Electrical Conductivity Of Material Research Articles

Influence of Electrode Cooling on Recast Layers and Micro Crack in EDM of Titanium

Electrical discharge machining (EDM) process is a manufacturing method for shaping hard metals and formation of deep and complex shaped hole by spark erosion in electrical conductive materials such as metals, metallic alloys, ceramics etc. EDM process is achieved by a series of recurring electrical discharges between the electrode and workpiece in the presence of dielectric fluid. EDM unique feature of using thermal energy to machine conductive materials irrespective of material hardness has been its major advantage in the manufacture of aerospace, surgical, mould, die, automotive and as well as sport components. The effectiveness of EDM process depends among other factors on the thermal properties of the electrode material. The objective of this study is to study the influence of electrode cooling on recast layers and micro crack in EDM of titanium. The machining parameters investigated in the present study are current intensity (I), pulse on-time (Ton), pulse off-time (Toff) and gap voltage (V), which are of great interest for EDM researchers. The copper electrode is used to EDM titanium workpiece at room temperature and at sub-zero temperature using liquid nitrogen. The influence of cooling of copper electrode on recast layers and micro crack on titanium were investigated using scanning electron microscope (SEM) and has been reported in this study.

Research on Low Temperature Performance of the F-doped LiFePO<sub>4</sub>/C Cathode Materials

F-doped LiFePO4/C cathode materials were synthesized by two-step solid-state reaction route. The F-doped LiFePO4/C increases the intrinsic conductivity, the diffusion of lithium ions, also improves the high-rate and low-temperature performances of LiFePO4. The SEM images reveal some small morphology changes of the two kinds of the materials, so the improved properties may not due to grain size changes but crystal structure changes. The F-doped material has a higher capability at low temperature. At -20°C, with the rate of 0.5C, the discharge capacity was 82mAhg-1, higher than that of undoped material(65mAhg-1) and the result is better than the previous study[17](65mAhg-1 at the rate of 0.3C), and the disparity would enlarge with the rate increased. The CV plots indicate that the doped material reveals less degree of polarization. F-doping sample improves the electrical conductivity of material, accelerating the process of Li+ deintercalation, therefore, improving the electrochemical performances at low temperature.

Numerical modelling as a cost-reduction tool for probability of detection of bolt hole eddy current testing

Probability of detection (PoD) studies are broadly used to determine the reliability of specific nondestructive inspection procedures, as well as to provide data for damage tolerance life estimations and calculation of inspection intervals for critical components. They require inspections on a large set of samples, a fact that makes these statistical assessments time- and cost-consuming. Physics-based numerical simulations of nondestructive testing inspections could be used as a cost-effective alternative to empirical investigations. They realistically predict the inspection outputs as functions of the input characteristics related to the test piece, transducer and instrument settings, which are subsequently used to partially substitute and/or complement inspection data in PoD analysis. This work focuses on the numerical modelling aspects of eddy current testing for the bolt hole inspections of wing box structures typical of the Lockheed Martin C-130 Hercules and P-3 Orion aircraft, found in the air force inventory of many countries. Boundary element-based numerical modelling software was employed to predict the eddy current signal responses when varying inspection parameters related to probe characteristics, crack geometry and test piece properties. Two demonstrator exercises were used for eddy current signal prediction when lowering the driver probe frequency and changing the material's electrical conductivity, followed by subsequent discussions and examination of the implications on using simulated data in the PoD analysis. Despite some simplifying assumptions, the modelled eddy current signals were found to provide similar results to the actual inspections. It is concluded that physics-based numerical simulations have the potential to partially substitute or complement inspection data required for PoD studies, reducing the cost, time, effort and resources necessary for a full empirical PoD assessment.

