bluuebunny/crossref_metadata_2025 huggingface dataset:
Inverse Heat Transfer Using Levenberg-Marquardt and Particle Swarm Optimization Methods for Heat Source Estimation
Authors: Cortés O. , Urquiza G. , Hernández J. Alfredo
Published: September 2009

The present work uses the Levenberg-Marquardt Method (LMM) and a Particle Swarm Optimization (PSO) for estimating the heat generation function for a Guarded Hot-Plate Apparatus (GHPA). This device is used for thermal conductivity determination of insulating materials. The problem is one-dimensional in cylindrical coordinates. Geometries are a disc (Hot-Plate) and an annulus (Guard). A heat generation function is estimated considering one to five parameters. Capability of each method for recovering the analytical function is tested. Results are satisfactory for this kind of problem.
Effect of Maximum Temperature and Heating-Cooling Repeated Cycles on Thermal Contact Resistance of a Composite Tube
Authors: Carvajal-Mariscal I. , Sánchez-Silva F. , Polupan G. , Basualdo-Rojo J.A.
Published: September 2009

Experimental research results of the operational parameter effect on Thermal Contact Resistance (TCR) in a copper-aluminum L-type finned tube are presented. The investigated operational parameters were the maximum operational temperature and the number of repeated heating-cooling cycles. The TCR was experimentally determined by measuring the total heat supply, core tube wall and inner fin surface temperatures for steady-state and natural-convection conditions. In addition, the specimen was tested through up to 200 heating-cooling cycles. The experimental results showed a TCR increase of 81% at the same time as the average temperature difference between the hot inner flow and cooling air increased from 30°C to 130°C; over the maximum operational temperature (120°C), the TCR increased faster than before; and, after the heating-cooling cycle testing the TCR presented an increase of 31% in respect with the initial value. Such findings may be useful as a reference for preliminary thermal design and as recommendations for optimal operation of heat exchangers based on copper-aluminum L-type finned tubes.
Trajectory Generation of Robot Manipulators Using an Artificial Potential Function and Genetic Algorithms
Authors: Ramírez-Gordillo J. , Muñoz-César J.J. , Gómez-Terán A. , Valencia-Lazcano A. , Soria-Moya A.L.
Published: September 2009

This work presents the problem of trajectory generation based on the use of artificial potential fields associated to articulated robotic manipulators, in order to find a trajectory so that a manipulator reaches a goal from an initial position without colliding with obstacles within its workspace. The search of a continuous sequence of collision-free configurations between an initial configuration and the final position implies the exploration of a non-linear solution space which can be described and solved with an optimization approach. It does not take into account the use of complex mathematics in an analytical or numerical solution of the inverse kinematics, where are shown manifolds solutions as a result of the angular displacements of each joint of the robot. The genetic algorithm used as strategy, reduces the complexity of the problem, because the geometric connection equations are obtained systematically. In addition, the artificial potential field simulates the attraction and repulsion forces between the goal and the obstacles, where the goal is identified as the global minimum and the obstacles as restricted points. Altogether the potential field and the genetic algorithm generate trajectories for the robot among the obstacles through the design of an appropriate fitness function that effectively drives the manipulator to the desired while avoiding collide with the obstacles.
Model Derivation and Numerical Simulation for a Pivoted Rigid Rotor-Bearing System
Authors: Gómez-Mancilla J.C. , Meda-Campaña J.A. , Torres-Cedillo S.G. , Nossov V.R.
Published: September 2009

This work addresses the obtainment of a mathematical model for a rotor-bearing system with orbital movement pivoted on a lubricated bushing. This kind of model allows the rotodynamic system to be analyzed using its angular displacement. Nonlinear dimensionless model is developed in order to present an approach capable of being used in general situations. Both numeric simulations and experimental results, which show the vibration response of the system and the angular orbits, illustrate the validity of the proposed approach.
Study of Flow over a Step Cylinder
Authors: Morton C. , Yarusevych S. , Carvajal-Mariscal I.
Published: September 2009

Flow over a step cylinder at ReD = 2000 and D/d = 2 was investigated using a URANS-based numerical approach. The results illustrate the downstream development and interaction of wake vortices and identify streamwise vortical structures originating at the step. The observed flow development is shown to be in agreement with experimental results. Also, a comparison of the computational results and previous experimental findings is carried out for the drag coefficient and the pressure coefficient.
Numerical Simulation of Multiple Scattering by Hidden Cracks under the Incidence of Elastic Waves
Authors: Rodríguez-Castellanos Alejandro , Sánchez-Sesma Francisco José
Published: September 2009

In this paper, the scattering of P-waves by hidden cracks located near to a free surface is investigated. The Indirect Boundary Element Method was used in order to study the wave propagation phenomenon in a halfspace considering various crack models. A near free-surface crack generates scattered surface waves whose amplitude spectra show conspicuous resonance peaks. Such effect has been attributed to local resonances of a virtual layer formed by the free surface and the up crack´s face. For the case of two-near-free-surface cracks the amplitude spectra show additional peaks, which can be associated to the presence of the second crack. Given similar sizes between these two cracks, the characteristic resonance frequency measured at the free surface corresponds mainly to the equivalent layer formed by the shallowest crack and the free surface. However, when the deepest crack becomes sufficiently large with respect to the shallow crack, two characteristic resonance frequency peaks appear. To illustrate the response and multiple scattering effects due to the presence of a second crack, results in frequency domain are provided. For the case of a near free-surface crack, results obtained by means of the formulation shown here have been verified against those obtained by using an analytical solution and good agreement was obtained.
Transferability of the Gurson Damage Model Parameters with Charpy and Tensile Tests with Different Constrain Level
Authors: Cuamatzi-Melendez Ruben , Yates J.R.
Published: September 2009

