PIV analysis and high-speed photographic observation of cavitating flow field behind circular multi-orifice plates

Based on a self-developed hydrodynamic cavitation device with different geometric parameters for circular multi-orifice plates,turbulence characteristics of cavitating flow behind multi-orifice plates,including the effects of orifice number and orifice layout on longitudinal velocity,turbulence intensity,and Reynolds stress,were measured with the particle image velocimetry(PIV)technique.Flow regimes of the cavitating flow were also observed with high-speed photography.The experimental results showed the following:(1)high-velocity multiple cavitating jets occurred behind the multi-orifice plates,and the cavitating flow fields were characterized by topological structures;(2)the longitudinal velocity at each cross-section exhibited a sawtooth-like distribution close to the multi-orifice plate,and each sawtooth indicated one jet issuing from one orifice;(3)there were similar magnitudes and forms for the longitudinal and vertical turbulence intensities at the same cross-section;(4)the variation in amplitude of Reynolds stress increased with an increase in orifice number;and(5)the cavitation clouds in the flow fields became denser with the increase in orifice number,and the clouds generated by the staggered layout of orifices were greater in number than those generated by the checkerboard-type one for the same orifice number.The experimental results can be used to analyze the mechanism of killing pathogenic microorganisms through hydrodynamic cavitation.

Kinematical Analysis and Simulation of High-Speed Plate Carrying Manipulator Based on Matlab

In order to construct the more effective kinematics method for industry, by taking a high-speed plate handing robot as an example, the structure and parameters of the robot linkages are analyzed, and the standard Denavit-Hartenberg method is applied to establish the coordinates and the kinematic equation of the linkages. Depending on the graphics and matrix calculation ability of Matlab especially including the Robotics Toolbox, the handling robot has been modeled and its kinematics, inverse kinematics and the trajectory planning have been simulated. Therefore, the correctness of kinematic equation has been verified, meanwhile, the functions of displacement, velocity, acceleration and trajectory of all the joints are also obtained. In a further step, this has verified the validity of all the structure parameters and pro- vided a reliable basis for the theoretical research on the design, dynamics analysis and trajectory planning of the ma- nipulator control system.

Study on Physical and Chemical Behaviors of Rare Earths in Preparing Ceramic Tube Supported Palladium Film by Electroless Plating

The rare earths of ytterbium, lanthanum, praseodymium, neodymium and their binary mixtures were respectively added into the traditional electroless plating solution to prepare thin palladium film on the inner surface of porous ceramic tube. The experimental results shows that the addition of rare earths increases palladium deposition rates and the binary mixtures are superior to the single rare earths and the mixture of ytterbium-lanthanum is the most efficient. Adding the mixture of ytterbium-lanthanum can also reduce the plating temperature by 10 ~ 20℃, shrink the metal crystal size and improve the film densification compared to those by traditional electroless plating. A thin palladium film with 5μm was prepared and the film made a highly pure hydrogen with a molar fraction of more than 99.97% from a H2-N2 gas mixture. More attentions were paid to analyze the physical and chemical behaviors of the rare earths in palladium film preparation.

Composition and corrosion resistance of palladium film on 316L stainless steel by brush plating

Palladium films with good adhesive strength were deposited on 316L stainless steel by brush plating. Scanning electronic microscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy （XPS）, mass loss tests and electrochemical methods were used to study the properties of the films. The brush plated palladium film mainly consisted of palladium. XPS analysis indicated that palladium was present in the films as metal state. The palladium plated stainless steel samples showed excellent corrosion resistance in boiling 20% H2SO4 solution and boiling acetic/formic acids with 0.005 mol/L Br- ions added. The corrosion rates of the palladium plated 316L stainless steel samples were about two orders of magnitude lower than those of the original 316L stainless steel samples. This method provides a possibility to prepare protective palladium films on stainless steel facilities with large areas in industrial sites.

A New Activation Method for Electroless Metal Plating: Palladium Laden via Bonding with Self-Assembly Monolayers

A new activation method has been developed for electroless copper plating on silicon wafer based on palladium chemisorption on SAMs of APTS without SnCl2 sensitization and roughening condition. A closely packed electroless copper film with strong adhesion is successfully formed by AFM observation. XPS study indicates that palladium chemisorption occurred via palladium chloride bonding to the pendant amino group of the SAMs.

