Study of the recast layer of a surface machined by sinking electrical discharge machining using water-in-oil emulsion as dielectric

Electrical discharge machining (EDM) caused a recast layer to form at the machined surface of the workpiece. The characteristics of the recast layer have a great relationship with the type of dielectric. The research work in this paper aims to acquire a profound knowledge of the recast layers of a surface machined by sinking EDM using water-in-oil (W/O) emulsion as dielectric. Scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectrograph (EDS) and micro hardness analysis were performed. The characteristics of the recast layer formed in W/O emulsion were investigated by comparing them with those of the recast layer formed in kerosene and de-ionized water dielectric. It was found that the recast layer formed in W/O emulsion exhibited larger surface roughness, thickness and micro hardness compared with that formed in kerosene and de-ionized water. Both carbide and oxide were detected in the recast layer formed in W/O emulsion whereas only carbide was detected in the recast layer formed in kerosene. Due to the higher supersaturation of gases in the melted material, the recast layer formed in W/O emulsion was found to possess more micro-voids than that formed in kerosene and de-ionized water.     

Выделение меченых соединений методом препаративной хроматографии

Mica Track Microfilters (MTM) are successful applied to separate two different and strongly mixed liquid phases (emulsion). The organic and the inorganic phase of the emulsion were 30% tributyl phosphate (TBP) in kerosene and 2 N HNO₃ (or H₂O), respectively. Mica filters with sharp edges (i.e. etched with H₂F₂) and having pore sizes k of 8 μm > k > 2 μm are used to get under some well defined conditions a rather complete extraction of the aqueous phase out of the emulsion. The system was calibrated with the pure phases (water as well as TBP in kerosene), and the liquid throughput is shown as a function of the pore size of the filter. The throughput depends mainly on the pore size and not that much on the kind of liquid, it is slightly larger for water as compared to that of TBP in kerosene.     

水中针-板结构小能量脉冲火花放电特性北大核心CSCD

开展了J量级系统储能下电脉冲参数对水中火花放电特性影响研究。驱动源采用参数可调的固态重频纳秒脉冲电源,放电负载为水中针-板结构(间距1 mm),在低重频条件(约5 Hz)下进行实验。通过调节放电参数、拍摄高速阴影图像、光谱诊断以及声信号测量,研究水中脉冲放电的物理特性,得到不同放电参数下放电演化规律及其对声学、光谱特性影响。实验发现:在J量级储能下,放电通道连通两极后,回路电流在几百ns内快速上升至10 A左右,随后缓慢下降,持续50~60μs。发现预设脉宽对放电影响较大,短脉宽条件下放电会被电源固态开关强制截断出现反向放电,而长脉宽条件下放电通道在后期变得不稳定甚至熄弧中断,出现气泡中二次放电现象。辐射光谱揭示了更多等离子体信息,推断通道电子密度在1018 cm-3量级,随着脉宽增加,特征谱线强度增加,表明活性粒子数密度增加,但粒子种类不变。短脉冲(<150μs)作用下产生的脉冲声波的特征宽度在110~150μs,而当脉宽继续增大,声波脉宽并不继续增加而是保持不变,保持在150μs左右。研究结果对水中小能量火花放电的机理研究有一定参考价值,为水声学、液相等离子体等领域的应用提供思路。     

Structure and surface layers of Mg-C nanocomposites produced by ball milling

X-ray diffractometry (XRD), X-ray photoelectron spectrometry (XPS), Auger electron spectrometry (AES) and transmission electron microscopy (TEM) were used to investigate the structure and surface layers properties of nanocomposites produced by the mechanical activation (ball milling) of elemental magnesium with carbon materials (amorphous carbon and graphite). Amorphous carbon was synthesized by electric discharge treatment in kerosene. It was shown that ball milling, the allotropic form of carbon materials, and features of hydrogenation have a considerable effect on the structure, surface layer properties, and hydrogen adsorption of a formed composition. XPS and Auger spectroscopy revealed the surface layer of the composite particles to be enriched with carbon. In addition, there were oxide layers on their surfaces due to the particles’ interaction with the environment.     

A Method of Separation of Polydisperse Particles in the Plasma of Radio‐Frequency Discharge

A method of separation of polydisperse dust particles in the plasma of radio‐frequency (RF) capacitive discharge is considered. Investigations of plasma equipotential field enabled us to determine conditions for separation of polydisperse dust particles. The simplicity of the technology made it possible to obtain small dispersed particles of different materials. Samples of small dispersed microparticles of silica and alumina were obtained. The size and chemical composition of samples were examined using a Quanta 3D 200i scanning electron microscope (SEM, FEI, USA). The average size of separated silica nanoparticles was 600 nm, that of silica and alumina microparticles was 5 μm. Two separation methods were developed: the first one used a special trap and shape of the bottom electrode of RF discharge (for separation of microparticles) and the second used an electrical trap (for separation of nanoparticles). The graphs of particle size distribution were constructed using graphical and mathematical calculations. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of conductivity on corona discharge current from a water droplet and on ejection of nano-sized droplets

The influence of the conductivity of a water droplet formed at a capillary electrode on the negative corona discharge and production of nano-sized droplets was investigated. Conductivity of a water droplet was adjusted from 1 μS/cm of deionized water to 48 mS/cm of nitric acid water solution. The size distribution of nanometer sized water particles yielded at a disruption of a Taylor cone was measured. The higher conductivity of a droplet, the larger corona pulses appeared and the more number of charged droplets was generated.     

