超声辅助内圆磨削40Cr15Mo2VN轴承套圈的试验研究#br#

针对传统加工方式难以获得轴承套圈较小的表面粗糙度和表面波纹度的问题,采用超声辅助内圆磨削的加工方法来改善轴承套圈的表面质量。基于超声内圆磨削单颗磨粒运动轨迹分析,建立了表面粗糙度的理论模型,通过对轴承套圈进行超声内圆磨削试验,研究了各个加工参数对轴承表面质量的影响。研究结果表明：超声内圆磨削加工方法可明显改善轴承的表面质量;增大超声振幅可减小表面粗糙度而表面波纹度会先减小后增大;随着砂轮转速的增大,表面粗糙度及表面波纹度会先减小后增大;磨削深度和进给速度的增大会使表面粗糙度及表面波纹度增大,但超声内圆磨削可减小它们的增加量。     

微型超声电机驱动及其优化研究

针对某微小型超声电机驱动要求,设计直流升压变换器,采用小型微控制器产生信号相位差90度的驱动信号.基于该微小型超声电机的电容性负载特性,采用RC放电回路设计了电机驱动电路,分析了驱动电路电压波形参数对驱动性能的影响,得到了最佳驱动电路参数.采用电路仿真软件对所设计的电路进行仿真验证.针对电机驱动电路工作中的低效率,进行...     

GIS内部缺陷模拟试验在线检测的研究

分析超声波局部放电法对于GIS内部缺陷检测的特点、方法,并通过在平顶山高压开关厂内的几种GIS内部缺陷模拟试验,对各种缺陷模拟下的超声波典型数据进行了分析,得出了电压大小、电流大小、超声波探头位置、SFS气体品质、传统pc值与超声波幅值的关系,以及超声局部放电法对各种模拟缺陷的灵敏度。     

导波技术在输电线路无损监测中的应用

输电线路损伤的定位及类型识别对于保障电力系统安全运行有着重要的意义.提出了基于超声导波的输电线路无损监测方法并进行了实验验证.实验采用磁致伸缩换能器产生和接收超声导波,对钢绞线地线的断股损伤进行了检测研究,通过得到的实验信号可以确定损伤位置,并对损伤信号进行时频分析,研究损伤信号与损伤程度的关系.实验验证了该方法的可行...     

超声波加工中的动力效应与裂纹分析

发电设备的陶瓷部件主要用超声波进行加工,材料的去除率直接影响加工的效率.在加工中工件材料的表面受到磨料的碰撞,接触区域将发生变形.这种局部变形不能立即传遍整个工件,而是以波的方式逐渐传播.当应力大于其压缩强度后,接触面下面的材料开始破碎,材料中产生的裂纹沿撞击方向逐渐扩展.破裂是由于应力波从拐角的两个面反射结果造成的高...     

Large-eddy-simulation-based multiscale modeling of TiO2 nanoparticle synthesis in a turbulent flame reactor using detailed nucleation chemistry

In this work, we present a multiscale computational model for flame synthesis of TiO₂ nanoparticles in a turbulent flame reactor. The model is based on large-eddy simulation (LES) methodology in conjunction with detailed gas-phase chemical kinetics to accurately model the highly complicated combustion and nucleation processes in a turbulent flame. A flamelet-based model is used to model turbulence–chemistry interactions. In particular, the transformation of TiCl₄ to the solid primary nucleating TiO₂ nanoparticles is represented using an unsteady kinetic model considering 30 species and 69 reactions in order to accurately describe the important event of nanoparticle formation. The evolution of the TiO₂ number density function is tracked using the quadrature method of moments (QMOM). For validation purposes, the detailed computational model is compared against experimental data and reasonable agreement is obtained.     

