Pulse Current Method Research Articles

Low noise measurement system for determination of the critical currents in superconducting tapes by a pulse method

Steady state measurements of the high critical currents in superconducting composite wires and tapes might be burdened with some errors. The origin of the errors is mainly associated with the Joule heat generated at current leads contacts, which at high transport currents can considerably increase temperature of an investigated sample wire. To avoid this unwanted heating phenomenon pulsed current methods are widely used. A waveform of the current pulse is usually shaped by means of a series RLC circuit with the subcritical dumping condition. Measurement results (i.e., a value of current peak, its time derivative, and a voltage drop along a superconducting sample) are recorded by means of a 4-channels, 12-bit resolution, 50 ns sampling time, digital recorder. Very low noise, broadband, voltage preamplifiers, based on rf bipolar transistors, were designed and fabricated. From the data, current-voltage characteristics are plotted and then the critical currents of investigated tapes are determined. Presented in the work our home-made, low noise, measurement setup allows to obtain a current pulse of about 4000 A at duration time of several milliseconds.

Evaluation of Al-specimen fatigue using a “smart sensor”

We develope a new methodology for the characterization and evaluation of precritical crack propagation. Our experiments were performed with Al-alloy specimens that had special thin Al single crystal films, the so-called a “smart sensor” glued to their surfaces. These sensors were used as tools for evaluation of damage developed in the specimen bulk. The specimens were plastified by tensile tests and fatigued by low cycles fatigue load. The on-line measurement for damage characterisation were done for the different stage of fatigue tests on the thin-film sensor. Two techniques were applied for experiments, namely the optical microscopy and pulsed eddy current method. We introducted the fractal dimension Dt of the surface topography as a parameter for evaluation of the fatigue damage. The optical images were evaluated by the use of Gaussian smoothing algorithm and the eddy current signals by use of the autocorrelation function. The two approaches confirmed that the mesostructural changes of the Al-film surface are characteristic for the fatigued material and can be described and evaluated by the fractal dimension quantitatity Dt. It was found that the values of the Dt parameter calculated from the optical images increased as the fatigue damage evolved with the indications of the transition to characteristic pattern. A similar analysis of the pulsed eddy current measurements in tension tests results in similar characteristics. However, in the case of fatigue tests the fractal analysis of the pulsed eddy current signals yields to ambiguous results.

On the Improved Current Pulse method for the thermal diffusive characterization of lithiated ceramic pebble beds

Packed pebble beds are granular systems composed of small particles generally arranged in irregular lattices and surrounded by a gas filling their interstitial spaces. They show non-linear and coupled thermal and mechanical behaviours, which are under theoretical and experimental investigation to set-up a realistic constitutive model to be adopted for design-oriented purposes.At the Department of Nuclear Engineering (DIN) of the University of Palermo a realistic constitutive model of fusion-relevant pebble beds thermo-mechanical behaviour was developed adopting a “continuous” approach, based on the assumption that a pebble bed could be considered as a continuous, homogeneous and isotropic medium, characterized by effective thermal and mechanical properties strictly depending on its temperature, pressure and/or mechanical volumetric strain.Within this framework, an experimental campaign was launched at DIN to assess the functional dependences of lithium orthosilicate polydisperse pebble bed effective thermal diffusive properties on both temperature and pressure, by means of the purposely-outlined Improved Current Pulse method.The ATTAR-1 test section was set-up and a test campaign was carried out on a 24 mm high reference polydisperse lithium orthosilicate pebble bed, at temperatures ranging from 20 °C up to 300 °C and pressures up to 30 bar. The functional dependences of the pebble bed thermal diffusive properties on both temperature and pressure were derived and they agree quite well with those shown in literature.

Transport critical current of MgB2 wires: pulsed current of varying rate compared to direct current method

The measurement of transport critical current (Ic) forMgB2 wires and tapes has been investigated with two different techniques, the conventionalfour-probe arrangement with direct current (DC) power source, and a tailored trianglepulse at different rates of current change. The DC method has been widely used andpracticed by various groups, but suffers from inevitable heating effects when highcurrents are used at low magnetic fields. The pulsed current method has no heatingeffects, but the critical current can depend on the rate of the current change (dI/dt) in the pulse. Our pulsed current measurements with varyingdI/dt show that thesame values of Ic are obtained as with the DC method, but without the artifacts of heating. Our method isparticularly useful at low field regions which are often inaccessible by DC methods. We alsoperformed a finite element method (FEM) analysis to obtain the time dependent heat distributionin MgB2 due to the electric potential produced at the current contacts to the superconductingsample and its gradient around the contacts. This gradient is defined as the currenttransfer length (CTL) of the samples and leads to Joule heating of the wire near thecontacts. The FEM results provide further evidence of the limitation of the DC method inobtaining high transport critical current.

