并通过X射线衍射(XRD), 程序升温还原(TPR) 和光电子能谱 (XPS) 等分析方法研究了La2O3对Cu/Al2O3甲醇水蒸汽重整制氢催化剂性能的影响. 结果表明 La2O3的加入促进了铜在催化剂表面的高度分散, 阻止了铜晶粒团聚、烧结, 促使铜晶粒细小化, 促进了铜的还原, 从而改善了催化剂的性能, 提高了催化剂的活性.     

新型固体电解质La2Mo2O9的制备及其性能

用固相法制备了新型固体电解质La2Mo2O9, 用热膨胀仪、 X射线衍射仪和Raman光谱分析了La2Mo2O9相的形成过程. 用交流阻抗谱和热膨胀仪对合成样品的电学和热学性能进行了研究, 分析了热处理温度对La2Mo2O9相的形成过程和电学性能的影响, 确定了样品获得高电学性能的最佳条件. 研究结果表明: 600 ℃时样品中开始形成La2Mo2O9相, 700 ℃以上烧结的样品可获得具有完整氧空位的La2Mo2O9相. 900 ℃烧结10 h可获得具有高密度和高电导率的La2Mo2O9氧离子导体. 样品的电学性能随烧结温度的升高而增大, 900 ℃时烧结的样品在800 ℃时的电导率为0.067 S·cm-1, 远高于同温度下YSZ的电导率, 与晶粒电阻相比, 晶界电阻非常小. 用热膨胀仪测得La2Mo2O9在555 ℃时有一个一级相变, 对应α-La2Mo2O9到β-La2Mo2O9的相变.     

Pr2O3掺杂SnO2陶瓷电极的制备及性能表征

通过共沉淀法制备了掺杂Pr2O3的二氧化锡电极样品,主要研究了在SnO2陶瓷电极中添加不同含量的Pr2O3对形貌结构及性能的影响.借助于XRD和SEM分析试样的晶型结构和微观形貌,结果表明Pr2O3能促进二氧化锡晶粒长大,并产生新的第二相Pr2Sn2O7.当Pr2O3含量从1%增加到5%(质量分数)时,第二相依次增多并镶嵌在主晶格中.通过电阻率和力学性能的测定,发现掺杂3%Pr2O3有利于提高SnO2电极的烧结致密化和降低电阻率,过量的Pr2O3则会产生过多第二相而不利于致密化烧结.     

通过微观形貌对Ba(Ti,Sn)O_3压电陶瓷的结构及压电性能分析

本文采用传统固相合成法制备了(Ba_(1-x)Ca_x)(Ti_(0.98)Sn_(0.02))O_3(BCTS,x=0.00、0.01、0.02、0.03)无铅压电陶瓷,研究了不同烧结温度下Ba(Ti,Sn)O_3压电陶瓷材料的微观形貌对相结构及压电性能的影响。X-射线衍射(XRD)分析表明,所有陶瓷样品均为单一、纯钙钛矿结构,无第二相生成。通过扫描电子显微镜(SEM)图片可知,陶瓷样品在烧结温度为1450℃时,晶粒更加均匀、陶瓷结构更加致密,气孔较少并且晶粒成螺旋状结构生长。当陶瓷烧结温度为1450℃,并且x=0.01时,陶瓷的综合性能达到最佳,其压电常数(d33)达到346pC/N。     

La2O3对Mo5Si3/MoSi2复合材料的改性研究

通过粉末冶金方法制备了Mo5Si3/MoSi2和La2O3/Mo5Si3/MoSi2复合材料,探讨了其烧结工艺.检测了其密度、维氏硬度、抗弯强度和断裂韧性,运用X射线衍射仪和扫描电镜（SEM）研究了La2O3对Mo5Si3/MoSi2复合材料显微结构和力学性能的改性影响.结果表明,La2O3/Mo5Si3/MoSi2复合材料的合理烧结温度为1600 ℃,比MoSi2材料提高了100 ℃; 稀土氧化物的加入细化了晶粒,且明显提高了材料的致密度、维氏硬度和抗弯强度; 其强化机制为细晶强化和弥散强化; 韧化机制为细晶韧化、裂纹偏转、裂纹分支和微桥接.     

