Molybdenum Electrodes Research Articles

Electrochemistry of Neodymium in an Equimolar NaCl-KCl Melt without and with Addition of Fluoride Ions

An investigation of compounds of those few elements in the oxidation state (II), by opposition to the general trivalent lanthanides is of special interest. The present work follows our previous investigations on samarium, europium ytterbium chloride systems and, in particular, the electrochemical behavior of the Sm(III)/Sm(II), Eu(III)/Eu(II) Yb(III)/Yb(II) redox couples. It deals with neodimium compounds.The electrochemical behavior of NdCl3 in molten salts was studied in few works, but only melts with a low melting point LiCl-KCl and LiCl-KCl-CsCl were investigated.The electroreduction of NdCl3 in an equimolar NaCl-KCl mixture was studied in the temperature range 973-1123 K by different electrochemical methods. It was shown that the discharge of Nd(III) to Nd(II) is complicated by the disproportionation reaction (DPP):3Nd(II) ↔ 2Nd(III) + Nd (1)Ignoring of reaction DPP can lead to incorrect determination of values diffusion coefficients and formal standard redox potentials of the Nd(III)/Nd(II) redox couple. The relatively narrow interval of polarization rate was found when the recharge process was reversible and not accompanied by the DPP reaction. At these scan rates the diffusion coefficients and formal standard redox potentials of the Nd(III)/Nd(II) redox couple were determined by cyclic voltammetry.The standard rate constants for the redox reaction Nd(III) + e- ↔ Nd(II) were calculated on the basis of cyclic voltammetry at sweep rates corresponding to the quasy-reversible process. The nature of working electrode on the rate of charge transfer for the Nd(III)/Nd(II) redox couple was studied. It was found that the values of k s determined at a molybdenum electrode were higher than those at a glassy carbon electrode.The introduction of fluorine anions into a chloride melt at a molar ratio of F-/Nd(III) = 5 leads to the disappearance of the recharge wave and only an ascending section associated with joint discharge of neodymium complexes and sodium and potassium cations was observed. Thus, the introduction of fluorine anions leads to stabilization of the highest oxidation state of neodymium in chloride-fluoride melt and neodymium in the oxidation state +2 does not exist in the melt.Introducing of fluoride ions to the melt NaCl-KCl containing Nd(II) accompanied by reaction of disproportionation:3NdCl4 2- + 12F- ↔ 2NdF6 3- + Nd + 12Cl- (2)The standard rate constants of charge transfer for the Nd(III)/Nd(II) redox couple were compared with the values obtained for other redox couples of lanthanides and these results were discussed in connection with the strength and stability of complexes.

Complementary-Switchable Dual-Mode SHF Scandium Aluminum Nitride BAW Resonator

This article presents a bulk acoustic wave (BAW) resonator with complementary switchable operation in the first and second thickness extensional modes (TE1 and TE2) at 7.04 and 13.4 GHz. Two ferroelectric scandium aluminum nitride (Sc0.28Al0.72N) layers are alternatively stacked with three molybdenum electrodes, creating a laminated BAW resonator with independent switchability of polarization in constituent transducers. This enables intrinsic switchability of the resonator in TE1 and TE2 modes, when the ferroelectric Sc0.28Al0.72N layers are poled in the same or opposite directions, respectively. A generalized analytical proof of complementary switchable operation, extended to laminated BAW resonators consisting of arbitrary number of ScxAl1-xN layers, is presented. For the demonstrated prototype, electromechanical coupling coefficients ( k2t ) of 10.1% and 10.7%, and quality factors ( Q ) of 115 and 151, are measured for TE1 and TE2 modes, respectively, when the resonator is configured in the corresponding operation states. Besides showing intrinsically configurable operation in super-high-frequency regime with high k2t and Q , a laminated Sc0.28Al0.72N BAW resonator exhibits repeatable operation under switching cycles.

A Transient Supercapacitor with a Water-Dissolvable Ionic Gel for Sustainable Electronics.

