用磁天平测定稀土氧化物催化剂中Mn的含量

本文根据物质的磁化率具有加和性的原理，提出了用Ｆａｒａｄａｙ式磁天平测定稀土氧化物催化剂中Ｍｎ含量的方法，该法不需进行样品的分解和分离，具有快速简便，不破坏样品的优点。

稀土-钛氧簇合物的研究进展

稀土-钛氧簇合物作为团簇化学的一个新分支,不但结合了稀土和钛离子的特性,而且由于二者的协同效应而表现出优异的光、电、磁和催化性能.本文综合评述了不同配体稀土-钛氧簇合物的合成与结构,介绍了稀土-钛氧簇合物的代表性成果,并对其合成策略和发展前景进行了总结和展望.

稀土-钛氧簇合物EuTi6,EuTi7和La2Ti14的可控合成

相比于纳米材料,原子精度的金属簇合物具有精确的表面结构和晶体结构,更有利于在原子水平上去理解化学反应的活性与结构的关系。作为团簇的一个有趣的分支,异金属的稀土-钛氧簇合物因其有趣的化学性质引起了人们的广泛关注。但是稀土-钛氧簇合物的精准合成是目前的重要挑战,这阻碍了其性能的进一步研究。因为螯合配体可以降低Ti4+的水解速度,因此选择合适的螯合配体是制备稀土钛氧团簇的有效方法。最近,我们以螯合作用较强的3,5-二叔丁基水杨酸(H2dtbsa)为配体,稀土盐和Ti(OiPr)4为原料,通过溶剂热法成功合成了四个新的稀土-钛氧簇合物[EuTi6(μ3-O)3(OC2H5)8(dtbsa)6(Hdtbsa)]·(C2H5OH)(1),[EuTi7(μ3-O)3(μ2-OH)2(OiPr)9(dtbsa)6(Hdtbsa)Cl]·(HOiPr)3(2),[EuTi7(μ3-O)3(μ2-OH)2(OiPr)8(dtbsa)7(Hdtbsa)]·(HOiPr)2(3)和[LaTi7(μ3-O)3(μ2-OH)2(OC2H5)8(dtbsa)7(Hdtbsa)]2·(C2H5OH)4(4)。单晶分析表明,七核化合物1内核EuTi6具有三角棱柱的结构,其中Eu3+位于六个Ti4+离子形成的棱柱中心。八核化合物2和3的金属内核结构可以看作是化合物1中三棱柱的一侧连接一个Ti4+。化合物4中,Ln2Ti14的金属骨架可看作是EuTi7的二聚体。紫外-可见漫反射光谱估算的带隙值表明,簇合物1、2和3的禁带宽度值分别为2.35、2.07和2.16 eV,明显小于锐钛矿的禁带宽度值。光电响应测试发现这三种簇合物具有明显的光电响应,而且簇合物1和2的电荷分离效应好于簇合物3。为了探索这类簇合物在光催化方面的应用,我们做了在甲醇水溶液中的光催化(300–800 nm)分解水产氢实验。簇合物1、2和3的产氢率分别为112、106和87μmol?h-1?g-1,高于商用P25。粉末X射线衍射(PXRD)和热重分析(TGA)证明了簇合物的光热稳定性。本文不但提供了一种制备稀土钛氧簇合物的螯合配体策略,而且还表明稀土钛氧簇合物具有较低的带隙和光驱动的催化活性。

稳定自由基与六氟乙酰丙酮稀土配合物的合成和磁性研究

对稳定自由基与六氟乙酰丙酮稀土配合物的合成进行了研究,通过元素分析、电导测定、热重分析、红外光谱、电子光谱、ESR谱等对配合物进行了表征。

添加稀土对吸波材料性能的影响

在铁砂、铁氧体和铁磁 -铁电等复合电波吸收材料中掺入微量稀土氧化物能全面大幅度提高材料的吸波特性。最大吸收量可提高 5 4 %～ 1 2 5 % ,1 0 d B带宽扩展近一倍。匹配厚度也有所降低。还发现 ,稀土氧化物的掺入量存在极值 ,添加混合稀土氧化物比添加高纯度稀土氧化物能获得更好的效果。

NiO－RE_2O_3／α－Al_2O_3催化剂制备过程中稀土的流失

用浸渍法考察先浸硝酸稀土、后浸硝酸镍制备ＮＩＯ－ＲＥ２Ｏ３／α－Ａｌ２Ｏ３催化剂过程中浸渍液的酸度、温度等因素对催化剂上稀土（ＲＥ２Ｏ３）流失的影响，并讨论了抑制稀土流失的方法。

Impedance spectroscopy study of high-temperature oxidation of Gd_2O_3-Yb_2O_3 codoped zirconia thermal barrier coatings

