A Study on La2O3－Y2O3－Mo Secondary Emission Material

The substrate molybdenum doped with La2O3, Y2O3 cathode material was made by the powder metallurgy method. The secondary emission coefficients of the materials were tested. The experimental results show that Mo cathodes doped with La2O3, Y2O3 have good secondary emission properties. When the cathodes are activated, the maximal secondary emission coefficients of these cathodes are higher than 2.0 and can meet the practical requirement. The distribution of the rare earth in the interior and at surface of this kind of cathode material before and after emission was studied using Scanning Electronic Microscopic (SEM) and X-Ray Photoelectron Spectrum(XPS). The analysis results show that the rare earth is easy to gather at grain boundaries and the relevant concentration of rare earth on the surface after emission is obviously greater than that before emission.     

Y2O3和La2O3对金属陶瓷内衬显微硬度和耐蚀性的影响

研究了钇、镧等添加物对金属陶瓷内衬显微硬度和耐蚀性的影响。结果表明:加入Y2O3、L a2O3和S iO2可使陶瓷层的孔隙度降低,一定程度上使耐蚀性增加。L a2O3对提高陶瓷层性能的效果比Y2O3要好。     

Optical performance study of Sr_2ZnSi_2O_7:Eu~(2+),Dy~(3+), SrAl_2O_4:Eu~(2+),Dy~(3+) and Y_2O_2S:Eu~(3+),Mg~(2+),Ti~(4+) ternary luminous fiber

In this study, down-conversion fluorescent powder of Sr_2ZnSi_2O_7:Eu~(2+),Dy~(3+), SrAl_2O_4:Eu~(2+),Dy~(3+) and Y_2O_2S:Eu~(3+),Mg~(2+),Ti~(4+), which were the common three primary colors materials with long afterglow, were synthesized by high temperature solid state method. The blends of rare earth(RE) luminescent materials have been of interest to reinvest the luminescent characteristics of polyethylene terephtahalate(PET) luminous fiber. The scanning electron microscopy(SEM) and an inversion fluorescence microscope were used to characterize the surface morphology and the dispersion of inclusion. Through analysis of microcosmic morphology, three typical dispersions of luminescent particles were summarized. The X-ray diffraction indicated that the phase structure of fiber samples and crystal structure of luminescence materials kept complete after prilling and spinning. From the fluorescence spectra and CIE 1931 coordinates, it could be found that different combinations of luminous fibers were desired to obtain divers colors emission luminous fiber. And the fiber samples were a light sensation which could induct different excitation wavelengths and convert it down to different colors. The afterglow decay curve and its differential curve were summarized indicating the three decay stages. The decay curve and decay rate curve showed that the contents of Sr_2ZnSi_2O_7:Eu~(2+),Dy~(3+), SrAl_2O_4:Eu~(2+),Dy~(3+) and Y_2O_2S:Eu~(3+),Mg~(2+),Ti~(4+) had obvious influence on the afterglow of fiber samples.     

Microstructure and high-temperature properties of Fe-Ti-Cr-Mo-B-C-Y_2O_3 laser cladding coating

Fe-based composite coatings were fabricated on 5 CrNiMo die steel by laser beam melting a precursor mixture of ferrotitanium,ferrochromium,ferromolybdenum,B4 C and Y_2 O_3 powders.Micro structure and properties of the coatings were studied by X-ray diffraction(XRD),scanning electron microscopy(SEM),energy-dispersive spectrometer(EDS),resistance furnace and high-temperature tribometer.The results show that(Ti,Mo)C particles with flower-like and(Ti,Mo)B_2 with block-like shapes are in situ formed during laser cladding.Volume faction of multiple ceramic particles increases with the increasing of Y_2 O_3.The cumulative oxidation mass of the coating with 2 wt% Y_2 O_3 is decreased by one-third than that of the coating without Y_2 O_3.The oxidation layer of the coating with Y_2 O_3 is getting smooth.Meanwhile,high temperature wear volume loss of the coating with 2 wt% Y_2 O_3 is about 40% that of the coating without Y_2 O_3.The coating with 2 wt% Y_2 O_3 shows a smoother wear scar and few flat grooves are observed after high temperature wear test.     