R2R-Technologies for the Production of OPV

As research and development for organic electronic devices shifts into high gear the need for larger-than-lab production equipment becomes evident. As experts in laser micro machining, 3D-Micromac started the development of laser based roll-to-roll patterning processes for organic electronic devices six years ago.Working hand in hand with leading research partners, 3DMicromac strives to offer complete modular production lines including not only the laser patterning step but also deposition processes such as coating and printing, as well as required processes for thermal treatment, packaging and separation steps.For the coating step the so-called “slot-die coating” technology is proposed as an easy, precise and effective way for applying solution-based materials to a substrate. Depending on the ratio of solid parts, such as metal nano scaled particles or conjugated polymers, dry layers of several microns down to 30nm can be deposited with a very homogenous distribution. Typical values for the relative thickness variation of the wet film range from 10% down to 1% in cross direction and machine direction making the slot-die coating technology a suitable fit for post process steps with high demands on the layers homogeneity.In order to achieve the best possible efficiency of the OPV follow-up process steps like drying and annealing are of utmost importance. 3D-Micromacs solution for these thermal treatments is the integration of micro-wave and hot air into a single drying and annealing system. In contrary to pure classic hot air ovens the integration of microwave technology allows for a very efficient energy transport into the material which reduces the operational costs and increases the maximum throughput of the oven. However, as the microwave radiation has to be able to interact with the material, the use is commonly known to be limited to a very small range of materials. The major and most obvious use of microwave technology therefore is the drying of water based thin films (comparable to consumer electronic microwaves), but the technology is also able to introduce energy into electrical conductive materials and thin films with a surface resistivity of down to 7Ω/□. This feature enables the use for the production of OPV based on substrates with TCO layers. In device layouts the energy can be introduced into the TCO material and the generated heat is then dissipated into the surrounding material and can be used for not only drying but also annealing steps. The required control of the energy distribution in the oven is realized through a special design of the dryer chamber and magnetrons. With this approach the overall size and energy demand of the unit compared to a dryer using solely hot air can be reduced significantly.The patterning step for the functional surface covering layer can be realized by laser micromachining processes applying ultrashort pulsed laser sources. These laser sources provide laser pulses with pulse durations well below 10ps which is necessary in order to minimize negative effects such as particle generation bulging and heat affected zones making them feasible for thin film applications. Furthermore different wavelengths and optical setups for the beam guidance can be chosen depending on the material system and the layout of the OPV.The combination of such a variety of processes into one modular production line, 3D-Micromac's microFLEX, which not only meets the requirements for a controlled environment but also allows for a later change of the process sequence or an easy extension of existing capabilities is unique in the current landscape of available equipment and will be presented in the talk.

Electrically conductive acrylic pressure-sensitive adhesives containing carbon black

Electrically conductive acrylic pressure-sensitive adhesives containing carbon black Acrylic pressure-sensitive adhesives (PSA) are non electrical conductive materials. The electrical conductivity is incorporated into acrylic self-adhesive polymer after adding electrically conductive additives like carbon black, especially nano carbon black. After an addition of electrical conductive carbon black, the main and typical properties of pressure-sensitive adhesives such as tack, peel adhesion and shear strength, are deteriorated. The investigations reveals that the acrylic pressure-sensitive adhesives basis must be synthesised with ameliorated initial performances, like high tack, excellent adhesion and very good cohesion. Currently, the electrical conductive solvent-borne acrylic PSA containing carbon black are not commercially available on the market. They are promising materials which can be applied for the manufacturing of diverse technical high performance self-adhesive products, such as broadest line of special electrically conductive sensitive tapes.

An Electrochemical Machining Device for Residual Stresses Measurement in PM Parts by Layer Removal Method

Residual stresses play an important role in the performance of materials and the components produced from them. All manufacturing processes introduce residual stresses. These stresses can have a positive effect, for example by increasing the fatigue limit in the case of compressive surface residual stresses. Layer removal by electrochemical machining (ECM) can be used for measurement of the residual stresses in the PM parts. The device removed the layers by aid of electrochemical machining for this purpose is designed and developed. The device setup for residual stress measurement is based to the changes on deformation quantity. Since ECM is a non-mechanical metal removal process, ECM is capable of machining any electrically-conductive material with attendant high removal rates, regardless of mechanical properties. In particular, the removal rate in ECM is independent of the hardness, the porosity and toughness of the PM parts being machined. The micro constituents in PM steels resulting from different processing routes exhibit different thermal and mechanical behavior. This will lead to the formation of residual stresses around these micro constituents. Here we give the results of the first work carried out on PM steels in relation to residual stress measurements by the electro-chemical layer removal technique. The device works as follows. As a layer of thickness is removed, a certain amount of stress is removed from the sample. Equilibrium is violated and the sample deforms elastically to compensate for the stress removed. This elastic deformation in the sample is measured by the linear displacement gauge. This gauge pushes on the end of sample and deformation is recorded by this gage. The linear gauge send a signal to a display and then to the data converter. As simultaneous, this signal sent to the computer from the data converter for further calculations by RS 232.

