Tungsten Wire Research Articles

Steady-state voltammetric characterization and simulation-aided study of the mass transfer enhancement at conical W/WO2 ultramicroelectrodes

Ultramicroelectrodes (UMEs) have demonstrated their utility in different applications, ranging from probing chemistry to high-resolution electrochemical imaging. Conical UMEs with the apex in the nanometer range are of special interest because their geometrical features may allow the study of single/few nanoparticles, single entities, or electrochemical reactions occurring in the inner structures of living cells which are difficult to access with other types of UMEs. However, there is a lack of experimental studies with individual unshielded conical electrodes aiming at quantifying the impact of the geometry and dimensions on their electrochemical response. In this work, W / WO2 conical UMEs with aspect ratios ranging from 6.6 to 22 and apexes with nm-size dimensions were prepared by electrochemical etching of tungsten wires through an induced dynamic meniscus regime, and in one case followed by focused ion beam milling. The electrodes were characterized by scanning electron microscopy and by cyclic voltammetry in 5 mM [Fe (CN)6]3− and 5 mM [Fe (CN)6]4− in 0.5 M KCl as a function of the depth of the UME immersed in the electrolyte solution. Computational fluid dynamics simulations were used to investigate the mass transfer of the electroactive species at the vicinity of the electrodes. Analytical expressions to predict the steady-state current of conical electrodes with aspect ratios from 3 to 22 and radius of curvature below 110 nm were also derived. It was found that the ratio of the electrochemical surface area to the geometric one rapidly increases when the depth of the UME's in solution is lower than 15 µm, in agreement with a rapid increase of the magnitude of the total flux towards the UMEs apex. Both experimental and simulation studies point to the radius of curvature as the most important parameter determining the rate of the oxidation / reduction of the [Fe (CN)6]3−/ [Fe (CN)6]4− species at non-insulated conical UMEs with high aspect ratio.

Detonation of a nitromethane-based energetic mixture driven by electrical wire explosion

The combination of energetic material (EM) and an electrical wire explosion (EWE) is an important way to achieve effective release and conversion of electrical and chemical energy, e.g. by generating strong underwater shock waves (SWs) that can be used for dynamic reservoir fracturing in unconventional gas exploitation. This letter proposes a mud-like EM composed of nitromethane, aluminium and copper oxide powder, which can be detonated directly by a tungsten wire explosion. The detonation and successive deflagration result in notably enhanced SWs: with 2.8 g EM, the SW amplitude, impulse and energy are respectively increased by 1.7, 2.1, and 7.9 times compared to an optimal underwater EWE. A direct thermal initiation mechanism for the detonation process is proposed, with the exploding wire, the Joule heating along the current path in the EM and the Al/CuO thermite reaction all serving as heat sources. It is found that the Joule heating and chemical reactions reinforce each other, which is likely the key to the ‘easy’ detonation of nitromethane.

Electrochemical Microslot Machining by Ultrasonic-Vibration-Aided Electrolyte on Nitinol Wire

In this research, the main purpose was to study the applicability of a machining method on microscale medical-equipment manufacturing. The characteristics of wire electrochemical micromachining (WECMM) against NiTi 50-50 wire was investigated. The study utilized a tungsten wire 0.03 mm in diameter as an electrode to cut a fine slot into the nickel–titanium wire. In order to reach a high-precision WECMM finish, an ultrashort pulse power generator was used as a power source to minimize the stray current effect, thus improving the machining accuracy. During the process, various machining parameters were tested for their effects on machining characteristics. In addition, ultrasonic-vibration-aided WECMM was investigated to determine whether it benefited the machining characteristics. The experiment’s results showed that under such an experiment setting, microslots can be successfully manufactured. Furthermore, with the advance adjustment of experimental parameters, the machining accuracy was improved. Finally, a fine slot was manufactured under the optimum experiment parameters and aided by ultrasonic vibration.