Effects of Sn residue on the high temperature stability of the H_2-permeable palladium membranes prepared by electroless plating on Al_2O_3 substrate after SnCl_2–PdCl_2 process: A case study

The stability of composite palladium membranes is of key importance for their application in hydrogen energy systems. Most of these membranes are prepared by electroless plating, and beforehand the substrate surface is activated by a SnCl_2–PdCl_2 process, but this process leads to a residue of Sn, which has been reported to be harmful to the membrane stability. In this work, the Pd/Al_2O_3 membranes were prepared by electroless plating after the SnCl_2–PdCl_2 process. The amount of Sn residue was adjusted by the SnCl_2 concentration, activation times and additional Sn(OH)_2coating. The surface morphology, cross-sectional structure and elemental composition were analyzed by scanning electron microscopy(SEM), metallography and energy dispersive spectroscopy(EDS), respectively. Hydrogen permeation stability of the prepared palladium membranes were tested at450–600 °C for 400 h. It was found that the higher SnCl_2 concentration and activation times enlarged the Sn residue amount and led to a lower initial selectivity but a better membrane stability. Moreover, the additional Sn(OH)_2coating on the Al_2O_3 substrate surface also greatly improved the membrane selectivity and stability.Therefore, it can be concluded that the Sn residue from the SnCl_2–PdCl_2 process cannot be a main factor for the stability of the composite palladium membranes at high temperatures.

Electroless Plating of Palladium Membranes on Porous Substrates for Hydrogen Separation and the Effects of Process Factors on Plating Rate and Efficiency: A Review

The electroless plating of palladium and palladium alloy membranes is fast becoming an important and enabling technology. This is more so when juxtaposed with the rising demand for high purity hydrogen for applications particularly in proton exchange membrane fuel cells (PEMFC). The effect of process factors such as sensitization and activation during surface modification, concentration of the reducing agent, plating temperature, time, pH, additives, air aeration on plating efficiency, quality of the palladium film and deposit morphology is reviewed with the aim of identifying areas requiring further investigation. The paper also reviews how these process factors could be optimised for better plating efficiency and overall membrane quality. The concentration of the reducing agent has been identified as the limiting factor on plating efficiency albeit other process factors separately impact on the plating efficiency. Furthermore, bulk precipitation caused by concentration of the reducing agent has been identified as a major problem during electroless plating with hydrazine based plating baths. To ameliorate this problem, a multi step addition of the hydrazine reducer in separate portions has been recommended.

Preparation of Thin Palladium Composite Membranes and Application to Hydrogen/Nitrogen Separation

Thin palladium composite membranes were prepared by modified electroless plating method on a-alumina supports and a dense Pd/α-Al2O3 composite membrane with high hydrogen flux, good selectivity for hydrogen was obtained. It was tested in a single gas permeation system for hydrogen permeance and hydrogen selectivity over mtrogen. The hydrogen permeance of the corresponding membrane was ashigh as 2.45×10^-6mol·m^-2·s^-1.Pa^-1 and H2/N2 selectivityover700 at 623K and a pressure difference of 0.1MPa. The-main resistance of the composite membrane to H2 permeation lies in the aluminum ceramic support rather than the thin Pd layer.

Pd-ZSM-5复合膜的制备及其氢气分离性能

为了能够在大孔氧化铝载体表面得到透氢性能良好的钯膜,利用二次生长法在多孔Al_(2)O_(3)载体上生长出一层连续完整的ZSM-5沸石分子筛修饰层,通过化学镀过程在ZSM-5沸石分子筛修饰的载体上沉积一层钯膜,从而得到Pd-ZSM-5复合膜。利用扫描电子显微镜(SEM)对载体、ZSM-5沸石分子筛修饰后的载体和Pd-ZSM-5复合膜的形貌进行详细分析,并通过X线能量色散光谱(EDX)对Pd-ZSM-5复合膜的表面和截面元素分布进行了研究。而且,为了确定该Pd-ZSM-5复合膜的H_(2)渗透性能,在623~773 K范围内,研究了操作温度、操作时间和测试压力对Pd-ZSM-5复合膜透氢性能的影响。研究结果表明,ZSM-5沸石分子筛修饰层能够有效改进载体的表面粗糙度和降低其表面孔径,有助于Pd膜的沉积。所制备的Pd-ZSM-5复合膜表面完整、致密,Pd膜层厚度约为5μm, ZSM-5沸石修饰层厚度约为3μm。当操作温度为773 K、渗透压力为0.1 MPa时,Pd-ZSM-5复合膜的H_(2)渗透通量和H_(2)/N_(2)渗透选择性分别为0.113 mol/(m·s)和468。而且,该Pd复合膜在773 K下,连续操作300 h后,其H_(2)渗透性能保持相对稳定。

