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21.
Partitioning adsorption properties of palladium cations on composite supports of MgO/-Al2O3 were explored by IR, TPR and catalytic performance tests for CO oxidation. The experimental results revealed that palladium cations in conventional impregnation was dispersed completely on -Al2O3, when the amount of MgO in the samples was lower than 5%. For the catalysts prepared by double impregnation, part of palladium dispersed on MgO phase due to the complexing action of EDTA. Pd–MgO interaction suppressed the reaction of CO oxidation. 相似文献
22.
23.
以碳纳米管(CNT)作为低铂载量膜电极(CCM)催化层(0.1 mgPt·cm-2)添加剂,研究了CNT的添加方式对催化层微观结构以及膜电极性能的影响.结果表明,与常规低铂载量催化层相比,在其表面喷涂一层CNT或将CNT均匀分散到Pt/C催化层中均有利于提升低铂载量膜电极的输出性能,在70℃和100%相对湿度条件下最高输出功率比常规低铂载量膜电极的0.522 W·cm-2分别提升了22.4%和60.0%,并且均匀分散添加方式优于分层添加方式.其原因在于分层添加CNT后改善了低铂催化层和气体扩散层之间的接触界面,降低了催化层与扩散层间的接触电阻,而均匀分散添加方式除了可降低界面接触电阻外,还显著改善了低铂催化层中的气体传输,大幅提升了Pt催化剂的利用效率,使得膜电极电化学反应电阻明显降低.进一步对均匀分散添加方式中CNT的载量进行优化,表明CNT添加量为37.5 μg·cm-2时电池输出性能最佳,70℃和100%相对湿度条件下的最大输出功率达到0.91 W·cm-2.本研究工作表明,将CNT均匀分散添加到催化层中是一种有效提升低铂载量膜电极性能的方法. 相似文献
24.
Guadalupe Fortuño 《Plasma Chemistry and Plasma Processing》1988,8(1):19-34
A parametric study of the etching of Si and SiO2 by reactive ion etching (RIE) was carried out to gain a better understanding of the etching mechanisms. The following fluorocarbons (FCs) were used in order to study the effect of the F-to-Cl atom ratio in the parent molecule to the plasma and the etching properties: CF4, CF3Cl, CF2Cl2, and CFCl3 (FC-14, FC-13, FC-12, and FC-11 respectively). The Si etch rate uniformity across the wafer as a function of the temperature of the wafer and the Si load, the optical emission as a function of the temperature of the load, the etch rate of SiO2 as a function of the sheath voltage, and the mass spectra for each of the FCs were measured. The temperature of the wafer and that of the surrounding Si load strongly influence the etch rate of Si, the uniformity of etching, and the optical emission of F, Cl, and CF2. The activation energy for the etching reaction of Si during CF4 RIE was measured. The etch rate of Si depends more strongly on the gas composition than on the sheath voltage; it seems to be dominated by ion-assisted chemical etching. The etching of photoresist shifted from chemical etching to ion-assisted chemical etching as a function of the F-to-Cl ratio and the sheath voltage. The etch rate of SiO2 depended more strongly on the sheath voltage than on the F-to-Cl ratio. 相似文献
25.
A hybrid meshless technique based on composition of meshless local Petrov–Galerkin method (for spatial variables) and Newmark finite difference method (for time domain) is developed for natural frequencies analysis of thick cylinder made of functionally graded materials (FGMs). The FG cylinder is assumed to be under suddenly thermal loading, axisymmetric and plane strain conditions. The dynamic behaviors and time history of displacements are obtained in time domain using Green–Naghdi (GN) theory of coupled thermo-elasticity (without energy dissipation). Using fast Fourier transform (FFT) technique, the displacements are transferred to frequency domain and all natural frequencies are illustrated for various grading patterns of FGMs. The variations of mechanical properties in FG thick hollow cylinder are considered to be in nonlinear volume fraction law through radial direction. The presented hybrid meshless technique furnishes a ground to analyze the effects of various grading patterns of FGMs on natural frequencies, which are obtained employing GN coupled thermo-elasticity governing equations. Also, the frequency history and natural frequencies are illustrated for various grading patterns at several points across thickness of cylinder. 相似文献
26.
