Catalytic properties of rare earth cobaltites and related compounds

The activity for conversion of methanol to CO₂ on rare-earth cobaltites is greatest for SmCoO₃, which has the highest room-temperature ratio of high-spin to low-spin cobalt ions. The sequence of the activities for Sm_0.5·M_0.5CoO₃ (M=Ca,Sr,Ba), Ba>Sr>Ca, is shown to vary as the amount of high-spin cobalt ion in these compounds at 200°C.     

Effects of rare earths on properties and microstructures of lead-free solder alloys

In order to further enhance the properties of lead-free solder alloys such as SnAgCu, SnAg, SnCu and SnZn, trace amount of rare earths were selected by lots of researchers as alloys addition into these alloys. The enhancement include better wettability, physical properties, creep strength and tensile strength. For Sn3.8Ag0.7Cu bearing rare earths, when the rare earths were La and Ce, the creep-rupture life of solder joints can be remarkably improved, nine times more than that of the original Sn3.8Ag0.7Cu solder joints at room temperature. In addition, creep-rupture lifetime of RE-doped solders increases by over four times for SnAg and seven times for SnCu. This paper summarizes the effects of rare earths on the wettability, mechanical properties, physical behavior and microstructure of a series of lead-free solders.     

Catalytic wet oxidations of aromatic compounds over supported copper oxides

Catalytic wet oxidations of naphthalene as a model compound of persistent aromatic compounds were carried out with hydrogen peroxide in a closed autoclave lined with Teflon. CuO/Al₂O₃ and CuO/AC catalyst showed the high activity for the naphthalene oxidation with hydrogen peroxide of 1.0 mol L⁻¹ at 100 °C. Naphthalene, whose initial concentration was 1.0 g L⁻¹, was converted completely and the concentration of water-soluble organic compounds in the resultant aqueous solution was less than 25 ppm-C. In contrast, platinum, and manganese oxide, silver oxide, and ruthenium oxide catalysts consumed hydrogen peroxide preferentially. Iron and nickel oxides catalysts showed lower activity than the copper oxide catalyst. During the reaction, the intermediate organic acids were formed and then were oxidized. Simultaneously, copper species of CuO catalysts were dissolved and then were precipitated. The precipitated copper species on the catalyst support showed the catalytic activity. CuO/Al₂O₃ catalysts showed high activity for the six successive batch reactions with the treatment of sodium carbonate after the reaction to precipitate copper ions.     

Separation of rare earths by ion exchange

Separation of rare earths from monazite source by ion-exchange process is discussed. Optimum conditions for obtaining kilogram quantities of individual rare earths of high purity are reported.     

Microstructures and electrical properties of copper oxide doped terbium oxide ceramics

The effects of copper oxide (CuO) on the microstructure and electric properties of nonstoichiometric compound terbium dioxide (Tb₄O₇) ceramics were investigated. Results included a reduction in the sintering temperature to 1,100 °C, a grain size of 4.2 μm, and a density of 96.2 %, which are larger than the values in previous investigation for Tb₄O₇ ceramics (grain sizes between 0.4 and 1.0 µm). Among the sintered ceramics, the sample doped with 10.0 wt% CuO showed the maximum nonlinear coefficient α = 43.5, which is obviously greater than α = 3.03 of the pure sample. Doping with 10.0 wt% CuO also exhibited nonlinearity α = 2.14 even at 1,123 K. In addition, the impedance spectra of the sample doped with 5.0 mol% CuO showed the largest grain boundary semicircle; 0 and 20 % samples showed both inductive and capacitive reactance.     

Catalytic combustion of ethyl acetate on supported copper oxide catalysts

Total oxidation of ethyl acetate on supported copper oxide catalysts was investigated. The catalysts have been prepared by wet impregnation method and characterized by XRD, TEM and XPS. Among the catalysts with the supports of TiO2, CeO2/TiO2 and CeO2-ZrO2/TiO2, CeO2-ZrO2 solid solutions doped TiO2 supported catalyst gives the highest catalytic activity. Catalyst with the composition of 5 wt.% CuO/10 wt.% CeO2-ZrO2-TiO2 shows the total oxidation of ethyl acetate at about 270 degrees C with the 100% CO2 selectivity. The characterization studies of supported copper oxide catalysts showed that the highly dispersed CuO is one of the active phase which contacts intimately with the support, the action of the interface between the components was not be ignored.     

Effects of different rare earths on the temperature dependence of rare earth cobalt magnets

In many applications, it is necessary to have permanent magnets whose characteristics vary little around a temperature Tr. We have developed a calculation to describe the thermal variation of the magnetization of the rare earth (RE) in such magnets including the effects of crystalline field. The exchange field of cobalt has been deduced at all temperatures from magnetization measurements on a single crystal of YCo5. From the calculation we can deduce the concentration x0, which gives dM/dT = 0 around room temperature, the resulting magnetization and the correspondingd^{2}M/dT^{2}.     

