Study on Mg PSZ Ceramics Doped with Y_2O_3 and CeO_2

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Ti_3AlC_2自蔓延高温合成中组织分析

用燃烧波淬熄法及借助X射线衍射仪(XRD)、扫描电子显微镜(SEM)和能谱分析仪(EDS)研究了Ti3AlC2自蔓延高温合成(SHS)中的显微组织变化,淬熄试样保留了未反应区、预热区、燃烧波前沿、反应区、产物区。试验结果表明,Ti3AlC2自蔓延高温合成机理为溶解-析出-熔化-包晶机制:一方面,Ti和C向Al熔液中溶解,最终导致Al3Ti析出;另一方面,随着C向Ti中扩散,最终导致TiC从Ti-Al-C熔体析出;当温度超过Al3Ti的熔点后,Al3Ti熔化,促使Al3Ti和TiC发生包晶反应生成Ti3AlC2。最终的产物中除了大量的Ti3AlC2外还存在少量Al3Ti和Ti,这与试验使用了较粗的Ti粉有关。     

Ti3AlC2陶瓷材料制备工艺研究进展

综合阐述了合成Ti3AlC2新型陶瓷材料的几种主要的制备方法.由于三元层状陶瓷材料Ti3AlC2具有特殊的结构特征,因此它同时具备金属和陶瓷的双重优点.从粉体材料和块体材料两方面,分别介绍了Ti3AlC2的几种主要的制备方法,有自蔓延高温合成(SHS)、无压合成(PLS)、机械合金化(MA)或机械诱发自蔓延反应合成(MSR)、放电等离子烧结(SPS)、热压烧结(HP)以及热等静压(HIP)烧结.     

Gd2O3掺杂CeO2纳米粉体的烧结动力学

对Gd2O3掺杂CeO2纳米粉体进行了等速烧结实验研究。得出了试样的线收缩率、密度、气孔率随烧结温度的变化规律,回归出了描述这些物理量与烧结温度之间关系的动力学方程。     

掺杂氧化铈钡钨阴极的结构和发射性能的研究

采用CeO2与钨粉机械混合,制备了满足大功率微波器件要求的高性能掺杂CeO2钡钨阴极,利用扫描电镜、压汞仪等测试手段分析了阴极的微观结构.用水冷阳极二极管检测了阴极的发射性能.研究表明,掺杂CeO2钡钨阴极孔径分布较窄,为0.4～3.6um,平均孔径为2um.在阳极正常工作温度1050。C下,掺杂CeO2钡钨阴极的直流发射电流密度和脉冲发射电流密度分别为6.33,17.48A·cm-2,明显优于传统钡钨阴极,满足大功率微波器件要求.     

CeO2-Co3O4 Catalysts for CO Oxidation

CeO2-Co3O4 catalysts for low-temperature CO oxidation were prepared by a co-precipitation method. In combination with the characterization methods of N2 adsorption/desorption, XRD, temperature-programmed reduction （TPR）, and FT-IR, the influence of the cerium content on the catalytic performance of CeO2-Co3O4 was investigated. The results indicate that the prepared CeO2-Co3O4 catalysts exhibit a better activity than that of pure CeO2 or pure Co3O4. The catalyst with the Ce/Co atomic ratio 1 ： 16 exhibits the best activity, which converts 77% of CO at room temperature and completely oxidizes CO at 45 ℃.     

大尺寸Ti3AlC2陶瓷的制备及耐磨性研究

采用燃烧合成结合准热等静压技术(SHS/PHIP)制备了大尺寸Ti3AlC2陶瓷材料(φ240 mm×40mm),利用销-盘式摩擦磨损试验机,研究了不同滑动速度下Ti3AlC2的摩擦磨损性能.结合XRD分析、SEM观察和EDS能谱分析,讨论了Ti3AlC2在不同条件下的摩擦磨损机理.结果表明:载荷分别为30N、50N和70N时,随滑动速度的增大,Ti3AlC2的摩擦因数和磨损率均呈现降低趋势,在载荷70N、滑动速度4.8 m/s时,摩擦因数和磨损率分别为0.24和2×10-6 mm3/N·m;材料磨损以磨损表面磨粒磨损和氧化膜的轻微划痕磨损为主.     

