固相烧结法制备锂离子电池正极材料Li2FeP2O7及其电化学性能研究

介绍了一种先冷冻干燥后固相烧结制备正极材料Li₂FeP₂O₇的方法. 利用X射线衍射(XRD)、 扫描电子显微镜(SEM)、 透射电子显微镜(TEM)和傅里叶变换红外光谱(FTIR)对材料的组成和形态进行表征, 并通过循环伏安曲线(CV)和电化学阻抗谱(EIS)研究了Li₂FeP₂O₇材料的电化学性能. 研究发现, 合成Li₂FeP₂O₇的最佳温度为590 ℃, 此温度下反应较完全且产物杂质较少, 1.6C倍率下的放电比容量达到55 mA·h·g^?1, 明显高于其它温度下合成样品的放电比容量. 该温度下合成的Li₂FeP₂O₇还具有低阻抗和较大的交换电流密度, 说明这种合成方式有利于提高锂离子在Li₂FeP₂O₇中的扩散.     

BiVO4的添加对Nd0.2Ce0.8O1.9电解质微观结构和性能的影响

采用溶胶凝胶法制备BiVO₄（BV）和Nd_0.2Ce_0.8O_1.9（NDC）粉末,研究BV的加入对NDC电解质结构、形貌及电性能的影响。实验结果表明,NDC-5BV电解质的微观结构更致密,700℃时总电导率（σ_t）提高至3.35×10^-2 S·cm^-1,极化电阻（R_p）降低34%以上。单电池在700℃时的最大功率密度（MPD）为514 mW·cm^-2,开路电压（OCV）在70 h内可以保持良好的长期稳定性。     

The effect of short glass fibers on the process behavior of polyamide 12 during selective laser beam melting

In additive manufacturing, polymer composites are used for setting tailored properties. Short glass fibers can be used as fillers for polyamide 12 for enhancing stiffness or tensile strength as well as for reducing shrinkage. In this paper, the effects of short glass fibers on polyamide 12 concerning powder properties, process behavior and part properties in laser beam melting of polymers (SLS) are investigated. It could be shown that by increasing the short glass fiber content powder properties as well as part properties are immensely affected. By adding glass fibers, powder properties, like flowability and diffuse reflection decrease. The isothermal crystallization changes resulting in a narrower processing window. Concerning mechanical properties, short glass fibers allow for a higher stiffness until a critical limit of filler concentration within this study is reached, after which the tensile strength decreases. The elongation of break decreases by rising the filler content.     

Harmonic and intermodulation performance of hearing aids under large sound pressure levels

A mathematical model for the input-output functions of the hearing aids is presented. The model, basically a sine-series function, can easily yield closed-form expressions for the amplitudes of the harmonic and intermodulation components of the output when the input is formed of multitone large sound pressure levels. The special case of two-tone equal-amplitude incident pressure level is considered in detail. The results show that the third-order intermodulation component is always higher than the third-harmonic component. The results also show that the input-output functions exhibiting peak clipping exhibit the worst harmonic and intermodulation performance for large sound pressure levels. The simple wide-dynamic range compression (WDRC) input-output function exhibits the best harmonic and intermodulation distortion performance under large sound pressure levels. These results are consistent with the previously reported observations and reveal that there is a correlation between intelligibility of high-level speech and the harmonic and intermodulation performance of the hearing aid under large sound pressure levels.     

The Measurement of the Dispersion of Pd/C Catalysts

A 10 w/o Pd/C catalyst from Johnson Matthey has been examined by three different techniques: chemisorption, line broadening of X-ray diffraction, and TEM (transmission electron microscopy) to investigate the size of the palladium crystallites. The dispersion of this catalyst was determined to be 20%. Among these techniques, the X-ray diffraction was found to be the most convenient method. Through this method, the dispersion of Pd was found to decrease on catalyzing hydroxylamine reactions at 330 K. The deactivation of Pd/C for these reactions was correlated to the sintering of palladium. H₂ chemisorption at 373 K was found to be a good way to accurately measure the number of active palladium sites in the Pd/C catalysts.     

Microstructural prototyping of ceramics by kinetic engineering: applications of spark plasma sintering

The significance of kinetics on the development of microstructures in connection with sintering of ceramics is well recognized. In practice, however, it still remains a challenge to prepare designed microstructures via engineering the sintering kinetics because of an insufficient understanding of the different operative mechanisms that are in many cases overlapping. In this article the kinetic issues involved in sintering are described and discussed with respect to their potential for prototyping microstructures that yield desired properties. By exploiting and mastering the differences present in the kinetics of grain sliding, densification, chemical reactions, and grain growth, respectively, we have established processing principles for producing bulk ceramics with microstructures consisting of nano-sized grains, aligned grains, and/or non-equilibrium-phase constitutions, and for achieving radically improved superplasticity in brittle ceramics. Although the studies quoted in this article were mainly carried out by spark plasma sintering, more general implications of them are expected, including efficient particle sliding, deformation-induced dynamic ripening, superplastic deformation-induced dynamic ripening, and non-equilibrium integration.     

制备工艺对p型碲化铋基合金热电性能的影响

利用区熔法、机械合金化、放电等离子烧结(SPS)技术、热压法等多种工艺制备了p型碲化铋基热电材料.在300—500K的温度范围内测量了各热电性能参数，包括电导率(σ)、塞贝克系数(α)和热导率(κ)，研究了制备工艺对热电性能的影响.结果表明，所制备的块体材料与同组成区熔晶体相比，性能优值ZT均有不同程度的提高.其中，利用区熔法结合SPS技术可获得热电性能最佳的块体材料，其ZT值达1.15. 关键词： 碲化铋 放电等离子烧结 区熔法 热电性能     

高压烧结法合成致密纳米BaTiO3陶瓷结构和铁电性能研究

 在6 GPa压力、1 000 ℃温度条件下制备了致密的纳米BaTiO₃陶瓷，合成样品的平均晶粒尺寸为50 nm，理论密度在97%以上。通过介电测量，观察到了样品宽化的相变峰，它与粗晶陶瓷的相变峰大不相同。由于90°电畴的减少和退极化场的存在，观察到了细长的电滞回线，它是样品铁电性存在的有力证据，表明钛酸钡陶瓷的临界尺寸在50 nm以下。     

Effects of process parameters on electrical properties of n-type Bi2Te3 prepared by mechanical alloying and spark plasma sintering

n-Type Bi₂Te₃ thermoelectric materials were prepared by spark plasma sintering (SPS) using mechanically alloyed powders. Seebeck coefficient and electrical conductivity of the resultant materials were measured, with emphasis on the effects of sintering process parameters on the electrical properties. The power factor was improved from 1.5 to 1.6 mW/mK² when the SPS pressure was increased from 20 to 50 MPa at 623 K, and was further increased to 2.1 mW/mK² under 50 MPa by raising the SPS temperature from 623 to 673 K. The maximum power factor was obtained for the sample sintered under optimized SPS process parameters, in which the sintering temperature and the sintering pressure are 673 K and 50 MPa, respectively.