Little work has been published concerning the transferability of Gurson’s ductile damage model parameters in specimens tested at different strain rates and in the rolling direction of a Grade A ship plate steel. In order to investigate the transferability of the damage model parameters of Gurson’s model, tensile specimens with different constraint level and impact Charpy specimens were simulated to investigate the effect of the strain rate on the damage model parameters of Gurson model. The simulations were performed with the finite element program ABAQUS Explicit [1]. ABAQUS Explicit is ideally suited for the solution of complex nonlinear dynamic and quasi–static problems [2], especially those involving impact and other highly discontinuous events. ABAQUS Explicit supports not only stress–displacement analyses but also fully coupled transient dynamic temperature, displacement, acoustic and coupled acoustic–structural analyses. This makes the program very suitable for modelling fracture initiation and propagation. In ABAQUS Explicit, the element deletion technique is provided, so the damaged or dead elements are removed from the analysis once the failure criterion is locally reached. This simulates crack growth through the microstructure. It was found that the variation of the strain rate affects slightly the value of the damage model parameters of Gurson model.
Effect of Mixed Mode Loading Induced by Asymmetrical Stress upon Crack Initiation from Corrosion Pits
Authors: Acuña-González Narciso , González-Sánchez J. , Contreras E. , Sauceda Israel
Published: September 2009

This work focuses on determining the influence of mixed stress conditions on the initiation of fatigue cracks from corrosion pits in a UNS S31603 stainless steel. Fatigue limit was established as a threshold stress criteria for fatigue crack initiation from semi-elliptic surface pits. The strain energy release rate range (G) around semi-elliptic surface pits was determined as a function of the pit aspect ratio (depth/major width axes: a/c), pit contour and the orientation of the nominal stress from a linear elastic fracture mechanics approach. Results indicated that stress conditions for crack initiation in mixed mode overcome the minimum stress level or single threshold stress established from the fatigue limit concept. Under mixed mode condition a crack will grow at the surface zone (φ = 0˚) when a/c ≥ 0.60 and for orientation angles from 5˚ to 75.
Evaluation of Brittle Layers Obtained by Boriding on AISI H13 Steels
Authors: López-Perrusquia N. , Campos-Silva Ivan , Martínez-Trinidad José , Avilés A. , Alvárez-Castañeda E. , Juárez-Torres S.
Published: September 2009

The fracture toughness of AISI H13 borided steel and the strength adhesion of the coated system were estimated in the present work. The formation of the layers was carried out by the powder pack boriding process at 1273 K with 8 h of treatment. The fracture toughness (KC) of the layer is estimated at 25 and 45 m from the surface using four different Vickers indentation loads. The KC values were estimated by the extension of Palmqvist cracks parallel and perpendicular to the surface obtained at the indentation corners. The adherence of the layer/substrate was evaluated in qualitative form through the Rockwell-C indentation technique. The results obtained by both techniques, show, in first instance, that the fracture toughness of the boride layer can be expressed in the form (KC) (π/2) > (KC) > (KC) (0). Also, high delamination is obtained around the Rockwell-C indentation prints that denote poor adhesion in the coating-substrate interface.
Short Crack Propagation Model Applied to Shot Peened Aluminium Alloys
Authors: Solis J. , Oseguera-Peña J. , Betancourt I.
Published: September 2009

The Navarro-Rios micromechanical model was used to assess the bounds of two different damage zones: crack arrest region and crack propagation region of controlled shot peening (CSP) of high strength aluminium alloys. Performance of CSP in terms of fatigue resistance was investigated. This comparison indicated that CSP in terms of fatigue depends on the competition between its beneficial and detrimental products, i.e. surface roughness and compressive residual stresses respectively. The gathered information can be used for safe load determinations in design.
Effect of Boriding on the Mechanical Properties of AISI 1045 Steel
Authors: Rodríguez-Castro G. , Campos-Silva Ivan , Martínez-Trinidad José , Figueroa-López U. , Meléndez-Morales D. , Vargas-Hernández Jesus
Published: September 2009

Some mechanical properties of AISI 1045 borided steels were estimated in the present work. The boriding process was carried out by the powder pack method at 950°C with 8 h of treatment. The fatigue strength on borided notched specimens was evaluated with rotating bending tests (R=1) considering a stress concentration factor (Kt) of 2.53. Likewise, the presence of residual stresses in boride layers was established by the XRD technique. The Daimler-Benz Rockwell C test was used, also, to estimate the strength adhesion of the coated system. The results show a decrease in the fatigue strength of AISI borided steels due to the presence of high porosity in the layers. Finally, the Rockwell-C adhesion test showed no coating failure for the boride layer.
Verification of the Ultrasonic Qualification for Structural Integrity of Partially Concrete Embedded Steel Elements
Authors: López J. Alfredo , Carrión Francisco J. , Quintana Juan A. , Samayoa Didier , Lomelí María G. , Orozco Pablo R.
Published: September 2009

Failure of one upper anchorage element in a cable-stayed bridge and its consequent analysis concluded that the main cause of the failure was a deficient heat treatment that resulted in large micro structural grain size and low fracture toughness, vulnerable to fatigue damage. Previous research studies demonstrated that ultrasonic evaluation could provide some insight of the microstructural integrity by correlating the ultrasonic response to the grain size. Thus, this technique was used to inspect the 112 elements in service in the bridge and 16 were qualified as structurally deficient, without direct verification of the grain size, since these elements were partially embedded in the concrete structure.

