微波加热法向分子筛中引入稀土离子

微波加热法制备Ｌａ－ＮａＸ沸石分子筛催化剂;考察微波加热条件下,交换液浓度,交换时间、微波加热功率等因素对离子交换的影响;利用正交实验,寻找交换反应的最佳工艺条件,用对比实验与传统方法进行比较。     

Mechanism of PZT crystallisation under hydrothermal conditionsDevelopment of a new synthesis route

On the basis of a 1-stage hydrothermal process, we first investigated the reaction mechanism responsible for the PZT precipitation. In a first sequence, lead diffuses into the amorphous coprecipitate. By increasing the reaction temperature, these particles dissolve, leading to nucleation and growth of PZT well faceted particles. In a second step, we demonstrated that starting from very fine oxide precursors, a homogeneous PZT solid solution could be formed. Under the same conditions but without any lead precursor, a mixture of KTO (a potassium titanium oxide phase) and tetragonal zirconia is formed. A 2-stage process was developed on these assumptions. The first stage consists in producing the KTO–ZrO₂(T) mixture. In the second stage, this mixture is hydrothermally treated in presence of lead precursor. Pure and homogeneous PZT and PLZT powders were obtained throughout this new synthesis route.     

环己氧基硼酸镧的摩擦学性能研究

以硼砂为原料合成了环己氧基硼酸镧,采用ＭＳ－８００Ａ摩擦试验机和ＨＱ－１摩擦磨损试验机研究了其抗磨减摩性,并采用Ｘ－射线光电子能谱仪（ＸＰＳ）分析了磨斑表面膜表面组成和价态。实验结果表明,环己氧基硼酸镧具有良好的抗磨减磨性。其作用机理可能是环己氧基硼酸镧在摩擦过程上分解为三氧化二和三氧化二硼等反应物膜,从而起到了抗磨减摩作用。     

Oxidation of magnetron sputtered La-Si thin films for solide oxide fuel cell electronlytes

La-Si thin films were deposited on stainless steel substrates by magnetron sputtering from pure La and Si targets. The Si/(Si + La) atomic ratio in the films was varied from 43.2 to 59.3% by adjusting the discharge current on the La target. The films had a homogeneous chemical composition down to the substrate and sharp interfaces. Annealing the films in air at 1173 K promotes the formation of apatite-structure La_9.33Si₆O₂₆ and the diffusion of different species from the film to the substrate and vice-versa, resulting in broadening the interfaces. X-Ray diffraction showed that all the as-deposited films had an amorphous structure. The formation of the LaSi₂ phase at intermediate temperatures was observed for the films deposited with higher Si contents while the films deposited with lower Si contents remained amorphous up to the start of the apatite structure crystallization process. The lanthanum silicate apatite-like phase (La_9.33Si₆O₂₆) was obtained only after annealing at 1173 K, excepted for the film with the lower Si content which is already partially crystallized after annealing at 1073 K. Quite pure La_9.33Si₆O₂₆ was obtained only after annealing the film with the highest Si content (Si/(Si + La) = 59.3%) although the theoretical Si/(Si + La) atomic ratio for apatite structure lanthanum silicate is 39%. For the other films, La₂O₃ was always detected when the lanthanum silicate phase was formed. Both phenomena clearly resulted from the strong diffusion of silicon excess towards the stainless steel substrate.     

Characteristics of high-k dielectric ECR-ALD lanthanum hafnium oxide (LHO) films

In this study, we investigated the characteristics of various lanthanum hafnium oxide (LHO) films with different lanthanum (La) concentrations deposited by an electron cyclotron resonance plasma-enhanced atomic layer deposition (ECR-ALD). Tris(isopropyl-cyclopentadienyl)lanthanum (La(iPrCp)₃) and tetrakis(ethylmethylamino)hafnium (TEMAHf) were utilized as the La and hafnium (Hf) precursors, respectively. When the La/(La + Hf) atomic percent ratio was 49.1%, the growth rate of the LHO film was 0.5 Å/cycle, with a dielectric constant of 16.3. As the La concentration was increased, the dielectric constant decreased. In addition, we found that a La-hydrate phase (La-O-H) can be easily formed when the La/(La + Hf) is over about 50%.     

