Experimental and theoretical approaches for electrical,magnetic, micromechanical,and structural characterization of BSCCO ceramic superconductors

This study investigates how the preparation and re-pelletization of BSCCO ceramic superconductors affects their structural, magnetic, electrical, and mechanical properties. Samples were prepared using conventional methods including the dry solid state (SS) reaction and wet ammonium nitrate (AN) precipitation, with three variations prepared for each technique. The fabricated samples were then characterized with X-ray powder diffraction (XRD) and scanning electron microscopy. The density, resistance vs. temperature characteristics, AC susceptibility vs. temperature characteristics, and magnetic hysteresis properties were measured. In addition, Vicker's microhardness was measured and revealed that all six samples exhibit the reverse indentation size effect (RISE). Microhardness modeling was also conducted. Calculations with Meyer's law, the Hays and Kendall model, and the proportional sample resistance model indicate that the samples are far from the plateau region, whereas the indentation-induced cracking model was consistent with the experimental results. The elastic modulus, Young's modulus, yield strength, and brittleness index were also calculated for each sample.     

Enhanced high-temperature dielectric properties and microwave absorption of SiC nanofibers modified Si3N4 ceramics within the gigahertz range

Si₃N₄ ceramics modified with SiC nanofibers were prepared by gel casting aiming to enhance the dielectric and microwave absorption properties at temperatures ranging from 25?°C to 800?°C within X-band (8.2–12.4?GHz). The results indicate that the complex permittivity and dielectric loss are significantly increased with increased weight fraction of SiC nanofibers in the Si₃N₄ ceramics. Meanwhile, both complex permittivity and dielectric loss of SiC nanofibers modified Si₃N₄ ceramics are obviously temperature-dependent, and increase with the higher test temperatures. Increased charges mobility along conducting paths made of self-interconnected SiC nanofibers together with multi-scale net-shaped structure composed of SiC nanofibers, Si₃N₄ grains and micro-pores are the main reason for these enhancements in dielectric properties. Moreover, the calculated microwave absorption demonstrates that much enhanced microwave attenuation abilities can be achieved in the SiC nanofibers modified Si₃N₄ ceramics, and temperature has positive effects on the microwave absorption performance. The SiC nanofibers modified Si₃N₄ ceramics will be promising candidates as microwave absorbing materials for high-temperature applications.     

Thermal stability of CaCu3Ti4O12: Simultaneous thermal analysis and high-temperature mass spectrometric study

Thermal stability of calcium copper titanate was studied by differential scanning calorimetry, thermogravimetry and high-temperature mass spectrometry. Calcium copper titanate (CCTO) had no thermal effects and mass losses caused by thermal dissociation or any phase transitions, besides melting, in the temperature range of 298–1423?K. The melting point of calcium copper titanate is 1398?K. The endothermic effect at 1250?K was associated with the decomposition of copper (II) oxide segregated in the intergrain space of the CaCu₃Ti₄O₁₂-CuO ceramics. In this connection, we proposed a simple method for estimating the content of copper oxide in the CaCu₃Ti₄O₁₂-CuO composite. The processes of evaporation of CaCu₃Ti₄O₁₂ in the temperature range of 1500–2100?K were studied by high-temperature mass spectrometry. In the temperature range of 1500–1750?K, easily volatilized copper oxide was evaporated selectively from the calcium copper titanate. At the temperature of 2100?K, atomic calcium and titanium oxides, TiO and TiO₂, were present in the vapor.     

钛基Ce掺杂SnO_2-RuO_2电极的制备及其对焦化废水的电解处理

采用溶胶-凝胶法制备了经稀土元素Ce掺杂改性的Ti/RuO_2-SnO_2-Ce电极,利用SEM、XRD、EDS等分析方法对电极表面的形貌、物相和涂层成分进行了表征,利用CV曲线、LSV曲线等检测手段对电极的电化学性能进行了测试。以Ti/RuO_2-SnO_2-Ce电极为阳极,钛板为阴极,构建电化学氧化反应装置,并采用其对焦化废水进行电解处理。结果表明,Ti/RuO_2-SnO_2电极经稀土Ce改性后极板表面活性位点数量明显增大,金属涂层的结晶化程度明显增强,电极的催化氧化活性显著提高。室温条件下,保持pH值为7.83,在电流密度为30mA/cm~2,电解时间为30min时,焦化废水经电解处理后COD去除率可达91.63%,TOC去除率可达66.22%,UV254值下降到0.921。     

综放工作面风量及采空区漏风定量检测

通过对中煤塔山煤矿30509综放工作面采空区漏风及有害气体分析的研究，总结了通过定量连续释放SF₆示踪气体，来检测工作面风量与采空区漏风的方法，测定了沿工作面采空区的漏风分布及漏风流线的深度。采用定时测量法，确定了30509工作面随工作面不断推进，与对应地表发生了导通现象；采用定量测量法，确定了内部漏风量和外部漏风量较大，对综采工作面采空区自然发火存在较大风险，同时提出了防范措施，为减少综放工作面采空区漏风、防止自然发火的发生提供了参考。     

Hot corrosion studies of a salt-coated Ni-based superalloy under flowing wet air and sulfur vapor ambient

Corrosion of a salt-coated Ni-superalloy has been studied at 900°C under a wet air and sulfur vapor ambient. The corrosion thickness, after an incubation of ~60 hr, linearly increases with the corrosion time t and the onset of surface spallation occurred at t ≈ 60 hr. The corroded layer consists of a corrosion front dominated by Cr₃S₄ scales and linear precipitate structures, an inner corrosion layer dominated by Ni₃S₂ and NiO, and an outer corrosion layer dominated by Al₂O₃ networks surrounding the Ni₃S₂ and/or NiO scale structures. The corrosion mechanism is discussed based on the coexistence of H₂O, sulfur, and oxygen.     

