Effective ignition energy for capacitor short-circuit discharge in explosive environments

ABSTRACTHigh-performance machining of free-form surfaces is highly critical in automotive, aerospace, and die–mold manufacturing industries. Therefore, electrochemical machining (ECM) process has been used in such cases in that sense. The most important challenges of using ECM process are the lack of accuracy and difficulty in designing proper machining tool (cathode) surfaces. In this article, a simplified mathematical model is presented to obtain a cathode surface for ECM of free-form surfaces which have high curvatures. In this theoretical approach, the finite-element method (FEM) is used to solve the 3-D Laplace equation and to determine the potential distribution between the anode (workpiece) and cathode (tool) surfaces. A compact and simple program was developed to obtain a proper cathode surface that only requires some nodal coordinates on the anode surface and boundary conditions. In this work, a trial cathode surface is constructed for a given gap distance. For the determined ECM parameters, cathode shape that satisfies the boundary conditions is obtained for the 45th layer. The results are compared with the literature and ANSYS Workbench for verification. The developed theoretical approach benefits simpler and faster FEM solutions, accurate cathode surface, and consequently correct form of machined surface.

The objective of this paper is to compare the state of cathode surface of different axial magnetic field (AMF) contact systems (CSs) during arcing and after arc extinction. The arcs were ignited by opening of electrodes and were fed by sine half-wave current pulses with a duration of 10 ms. Investigations were performed in the range of arc currents up to the levels of guaranteed failure. The measurements were done by a high-speed Phantom M310 video camera. The cathode surface state during arcing was studied using a set of neutral density filters. It was discovered that melting of a part of the cathode surface during arc burning takes place in high-current vacuum arcs. A changing relief in the form of hillocks and hollows forms on the melted surface. We found out that there are two components in droplet erosion of the cathode, when its surface is partially melted: in addition to droplets formed directly in the cathode spot (which can be called droplets of the first type), the liquid part of the surface also emits droplets (which can be called droplets of the second type) significantly different in their sizes and velocities. The formation mechanisms of droplets of the first and the second type are different. The cathode surface temperature distribution immediately after current zero was obtained by comparing the results of cathode surface filming to the results of calibrated band-lamp filming in identical conditions. Reflection of anode radiation from cathode surface was analyzed by mathematical simulation. The filming was carried out using an interference filter. We found that the distribution of the cathode surface temperature is substantially nonuniform. The axial region is the most heated. We conclude that in all investigated CSs with the same amplitude value of the current, the temperature of the most heated parts of the cathode surface is significantly lower than the temperature of the most heated parts of the anode surface. Analysis of obtained results shows that switching failure can be provoked by the cathode and by the anode processes depending on CS design.

In the explosive environments, the electrical sparks with short circuit of capacitor output will ignite the surrounding explosive medium, and the relationship between effective ignition energy, capacitance energy conversion rate, capacitor capacitance and capacitor terminal voltage is unclear. Based on the three stages of breakdown, discharge and attenuation of the discharge characteristic curve of capacitive circuit, this paper deduces the expressions of spark resistance and discharge current including voltage, capacitance and polar distance parameters. Based on the programmable micro-nano gap discharge experimental platform, experiments under different voltages and different capacitances were carried out. It is found that the theoretical voltage-current curve and spark energy conversion rate are in good agreement with the experimental fitting curve and spark energy conversion rate. And with the increase of capacitance or voltage, the peak current and discharge time increase, which leads to the increase of energy. The conversion rate of spark energy decreases with the increase of capacitance or voltage, and the conversion rate changes between 20% and 30%. The change of spark energy conversion rate is also related to spark resistance, and with the decrease of spark resistance, the spark energy conversion rate also decreases. This study can further understand the energy variation in the discharge gap and is of great significance for the research of intrinsically safe circuits.

An anti-icing copper-based superhydrophobic layer prepared by one-step electrodeposition in both cathode and anode

This paper presents the results of the synthesis of nanodiamonds and carbon nanotubes in silicon-argon plasma. At a pressure of 500 Torr in the plasma reactor, carbon atoms evaporated from the surface of the graphite anode of the electric arc. The peculiarity of the graphite anode was that small pieces of silicon were embedded on the surface of the anode. As a result of the experiment, nanodiamonds and carbon nanotubes were formed on the surface of the graphite cathode. The linear dimensions of nanodiamonds range from 10 to 50 nm. The diameters of carbon nanotubes range from 4 nm to 20 nm, and their length is from 100 to 2 microns.

