Enhanced cycle stability of spinel LiMn2O4 by a melting impregnation method

Spinel LiMn₂O₄ particles were successfully coated with CuO, MgO, ZnO, Al₂O₃ and CeO₂ by a melting impregnation method. Except for the CeO₂-coated sample, all the others exhibit better cycling stability than bare LiMn₂O₄ at room temperature and at 55°C. Among these samples, the ZnO-coated sample shows the best cycling stability. A capacity of 100 mA·h·g⁻¹ still remained after 100 cycles at 55°C while the bare LiMn₂O₄ retains a capacity of only 80 mA·h·g⁻¹ after the same number of cycles. The improvement in the cycling stability is attributed to the suppressed Mn dissolution caused by HF.     

The melting point of palladium by a pulse heating method

The melting point of 99.95⁺% pure palladium was measured by means of a subsecond duration pulse heating technique. The average temperature at the melting point for three specimens was 1827 K with an average absolute deviation from the mean of 0.1 K. The total error in temperature is estimated to be not more than ±4 K.     

Corrosion resistance of molybdenum coatings obtained by a contact melting method

The corrosion resistance and fatigue strength of molybdenum coatings obtained by a contact melting method on 1Cr18Ni9Ti steel and on EI 437B alloy were investigated. It was shown that the use of such a coating on EI 437B alloy quadruples its fatigue strength in liquid Pb-Bi eutectic.Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 5, No. 6, pp. 704–708, November–December, 1969.     

Enhanced stability of organic thin films for electroluminescence by photoirradiation

Enhanced stability against heat and moisture in organic vapor-deposited TPD thin film having hole transport property has been achieved by UV irradiation. The crystallization of TPD film without any treatment was started within a week even at RT and accelerated with increasing temperature under the air. By photoirradiation using UV light, however, the TPD thin film was found to be difficult to form crystallized state and showed good contact with substrate even at 60 °C and in water for more than one month. Furthermore, the molecular interdiffusion by heat between organic layers in Alq3/TPD bilayer was remarkably suppressed by the UV irradiation due to the enhanced stability of the TPD film.     

浸渍硼氧化物改善柔性石墨的氧化稳定性和力学性能

膨胀石墨经硼氧化物浸渍修后辊轧制成柔性石墨箔.应用激光质谱、X-光电子谱、扫描电镜和热重测定分析了所制柔性石墨箔.结果表明:浸渍硼氧化物后石墨箔的初始氧化温度提高了约150℃.即使浸渍少量(质量分数低于2％)的硼氧化物也能提高此材料的拉伸强度.纵观其浸渍改善效果,可能归因于膨胀石墨粒中与石墨片层化学键合的硼氧化物堵塞了其活性位点所致.     

Radiation stability of ceramics: Test cases of zirconia and spinel

The study of the effects of radiation in ceramics of potential use in electronic, space and nuclear industries appears to be a major challenge in the next decades. The collect and analysis of data dealing with the production and recovery of radiation damage in this type of materials are thus tasks of prime interest. In this article, we present a review of the main structural and chemical modifications observed in test case ceramics (yttria-stabilized zirconia and magnesium-aluminate spinel) submitted to ion bombardment and thermal treatments. We show that the stability under irradiation depends on the intrinsic properties of the materials and on irradiation parameters such as the ion energy, fluence and temperature. We also demonstrate that the recovery of damage upon annealing at elevated temperatures induces drastic physico-chemical modifications of the matrix.     

Preparation and characterization of nanosized Zn-Co spinel oxide by solid state reaction method

ZnCo₂(C₂O₄)₃·6H₂O nanocrystal was prepared by a one-step solid state reaction method at room temperature under ambient conditions using oxalic acid as a chelating agent. Adding oxalic acid to the mixture of zinc acetate dihydrate and cobalt acetate tetrahydrate, grinding and subsequently calcining the precursor at different temperatures, the pink precursor was attained. Thermogravimetric analysis and differential scanning calorimetry have been used to study the thermal behaviors of the precursor, which reveal that the precursor is a compound. Powder X-ray diffraction data show that the sample obtained by heating the precursor between 350 °C and 550 °C for 3 h is a single-phase cubic material having the spinel-type structure, which can be confirmed by infrared spectra. Transmission electron microscopy images show that the grain size of the precursor and the products are about 50 nm and 20 nm, respectively.     

