Engineering Commons^™

Synchronous Motor Phase Control By Vector Addition Of Induced Winding Voltages, Daniel J. Simon, Dennis L. Feucht

Electrical and Computer Engineering Faculty Publications

We propose a simple low-cost approach to the winding-sensed control of three-phase synchronous permanent-magnet motors. Our approach results from a straightforward but elegant application of vector-based motor theory. The method therefore does not depend on the differential equations that describe the motor dynamics, and it does not depend on the particular motor parameters. The single method we derive applies to both wye- and delta-configured motors. We vectorially sum the voltage waveforms at the motor terminals in a certain way and use their zero crossings to produce a correctly phased six-step switch sequence. We discuss the implementation for both wye- and …

Crystallization Kinetics Study Of The Glasses In Se–Te System, Fareed Abdul Raheem Al-Gheyath

Theses

The aim of the present work is to study the crystallization kinetics of some chalcogenide glassy alloys in the Selenium-Tellurium system. Four glassy systems have been prepared: Se₈₀Te_20-xSb_x (x= 0, 4, 6, 8, and 10); Se₇₀Te_30-xSb_x (x= 2, 6, 8, and 10); Se₈₀Te_20-xCd_x (x= 2, 4, and 10); and Se₈₀Te_20-xSn_x (x= 2, 4, and 10). The starting materials of (99.999%) purity were weighted according to their atomic percentages and sealed in evacuated silica tubes, under a pressure of about 10 …

Rehabilitation Of Concrete Structure Using Composite Materials, Ibtesam J.Saeed Al-Saifi

Theses

In the United Arab Emirates, most of the concrete structures including road, infrastructure and different types of buildings have been reported to be in need of rehabilitation. It is universally acknowledged that the environment of the countries in the Arabian Gulf is extremely severe and very aggressive to construction materials and operations. It is anticipated that the cost of rehabilitation of civil infrastructure will gradually increase over the next decade as a direct consequence of the increase in the number of structures reaching their expected service life.

Accordingly demand on rehabilitation methods will increase. In addition the severe climatic conditions …

Optimization Studies Of Thermal Bimorph Cantilevers, Electrostatic Torsion Actuators And Variable Capacitors, Wuyong Peng

Dissertations

In this dissertation, theoretical analyses and optimization studies are given for three kinds of MEMS devices: thermal bimorph cantilevers, electrostatic torsion actuators, and variable capacitors. Calculation, simulation, and experimental data are used to confirm the device behavior and demonstrate the application of the design approaches.

For thermal bimorph cantilevers, an analytical model is presented which allows theoretical analysis and quantitative optimization of the performance based on material properties and device dimensions. Bimorph cantilevers are divided into two categories for deflection optimization: either the total thickness is constant, or the cantilever has one constant and one variable layer thickness. The optimum …

Mechanisms Of Layer-Transfer Related To Silicon-On-Insulator Structures, Bo Chen

Dissertations

The objective of this dissertation was to study the mechanisms that affect an efficient hydrogenation process in silicon and to validate a hypothesis concerning the hydrogenation mechanism of pre-implanted silicon wafers under hydrogen-plasma processing. These studies are related to a general process. A trapping layer for hydrogen was introduced by ion beam implantation into the silicon wafer. Next, this wafer was hydrogenated using a hydrogen plasma. It was hypothesized that the trapping layer acts as a getterer for the hydrogen diffusing into the silicon wafer. It was found that a large amount of hydrogen could be absorbed in the trapping …

Boron And Phosphorous Implantation Into (100) Germanium : Modeling And Investigation Of Dopant Annealing Behavior, Yong Seok Suh

Dissertations

Germanium is increasingly being considered at this time for future silicon compatible optoelectronic and complementary metal oxide semiconductor (CMOS) device application. Germanium implantation will be a critical process for future device fabrication. However, critical properties like Pearson parameters and dopant activation temperatures are not well established. In this study, boron and phosphorus were implanted into (100) germanium with energies ranging from 20 to 320 keV and doses of 5 x 10¹³ to 5 x 10¹⁶ cm^-2. The behavior of the boron and phosphorus before and after annealing for 3 hours at 400, 600 or 800°C in …