The cycling performance of the LiNi0.5Mn1.5O4/graphite cells cycled to 4.8 V versus Li/Li(+) at room temperature has been investigated. The control electrolyte is 1.0 M LiPF6 ethylene carbonate (EC)/ethylmethyl carbonate (EMC)/fluoroethylene carbonate (FEC) (10/70/20, v/v) with 2 wt% lithium bis(oxalate)borate (LiBOB). Biphenyl (BP) (0.5 wt% and 1 wt%) is employed as the in situ electrochemical coating additive for LiNi0.5Mn1.5O4 cathode. The results indicate the potential window of electrolyte without BP is up to 5.5 V versus Li/Li(+) on Pt electrode, but still decomposed seriously on both cathode and anode surfaces during prolonged cycles. The improved cycling performance with added 0.5 wt% BP in the control electrolyte can be attributed to the in situ electrochemical coating film on LiNi0.5Mn1.5O4 surface derived from BP electro-polymerization, which decreases the Mn dissolution and the lattice changes of LiNi0.5Mn1.5O4 cathode, and further inhibits Mn deposition and additional SEI formation on graphite surface. However, the thicker and compact BP electro-polymerization film using 1BP electrolyte on the cathode surface might inhibit the lithium intercalation/deintercalation and increase the polarization, then accelerates the capacity fading.

The calculation of the temperature and radiation intensity in a region at the boundary of which multiple reflection and refraction of light is possible is, in general, a complex and little-investiga ted probh~m in the theory of complex heat transfer. It is therefore natural that we should wish to consider models which, without losing sight of the main features of the phenomena and remaining of practical value, enable one to reduce the mathematical difficulties to reasonable limits. The traditional problem of radiant heat transfer is a problem of a plane layer in which the temperature and radiation intensity vary only over its thickness [1, 2]. Another type of problem arises when investigating heat transfer in thin regions when the mean temperature variation occurs along the region, while transverse to the region the temperature can be regarded as practically constant. Such a "one-dimensional " approach has been known for a long time in the theory of heat conduction. However, in the theory of radiation-conduc tion heat transfer it has only recently been developed, although the problem in this formulation is not only of theoretical but also of considerable practical interest, for example, when extracting semitransparent crystals from a melt using the Czochralski or Stepanov method. In this paper we consider heat transfer in a thin circular cylinder surrounded by a cylindrical screen with an axisymmetrical temperature distribution. The gap between the screen and the cylinder is evacuated or filled with a gas having a low absorption. It is assumed that the following relations are satisfied:

Quasiequilibrium power flow in two radial magnetically insulated transmission lines (MITLs) coupled to a vacuum post-hole convolute is studied at $50\text{ }\text{ }\mathrm{TW}--200\text{ }\text{ }\mathrm{TW}$ using three-dimensional particle-in-cell simulations. The key physical dimensions in the model are based on the ZR accelerator [D. H. McDaniel, et al., Proceedings of 5th International Conference on Dense Z-Pinches, edited by J. Davis (AIP, New York, 2002), p. 23]. The voltages assumed for this study result in electron emission from all cathode surfaces. Electrons emitted from the MITL cathodes upstream of the convolute cause a portion of the MITL current to be carried by an electron sheath. Under the simplifying assumptions made by the simulations, it is found that the transition from the two MITLs to the convolute results in the loss of most of the sheath current to anode structures. The loss is quantified as a function of radius and correlated with Poynting vector stream lines which would be followed by individual electrons. For a fixed MITL-convolute geometry, the current loss, defined to be the difference between the total (i.e. anode) current in the system upstream of the convolute and the current delivered to the load, increases with both operating voltage and load impedance. It is also found that in the absence of ion emission, the convolute is efficient when the load impedance is much less than the impedance of the two parallel MITLs. The effects of space-charge-limited (SCL) ion emission from anode surfaces are considered for several specific cases. Ion emission from anode surfaces in the convolute is found to increase the current loss by a factor of 2--3. When SCL ion emission is allowed from anode surfaces in the MITLs upstream of the convolute, substantially higher current losses are obtained. Note that the results reported here are valid given the spatial resolution used for the simulations.

A general microwave electron gun (rf gun) theory and some new ideas about further reducing the emittance of electron beams are reviewed and introduced briefly. Experimental results are presented from a thermionic cathode rf gun which has been developed for Beijing Free-Electron Laser Project (BFELP) at Institute of High Energy Physics (IHEP), Academia Sinica as the injector of 30 MeV constant gradient linac. LaB6 is used as the thermionic emitter with 100 crystal surface and the temperature around 1620 °C. Back bombardment heating effect and another effect connected with the cathode surface temperature was observed. An electron beam with macropulse length 4 μs, repetition rate 12.5 Hz, greater than 500 mA beam current during macropulse and around 1 MeV maximum energy has been obtained. In the last section of this article, two useful formulas used to determine electric field distribution near the cathode surface and coupling coefficient β of a rf gun are introduced.

A method for generating second-harmonic light from silica glass by doping its surface layer with ions is presented. When anions CO32−, OH− or Cl− are introduced from the cathodic surface during poling, the second-harmonic signal generated near that surface is enhanced by two orders of magnitude with respect to the case of poling without doping. The penetration depths of CO32−, OH− and Cl− have been measured by the etching technique. In contrast, by doping the anodic surface with cations Li+, Na+ or K+, the second-harmonic signal drops to one tenth of that corresponding to the case of poling without doping. This indicates that in the anodic surface the main charges are negative, and the positive charges neutralize them to decrease the strength of the electric field that is at the origin of the second-order susceptibility. Secondary ion mass spectroscopy detection shows the concentration distribution of the injected lithium in the surface layer. The second-harmonic signal from the anodic surface decreases monotonically with increasing poling-doping time up to 300 min. Doping from interfaces far from the electrodes is inefficient for influencing the second-harmonic generation.

