La2O3对ZTM陶瓷晶界性能的影响

以电熔莫来石为原料制备的ＺｒＯ２增韧莫来石陶瓷在高温下力学性能不像莫来石那样随温度升高反而呈现有所增长的趋势，研究发展这一变化与原料中含有的Ｋ，Ｎａ等有害杂质有关，本文主要研究以稀土氧化物做添加剂来抑制或消除该陶瓷玻璃相中存在的有害杂质的作用，从而改善ＺＴＭ陶瓷的力学性能，并探讨Ｌａ２Ｏ３对ＺＴＭ陶瓷晶界改性的作用机制。     

基于高温熔凝法Al_2O_3/ZrO_2/YAG共晶陶瓷显微组织演变规律

作为超高温结构材料,共晶氧化物陶瓷的力学性能和显微组织密切相关。采用高温熔凝法制备Al_2O_3/ZrO_2/YAG共晶陶瓷体,研究熔体温度和结晶种子对凝固组织影响规律,运用经典形核机制和Jackson-Hunt共晶生长模型探讨了凝固组织的演变机理。研究表明,随着熔体温度升高(1750~2000℃),凝固体物相组成从α-Al_2O_3,c-ZrO_2和YAG转变为α-Al_2O_3,c-ZrO_2和亚稳相YAP。凝固组织依次经历:非共晶Al_2O_3/ZrO_2/YAG、不规则共晶Al_2O_3/ZrO_2/YAG、纳米纤维状共晶Al_2O_3/ZrO_2/YAG和复杂粗大的亚稳复合陶瓷Al_2O_3/ZrO_2/YAP。分析表明,凝固组织的演变源于异质晶核点不断钝化导致形核过冷度和凝固路径改变,所以合理选择熔体温度和结晶种子是共晶组织调控的关键。     

光悬浮区熔定向凝固Al2O3/Er3Al5O12和Al2O3/Yb3Al5O12共晶陶瓷的制备与性能研究

本研究探索了光悬浮区熔法制备Al₂O₃/Er₃Al₅O₁₂(ErAG)和Al₂O₃/Yb₃Al₅O₁₂(YbAG) 定向凝固共晶陶瓷。在10 mm/h的抽拉速率下成功获得了凝固组织均匀、内部无裂纹或孔洞的高质量共晶陶瓷。通过高分辨三维X射线衍射仪研究了Al₂O₃和RE₃Al₅O₁₂在三维空间的分布与组织结构; 利用电子背散射衍射技术分析了定向凝固末期Al₂O₃和RE₃Al₅O₁₂两相的晶体学择优取向和相界面关系。力学性能表征结果显示, Al₂O₃/ErAG和Al₂O₃/YbAG具有优异的力学性能, 二者的维氏硬度分别为(13.5±0.4)和(12.8±0.1) GPa;断裂韧性分别为(3.0±0.2)和(3.2±0.1) MPa·m^1/2。     

大尺寸La2O3-TiO2-ZrO2非晶塑性烧结行为

La₂O₃-TiO₂-ZrO₂玻璃具有很高的折射率, 在镜头材料和上转换发光基质材料等领域表现出良好的应用前景, 但其玻璃形成能力低, 通常只能采用快速冷却的方法制备, 因此难以获得大尺寸材料。为了获得大尺寸La₂O₃-TiO₂-ZrO₂玻璃, 本研究采用La₂O₃-TiO₂-ZrO₂非晶粉末为原料, 利用非晶在玻璃转变温度以上的塑性行为, 在温度动力学窗口ΔT内进行热压烧结制备了大尺寸La₂O₃-TiO₂-ZrO₂玻璃, 在保持非晶的前提下实现了La₂O₃-TiO₂-ZrO₂粉末的完全致密化。采用SEM、XRD等方法研究了样品的显微结构和相组成。研究发现, 当烧结温度高于910 ℃时, 烧结过程中会析出La₄Ti₉O₂₄晶相; 当烧结温度低于900 ℃时, 样品保持良好的非晶性, 并随着烧结温度的增加, 样品的致密度有所升高。烧结压力也会影响烧结过程, 样品的致密度随着烧结压力升高而增加。大尺寸La₂O₃-TiO₂-ZrO₂非晶材料具有很高的折射率, 在587.6 nm处折射率可达到2.33。在La₂O₃-TiO₂-ZrO₂非晶粉末烧结过程中, 塑性流动是其主要的传质机理。     

La2O3添加剂对ZTM陶瓷中柱状莫来石晶粒自生长的影响

在以富铝莫来石为基质的ＺＴＭ（２．０ｍｏｌ％Ｙ２Ｏ３）材料中加入Ｌａ２Ｏ３，制备出致密烧结的ＺＴＭ（Ｌａ２Ｏ３）试样。试样显微结构由柱状莫来石晶粒和等轴状晶粒组成。Ｌａ２Ｏ３与莫来石中Ａｌ２Ｏ３反应生成ＬａＡｌ２Ｏ３，并作为高铝莫来石晶粒的晶种，在烧结过程形成的液相作用下发育长大为柱状莫来石晶粒。高铝莫来石晶种的存在是柱状莫来石晶粒生成的必要条件。     