Modeling Corrosion In Oxygen Controlled Lbe Systems With Coupling Of Chemical Kinetics And Hydrodynamics-Task V: Third Quarterly Report 03/01/2004-05/31/2004, Samir Moujaes, Yitung Chen

Transmutation Sciences Materials (TRP)

The Lead-Bismuth eutectic (LBE) has been determined from previous experimental studies by the Russians and the European scientific community to be a potential material that can be used as a spallation target and coolant for the TRP proposed application. Properly controlling the oxygen content in LBE can drastically reduce the LBE corrosion to structural steels. However, existing knowledge of material corrosion performance was obtained from point-wise testing with only very sparse experimental data. Scientists have noticed that the concentration of oxygen dissolved in the liquid alloy could control the corrosion rate of steels exposed to Pb or Pb-Bi. At high …

Exchange Model For Oscillatory Interlayer Coupling And Induced Unidirectional Anisotropy In [Pt/Co]3/Nio/[Pt/Co]3 Multilayers, Mikhail Ye Zhuravlev, Evgeny Y. Tsymbal, Sitaram Jaswal

Materials Research Science and Engineering Center: Faculty Publications

In a recent Letter [1] Liu and Adenwalla found an interesting oscillatory behavior of the interlayer exchange coupling (IEC) through an insulating NiO (111) layer with a period of 2 monolayers (ML). They interpreted this phenomenon in terms of multiple reflections of electronic waves from a periodic atomic potential in the spirit of the model of Ref. [2]. However, this interpretation is not consistent with the tunneling mechanism used by the authors which would result in a modulated exponential decrease of the IEC but no periodic change in sign. In this Comment we show that the observed oscillatory IEC can …

Studies Of Infrared Optical Properties Of Palladium Nanoparticles With Different Sizes And Dispersed States, Yan-Xia Jiang, Hong-Gang Liao, Wei Chen, Shi-Gang Sun

Journal of Electrochemistry

Pd nanoparticles with different sizes and dispersed states were prepared. Their infrared optical properties were studied with CO molecule probe. The infrared spectroscopic investigation revealed that Pd_n of 6.6 nm and Pd_n(cube)of 100～150nmexhibit normal IR absorption. The center of IR bands are around 1970 cm^-1 and 1910cm^-1. Pd_nis introduced into the surface of electrode, and is induced by interface electric fieldto form the aggregation of nanoparticles Pd_n(ag). The Pd_n(ag) has a different IR optical property from Pd_n. The direction of IR absorption band of Pd_{n …}

Preparation And Optical Properties Of Highly Ordered Cds Nanowire Arrays, Lan Sun, Chang-Jian Lin

Journal of Electrochemistry

Highly ordered CdS nanowire arrays have been prepared by using dc electrodeposition in the porous anodic aluminum oxide template. Scanning electro microscopy (SEM) and transmission electron microscopy (TEM) reveal that the nanowires are uniform and highly ordered. The measurements of X-ray diffraction and high-resolved electron microscopy (HRTEM) show that the nanowires are hexagonal structure with the crystallographic c-axis preferentially oriented along the length of the pore. The UV-Vis absorption spectra of CdS nanowire arrays show that the absorption edges of the nanowire arrays shift towards short wavelength with the decrease of the nanowire size. The photoluminescence measurements show that the …

Preparation, Characterization And Photoelectrochemical Activities Of Cu-Tio2/Ito Films, Dong Shu, Chun He, Han-Xia Zhang, Ya Xiong