Late rehabilitation of the bridge considered the replacement of the 16 structural deficient anchorage elements, plus 4 elements qualified in good condition, to complete a reliability analysis for the remaining 92 elements from the statistical mechanical properties of the removed pieces. Rehabilitation made possible the confirmation of the initial diagnosis made by ultrasonic inspection and fatigue cracks were identified in some elements. This study demonstrated that the ultrasonic non destructive evaluation is highly reliable for structural integrity qualification of steel structural elements partially embedded in concrete.
Residual Strength and Fracture Path for Drilled Epoxy-Glass Composites
Authors: Torres Mauricio , Gonzalez Jorge Luis , Hernandez Hilario
Published: September 2009

Aircraft composite structures are mostly joined by mechanical fasteners like bolts, pins or screws. However, the effect of the presence of holes in the remaining strength of the composite structures is still being studied extensively. In this work, epoxy/glass laminates with drilled holes of different sizes were tensile tested and from these results, the residual strength was plotted. Strength vs. hole’s diameter at different fiber orientation was obtained. The fracture path and failure mechanism were identified by fractographic examination. The Point Stress Criterion (PSC) was used, in order to establish the stress intensification due to the presence of a drilled hole. A numerical model by Finite Element Method was carried out to verify the experimental results and the analytic failure predictions. A reduction of 50% in laminate strength was observed when diameter-width ratio was 0.12. The principal fracture mechanism observed in composite laminates was interface breakup. FEM results and analytic results by PSC show accuracy of 90% for predicting the damage in drilled composites.
Thermal Shock-Resistance Performance of Al2TiO5/Al2O3 Composites
Authors: Hu Yong , Li Ming Zhong , Shen Qiang , Xu Wei Ping
Published: September 2009

In the present paper, Al2TiO5-Al2O3 composites with 10, 20, 40, 60, 80, and 90 Vol. % of Al2O3 respectively were prepared by the sintering of Al2TiO5 and Al2O3 powers. The thermal expansion ratio was measured and the quenching-strength method was used to study the thermal shock-resistance performance. The thermal expansion ratio was found to increase from zero for the sample with 10-20Vol.%Al2O3 to that of 0.007% as the content of Al2O3 increased . The results of quenching-strength test showed that the residual strength of Al2TiO5-Al2O3 composites decreased with increasing of Al2O3 content and the thermal shock cycles. The Al2TiO5/Al2O3 composite with 20Vol.% Al2O3 remained a strength of 33.4MPa after three cycles and exhibited good thermal shock-resistance performance.
Fabrication and Resistance-Switching Behaviors of NiO Thin Films by Thermal Oxidation of Evaporated Ni Films
Authors: Cao X. , Li Xiao Min , Yu Wei Dong , Yang Rui , Liu Xin Jun
Published: September 2009

Polycrystalline NiO thin films were fabricated on Pt (111)/Ti/SiO2/Si substrates by thermal oxidation of the evaporated Ni films. Pt/NiO/Pt structures were prepared, and they showed reversible resistance switching behaviors. When the compliance set current was varied from 5 mA to 40 mA, the on-state currents increased, while the on-state resistances decreased. It is probably attributed to higher current compliance resulted in the formation of stronger and less resistive filaments, which in turn need more energy and power for their rupture. The resistive switching in NiO thin films is closely related to the formation and rupture of conducting filaments.
Synthesis of Metastable Tungsten Carbide Nanoparticles by Mechanochemical Alloying Process
Authors: Tan Guo Long
Published: September 2009

Thermodynamically metastable tungsten carbide (W2C) nanoparticles have been synthesized by mechanochemical alloying (MCA) process. Mg was used as reductive agent and graphite as carbon source. The reduction reaction of WO3 and Mg gave nanometer W powders. Subsequent diffusion reaction of fresh W with carbon produced metastable W2C and a small amount of WC nanoparticles in a W rich environment. WC was then transferred to W2C during the prolonged MCA process. The mechanism of such a chemical transformation has been discussed from a point of view of thermodynamics. The subsequent self-propagation diffusion reaction of fresh W with C source controlled the rate of the whole reaction process due to its slow reaction speed. The final product of the MCA process mainly depends on the composition ratio of W to C in the raw materials. W2C nanoparticles in single phase have been finally fabricated by MCA process at a W rich environment. The structure of the final product has been determined by x-ray diffraction, while the morphology and microstructure of the as-milled W2C nanoparticles have been demonstrated by transmission electron microscopy images.
Effect of Surfactant on the Properties of Gel Ink
Authors: Liu Zhong Xin , Chen Ai Ping , Qian Ji Jun , Shen Hui
Published: September 2009

The polyoxyethylene nonyl phenol ethers (OP), fluorocarbon surfactant (FSO) and ammonium solution of styrene-maleic anhydride resin (SMA) were selected in the preparation of gel ink using carbon black as pigment. And the effect of the surfactants on the viscosity, surface tension, particle size and writing performance of the gel ink was investigated. The composite effect of OP and FSO was also studied. The results indicated that with the composite surfactant of OP and FSO, the surface tension of the gel ink could be adjusted to the appropriate value and the viscosity stability could be improved effectively. In addition, the particle size distribution of the carbon black pigment in the ink was more uniform. And the pens filled with such gel ink behaved good writing performance.
Controlled Growth of SnO2 Micro/Nanocrystals with Different Morphologies via a Solution Method
Authors: Jia Tie Kun , Wang Wei Min , Fu Zheng Yi , Huang Fei , Wang Hao
Published: September 2009