Mass synthesis of nanocrystalline spinel ferrites by a polymer-pyrolysis route

Nanocrystalline MeFe₂O₄ (Me = Mn, Ni and Zn) spinel ferrites have been synthesized by polymer-pyrolysis method. The pyrolysis behaviors of the polymeric precursors prepared via in situ polymerization of metal salts and acrylic acid are analyzed by use of simultaneous thermogravimetric and differential thermal analysis (TG-DTA). Then, the structural characteristics of the products are studied by powder X-ray diffraction (XRD), infrared spectroscopy (IR), transmission electron microscope (TEM) and electron diffraction (ED) pattern. The results revealed that the spinel ferrites have nano-sized morphology and good crystallinity even if calcined at moderate temperature like 500 °C for 3 h. The average sizes of nanocrystalline spinel ferrites range from 10 to 30 nm with narrow size distributions. Magnetic measurements at room temperature show that Mn, Ni and Zn ferrites with the small coercivity and remanence exhibit soft magnetic behaviors. The spinel ferrites (MnFe₂O₄ and NiFe₂O₄) obtained here show higher saturation magnetization than the corresponding spinel ferrites produced by other methods such as conventional ceramic and wet chemical route.     

聚丙烯酸法合成锂离子电池正极材料LixMn2O4

以聚丙烯酸为载体通过溶胶凝胶法合成纳米级尖晶石结构的锂离子电池正极材料LixMn2O4(1＜x＜1.12).讨论锂锰摩尔比、烧结温度对产物结构的影响.此外,改进了传统烧结方法,对烧结产物进行回火处理.实验结果表明,烧结温度为550℃时晶化完全,结构完整;当锂锰比为1.082时性能较佳,初始容量为125mAh/g;回火可改善LixMn2O4材料的性能.     

Aqueous dispersion stability of nickel powders prepared by a chemical reduction method

Spherical nickel powders with the very smooth surface and the uniform size of 300 nm have been manufactured by the chemical reduction and post-treatment technique. The adsorption isotherms of various water-soluble polymers on nickel powders were measured, and their effects on the dispersion stability were investigated. The adsorption amounts of polymers such as PVP (polyvinyl pyrrolidone), PMAA (polymethacrylic acid), and PAAm (polyacrylamide) on nickel powders could be successfully determined by the UV-absorbance analysis technique. Simultaneously, the dispersion stability of nickel powders in the polymer solution was evaluated in terms of the sedimentation behavior and relative coagulation rate. These results showed that the polymers such as PAAm and PVP (Mwt. 1,300,000) were found to be very effective for stabilizing the aqueous nickel dispersion system, and consequently, the coagulation rate of nickel powders in the PAAm solution was almost 100 times slower than that in pure water.     

Enhanced stability of enzymes adsorbed onto nanoparticles

We have discovered that the highly curved surface of C60 fullerenes enhances enzyme stability in strongly denaturing environments to a greater extent than flat supports. The half-life of a model enzyme, soybean peroxidase, adsorbed onto fullerenes at 95 degrees C was 117 min, ca. 2.5-fold higher than that of the enzyme adsorbed onto graphite flakes and ca. 13-fold higher than that of the native enzyme. Furthermore, this phenomenon is not unique to fullerenes, but can also be extended to other nanoscale supports including silica and gold nanoparticles. The enhanced stability was exploited in the preparation of highly active and stable polymer-nanocomposite films. The ability to enhance protein stability by interfacing them with nanomaterials may impact numerous fields ranging from the design of diagnostics, sensors, and nanocomposites to drug delivery.     

Axisymmetric problem on the impregnation of a heated filler by a viscoplastic liquid

This article examines the penetration of a viscoplastic liquid (binder) into a preheated porous cylindrical braid (filler) moving inside it.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 50, No. 4, pp. 617–620, April, 1986.     

熔融法制备高岭石/2-吡啶甲酸插层复合物

以高岭石/二甲亚砜(DMSO)作为前驱体,采用熔融插层法在130℃温度下制备了高岭石/2-吡啶甲酸插层复合物,采用X射线衍射和Fourier变换红外光谱进行了表征.结果表明:高岭石/2-吡啶甲酸插层复合物中,高岭石的层间距由0.72nm扩张到1.409nm,插层率达到84％;在此基础上,分析了2-吡啶甲酸的插层机理,即2-吡啶甲酸分子中羰基与高峰石的内表面羟基形成了氢键,2-吡啶甲酸分子可能以单分子层近似垂直排列与高岭石层间.     

Synthesis of nanocrystalline MgAl2O4 spinel powders by a novel chemical method

A novel chemical method for the preparation of nanocrystalline MgAl₂O₄ spinel powders has been developed in this paper. The mixed magnesium-aluminum hydroxide precipitates were initially formed in a three-dimensional space network microarea. After being calcined at above 700 °C, the nanocrystalline MgAl₂O₄ spinel powders were obtained. The precursor and as-calcined powders were characterized using TGA-DTA, XRD and TEM. The MgAl₂O₄ spinel powders calcined at 850 °C for 2 h are of narrow distribution, little agglomeration and small particle size of ∼ 24 nm. The reason for the synthesis of high-quality powders was explained.