Yttria-Coated Tungsten Fibers for Use in Tungsten Fiber-Reinforced Composites: A Comparative Study on PVD vs. CVD Routes

Tungsten fiber-reinforced tungsten (Wf/W) composites are being developed to improve the intrinsic brittleness of tungsten. In these composites, engineered fiber/matrix interfaces are crucial in order to realize toughening mechanisms. For such a purpose, yttria (Y2O3), being one of the suitable interface materials, could be realized through different coating techniques. In this study, the deposition of thin films of yttria on a 150 µm tungsten wire by physical and chemical vapor deposition (PVD and CVD) techniques is comparatively investigated. Although fabrication of yttria is feasible through both CVD and PVD routes, certain coating conditions such as temperature, growth rate, oxidation of Wf, etc., decide the qualitative nature of a coating to a particular extent. In the case of PVD, the oxidation of Wf is highly reduced compared to the WO3 formation in high-temperature CVD coating processes. Yttria-coated tungsten fibers are examined comprehensively to characterize their microstructure, phase, and chemical composition using SEM, XRD, and Raman spectroscopy techniques, respectively.

On altering the wetting behaviour and corrosion resistance of a large metallic surface area by wire electrochemical texturing

This paper presents a novel and practically applicable method for a quick fabrication of uniform surface patterns (periodic micro-pillars with rectangular and square cross-section) on a large surface area of any conducting or semi-conducting material using Wire Electrochemical Micromachining (Wire-ECMM). Micro pillars with a rectangular cross-section are generated by machining mutually perpendicular micro channels. The depth, spacing, and cross-sectional area of pillars are controlled by varying the process parameters and tool travel distance. Primary pillars (level-1 texture) are machined with a constant Direct Current (DC) voltage and secondary pillars (level-2 texture) are machined with a pulsed DC voltage using a tungsten wire of diameter 100 μm. An aqueous solution of sodium nitrate (NaNO 3 ) is selected as an electrolyte having a pH of about 7.01. A good repeatability in the geometrical parameters of a pillar profile is observed on analysing 3D profilometer micrographs of the textured surfaces. Wetting behaviour of textured surfaces with different geometrical parameters is observed using drop shape analyser. A surface with two levels of textures offers highest contact angle of 147.3° with deionized water. Corrosion current and resistance of the textured surfaces are obtained using Linear Sweep Voltammetry (LSV) and Electrochemical Impedance Spectroscopy (EIS), respectively. Results suggest that corrosion resistance depends upon the area of texture and is highest for the sample with the largest textured area. Also, a sample with the smallest value of area factor (ratio of total area of the top surface of all the pillars in a region to the total projected area of a region) offers highest resistance to corrosion. • A novel approach for large area texturing on any conducting and semi-conducting surface using Wire Electrochemical Micromachining (Wire-ECMM). • A study of the influence of different process parameters on various geometrical features of a textured surface. • A detailed characterization of different textured surfaces using SEM imaging and surface topography. • In depth analysis of the wetting and corrosion behaviour of the textured surfaces using drop shape analyser and Electrochemical Impedance Spectroscopy (EIS).

Improvement of thermal conductivity by adding tungsten and/or copper wire in F82H

ABSTRACT The F82H, which is one of reduced activation ferritic/martensitic steels, is a strong candidate structure material for fusion reactor because of its satisfactory mechanical property and high swelling resistance in the operating temperature range. One disadvantage of F82H would be its low thermal conductivity as a structural material for divertor. In this study, we have fabricated several F82H-based composite materials by the spark plasma sintering to improve its thermal conductivity by adding tungsten and/or copper wires. F82H-20 vol.% W and F82H-10 vol.% W-10 vol.% Cu composites included reaction layers at the interface between tungsten wire and F82H matrix, resulting in the decrease in ductility and tensile strength because of the formation of tungsten carbide. On the other hand, F82H-20 vol.% Cu composite, sintered for 120 min at 1000°C, included no reaction layers and showed the highest thermal conductivity with a high relative density. Furthermore, it showed a great tensile property, which is comparable to that of the original F82H.