Microstructure and mechanical properties of M50NiL steel plasma nitrocarburized with and without rare earths addition

M50NiL steel was plasma nitrocarburized at 500 °C with and without rare earth (RE) addition. The nitrocarburized layers were characterized by optical microscope, scanning electron microscope equipped with an energy dispersive X-ray analyzer, X-ray diffraction, hardness tests and pin-on-disc tribometer. The results show that the RE atoms can diffuse into M50NiL steel surface and change the surface morphology of the nitrocarburized layer. The incorporation of RE atoms increases the surface hardness of the nitrocarburized layer (approximately 130HV_0.1 higher), layer thickness (about 14% thicker) and carbon content of the modified layer, respectively. The wear rates of the nitrocarburized specimens are significantly lower than that of the un-nitrocarburized one. The wear mechanisms of the specimens plasma nitrocarburized with and without RE addition are different mainly due to the differences in the surface morphology, the phase proportion and the hardness of the modified layer.     

Nutational nuclear quadrupole resonance in metal oxide compounds of copper

A pulsed nuclear quadrupole resonance method that can be used to study compounds with broad lines, especially metal oxide compounds of copper, is considered for the first time. Pis’ma Zh. Tekh. Fiz. 25, 74–77 (June 12, 1999)     

The preparation and properties of iron base self-fluxing alloy spray-welding coatings with different rare earths and chromium content

This investigation studied the effects of rare earths (RE) and chromium on the high temperature oxidation resistance and aqueous corrosion resistance of iron base self-fluxing alloy coatings. Four coatings were prepared through smelting-atomizing and oxide-acetylene flame spraying. The properties of the coatings were evaluated by cyclic oxidation tests, weight loss experiments, electrochemical impedance spectroscopy (EIS), potentiodynamic scanning technique, scanning electron microscopy (SEM) and electron dispersive X-ray analysis (EDAX). The addition of RE greatly enhanced the oxidation resistance of the coatings. This effect was attributed to the fact that RE changed the ion diffusion patterns of the coatings in the process of scale forming, resulting in more protective scales with high adhesion. The increase of chromium content in the coatings enhanced the corrosion resistance of the coatings in nitric acid solution, but in hydrochloric acid and sulfuric acid solutions the result was reversed. Rare earth addition had a beneficial effect in sulfuric acid and nitric solutions, but in hydrochloric acid, the samples with RE had a corrosion rate slightly higher than that of the samples without RE addition. These results are explained by the effect that the addition of RE minimized the cathodic area of the coatings.     

Luminescent properties of rare earth ions in one-dimensional oxide nanowires

Rare-earth doped one-dimensional oxide nanowires including LaPO4, La2O3, and Gd2O3 were synthesized by the hydrothermal method. Their luminescent properties including local environments, electronic transitions, energy transfer, and frequency up-conversion luminescence processes were systematically studied. In LaPO4:Eu and La2O3:Eu nanowires, different symmetry sites of Eu3+ ions were identified, which obviously differed from those of the corresponding micrometer-sized particles. This was attributed to crystal field degeneration in the fringe along the length axis. In LaPO4:Eu nanowires, the electronic transition rate of 5D1-sigmaJ7FJ increased approximately 2 times over that of the zero-dimensional nanoparticles and micrometer-sized particles, which was related to the variation of dipole field induced by shape anisotropy. Considering the nonradiative relaxations, meanwhile, the luminescent quantum efficiency for 5D1-sigmaJ7FJ transitions of Eu3+ in nanowires increased 100% over that in nanoparticles and 20% over that in micrometer particles. In Gd2O3:Eu3+, LaPO4:Ce3+, and LaPO4:Tb3+ nanowires and micrometer-sized particles, the electronic transition rate of rare earths had only a little variation. In LaPO4:Ce3+/Tb3+ nanowires, the energy transfer rate of Ce3+--> Tb3+ decreased 3 times compared to that in micrometer rods. Despite this, the brightness for the 5D4-7F5 green emissions of Tb3+ increased several times due to decreased energy transfer from the excited states higher than 5D4 to some defect levels. In Gd2O3:Er3+/Yb3+ nanocrystals, as the shape varied from nanopapers to nanowires, the relative intensity of up-conversion luminescence of 2H(11/2)/4S(3/2)-4I(15/2) and 4F(9/2)-4I(15/2) to the infrared down-conversion luminescence of 4I(13/2)-4I(15/2) increased remarkably, indicating efficient up-conversion luminescence. Our present results indicate that rare-earth-doped oxide nanowires is a type of new and efficient phosphors.     

