An experimental investigation of fracture processes in glass-ceramic sealant by means of acoustic emission

One of the essential components for ensuring the long service life of solid oxide cell (SOC) stacks is the sealant used. Therefore, in this work, an experimental investigation of the glass ceramic sealant (GCS) fracture process was carried out using an Acoustic Emission (AE) based approach. A series of tensile tests at room temperature were performed and the acoustic activity emitted was recorded by two AE sensors. An AE signal analysis was then performed using two approaches: wave mode identification and frequency content analysis. To understand the fracture process of the GCS, the analysis was supported with prior knowledge of the GCS microstructure and a post-test visual analysis. This demonstrated the presence of low-frequency failure mechanisms (50–400 kHz) such as debonding, fiber pull-out and matrix cracking, and high-frequency mechanisms (>400 kHz) such as fiber breakage. The results confirm the suitability of using the acoustic emission approach for monitoring failure events and show its potential application in SOC stacks monitoring.     

Highly efficient photocatalytic reduction of Cr(VI) by bismuth hollow nanospheres

Uniform bismuth hollow nanospheres with efficient Cr(VI) adsorption capacities were used to the photodegradation of highly toxic Cr(VI) for the first time, which exhibited outstanding visible-light photocatalytic abilities for the reduction of Cr(VI) to less toxic Cr(III).     

Up-conversion luminescence and optical temperature sensing behaviour of Yb3+/Er3+ codoped CaWO4 material

Present article report on structural and optical properties of Er³⁺/Yb³⁺ codoped CaWO₄ phosphors. Structural properties are explored using XRD and Raman technologies. The upconversion emission has been investigated with 980 nm excitation. The upconversion emission intensity is dependent on the concentrations of Yb³⁺ ions and reaches a maximum at 7%. Logarithmic plots of power dependencies reveal that the green and red emissions originate from a two-photon upconversion process. Based on the photon energy and the emission spectra, the possible upconversion processes and emission mechanisms are discussed. Finally, the optical temperature sensing properties has been performed using the fluorescence intensity ratio technique based on green upconversion emissions. Its temperature sensitivity is found to be above 0.0025 K^-1 in the whole temperature range of 300–540 K, revealing this phosphor to be a promising optical temperature sensing material.     

Ferroelectric and dielectric behaviors of sol-gel derived perovskite PMN-PT/PZT heterostructures via compositional development: An interface-dependent study

Phase-pure perovskite 0.67Pb(Mg_1/3Nb_2/3)O₃-0.33PbTiO₃/Pb(Zr_0.52Ti_0.48)O₃ (PMN-PT/PZT) heterostructures were prepared via compositional development using a sol-gel route. Interface-dependent microstructure, insulating, ferroelectric and dielectric performance were investigated. Relatively enhanced ferroelectricity (P_r?=?21.81 μC/cm², E_c?=?61.88?kV/cm) and dielectricity (ε_r?=?1959, tanδ?=?0.0152) were obtained for the heterostructure with the maximum number of interfaces (7 interfaces, namely F-7 type). Presumably, this behavior is due to the reduced leakage current density (10^?9–10^?8 A/cm² at ±400?kV/cm), which arises from columnar grain growth mode with more depletion layers generated between different compositions acting as a potential barrier for the movement of free carriers. A simplified equivalent circuit is used to provide a comprehensive explanation of the enhanced performance mechanism. These results highlight inherent issues in designing structures with specific interfaces and provide a new approach for designing high-performance PMN-PT-based thin film.     

种群分布式并行遗传算法解化工多目标优化问题

带精英策略的非支配排序遗传算法(NSGA-II)在与流程模拟软件Aspen Plus结合求解化工多目标优化问题方面耗时较高.为了解决这一问题,本文提出了一种种群分布式的并行遗传算法(populations distributed parallel genetic algorithm,PDPGA),将模拟计算任务分配给局域网的多台子节点计算机并行执行.以氯乙烯精制的多目标优化过程为研究对象,选取氯乙烯采出量最大化和系统总能耗最小化为两个目标,低沸塔和高沸塔的质量回流比、塔顶馏出率和塔压6个操作参数为优化变量.分别应用PDPGA和NSGA-II对上述过程进行优化求解,二者的种群规模均设为70,进化代数均设为70,PDPGA使用1主节点和2子节点共3台计算机.结果表明,与直接应用NSGA-II进行串行优化相比,PDPGA优化方法能充分利用闲置的计算机资源、有效提高解得质量和大幅降低优化计算的时间.     