Novelty of Ni - Co - WC Nanocomposite Coatings Prepared from Pulse and Direct Current Methods

not Available.

Fortification of Ni–Y2O3 nanocomposite coatings prepared by pulse and direct current methods

Ni–Y2O3 nanocomposite coatings were prepared under direct current (DC) and pulse current (PC) using acetate bath. The microstructure and corrosion resistance of the coatings were characterized by means of XRD, SEM, AFM, and EIS. The results showed that the microstructure and performances of the coatings were greatly affected by Y2O3 content on the deposits prepared by DC and PC methods. The microhardness and corrosion resistance were enhanced in the optimum percentage of Y2O3 composite coatings. The PC composite coatings were exhibited compact surface, higher microhardness, and good corrosion resistance compared with that of the DC composite coatings.

Electrochemical Behavior of Nickel ACD-Electroless Deposition

Deposition of metals and other materials (oxide, polymer, salt) from aqueous solutions without an external current are described in the literature as electroless deposition. The mechanism to explain ACD-electroless deposition of nickel layers are reviewed and the fundamental characteristics of the process underlined, in comparison with the nickel electrodeposition. Results obtained with the secondary current pulse method during deposition with the ACD-electroless process are presented and show the main differences between the two processes: ACD-electroless process shows a reversible behaviour, whilst electroplating process is strongly irreversible. The results are interpreted according to the reactions prevailing at the reacting surface and strengthened by the electrochemical characterization performed in the ACD electrolyte and in sodium hypophosphite only solution.

Fabrication of TiB2-(Fe-Al) Cermets by Short Time Pulsed Current Sintering

Short time fabrication of TiB2-30mass% Fe3Al cermet was performed by pulsed current sintering method. Milled powder mixture of TiB2, Fe and Al was consolidated using a pulsed current of 0 A-1000 A with 50 % duty ratio for 50 s with 1, 10 and 100 Hz frequency. Microstructures, densities and phases present in the cermets fabricated in such a way were examined. TheTiB2-30mass% Fe3Al cermet without formation of Fe2B was successfully fabricated. Increase in the pulse frequency led to an increase in the sample density and homogeneous distribution of TiB2 particles.

Pulse Current Heating Method for Light Alloy Superplastic Forming and Macroscopic and Microscopic Effects Analysis

To improve the heating efficiency and reducing the energy consumption,a pulse current heating method for light alloy sheet hot forming has been purposed.Through the heating experiment in combination with the electrothermics theory,the effects of current density on the heating rate and the final temperature of the different metals have been investigated systematically.The temperature distribution became homogeneous by installing the resistance heat slice between the electrode and the heating blank.In the microscopic aspect,the effects of current density on the crack,cavity and the grain size of the material have been investigated briefly by the finite element method and metallographic microscopic analysis method.The results shows that the grain of the alloy has no obvious grown up,and the defects of the alloy have been got certain inhibition during the heating process because of the heavy pulse current.Aiming at a certain AZ31 Mg alloy superplastic forming process,the parameters of the pulse current have been determined.Through the results,the heating efficiency has been increased and the energy consumption has been reduced.

Synthesis of Dual Two-Phase Ni<SUB>3</SUB>Al-Ni<SUB>3</SUB>V Intermetallic Alloys Containing Nb by Pulse Current Sintering

A dual two-phase Ni3Al-Ni3V intermetallic alloy with a nominal composition of Ni75.0Al7.5V15.0Nb2.5 (at%) doped with 50 mass ppm boron was synthesized by the powder metallurgy process using elemental powders. Raw powder mixture was sintered at temperatures from 1073 K to 1373 K by the pulse current sintering method and then annealed in a vacuum at 1553 K for 3 h. The dual two-phase intermetallic alloy whose microstructure exhibits the cuboidal primary Ni3Al phase and the surrounding channel region composed of Ni3Al and Ni3V phases, and contains neither voids nor intermediate products were obtained by sintering at a high temperature of 1373 K and by subsequent annealing at 1553 K. Also, the well synthesized and annealed samples showed finer grain sizes, i.e., about 30 μm than the cast alloys fabricated by the ingot metallurgy process. The hardness of the synthesized samples increased with increasing sintering temperature and also by the subsequent annealing at 1553 K.