We develop an environmentally benign supercapacitor, which decomposes by contact with water, incorporating an ionic liquid, carbon powder, a cellulose separator, and a molybdenum electrode. The ionic liquid is dispersed into a water-dissolvable polymer, poly(vinyl alcohol), to produce a solid electrolyte, so-called ionic gel. A carbon composite mixed with the ionic liquid maintains a gel form. The ionic gel and the carbon composite enable an all-solid-state supercapacitor, which can be charged at a voltage of 1.5 V. The supercapacitor shows areal and volumetric capacitances of 65 mF/cm2 and 2.2 F/cm3, respectively. A cycle test reveals that capacitance retention and Coulombic efficiency are 77 and 90%, respectively. As for the dissolution test, the ionic gel and carbon composite dissolves in phosphate buffer solution in 18 days, and the Mo electrode is able to fully dissolve in 500-588 days. Potential applications of the environmentally benign supercapacitor include smart agriculture by monitoring of soil and disaster prevention by a wireless sensor network without the need for retrieval of devices after use.

Cyclic Voltammetric Experiment-Simulation Comparisons of the Complex Zr4+ to Zr0 Reduction Mechanism at a Molybdenum Electrode in LiF-CaF2 Eutectic Molten Salt

Nuclear energy represents an important option for generating largely clean CO2-free electricity. Zirconium is a fission product in the nuclear reaction that needs to be extracted from irradiated fuels used in Gen-IV molten salt reactors. The present investigation addresses the electrochemical reduction of solution soluble Zr4+ (soln) to surface confined Zro (s−c) at a molybdenum electrode in a LiF—CaF2 eutectic molten salt at 840 °C using DC cyclic, square-wave and AC voltammetry. Cyclic voltammograms simulated by the reaction scheme: Zr4+ (soln) + 4e− → Zro (soln); Zro (soln) ↔ Zr*(s−c); Zr*(s−c) → Zr4+*(s−c) + 4e−; Zr4+*(s−c) → Zr4+ (soln); Zr*(s−c) + Zr4+ (soln) ↔ 2Zr2+ (soln); Zr2+ (soln) ↔ Zr2+*(s−c) and Zr2+*(s−c) → Zr4+*(s−c) + 2e− provided excellent agreement with experimental data over the scan rate range of 50 to 500 mV s−1. The interpretation of the simulation is that the reduction of Zr4+ (soln) to Zro (metal) takes place via a transiently soluble Zro (soln) in an overall 4-electron essentially reversible diffusion-controlled process having a reversible formal potential (Eo f) of −1.22 V (vs Pt). A minor oxidation process observed at −0.455 V (vs Pt) on the reversing the potential scan direction is simulated via the reaction step Zr(s−c) + Zr4+ (soln) ↔ 2Zr2+ (s−c) followed by Zr2+ (s−c) → Zr4+ (sol) + 2e−. The sharply rising initial component where reduction of Zr4+ (sol) commences, contains evidence of a nucleation-growth mechanism associated with the electrocrystallisation of zirconium metal. This initial rapid growth of current is not fully accommodated in the simulations, but all features found beyond the peak potential are supported by the theory. A comparison with theory based on a direct reduction of Zr4+ (soln) to the metallic state having unit activity is provided. It is proposed that an analogous mechanism applies at a Ni electrode, except that a Ni-Zr alloy formation occurs instead of Zr metal.

MXene‐Sponge Based High‐Performance Piezoresistive Sensor for Wearable Biomonitoring and Real‐Time Tactile Sensing (Small Methods 2/2022)

Flexible Piezoresistive Pressure Sensor In article number 2101051, Ye, Xie, Su, Chen and co-workers were inspired by Helium embrittlement during nuclear fusion processes, to utilize Helium plasma irradiation to yield a nano-fuzz-shaped molybdenum electrode for a flexible piezoresistive pressure sensor, which was demonstrated to measure human radial pulse, detect the tapping, stamping, and perform object identification, revealing great feasibility in wearable biomonitoring and healthcare assessment.