Study of Bi_2O_3-based Rare Earth Solid Electrolyte Used in Fuel Cell

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Effect of rare earth oxides on the properties of bio-soluble alkaline earth silicate fibers

Using natural mineral wollastonite, talc and quartz sands as raw materials, rare earth oxides(La_2O_3, Nd_2O_3 and Y_2O_3) as additives, the bio-soluble alkaline earth silicate fibers were prepared by melting and blowing process. The viscosity of the molten materials, bio-solubility and crystallization behavior of the fiber were investigated. The results indicated that the fiber drawing temperature range could be broadened since the slope of the temperature-viscosity curve decreased with adding rare earth oxide. The addition of rare earth oxide was beneficial to the increase of crystallization temperature by strengthening the network structure of the fiber. The existence of rare earth oxide in the fibers would reduce the solubility of the fibers, which still belonged to bio-soluble fibers.     

Rare earths (Ce,Y, Pr) modified Pd/La_2O_3-ZrO_2-Al_2O_3 catalysts used in lean-burn natural gas fueled vehicles

14%REO_x-2.5%La_2 O_3-33.5%ZrO_2-50%Al_2 O_3(RE = Ce, Y, Pr) composites were prepared by a coprecipitation method. The Pd catalysts were obtained by an aqueous solution of Pd(NO_3)_2 loaded on the rare earths modified composites with an initial wet impregnated method. The experiment results show that catalytic activity of the rare earths modified Pd/La_2 O_3-ZrO_2-Al_2 O_3 catalysts is better than bare sample for methane oxidation. The structural characterization results reveal that the rare earths modified Pd catalysts increase amounts of surface active oxygen species by X-ray photoelectron spectroscopy(XPS) analysis and improve the dispersion of active component from H2-temperature programmed reduction(H2-TPR) measurement compared with bare sample. Especially,Pd/14%Y_2 O_3-2.5%La_2 O_3-33.5%ZrO_2-50%Al_2 O_3 sample exhibits highly active stability, it is related to the Pd particles highly dispersion,which was observed by transmission electron microscope(TEM) images.     

A Study on the Thermal Stability of La_2O_3-TiO_2 Supports

In this paper,various techniques including BET,XRD,SEM and XPS were used to study the sintering ofpure and La_2O_3-doped titania.The experimental results show that sintering of titania proceeds via volume diffu-sion.Adding of lanthanum oxide decreases the rate of sintering and hinders the phase transition from anatase torutile crystal by strong surface interaction between the mixed crystals(La_4Ti_9O_(24),La_(0.66)TiO_(2.99))and TiO_2.     

ZrO_2-Al_2O_3(Y_2O_3)材料的相结构研究

本文通过X衍射技术和多晶法计算研究了ZrO_2-Al_2O_3和ZrO_2-Al_O_3-Y_2O_3陶瓷材料的相结构变化。结果表明,在ZrO_2-Al_2O_3体系中,在低Al_2O_3含量时,主要相是单斜相。随着Al_2O_3含量增大,单斜相比率系数X_m下降,四方相含量明显增大。在ZrO_2-Al_2O_3体系中添加Y_2O_3后,Y_2O_3可以促进形成四方相和稳定相系的作用,使三元系转变为四方结构。烧结温度对ZrO_2-Al_2O_3系相结构变化影响不明显,但对ZrO_2-Al_2O_3-Y_2O_3系影响较大,低Y_2O_3含量时,温度升高可促进相系的转移;而高Y2O_3含量时,已完全转变为四方结构。所以,烧结温度对相结构变化无影响。     

Enhancement of secondary emission property of molybdenum cathode co-doped with La_2O_3 and Y_2O_3

La2O3 and Y2O3 co-doped Mo secondary emitters were prepared by three kinds of doping method combined with high temperature plasma sintering.The secondary electron emission property and microstructure of the cathodes were studied.It showed that the cathode prepared by liquid-liquid doping method exhibited the best emission property among all the samples prepared by liquid-solid doping,solid-solid doping and liquid-liquid doping methods due to a uniform distribution of different substances.RE2O3 existed unifo...     