Photocatalytic behavior of a new composite ternary system: WO3/SiC-TiO2. Effect of the coupling of semiconductors and oxides in photocatalytic oxidation of methylethylketone in the gas phase

It has been found that the photocatalytic activity of classical TiO₂ for the purification of polluted effluents containing volatile organic compounds (VOCs) can be greatly improved using the effect of the coupling of semiconductors and oxides. Thus, a new mixed photocatalyst has been prepared leading to a composite ternary system, WO₃/SiC–TiO₂. The results indicate that this combination can result in an enhancement in the photocatalytic activity toward methylethylketone (MEK) oxidation at room temperature by a factor greater than four with a total mineralization into CO₂ and H₂O, without creating toxic by-products. The efficiency of the composite system strongly depends on the relative amounts of WO₃ and SiC in the various samples because an optimum in photo-activity is observed when the weight ratios WO₃ and SiC are about 3.5 and 20%, respectively. The increase and synergy in photo-oxidation activity, in comparison to TiO₂ and to the binary TiO₂-based systems, WO₃/TiO₂ and SiC–TiO₂, are obtained as the simultaneous effect of WO₃ and SiC. Addition of WO₃ mainly results in the retarding of electron-hole recombination process by an electron trapping effect and in the modification of surface acidity compared to the case of pure TiO₂. On the other hand, the coupled system of the two illuminated semiconductors, TiO₂ and SiC, leads to a simultaneous electron transfer from SiC to TiO₂ and hole transfer from TiO₂ to SiC, increasing spatial charge separation and thus preventing charge recombinations, detrimental to photocatalytic efficiency.     

Surface Chemical Modification of Cellulose Nanocrystals and Its Application in Biomaterials

Cellulose nanocrystals (CNCs) have been widely applied in biomaterials and show great biocompatibility and mechanical strength. In this review, the chemical reactions applied in CNC surface modification and their application in CNC based biomaterials are introduced. Furthermore, the conjugation of different functional molecules and nanostructures to the surface of CNCs are discussed, with focus on the binding modes, reaction conditions, and reaction mechanisms. With this introduction, we hope to provide a clear view of the strategies for surface modification of CNCs and their application in biomaterials, thus providing an overall picture of promising CNC-based biomaterials and their production.     

Yttrium-dopants-induced phase-controllable and luminescence-tunable lanthanide-doped α/β-NaYbF4 nanocrystals in glass for laser-driven upconverted lighting

In-situ glass crystallization is an effective way to integrate lanthanide-doped upconversion nanocrystals into amorphous glass, producing bulky nanocomposites for specific applications. However, the precipitation of hexagonal NaYbF₄ nanocrystals from glass is rarely reported owing to the preferred crystallization of cubic phase. Herein, phase-controllable in-situ crystallization of cubic/hexagonal NaYbF₄ nanocrystals in glass is achieved via Y³⁺ doping. A series of structural and spectroscopic characterizations evidence the formation of Na(Yb/Y)F₄ solid-solution nanocrystals in glass and the incorporation of lanthanide emitting centers (Er³⁺, Tm³⁺, Eu³⁺) into the crystalline lattice. Introducing high-content Y³⁺ dopants is beneficial to induce the crystallization of hexagonal NaYbF₄ phase in glass and enables elaborated tunability of Er³⁺ upconversion emissive colors. Finally, a prototype upconverted solid-state-lighting device is constructed by coupling 980 nm laser with the as-prepared Er/Tm doped monolithic glasses containing Na(Yb/Y)F₄ nanocrystals, producing bright upconversion white-light with luminous efficiency of 1 lm/W and energy efficiency of 0.5%.     

活性硅醇基聚氨酯水分散体的合成及其防腐性能

水玻璃作为一种廉价的矿物质,经提纯可得到活性硅醇,以其作为内交联剂可应用于聚氨酯的合成中。对不同活性硅醇添加量合成的聚氨酯水分散体粒径及其涂膜的吸水率、接触角、动电位极化曲线、热重和扫描电镜作了测试分析,结果表明当活性硅醇添加量为30%时,水分散体平均粒径最小,为28.83nm;随着活性硅醇添加量的增加,涂膜吸水率增大,接触角反而减小;动电位极化曲线拟合结果表明,当活性硅醇添加量为70%时,涂膜腐蚀电流密度最小且极化电阻最大;红外光谱和扫描电镜分别可以确定水分散体结构中含有Si-O-Si、Si-O-C的基团以及涂膜中含有二氧化硅粒子,说明活性硅醇在体系中不仅参与主链反应,还以无机粒子的形态存在于其中;热重分析表明活性硅醇的引入显著提高了涂膜的热稳定性。