高铁酸盐-亚硫酸盐体系氧化降解水中污染物阿特拉津

针对目前日益严峻的农药污染问题，本文以阿特拉津（ATZ）为目标污染物，利用高铁酸盐活化亚硫酸盐的方式对其进行降解。探究了亚硫酸盐浓度、高铁酸盐浓度、ATZ浓度、pH以及亚硫酸盐投加方式对ATZ去除率的影响。研究结果表明，在pH为7、高铁酸盐浓度为100μmol/L、亚硫酸盐浓度为400μmol/L、ATZ的浓度为5μmol/L的条件下，10s时间内可以去除95%的ATZ。利用自由基淬灭实验对体系中的活性物质进行鉴定，结果表明，高铁酸盐-亚硫酸盐体系中起主要作用的是硫酸根自由基（SO{}_{\mathrm{4}}^{·-}），其对ATZ降解的贡献约占53%；其次是羟基自由基（·OH），约占36%。通过改变亚硫酸盐投加方式，减少了SO{}_{\mathrm{4}}^{·-}的自我消耗，提高了高铁酸盐-亚硫酸盐降解ATZ的效率。这些实验结果有助于高铁酸盐-亚硫酸盐体系的实际水处理应用。     

Evolution mechanism of active groups and thermal effects of Chinese lignite in low-temperature oxidation

Abstract

The evolution of active groups at low temperature was examined using Chinese lignite by infrared technology and X-ray photoelectron spectroscopy (XPS). The results showed that the hydroxyl, aliphatic ether, methylene, and methyl groups played important roles in the low-temperature oxidation of lignite below 200?°C. Carbonyl and carboxyl groups were important intermediates. Thus, a multi-step evolution mechanism involving the hydroxyl, aliphatic ether groups, and alkane was reasoned to describe the low-temperature oxidation of lignite. In addition, according to the oxidation kinetics experiment and the evolution laws of the active groups, the ratios of the reaction lines were determined considering the accuracy of thermal effects. The thermal effects and the heat release intensities of each temperature interval were obtained based on the evolution mechanism and the reaction ratios. The shortest spontaneous combustion period of lignite was calculated and compared with the experimental value, which proved that the reasoned evolution mechanism of the active groups and the calculations of the thermal effects were reliable.     

Pt–Ru nanoparticles anchored on poly(brilliant cresyl blue) as a new polymeric support: Application as an efficient electrocatalyst in methanol oxidation reaction

The glassy carbon electrode is modified by poly(brilliant cresyl blue) (PBCB) to be applied as a new green and efficient platform for Pt and Pt–Ru alloy nanoparticles deposition. Surface composition, morphology and catalytic activity of these modified electrodes towards methanol oxidation are assessed by applying X-ray diffraction, field emission scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy techniques. The X-ray diffraction patterns reveal that the highly crystalline Pt and Pt–Ru alloy and RuO₂ nanoparticles with low crystallinity are deposited on the PBCB modified glassy carbon electrodes. The microscopic images indicate smaller size and better distribution of deposited nanoparticles on the surface of PBCB modified electrodes. Cyclic voltammetry and electrochemical impedance spectroscopy results reveal that PBCB supported Pt and Pt–Ru nanoparticles have better electrocatalytic performance and durability towards methanol oxidation rather than the unsupported nanoparticles. From the obtained results it can be concluded that the presence of PBCB not only improves the stability of nanoparticles on the surface, but also leads to the formation of smaller size and more uniform distribution of nanoparticles on the surface, which, in turn, cause the nanoparticles to provide a higher accessible surface area and more active centers for the oxidation of methanol. The results will be valuable in extending the applications of this polymer in surface modification steps and in developing promising catalyst supports to be applied in direct methanol fuel cells.     

Multi-objective optimization for efficient modeling and improvement of the high temperature PEM fuel cell based Micro-CHP system

Fuel cells due to different useful features such as high efficiency, low pollution, noiselessness, lack of moving parts, variety of fuels used and wide range of capacity of these sources can be the main reasons for their tendency to use them in different applications. In this study, the application of a high temperature proton exchange membrane fuel cell (HT-PEMFC) in a combined heat and power (CHP) plant has been analyzed. This study presents a multi-objective optimization method to provide an optimal design parameters for the HT-PEMFC based micro-CHP during a 14,000 h lifetime by considering the effect of degradation. The purpose is to optimize the net electrical efficiency and the electrical power generation. For the optimization process, different design parameters including auxiliary to process fuel ratio, anodic stoichiometric ratio, steam to carbon ratio, and fuel partialization level have been employed. For optimization, A new technique based on Tent mapping and Lévy flight mechanism, called improved collective animal behavior (ICAB) algorithm has been employed to solve the algorithm premature convergence shortcoming. Experimental results of the proposed method has been applied to the data of a practical plant (Sidera30) for analyzing the efficiency of the proposed ICAB based system, it is compared with normal condition and another genetic algorithm based method for this purpose. Final results showed that the difference between the maximum electrical power production under normal condition and ICAB based condition changes from 2.5 kW when it starts and reaches to its maximum value, 3.0 kW, after 14,000 h lifetime. It is also concluded that the cumulative average for the normal and the ICAB based algorithm are 24.01 kW and 27.04 kW, respectively which showed about 3.03 kW cumulative differences.