离子交换树脂法制备纳米La_2O_3及表征

以La(NO3)3.6H2O为原料,用强碱性阴离子交换树脂为沉淀剂,制备了纳米La2O3。前驱物及产物进行了TG-DTA、XRD、TEM、HRTEM、SAED、BET等表征。实验结果表明,前驱物是La(OH)3,产物为宽约20nm~25nm、长约为80nm~200nm的板状或棒状La2O3纳米多晶体。     

Phase equilibria in low basicity region of CaO-SiO_2-Nb_2O_5-(5 wt%,10 wt%,15 wt%) La_2O_3 system

The lack of thermodynamic information,such as primary phase fields and liquidus temperatures,in the CaO-SiO_2-Nb_2O_5-La_2O_3 quaternary system phase diagram has restricted the comprehensive utilization of the niobium(Nb) and rare earth(RE) resources.In this work,the phase equilibria in low basicity region(w(CaO)/w(SiO_2)1) of CaO-SiO_2-Nb_2O_5-(0-15 wt%)La_2O_3 system at 1373-1873 K were experimentally studied by thermodynamic equilibrium experiment,and then,the results were analyzed by X-ray diffraction(XRD),scanning electron microscopy(SEM),and energy dispersive spectrometry(EDS).Additionally,an optimized method was proposed to process the compositions of equilibrium liquid phases at different temperatures.According to the experimental results,the univariate line between CaNb_2O_6,SiO_2 and LaNbO_4 primary phase fields,interface between CaNb_2O_6 and SiO_2 primary phase fields and isothermal liquidus surfaces in SiO_2 primary phase field were determined.Finally,the spatial phase diagram of CaO-SiO_2-Nb_2O_5-La_2O_3 within specific region was constructed,and furthermore,the phase diagram was also presented in CaO-SiO_2-Nb_2O_5 pseudo-ternary system with w(La_2O_3)=5 wt%,10 wt% and 15 wt%.The research results have guiding significance for the improvement of related phase diagram and the comprehensive utilization of Nb and RE resources.     

Can lanthanum doping enhance catalytic performance of silver in direct propylene epoxidation over NaMoAg/SiO_2?

In the attempt to reduce surface free energy of silica to improve interaction of silica with silver, silica was doped by different amounts of low surface energy lanthanum, La_2O_3, through impregnation. The doped and undoped silica were used as supports for preparation of Na/Ag/Mo/La_2O_3-SiO_2 catalysts. Catalytic performances of the catalysts were evaluated in direct epoxidation of propylene(DPO) using molecular oxygen under atmospheric pressure and without adding hydrogen. Adding 5 wt%La to the Na/Ag/Mo/SiO_2 catalyst improves both the catalysts electivity in DPO and its stability over 20h of time-on-stream.The characterization results show that La_2O_3 species interact strongly with silver particles on the silica surface which result in significant improvement in the dispersion profile of silver and marked decrease in the size of silver nanoparticles(AgNPs). The estimated mean diameter of AgNPs is ca. 4.0 nm in Na/Ag/Mo/5 wt%La_2O_3-SiO_2, which is smaller than that(53.9 nm) found in Na/Ag/SiO_2. The presence of subnanometer AgNPs on Ag/La_2O_3-SiO_2 prior addition of MoO_3 and NaCl to the sample can enhance the mutual electronic synergism between Ag, MoO_3 and Na for selective production of propylene oxide.     

纳米La_2O_3粉晶的制备及其表征

以La(NO_3)_3·6H_2O、NH_4HCO_3和聚乙二醇为原料,利用沉淀法制备了纳米La_2O_3粉体,利用XRD,TG-DTA和TEM等测试方法对干凝胶热分解过程及最终形成的纳米La_2O_3粉体进行了分析和表征,XRD法考察了前驱体在不同热处理条件下产物物相和晶粒度的变化情况,实验结果表明,在适当工艺参数下,前驱体经720℃,1h焙烧所得产物为平均粒径小于50nm的La_2O_3粉体.     

稀土钼合金力学和热发射性能的研究

稀土氧化物 (La2 O3 、Y2 O3 )在强化钼的同时 ,对钼具有显著的韧化作用 ,即具有综合强韧化作用。稀土钼材作为高温结构材料正逐步取代Al Si K掺杂钼 (ASK)和TZM钼合金 ;通过成分设计和加工工艺优化 ,稀土钼还是一种工作温度低、无放射性污染的新型阴极材料 ,由稀土钼作为阴极的电子管 ,发射性能与寿命均达到或超过同类型W ThO2 阴极电子管 ,达到实用化水平。因此 ,稀土钼作为一种集结构与功能于一身的新型材料 ,有广泛的应用前景     