SnO2 nanocrystals with various morphologies were synthesized via a hydrothermal method assisting by the surfactant CTAB. The morphologies of the products were significantly dependent on the synthesis conditions. The products were characterized by X-ray diffraction (XRD) and field scanning electron microscopy (FESEM).The results showed products SnO2 nanoparticles and spheres like structure assembled with nanocones were obtained by varying the dosage of CTAB and the concentration of NaOH. The forming process of SnO2 sphere like structure was discussed and the proposed mechanism was put forward in this work.
Thermal Decomposition and Flame Retardance Behavior of Nanometer Magnesium Oxychloride Crystal Salt Involved in SMC
Authors: Li Jian , Huang Zhi Xiong , Zhao Ying
Published: September 2009

A detailed study of thermal decomposition behavior of nanometer magnesium oxychloride crystal salt involved in sheet molding compound has been carried out using differential scanning calorimetry, thermogravimetry and X-ray diffraction. The decomposing temperature changed from 112°C at the initial stage to 559°C at the end of the process. The results indicated that the thermal decomposition was carried out in the following three steps: releasing crystal water, then HCl secondly and finally structural water, the residua was magnesia. Nanometer magnesium oxychloride crystal salt addictives was used as flame retardance in sheet molding compound.
Effect of Processing Parameters on the Microstructure of Silicon Nitride Coatings by Chemical Vapor Deposition
Authors: Li Jia Liang , Chen Fei , Niu Jin Ye , Jiang Hong Yi
Published: September 2009

Silicon nitride coatings were prepared by chemical vapor deposition (CVD) method. The effect of raw precursor materials (SiH4 and NH3) ratio, gas flow amount, reaction temperature, and reaction pressure and deposition time to the microstructure, chemical compositions and crystal structures of the silicon nitride coatings are investigated. The results suggest that when the SiH4 and NH3 are used as the precursors, Ar is used as the protect gas, H2 is used as the carrier gas, the flow amount of SiH4 and NH3 is 200 sccm and 1000 sccm, the reaction pressure is 100 Pa, the reaction temperature is 900 oC and the deposition time is 30 min, the silicon nitride coatings with high deposition rate (~ 85 Å/min), small grain size (~ 0.2 µm) and high density are obtained. XRD results of the obtained silicon nitride coatings suggest their phase structure is amorphous.
Preparation of the Boron Nitride Fibers by Chemical Reaction
Authors: Cheng Zhi Qiang , Yu Hong Lin , Li Ling , Li Yong , Zhang Xiao Li , Jiang Hong Yi
Published: September 2009

In this study, boron nitride (BN) fibers were prepared via chemical method using boric acid as the raw material, under the atmosphere of NH3 and N2, respectively. Firstly, the boric acid was heated to melt in order to acquire B2O3 fibers. Secondly, the B2O3 fibers were pre-azotized under a NH3 atmosphere and held for 1 h at 970°C, and the sample was then sintered in N2 to the temperature of 2000°C and held for 1 h. The obtained samples were texted to analyze nitrogen content, morphology, tensile strength, and elastic modulus by neutralization titration, SEM, XRD and so on. The results show that the diameter of the BN fibers is ~ 4-6 μm with the nitrogen content of 54%, tensile strength of 1400 MPa, and elastic modulus of 120 GPa.
Preparation and Characterization of Pt/YSZ Composite Electrode
Authors: Luo Zhian , Xiao Jian Zhong
Published: September 2009

Substrates of ytrria stabilized zirconia electrolyte were prepared by the ceramic injection molding, and then composite electrode slurry was made of platinum powder and yttria stabilized zirconia powder by ball milling, and then was brushed on both surfaces of the zirconia substrate. After this, the Pt/YSZ composites were sintered on the YSZ substrate under various temperatures. The microstructure of the surface and interface of the electrodes was characterized by scanning electronic microscope, and the results showed that the sintering temperature of the electrode has a remarkable effect on the microstructure of the composite electrode, and that the electrode and substrate was interconnected and interpenetrated. The electrochemical properties of the as-prepared electrodes were investigated by electrochemical impedance spectroscopy (EIS). The EIS experimental results reveal that the Pt/YSZ composite electrodes show the favorable electrochemical catalysis performance compared with the Pt electrodes.
Laser Cladding of Zr52.5Cu17.9Ni14.6Al10Ti5/TiC Composite Coating on AZ91D Magnesium Alloy for Improvement of Wear Resistance
Authors: Huang Kai Jin , Wang Cun Shan , Xie Chang Sheng
Published: September 2009

To improve the wear property of magnesium alloy, wear-resistant TiC and in-situ ZrC co-reinforced Zr-based amorphous composite coating has been fabricated on AZ91D magnesium alloy by laser cladding using mixed powders of Zr52.5Cu17.9Ni14.6Al10Ti5-TiC. The microstructure of the coating was characterized by XRD and SEM techniques. The wear resistance of the coating was evaluated under dry sliding wear test condition. The results show that the coating mainly consists of amorphous and different crystalline phases. The coating exhibits excellent wear resistance due to the recombination action of amorphous and crystalline phases, and the wear resistance improves further with the increase of TiC content. The main wear mechanism of the coating and the AZ91D sample are different, the former is abrasive wear and the latter is adhesive wear.
Study on Low-Temperature Sintering of Microwave Dielectric Ceramics by Sol-Coating Method
Authors: Xu Jian Mei , Jin Zhen Min , Gao Hui Juan
Published: September 2009