A Semi-Empirical Approach to Gas Flow Velocity Measurement by Means of the Thermal Time-of-Flight Method.

This paper presents a method of measuring gas flow velocity based on the thermal time-of-flight method. The essence of the solution is an analysis of the time shift and the shape of voltage signals at the transmitter and at a temperature wave detector. The measurements used a probe composed of a wave transmitter and a detector, both in the form of thin tungsten wires. A rectangular signal was used at the wave transmitter. The time-of-flight of the wave was determined on the basis of the time shift of two selected characteristic points of the voltage waveform at the transmitter and the wave detector. To obtain the correct velocity indication, a correction in the form of a simple power function was applied. From the measurements performed, the relative uncertainty of the method was obtained, from approx. 4% of the measured value at an inflow velocity of 6.5 cm/s to 1% for an inflow velocity of 50 cm/s and higher.

Moldable capillary suppressor for open tubular ion chromatography based on a polymeric ion exchanger.

We successfully fabricated 45 μm bore microchannels in PVA-Poly(styrenesulfonate) cation exchange polymers. by casting aqueous prepolymer mixtures around fine tungsten wire mandrels, curing, crosslinking by thermal annealing, and subsequently removing the microwire. This was then used as a chemically regenerated microsuppressor (with a cleaner MS background than its commercial macro counterparts) for open tubular ion chromatography, with an integrated tubular conductivity cell, tested to backpressures up to 600 psi. The overall system permits detection limits for common inorganic ions in the low μg/L levels with a 4-nL injection, isocratic elution and regeneration with poly(styrene sulfonic acid).

Development of a Lightweight Tungsten Shielding Fiber That Can Be Used for Improving the Performance of Medical Radiation Shields

Radiation exposure in medical institutions is mainly due to low doses. Low-dose radiation mainly means scattered radiation, and such scattered radiation can be shielded with a lightweight shielding suit. In this study, the shielding performance of shielding fabrics woven by winding polyethylene (PE) yarn around a 30 μm tungsten wire was evaluated. To improve the shielding performance, an air pressure dispersion process of coating tungsten nanopowder on the fiber was developed. The radiation shielding effectiveness of the shielding fibers with and without dispersed tungsten nanopowder were compared by measuring the spatial dose inside the diagnostic X-ray imaging room of a medical institution. The results of the experiment confirmed that the fabric coated with tungsten nanopowder improved the shielding performance of the general tungsten fiber by approximately 15% and provided relatively effective low-dose radiation shielding at approximately 1.2 m of the X-ray imaging equipment. This study shows that tungsten fiber can be helpful in manufacturing lightweight shielding clothing for protection from scattered radiation in medical institutions.

Synovial fluid pH sensor for early detection of prosthetic hip infections.

We describe an implantable sensor developed to measure synovial fluid pH for noninvasive early detection and monitoring of hip infections using standard-of-care plain radiography. The sensor was made of a pH responsive polyacrylic acid-based hydrogel, which expands at high pH and contracts at low pH. A radiodense tantalum bead and a tungsten wire were embedded in the two ends of the hydrogel in order to monitor the change in length of the hydrogel sensor in response to pH via plain radiography. The effective pKa of the hydrogel-based pH sensor was 5.6 with a sensitivity of 3 mm/pH unit between pH 4 and 8. The sensor showed a linear response and reversibility in the physiologically relevant pH range of pH 6.5 and 7.5 in both buffer and bovine synovial fluid solutions with a 30-minute time constant. The sensor was attached to an explanted prosthetic hip and the pH response determined from the X-ray images by measuring the length between the tantalum bead and the radiopaque wire. Therefore, the developed sensor would enable noninvasive detection and studying of implant hip infection using plain radiography.

