Wide Range Of Power Densities Research Articles

Study of the transition from self-organised to homogeneous plasma distribution in chromium HiPIMS discharge

The self-organised plasma patterns, known as spokes or ionisation zones in magnetron sputtering discharges, were observed in a wide range of power densities, from low power direct current magnetron sputtering (dcMS) discharge to high power impulse magnetron sputtering (HiPIMS) discharge. For some target materials and non-reactive gases, it was observed that at very high power densities (>) the plasma exhibits a transition from a regime where spokes are observed to a homogeneous plasma regime. In this contribution, we present a comparison of plasma properties: plasma emission (optical emission spectroscopy) and flux of argon and chromium ions (mass spectrometry), measured both in the spoke regime and in the homogeneous plasma regime, aimed to expand the understanding of the plasma transition between the two modes. A simple biased flat probe was used to distinguish between the spoke regime and the homogeneous plasma regime. It was found that the flux of multiply charged ions (Ar2+ , Cr2+ , Cr3+ , Cr4+) increases abruptly at the transition between the spoke regime and the homogeneous plasma regime. Similarly, the emission from Cr+ ions exhibits a strong increase of about 50% when the plasma torus becomes homogeneous. These observations are interpreted as an increase in electron temperature and a change in the electron heating mode, from a combination of secondary electron heating and Ohmic heating towards pure Ohmic heating. The transition to the homogeneous plasma regime and pure Ohmic heating is only observed in non-reactive HiPIMS discharges for target atoms with the second ionisation potential higher than the first ionisation potential of Ar (15.76 eV), and a self-sputter yield larger than 1.

Rational Surface Tailoring Oxygen Functional Groups on Carbon Spheres for Capacitive Mechanistic Study

Porous carbons represent a typical class of electrode materials for electric double-layer capacitors. However, less attention has been focused on the study of the capacitive mechanism of electrochemically active surface oxygen groups rooted in porous carbons. Herein, the degree and variety of oxygen surface groups of HNO3-modified samples (N-CS) are finely tailored by a mild hydrothermal oxidation (0.0-3.0 mol L-1), while the micro-meso-macroporous structures are efficiently preserved from the original sample. Thus, N-CS is a suitable carrier for separately discussing the contribution of oxygen functional groups to the electrochemical property. The optimized N-CS shows a high capacitance of 279.4 F g-1 at 1 A g-1, exceeding 52.8% of pristine carbon sphere (CS) (182.8 F g-1 at 1 A g-1) in KOH electrolyte. On further deconvoluting the redox peaks of cyclic voltammetry curves, we find that the pseudocapacitance not only associates with the surface-controlled faradic reaction at high scan rate but also dramatically stems from the diffusion-controlled capacitance through potassium and hydroxyl ion insertion/deinsertion into the underutilized micropores at low scan rate. The assembled supercapacitor based on N-CS presents a stable energy density of 5 Wh kg-1 over a wide range of power density of 250-5000 W kg-1, which is higher than 0.0N-CS in KOH electrolyte. In TEABF4 electrolyte, the N-CS supercapacitor has an energy density of 26.9 Wh kg-1 at the power density of 1350 W kg-1 and exhibits excellent cycling stability with a capacitance retention of 93.2% at 2 A g-1 after 10 000 cycles. These results demonstrate that surface oxygen groups alter the capacitive mechanism and contribution of porous carbons.

Influence of weld parameters on weld regimes and vaporization rate in electron beam welding of Ti6Al4V alloy

Electron beam welding (EBW) is the most preferable and efficient joining technique to weld titanium alloys, since it provides a vacuum atmosphere and eliminates the use of shielding gas during the welding process. The present work is focused on understanding the electron beam weld parameters which controls the weld limits, microstructural and mechanical properties and vaporization rate of metal elements in the Ti6Al4V alloy. The influence of power density on characteristics of electron beam welded Ti6Al4V alloy at constant linear energy conditions is examined. The welding experiments were performed to evaluate the weld geometry, weld regimes, microstructural properties and microhardness characteristics using fundamental parameters such as power density and interaction energy per unit volume (IE). Moreover, the vaporization heat transfer model of the EBW process is developed by employing Fourier’s law of heat conduction to estimate the vaporization rate of Ti6Al4V alloying elements. The rate of vaporization of major alloying elements of Ti6Al4V is analysed with respect to power density. Based upon the results obtained, it is witnessed that the weld bead geometry, weld limits and grain size are controlled by power density for constant linear energy conditions. Also, the solidified microstructure in the weld zone at different power density significantly effects the final strength of the weld joint. The conduction and keyhole weld limits are identified for power density values below 0.31 W cm−2 and above 2.12 W cm−2, respectively. The transition mode welding in the Ti6Al4V alloy is identified by a nominal increase in aspect ratio for a wide range of power density and IE values. The results also established that the size of β grain in the fusion zone reduces with increase in power density at constant linear energy condition. Also, the average α1 martensitic grain size in the weld zone is determined to be higher in keyhole welds (128 µm) relative to conduction welds (48 µm) on account of higher solidification rate. In effect, the solidified martensitic phases influence the microhardness distribution proportionately across the weld sample of Ti6Al4V alloy. Vaporization of metal elements of the Ti6Al4V alloy is induced in few milliseconds and evaporation rate of ‘Al’ element is least followed by ‘Ti’ and ‘V’ elements. It is also observed that by reducing the power density from 2.54 to 2.12 W cm−2, keyhole mode welding can be acquired and vaporization rate of ‘Al’ is reduced by 20.5%.