添加Y2O3的ZrO2—Al2O3复相陶瓷力学性能的研究

采用工业ZrO2, Al2O3原料, 以Y2O3作为稳定剂, 通过适当的工艺制备出ZrO2-Al2O3复相陶瓷. 研究结果表明, Y2O3添加量为3.5%(摩尔分数)的ZrO2基陶瓷中加入Al2O3可有效地抑制ZrO2晶粒的生长, 有利于使ZrO2晶粒以亚稳四方相存在, 从而提高材料的强度与断裂韧性. Al2O3含量为20%(质量分数)时, 复相陶瓷的抗弯强度、断裂韧性分别为676.7和10 MPa*m1/2, 其值接近湿化学法制备的复相陶瓷的力学性能. 相变增韧与颗粒弥散增韧作用相互叠加提高了复相陶瓷材料的力学性能.     

La2O3对Yb3+掺杂的氧化钇透明激光陶瓷性能的影响

本文研究了La2O3的含量对(Yb0.05 Y0.95)2O3透明激光陶瓷的结构性能和烧结性能的影响.结果表明:随着La2O3含量的增加,拉曼光谱特征峰发生红移,声子能量降低,半高宽增大,相对强度先增大后减小;同时密度、相对密度和透过率都增大,陶瓷的晶粒减小,而当La2O3含量继续增加时,晶粒基本保持不变.但适量的La2O3掺杂量对(Yb0.05Y0.95)2O3透明激光陶瓷的发射性能影响不大.最合适的La2O3添加量为10at%,最合适的烧结温度为1700℃,最后样品的直线透过率可达到75%.     

PbF2·SiO2基玻璃陶瓷的溶胶-凝胶制备及结构转变研究

采用溶胶-凝胶法制备了PbF2·SiO2纳米晶玻璃陶瓷块体;利用TG-DSC和IR技术分析了干凝胶在热处理过程中有机基团的分解及内部原子键合方式的演变;结合XRD和TEM研究了凝胶玻璃中PbF2纳米晶粒的长大过程,并分析了Er3+掺杂的影响.结果表明,采用此方法制备的PbF2.SiO2纳米晶粒玻璃陶瓷具有较好的成形性,晶化温度在320℃左右;经480℃热处理,镶嵌在玻璃基体中的PbF2晶粒尺度约为10-25nm,材料透明性良好.在PbF2·SiO2系统中掺入少量的Er3+,将提高PbF2的晶化温度,降低玻璃陶瓷的显微硬度;掺杂可能对PbF2晶粒表面原子的活性起抑制作用,阻碍晶粒的表面迁移,使晶粒的生长速度明显降低.     

稀土对Al2O3陶瓷烧结温度、显微组织和力学性能的影响

研究了Y2O3, La2O3 等稀土氧化物对Al2O3陶瓷烧结温度、力学性能和显微组织的影响. 结果表明, 添加稀土氧化物可以降低Al2O3陶瓷的烧结温度, 改善显微组织, 提高力学性能. 添加复合稀土氧化物(Y2O3+La2O3)后, Al2O3陶瓷的抗弯强度和断裂韧性分别提高1.8倍和2.08倍. 其性能提高的主要原因是稀土氧化物对细晶强化、净化界面、固溶强化、自增韧补强等作用的贡献.     