浸镀时间对镀钯无氧铜线镀层质量的影响

采用直接镀法和扫描电子显微镜研究了影响无氧铜线镀钯层质量的因素。结果表明:浸镀时间和纳米钯粉含量对无氧铜线镀钯层质量有显著影响。当镀液中纳米钯粉的质量分数为2%、表面活性剂OP-10的质量分数为3%时,在室温浸镀15 min以上的无氧铜线表面纳米钯颗粒团聚较少,几乎无露铜现象;纳米钯粉和OP-10的质量分数分别增加至4%和6%时,在室温浸镀20 min的无氧铜线镀层质量最好。此外,当镀液温度升高至约60℃时,浸镀15 min的无氧铜线镀层不均匀,漏铜现象明显。在450℃真空退火后,镀钯铜线的镀层界面结合强度和平整度提高。

电镀液添加剂成分对钯镀层的影响研究

采用二氯四氨钯为主盐,润湿剂A、光亮剂B、稳定剂C为组合添加剂配制成电镀液,进行侯氏槽测试,电沉积获得钯镀层。通过设计正交试验对添加剂的组成及含量进行了筛选,采用扫描电子显微镜、X射线衍射表征了钯镀层的形貌和结构,考察了添加剂组分及含量对镀钯层表观形貌、微观形貌以及硬度的影响。正交试验研究结果表明:在电流密度0.85 A/dm^(2)、镀液pH 8.0,50℃施镀20 min的电镀工艺下,添加剂中稳定剂含量对于电沉积的影响较为明显,稳定剂含量大的镀层外观和硬度比较好,而光亮剂和润湿剂起辅助性作用。稳定剂与钯离子络合,阻止钯离子被还原,提高了镀液稳定性;光亮剂吸附在阴极表面,增大阴极极化值,形成活性位点,提高了晶核的生成速度,能够获得结晶细致紧密的镀层;润湿剂降低了阴极电沉积过程中产生的氢气气泡附着力,扩展了低电流区镀层,提高抗杂质干扰能力使镀层光亮平整。添加剂中各组分的协同提高了镀液整平能力及低电流密度区镀层光亮性,获得的纯钯镀层阴极电流密度范围更宽。

铝焊盘镀钯铜丝多焊球脱焊失效的电化学评价

研究铝焊盘的镀钯铜丝(PCC)焊点的多焊球脱焊(MLB)失效过程,对提高产品的可靠性至关重要。利用电化学方法测定了在不同氯离子浓度、pH值和铜暴露面积等条件下电极的腐蚀电流,以表征铝及其金属间化合物(IMC)的腐蚀速率。结果表明,氯离子可以改变阳极极化率,从而影响腐蚀电流;pH值的变化可以改变阴极极化率,从而影响腐蚀电流。钯作为铜丝的保护层,在镀层分布不均或参数选择不当的条件下,与暴露的铜表面形成腐蚀电偶,导致铝及其IMC成为牺牲阳极并被腐蚀。

氟碳型表面活性剂浓度对离子钯活化液活性的影响

采用离子钯活化液进行绝缘基材化学镀铜前的表面活化,探究不同浓度的氟碳型表面活性剂对离子钯活化液活化效果的影响。利用激光共聚焦显微镜(CLSM)分析化学镀铜后基材表面粗糙度,采用扫描电子显微镜(SEM)表征化学镀铜后的形态和结构,结合X射线能谱仪(EDS)检测样品表面元素含量,对化学镀铜后的基材表面进行背光测试及电化学分析。结果表明:氟碳型表面活性剂存在临界浓度0.01 g/L,氟碳型表面活性剂浓度由0.001 g/L增加至0.01 g/L时,离子钯活化液活化效果随表面活性剂浓度的增加而提高,但氟碳型表面活性剂浓度由0.01 g/L继续增加至1 g/L时,离子钯活化液的活性效果反而降低,当氟碳型表面活性剂的浓度为临界浓度0.01 g/L时,离子钯活化液的活性最高,化学镀铜的效果最好。

High-speed measurement of thickness of a water film formed by a jet obliquely impinging onto a plate using an LED-induced fluorescence method

A transient thickness distribution measured with a high temporal resolution is elemental for exploring the flow characteristics and mechanism of a liquid film formed by an impinging jet.Therefore,this paper develops a high-speed Light-Emitting Diode-Induced Fluorescence(LEDIF)system based on the brightness measured directly above the liquid film.An Ultraviolet(UV)LED lamp is used to provide sufficient and continuous excitation light.Then,a system performance analysis proves that the system can continuously measure the global film thickness at a high acquisition frequency of 5000 Hz when the dye concentration is 200 mg/L.The influence of the irregularity of the excitation intensity,including the spatial non-uniformity,temporal instability,and long-term instability,on the measurement uncertainty is analyzed in detail.The analysis indicates that the system has an acceptable uncertainty of 10%.Compared with theoretical results,experimental results verify that the LEDIF system can accurately measure the global thickness of a liquid film formed by a water jet obliquely impinging onto a plate.An experimental investigation of the radial section of the raised zone demonstrates that the radial section changes from a sewing needle to an oval when the azimuth angle increases from 10°to 90°.Meanwhile,the dynamic contact angle exponentially decreases from 41.4°to 30.1°.A dynamic analysis of surface waves shows that the measured wave velocity decreases from 12 m/s to 1 m/s and the dominant frequency decreases from 1000 Hz to 10 Hz along the flow direction.