Mesoporous niobium pentoxide/carbon composite electrodes for sodium-ion capacitors

Sodium-ion capacitors with unique characteristics such as higher energy density than electrical double-layer capacitors, higher power density than rechargeable batteries, and abundant sodium resources represent current research trend in developing large-scale electrical energy storage technology. One of the key challenges presently facing the development of this technology is the imbalanced kinetics between the sluggish Faradaic sodium insertion in the anode and the fast capacitive ion adsorption on the cathode. Here we demonstrate the sol-gel synthesis of a novel, high-rate, stable composite anode material for sodium-ion capacitors (NICs). The composite consisted of Nb2O5 nanoparticles embedded in a carbon matrix (denoted by m-Nb2O5/C). Sodium-ion capacitors employing the m-Nb2O5/C anode and a commercial activated carbon as the cathode showed an admirable performance, delivering high energy densities in a wide range of power densities (73 Wh kg−1@250 W kg-1 and 16.8 Wh kg−1@20 kW kg−1). These favourable cell characteristics are attributed to the properties of the m-Nb2O5/C anode: the mesoporous structure that facilitates electron and ion transport, the presence of the niobium carbide interlayer between the Nb2O5 nanoparticles and the surrounding graphitic carbon that additionally improves the electron conductivity, and the predominant capacitive charge storage mechanism.

The influence of the graphite structure changes on the high-energy electrochemical capacitor performance

Combining the advantages of lithium-ion batteries and supercapacitors is an interesting solution to high-energy devices with the maintenance of high power output. Herein we report on the performance of the lithium-ion capacitors (LICs), exploiting graphene-based materials and activated carbon as negative and positive electrodes, respectively. The electrochemical properties of pre-lithiated reduced graphite oxides (reduced thermally—TRGO, or chemically—CRGO) and pristine graphite are compared based on measurements conducted in two- and three-electrode cells. Chemically reduced graphite oxide (CRGO) displays excellent performance at current densities up to 8 A g−1. The assembled hybrid capacitor delivers the energy density around 80 Wh kg−1 along a wide range of power densities. Promising results show that even at power value of 24.8 kW kg−1, the device retains energy density over 35 Wh kg−1. The cycle performance also shows good energy retention comparing with a graphite anode. However, better energy retention is observable for the TRGO-negative electrode material. After the 2000 of cycles, the AC/TRGO(Li) system loaded with the current density of 1 A g−1 provides energy of 58 Wh kg−1.

Scalable synthesis of hierarchical macropore-rich activated carbon microspheres assembled by carbon nanoparticles for high rate performance supercapacitors

Abstract A scalable inverse-microemulsion-polymerization-phase-separation coupling method is applied to successfully prepare hierarchical macropore-rich activated carbon microspheres (ACS) using a phenolic resin (PR) precursor followed by carbonization and KOH activation for the first time. The formed ACS materials are assembled by carbon nanoparticles (CNPs). The macropores interspersed among the component CNPs are formed after removing the non-reactive solvent phase in the course of the polymerization of the reactive PR phase, which occupies ∼64% of the total pore volume (∼2.779 cm 3 g −1 ) of the optimized ACS. In combination with mesopores (∼18% of the total pore volume), the ACS possesses meso/macropores approaching 82% of the total pore volume. Micropores are created in the component CNPs via KOH activation, showing shortened ion transport distances in the nanoscale dimension. Both the hierarchical micro/meso/macroporous structure and the inner nanoparticle morphology (short ion diffusion pathways) can significantly contribute to the rapid transport of electrolyte ions throughout the carbonaceous matrix, resulting in superior rate performance of ACS-based supercapacitors. More importantly, the energy densities of the ACS supercapacitors operating in both aqueous and organic electrolyte retain steady over a wide range of power densities varying dramatically from 0.25 to 14.5 kW kg −1 and to 7.0 kW kg −1 , respectively.