Optimization of pulsed electrodeposition of aluminum from AlCl 3-1-ethyl-3-methylimidazolium chloride ionic liquid

In this study, Al was electrodeposited on a platinum substrate at room temperature from an ionic liquid bath of EMIC containing AlCl 3 using potentiostatic polarization (PP), galvanostatic polarization (GP), monopolar current pulse polarization (MCP) and bipolar current pulse polarization (BCP). Transition of current or potential during galvanostatic or pulse polarization revealed that the initial stage of the deposition process was controlled by a nucleation process depending on the polarization condition. For example, the average size of Al deposits decreased with increasing current density in the case of GP. FE-SEM observation showed that dense and compact Al deposits with a smooth surface were obtained by the current pulse method. Roughness factor evaluated from electrochemical impedance measurement confirmed the smooth surface of these deposits. Adhesion strength of Al deposits was greatly improved using BCP in which an anodic pulse was combined with a cathodic pulse for electrodeposition. In this study, the optimal parameters for BCP were found to be I C = −16.0 mA cm −2, I A = 1.0 mA cm −2, r C (duty ratio) = 0.5, and f = 2 Hz. The mechanisms of electrodeposition by these three methods are discussed.

Study of short duration heat treatments of an in situ copper-sheathedMgB2 wire

The powder-in-tube technique has been used to fabricate Cu-sheathed magnesium diboride(MgB2) wiresusing an in situ reaction method. The effects of high heating rate, short duration heat treatments ofMgB2/Cu wires were studied by means of optical and scanning electron microscopy, x-ray diffraction, resistivity,ρ(T), andsusceptibility, χ′(T), measurements. The transport critical currents,Ic(B), of the wires were measured using both direct current in a constant field andpulse field–pulse current methods. Usage of high heating rates allows theprocesses of interest to occur in conditions closer to isothermal, which permitsthe influences of heat treatment time and temperature to be more readilydistinguished. The results show that the microstructure and properties of theMgB2/Cu wires are strongly dependent on the heat treatment temperature butquite insensitive to the reaction time: a short heat treatment for 5 min at700 °C was sufficient for obtaining the highest critical current achieved in this work.

Effect of boron-doping on thermoelectric properties of rutile-type titanium dioxide sintered materials

The electrical and thermal transport properties of boron-doped rutile-type TiO 2 were investigated. The rutile-type TiO 2 powder was mixed with B 2O 3, TiB 2 or B and the mixtures were sintered using the pulse current sintering method at 1473 K. Secondary ion mass spectroscopy (SIMS) and X-ray diffraction (XRD) measurements showed that B or TiB 2 addition was effective for boron-doping. The boron was well distributed in the sintered materials and the unit cell volume of rutile increased as the amounts of added B or TiB 2 increased. The electrical resistivity and Seebeck coefficient at 300 K decreased with an increase in the unit cell volume indicating that boron addition leads to an increase in the electron concentration. Thermal conductivity at room temperature also decreased with an increase in unit cell volume and as a result the thermoelectric figure of merit for rutile-type TiO 2 was enhanced by boron-doping.

The electrochemical oxidation of methanol on a Pt/TNTs/Ti electrode enhanced by illumination

A Pt/TNTs/Ti electrode is prepared by electrochemically depositing Pt using the modulated pulse current method onto high density, well ordered and uniformly distributed TiO 2 nanotubes (TNTs) on a Ti substrate. The results show that the performance and anti-poison ability of the Pt/TNTs/Ti electrode for methanol electro-oxidation under illumination is remarkably enhanced and is even better than the best bi-metallic Pt–Ru catalysts. CO poisoning is no longer a problem during methanol electro-oxidation with the Pt/TNTs/Ti electrode under illumination.

Pulsed Current Electrochemical Synthesis of Nickel Nanoclusters and Application as Catalyst for Hydrogen and Oxygen Revolution

The main objective of this research is to prepare nickel nanoparticles with more porous structure by the pulsed current electrochemical method. A nickel optimized nanopowder was synthesized by using nickel chloride (0.005 M) as precursor, silver nitrate as a nucleation agent (at 0.5% mole of nickel salt in the starting solution), polyvinyl pyrrolidone (PVP) as structure director (with PVP/Ni = 1.7 g/g), ammonia (2 M), and hydrazine as reduction agent (with Hydrazine/Ni = 16 g/g) by pulsed current of 58 mA cm−2 with a frequency of 12 Hz. The morphology and particle size of each synthesized sample was studied by scanning electron microscopy (SEM). The obtained results showed that temperature has no considerable effect on the morphology and particle size of nickel nanopowder. The nickel nanopowder synthesized in optimum conditions has excellent uniform and a more porous structure including nanoclusters with a particle size of approximately 10–20 nm. The obtained results indicate that the pulsed current electrochemical method can be used as a confident and controllable method for the preparation of nickel nanoparticles. Optimized nickel nanoclusters were used as catalyst for hydrogen and oxygen revolutions. Cyclic Voltammetry results showed that the synthesized nanoclusters can facilitate hydrogen reduction and increase hydrogen and oxygen revolution rates.