The electrical properties of chemically obtained barium titanate improved by attrition milling

Barium titanate ceramics were prepared using the nanopowder resulting from a polymeric precursor method, a type of modified Pechini process. The obtained nanopowder was observed to agglomerate and in order to de-agglomerate the powder and enhance the properties of the barium titanate the material was attrition milled. The impact of this attrition milling on the electrical properties of the barium titanate was analysed. The temperature dependence of the relative dielectric permittivity showed three structural phase transitions that are characteristic for ferroelectric barium titanate ceramics. The relative dielectric permittivity at the Curie temperature was higher for the attrition-treated sample than for the non-treated barium titanate. The dielectric losses were below 0.04 in both barium titanate ceramics. The grain and grain-boundary contributions to the total resistivity were observed using impedance analyses for both ceramics. A well-defined ferroelectric hysteresis loop and piezoelectric coefficient d₃₃ = 150 pC/N were obtained for the ceramics prepared from the de-agglomerated powder. In this way we were able to demonstrate that by attrition milling of chemically obtained powders the ferroelectric and piezoelectric properties of the ceramics could be enhanced.     

Nd2O3掺杂(BaSr)TiO3对陶瓷结构和性能的影响

采用常规固相反应法,以Ba0.6Sr0.4TiO3 10%MgO(BSTO)体系为基体成分,研究了Nd2O3掺杂对其显微组织结构和介电性能的影响规律,结果表明掺杂Nd2O3后,抑制了BSTO晶粒的生长;随着Nd2O3掺杂量的增加,陶瓷的晶粒尺寸变小,密度增大,材料的居里温度向负温度方向移动,并且展宽了介电峰,使材料的温度稳定性提高,此外,随着Nd2O3掺杂量的增加,材料的可调性减小,介电常数减小。     

Microstructure,dielectric and piezoelectric properties of (Pb1−xSrx)Nb1.96Ti0.05O6 ceramics

(Pb_1−xSr_x)Nb_1.96Ti_0.05O₆ with 2 wt% excess PbO (x = 0, 0.02, 0.04, 0.06, 0.08) piezoelectric ceramics with high Curie temperature were fabricated via the conventional solid state reaction method. Effects of Sr²⁺ amount on crystallite structure, microstructure, dielectric and piezoelectric properties were studied. The substitution of Sr²⁺ ions for Pb²⁺ ions is effective to lower sintering temperatures. X-ray diffraction patterns indicate that all ceramics form the single orthorhombic ferroelectric phase. The doping of Sr²⁺ ions facilitates improving densification of the ceramics. Grain size and lattice parameters of the ceramics vary with the change of the Sr²⁺ contents. Both Curie temperature and maximum dielectric constant change with increasing the Sr²⁺ amounts. The dielectric constant data were also studied using the Curie–Weiss law and modified Curie–Weiss law. The ceramic with x = 0.04 possesses excellent piezoelectric and dielectric properties, presenting a high potential to be used in high-temperature applications as piezoelectric transducers.     

The Solgel Preparation and Electric Properties of MnO2-doped PbTiO3 Ceramics

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预烧温度对CaO-Li_2O-Sm_2O_3-TiO_2微波介质陶瓷介电性能的影响

用固相反应法制备了CaO-Li2O-Sm2O3-TiO2(CLST)微波介质陶瓷。通过改变预烧温度(1 000~1 200℃)研究其对CLST微波介质陶瓷介电性能的影响。研究过程中,对预烧粉体与烧结陶瓷进行XRD与SEM分析,对陶瓷的介电性能εr、Q、τf进行了测试。结果表明,预烧温度对CLST微波介质陶瓷介电性能有较大影响,在预烧温度1 150℃,烧结温度1 340℃时可获得较好的介电性能:εr=112,Q=845,τf=52×10-6/℃。     

Bi4(Ti1/3Sn2/3)3O12掺杂BaTiO3基X8R陶瓷微观结构与介电性能

研究了Bi4(Ti1/3Sn2/3)3O12掺杂对钛酸钡基陶瓷微观结构和介电性能影响。结果表明,掺杂Bi4(Ti1/3Sn2/3)3O12后钛酸钡基陶瓷晶粒明显长大,同时烧结温度可由1 280℃降低至1 180℃。系统的介电性能和Bi4(Ti1/3Sn2/3)3O12的掺杂量有密切关系。当Bi4(Ti1/3Sn2/3)3O12的掺杂量从0.5mol%增加到2mol%,体系的居里峰被明显压低和展宽,当掺杂量为2mol%时居里峰变得不明显。当Bi4(Ti1/3Sn2/3)3O12的掺杂量从0.5mol%增加到2mol%,系统的居里温度由131℃升高至139℃。当Bi4(Ti1/3Sn2/3)3O12的掺杂量为1mol%时,钛酸钡基陶瓷介电常数为1 930,介电常数温度变化率为5%(-55℃),13%(134℃),-8%(150℃),满足X8R标准。     