Coatings-electrodes for processing dielectric aluminum oxide ceramics on a wire electrical discharge machine

Despite its excellent exploitation properties, the non-conductivity of aluminum-$$$based oxide ceramics significantly limits its application and remains an actual science and technology challenges. An approach to the electrical discharge machining of Al2O3 ceramics using a triple copper coating with a thickness of ∼120 µm as an auxiliary electrode and assisting TiO2-suspension a powder particle concentration of 50, 100, 150 g/l is investigated. The experiments were carried out with unprofiled brass (Ø 0.25 mm) and tungsten (Ø 0.1 mm) wire tool electrodes in a deionized water medium. The highest performance (material removal rate) was obtained for 100 g/l concentration, the pulse frequency of 5 – 8 kHz with a brass tool.

Design of a hollow cathode thruster: concepts, parameter study and initial test results

Two electric propulsion concepts have been developed at Technische Universität Dresden as spin-off devices of regular hollow cathodes and initial testing has been conducted. Both devices represent millinewton thrusters that take advantage of thermionic electron emission using the low work function materials C12A7, LaB6, and thoriated tungsten in different design configurations. The first concept represents an electrothermal thruster which generates thrust by expanding and accelerating a heated propellant in a nozzle. Initial thrust measurement tests were carried out which showed thrust levels well above cold gas thrust, but low thrust efficiencies. The influence of different geometric parameters on the discharge properties and the performance is investigated and presented. The second thruster concept is a novel electromagnetic device in which charge carriers in a plasma discharge are accelerated by an applied magnetic field that is orthogonally oriented to the discharge current. Initial tests with C12A7 were not successful, but the functionality of the concept was shown by thrust measurements using a thoriated tungsten wire as an electron emitter.

Causal relationship of CA3 back-projection to the dentate gyrus and its role in CA1 fast ripple generation

BackgroundPathophysiological evidence from temporal lobe epilepsy models highlights the hippocampus as the most affected structure due to its high degree of neuroplasticity and control of the dynamics of limbic structures, which are necessary to encode information, conferring to it an intrinsic epileptogenicity. A loss in this control results in observable oscillatory perturbations called fast ripples, in epileptic rats those events are found in CA1, CA3, and the dentate gyrus (DG), which are the principal regions of the trisynaptic circuit of the hippocampus. The present work used Granger causality to address which relationships among these three regions of the trisynaptic circuit are needed to cause fast ripples in CA1 in an in vivo model. For these purposes, male Wistar rats (210–300 g) were injected with a single dose of pilocarpine hydrochloride (2.4 mg/2 µl) into the right lateral ventricle and video-monitored 24 h/day to detect spontaneous and recurrent seizures. Once detected, rats were implanted with microelectrodes in these regions (fixed-recording tungsten wire electrodes, 60-μm outer diameter) ipsilateral to the pilocarpine injection. A total of 336 fast ripples were recorded and probabilistically characterized, from those fast ripples we made a subset of all the fast ripple events associated with sharp-waves in CA1 region (n = 40) to analyze them with Granger Causality.ResultsOur results support existing evidence in vitro in which fast ripple events in CA1 are initiated by CA3 multiunit activity and describe a general synchronization in the theta band across the three regions analyzed DG, CA3, and CA1, just before the fast ripple event in CA1 have begun.ConclusionThis in vivo study highlights the causal participation of the CA3 back-projection to the DG, a connection commonly overlooked in the trisynaptic circuit, as a facilitator of a closed-loop among these regions that prolongs the excitatory activity of CA3. We speculate that the loss of inhibitory drive of DG and the mechanisms of ripple-related memory consolidation in which also the CA3 back-projection to DG has a fundamental role might be underlying processes of the fast ripples generation in CA1.

Thermally tunable dispersion modulation in a chalcogenide-based hybrid optical fiber.