Speciation of dysprosium in molten LiCl–KCl–CsCl eutectic: An electrochemistry and spectroscopy study

Speciation and behavior of dysprosium (III) chloride in the ternary low melting LiCl–KCl–CsCl eutectic was studied by electrochemistry and spectroscopy techniques. Electronic absorption spectra of Dy(III) ions were recorded at 723–1023 K. Prolonged holding of relatively concentrated DyCl3 solutions in the melt resulted in a very subtle decomposition of Dy(III) to Dy(II) chloro-species. Cathodic reduction of Dy(III) ions on inert molybdenum electrode was studied at 623–973 K in the inert atmosphere by transient electrochemical techniques (cyclic and square-wave voltammetry). In dilute solutions the cathodic reduction of Dy(III) ions was irreversible, proceeded in one stage, and was controlled by the charge transfer. The diffusion coefficients of [DyCl6]3- complex ions in fused LiCl–KCl–CsCl eutectic were determined at different temperatures. The apparent standard potential of Dy(III)/Dy couple was determined by the open-circuit potentiometry and the principal thermodynamic properties of dysprosium trichloride in fused solvent were calculated.

Optimization of Material Removal Rate, Surface Roughness and Kerf Width in Wire-ED Machining of Ti-6Al-4V Using RSM and Grey Relation

Wire-Electric Discharge (WED) Machining is one of the most suitable machining techniques for machining hard-to-cut materials such as Titanium, with precision. It is of utmost importance to optimize the control parameters to achieve the desired levels of machining performance characteristics. Considering this goal, this research investigates the effects of current, pulse on time (Ton) and pulse off time (Toff) on the material removal rate, surface roughness and kerf width of WED machined Ti-6Al-4V. The results of optimization showed that, current – 5.19 A, Ton – 20 µs, Toff – 30 µs, is the optimized settings for machining of Ti-6Al-4V alloy using molybdenum electrode for the best machining performance. Based on the analysis of grey relational grades, the order of influence of the control parameter is ranked as: Ton – I, Toff – II and Current – III. The efficacy of GRA based approach was evaluated through confirmation experiments wherein the theoretical predictions showed errors < 3%.

Tunable and Miniaturized Microwave Filters Using Carbon Nanotube-Based Variable Capacitors

In this paper, we introduce a novel concept of tunable and miniaturized filtersthat embed, as voltage-controlled elements, state-of-the-art variable capacitors, based on vertically aligned carbon nanotubes (VACNTs). Starting from a theoretical estimation of the voltage-dependent capacitance between two adjacent CNTs, we extended this physics principle to a large matrix of CNTs, suitably placed on the molybdenum electrodes of an interdigitatedcapacitor (IDC), since molybdenum can withstand the high temperature necessary in the plasma process for the growth of the VACNTs. The IDC is the tunable element of a microwave filter, which must fulfill the need for both reconfigurability (being either a low-pass, a high-pass, or a band-pass filter, at discretion) and low-voltage frequency tuning of reflection&#x002F;transmission coefficients. For all these reasons, a very compact layout made of T-type cells (comprising VACNT-based variable capacitors and distributed inductors) was designed, simulated, fabricated, and tested, targeting the C, X, and K_u bands (4&#x2013;16 GHz) for wireless and radar applications. Taking as a reference the free-space wavelength <i>&#x03BB;</i>₀ at 10 GHz, the band-pass filter has overall dimensions of just 3.19 mm &#x00D7; 3.47 mm (i.e., 0.11<i>&#x03BB;</i>₀ &#x00D7; 0.12<i>&#x03BB;</i>₀), with the minimum of the reflection coefficient shifting of 1.16 GHz (within the X band) for an applied dc bias voltage of just 4 V and spanning between &#x2212;24.81 dB and &#x2212;36.13 dB. Furthermore, the maximum rejection is 31.65 dB, and the 3-dB fractional bandwidth is 12.44&#x0025;. The proposed filters are the proof that nanomaterials can be profitably integrated into microwave components for next-generation transceivers.