Scalable Parasitic Charge Redistribution: Design of High-Efficiency Fully Integrated Switched-Capacitor DC–DC Converters

This paper introduces a technique, called scalable parasitic charge redistribution (SPCR), that reduces the parasitic bottom-plate losses in fully integrated switched-capacitor (SC) voltage regulators up to any desired level. This is realized by continuously redistributing the parasitic charge in-between phase-shifted converter cores. Because earlier models described the ratio of this parasitic coupling to the flying capacitance as the only limiting factor on the achievable fully integrated efficiency, the use of SPCR allows SC converters to achieve efficiencies previously deemed impossible. Transistor leakage is shown to be another limiting factor and is added to existing models which are then used to prove the effectiveness of SPCR over a wide range of power densities (up to 10 W/mm2) and technological parameters. The implementation of SPCR requires little overhead thanks to the use of charge redistribution buses. A 1/2 converter is fabricated in a 40 nm bulk CMOS technology that demonstrates SPCR by achieving a record efficiency for fully integrated closed-loop SC converters of 94.6%.

Laser-induced photoprocesses in solutions and films of the CdSe/ZnS nanoparticles

The photophysical properties of solutions and films with relatively high concentrations of CdSe/ZnS nanoparticles are studied in the presence of the visible laser irradiation in a wide range of power densities. The short-wavelength wing detected in the photoluminescence spectra of the solutions of quantum dots is due to the selective laser excitation of small-size nanoparticles. A comprehensive analysis of the anti-Stokes photoluminescence of the nanoparticles in solutions and films indicates the thermal mechanism of this phenomenon. The dimensional quantization effect, narrow spectra, and a relatively high luminescence yield are retained in the films with a high nanoparticle concentration. The luminescence spectra of the films remain unchanged when the laser flux density increases to 1 × 106 W/cm2. The effect of the laser radiation on the nanoparticle films is studied at the flux densities exceeding the damage threshold (5 × 106–1 × 109 W/cm2).

Effects of Thin Film Layers on Actuating Performance of Microheaters

We investigated effects of thin film layers on actuating performance of microheaters. Bubble behaviors on microheaters were observed experimentally, and heat conduction characteristics in thin film layers were analyzed numerically. Nine kinds of tantalum nitride (TaN) microheaters were prepared. Step-stress test showed that voltage limits of nonpassivated heaters were <50% of those of passivated heaters. Open pool bubble test was carried out using deionized water as a working fluid. Nonpassivated heaters produced comparable bubbles with only 20-50% of input energy required for passivated heaters. However, nonpassivated heaters could be operated only in a narrow range of driving voltage. We constructed a hybrid model for bubble nucleation prediction correlating nucleation times with driving powers. Based on work of bubble formation estimated from bubble volume evolution, actuation efficiencies of microheaters were calculated and compared. Efficiencies of nonpassivated heaters were much higher than those of passivated heaters. However, nonpassivated heaters failed to show robust actuating characteristics over a wide range of power density. As promising microactuators, nonpassivated heaters need further investigation from a viewpoint of reliability.

Effects of Thin Film Layers on Actuating Performance of Micro Heaters

Effects of thin film layers have been investigated on the actuating performance of micro heaters. Bubble behaviors on micro heaters were observed experimentally, and heat conduction characteristics in thin film layers were analyzed numerically. Nine (9) kinds of tantalum nitride (TaN) micro heaters were prepared. Step-stress test (SST) showed that maximum endurable voltage levels in the non-passivated heaters are less than 50% of those in the passivated heaters. Open pool bubble test was carried out using de-ionized (DI) water as a working fluid. The non-passivated heaters could produce comparable bubbles with only 20 to 50% of the input energy required for the passivated heaters. However, the non-passivated heaters could operate only in a narrow range of driving voltage. A hybrid model for bubble nucleation was newly proposed to correlate the nucleation times obtained experimentally. The hybrid model adopts different nucleation criterion depending on the input power level. Based on the bubble work obtained from the bubble volume estimated experimentally, actuating efficiencies of micro heaters were calculated and compared. Efficiencies of the non-passivated heaters were much higher than those of the passivated heaters. However, robust actuating characteristics were difficult to obtain in a wide range of power density. Applicability of non-passivated heaters as promising micro actuators needs further investigation from the viewpoints of robustness and reliability.