Journal of Electrochemistry

Cu-TiO₂/ITO films were prepared by direct photo-reduction deposition of Cu²⁺ on TiO₂/ITO films. The nanocomposite films were characterized by UV-vis diffuse reflectance spectra (DRS), XRD spectra, Scanning Electron Microscope (SEM) technology, and photovoltage measurement. The feasibility of improving the photocatalytic activity of TiO₂ film by combining the modification of Cu nanoparticles with the application of anodic bias was investigated. The experimental results showed that the deposited Cu has an apparent enhancement effect with respect to suppressing the recombination between the photogenerated charge carriers and enhancing the photocatalytic oxidation of formic acid. The combination could …

Investigation Of Adsorption And Oxidation Behavior Of Isosafrole On A Smooth Pt, Xiao-Hong Zhang, Xiao-Jing Su, Qi-Ling Zhong, Lei Zhang, De-Sheng Mei, Bin Ren, Zhong-Qun Tian

Journal of Electrochemistry

The electro-oxidation of isosafrole on a smooth platinum electrode was investigated in the non-aqueous solution. The CV curve shows two oxidation peaks and one reduction peak in the potential region between -0.5 V and 1.95 V. The relation between the oxidation and reduction peaks has been determined also by CV. The adsorption behavior of isosafrole on Pt was also investigated.

Study On Electrochemical Performance Of Electroless Cobalt Coating For Microencapsution Of Hydrogen Storage Alloys, Tong-Chi Xia, Sheng-Li Zhang, Shu-Xin Wang, Kun Huang, Wen-Zeng Tian

Journal of Electrochemistry

The chemical cobalt plating method is used to treat on the hydrogen storage alloys. Effect of the surface treatment on the electrochemical performance of MH eletrodes was investigated by carrying out experimental methods of CV, AC and charge/discharge cycle tests. The results showed that after microencapsulation with cobalt, the impedance of electrochemical reaction on the surface and polarization during chare/discharge process was markedly decreased; and the electrocatalytic activity on the surface, discharge capacity, charge efficiency was improved. It was also indicated that the anode reaction of MH electrode treated was controlled by diffusion process.

Two Kinds Of Polarons Observedin Polyaniline In Aqueous H2So4, Qin Zhou, Lin Zhuang, Jun-Tao Lu

Journal of Electrochemistry

Simultaneous electrochemistry electron spin resonance (ESR) conductance measurements were carried out on electropolymerized polyaniline and ESR spectra were obtained with high signal/noise ratio. Spectral simulation revealed that in the early stage of polymerization, there were two kinds of polarons. According to the potential dependence of the ESR line width and the corresponding conductivitychange of the polymer, the two polarons are thought to be in ordered and disordered domains, respectively. With increasing doping level, the two polarons underwent similar transfer from Curie spin to Pauli spin and both polarons were charge carriers in the conducting polymer. This deduction was further supported …

Electrochemical Lithium Insertion Of Nanosized Tio2, Ying Lan, Jian-Wen Liu, Xue-Ping Gao, Xing-Di Zhou, Jin-Qiu Qu, Feng Wu, De-Ying Song

Journal of Electrochemistry

The protonic titanate nanotubes with the diameter of 10～15 nm were synthesized via hydrothermal method in NaOH solution and the calcined nanotubes at 500 ℃ were transferred to anatase nanorods with the diameter of 12～20 nm due to dehydration.The electrochemical behavior of the anatase nanorods as lithium insertion materials was examined. The results showed that the nanorod electrode had the high initial discharge capacity of 232 mAh/g and second reversible capacity of 198 mAh/g. The capacity of nanorod electrode maintained 152mAh/g after 20 cycles.