3Gd2O3-3Yb2O3-4Y2O3 （mole fraction, %） co-doped ZrO2 （GY-YSZ） thermal barrier coatings （TBCs） were produced by electron beam physical vapor deposition （EB-PVD）. The oxidation behavior of GY-YSZ at 1 050 ℃ was investigated using impedance spectroscopy （IS） combined with scanning electron microscopy （SEM）, Raman spectroscopy and X-ray diffractometry （XRD）. Various electrical responses observed in the impedance spectra corresponding to GY-YSZ grains and grain boundaries were explained using circuit modeling. The change in the conduction mechanism of GY-YSZ was found to be related to the O^2- vacancy and lattice distortion due to the stabilizer diffusion during the oxidation. The results also suggested that the specific oxidation information about the GY-YSZ grains and grain boundaries should be acquired at a moderate measurement temperature, which was related to the resistance value in the impedance spectra. The resistance values of the GY-YSZ grains and grain boundaries should be measured at 200 ℃ and 300 ℃, respectively.

Calculating models on surface tension of RE_2O_3-Mg O-SiO_2(RE=La, Nd, Sm, Gd and Y) melts

A thermodynamic model was developed for determining the surface tension of RE2O3-MgO-SiO2(RE=La, Nd, Sm, Gd and Y) melts considering the ionic radii of the components and Butler's equation. The temperature and composition dependence of the surface tensions in molten RE2O3-MgO-SiO2 slag systems was reproduced by the present model using surface tensions and molar volumes of pure oxides, as well as the anionic and cationic radii of the melt components. The iso-surface tension lines of La2O3-MgO-SiO2 slag melt at 1873 K were calculated and the effects of slag composition on the surface tension were also investigated. The surface tensions of La2O3, Gd2O3, Nd2O3 and Y2O3 at 1873 K were evaluated as 686, 677, 664 and 541 m N/m, respectively. The surface tension of pure rare earth oxide melts linearly decreases with increasing cationic field strength, except for Y2O3 oxide, while Y2O3 has a much weaker surface tension. The evaluated results of the surface tension show good agreements with literature data, and the mean deviation of the present model is found to be 1.05% at 1873 K.

ErCl_3－CaCl_2－LiCl三元体系相图的研究

利用ＤＴＡ研究了ＥｒＣｌ_３ＣａＣｌ_２ＬｉＣｌ三元体系相图。发现该相图有对应于ＥｒＣｌ_３、ＣａＣｌ_２、ＬｉＣｌ和Ｌｉ_３ＥｒＣｌ_６的４个液相面，５条二次结晶线，一个三元低共熔点Ｅ（５８．５％ＥｒＣｌ_３，２３．７％ＣａＣｌ_２，１７．８％ＬｉＣｌ，３９７℃），一个三元转熔点Ｐ（５２．５％ＥｒＣｌ_３，２７．２％ＣａＣｌ_２，２０．３％ＬｉＣｌ，４２８℃）。相应的４相平衡反应为：Ｌ＝ＥｒＣｌ_３＋Ｌｉ_３ＥｒＣｌ_６＋ＣａＣｌ_２；Ｌ＋ＬｉＣｌ＝Ｌｉ_３ＥｒＣｌ_６＋ＣａＣｌ_２．

ANALYSES OF WAGNER'S MODEL

To achieve a better understanding of the effects of the colossal magnetoresistivity in the mixed valence manganites,the model of a negative magnetoresistivity scaling proposed by Wagner et al is explored in both mathematical and physical analyses.The inconsistency in Wagners model is discussed and corrected. The behaviors of the large spin polarons in Nd 0.52 Sr 0.48 MnO 3 film at T c are studied and analyzed.The results show that only through necessary corrections can Wagners model become self consistent. A further exploration of the nature of the magnetically aligned clusters will make the model more convincing.

Separation and Manipulation of Rare-earth Oxide Particles by Dielectrophoresis

A challenge in chemical engineering is the separation and purification of rare-earth elements and their compounds. We report the design and manufacture of a dielectrophoresis(DEP) microchip of microelectrode arrays. This microchip device is constructed in order to use DEP to capture micro-particles of rare-earth oxides in petro-leum. Dielectrophoretic behavior of micro-particles of rare-earth oxides in oil media is explored. The dielectropho-retic effects of particles under different conditions are investigated. It is showed that the prepared microchip is suit-able for use in the investigation of dielectrophoretic responses of the rare-earth oxides in oil media. The factors such as frequency,particle size and valence of rare-earth metal are discussed. When the frequency is fixed,the transla-tion voltage decreases as particle size increases. Lower frequencies are more effective for manipulation of inorganic particles in oil media. Particles of the same rare-earth oxide with different size,as well as particles of different rare-earth oxides,are captured in different regions of the field by regulating DEP conditions. This may be a new method for separation and purification of particles of different rare-earth oxides,as well as classification of particles with different size.