Microwave dielectric ceramics with low sintering temperature were obtained by sol-coating method. The effect of glass additives on the sintering temperature and microwave dielectric properties of BaO–Nd2O3–TiO2 ceramics were investigated. The ceramics added with NBS glass have much higher quality factor Qf= 4658.9 GHz. The ceramics added with BBS glass have the highest dielectric constantεr=71.4 and lest temperature coefficient of resonant frequency τf =29.15×10-6/ °C. The ceramics added BBS glass are as follows:εr=58.58, Qf= 2986GHz, τf =29.15×10-6/ °C sintered at 1060°C where the ceramics can be co-fired with copper electrode.
Effect of Hydrogen Peroxide on TiB2-Based Materials
Authors: Huang Fei , Fu Zheng Yi , Yan Ai Hua , Jia Tie Kun , Wang Wei Min , Wang Hao , Wang Yu Cheng , Zhang Jin Yong
Published: September 2009

TiO2/TiB2 heterostructures were successfully synthesized by a facile hydrothermal approach in an aqueous solution of hydrogen peroxide (H2O2). The influence of H2O2 on TiB2-based materials was systematically investigated using X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that TiB2 is prone to oxidize in the presence of H2O2. TiO2/TiB2 heterostructure which high-density anatase-TiO2 stand on the surface can be gained in the presence of H2O2 solvent and the final composition can be controlled by the temperature and time. The investigation may provide a path to further understand the chemical property of TiB2-based materials and synthesis method of heterostructure.
Preparation and Characterization of the Coated ZrB2 @ ZrO2 Ceramic
Authors: Song Jian Rong , Shen Qiang , Li Jun Guo , Zhang Lian Meng
Published: September 2009

In this work, ZrB2 powder coated with ZrO2 (ZrB2 @ ZrO2) were applied to promote the densification of ZrB2 prepared by pulsed electric current sintering (PECS). The coating process and sintering behavior were investigated. While the pH value was about 9, the ZrB2 particles were successfully coated with ZrO2 by co-precipitation methods. The thickness of ZrO2 layer was about 3-5nm. The coated powder was sintered at 1600°C ~1950°C by PECS in vacuum. For comparison, the pure ZrB2 powder was sintered at the same conditions. The relative density of the sample coated with ZrO2 was 97.8% at PECS 1950°C, which was higher than that of sample without coating. The densification process can be divided into three stages. The ZrO2 coating layer plays an important role on the densification of ZrB2.
Dielectric Properties of PMN/CB/CIIR Composites
Authors: Yan Hao , Huang Zhi Xiong , Wang Yan Bing
Published: September 2009

The Magnesium Niobate-Lead Titanate (PMN) / conductive carbon black (CB)/ chlorobutyl rubber(CIIR) composites were prepared by blending-vulcanization method, and the dielectric properties were studied. The results showed that the dielectric constant and dielectric loss of composites increased nonlinearly when increasing the content of PMN or CB. From the curve of dielectric constant vs frequency, it is obtained that in the frequency range from 103 to 106 Hz, the dielectric constant of PMN/CB/CIIR composites decreased with the frequency increasing and the dielectric constants are more stable under high frequency.
Preparation of Mg-Cu Composite by Tape Casting and Hot-Pressing
Authors: Li Jun , Luo Guo Qiang , Shen Qiang , Zhang Lian Meng
Published: September 2009

The preparation of 50Mg/50Cu composite by tape casting and hot-press sintering was studied. During the preparation of the slurry and tapes, the effects of different organic additives were discussed and the contents of the organic additives were optimized. Then the sintering temperature of the green samples were discussed to get densified 50Mg-50Cu samples. The slurry was characterized by viscosity. And the tapes and the final 50Mg-50Cu sample were anaylsed by density, XRD and SEM. The viscosity results indicated that the slurry with well-dispersed and stable properties for tape casting could be obtained. The solid loading of the slurry is 48wt%. After tape casting, the density and uniform tapes were made. The XRD and SEM results demonstrated that the optimal sintering temperatures of Mg-Cu composite were from 460°C to 470°C.
Spark Plasma Sintering Process of Fe-6.5%Si Alloy from Fe and FeSi Powders
Authors: Zhang Xiang , Li Jun Guo , Qi Qing Qing , Zhang Lian Meng
Published: September 2009

Powder metallurgy (PM) method to fabricate 6.5% silicon steel attracts much attention due to the lower energy consumption and cost. In this paper, Fe-6.5%Si alloy was prepared by spark plasma sintering (SPS) from the mixture of Fe and FeSi powders with different size. The sintering process was investigated through the shrinkage behavior, phase change and microstructure. The results show that the shrinkage starts from 500°C, lower than conventional sintering methods. The sintering temperature and FeSi powder size influence the reaction between Fe and FeSi.
Study on Electrical Properties of Carbon Fiber Reinforced Cement Paste with CCCW
Authors: Fan Xiao Ming , Dong Xu , Sun Ming Qing , Li Zhuo Qiu
Published: September 2009

In this work, CCCW (cementitious capillary crystalline waterproofing materials) was added in CFRC (carbon fiber reinforced cement paste). Variations of electrical conductivity of CFRC with fiber contents (0.2%~2.0% by the weight of cement) and CCCW (3% by the weight of cement) were studied. The results showed that the resistivity of CFRC containing CCCW versus the concentration of carbon fiber curves had typical features of percolation phenomena. The percolation threshold was 1.2 wt.%. The relationship between resistance and compressive stress was repeatable in CFRC with carbon fiber content of 1.2 wt.%. The resistance decreased in nearly linearity to the compression stress during loading, and increased during unloading.
Synthesis of Co2O4 Microspheres by Hydrothermal-Precipitation for Electrochemical Supercapacitors
Authors: Yu Zhan Jun , Dai Ying , Chen Wen
Published: September 2009