Regularity and sensitivity analysis of main parameters of plate effects on the aerodynamic braking drag of a high-speed train

With increase of train speed,braking plate technology has a good application prospect in the high-speed stage of the train.Based on the 1/8 scaled symmetrical train model composed of two half cars,the Reynolds Av era ge Navier-Stokes(RANS)equations and Shear Stress Transfer(SST)k-ωturbulence model are adopted to simulate the aerodynamic performance of the train with plate.The aer odynamic dra g de pendence of single par ameter of the plate(shape,area,angle,position and n umber)is anal ysed,and identification resear c h of the main aerodynamic parameters of the plate is carried out.The numerical settings used in this paper are verified by wind tunnel test data.Results show that the braking plate with an aspect ratio of one has better performance on aerodynamic drag.The area,opening angle and number of plates are basically positively correlated with the total aerodynamic drag of the target car and plate.Arr anging plates at the downstream of the vehicle is a good method of raising total aerodynamic drag.Within the range of plate parameter design in this paper,by using orthogonal design of experiment and the method of range analysis and analysis of variance,the influence degrees of plate parameters on aer odynamic dra g ar e determined,and the order is n umber,ar ea and opening angle of plate.The research results provide theoretical support for the design and safe operation of high-speed trains with aerodynamic braking plates.

电镀竖向同电位铜厚差异的改善探讨

垂直连续电镀(VCP)线由于其高效率、高稳定性、高精度、低成本等优点,在印制电路板(PCB)生产中已逐步取代传统龙门式电镀设备,广泛运用于全板电镀、图形电镀及微孔电镀。针对VCP的导电结构及电镀原理展开分析,通过对比实验,研究分析了造成整板电镀竖向同电位铜厚异常的原因,并通过制定相应的措施,有效解决了因飞钯导电不良导致的镀铜差异性问题。

非金属表面化学镀活化方法的研究现状

介绍了近年来国内外非金属基体化学镀的活化工艺。分析表明,胶体钯活化法工艺成熟、性能优异,但存在成本高、污染重等不足;无钯活化法弥补了钯活化工艺的缺陷,显示出广阔的发展前景,但活化效果差、工艺复杂限制了它的应用。因此,开发工艺简单、活化效果显著的无钯活化工艺是今后研究的重点。

自组装膜吸附钯的化学镀前活化研究

提出了一种无需氯化亚锡敏化、基于分子自组装膜(SAMs)吸附钯的活化方法,成功地引发了在氧化铝粉末表面的化学镀铜.用XPS、AES、FTIR研究了钯的吸附机理,认为是由于氯化钯与SAMs上向外突出的氨基形成了化学键,并提出了相应的活化机理.金属化产物经XRD、FTIR、剖面金相显微表征分析与压片电阻率测定,示为金属铜完全包覆氧化铝的复合材料.该活化工艺具有活性引发层厚度薄、寿命长和与基底结合力强等优点,也可应用于其它表面富羟基的基底材料.

钯改性铝化物涂层的工艺及组织

研究了用二氯二氨基钯为主盐电镀Ｐｄ 及ＰｄＮｉ 合金的配方及工艺条件，再通过传统固渗铝方法制备高温合金Ｍ３８ 的防护涂层．研究了镀层状态、渗铝方式、渗铝活化剂、预扩散处理等工艺条件对钯改性铝化物涂层组织的影响，经ＸＲＤ、ＥＰＭＡ及金相观察，发现该涂层为固溶Ｎｉ 的βＰｄＡｌ 或固溶Ｐｄ 的βＮｉＡｌ 单相结构，随工艺改变，涂层中Ｐｄ、Ｎｉ 含量不同．

关键因素对化学镀铁镀速的影响研究

以有机玻璃为镀件,通过化学镀铁工艺构建了应用于惯性约束核聚变实验的铁黑腔。采用离子钯为活性剂,考察了氯化钯质量浓度对镀层覆盖率的影响;详细研究了镀液中主盐硫酸亚铁、还原剂硼氢化钠和缓冲剂硼酸、工艺条件(pH值和温度)对镀速的影响规律。实验结果表明,随着镀液中主盐和还原剂质量浓度的增加,镀速明显加快;而缓冲剂对镀速的影响相对较小;随着pH值和温度的升高,镀速也明显加快。对相应的影响机制进行了探讨,为最终建立动力学方程打下了基础。