Manufacturing catalyst-coated membranes by ultrasonic spray deposition for PEMFC: Identification of key parameters and their impact on PEMFC performance

This study deals with the manufacturing of catalyst-coated membranes (CCMs) for newcomers in the field of coating. Although there are many studies on electrode ink composition for improving the performance of proton-exchange membrane fuel cells (PEMFCs), there are few papers dealing with electrode coating itself. Usually, it is a know-how that often remains secret and constitutes the added value of scientific teams or the business of industrialists. In this paper, we identify and clarify the role of key parameters to improve coating quality and also to correlate coating quality with fuel cell performance via polarization curves and electrochemical active surface area measurements. We found that the coating configurations can affect the performance of lab-made CCMs in PEMFCs. After the repeatability of the performance obtained by our coating method has been proved, we show that: (i) edge effects, due to mask shadowing - cannot be neglected when the active surface area is low, (ii) a heterogeneous thickness electrode produces performance lower than a homogeneous thickness electrode, and (iii) the origin and storage of platinum on carbon powders are a very important source of variability in the obtained results.     

Synthesis and characterization of ZnO NRs with spray coated GO for enhanced photocatalytic activity

Zinc oxide nanorods, ZnO NRs, were synthesized on a clean glass and coated with graphene oxide (GO) using spray coating method to enhance the photocatalytic activity in wastewater treatment. The ZnO NRs were synthesized using the solution process synthesis that was optimized using Taguchi method. Several synthesis parameters have been optimized and studied to determine the best synthesis parameter to grow ZnO NRs for the photodegradation of organic contaminants. Field emission scanning electron microscopy (FESEM) with EDX, X-ray diffraction (XRD), Raman, ultraviolet visible near-infrared (UV-VIS-NIR), and photoluminescence (PL) spectroscopies were used to investigate the structural and optical properties of the produced nanorods. FESEM images revealed the vertical growth of ZnO NRs as well as layers of GO covering the ZnO NRs' top surface. The Raman study demonstrates the combination peak of GO and ZnO, hence proving the GO layer's successful coating. After the GO coating, decrease in the bandgap of the synthesized photocatalyst was detected by PL and UV–Vis absorption measurements. Under UVC exposure with treatment time of 6 h, the degradation of MB with ZnO NRs/GO photocatalyst reached a degradation percentage of 97.86%, which is greater than the degradation percentage achieved using pristine ZnO NRs, which is 93.28%. The results validated that the coating of GO enhances the photocatalytic activity of the host material, ZnO NRs.     

非径向管板焊接接头的超声检测

对AP1000压水堆核电站安全壳贯穿件的非径向管板焊接接头结构特点进行了介绍,并分析其超声检测工艺的重点和难点。通过建立统一的缺陷定位坐标系并结合被检构件的几何特点进行综合分析,推导得出了h值(缺陷回波最高点距套管外壁的距离)的计算方法。为超声检测对这类焊接接头缺陷的准确识别和定位提供了行之有效的方法,为解决这类焊接接头的超声检测技术受限区提供了行之有效的措施。     

Spray dryer processed graphene oxide/reduced graphene oxide for high-performance supercapacitor

This study deals with the utility of mini spray dryer process to improve the dispersibility, of graphene oxide(GO) and its application for high-performance supercapacitor. Initially, the neutral solution of GO was obtained using the modified Hummer's method. After this, the prepared GO solution was processed by mini spray dryer to obtain a more purified, lighter, and dispersed form of GO which is named as spray dryer processed GO (SPGO). The SPGO thus obtained showed excellent dispersibility behavior with various solvents, which is not found in case of conventional oven drying. Furthermore, utility of SPGO and its reduced form (r-SPGO) for supercapacitor applications have been investigated. Results obtained from the cyclic voltammetry(CV) analysis, impedance, and charge-discharge behavior of supercapacitor fabricated using r-SPGO shows enhanced features. Therefore, the simple spray dried GO and its reduced form, that is, r-SPGO can be utilized as a potential candidate for the supercapacitor application. Herein, as synthesized SPGO exhibited the specific capacitance of 12.07 and 37.6 F/g with PVA-H₃PO₄ and 1 mol/L H₃PO₄, respectively, at a scan rate of 5 mV/s. On the other hand, reduced form of SPGO, that is, r-SPGO showed the specific capacitance of 27.16 and 230 F/g with PVA-H₃PO₄ and 1 mol/L H₃PO₄, respectively.     