Luminescent properties of BaO-La_2O_3-B_2O_3 glasses with dopant

The luminescent properties of glasses synthesized in air atmosphere by conventional high temperature process were studied. The emissions spectra of Eu2+ and Eu3+ were observed in BaO-La2O3-B2O3-Eu2O3 glasses. The results show that the broad emission peaks at 430 nm correspond to 5d→4f emission transition of Eu2+, the sharp emission peaks at 592, 616, 650 and 750 nm correspond to 5D0→7Fj（j=1-4） emission transition of Eu3+, respectively, which indicates that the BaO-La2O3-B2O3-Eu2O3 glass can convert ultraviolet and green components of sunlight into blue and red light so as to increase the intensity of blue and red light, respectively. The luminescent intensity of Eu2+ increases with increasing the molar ratio of Tb3+ in BaO-La2O3-B2O3-Eu2O3-Tb4O7 glasses, whereas the luminescent intensity of Eu3+ decreases. So the luminescent intensity of Eu（III, II） is influenced by Tb3+. These phenomena can be explained by electron transfer mechanism: Eu3+（4f6）+Tb3+（4f8）→Eu2+（4f7）+Tb4+（4f7）. Taking advantage of the luminescent properties of BaO-La2O3-B2O3-Eu2O3 glasses, light-conversion glass for agriculture can be produced.

Effects of various rare earth oxides on morphology and size of oxide dispersion strengthening(ODS)-W and ODS-Mo alloy powders

Ultrafine oxide dispersion strengthening(ODS)-Mo and ODS-W alloy powders containing different types of oxide nanoparticles were successfully synthesized by spraying method(solid−liquid mixing method)combined with the reductions with carbon black and hydrogen in sequence.It is concluded that the solution concentration and type of rare earth oxide have no effect on the grain size of ODS-Mo alloy powder,but have obvious effect on that of ODS-W alloy powder.The higher the concentration of rare earth solution is,the smaller the average grain size of ODS-W alloy powder is.Furthermore,compared with doping with CeO_(2),the grain sizes of reduction products of La_(2)O_(3) and Y_(2)O_(3) doped WO_(3) are relatively larger.Compared with the undoped case,there is almost no change for grain size of ODS-Mo alloy powder,while the grain size of ODS-W alloy powder becomes much larger.This is probably due to the appearance of the composite oxide(such as La_(2)WO_(6))formed by the reaction between tungsten oxide and rare earth oxides,which promotes the heterogeneous nucleation and growth of tungsten grains during the reduction process of ODS-W,while there is no complex oxide composed of molybdenum and rare earth oxides in the reduction process of ODS-Mo.

Effect of capacitance on ZnO-Bi_2O_3-Yb_2O_3 based varistor for nanosecond transients

The microstructure and electrical properties of ZnO-Bi2O3-Yb2O3 based varistor ceramics were investigated with various temperature effects from 900°C to 1050°C.From the results,it was observed that the increase of sintering temperature offers a reduced capacitive effect from 0.460 nF to 0.321 nF.Furthermore,the grain sizes of varistors were varied from 6.8μm to 9.8μm.The consequence of such smaller grain sizes provided a better voltage gradient of about 895 V/mm for the disc sintered at 900°C and fallen drastically to 410 V/mm for the sample sintered at 1050°C.In addition,there was an increase of non-linearity index to a maximum value of 36.0 and reduced leakage current of 0.026 mA/cm2.However,the density of the varistor decreased with an increase of temperature from 5.41 g/cm3 to 5.24 g/cm3.With this base,the influence of varistor capacitance and high voltage gradient were scrutinized and it led an improved transition speed of the varistor assembly from non-conduction to conduction mode during intruding nanosecond transients.

Microstructures and properties of WC-20Co-1Y_2O_3 cemented carbide by hot-press and liquid phase sintering

Ultrafine tungsten carbide and fine cobalt as well as nano yttrium oxide powders were used as the raw materials. The effects of hot-press below the eutectic temperature and conventional liquid phase sintering on the structures and properties of WC-20Co-1Y2O3 cemented carbide were studied. It is shown that hot-pressed alloy has the character of isotropic properties and microstructure with homogeneous and ultrafine WC grains. However, the ultrafine and fully-densified structure is developed at the cost of the presence of large amount of cobalt-lake （unevenly distributed binder phase）, and thus lower strength. Yttrium oxide in the alloy cannot play the role of grain growth inhibitor fully when cemented carbide with high content of cobalt and ultrafine raw materials is sintered at high liquid phase sintering temperature. Peculiar platelet-enhanced bi-model structure is formed in WC-20Co-1Y2O3 cemented carbide by conventional liquid phase sintering, which points out that yttrium oxide in the alloy facilitates the formation of plate-like WC grain.