Co3O4 microspheres were synthesized by hydrothermal-precipitation method using NH3•H2O, H2O2, n-butanol and polyethylene glycol as precipitator, oxidant, assistant solvent and dispersant respectively. The products were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical properties of the Co3O4 electrode were performed by cyclic voltammetry (CV) and galvanostaitc charge/discharge methods. The results exhibited that the Co3O4 single electrode had excellent stability, cyclic performance and high specific capacitance in KOH electrolyte. The specific capacitance as a single electrode was up to 653.74 F/g in the 6mol/L KOH solution with 0-0.4V potential at 2mA/cm2 current density. The effects of electrolyte concentrations and current densities on its capacitive performance were investigated. The Co3O4 prepared material is potential candidate for the preparation of power source devices.
Optimal Design for Ceramic Radomes with A-Sandwich Structure
Authors: Liu Qi Wen , Chen Fei , Shen Qiang , Zhang Lian Meng
Published: September 2009

The radome performance is evaluated by means of a computer aided design (CAD) for the wall structure of multilayer ceramic radome in accordance with the microwave propagation theory. The calculation model for the ceramic radome with A-sandwich structure is built. By optimizing the thickness of the whole wall and the thickness and dielectric constant of skins and core layer, the power transmission efficiency at a broadband frequency of A-sandwich structure ceramic radome is calculated especially. The calculation results suggest that when the wall thickness is 6 mm, the thickness ratio of surface layer to core layer is 1:15 and dielectric constant of core layer is less than 2.5, the maximal broadband transmission efficiency is obtained.
Effect of Bi Doping on the Thermoelectric Properties of Mg2Si0.5Sn0.5 Compound
Authors: Luo Wei Jun , Yang Mei Jun , Shen Qiang , Jiang Hong Yi , Zhang Lian Meng
Published: September 2009

The single phase of Bi-doped Mg2Si0.5Sn0.5 compounds have been successfully fabricated by solid state reaction-spark plasma sintering (SPS). The effect of Bi doping concentration on the thermoelectric properties of Mg2Si0.5Sn0.5 is mainly investigated. The doping of Bi atom introduces impurity energy to Mg2Si0.5Sn0.5 compounds, which results in the increase of carrier concentration ( ), meanwhile it causes the increase of crystal distortion, enhancing the scatter of phonon. The results show that with the increasing of Bi doping content, the electrical conductivity (σ) increase, the absolute Seebeck coefficient ( ) and thermal conductivity ( ) decrease slightly in the measuring temperature range between 300 K and 800K. When the doping concentration of Bi is up to 2.5at% (nominal molar percent), the sample shows a maximum value of the figure of merit, ZT, is 0.78 at 800K.
Damping Properties and Mechanism of 0-3 PMN/CB/EP Composites
Authors: Shi Min Xian , Huang Zhi Xiong , Wei Tao , Zhang Lian Meng
Published: September 2009

0-3 piezoelectric ceramic PMN/conductive carbon black(CB)/epoxy resin(EP) composites were prepared by resin casting method. The electric and damping properties of PMN/CB/EP composites were detected. The volume resistivity of the composites decreases with the addition of conductive carbon black, and the composites experience transition from insulator to semiconductor when the CB content is 6% weight of the resin in the composites. Damping loss factor-temperature curves scanned by DMA showed that the peak value of damping loss factor(tanmax), the loss factor area(TA) and the damping temperature range(T) of the composites increase and reach to maximum values when CB content is 6% weight of EP resin, then drop a little with CB contents further increasing. When CB was just at threshold content 6% of epoxy weight the composite converts from insulator to semiconductor with the volume resistivity being about 108 Ωm and piezo-damping mechanism plays efficiently.
Molten Salt Synthesis and Photoluminescence of YVO4:Eu Microcrystalline Phosphors
Authors: Liang Yu Jun , Liu Rong , Yan Wen Shuai , Wu Xiao Yong
Published: September 2009

Tetragonal phase of YVO4:Eu3+ powders have been successfully synthesized via a molten salt synthesis process. During the process, rare earth nitrates and ammonium vanadate were used as precursors, the mixture of KCl and NaCl as a molten salt. As shown in XRD and SEM, the resultant product was a pure phase of YVO4 without any other impurities. Under the excitation of 326 nm, all the materials show the characteristic emission of Eu3+ which is the strong red emission originating from the 5D0 level, with 5D0→7F2 at 619 nm as the most prominent group.
Microstructure and Properties of Mulite-FeCr Multifunctional Composite
Authors: Wang Hao , Wang Wei Min , Fu Zheng Yi
Published: September 2009

Mullite-based FeCr multifunctional composites were prepared by reducing (Fe, Cr)-doped mullite solid solution powders with different Cr/Fe ratio and successively hot pressing. Structural characterization revealed that the dispersion of intragranular FeCr alloy nanoparticles and intergranular iron grains in mullite matrix was obtained in nanocomposite powders. Dense mullite-FeCr composites were fabricated from nanocomposite powders by sintering at 1650 °C. The microstructures, mechanical and ferromagnetic properties of composites were strongly affected by the Cr/Fe ratio in initial solid solutions.
Effect of Sintering Temperature on the Properties of Porous Silicon Nitride Ceramics
Authors: Li Ling , Li Yong , Yu Hong Lin , Chen Fei , Wang Hong Sheng , Jiang Hong Yi
Published: September 2009