Mechanism for electrochemical reduction of Zr(IV) in molten NaCl–KCl

The electrochemical behavior of Zr (IV) at molybdenum and nickel electrodes was investigated by cyclic voltammetry, square-wave voltammetry, chronoamperometry, and chronopotentiometry at 1023 K to investigate the mechanism through which zirconium was electrochemically reduced. The number of electrons transferred in the two-step reduction of Zr(IV) at a molybdenum electrode in molten NaCl–KCl was calculated from the square-wave voltammetry results. Zr(IV) reduction to Zr (0) was found to be a two-step reaction described by the equations Zr(IV)+2e−→Zr(II) and Zr(II)+2e−→Zr (0). The diffusion coefficient for the transfer of Zr(IV) to the molybdenum electrode in molten NaCl–KCl was calculated from the chronoamperometry results. The phase and structure of the product of Zr(IV) reduction at a nickel electrode were determined by X-ray diffractometry and by scanning electron microscopy with energy dispersive X-ray spectroscopy, and a NiZr intermetallic compound was found.

Electroluminescence of NV by impact excitation and Stark shift in a MIM diamond structure

Electrically driven emission of nitrogen-vacancy (NV) color centers in diamond has recently emerged as a viable candidate for quantum photonics. However, it is challenging to efficiently excite NV centers by an electric field because of the low density of free carriers in doped diamond. Here, we report efficient electroluminescence of neutrally charged nitrogen-vacancy (NV0) color centers under a high electric field (105 V/cm) and study its Stark effect in a MIM (Metal–Insulator–Metal) diamond device. The MIM device was fabricated by electron beam evaporating molybdenum electrodes and microwave plasma chemical vapor depositing a nitrogen-doped diamond epilayer successively on a single-crystal diamond substrate. We demonstrate the field dependence of the electrically driven emission and extract the NV0 ground state electric field susceptibility of 15.83 ± 0.86 GHzmMV−1 from the Stark effect at 5.5 K. Our findings provide a perspective toward electrically exciting color centers in diamond and help one to understand the inherent features of NV0.

Analysis of the Quality of Sulfomolybdenum Coatings Obtained by Electrospark Alloying Methods.

The authors of this paper have attempted to improve the quality of surface layers applied to steel elements of machine parts constituting friction couples. The main goal of the research was to investigate an electrospark alloying method process for obtaining abrasion-resistant tribological coatings containing molybdenum disulfide on a steel surface. A substance in the form of sulfur ointment with a sulfur content of 33.3% was applied on the surfaces of C22 and C40 steel specimens. In order to determine the influence of the energy parameters of ESA equipment on the quality parameters of coatings, the ESA process was carried out using a molybdenum electrode with discharge energies Wp = 0.13; Wp = 0.55; Wp = 3.4 J. The following tests were carried out on specimens with such coatings: metallographic analysis, microhardness tests, surface roughness, and local X-ray diffraction microanalysis. The experiments revealed that sulfomolybdenum coatings consist of four zones with different mechanical properties. Depending on the discharge energy and the substrate material, the hardness of these zones varies from approx. 1100 to over 10,000 MPa. Differences in the distribution of, among others, sulfur and molybdenum in the obtained coatings, as well as differences in the microstructure of the observed coatings, were observed.

Electrochemical Study on the Reduction of Si and Ti from molten TiO2–SiO2–Al2O3–MgO–CaO Slag

The reduction process during the electrochemical production of titanium via the electrolysis of molten TiO2–SiO2–Al2O3–MgO–CaO slags has been investigated. A laboratory scale, electrolytic cell was designed to study the effect of TiO2 concentration at ultra-high temperatures. Galvanostatic and potentiostatic experiments were performed and results were consistent with thermodynamic predictions using FactSage. We demonstrate the direct production of Si-Ti alloys from the molten oxide mixture. The reduction of Si and Ti ions from the melt on a molybdenum electrode is a complex process that combines electron transfer and chemical phenomena. For the concentrations studied, the extraction of pure metallic Ti directly from ironmaking slag is unlikely without the prior removal of SiO2 or other chemical modifications to the system.