In this work crack formation and development is addressed and implemented in a planar layered reinforced-concrete beam element. The crack initiation and growth is described using the strength criterion in conjunction with exact kinematics of the interlayer connection. In this way a novel embedded-discontinuity beam finite element is derived in which the tensile stresses in concrete at the crack position reaching the tensile strength will trigger a crack to open. Since the element is multi-layered, in this way the crack is allowed to propagate through the depth of the beam. The cracked layer(s) will involve discontinuity in the cross-sectional rotation equal to the crack-profile angle, as well as a discontinuity in the position vector of the layer’s reference line. A bond–slip relationship is superimposed onto this model in a kinematically consistent manner with reinforcement being treated as an additional layer of zero thickness with its own material parameters and a constitutive law implemented in the multi-layered beam element. 相似文献
27.
探究岩石的受力特点及破坏特性是研究岩石地下工程安全性的关键,诸多学者都期望能在岩石本构模型的研究上取得突破性进展。在此背景下,提出了一种能够描述循环加-卸载条件下岩石的本构模型。首先,假设岩石的微元强度服从八面体剪应力理论并且微元破坏服从Weibull概率公式,将岩石本构中的损伤变量以及岩石微元强度表达式里包含的损伤因子进行本构变换,得到关于应力、应变等其他表现加-卸载下岩石损伤本构模型的参数,表示出岩石微元强度和损伤变量,再将得到的岩石微元强度和损伤变量代入所提出的岩石本构模型中,并进行等式变换得到一个函数表达式。通过将其与实验数据进行拟合对比分析,得出修正后的拟合参数,将其代入函数式中,得到损伤本构模型的修正式。最后将拟合参数进行必要的敏感性分析,得出各拟合参数的实际物理意义。 相似文献
28.
目的观察并分析凝血四项检测结果与不同比例下的全血与抗凝剂之间的关系。方法研究对象取2015年6月来湖北省宜昌市第二人民医院参加体检的110例健康人员,抽取全血血液样本后按照不同比例与抗凝剂混匀,常规分离血浆并测定受试者凝血酶时间(TT)、凝血酶原时间(PT)、激活部分促凝血酶原激酶时间(APTT)以及纤维蛋白原(FIB),并对研究结果相关数据作统计学处理。结果当血液量与抗凝剂比例为1∶5时,标本TT、PT、APTT以及FIB各项指标较1∶9时差异显著而具有统计学意义(P0.05);抗凝比例1∶7的情况下,TT指标差异与1∶9抗凝比例标本相比差异具有统计学意义(P0.05),而PT、FIB以及APTT三项指标差异并无统计学意义(P0.05);抗凝比例为1∶11与1∶13的情况下,TT指标与1∶9抗凝比例标本相比差异具有统计学意义(P0.05),而PT、FIB以及APTT三项指标差异并无统计学意义(P0.05)。结论凝血四项检测工作中,标本质量检测控制最关键的环节在于准确采集血液量,倘若采集血量过多或过少,导致与抗凝剂比例失调往往会影响测定结果准确性,检验科工作人员应予以重视。 相似文献
29.
The analysis on the recovery performance and characteristics in shape memory effects is helpful for the optimal design and engineering applications of shape memory polymers and their composites. To investigate the relationships among recovery performance, material parameters, and loading conditions, by taking aliphatic polyether urethane as an example, the researchers simulate the shape memory behaviors numerically using a three‐dimensional viscoelastic model. The material parameters for this model are taken from stress relaxation tests, rather than dynamic mechanical analysis tests. Both the unconstrained and the constrained recovery behaviors during strain‐controlled shape memory processes are analyzed. The results reveal that the unconstrained recovery occurs at the same temperature regardless of the applied strain values. Another interesting result is that the shape recovery temperature in unconstrained recovery situations increases and the maximum recovery stress under constrained recovery conditions decreases with the increase of heating rates. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
30.
采用浸渍法制备了CuO/TiO2负载型催化剂,并将其用于CO2加氢制甲醇反应。重点考察了铜的负载量对催化剂性能的影响,并对其物化性能和催化性能之间的关系进行了讨论。结果发现,随着铜负载量的增加,催化剂中金属铜的比表面先增加后减小,当铜的负载量为10%(质量百分数)时达到最大值。催化剂的表面碱性位数量随铜含量的增加持续减小,中等碱位和强碱位的强度下降。当铜的负载量不高于10%时,CO2的转化率与铜的比表面积呈线性关系。甲醇选择性与催化剂的表面碱位性质有关,过强的碱性位会降低甲醇选择性。 相似文献