Dielectric Properties of CeO2 -Doped Ba( Zr, Ti)O3 Ceramics

The influence of additive amount of CeO2 on the properties of Ba(Ti, Zr)O3 (BTZ) capacitor ceramics prepared using conventional solid-state reaction method was investigated. The dielectric constant(ε) increases to a maximum when w( CeO2 ) is about 1.0% and then decreases again at higher doping concentration of CeO2. The dielectric constant gets a maximum while w ( CeO2 ) is about 1. 0%, and the dielectric loss is minimum while w ( CeO2 ) is0.5 %. CeO2 can decrease the curie temperature, widen the εr-T peak and decrease the absolute value of dielectric constant temperature coefficient. The influence mechanism of CeO2 additive on the properties of the BTZ ceramics was discussed. The results show that CeO2 additive influences the properties of BTZ ceramics by means of forming defect solid solution , shifting curie temperature peak effect, segregating in crystal boundary , and impeding grain growth.     

自蔓延高温合成Ti3AlC2陶瓷材料

以Ti、Al、C、TiC粉末为原料,研究掺杂Si及Al含量对自蔓延高温合成Ti3AlC2的影响,合成材料的X射线衍射仪(XRD)及扫描电子显微镜(SEM)分析结果表明:物质的量比n(Ti)∶n(Al)∶n(C)∶n(TiC)∶n(Si)=2∶1.2∶1∶0.9∶0.1的原始混合粉末,经50 MPa压力压制的压坯在空气中...     

Preparation and Characterization of Graphite Powder Covered with CeO2

In order to improve the wetting properties of graphite with Al melt and reduce the oxidation of the graphite, by which the segregation of components during the liquid-stir-casting process could be prevented. In this paper, a uniform thin nano-film of CeO2, about 20 nm thick, was successfully prepared onto graphite powder surface by heterogeneous nucleation process. The results show that an obvious chemical reaction did exit between CeO2 film and graphite with the formation of Ce-O-C bond, leading to a shift of the binding energy of C and Ce. The cover with CeO2 film illustrates a distinct change of surface state of graphite with a decrease of angle of contact.     

Structure and Mechanical Properties of Ni-P-Nano Al2O3 Composite Coatings Synthesized by Electroless Plating

Ni-P-nano Al2O3 composite coatings were deposited by electroless plating,and their microstructures were observed by SEM（scanning electron microscope）.The microhardness and the wear resistance of the Ni-P-nano Al2O3 composite coatings were measured using microhardness tester and block-on-ring tribometer,respectively,and the comparison with those of Ni-P coatings or Ni-P-micro Al2O3 coating was given.The influences of aging temperature on their hardness and wear resistance were analyzed.The results showed that the nano Al2O3 particles were distributed uniformly in the Ni-P-Al2O3 coatings.Among three kinds of Ni-P based coatings,the hardness and wear resistance of Ni-P-nano Al2O3 coatings were largest,and the maximum values could be obtained at 400 ℃.This indicated that the precipitation of nano Al2O3 particles would improve the hardness and wear resistance of the Ni-P coatings.     

Catalytic Reduction of SO2 on CeO2-La2O3 Rare Earth Mixed Compounds

Adding rare earth oxide CeO2 with variable valences to La2O3 formed a mixture of rare earth oxides. By means of dipping CeO2, La2O3 and their mixture, whose carriers were all γ-Al2O3, were used as the catalyst for the reduction of SO2 by CO. The activation process of this catalyst and the impact of temperature and reactant concentration on the activation process were investigated. Using X-ray diffraction, the structure characteristics of catalyst before and after reaction were analyzed to reveal the change of phase structure. The result shows that the rare earth oxide mixtures composing of CeO2 and La2O3, as the catalyst for the reduction of SO2 by CO, diminish activation temperature 50～100℃ less and have higher activity than a single oxide CeO2 or La2O3. The reason possibl is that La2O3 goes into in the lattice of CeO2 to form solid phase complex CeO2-La2O3 and increases the capability of CeO2-La2O3/γ-Al2O3 catalyst to store oxygen, which supplies the redox of CeO2 reaction with a better condition. At the same time, elemental sulfur formed in the redox reaction impels La203 to be transformed to activation phase La2O2S in a lower temperature, which can be explained with the synergism between redox reaction and COS intermediate mechanism reaction.     