Electrocatalytic And Lifetime Studies Of Commercial Catalystsin A Pemfc, Cheng Xuan, Yan-Yun Ma, Li Qi, Cheng Peng, Ling Chen, Jun Zhao, Ying Zhang, Qin-Bai Fan

Journal of Electrochemistry

A particularly designed H-type cell was used to simulate the operating condition of a hydrogen-air proton exchange membrane fuel cell (PEMFC). The electrocatalytic activity, morphology, structure and lifetime of commercially available catalysts, carbon support platinum (Pt/C) and unsupported platinum-ruthenium (Pt-Ru), were preliminary studied by carrying out electrochemical measurements and by SEM, XRD techniques. The catalysts were simultaneously tested in the H-cell under operation, and also separately tested in a conventional electrochemical cell for comparison. It was found that the characteristic peaks of hydrogen adsorption/desorption on cyclic voltammograms shifted considerably to a more positive direction for Pt/C, while a more negative …

Direct Electron Transfer Of Redox Proteins And Enzymes Promoted By Carbon Nanotube, Chen-Xin Cai, Jing Chen

Journal of Electrochemistry

The redox proteins (enzymes), such as hemoglobin (Hb), horseradish peroxidase (HRP) and glucose oxidase (GOx) were immobilized on the surface of the carbon nanotube modified with glassy carbon (CNT/GC) electrode, respectively. The experimental results showed that the redox proteins (enzymes) underwent effective and stable direct electron transfer reaction at the surface of CNT/GC electrode with a pair of nearly symmetrical redox peaks in phosphate buffer solution. The formal redox potential, E^0' , is almost independent on the scan rates, the average value of E^0'  for Hb, HRP and GOx is -0.343±0.001, -0.319±0.002 and -0.456±0.001 V (vs.SCE,pH 6.9), respectively. …

Exceptional Electrochemical Activities Of Amorphous Fe-B And Co-B Alloy Particles Used As High Capacity Anode Materials, Ya-Dong Wang, Xin-Ping Ai, Han-Xi Yang

Journal of Electrochemistry

Ultrafine amorphous alloy particles (UAAP) of Fe-B and Co-B were synthesized and tested for possible use as electroactive anode materials. It is found that unlike their parent elements, the alloy particles of transition metal (TM) and boron, the Fe-B and Co-B showed superior electrochemical activities when used as anodic materials in aqueous alkaline solution. The discharge capacities of Fe-B and Co-B electrodeswere observed to be 1200 mAh/g and 1100 mAh/g at moderately high rate of 100 mAh/g, respectively, much higher than the theoreticalcapacity of currently used zinc metal (820 mAh/g). The exceptional high capacities of the boride alloys were probably …

Stability And Electrochemical Performance Of Nio Cathode Modified By Zno Additive For Mcfc In Molten Carbonates, Bo Huang, Fei Li, Qing-Chun Yu, Gang Chen, Ke-Ao Hu

Journal of Electrochemistry

The ZnO/Ni composite cathode was fabricated by tape-casting method, which microstructures and phases were studied. The electrochemical behaviors of ZnO impregnated NiO cathodes were also evaluated in molten 62 mol%Li₂CO₃ + 38 mol%K₂CO₃eutectic at 650 ℃ by electrochemical impedance spectroscopy (EIS) as a function of ZnO content and immersion time. The ZnO impregnated nickel cathodes showed the similar porosity, pore size and morphology to the reference nickel cathode. The stability tests of ZnO impregnated NiO cathodes showed that the ZnO additive could dramatically reduce the solubility of NiO in a eutectic carbonate mixture …

Structures And Redox Activities Of Poly(M-Methoxyaniline), Yun-You He, Yi-Ting Xu, Li-Zong Dai, Jean-Yves Gal, Hui-Huang Wu

Journal of Electrochemistry

Poly(m-methoxyaniline), PmMAn, was prepared in the presence of HCl, p-toluene-sulfonic acid and perchloric acid. By using cyclic voltammetry, the effect of different acid dopant on electrochemical activities of PmMAn was studied. The results showed that perchloric acid is the best acid to prepare PmMAn with good electrochemical activities The FTIR spectra indicate that the acid radical anions have embedded into PmMAn molecularchain as counter-ion during synthetic process, and this great influences the redox activities of PmMAn. SEM and XRD measurements illustrate that PmMAn is characterized by its typical molecular crystalline being monoclinic.