A hybrid optical fiber comprising metal electrodes, high performance polymers, and a highly nonlinear glass core is presented in this work as a novel, to the best of our knowledge, platform for mid-infrared nonlinear devices. The fiber allows for electrical tuning of the temperature by joule heating using a set of embedded tungsten wires. Unlike temperature tuning by an external heater, this results in a strong modulation, which introduces alternating signs of its dispersion. Enhanced spectral broadening through supercontinuum generation in the mid-infrared due to this modulation is investigated numerically.

Single step synthesis of WO3 nanoparticles by wire explosion process and its photocatalytic behaviour

Tungsten (W) wires are exploded in oxygen ambience to get tungsten oxide (WO3) nanoparticles (NPs). Energy stored in the capacitors (EC) is used to overcome the sublimation energy of wire. Energy ratio (K, ratio of EC and sublimation energy) and oxygen pressure (P) are two control parameters for the particle phase and morphology in the wire explosion process. X-ray diffraction (XRD) patterns confirmed the partial oxidation of W for low values of K. For K = 2, oxidation increases with increase in P. For K = 10, complete oxidation was achieved irrespective of P. Particles are spherical in shape as observed from scanning electron microscope (SEM) and transmission electron microscope (TEM) micrographs. Particle size follows a log-normal distribution with a least mean size of 24.1 nm. UV-vis diffuse reflectance spectroscopy (DRS) was used to measure the absorbance of NPs (complete WO3 with least mean size) for band gap measurement. The band gap was found to be 2.92 eV (visible region). NPs are used as photocatalyst to degrade aqueous solution of methylene blue (MB) under visible light irradiation. 500 mg l−1 of WO3 NPs were optimum to degrade 10 mg l−1 MB in 120 min.

Wire calorimeter for direct neutral beam power measurements on C-2W.

The C-2W experiment produces advanced beam-driven field reversed configuration (FRC) plasmas, which are sustained in steady state utilizing variable energy neutral beams (15-40 keV, total power up to 21MW), advanced divertors, end bias electrodes, and an active plasma control system. Since heating, current drive, and refueling from neutral beam injection are essential to FRC sustainment, it is crucial to have accurate measurements of the beam power being injected into the plasma. A new tungsten wire calorimeter has been designed, built, calibrated on a test stand, and implemented to make the first direct measurements of the time-average injected beam power into C-2W. This paper outlines the design of the diagnostic, along with calibration methods and experimental results.

Growth anomalies in CVD silicon carbide monofilaments for metal matrix composites

The industrial scale production of silicon carbide monofilaments by chemical vapour deposition (CVD) can be disrupted by growth anomalies that initiate filament fracture during its manufacture. The anomalies take the form of growth warts on the surface of the silicon carbide fibre. Complementary 3D imaging techniques, micro X-ray computed topography (XCT) and plasma focused ion beam scanning electron microscopy (PFIB-SEM), in combination with other materials characterisation techniques (Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and X-ray diffraction (XRD) analysis) have been used to investigate the nature and cause of the anomalies. Metallic tungsten particulates with an unusual dendritic morphology attached to the tungsten core were found to be the origin of the anomalies. Further investigation of the CVD system led to the observation of process-induced W oxide particulate agglomerates accumulating at the cleaning stage inlet to the reactor. These particulates became attached to tungsten wire in the cleaning stage of the CVD reactor and were rapidly reduced to elemental tungsten prior to entering the silicon carbide deposition chamber. Silicon carbide growth on the tungsten particulates results in the development of a wart-like morphology on the fibre surface. An understanding of this mechanism enabled minor modifications to reactor conditions, which prevented W oxide particulate formation and greatly reduced the occurrence of such growth anomalies.