Vibrational CARS measurements in a near-atmospheric pressure plasma jet in nitrogen: I. Measurement procedure and results

The non-equilibrium ro-vibrational distribution functions of molecules in a plasma can heavily influence the discharge operation and the plasma-chemistry. A convenient method for measuring the distribution function is coherent anti-Stokes Raman scattering (CARS). CARS spectra are measured in a ns-pulsed plasma between two parallel, 1 mm spaced molybdenum electrodes in nitrogen at 200 mbar with pulse durations of 200 ns/250 ns and a repetition rate of 1 kHz. The CARS spectra are analyzed by a fitting routine to extract information about the vibrational excitation of the nitrogen molecules in the plasma. It is found that during the discharge the vibrational distribution for can be described by a vibrational two-temperature distribution function. Additionally, the electric field is measured by the electric field induced second harmonic generation method during the discharge pulse. It is found to be constant in time after the initial ionization wave with values close to 81 Td for the investigated conditions. During the afterglow between two discharge pulses a more general fitting approach is used to obtain the population differences of two neighboring vibrational states. This allows to capture the more complex vibrational dynamics in that time period. The measurement results are discussed in more detail and compared to simple plasma models in a companion paper Kuhfeld et al (2021 J. Phys. D: Appl. Phys. 54 305205).

Vibrational CARS measurements in a near-atmospheric pressure plasma jet in nitrogen: II. Analysis

The understanding of the ro-vibrational dynamics in molecular (near)-atmospheric pressure plasmas is essential to investigate the influence of vibrational excited molecules on the discharge properties. In a companion paper Kuhfeld et al (2021 J. Phys. D: Appl. Phys. 54 305204), results of ro-vibrational coherent anti-Stokes Raman scattering (CARS) measurements for a nanosecond pulsed plasma jet consisting of two conducting molybdenum electrodes with a gap of 1 mm in nitrogen at 200 mbar are presented. Here, those results are discussed and compared to theoretical predictions based on rate coefficients for the relevant processes found in the literature. It is found, that during the discharge the measured vibrational excitation agrees well with predictions obtained from the rates for resonant electron collisions calculated by Laporta et al (2014 Plasma Sources Sci. Technol. 23 065002). The predictions are based on the electric field during the discharge, measured by electric field induced second harmonic generation Kuhfeld et al (2021 J. Phys. D: Appl. Phys. 54 305204), Lepikhin et al (2020 J. Phys. D: Appl. Phys. 54 055201) and the electron density, which is deduced from the field and mobility data calculated with Bolsig+ Hagelaar and Pitchford (2005 Plasma Sources Sci. Technol. 14 722–33). In the afterglow a simple kinetic simulation for the vibrational subsystem of nitrogen is performed and it is found, that the populations of vibrational excited states develop according to vibrational-vibrational transfer on timescales of a few microseconds, while the development on timescales of some hundred microseconds is determined by the losses at the walls. No significant influence of electronically excited states on the populations of the vibrational states visible in the CARS measurements () was observed.

Redox behavior of indium in molten chlorides

An electrochemical study on the redox behavior of indium in the eutectic LiCl-KCl system at 450 °C was carried out with the transient techniques of cyclic voltammetry and chronopotentiometry on an inert molybdenum electrode. The reduction of In(III) was found to be a two-step process involving In(III)/In(I) and In(I)/In couples at the potentials of about −0.4 and −0.8 V versus Ag/AgCl, respectively. The redox mechanism was further confirmed by the theoretical evaluation of the number of transferred electrons based on cyclic voltammetry and characterizations of the precipitates generated by the potentiostatic electrolysis. The diffusion coefficients of indium ions in the eutectic LiCl-KCl melt at 450 °C were estimated by cyclic voltammetry and chronopotentiometry. The results obtained through the two methods are in fair agreement, delivering an average diffusion coefficient of approximately 1.8×10−5 cm2/s for In(III), and 1.4×10−4 cm2/s for In(I).

A Study on the Manufacturing of Molybdenum Pins for Electrodes

The molybdenum cup and molybdenum pin, which are the main materials of the molybdenum electrode used for the LCD BLU CCFL electrode, have not been developed in Korea and imported from Japan. In this paper, especially, research on prototype manufacturing and CAE analysis is performed to develop a molybdenum pin. In this research, to develop the manufacturing technology of molybdenum pin used for CCFL electrode of LCD BLU, development of linear processing technology, development of molybdenum wire surface treatment technology, development of wire cutting technology, production of molybdenum pin, design and fabrication of JIG and Fixture for inspection, molybdenum pin prototyping and analysis, and development of 100% molybdenum pin inspection technology. The development of molybdenum pins developed through this research can overcome Japan's technological level, which depends entirely on imports from Japan, and it is thought that the development will have a significant impact on the overall industry using molybdenum pins.