无容器制备Er3+/Yb3+共掺La2O3-TiO2-ZrO2玻璃及其上转换发光研究

利用无容器技术制备了(La_0.94-xEr_0.06Yb_x)(Ti_0.95Zr_0.05)_2.25O₆(x=0~0.24, 间隔0.04)球状透明玻璃, 其稀土离子掺杂浓度最大值达到30%。通过DTA分析发现, 玻璃具有很好的热稳定性, x=0时玻璃化转变温度T_g和析晶起始温度T_o分别为818℃和906℃, ΔT(ΔT= T_o-T_g)为88℃, 玻璃形成能力较低。随着Yb³⁺浓度提高, T_g、T_o和ΔT逐渐下降, 说明Yb³⁺降低了玻璃的热稳定性和形成能力。利用紫外可见分光光度计测定了样品的吸收/透过光谱, 玻璃在975 nm具有很强的吸收峰, 表明Yb³⁺可以有效提高玻璃对入射光的吸收强度; 在可见光范围内除特征吸收外具有近70%的透过率, 说明玻璃具有良好的透可见光性能, 有望获得高强上转换发光输出。上转换荧光光谱研究表明: 在980 nm激光泵浦下, 获得了中心位于535、554和672 nm处的绿、红发光带, x=0.16的发光最强, 672 nm处的红光强度是x=0的近130倍。上转换发光强度与泵浦功率关系的分析表明: 535、554 nm处的绿光和672 nm处的红光发光均是双光子发光过程。     

La2O3/WO3平面VOCs气体传感器的研究

采用厚膜工艺制备平面气敏元件并通过溶胶-凝胶法制得纳米三氧化钨(WO_3)粉体,然后加入了不同用量的三氧化二镧(La_2O_3)为敏感材料,制得La_2O_3/WO3,并对样品进行了测试。研究发现,适量的La_2O_3的添加抑制晶粒的增长,提高粉体材料的气敏性能,其中La_2O_3用量为10%(wt,质量分数)制得的La_2O_3/WO3传感器,在3.5V工作电压条件下,对浓度为10×10-6乙醇、丙酮、苯和二甲苯的响应电压分别为1.7V、2.0V、1.5V和2.0V,传感器响应-恢复时间比较迅速,响应和恢复时间分别为5s和15s。     

添加La2O3对Mg2TiO4陶瓷的显微结构与微波介电性能的影响

采用传统烧结工艺,制备了具有不同La₂O₃含量的镁钛镧陶瓷,并研究了La₂O₃组份对材料晶相构成、晶粒、晶界的演变、介电常数和品质因数的影响.结果表明,不含La₂O₃的钛酸镁陶瓷主晶相为Mg₂TiO₄,其平均晶粒尺寸>60μm;引入La₂O₃后,出现新晶相La_0.66Ti_O2.99,材料的晶粒尺寸明显下降;随La₂O₃含量的增加,材料的介电常数线性增加,材料的品质因数Q在10GHz出现最大值(16558).     

二次浸浆法对非对称α-Al2O3陶瓷微滤膜结构的修饰

研究了采用二次浸浆法来修饰非对称α－Ａｌ２Ｏ３陶瓷微滤膜。经性能表生，在通过调整悬乐料浓度、粘度、浸涂时间和提拉速率而有效控制了修饰膜厚度的基础上，二次浸浆法不但可以修复膜表面缺陷，同时还能使膜也径分布变窄，孔径缩小，达到进一步修饰膜结构的目的。     

BaO-Ln2O3-TiO2体系微波介质陶瓷的成分与结构的关系

BaO-Ln2O3-TiO2体系高介电常数微波介质陶瓷属于类钙钛矿鸽青铜结构,其固溶体分子式为Ba6-3x-Lns 2xTi18O54.分析了结构中占据A1、A2位的离子种类及占有率随x值的变化规律.当x=2/3时,Ba2 离子和Ln3 离子分别占据A2位和A1位,离子占位处于有序状态,因而陶瓷的损耗最小.     

Competitive Nucleation and Rapid Growth of Co-Si Intermetallic Compounds during Eutectic Solidification under Containerless Processing Condition

The liquid-solid transitions of (Co2Si+CoSi) and (CoSi+CoSi2) eutectic alloys were realized in drop tube and the rapid eutectic growth mechanism of intermetallic compounds was examined. The experimental and calculated results indicate that with increasing Co content, the intermetallic compound prefers nucleating primarily. The eutectic microstructures experience the transitions of ’lamellar-anomalous-divorced’ eutectic with undercooling. In undercooled state, the growth of CoSi intermetallic compound always lags behind others, and no matter how large the undercooling is, this intermetallic compound grows under the solutal diflusion control. The calculated coupled zone demonstrates that (Co2Si+CoSi) eutectic can form within certain undercooling regime, when the composition is in the range from 23.6% to 25.4% Si. And the calculated coupled zone of (CoSi+CoSi2) covers a composition range from 40.8% to 43.8% Si.     