Formation of Titanium Carbide Reinforced Copper Matrix Composite by <i>In Situ</i> Processing

Composite materials with copper matrix and ceramic particle reinforcements provide basis for producing relatively high hardness and electrical conductivity materials. Most of the work on copper-based composites has involved transition metal carbide reinforcement, which is introduced in the copper matrix through a powder metallurgy (P/M) route. TiC particle is one of the interesting candidates for the reinforcement of the Cu composite. This is because of its high melting point, high hardness, good oxidation and corrosion resistance combined with good electrical and thermal conductivity. In this study, in situ prepared copper-titanium carbide using high energy ball milling was addressed. Cu-Ti-C mixture powder was mechanically alloyed by high energy ball milling at 400 rpm speed for 4 hours to investigate the formation of TiC phase during milling. Then, MA was continued for 5, 20, 40,60 and 80 hours in order to determine the formation of titanium carbide phase by milling time. Then the as-milled powders were compacted at 400 MPa and sintered at 900°C for one hour. As-milled powder was characterized by x-ray diffraction for phase identification. From the XRD result, TiC peaks were found at 35.9˚, 41.7˚and 60.4˚.

METALLIC MATERIALS WITH NANO-SCALE TWINS

Strengthening materials is a central objective of materials research.Traditional approaches to strengthen materials,including solid solution strengthening,second phase strengthening, grain refinement strengthening,dispersion strengthening and work hardening strengthening etc.,aim at creation of internal defects and boundaries so as to obstruct the motion of dislocations.Such strategies for strengthening invariably compromise the ductility and electrical conductivity of the material.By reviewing recent advances in our understanding of nanostructured metals and alloys,we propose a novel approach to optimize the strength,ductility and the electrical conductivity of materials by means of coherent twin boundaries at nano-meter scale.We assess current understanding of strengthening mechanism of twin boundaries(instead of incoherent boundaries as conventionally used).Additionally, some mechanical properties(such as strength,ductility,strain rate sensitivity,work hardening) and the physical properties(electrical conductivity and electrical migration) as well as the relative preparation techniques of the metallic materials with nano-scale twins will be reviewed in this paper.

Analysis on the relationship between EMAT transmitting efficiency and the electrical conductivity of the coating on material surface

The conductive or ferromagnetic material with coating layer can be tested by electromagnetic acoustic transducer (EMAT) without pre-treatment. The electro-acoustic converting occurred on the surface of the specimens is mainly concentrated within the skin depth of the eddy current. Thus, the electromagnetic property of the material surface has great influence on the efficiency of EMAT. The eddy current densities induced in the coating of specimens and Lorentz force are calculated with fi nite element software ANSYS when EMAT is applied to the 20 steel-based specimens coated with different electrical conductivity materials. With shear wave EMAT, the specimens are tested and the relationship between the amplitude of the first echo wav e signal and electrical conductivity of the coating is analys ed. The theoretical analysis and experimental results show that under the fixed excitation condition, the higher the electrical co nductivity of the coating material, the larger the induced e ddy current density and Lorentz force are; the increase of the electrica l conductivity of the coating is beneficial to the electromag netic acoustic excitation and the acquisition of higher voltage a mplitudes of the echo waves signals.

Production of Flaky Graphite Particles by the Exfoliation Method and their Application to Electrical Conductive Composite Films

Composite films composed of graphite particles and polymer resin should exhibit functional properties such as electrical conductivity and elasticity. This study aims to produce fine flaky graphite particles for use as electrical conductive source materials within graphite / phenol resin composite films. We prepared graphite intercalation compounds with exfoliated graphite layers due to the insertion of two types of guest molecules. Then planetary ball wet milling was performed to produce flaky graphite particles by removing the exfoliated layers of the graphite intercalation compounds. Some composite films derived from the phenol resin and the obtained flaky graphite particles displayed much higher electrical conductivities compared to films composed of feed graphite particles. Additionally, we successfully applied the grinding method proposed in this study to decrease the weight fraction of the graphite particles in the composite films, and these films exhibited high electrical conductivities.

Optimization of electrochemical properties of LiFePO4/C prepared by an aqueous solution method using sucrose

LiFePO4 can be used as a positive electrode material for lithium-ion batteries by making composite with electrical conductive carbonaceous materials. In this study, LiFePO4/C (carbon) composite was prepared by a soft chemistry route, in which sucrose was used as a carbon source of a low price. We tried to optimize a Li/(LiFePO4/C) cell performance through changing synthetic conditions and discussed the factors affecting the electrochemical performances of the cell, such as the amount of the carbon source, synthetic temperature, gas flow rate of pyrolysis and the formation of secondary phases. It was found that the connection of the residual carbon and Fe2P to LiFePO4 particles and the amount of these two phases were important factors. In our experimental conditions, LiFePO4/C including 9.72 wt.% of residual carbon, prepared at 800 °C for 12 h showed the highest reversible capacity and the best C rate performance among the synthesized materials; 130 mAh g−1 at 10C rate and 50 °C.