On the Photoinhibition of Passivity Breakdown on Iron in Chloride‐Containing Solutions

The photoinhibition of passivity breakdown (PIPB) on iron in buffered chloride‐containing solution has been explored using monochromatic light (λ = 325 nm, hv = 3.815 eV) over a wide range of power densities . Our studies have confirmed the observation of Schmuki and Böhni [Electrochim. Acta, 40, 775 (1995)] that irradiation of iron with high‐intensity, super‐bandgap light prior to the introduction of chloride and prior to inducing breakdown by sweeping the potential in the positive direction, renders the metal unsusceptible to the nucleation of pits on the surface. Furthermore, we have confirmed the persistence of the effect after cessation of irradiation. However, we find that the extent of PIPB is a strong function of the light power density (i.e., intensity) for power densities less than . At higher power densities, after irradiation for more than 20 min, iron is rendered immune to pitting attack. Part of the enhanced resistance can be attributed to aging of the passive film, as characterized under dark conditions, but photoinhibition becomes increasingly important for passivation times (under irradiation) greater than 30 min. Finally, we explore the relative merits of the two mechanisms that have been previously advanced for PIPB (i.e., photoquenching of the electric field/modification of the vacancy structure and modification of the electronic structure via increases in the bulk doping and surface state density), and we conclude that PIPB is consistent with the point defect model for passivity breakdown. © 1999 The Electrochemical Society. All rights reserved.

Deposition of thick diamond films by pulsed d.c. glow discharge CVD

Polycrystalline diamond films were deposited on molybdenum substrates by pulsed d.c. glow discharge chemical vapour deposition. A stable discharge with a methane in hydrogen mixture (0.5–7 vol.%) was maintained by the plasma generator over a wide range of power density (1–7 A cm −2). Deposition areas from 0.4 to 3 cm 2 were used and growth rates of more than 40 μm h −1 were achieved. The well-faceted diamond layers were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), micro-Raman and Fourier transform IR (FTIR) spectroscopy.

Proposal for a standard for laser plume filter technology

A methodology to critically appraise and assess the efficiency and efficacy of filters used in smoke evacuation systems is proposed. Currently the methods for evaluation of laser smoke evacuation systems and filtering are fraught with inconsistency, and laced with innuendo and extraopolation. A variety of tissues including beef, chicken, pork, mouse and human have been described. Both carbon dioxide and ND:YAG lasers have been used. A wide range of power densities have been applied. Environmental conditions during the studies either have not been described, are unknown or were not considered as impacting the results. Length of time of thermal interaction was extremely variable. As a result, these studies have not offered or established a methodology of design or proposed a standard which would hold up under scientific scrutiny. The methodology presented uses known concentrations of individual chemical components of laser plume generated by aerosolization. Following precise scientific protocols a smoke/plume evacuation system was challenged. Test parameters evaluated include measurement of airflow, chemical concentration of the challenge analyte, and testing of chemical concentration of analyte prior to a subject filter and at the exit point. NIOSH protocols for chemical analysis by spectrophotometry were used. This methodology allows for standardization of the effects of a smoke/plume evacuation system that is scientifically reproducible and exact. The protocol then allows for comparison which is meaningful to establish system efficiency.

Thermal Control of Ceramic Breeder Blankets

AbstractThermal control is an important issue for ceramic breeder blankets since the breeder needs to operate within its temperature window for the tritium release and inventory to be acceptable. A thermal control region is applicable not only to situations where the coolant can be run at low temperature, such as for the International Thermonuclear Experimental Reactor (ITER) base blanket, but also to ITER test module and power reactor situations, where it would allow for ceramic breeder operation over a wide range of power densities in space and time. Four thermal control mechanisms applicable to ceramic breeder blanket designs are described: a helium gap, a beryllium sintered block region, a beryllium sintered block region with a metallic felt at the beryllium-cladding interface, and a beryllium packed-bed region. Key advantages and issues associated with each of these mechanisms are discussed. Experimental and modeling studies focusing on beryllium packed-bed thermal conductivity and wall conductance, ...

Absorption and scattering of laser radiation of different wavelengths by plasma

A numerical investigation was made of the interaction of high-power laser radiation with a plasma, taking into account classical, resonant, and anomalous absorption mechanisms, as well as stimulated Brillouin scattering and specular reflection. The proposed model ensures a qualitative and quantitative agreement of the reflection coefficients, the radiation scattering spectra, and the plasma temperature with the results of experiments performed using an apparatus with an Nd3+ laser operating at the wavelengths 1.06, 0.53, and 0.35 μ in a wide range of power densities from 1013 to 3×1015 W/cm2 .