红外菲涅尔透镜的注射超声辅助成型优化

为了提升聚合物红外菲涅尔透镜的光学性能,以其表面微沟槽的成型质量为目标,提出了一种高效的注射超声辅助成型方法,并对工艺参数进行了综合质量优化。首先分析了超声振动对聚合物的加热和加压效应,设计了一套一模两腔的对比试验模具;接着以红外菲涅尔透镜的调制传递函数MTF和齿形平均高度h为优化质量目标,设计了四步骤的多目标优化流程,通过试验设计、基于BP神经网络的质量目标与注射工艺参数关系建模、基于NSGA-Ⅱ的多目标优化和试验验证进行工艺参数的综合优化。实验结果表明:该多目标优化流程具有很高的精度,MTF和h的平均预测误差MPE分别为4.16%和3.32%;注射超声辅助成型的菲涅尔透镜微沟槽具有更高的复制质量,其齿沟槽平均高度h增加了15.6%,且h值的波动量随着h值的增大而增大,MTF值受齿高h均匀性的影响大于齿高h对其的影响。     

喷射成形Al-Zn-Mg-Cu合金挤压态的组织和力学性能

研究了利用喷射成形辅以挤压制备Al-5.72Zn-2.36Mg-1.66Cu合金后优化的组织结构特征和力学性能。结果表明,合金基体组织均匀细化,晶粒形貌趋于圆整,平均晶粒大小达到10 μm左右。当合金的冷却条件通过快速凝固技术改变时,会产生不同程度的固溶强化效果和第二相弥散强化效果,从而改善了合金的整体性能。合金的屈服强度和抗拉强度分别平均提高了20%左右,且伸长率也略有提高。     

Inhalation risk of indoor aerosol spray products commercially available in Bangladesh

Today, urbanised people spend most of their time in indoor environments, and the risk of exposure to toxic materials in an indoor environment is of great concern. This paper considers sources for the inhalation risk of aerosol sprays by measuring the particle size distributions of some of the most popular products that are commercially available in Bangladesh, and examines the degree of toxicity and the health risk via the respirability of the products. Results show that thoracic and respirable fractions of the suspended particulate matter are present in the tested samples and hence the spray products may pose a significant health risk.     

海水淡化用空心锥喷嘴喷淋性能理论及实验研究

设计开发一种具有高通量、低流阻特征的空心锥喷嘴,并通过理论与实验方法研究空心锥喷嘴的喷淋性能,基于准自由涡理论建立空心锥喷嘴内部流体流动的数学模型,阐明流量系数、喷淋锥角、喷嘴流量与喷嘴结构参数之间的定量关系,并利用多效蒸馏海水淡化喷淋实验台对理论计算结果进行实验测试和验证。研究结果表明:正常工作状态下喷嘴流量系数、喷淋锥角、喷淋流量等参数理论值与测量值之间的误差小于5%,验证了设计模型的准确性。同时根据实验测试数据,拟合得到该类型空心锥喷嘴喷淋锥角与雷诺数之间的经验公式,可为蒸馏海水淡化用大流量空心锥喷嘴的结构设计、工艺选型提供理论指导和数据支持。     

喷淋液滴在空气环境下的运动特性

本文以喷淋液滴在空气环境下运动特性为工程背景，建立单个液滴在常温、常压空气环境中的动量方程，分析液滴沉降特性、追赶特性及运动轨迹行为。计算结果表明，不同喷淋液滴初始条件下，短时间内存在重力大于曳力和重力小于曳力两种情况，但最终减速液滴均会达到受力平衡状态；液滴离开喷淋头后，垂向位移均迅速增大，液滴粒径越大、初始速度越大，垂向位移增长的速率也越大，达到相同位移的用时越短；液滴尺寸、初始速度相差越大，液滴追赶所用的时间越短，追赶位移越小，液滴尺寸、初始速度越接近，液滴追赶所用的时间越长，追赶位移越大；液滴初始速度越大、初始直径越大、喷射角度越大，横向速度消失越慢，达到的横向位移越大，喷射液滴覆盖的面积也越大。计算结果有助于优化工程实际中喷淋系统的设计与布置。     

Relations between asphaltene content,viscosity reduction rate of heavy oil and ultrasonic parameters

Ultrasonic treatment could decrease the viscosity of heavy oil and previous study on had focused on one heavy oil sample and involved less on the influence of asphaltene content. This study examined the effect of asphaltene content on viscosity reduction rate by ultrasonication. A comparison on samples with various asphaltene content and vibration parameter was made. The results showed that the optimal vibration frequency might decrease as the asphaltene content increased, whereas the optimal vibration intensity and the optimal treatment time were suggested to be enlarged. A semi-quantitative correlation was matched, which helped for numerical simulation about ultrasonic treatment.