Three-dimensional machining of insulating ceramics materials with electrical discharge machining

The insulating ceramics were processed with sinking and wire cut electrical discharge machining(EDM). The new technology was named as the assisting electrode method. In the machining, the electrical conductive material was adhered on the surface of insulating workpiece as the starting point of electrical discharge. As the processing operated in oil, the electrical conductive product composed of decomposition carbon element from working oil adhered on the workpiece during discharge. The discharges generated continuously with the formation of the electrical conductive layer. So, the insulating ceramics turn to the machinable material by EDM. We introduced the mechanism and the application of the machining of insulating ceramics such as Si 3N 4 and ZrO 2.

Theory-Inspired Development of Organic Electro-optic Materials

Correlated time-dependent density functional theory (TDDFT) quantum mechanical and pseudo-atomistic Monte Carlo (PAMC) statistical mechanical methods have been used to assist in the understanding of and to guide the improvement of organic electro-optic (OEO) materials, prepared by electric field poling of pi-electron chromophore-containing materials near their glass transition temperature. Theoretical treatment of the effects of dielectric permittivity and optical frequency on molecular (chromophore) first hyperpolarizabilities has been carried out as well as the analysis of the influence of spatially anisotropic intermolecular electrostatic interactions on the poling-induced noncentrosymmetric order of chromophores. Three classes of OEO materials have been considered in correlated theoretical and experimental investigations: (1) traditional chromophore/polymer composite materials, (2) chromophores covalently incorporated into polymers, dendrimers, and dendronized polymers, and (3) recently discovered materials consisting of chromophores incorporated into chromophore-containing host materials. This latter class of materials is referred to as binary chromophore organic glasses (BCOGs). These BCOGs exhibit exceptional electro-optic activity because of a combination of high chromophore number density, the effect of high dielectric permittivity on molecular first hyperpolarizability, and improved acentric order arising from the intermolecular electrostatic interactions among the two types of chromophores. The electrical conductivity of materials can also influence achievable electro-optic activity, and thin metal oxide buffer layers, introduced to limit charge injection, can significantly improve poling efficiency. Chromophore order can also be influenced, in some cases, by novel processing techniques, such as laser-assisted electric field poling. Thermal and photostability are important parameters for practical application of materials and have been improved dramatically in recent times. Diels-Alder and fluorovinyl ether cycloaddition reactions have been used to elevate final material glass transition temperatures to above 200 degrees C. Photostability is dominated by the photoactivation of singlet oxygen and subsequent attack on electro-optic chromophores. Photostability can be improved by more than 4 orders of magnitude by chromophore modification and material packaging.

Influence on Launching Velocity by the Figure and Material Characteristic of Projectiles

A solid metal plate is often used as the projectile in reconnection electromagnetic launcher. Yet, the performance is not optimum. In this paper, analysis is made about the laws of influence on magnetic field distribution of driving coils by using projectiles with different figures and materials. Further analysis is made about the influence on launching velocity of the aforementioned factors. A single-stage reconnection electromagnetic launcher is made. Experiments are carried out separately on latticed projectiles, hollow projectiles, aluminum projectiles, iron projectiles, and copper projectiles. Some significant conclusions are drawn. Under the same condition, hollow projectiles achieve the highest velocity, while latticed projectiles have a weaker shielding effect upon magnetic field. The magnetic permeability and electric conductivity of material have a great influence upon launching velocity. Based on magnetic domain theory, qualitative analysis is made about the causation of magnetic hysteresis loss, classical eddy current loss, and abnormal loss. As the loss under high-frequency alternating magnetic field increases rapidly, ferromagnetic materials are not suitable here. The electric conductivity of projectiles, as well as the thickness and the density, makes sense to launching velocity. As the frequency grows higher in pulsed magnetic field, the influence from thickness and electric conductivity of projectiles becomes weaker. Therefore, hollow projectiles made up of aluminum material which has a higher electric conductivity and a lower density will be the best choice.