In this study, the porous silicon nitride ceramics with low permittivity was prepared by decomposition reaction of Si2N2O. The effect of sintering temperature on the properties of composites was investigated. The results show that the sintering process of porous silicon nitride ceramics is liquid crease-densititive-crease gas in high temperature-forming close pore-break of close pores and crease open pores. The density is 0.9-2.44 g/cm3, the porosity of sample varies from 0-47%, and the permittivity can be well controlled from 2.2 to 4.8.
Erosion Resistance of Al2TiO5/Al2O3 Composites to Molten Aluminum
Authors: Li Ming Zhong , Hu Yong , Chen Fei , Shen Qiang , Zhang Lian Meng
Published: September 2009

In this paper, the molten aluminum erosion resistance of Al2TiO5/Al2O3 composites which were soaked in molten aluminum for long-time were characterized by cross section of microstructure and element distribution of samples. The results show that Al2TiO5/Al2O3 composites have good erosion resistance to molten aluminum.
Analysis of Electrical Conductance of Carbon Nanotubes
Authors: Jain Neeraj , Harsh  , Sinha R.K.
Published: September 2009

Carbon nanotubes show great promise as a new class of electronic materials owing to the change in their electrical properties with chirality of the nanotube. On one hand, they can rival the best metal and on the other, a semiconducting nanotube can work as a channel in a nano field effect transistors. The energy band structure and density of states of SWNTs of different chiralities is reviewed here and using a diameter dependent model, the electrical conductance of a single wall nanotube (SWNT) and a multi wall nanotube (MWNT) is analyzed. It is found that conductance of a CNT depends largely on its geometry and an MWNT shows very high conductance which varies with average tube diameter, length and number of shells in the tube. This study would play an important role in understanding the working of various CNT based electronic devices.
Electrical Properties of Pulsed Laser Deposited ZnO Thin Films
Authors: Sourav Chattopadhyay , Tapan Kumar Nath
Published: September 2009

Epitaxial Single-crystal ZnO thin films have been grown on c-plane (0001) sapphire by Pulsed Laser Deposition process at different substrate temperatures (300 – 800 °C) with 10-1 mbar oxygen pressure. The thicknesses of the films have been varied by varying number of pulses with a repetition rate of 10 pulse/sec. It is found that the sheet resistivity of ZnO thin films grown on c-plane sapphires are in the order of 10-2 Ω-cm and it increases with increasing substrate temperatures and film thickness. The carrier concentrations and Hall mobility are found to be in the order of 1017 cm-3 and ~195 cm2/V-s, respectively. The Hall mobility slightly decreases with increase of substrate temperature and thickness of the films. It is also found that the ZnO films are structurally uniform and well oriented with perfect wurtzite structure with c/a ratio 5.1. We have also deposited non-epitaxial ZnO films on (100) p-Silicon substrates at the same conditions. From HR FE-SEM micrographs, surface morphology of ZnO films grown at lower substrate temperature are found to be uniform compared to the films grown at higher temperatures showing non-uniformity and misoriented wurtzite structures. However, the surface morphology of ZnO flims grown epitaxially on (0001) sapphire are found to be more uniform and it does not change much with growth temperature. The resistivity of the films grown on p-Silicon at higher temperatures is in the order of 103 Ω-cm whereas films grown at lower substrate temperatures show comparatively lower resistivities (~ 102 Ω-cm). From the recorded UV-Visible absorption spectrum the band gap of the film has been estimated to be 3.38 eV.
Growth and Characterization of Urea Doped p-Type ZnO Thin Film Grown by Pulsed Laser Deposition
Authors: Sayanee Majumdar , Pallab Banerji
Published: September 2009

In the present study we have used urea as the source for doping nitrogen in ZnO since the most successful acceptor type dopant is the group V element like nitrogen. The nitrogen doped ZnO films have been deposited on glass substrates using Pulsed Laser Deposition technique using 248 nm KrF laser at energy 300 mJ by varying the number of laser pulses with a repetition rate of 10 pulse/sec in vacuum (10-6 mbar) at a constant temperature of 300 °C. The XRD pattern confirms the formation of wurtzite structure of ZnO, which is polycrystalline in nature. We have also performed UV absorption spectroscopy and the band gap is found to be 3.4 eV. Resistivity of the film increases with the increase of thickness for the undoped ZnO samples where the carrier concentrations are found to be of the order of 1017 cm-3. The mobility of the as-grown film is found to be 24.9 cm2/V-s. After doping with nitrogen the carrier concentration drops to the order of 1015 cm-3 and the mobility becomes 1.5 cm2/V-s. The mobility slightly varies with thickness. The resistivity increases to 1.3 KΩ-cm and the film shows p-type behavior. The results are explained on the basis of the available theory.
Nano PTFE Polymer Films as Organic Insulating Barrier for Tunneling Magneto-Resistive Fe/PTFE/Fe Devices
Authors: Manoharan S. Sundar , Chandra Vimlesh
Published: September 2009