Study On Electrochemical Properties Of Peo-Based Composite Polymer Electrolytes, Hong-Yan Du, Hu Cheng, Yong Yang

Journal of Electrochemistry

Composite polymer electrolytes were prepared by introducing nano-scale SiO₂ into PEO₈-LiClO₄ matrix. The ionic conductivity, lithium transference number and the electrochemical stability windows were measured. The phase component was evaluated with DSC techniques. The results showed that the introduction of nano fillers enhanced the ionic conductivity. It reached 4.3×10^-5 S·cm^-1 at 22 ℃. The conductivity enhancement of the composite polymer electrolytes is analyzed and proposed.

Study On Reduction Process Of Electrolyic Manganese Dioxide In Situ By Ultraviolet-Visible Absorption Spectroscopy, Li-Cai Zhu, Zhong-Zhi Yuan, Wei-Shan Li

Journal of Electrochemistry

The concentrationsof soluble Mn(Ⅲ) species, during the reduction ofelectrolytic MnO₂ (EMD) in alkaline solution,have been monitored in situ by UV-visible spectroscopy. The concentration of Mn(Ⅲ) ion in solution changes with discharge time. The first electron discharge process of EMD can be described by three different steps: 1) the reduction of Mn⁴⁺ ions on the surface of EMD particles and the structural defect regions within the EMD, 2) the reduction of Mn⁴⁺ ions in ramsdellite, 3)the reduction of Mn⁴⁺ ions in pyrolusite. During the second electron discharge of EMD, the soluble Mn(Ⅲ) is reduced to Mn(Ⅱ) , …

The Matching Study Of Electrodes In C/Ni(Oh)2 Hybrid Capacitor, Yue-Feng Su, Feng Wu

Journal of Electrochemistry

The energy storage mechanisms of electrochemical double-layer capacitor (EDLC) and C/Ni(OH)₂ hybrid capacitor had been studied. The results proved that,the difference between the capacity of EDLC and C/Ni(OH)₂ hybrid capacitor was detemined by the effectiveness usage of the activated carbon negative electrode, which is a criterion to estimate or design the theoretic capacity of the C/Ni(OH)₂ hybrid capacitor. The electrochemical availability of activated matter in Ni(OH)₂ electrode was introduced, and the quantity of the activated matter in Ni(OH)₂ electrode should be compatible with the capacity of carbon electrode. When the capacities of Ni(OH)₂ electrode …

Electrodeposition Of Copper Into Trenches Under Rotating Hydrodynamic Condition, Jian-Jun Sun, Bu-Gao Xie, Wen-Hui Yin, Guo-Nan Chen

Journal of Electrochemistry

Silicon chips patterned with treneches were fixed onto a rotating electrode. Copper was electrodeposited into the trenches under rotating hydrodynamic conditions The sizes of the trenches are 1 m in height and 0.35 m, 0.50 m and 0.70 m in width, respectively. The effects of rotating of the chip, the current density and the concentration of Cu²⁺ on the filling of thetrenches were studied. It is found that lower current density and moderate concentration of Cu²⁺ resulted in a void free filling of the trenches.

Study Of Anti-Corrosion Property On Poly(An-Co-Oas)/Epoxy, Qing-Wu Wang, Geng-Chao Wang

Journal of Electrochemistry

Polyaniline, polyanisidine and their copolymer poly(An-co-oAs) were synthesized via the solution chemical oxidative polymerization of aniline and anisidine in an acidic aqueous medium, and their properties and structure were characterized. The electrochemical method were applied to evaluate the corrosion behavior of tined iron uncoated or coated by polyaniline, poly(An-o-oAs), polyanisidine and poly(An-co-oAs)/epoxy blend in acid or saline aqueous solution. The result showed that with the increase of anisidine content, the solubility of polymers is improved apparently but their oxidation extent decreases accordingly. It is also founded that polyaniline, poly(An-co-oAs) and polyanisidine all have good anti-corrosion properties, and their anti-corrosion capacity …