One-dimensional rare earth compounds and complexes: preparation and improved photoluminescence properties

One-dimensional nanosized phosphors demonstrate special structural and photoluminescence properties, which have application potential in some optical fields. In this article, we present our recent progress on preparation and luminescence properties of some one-dimensional rare earth compounds and complexes, the core-shell oxide nanowires prepared by a two-step hydrothermal route, the nanowires of some inorganic compounds doped with rare earths and rare earth complexes/PVP composites prepared by the electrospinning method, and the rare earth complexes in the SBA-15 mesoporous molecule sieves. In these systems, some novel or improved photoluminescence properties are observed such as improved luminescence quantum yield, thermal stability and/or photostability, and depressed thermal effect in upconversion luminescence.     

纳米级稀土材料在汽车尾气净化中的应用

汽车尾气是当今大气污染的主要来源之一 ,催化净化是国际普遍采用的汽车尾气净化法。本文根据我国贵金属贫乏而稀土资源丰富的国情 ,以及稀土纳米材料特有的性质和功能 ,综述了纳米级稀土材料在汽车尾气净化中的应用及其发展前景     

Catalytic combustion of benzene over copper oxide supported on SBA-15 using chelating method

The catalytic combustion of benzene over copper oxide supported on SBA-15 was investigated. The catalysts were prepared by the using chelating method and characterized. It is clear that the loading of CuO on the silica matrix drastically decreases the surface area and pore volume of the catalysts, as would be expected for the incorporation of CuO. The catalytic activity increased with an increase of CuO loading ratio. When CuO loading reached 5.8 wt%, the total conversion temperature was lowered to 350 degrees C.     

Effect of rare earths on impact toughness of a low-carbon steel

Studies of an industrial low-carbon steel (B450NbRE) suggest that the impact toughness is unexpectedly low under its practical service, probably resulting from the unstable recovery of rare earths (RE) in steelmaking. The purpose of this work is to investigate the effect of RE on the impact toughness in low-carbon steel. The B450NbRE steels with content of 0.0012–0.0180 wt.% RE were produced by vacuum induction furnace. The impact toughness and microstructure were investigated after hot rolled. The Gleeble-1500 thermal simulator was used to validate the effect of RE on the microstructure. The results indicate that the microstructure of hot-rolled steels is characterized by polygonal ferrite, quasi-polygonal ferrite, bainite and pearlite. The impact toughness increases with RE contents reaching the peak with content of 0.0047 wt.% RE, such a change exhibits the same rule as the case of the ferrite amount. However, this improvement in impact toughness is not only due to an increase in ferrite amount, but also the fine grained structure and the cleaner grain boundaries. And content of 0.0180 wt.% RE is excessive. Such an addition of the RE resulted in the martensite precipitates at the grain boundaries, which are extremely detrimental to impact toughness.     

多元稀土氧化物掺杂二氧化锆基陶瓷材料的热物理性能

稀土氧化物(RE)掺杂氧化钇稳定二氧化锆(YSZ)是提高传统YSZ热障涂层隔热性能和高温稳定性的有效途径之一。在1500 ℃高温固相反应烧结24 h制得Gd₂O₃和Yb₂O₃多元稀土氧化物掺杂的YSZ(含3.5%Y₂O₃(摩尔分数))(GY-YSZ)陶瓷材料。采用XRD研究了GY-YSZ 陶瓷材料的晶体结构和物相组成; 采用激光脉冲法研究了Gd₂O₃和Yb₂O₃掺杂对GY-YSZ 陶瓷材料的热物理性能的影响规律。研究发现, 掺杂2.0%~3.0%Gd₂O₃和Yb₂O₃(摩尔分数)后GY-YSZ的热导率为0.90~1.15 W·(m·K)-1, 比YSZ降低30%以上, 显示了良好的隔热性能。稀土氧化物掺杂对YSZ陶瓷材料热物理性能的影响机制为: 掺杂Gd₂O₃和Yb₂O₃导致YSZ中单斜相(M)、 四方相(T)和立方相(C)含量发生变化, 同时YSZ晶格发生畸变。      

Synthesis and properties of copper and samarium doped yttria-bismuth oxide powders and membranes

Powders of Bi_1.5Y_0.5–y Cu _y O_3– (BYC) and Bi_1.5Y_0.3Sm_0.2O₃ in the fluorite phase structure were prepared by the citrate method. The chemical reactions involved in the synthesis of these powders were proposed and verified experimentally. Dense BYC and BYS membranes were prepared from the powders by the press and sintering method. The optimum conditions for powder preparation as well as for membrane fabrication were determined in this study with the aid of various characterization methods. The BYC and BYS membranes were gas-tight to helium. These doped bismuth-yttrium (BY) oxide membranes show similar ionic conductivity but much higher oxygen permeability (electronic conductivity) as compared to the undoped BY membrane.