Preparation and properties of composite polymer electrolyte modified with nano-size rare earth oxide

Poly（vinylidene fluoride-co-hexafluoropropylene） （PVDF-HFP） based composite polymer electrolyte （CPE） modified with CeO2, La2O3 and Y2O3 nano-rare earth oxides was prepared by phase inversion technique. Physical and chemical properties of the modified CPEs were studied by SEM, TG-DSC and electrochemical methods. The results show that the CPE modified with 10% La2O3 （mass fraction） has the best practical applicability, which indicates that the thermal and electrochemical stability can reach over 400 ℃ and 4.5 V, respectively, and temperature dependence of ionic conductivity follows Vogel-Tamman-Fulcher （VTF） relationship and ionic conductivity at room temperature is up to 3.3 mS/cm. The interfacial resistance Ri reaches a stable value about 557 Ω after 6 d storage.

Distribution of rare earth elements of granitic regolith under the influence of climate

The distribution and anomalies of rare earth elements(REEs) of granitic regolith were studied in Inner Mongolia and Hainan Island, China. One profile showed slight REE enrichment of an upper layer and no obvious light REE/heavy REE(LREE/HREE) fractionation(La_N/Yb_N of 0.9). The second profile was significantly enriched in REEs and enriched in LREEs in the upper portion(La_N/Yb_N>1.8). Eu, Ce, and Gd anomalies of the two profiles are different. Slightly negative Eu, Ce, and Gd anomalies in NMG-3-1 indicate slow dissolution of primary minerals and little secondary products; in contrast, a positive Eu anomaly in HN-2 suggests the vegetation cycle may contribute to soil. The Ce anomaly of HN-2 reflects oxidation of Ce and coprecipitation by Fe-and Mn-oxides and organic matter. Correlation between Ce and Gd anomalies in HN-2 suggests Ce and Gd are both influenced by redoxreduction.

Preparation of Rare-Earth Composite Ferrite Magnetic Fluid

Water-based rare-earth ferrite (Re xFe 3- xO 4)magnetic fluids were prepared by chemical co-precipitation method. The result shows that saturation magnetic intensity of ferrite magnetic fluids can be improved by adding Dy 3+ and the saturation magnetic intensity will reach the highest if n(Fe)∶n(Dy 3+ )=30∶1. The modification and formation mechanism of Re xFe 3- xO 4 particles is discussed in detail. The physicochemical properties are investigated by the Gouy magnetic balance, IR, TEM, XRD, and EDX, etc.

Specific Adsorption of Trivalent La, Ce and Y by Soils and Ferro-manganese Oxides and Its Mechanism

In this paper, the adsorption-desorption variations of trivalent La, Ce, Y and mixed rare earths are discussed. The curves of pH-rare earth element adsorption were very well fitted to the equation: InD =a+b pH. The selectivity of RE (rare earth element) ions by the samples decreased in the following order: Ce> RE> La> Y, but the sequences were: La> Ce> Y on kaolinite and Y> La on amorphous iron oxide. Since the trivalent RE ions existed in the form of RE(OH)2+ in the solutions from pH < 5.45 to 7.0, the ratio of H+ displaced to RE3+ adsorbed in micromole was proposed to be about 2. The specific adsorption mechanism for RE was proposed to be that the RE ions complexed with oxide surface and the ion-surface complex of Ce3+ promoted oxidization on Mn hydroxide.

Facile and Efficient Method for the Adsorption and Separation of Lanthanum Rare Earth Metal Oxide Using Iron（Ⅱ） Sulfide Nanoparticles Coated on Magnetite

A novel iron sulphide adsorbent using magnetite embedded with nanosized Fe3O4 was prepared and applied to separation lanthanum （Ⅲ） from aqueous solution. This adsorbent combines the advantages of magnetic nanoparticle with magnetic separability and high affinity toward rare earth metals, which provides distinctive merits including easy preparation, high adsorption capacity, easy isolation from sample solutions by the application of an external magnetic field. The adsorption behaviors of lanthanum （Ⅲ） from an aqueous medium, using iron sulphide magnetite nanoparticles were studied using equilibrium batch and column flow techniques. The effect ofpH, contents of loaded iron sulphide nanoparticles, ionic strength, adsorbent dose, contact time, and temperature on adsorption capacity of the magnetic beads was investigated. All of the results suggested that the FeS/Fe3O4 Nanoparticles could be excellent adsorbents for La（Ⅲ） contaminated water treatment.