Flexible piezoelectric AlN transducers buckled through package-induced preloading for mechanical energy harvesting

There is a high demand for novel flexible micro-devices for energy harvesting from low-frequency and random mechanical sources. The research of new functional designs is required to strategically enhance the performances and to increase the control on mechanical flexibility. In this work we report the fabrication and characterization of bi-stable and statically balanced thin-film piezoelectric transducers based on Aluminum Nitride (AlN). The device consists of a piezoelectric layer sandwiched between two thin Molybdenum electrodes that were deposited on a Kapton substrate by reactive sputtering and patterned by UV lithography. In order to improve the out-of-plane flexibility, the mechanical design is distinguished by a post-buckled flexure that introduces a negative stiffness to compensate the otherwise positive stiffness of the system. The buckling was introduced by a new method, called Package-Induced Preloading (PIP) where the mechanisms are laminated over a package with a geometry extending out-of-plane. The induced buckling resulted in bi-stable and statically balanced mechanisms which demonstrated an enhanced voltage output during a triggered snapping step. A preliminary study shows potential for the statically balanced designs and the PIP method for wind energy harvesting, revealing prospective applications and future improvements for the development of energy harvesters.

High performance mid-wave infrared photodetector based on graphene/black phosphorus heterojunction

Black phosphorus (BP) as a promising candidate for mid-wave infrared (MWIR) detection has attracted much attention. However, the high-speed photoresponse at the MWIR is yet to be a challenge. In this paper, we report a BP-graphene heterostructure photodetector with fast photoresponse at MWIR range using molybdenum electrode as a contact to realizing a low Schottky barrier. The device exhibits a fast photoresponse in a broad-spectrum range from visible to MWIR (0.67–4.2 μm). A high photovoltaic responsivity up to 183 mA W−1 and EQE up to 35.6% were realized at the visible range of 0.637 μm light and respectively 7.9 mA W−1 and 0.31% at MWIR 3098 nm. The specific detectivity D* = 6.69 × 108 Jones is obtained at 1 mV bias under the illumination of the MWIR 4.25 μm in the ambient condition. Our work may open a new way to realizing fast MWIR photoresponse at the low light level.

Electrochemical Formation of Nd–Ni Alloys in Molten CaCl2–NdCl3

The electrochemical formation of Neodymium–Nickel (Nd–Ni) alloys was investigated in a molten CaCl2–NdCl3 (1.0 mol%) system at 1123 K. Cyclic voltammograms for Molybdenum (Mo) and Ni electrodes showed the electrodeposition/dissolution of metallic Nd and the formation/dissolution of Nd–Ni alloys, respectively. The equilibrium potential of Nd3+/Nd was determined at 0.27 V (vs. Ca2+/Ca) by open-circuit potentiometry for a Mo electrode. The potentials of 0.48, 0.68, and 0.95 V, corresponding to the two-phase coexisting states of (NdNi2 + NdNi3), (NdNi3 + NdNi5), and (NdNi5 + Ni), respectively, were confirmed using energy-dispersive X-ray spectroscopy and X-ray diffraction of the Ni electrode electrolyzed samples. The optimum electrolysis conditions for the Nd and Dysprosium (Dy) separation were discussed, and the standard Gibbs energies of formation were calculated for Nd–Ni alloys.

Performance improvement with plasma edge biasing on SPECTOR

A description of an edge-biasing experiment conducted on the spherical compact toroid plasma injector is presented with results. The insertion of a disk-shaped molybdenum electrode (probe), biased at up to +100 V, into the edge of the Compact Torus (CT), resulted in up to 1.2 kA radial current being drawn from the probe to the wall. Core electron temperature, as measured with a Thomson-scattering diagnostic, and CT lifetime, more than doubled in the optimal configuration tested. Temperature and density profiles become more centrally peaked with biasing. In contrast to previous biasing experiments, a significant reduction in electron density was observed; this may be due to the effect of a transport barrier impeding CT fueling and associated cooling, where, as verified by MHD simulation, a principal fueling source is neutral gas that remains concentrated around the gas valves after CT formation.