Aurivillius-type ceramics, a class of high temperature piezoelectric materials: Drawbacks, advantages and trends

The obtention of reliable and high performance piezoelectric ceramics for uses at high temperatures is still an open issue in the field of electroceramics. The materials used nowadays for such applications present limitations due to different causes: low piezoelectric coefficients, difficulties in processing that lead to the necessary use of single crystals, high cost of raw materials and more. In this sense, an increasing interest in materials with the so-called Aurivillius-type structure has occurred during recent years, due to their relatively high piezoelectric coefficients and high ferro–paraelectric phase transition temperature. However, some difficulties must be overcome, such as processing for obtaining highly dense ceramics and determining their real piezoelectric behaviour at high temperature. In this work, a review of the processing and properties of ceramics with this structure is shown. Effects of the use of precursors obtained by an alternative route mechanical activation on the microstructure are explained. A complete piezoelectric characterization at working temperatures (>300 °C), barely found in the literature, is also shown. The effects of trapped charges in the dielectric permittivity and in the piezoelectric radial resonance are also discussed.     

Nd-doped barium titanate ceramics with various Ti/Ba ratios prepared by sol-gel method

The Nd-doped BaTiO3 nanocrystalline powders and ceramics with different Ti/Ba ratios were prepared by sol-gel method. Phases and microstructures of the Nd-doped BaTiO3 based powders and ceramics were characterized by XRD, SEM and TEM methods. The results revealed that the powders synthesized by sol-gel method were nanometer scale (30-60 nm) and were mainly composed of cubic BaTiO3 with a small amount of BaCO3. After sintering at high temperature, both cubic BaTiO3 and BaCO3 were transformed into tetrahedron BaTiO3 phase. The dielectric properties of the ceramics were also determined and the influence of Ti/Ba ratio on the dielectric properties was discussed. The Tc did not change with the variation of Ti/Ba ratio, while theεmax increased firstly and then decreased. The excess TiO2 is benefit for the modification of ceramics' microstructure and dielectric properties.     

Improved dielectric properties of BaxSr1−xTiO3-based composite ceramics derived from core–shell structured nanopowders

We performed a study on the dielectric properties of Ba_xSr_1−xTiO₃–Mg_0.9Zn_0.1O (BST–MZO) composite ceramics derived from core–shell structured nanopowders with the shell of zinc doped MgO and core of Ba_xSr_1−xTiO₃. It was found that the ceramics exhibit a significant improvement in dielectric response under a DC electric field. The Curie temperature decreases more significantly in the BST–MZO composite ceramics compared to that of pure BST ceramics. The tunability of Ba_0.75Sr_0.25TiO₃–40%MZO is 23.49% at 20 °C. The dielectric properties at high frequency also show low dielectric constant and great reduction in dielectric loss. These ceramics are expected to be useful in microwave devices.     

稀土气相扩渗BaTiO3基PTC陶瓷的NTCR效应

采用稀土气相扩渗法制备了La改性的BaTiO3基PTC陶瓷,并对其室温电阻率的变化及温-阻效应进行了研究.结果表明,BaTiO3基PTC陶瓷经La气相扩渗后,室温电阻率从2.7×109Ω.m下降到220Ω.m,在25-500℃范围内,电阻率随温度升高单调递减,从220Ω.m降至5.8Ω.m,产生了明显的NTCR效应.结合XRD,SEM,EDAX以及介电性能测试结果分析了La气相扩渗BaTiO3基PTC陶瓷NTCR效应的形成机理,建立了NTCR效应的物理结构模型.