Ti4+ modified MgZrNb2O8 microwave dielectric ceramics with an ultra-high quality factor

Ti⁴⁺-modified MgZrNb₂O₈ (MgZr_1-xTi_xNb₂O₈, x = 0, 0.1, 0.2, 0.3, 0.4) ceramics were synthesized using the traditional solid-state reaction method. Pure MgZr_1–xTi_xNb₂O₈ was detected without any secondary phase via the X-ray diffraction patterns. According to the sintering behavior and the surface morphology results, the introduction of Ti⁴⁺ reduced the sintering temperature and promoted the grain growth. The correlations between the dielectric properties and the crystal structure were analyzed through the Rietveld refinement and Raman spectroscopy. The slight shifts of the Raman peaks, corresponding to different vibration modes, were induced by the substitution of Ti⁴⁺ for Zr⁴⁺ and related to the improved quality factor. In general, the sample of MgZr_0.9Ti_0.1Nb₂O₈ sintered at 1320°C for 4 h exhibited promising microwave dielectric properties with an ultra-high Q × f value of 130 123 GHz (at 7.308 GHz, 20°C), which is potential for 5G communication applications.     

Electrochemical investigation of La0.4Sr0.6TiO3 synthesized in air for SOFC application

Journal of Applied Electrochemistry - La-doped titanate materials have been widely investigated as alternative Ni-free anodes for solid oxide fuel cells (SOFCs). In this study, La0.4Sr0.6TiO3 (LST)...     

Spray-coated PDMS/PVDF composite membrane for enhanced butanol recovery by pervaporation

In this study, spray-coating was used to prepare dihydroxypolydimethylsiloxane (PDMS) composite membranes with high flux and separation factor for biobutanol recovery from aqueous solution. A thin, smooth, and defect-free PDMS layer was prepared by spray-coating on polyvinylidene difluoride ultrafiltration membrane with little PDMS penetration. The effects of process parameters for membrane fabrication and pervaporation on membrane performance were investigated. A membrane with 2 μm active layer was obtained with a high flux of 1306.9 g/m² h. The optimal membrane with the highest pervaporation separation index (PSI) (19.15 kg/m² h) showed a total flux of 530.6 g/m² h and a separation factor of 36.1 at 37°C, and a PSI of 65.61 kg/m² h and a flux of 1927.0 g/m² h at 70°C. Membrane performance was affected by feed composition and temperature. Acetone-butanol-ethanol solution and fermentation broth gave lower butanol fluxes and separation factors compared to butanol model solution.     

Thin-film composite forward osmosis membrane prepared from polyvinyl chloride/cellulose carbamate substrate and its potential application in brackish water desalination

Synthesized by the reaction between α-cellulose and m-tolyl isocyanate (MTI), cellulose carbamate (CC) was blended with polyvinyl chloride (PVC) to fabricate substrates for thin-film composite (TFC) forward osmosis (FO) membranes. The introduction of CC into substrates improved both membrane structure and performance. The substrates exhibited higher porosity and hydrophilicity, and better connective pore structure; while rejection layer exhibited better morphology but limited cross-linked degree decrease after the introduction of CC. According to the results, the CC blend ratio of 10% was the optimal ratio. With this blend ratio, the TFC-10 membrane presented favorable water permeability (1.86 LMH/bar) and structure parameter (337 μm), which resulted in excellent FO performance (water flux with a value of 40.40 LMH and specific salt flux with a value of 0.099 g/L under rejection layer faces draw solution [DS] mode when 1 M NaCl and deionized water were utilized as DS and feed solution). In addition, the TFC-10 membrane showed good water flux and low-sulfate ion leakage in the potential application of brackish water desalination.     

An improved strategy to synthesize graphite oxide with controllable interlayer spacing as coatings for anticorrosion application

A facile method to synthesize nanoscale graphene oxide (GO) with controllable interlayer spacing was carried out using two-step oxidation process and much less acid to improve the efficiency of the oxidation. The X-ray diffraction results demonstrated that GO had been successfully prepared from graphite because of disappearance of characteristic peaks of pristine graphite at about 2θ = 26.5° along with appearance of a sharp major peak of GO at about 2θ = 9.4°. The increased basal spacing d₀₀₁ of as-prepared GO could reach as high as 9.39 Å, suggesting higher degree of oxidation than that prepared by the classical Hummers' synthesis, and characterization results from Fourier transform infrared spectrometer, X-ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscopy and transmission electron microscopy further confirmed this conclusion. The influence of GO on anti-corrosion performance of nanocomposite coatings composited with the 2,5-dimethoxyaniline (DMA) conductive polymer was examined via potentiodynamic polarization curve tests in 3.5 wt% NaCl aqueous solution. The results demonstrated that the incorporation of GO significantly decreased the corrosion current density (i_corr = 2.62 μA/cm²) in the case of GO-PDMA coating, reflecting excellent physical isolation of GO and its synergistic effect with PDMA against the infiltration of water and corrosive electrolyte.     

