Comparison of different methods for determination of Pt surface site concentrations for supported Pt electrocatalysts

Platinum surface atom (or site) concentrations for a series of commercially available 10, 20, and 40 wt% Pt/C electrocatalysts have been determined using X-ray diffraction (XRD), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), selective chemisorption, and cyclic voltammetry (CV) methods. Each method of analysis was repeated for a sufficient number of times to determine reproducibility and standard deviation limits. Comparison of the results shows that XRD and STEM methods give Pt surface site concentrations much higher than for chemisorption analysis due to assumptions regarding Pt particle shapes and particle size distributions. The results from CV analysis agree reasonably well with those from chemisorption if the sample amounts and methods of sample deposition preceding CV analysis can be well-controlled and there is no loss of surface exposure by the Nafion over-layer. Because both chemisorption and CV analyses more directly measure actual site concentrations with fewer assumptions, these methods should be considered superior to XRD and STEM analyses. Further, since chemisorption uses substantially larger sample sizes (up to 0.25 g) compared to CV (<0.01 g), reliability of chemisorption data is much more reliable and should be considered as the metric for surface Pt site determination.     

Design of Infiltrating Basin by Soil Storage and Conveyance Capacities

Abstract

Design of storm water storage basins must take both surface infiltrating flow and subsurface seepage flow into consideration. Standing water can result from the condition that the subsurface seepage capacity is less than the surface infiltrating capacity or the basin storage volume exceeds the soil pore volume underneath the basin. To avoid a prolonged draining operation, an infiltrating basin must be designed under the constraints of the soil pore storage capacity before saturation and the soil conveyance capacity after saturation. In this study, the potential flow model is developed to estimate the soil pore storage volume underneath the basin and to predict the conveyance capacity through the saturated soil medium between the basin and the local groundwater table. The potential flow model for infiltrating water flow provides a quantifiable basis to define the soil constraints and to compare various alternatives at the basin site.     

乌拉泊水库除险加固勘察及其成果分析

制定了乌拉泊水库除险加固勘察工作要点,并对库区进行了实际勘察。通过对勘察成果的详细分析,为乌拉泊水库的除险加固工程提供了重要依据,同时也为该水库的安全运行提供了科学的资料。     

建筑结构渗水的成因与控制

随着社会经济的不断发展,我国的城市化进程也在不断推进,人们也在追求更加舒服安逸的生活。关于防治房屋建筑结构渗漏的问题,则需要我们结合实际情况,不断的进行探究活动。只有这样,才能总结出建筑结构渗水的成因以及相关的防治措施。     

诱导无线定位系统在行移台车上的运用

连铸机所配备的专用精确诱导无线位置检测系统必须具备高精度和高可靠性。文章通过对某钢厂实际工程应用，证明诱导无线定位在横移台车上使用，定位准确，误差满足设计要求，不大于10mm。     

AHP法在水利工程设计方案优选中的应用

以水利工程中某水库除险加固为例,采用层次分析法(AHP)对工程存在的风险进行分析。根据模型中各层次因素的相对重要性差异,定量表示客观现实情况,通过计算确定每一层次全部因素相对重要性权值,得到了各方案相对最高层目标的重要性次序组合权值,为定性问题的定量解决提供了理论依据和方法。计算结果表明:应用AHP法确定方案二最优。     

某车型制件托架拼板“毛毛虫”国产化模具的研究和工艺分析

对V362车型制件托架拼板国产化模具进行了研究和工艺分析,使用特殊设计理念和合理布局及完善的切边冲孔思路,达到了工业化生产的基本要求。将切边等3道工序的内容合并为一道工序,减少了模具数量,并使用侧斜楔侧冲孔侧修边,方便了制件操作,从而使操作中节约了成本,提高竞争力。     

双耳托板螺钉断裂原因分析及改进措施

双耳托板螺钉装配过程中在托板与杆部结合处发生断裂。对断裂螺钉进行断口形貌分析,确定断裂性质为过载断裂;对同批次螺钉进行了金相、硬度、拉力试验、楔负载试验以及模拟安装试验,结果表明,螺钉断裂原因主要与断裂位置流线密集有关,同时热处理制度不匹配和流线被切断对断裂有促进作用。针对螺钉断裂有关原因提出了改进冷镦工艺、调整热处理制度和优化头(托板)杆加工工艺等改进措施,并对改进效果进行了验证,结果表明改进有效,新工艺加工的螺钉装配过程未再发生相同断裂现象。     

60Si2Mn弹簧钢的断裂失效分析

60Si2Mn弹簧钢在正常服役过程中出现断裂,断裂后部分原件损失,根据材料力学原理,并结合断口特征,确定断裂起源位置;采用光学显微镜、扫描电镜、体视显微镜、直读光谱仪等对残留端口的显微组织、宏微观断口形貌和化学成分等进行观察和检测分析,以确定断口起源和断口特征。结果表明:由于生产过程操作不当,弹簧表面存在微裂纹,同时由于喷丸处理的工艺不恰当,造成弹簧表面形成较深的应力线,应力线发展成为沿应力线的开裂和脱落。这些微裂纹、开裂以及脱落,作为弹簧的疲劳断裂源,造成了弹簧的断裂。