Pulsed eddy current signal processing method for signal denoising in ferromagnetic plate testing

A signal denoising method is presented for ferromagnetic material pulsed eddy current (PEC) testing signal. The method firstly performs multiple measurements, and obtains an averaged signal and then transforms the averaged PEC signal from Cartesian domain to double logarithmic domain by the developed algorithm. A median filtering process is then performed for double logarithmic domain signal. An invert transform is optional to be performed to transform the processed signal from double logarithmic domain back to Cartesian domain. A signal-to-noise ratio (SNR) improvement quantification method is applied to evaluate the SNR improvement. The performance of the method is then verified by experiments. The effects of signal averaging number and median filter’s order are discussed. Experiment results show the method is able to increase SNR by about 40dB.

(Invited) Electrolytes, SEI and Charge Discharge Kinetics in Li-Ion Batteries

Charge discharge kinetics of Li-ion batteries is dominated by the lithium ion (Li+) charge transfer kinetics, which involves the process of transporting the solvated Li+ in the electrolyte to the insertion of Li+ and the accepting of an electron at the same time in the electrode active materials. The importance of electrolytes and recent studies of Li+ charge transfer kinetics were briefly reviewed. Using 3-electrode cells and a DC Pulse Current Impedance method, we examined the charge discharge kinetics of the anode and the cathode in the same electrolyte at the same time. We observed a slower kinetics at the graphitic carbon anode as indicated by higher activation energy than that at the lithium nickel cobalt aluminum mixed oxide (LiNi0.80Co0.15Al0.05O2) cathode. While desolvation is a dominating step as concluded in recent studies on the Li+ charge transfer kinetics, this study suggests that the nature of SEIs and electrode materials play crucial roles on Li+ charge discharge kinetics.

Properties of New TiC/TiB<sub>2</sub>/Fe-Al Cermet Alloy

Effect of TiB2 substitution on thermal conductivity and hardness in TiC / Fe-Al cermets was investigated. The (70-x)TiC / xTiB2 / 26Fe-4Al mass % cermets were fabricated by mechanical milling and subsequent pulsed current sintering method. The high relative density compacts was formed by sintering at 1423 K under 25 MPa for 60 s. The sintered materials were mainly composed of TiC, TiB2 and Fe-Al intermetallic compound. In addition, small amounts of Fe2B surrounding TiB2 were formed. The thermal conductivity of the sintered compact lineally increased with increasing TiB2 volume fraction. However, the hardness of the sintered compacts of x = 20 – 40 were higher than that of x = 0. Therefore, the substitution of TiC to TiB2 in the TiC / Fe-Al based cermet is effective to improve the thermal conductivity without the degradation of hardness.

The Production and Properties of Electrolytic Zn-Ni Layers Deposited by Pulse Current Method

The Zn-Ni layers were obtained by electrolytic method in the conditions of pulse current with symmetric current pause. The austenitic steel (OH18N9) was used as the cathode. The morphology, phase and surface chemical composition of the layers deposited at reduction current densities ic = 5 – 25 mAcm2, were defined. The surface morphology of deposited layers and surface chemical elements distribution were studied using a scanning electron microscope (JEOL JSM-6480). On the basis on this research, the possibility of deposition of Zn-Ni layers contained about 8 – 10 % at. Ni was exhibited. The optimal pulse current condition of Zn-Ni layers deposition were proposed namely ic=20mA•cm2, ton = toff = 2ms. It was stated, that surface chemical composition of Zn-Ni layers is independent on pulse current densities of deposition, whereas development of Zn-Ni surface increases with the increase in the pulse current density of deposition. The corrosion resistance investigations showed that passivation and heat treatment improved the corrosion resistance of Zn-Ni layers in 5% NaCl solution. Higher corrosion resistance of heated Zn-Ni layers is caused by the creation of Ni5Zn21 intermetallic phase. Moreover the heated Zn-Ni layers are characterized by slightly higher corrosion resistance compared with metallic Cd. Microhardness of the layers was investigated by Vickers diamond testing machine.

Preparation and Mechanical Property for WC-25vol%FeAl Using Wet Milling Process

WC-25vol%FeAl compacts have been prepared using wet milling and the subsequent pulse current sintering. Powder mixtures consisting of (1) WC, Fe-40at%Al and (2) WC, Fe, Al powders have been mixed to give the desired composition of WC-25vol%FeAl. They have been milled using a cylindrical ball mill with ethanol. Milled powders have been dried at room temperature and consolidated using pulse current sintering method at 1273 K in vacuum. The compacts thus obtained have had fine and homogeneous structure. Vickers hardness of both compacts has increased with increasing milling time. Transverse rupture strength of the former compact has increased with increasing milling time, but that of the latter one abruptly decreased. This is due to the formation of Fe3W3C and Al-O phase.