Activity of perovskite La1−xSrxMnO3 catalysts towards oxygen reduction in alkaline electrolytes

The behaviour of the perovskite-based series of compounds La_1−xSr_xMnO₃ (where x = 0, 0.2, 0.4, 0.6, 0.8 and 1.0) towards oxygen reduction in an ambient temperature alkaline 1 M KOH electrolyte is presented. Within this series, the intermediate compound La_0.4Sr_0.6MnO₃ exhibits the greatest catalytic activity, approaching that of the considerably more expensive fuel cell grade Pt-black examined under the same conditions. The origin of this activity is discussed in terms of material structure and morphology, which exists in the structural transition region between cubic LaMnO₃ and hexagonal SrMnO₃. The small crystallite size and relatively large BET surface area of this material reflect this high level of structural disorder. Furthermore, these features enable this compound to exhibit the greatest proportion of direct four-electron oxygen reduction (preferred) compared to the less efficient two-electron reduction to peroxide.     

Low-temperature electrochemical characterization of dense ultra-thin lanthanum strontium cobalt ferrite (La0.6Sr0.4Co0.8Fe0.2O3) cathodes synthesized by RF-sputtering on nanoporous alumina-supported Y-doped zirconia membranes

Dense ultra-thin nanocrystalline La_0.6Sr_0.4Co_0.8Fe_0.2O₃ (LSCF) films with thickness of ∼50 nm, have been sputtered on nanoporous anodic alumina-supported nanocrystalline thin film yttria-stabilized zirconia and patterned by photolithography into microelectrodes. This approach enables low-temperature (425-550 °C) electrochemical properties of dense ultra-thin nanocrystalline LSCF to be characterized. The results reveal that the electrochemical resistance of nanocrystalline ultra-thin LSCF is dominated by the oxygen surface exchange reaction at the electrode surface with an activation energy of 1.1 eV. Area-specific resistance of LSCF was obtained and the results are of potential relevance to utilizing nanostructured oxide cathodes for micro-SOFCs operated at low temperatures.     

Preparation and characterization of lanthanum carbide encapsulated carbon nanocapsule/lanthanum hexaboride nanocomposites

LaC₂@CNC/LaB₆ nanocomposites were prepared using a spark plasma sintering system, and their mechanical properties and the intensity of characteristic La X-rays from the composites were characterized for application as X-ray target material. Using LaB₆ as a binder, we succeeded in producing LaC₂@CNC/LaB₆ nanocomposites with a bulk density (2.91 g/cm³) and specific electric resistance (3.12 × 10^− 4 Ω cm) through solidification at 2123 K. The fracture bending strength of LaC₂@CNC/LaB₆ nanocomposites (224 MPa) was 1.5 times larger than that observed for graphite/LaB₆ composites. The most emitted characteristic La Lα X-ray from LaC₂@CNC/LaB₆ nanocomposites was 7743 counts/mm²/s in comparison with 6372 counts/mm²/s for graphite/LaB₆ composites.     

中子活化分析研究长期摄入氯化镧对大鼠脑中部分常量和微量元素含量的影响

利用中子活化分析技术,初步研究了长期从饮水中摄入不同剂量的稀土元素镧对大鼠脑中12种常量和微量元素含量的影响。结果发现,镧的剂量越高,实验大鼠脑组织中含量发生变化的元素种类越多。1000mg/L组大鼠脑组织中有5种元素的含量与对照组相比发生了明显改变,而且这些元素都与脑功能密切相关。因此,镧的摄入可能会对脑的功能产生不利影响。     

High photocatalytic activity over starfish-like La-doped ZnO/SiO_2 photocatalyst for malachite green degradation under visible light

In this work,the unique starlike La-doped ZnO-SiO2 photocatalysts were constructed by an evaporation and calcination method and characterized in detail.UV-vis reflectance and DFT calculation confirm that the doping with La allows to obtain a decrease of band gap of ZnO/SiO_2,which enhances visible light absorbance and oxidizing ability.The photoluminescence intensity reduces greatly,indicating more effective separation of the photo generated carriers of La-doped ZnO-SiO2.Photocatalytic activities of Ladoped ZnO-SiO2 with different doping ratios under simulated visible light irradiation were evaluated with malachite green(MG) as a model pollutant.Under optimized conditions including solution pH of 8,15 mg/L of MG solution and 15 mg of catalyst dosage,0.2% La-ZnO-SiO2 exhibits the best catalytic activity in photodegradations of MG in water.The removal and mineralization efficiency of MG can reach 96.1%and 70.9% in 140 min,respectively.The as-prepared catalysts present superior stability and recyclability after four times reuse.Moreover,selective quenching experiments indicate that hydroxyl radical(·OH),hole(h~+) and superoxide radical(·O_2~-) are the main reactive species responsible for MG degradation.Possible mechanism for photocatalytic elimination of MG over La-doped ZnO/SiO_2 photocatalyst is finally proposed.