定向凝固条件下Al-35%La过共晶合金的组织演变

在常规凝固条件下,Al-35%La过共晶合金可形成周期性双相枝晶组织,这种组织类似于带状组织,即其中枝晶的成分沿生长方向是周期性变化的。为了研究这种组织的形成条件,采用定向凝固技术研究了凝固速度对Al-35%La合金形貌特征的影响。结果表明:在不同凝固速度条件下,Al-35%La合金均形成周期性双相枝晶组织;同时发现:随着凝固速度的提高,初生相Al11La3呈现从周期性双相胞晶→周期性双相枝晶→周期性双相细胞晶的演变规律。在此基础上,讨论了这些组织形态的形成机理。     

Modeling Microstructural Evolution under the Influence of Thermosolutal Convection during Ingot Solidification Process

A model combined both macroscopic transport and microstructural evolution is applied to describe the influence of thermosolutal convection on microstructural evolution during the solidification process. Firstly, the volume average method and Simpler algor     

Phase equilibrium relations in the V2O3-La2O3 system

Phase equilibrium relations in the V₂O₃-La₂O₃ system were investigated by X-ray powder diffraction and metallographic techniques. Binary mixtures, prepared from high-purity V₂O₃ and La₂O₃ powders, were equilibrated at 1600° C and then arc-melted under a partial pressure of argon. The specimens were heat-treated at various predetermined temperatures for prolonged periods and the phases present were identified by reflected-light microscopy and X-ray powder diffraction. The system consists of only one binary compound LaVO₃. A eutectic between V₂O₃ and LaVO₃ was established at 1750° C and 19 mol % La₂O₃ and also between LaVO₃ and La₂O₃ at 1765° C and 75 moi % La₂O₃. No appreciable solid solubility was detected in the system.     

Liquidus surface in the HfO2-Y2O3-La2O3 system

The liquidus surface in the HfO₂-Y₂O₃-La₂O₃ system was studied by differential thermal analysis in helium at temperatures of up to 2500°C, derivative thermal analysis in air at temperatures of up to 3000°C, x-ray diffraction, optical microscopy, and electron microscopy. The liquidus surface was found to comprise five primary crystallization fields-those of theH-Y₂O_3-,C-Y₂O_3-,F-HfO_2-, andX-La₂O₃-based solid solutions and the pyrochlore phase La₂Hf₂O₇. Three invariant equilibria were identified in the system studied-two peritectics and one eutectic.     

Phase Diagram Prediction of the Al2O3-SiO2-La2O3 System

1.IntroductionRareearthoxidesareofgreatimportanceinsci-enceandtechnology.Mallyoftheseglassesexhibitanumberofextremepropertyvalues.Theyhavehighparamagneticsusceptibilities,hightransformationtemperatures,adustableexpansioncoefficieots,verylowheliumpermeabilityanddirectcurrelltcon-ductivity,highchemicaldurabilityandidealhightem-peraturepropertieswhichmakethembecomeexcel-lentcandidatematerialsinmanyfieldssuchasop-tics,laserapplicationsinsevereserviceconditionsandFaradayrotators.Extensiveexperimen…     

Microstructural Evolution of Rapidly Solidified Co-Mo and Ni-Mo Eutectic Alloys

Droplets of Co-37.6 wt pct Mo and Ni-47.7 wt pct Mo eutectic alloys were rapidly solidified during containerless processing in a 3 m drop tube. A kind of anomalous eutectic appears in these two eutectic alloys when undercooling is beyond 56 and 61 K, respectively. The two eutectic phases in anomalous eutectic were observed to grow in dendrite manner. The formation of anomalous eutectic is ascribed to the cooperative dendrite growth of the two independently nucleated eutectic phases. Current dendrite and eutectic growth theories are applied to describe the observed processes.     

Microstructural Evolution of Fe2O3 and ZnFe2O4 during Sonochemical Synthesis of Zinc Ferrite

The microstructural evolution of Fe₂O₃ and ZnFe₂O₄ during high-temperature (600–800°C) sonochemical synthesis of zinc ferrite is studied by x-ray diffraction analysis. The results are used to develop a qualitative model for ultrasonically activated solid-state reactions A _s +B _s C _s.     

TiO_2含量对Al_2O_3陶瓷涂层性能的影响

Ａｌ２Ｏ３是一种应用较为广泛的陶瓷涂层材料，但其熔点高，喷涂沉积效率较低。笔者以往研究表明，加入ＴｉＯ２可提高Ａｌ２Ｏ３涂层的致密性及喷涂沉积率。本文对加入ＴｉＯ２后Ａｌ２Ｏ３涂层的性能进行了试验。结果表明，当ＴｉＯ２含量为１３％～２０％时，涂层的耐磨性最好。