Interface characterization in tungsten fiber/Zr-based bulk metallic glass matrix composite

In this research, Zr55Cu30Al10Ni5 bulk metallic glass (BMG) alloy is used as the base material to form tungsten fiber reinforced BMG composites. The composites are synthetized using melt infiltration casting method and their microstructure and compressive properties are investigated. Two different infiltration times of 10 min and 15 min are used to produce the composites. The microstructural evaluation of the interface between tungsten fiber and BMG matrix reveals that a narrow reaction band emerges between the tungsten wires and BMG alloy. Some portions of this layer are broken into the fine Zr/W-rich particles and eventually are dispersed in the BMG matrix, when the infiltration time is 15 min. The results also showed that increasing the infiltration time from 10 min to 15 min improves the compression strength of the composite from 1333 MPa to 1396 MPa and also increases the compression strain of the composite from 0.11 to 0.13. This is attributed to the lack of porosities and better metallurgical bonding between tungsten fibers and BMG matrix.

Development and Comparative Analysis of Electrochemically Etched Tungsten Tips for Quartz Tuning Fork Sensor.

Quartz Tuning Fork (QTF) based sensors are used for Scanning Probe Microscopes (SPM), in particular for near-field scanning optical microscopy. Highly sharp Tungsten (W) tips with larger cone angles and less tip diameter are critical for SPM instead of platinum and iridium (Pt/Ir) tips due to their high-quality factor, conductivity, mechanical stability, durability and production at low cost. Tungsten is chosen for its ease of electrochemical etching, yielding high-aspect ratio, sharp tips with tens of nanometer end diameters, while using simple etching circuits and basic electrolyte chemistry. Moreover, the resolution of the SPM images is observed to be associated with the cone angle of the SPM tip, therefore Atomic-Resolution Imaging is obtained with greater cone angles. Here, the goal is to chemically etch W to the smallest possible tip apex diameters. Tips with greater cone angles are produced by the custom etching procedures, which have proved superior in producing high quality tips. Though various methods are developed for the electrochemical etching of W wire, with a range of applications from scanning tunneling microscopy (SPM) to electron sources of scanning electron microscopes, but the basic chemical etching methods need to be optimized for reproducibility, controlling cone angle and tip sharpness that causes problems for the end users. In this research work, comprehensive experiments are carried out for the production of tips from 0.4 mm tungsten wire by three different electrochemical etching techniques, that is, Alternating Current (AC) etching, Meniscus etching and Direct Current (DC) etching. Consequently, sharp and high cone angle tips are obtained with required properties where the results of the W etching are analyzed, with optical microscope, and then with field emission scanning electron microscopy (FE-SEM). Similarly, effects of varying applied voltages and concentration of NaOH solution with comparison among the produced tips are investigated by measuring their cone angle and tip diameter. Moreover, oxidation and impurities, that is, removal of contamination and etching parameters are also studied in this research work. A method has been tested to minimize the oxidation on the surface and the tips were characterized with scanning electron microscope (SEM).

Transparent Polyaniline Thin Film Synthesized Using a Low-Voltage-Driven Atmospheric Pressure Plasma Reactor.

The use of low-voltage-driven plasma in atmospheric pressure (AP) plasma polymerization is considered as a simple approach to reducing the reactivity of the monomer fragments in order to prevent excessive cross-linking, which would have a negative effect on the structural properties of the polymerized thin films. In this study, AP-plasma polymerization can be processed at low voltage by an AP-plasma reactor with a wire electrode configuration. A bare tungsten wire is used as a powered electrode to initiate discharge in the plasma area (defined as the area between the wide glass tube and the substrate stand), thus allowing plasma polymerization to proceed at a lower voltage compared to other AP-plasma reactors with dielectric barriers. Thus, transparent polyaniline (PANI) films are successfully synthesized. The surface morphology, roughness, and film thickness of the PANI films are characterized by field emission scanning electron microscopy and atomic force microscopy. Thus, the surface of the polymerized film is shown to be homogenous, smooth, and flat, with a low surface roughness of 1 nm. In addition, the structure and chemical properties of the PANI films are investigated by Fourier transform infrared spectroscopy, thus revealing an improvement in the degree of polymerization, even though the process was performed at low voltage.