Development of novel bioactive composites by electrophoretic deposition

Electrophoretic deposition (EPD), which is normally available on electric conductive materials, was applied to insulating materials. Wollastonite particles were deposited into the pores of porous alumina and porous ultrahigh molecular weight polyethylene (UHMWPE) substrates by EPD to yield alumina-wollastonite and UHMWPE-wollastonite composites, respectively. These composites were soaked in simulated body fluid (SBF) to evaluate their apatite-forming ability. Apatite was induced from the wollastonite particles, which grew on the surfaces and covered the entire composite surfaces. The bonding strength of the apatite layer to the substrates was as high as 8.9 MPa for alumina and 5.2 MPa for UHMWPE due to an interlocking effect. Thus, the formed alumina-wollastonite and UHMWPE-wollastonite composites should be useful as bone substitutes.

Macro- and microdispersion of carbon black in liquid silicone rubbers

A correlation between the online during mixing measured conductance of carbon black (CB) filled silicone rubber and macrodispersion of CB determined by optical microscopy and microdispersion analysed by AFM has been established. The online conductance is a suitable tool to characterise the effect of technological parameters (e.g. rotor type, speed, mixing temperature) and material parameters (matrix viscosity, CB type and content) on the macro- and microdispersion directly during the mixing process. Thus, a modified method of the online conductance measurement can be used as the in-process method for monitoring the production process of electrical conductive polymer materials with low viscosity, e.g. liquid silicone rubbers.

Electric Discharge Machining for Silicon Carbide and Related Materials

In order to cut the ingots and slabs of the silicon carbide (SiC), we developed the new method of electric discharge machining (EDM). EDM is usually used for the machining of the metals, and if it is electric conductive material, it is effective for the machining. However, if the electrical resistivity of SiC is high, the electric current cannot be large enough for and the EDM, and we failed the machining of SiC. Therefore, we use three methods to keep higher electric conduction. One is photoconductive, the second is high electric field effect and it is called avalanche effect, and the third is high temperature effect because usually the resistivity is low when the semiconductor or insulation materials are in high temperature. Thus, we applied three method, and finally can cut the SiC slabs of the resistivity of the order of 10 Ωm, which is almost 1000 times higher than that of the ordinary EDM at least. The flatness of the cutting surface is the same of the metals’ and the cutting rate for the SiC ingots is 10 times higher than that of diamond saw. This technique will be effective for the related materials of SiC, such as diamonds and GaN.

Hardware and Techniques for Cross- Correlative TEM and Atom Probe Analysis

Abstract Atom probe tomography has primarily been used for atomic scale characterization of high electrical conductivity materials. A high electrical field applied to needle-shaped specimens evaporates surface atoms, and a time of flight measurement determines each atom's identity. A 2-dimensional detector determines each atom's original position on the specimen. When repeated successively over many surface monolayers, the original specimen can be reconstructed into a 3-dimensional representation. In order to have an accurate 3-D reconstruction of the original, the field required for atomic evaporation must be known a-priori. For many metallic materials, this evaporation field is well characterized, and 3-D reconstructions can be achieved with reasonable accuracy.

Preparation and application of bamboo-like carbon nanotubes in lithium ion batteries

CNTs with bamboo-like structure (B-CNTs) has been prepared via a CVD process with novel carbon precursor. The potential application of B-CNTs as electric conductive additive and anode materials for lithium ion batteries was explored. The EIS spectra prove that it is better electric conductive additive than multiwalled CNTs and traditional carbon black (CB). The electric resistance of the electrode is decreased around 20 Ω when B-CNTs is used instead of CB. The cycle stability is also enhanced. However, the test cell with B-CNTs as anode material shows low reversible capacity of 135 mAh g −1 and very low initial cycle efficiency of 17.3%, which indicates that so-prepared B-CNTs is not suitable for anode material.

Development of New Transparent Conductive Material of Mg(OH)2-C

Indium oxide doped with tin oxide, ITO has beenwidely used as a key material for liquid crystal displaytechnologies because of its high transparency and electri-cal conductivity [1]. Recently, however, the scarcity ofrare-metal indium has been strongly pointed out so thatalternative transparent and electrical conductive materi-als have been actively studied over the last decade [2–4].As mentioned above, most transparent conductive ma-terials are based upon metal oxides. It is well knownthat the metal oxides are semiconductor so that in orderto obtain high electric conductivity together with opticaltransparency, the consideration on a balance between theband gap and conductivity is very important.Recently, Kondoh’s group reported very interesting re-sults on the transparency for Mg-C compounds [5]. Thestructure of compounds was identified to be amorphous.The elemental composition was controlled by magnesiumtarget area fraction. The colored glassy films were ob-tained.