反相微乳液碳吸附耦合法制备氧化钇稳定四方氧化锆纳米粉体及表征

采用反相微乳液和碳吸附法制备了氧化钇稳定四方氧化锆纳米粉体,探讨了碳黑的加入量对粉体比表面积的影响,得到最佳的碳黑量。分别采用XRD、TEM、BET和TG分析了不同温度下煅烧所得粉体的物相、颗粒度和比表面积以及前驱体热分解特性。实验结果表明,经700℃焙烧后制得了分散性好的四方相ZrO2纳米粉体,比表面积为97.4m2/g,平均粒径为9nm。     

Reduction of Tb~(4+) ions in luminescent Y_2O_3:Tb nanorods prepared by microwave hydrothermal method

Terbium doped yttrium oxide was prepared with the microwave hydrothermal method. The Y_2O_3:Tb nanomaterial crystallized as needle-like grains. Bright luminescence in the green region was observed. Significant luminescence intensity increase was obtained after thermal treatment. Reduction of terbium ions was observed after heating in the air atmosphere. Tb~(4+) ions were found to be stabilized by crystal impurities. Hydroxyl species were found to have impact on vacancies elimination. The terbium ions were used as optical and magnetic indicator of the material properties.     

铌硅化物基超高温合金Si-Y_2O_3共渗涂层的组织及裂纹形成

采用分别于1 050、1 150、1 250 ℃保温10 h的Si-Y_2O_3包埋共渗工艺,在铌硅化物基超高温合金表面制备了Y改性的硅化物涂层.利用SEM、EDS和XRD等方法分析了Y对涂层形貌及裂纹形成的影响,并与相同温度和时间下单独渗Si涂层的组织进行了对比.结果表明,涂层外层上部为分布均匀致密的(Nb,M)Si_2柱状晶,外层下部为疏松的(Nb,M)Si_2等轴晶;渗剂中添加质量分数为0.75%的Y_2O_3可以细化涂层组织,且当渗剂中的w(Y_2O_3)为0.50%～0.75%时,所制备涂层的纵向裂纹和横向裂纹的总长度均较小.     

Persistent luminescence from Y_3Al_2Ga_3O_(12) doped with Ce~(3+) and Cr~(3+) after X-ray and blue light irradiation

The persistent luminescence(PersL) dependence on the dopants and derived mechanism of trapping and de-trapping processes were investigated in Y_3Al_2Ga_3O_(12)(YAGG) based nanophosphor,doped with Ce~(3+) and/or Cr~(3+).It is found that the presence of Cr~(3+) ions produce electron and hole traps and capture suitable charge after X-ray irradiation.The effect of irradiation on the carriers trapping and their pathways after excitation was studied by means of thermo luminescence technique.On the other hand,for blue light irradiation the mechanism seems to be different.In the latter case,the Ce~(3+) ions,having the position of energy levels in the conduction band,become sensitizers for the electrons and main emission centres for the PersL(de-trapping process goes through Ce~(3+)).     

Synthesis and Property of H2La2Ti3O10/CdS Layered Nanocomposite Photocatalyst

H2La2Ti3O10/CdS nanocomposite with er photoactivity was synthesized by a stepwise exchange process from H2La2Ti3O10, which was obtained by H^＋ -exchanging reaction of H2La2Ti3O10 with HCl other than the normally used HNO3. The pillaring process was investigated by XRD, TEM, FT-IR and BET methods. The photocatalytic decomposition of aniline was used as the model system to evaluate the photochemical properties of H2La2Ti3O10/CdS,H2La2Ti3O10 and K2La2Ti3O10. It is found that the photoactivity of layered H2La2Ti3O10 is greatly improved by the intercalation of CdS in the interlayer. In general, the excellent photoactivity of the H2La2Ti3O10/CdS nanocomposite might be attributing to the extremely small particle size of incorporated CdS and good contact between CdS and La2Ti3O10^2- layers. On the other hand, the coupling of two semiconductor particles with different energy gap is useful to achieve effective charge separation. In H2La2Ti3O10/CdS, a photo-generated electron can transfer from CdS to the La2Ti3O10^2- layer, while the holes remain in the CdS particles. This helps to diffuse the electrons and holes before reaching the interface, and the holes and electrons can be effectively captured by the electrolyte in the solution. Simuhaneously, the optimal operating condition of photodecomposition aniline was investigated.