Polyethylene glycol modified epoxy acrylate UV curable 3D printing materials

The purpose of this paper is to research improvement in the flexibility of epoxy acrylate 3D printing materials so as to satisfy the requirements of clothing attachments or accessories. Tensile tests, differential scanning calorimeter, XRD, rheological and Fourier transform infrared analysis were used to measure and compare the performance and characteristics of polyethylene glycol modified bisphenol-A epoxy acrylate 3D printed samples with different molecular weights and contents. Based on a comprehensive analysis of the experimental results, the E/PEG₁₀₀₀(1/0.2)-AA sample was revealed to have an optimal composition ratio. After secondary curing, the tensile strength of the sample rose to 8 MPa, with the elongation being converged to 30%. This paper provides a reference for the modification and improvement of flexible UV-cured 3D printed products.     

Numerical Investigation of Integrated Design on Uniform Fluid Distribution for Radial Flow Adsorber

Theoretical Foundations of Chemical Engineering - Non-uniform distribution of air in radial flow adsorber restricts the development of large-scale air separation units (ASUs). The cross-sectional...     

基于变结构准Z源的双馈风电机组强励变换器

当电网电压发生深度跌落时,需要风力发电系统不脱网且向电网提供动态无功支撑,采用传统励磁变换器的双馈风电机组往往需要通过外加装置才能实现这一要求.外加装置使系统变得复杂,可靠性和效率降低.针对这一问题,文中分析了双馈风电机组低电压穿越的瓶颈,提出了构建坚强励磁系统的思想,并设计了一种基于变结构准Z源的新型双馈风电机组强励变换器.将传统的电容型母线替换为准Z源网络,当电网正常时该变换器运行于可调电压的单电容型母线状态,当电网电压发生深度跌落时,该变换器可以迅速升高直流链电压,从而保证转子侧变换器在故障期间始终可控.搭建了双馈风电机组低电压穿越仿真与实验系统,仿真与实验结果表明所提强励变换器拓扑具有良好的稳态与动态性能,在电压深度跌落时能够有效控制转子电流,实现双馈风电机组的低电压穿越和无功支撑.     

考虑动态输送容量机制的电力传输线过载风险评估

传输线动态输送容量(DLR)技术旨在使用动态环境参数计算整定传输线输送容量,相较于传输线静态输送容量整定方法,可真实反映传输线实时传输功率上限.然而,DLR数值的计算依赖于风速、光照强度、温度等不确定性较强且难以准确预测的环境参数,换言之,依照DLR机制整定得到的传输线最大传输功率上限也具有不确定性.若其预测偏差过大,可能会造成传输线过载,严重的甚至会引发电网连锁故障.为此,文中提出一种考虑DLR不确定性的电力传输线过载风险评估方法,以盒式不确定性集合描述传输线输送容量不确定性,将其过载风险作为评估指标,优化传输线零过载范围.文中提出的评估问题数学上属于两阶段鲁棒优化问题,应用列与约束生成算法实现模型的高效求解.最后,在搭建的测试系统中验证所提模型及算法的有效性.     

含虚拟惯量的双馈风电机组扭振阻尼特性分析与抑制方法研究

阻尼是影响双馈风电机组(doubly-fed induction generator,DFIG)轴系扭振的核心因素.在并网导则要求风电参与系统调频的背景下,当DFIG采用虚拟惯量控制响应系统频率变化时,其扭振的阻尼特性将更加复杂.采用阻尼转矩方法,首先分析了最大功率跟踪模式下DFIG轴系扭振的阻尼特性,推导了虚拟惯量引入后双馈风机的电磁转矩–转速环传递函数,解释了虚拟惯量控制降低DFIG扭振阻尼的原因.其次,分析了基于带通滤波器和相位补偿环节的扭振阻尼控制器(bandpass-filter and phase-compensation based torsional oscillation damping controller,BPB-TODC)附加于不同控制通道引起的扭振频率偏移问题.针对扭振频率偏移导致阻尼控制器性能下降的问题,在混合通道BPB-TODC基础上,通过对多扭振频率偏移场景下的控制器参数进行寻优,提出了抗扭振频率偏移的优化BPB-TODC.最后,通过仿真验证了上述理论分析的正确性和所提阻尼控制器的有效性.