Reed switches have been used in various fields of application due to excellent reliability and compactness. The progress of electronics is leading to increasing demand for enhanced functions of the reed switch. One such demand is high breakdown voltage between contacts. To achieve the improvement in breakdown voltage, fundamental research on discharge phenomena is very important. We studied the relationship between applied voltage to cause discharge and movement of carriers for rhodium-plated contact reed switches. Using Auger electron spectroscopy (AES), we analyzed contact surfaces before and after discharge caused by various applied voltages. Amount of nitrogen and amount of oxygen were found to increase on the cathode surface and on the anode surface, respectively, after discharge. Furthermore, we found that this increase was accelerated by enhancing applied voltage to cause discharge. On the contrary, amount of oxygen was found to decrease on the cathode surface after discharge. We found that this decrease was also accelerated by enhancing applied voltage to cause discharge. These results revealed that the nitrogen cation and oxygen anion moved as carriers through discharge and that this movement was accelerated by increasing applied voltage to cause discharge.

To improve the ECF leveling effect, according to the actual work of anodic and cathode surface micro-profile, based on the electrodynamics knowledge, established the mathematical model of current field. On the basis of this use of some software to simulate and proceeded numerical calculation, obtained for the influence rule the different cathode surface profile of the current field distribution, and was verified by the experiment. The experimental results show that the variation of the cathode surface micro-profile by changing the current distribution to affect the surface of the anodic and influence of leveling effect by copying the phenomenon will be its own surface profile is copied to the anode. The cathode surface profile is more pointed the affect for the anodic surface will be more obvious.

It has been reported earlier that when an electric current is externally applied between two sliding surfaces in a lubricated contact, an electrochemical cell is produced with the lubricant acting as an electrolyte and two sliding surfaces acting as electrodes. In this paper, the effect of an externally applied direct current on friction and wear of a sliding steel pair lubricated by engine oils has been investigated using a ball on disk machine. The current was passed through the contact by connecting the ball and disk specimens to a current source. It has been observed that the magnitude and the direction of current can significantly alter wear of sliding surfaces but does not greatly impact friction coefficients. The wear of the cathode surface decreased while that of the anode surface increased compared to the condition when no current passed through the contact. It was also observed that wear on anode and cathode surfaces was influenced by lubricant chemistry. The wear reduction on cathode surface is believed to be related to the modification of elemental composition of lubricant derived surface films due to the passage of an electric current.

Resistivity of the boundary-layer in the MHD generator duct with water-cooled metal electrodes is considered to be the limiting factor of the MHD generating performance. The voltage-current characteristics were studied by using water-cooled, segmented electrodes. The high resistivity parts of the characteristics were investigated with potential probes. Notable voltage-drop was found both in front or the cathode and the anode. The voltage-drop in front of the cathode seemed to be saturated beyond a certain value in the current, where thin arcs appeared on the cathode surfaces. The voltage-drop in this region is well explained by a theory of heat transfer under forced convection.

Lithium ion batteries have been investigated extensively due to their widespread applications in portable electronic devices and electrical/hybrid vehicles. However, significant challenges still exist for an extended calendar life at a wide temperature range. Due to the intrinsic drawbacks of the commonly used LiPF6-carbonate electrolyte systems, such as insufficient thermal stability at elevated temperature and unavoidable HF contaminants, much effort has been paid to exploring novel additives. It is well known that the introduction of additives into electrolyte systems is one of the most effective and economic approaches to improve performance of lithium ion batteries. In this dissertation, a novel class of borate compounds has been successfully synthesized and screened as additives for electrolyte of lithium ion battery. Nuclear magnetic resonance (NMR) spectroscopy was utilized to characterize compounds by dissolving additives into deuterated solvents. The cycling performance of these novel additives and other commercialized additives was compared by adding them into 1M LiPF6 EC/EMC electrolyte, LiNi0.5Mn1.5O4/Graphite cells are cycled under both room temperature and elevated temperature up to 4.8V. Electrochemical impedance spectroscopy (EIS) and Linear sweep voltammetry (LSV) were used to investigate electrochemical activity of additives. The investigation of the interrelationship of cycling performance, additive structure, and electrode surface film structure has been conducted by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and FT-IR instruments. SEM and TEM images showed that novel additives can form uniform solid electrolyte interface (SEI) and cathode solid electrolyte interface (CEI). XPS and FT-IR spectra were acquired to analyze main components of SEI and CEI, and they are beneficial for further understanding how addition of additives changed surface chemistry of electrodes. The surface reactions of both additives and electrolytes with the graphitic anode and lithium nickel manganese oxide cathode of lithium ion batteries have been speculated. New additives can not only form more uniform SEI on surface of anode, but also beneficial for forming uniform CEI on surface of cathode.