Nano films of polytetrafluoroethylene (PTFE; commercially coded as Teflon) shows advantage over inorganic spacer materials like Al2O3 and MgO in fabricating tunneling magneto resistive devices due to its relative dielectric constant and chemical inertness to provide a homogenous metal-organic interface. Pulsed electron deposition proves useful in fabricating such thin PTFE films (3-6 nm) for trilayer device such as Fe (100 nm)/ PTFE (3-6 nm) /Fe (100 nm) on Si (100). Characteristic magnetic hysteresis loops demonstrating the magnetic tunnel junctions were realized for a PTFE organic layer thickness >3 nm. The tunneling magnetoresistance measurement at room temperature shows a typical magneto resistive feature, increasing with increasing PTFE thickness.
Study of Electrical and Optical Properties of Zr-Doped ZnO Thin Films Prepared by DC Reactive Magnetron Sputtering
Authors: Yadav Satyesh Kumar , Vyas Satya , Chandra Ramesh , Chaudhary G.P. , Nath S.K.
Published: September 2009

This paper establishes DC reactive magnetron sputtering as synthesis process for Zr doped ZnO thin film. Zr can be doped in ZnO using various techniques. Some research groups have doped ZnO with Zr by radio frequency magnetron sputtering using target made of ZnO and ZrO2 powder. Radio frequency has low rate of deposition because deposition takes place only in one of two half cycles. Uniform mixing of small amount of ZrO2 powder in ZnO is expensive process as well as time consuming. To overcome the constraints, Zn and Zr metal target was used and film was made by DC reactive magnetron sputtering. Various parameters of the process was established by varying variables, such as sputtering power of the Zn and Zr, oxygen partial pressure in the chamber. Optimum flow rate of Argon is 16 sccm and Oxygen is 4 sccm. Sputtering power of 150 watt for Zn and 10 watt for the Zr gives good result. Films obtained are polycrystalline with a hexagonal structure and have preferred orientation along the c axis. Resistivity of the film is as low as 0.07 Ω-cm. Average transparency of film is above 85% in visible range.
Morphological and Dielectric Behavior of Carbon Nanotube-Ferroelectric Liquid Crystal Composite
Authors: Sharma Deepika , Tyagi Sachin , Raina K.K.
Published: September 2009

The present study deals with the effect of dispersing Carbon Nano Tubes in Ferro-electric liquid crystal material. Carbon nanotube dispersed ferroelectric liquid crystals have high dielectric constant, fast switching response, large electro-optic coefficient which makes them ideal for memories, capacitors and display devices etc. An attempt has been made to understand the influence of carbon nanotubes on dielectric and morphological properties of ferro-electric liquid crystal. The effect of carbon nanotubes concentration on the transition temperature of ferro-electric liquid crystal is also studied. Hot Stage Microscope is used to investigate the texture and phase transformations in the composite. Differential Scanning Calorimetry also indicated the phase transformations. The results are compared with the original ferro-electric liquid crystal material which showed that the dielectric permittivity is increased to a great extent with the addition of carbon nanotubes.
A Comparative Study on the Morphology and Magnetic Properties of Barium and Strontium Hexaferrite Nanoparticles Synthesized by Co-Precipitation Method
Authors: Tyagi Sachin , Agarwala Ramesh Chandra , Agarwala Vijaya
Published: September 2009

Nanocrystalline strontium hexaferrite (SrFe12O19) and barium hexaferrite (BaFe12O19) powders were synthesized by co-precipitation method. The ‘as synthesized’ powders were heat treated (HT) at different temperatures ranging from 800 to 1200°C at a heating rate of 30°C /min in nitrogen atmosphere. Decomposition behaviour and the phases associated therein are investigated by thermal analysis (DTA/DTG/TG) and X-ray diffraction (XRD). Formations of ultrafine particles have been confirmed through field emission scanning electron microscop (FESEM). The superparamagnetic behavior of both, barium and strontium hexaferrite is confirmed by vibrating sample magnetometer (VSM). The increase in saturation magnetization from 1.94 to 31.05 emu/gm in case of barium hexaferrite and from 2.44 to 43.38 emu/gm for strontium hexaferrite is observed with HT temperatures. The changes in coercivity and remanence with HT temperatures for both the ferrites are analysed.
Growth of Zinc Oxide Nanoparticles by the Reaction of Zinc with Ethanol
Authors: Ashraf Shah M.
Published: September 2009

A novel approach has been described for the synthesis of zinc oxide nanoparticles by a very simple reaction of zinc metal with ethanol at 100oC. The diameters of the nano-particles range from 50–100nm. The reaction involves the cleavage of C-O bond of the alcohol, which occurs readily on zinc metal surface. Addition of ethylenediamine to the reaction yields nanorods, thus acting as a shape directing agent. A plausible mechanism is proposed for the formation of these nanostructures and is expected that this synthetic technique can be extended to obtain other metal oxides.
Growth and Studies of S2- Doped ZnO Nanorods by Solution Growth Technique
Authors: Patra M.K. , Padhye A. , Manoth M. , Gowd G.S. , Singh V.K. , Vadera Sampatraj R. , Kumar N.
Published: September 2009

Large area arrays of highly oriented sulfur (S2-) doped ZnO nanorods are grown on silica glass substrate by wet chemical decomposition of zinc-thiourea precursor in an aqueous medium. A series of five samples were synthesized by varying the concentrtaions of sulfur ions in solution. The synthesized materials were studied by using XRD, SEM, AFM, UV-ViS spectroscopy and photoluminescence techniques. Microscopy studies reveal the formation of conical nanorods having length ~3.0μm with tip size ~ 50nm. XRD studies of these nanorods show formation of hexagonal phase of pure ZnO with c-axis preferred orientation. Reduction in band gap energy from 3.2 to 2.9 eV was observed from optical absorption studies when different mole concentrations of thourea was varied in the precursor solution. The photoluminiscence efficiency of the materials was found to decrease with increase in the concentartion of sulfur ions in ZnO nanorods.