Investigation Of Subcritical Fatigue Crack Growth In Gamma Titanium Aluminides, Blair London

Materials Engineering

Our titanium aluminide alloy was readily heat treated to a fully lamellar state by holding at 1345C for 1.5 hours and furnace cooling resulting in a grain size of 330 muon m. The yield stress, ultimate stress, and total elongation were 315MPa, 465MPa, and 0.46% respectively. The fully lamellar microstructure shows significant work hardening. No long cracks initiated at R=0.1 and variation max=300MPa with up to 1.4 million cycles.

Effect Of Interface Bonding On Spin-Dependent Tunneling From The Oxidized Co Surface, Kirill D. Belashchenko, Evgeny Y. Tsymbal, Mark Van Schilfgaarde, Derek A. Stewart, Ivan I. Oleynik, Sitaram Jaswal

Materials Research Science and Engineering Center: Faculty Publications

We demonstrate that the factorization of the tunneling transmission into the product of two surface transmission functions and a vacuum decay factor allows one to generalize Jullière's formula and explain the meaning of the "tunneling density of states" in some limiting cases. Using this factorization we calculate spin-dependent tunneling from clean and oxidized fcc Co surfaces through vacuum into Al using the principal-layer Green's-function approach. We demonstrate that a monolayer of oxygen on the Co(111) surface creates a spin-filter effect due to the Co-O bonding which produces an additional tunneling barrier in the minority-spin channel. This changes the minority-spin dominated …

Development Of Nanostructure Based Corrosion-Barrier Coatings On Steel For Transmutation Applications, Biswajit Das

Transmutation Sciences Materials (TRP)

The objective of this project is to develop a novel nanostructure based coating technology that will provide significantly improved corrosion resistance for steel in LBE at elevated temperatures (500 - 600^oC), as well as provide long-term reliability under thermal cycling. The nanostructure based coatings will consist of a layer of nanoporous alumina with the pores filled with an oxidizing metal such as Cr, followed by a capping layer of alumina. Alumina, which is a robust anti-corrosion material, provides corrosion resistance at elevated temperatures. The Cr serves two purposes: (1) it acts as a solid filler material for the …

Effect Of Silicon Content On The Corrosion Resistance And Radiation-Induced Embrittlement Of Materials For Advanced Heavy Liquid Metal Nuclear Systems, Ajit K. Roy

Transmutation Sciences Materials (TRP)

The purpose of this collaborative research project involving the University of Nevada Las Vegas (UNLV), Los Alamos National Laboratory (LANL) and Idaho State University (ISU) is to evaluate the effect of silicon (Si) content on the corrosion behavior and radiation-induced embrittlement of martensitic stainless steels having chemical compositions similar to that of the modified 9Cr-1Mo 2 steel. Recent studies at LANL involving Alloy EP-823 of different Si content have demonstrated that increased Si content in this alloy may enhance the corrosion resistance in molten lead-bismuth-eutectic (LBE). Since very little data exists in the open literature on the beneficial effect of …

A Comparison Between Growth Morphology Of "Eutectic" Cells/Dendrites And Single-Phase Cells/Dendrites, Surendra N. Tewari, S. V. Raj, L. E. Locci

Chemical & Biomedical Engineering Faculty Publications

Directionally solidified (DS) intermetallic and ceramicbased eutectic alloys with an in-situ composite microstructure microstructure containing finely distributed, long aspect ratio, fiber, or plate reinforcements are being seriously examined for several advanced aero-propulsion applications. In designing these alloys, additional solutes need to be added to the base eutectic composition in order to improve their high temperature strength, and provide for adequate toughness and resistance to environmental degradation. Solute addition, however, promotes instability at the planar liquid-solid interface resulting in the formation of two-phase eutectic “colonies.”[1–4] Because morphology of eutectic colonies is very similar to the single-phase cells and dendrites, the stability …