Mechanism of electrochemical oxidation of ammonia

The electrochemical oxidation of ammonia has been studied in the most detail in alkaline solution at platinized platinum. Almost all work supports the essence of a mechanism first proposed by Gerischer and Mauerer (1970) [19], in which elemental nitrogen is formed at mildly positive potentials with near quantitative current efficiency through dimerization of partly dehydrogenated ammonia molecules NH_x(ads). The major intermediate, NH₂(ads), is formed at Pt(1 0 0) domains on the metal surface, where it dimerizes to hydrazine, and rapidly oxidizes to N₂. At somewhat more positive potentials, the formation of adsorbed nitrogen atoms poisons the anode, and nitrogen evolution ceases. At potentials where water is oxidized, the Pt anode is modified by a surface oxide; under these conditions, nitrogen evolution is accompanied by nitrogen oxides and oxyanions. Similar mechanisms are most probably followed on other noble metals and their alloys, although there is less experimental information. In the past decade there has been preliminary study of other anode materials, such as Ni/Ni(OH)₂, Ti/IrO₂, and boron-doped diamond, with a view to finding inexpensive and long-lasting anodes for ammonia oxidation, but so far, little is known about the mechanism of oxidation at these materials.     

Hollow graphitic carbon spheres for Pt electrocatalyst support in direct methanol fuel cell

Hollow graphitic carbon spheres (HGCSs) with a high surface area are produced by the carbonization of hollow polymer spheres obtained by the polymerization of core/shell-structured pyrrole micelles. HGCSs are employed as a carbon support material in a direct methanol fuel cell catalyst, and their effect on the electrocatalytic activity toward methanol oxidation is investigated. Pt catalyst supported on HGCSs shows a better electrocatalytic activity compared to that on Vulcan XC-72, which has been commonly used in fuel cell catalysts. The observed enhancement in the electrocatalytic activity is attributed to the improved electronic conductivity and high surface area of HGCSs.     

Microwave-assisted synthesis of graphene-supported Pd1Pt3 nanostructures and their electrocatalytic activity for methanol oxidation

This work reports the development of a facile, one-step microwave heating method for the synthesis of graphene-supported Pd₁Pt₃ (Pd core/Pt shell) electrocatalysts. The structure and composition of the synthesized nanocomposites were characterized via transmission electron microscopy and atomic force microscopy as well as energy-dispersive X-ray, X-ray powder diffraction, FTIR, and Raman spectroscopies. Using voltammetry, the electrocatalytic characteristics of the graphene-supported Pd₁Pt₃ nanostructures were evaluated for the oxidation of methanol as a model reaction. The results show that the introduction of graphene increases the electrochemically active surface area of the Pd₁Pt₃ nanostructures. As compared to the unsupported Pd₁Pt₃ electrocatalyst, the graphene-supported Pd₁Pt₃ electrocatalyst exhibited 80% enhancement of the electrocatalytic specific mass current for the oxidation of methanol. This method may serve as a general, facile approach for the synthesis of graphene-supported bimetallic PtM electrocatalysts with increased utilization of the Pt metal, which is expected to have promising applications in fuel cells.     

Electrochemical oxidation of ethanol in acid media on titanium nitride supported fuel cell catalysts

In the present study, titanium nitride, TiN that possesses good electronic conductivity, high corrosion resistance combined with the ability to support metallic particles, has been used to anchor Pt catalysts and subsequently used for ethanol oxidation. Platinum deposited on TiN (Pt–TiN) surface is contrasted with the conventional support material, Vulcan carbon for the electrochemical oxidation of ethanol in acidic medium. Though the comparison is not straight forward due to different morphology/particle size of the Pt catalyst on the two supports, the present investigations reveal that the TiN support lead to surface Ti–OH type functional groups that help in reducing the accumulation of carbon monoxide on the catalyst surface. The Tafel slopes are similar but the exchange current density on Pt–TiN is approximately twice that of the value observed on Pt–C. X-ray photoelectron spectroscopy data support the long term stability and electrocatalytic activity of Pt–TiN electrocatalyst.