CeO2对不锈钢基SiO2-BaO-Al2O3-Cr2O3陶瓷涂层性能的影响

采用高温熔烧法于1Cr18Ni9Ti不锈钢基材表面制备掺CeO2的SiO2-BaO-Al2O3-Cr2O3陶瓷涂层,研究了不同含量CeO2对涂层的抗氧化性、抗热震性和硬度的影响。研究结果表明,含CeO2的不锈钢基SiO2-BaO-Al2O3-Cr2O3陶瓷涂层能有效阻止不锈钢基体的氧化增重,提高涂层的抗热震性能及硬度。本实验条件下,CeO2含量2.8%时,涂层具有最好的抗氧化性能和抗热震性能。     

Hydrogen and syngas production from two-step steam reforming of methane over CeO2-Fe2O3 oxygen carrier

Two-step steam reforming of methane(SRM)is a novel chemical looping process towards the production of pure hydrogen and syngas(synthesis gas),consisting ofa syngas production step and a water-splitting step.Renewable energy can be used to drive this process for hydrogen production,especially solar energy.CeO2-Fe2O3 complex oxide oxygen carrier was prepared by the impregnation method and characterized by means of X-ray diffractometer(XRD),Raman spectroscopy(Raman)and hydrogen programmed reduction(H2-TPR).CH4temperature programmed and isothermal reactions were adopted to test syngas production reactivity,and water splitting reaction was employed to investigate water-splitting activity.Moreover,two-step SRM performance was evaluated by a successive redox cycle.The results showed that CO-uncontaminated H2 and highly selective syngas(with H2/CO ratio close to 2)could be respectively obtained from two steps,and CeFeO3 formation was found in the first redox cycle and proved to be enhanced by the redox treatment.After 10 successive cycles,obvious CeFeO3 phase was detected,which may be responsible for favorable successive redox cycle performances.     

Growth of CeO2, Y2O3 Buffer Layers for YBCO Coated Conductor

The liquid citrate method was used to synthesize perovskite-type SrCe0.9 Y0.1O3-α powder. SrCe09Y01O3-α membranes were prepared from the powder by sintering at 1450℃ for 10 h. The reactions in the process of the heat treatment were studied by XRD and DSC/TG. The microstructure of the powder and the membrane was observed by SEM. The results indicate that the perovskite-type SrCe0.9Y0.1 O3-α can be synthesized at 1100℃. The particle size of the synthesized SrCe0.9Y0.1O3-α powder is less than 1μm. The powder can be densified at 1450℃.     

致密烧结Ti/Al2O3复合材料

利用放电等离子烧结技术(SPS)制备出相对密度、断裂韧性、弯曲强度分别为99.74%、19.73±0.4MPa·m1/2、1002±12MPa的40vol%Ti/Al2O3复合材料。SEM对复合材料表面形貌观察发现,Ti、Al2O3两相分布均匀,表面无明显气孔存在;断口的SEM和EDS表明,复合材料已形成网络导电结构;复合材料的HREM微观结构分析表明,Al2O3三角晶界处无其它杂质的偏聚,小颗粒的金属Ti富集在Al2O3的三角晶界结合处,界面结合紧密。     

纳米CeO2在水中的分散稳定性研究

利用氨水沉淀法制备纳米CeO2,并利用XRD对其物相进行了表征.在此基础上,选择了聚乙二醇1000(PEG1000)、聚甲基纤维素(CMC)以及十六烷基三甲基溴化铵(CTAB)作为CeO2在水中的分散剂,通过Zeta电位和吸光度讨论了pH值以及分散剂浓度对CeO2在水分散液中稳定性的影响.研究结果表明,在偏碱的条件下添加CMC和PEG1000,在偏酸的条件下添加CTAB时,CeO2在水中有较好的分散稳定性.通过Zeta电位和吸光度选择了分散剂的最佳添加浓度,CMC为0.1％,PEG1000为0.14％,CTAB为0.1％的添加量时,同时,CMC相对于其他两种分散剂而言对CeO2水分散液有较好的稳定性.     

Catalytic Oxidative Properties and Characterization of CuO／CeO2 Catalysts

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