Residual stresses and white layer in electric discharge machining (EDM)

The effect of dielectric liquid and electrode type on white layer structure in electric discharge machined surfaces has been studied in terms of retained austenite and residual stresses using X-ray diffraction method. The machining tests were conducted by using two different tool electrodes (copper and graphite) and dielectric liquid (kerosene and de-ionized water) under same operational conditions. The present work suggests that the surface is saturated with carbon irrespective of the tool electrode material when machining with kerosene dielectric liquid. But, retained austenite is formed on the surface due to carbon uptake from graphite tool electrode when machining with de-ionized water dielectric liquid. On the other hand, even though surface residual stresses increase with structural non-homogeneities in the white layer, no clear consequences have been observed in residual stress distribution beneath the white layer.     

Lasers based on electrodynamically dispersed media

We demonstrate the possibility of creating a suspension of active-media particles in a discharge tube by using an electrodynamic dispersing system. An electric discharge in an electrodynamically dispersed system of 30-μm Cu particles was studied. The velocity of Cu (30 μm), Al (30 μm), and W (6-μm flakes) particles was measured at atmospheric pressure using a laser Doppler velocimeter. The velocities were found to be in the 0.1−5-m/s range. The electric field strength required to levitate Cu, Al, and W particles was studied as a function of buffer gas (air) pressure in the range from 2 × 10⁻² Torr to 1 atm. It is shown that powders can be suspended with the help of electrodynamic dispersing system at air pressure below 0.1 Torr or above 100 Torr.     

Electrical discharge machining of titanium alloy (Ti-6Al-4V)

In this study, the electrical discharge machining (EDM) of titanium alloy (Ti-6Al-4V) with different electrode materials namely, graphite, electrolytic copper and aluminium and process parameters such as, pulse current and pulse duration were performed to explore the influence of EDM parameters on various aspects of the surface integrity of Ti6Al4V. Scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectrograph (EDS) and hardness analysis were performed. The experimental results reveal that the value of material removal rate, surface roughness, electrode wear and average white layer thickness are tendency of increase with increasing current density and pulse duration. However, extremely long-pulse durations such as 200 μs led to decrease MRR and surface roughness. Furthermore, the surface hardness is increasing due to the Ti₂₄C₁₅ carbides formed on the surface and obvious cracks are always evident in re-solidified layer when machining copper electrode. The surface crack densities and critical crack lines were determined for the tested material. The graphite electrode is beneficial on material removal rate, electrode wear and surface crack density but relatively poorer surface finish.     

Particle Size Classification of Glass Particles Using Aerodynamic Jet Vectoring

An experimental demonstration of a new, non‐contact particle characterization technique called Aerodynamic Vectoring Particle Sorting (AVPS) is presented. AVPS uses secondary blowing and suction control flows–flows that are a fraction of the jet flow rate–to sharply change the direction of a planar, particle‐laden jet. As the jet is vectored, particles present in the flow experience a resultant drag force, dependent upon their size, that balances inertia. Since this balance determines the particle's trajectory, vectoring the flow leads to a separation of particles downstream. This simple, low‐pressure‐drop sorting technique classifies particles with less risk of damage or contamination than currently available sorting devices. Particles from 10–40 μm and 2.5 times the density of water have been sorted to an accuracy of 1.5 μm. Sorting of heavy particles such as these is accomplished at very low speeds, reducing the tendency of damage to the particles. Lighter particles are sorted at higher speeds. Particles from 5–40 μm and 0.6 times the density of water were sorted to an accuracy of 6.6 μm. AVPS is also shown to be capable of concentrating aerosols. Our measurements indicate that an air sample containing water‐like particles can be concentrated by a factor of 10 using AVPS.     

Titanium Dioxide Nanoparticles Produced in Water-in-oil Emulsion

Titanium dioxide (titania) particles were prepared by a water-in-oil emulsion system, and studied for the photodecomposition property of methylene blue. Microemulsion (ME) consisted of water, cyclohexane or octane, and surfactant, such as polyoxyethylene (10) octylphenyl ether (TX-100), polyoxyethylene lauryl ether, or bis (2-ethylhexyl) sodium sulfosuccinate. Titanium tetraisopropoxide (TTIP) was dropped into the ME solution and then titania particles were formed by the hydrolysis reaction between TTIP in the organic solvent and the water in the core of ME. It was found that ME could be classified to the reversed micelle (RM) region and the swelling reversed micelle (SM) region according to the water content. The water droplets in RM were almost monodispersed, where the water content was small. On the other hand, the water droplets in SM had a size distribution, although most of the water molecules associated with surfactant molecules. The size of the particles prepared in the RM region was smaller than the ME size. In contrast, the size of the particles formed in the SM region was larger than the ME size, and coagulation of the particles was observed within a few hours. The smallest diameter of the particles was 2 nm in the system of cyclohexane with TX-100 surfactant when the molar ratio of water to surfactant was 2. Titania particles prepared in this condition were collected as amorphous powder, and converted to anatase phase at less than 500 K, which is lower than the ordinal phase transition temperature. These anatase phase titania particles only showed a significant photodecomposition of methylene blue by illumination with a Xenon lamp.     

Optical properties of silicon nanoparticles synthesized via electrical spark discharge in water

In this paper, we report a simple and low-cost technique for fabrication of silicon nanoparticles via electrical spark discharge between two plane silicon electrodes immersed in deionized water (DI). The pulsed spark discharge with the peak current of 60 A and a duration of a single discharge pulse of 60 μs was used in our experiment. The structure, morphology, and average size of the resulting nanoparticles were characterized by means of X-Ray Diffraction (XRD), Raman spectroscopy and transmission electron microscopy (TEM). TEM images illustrated nearly spherical and isolated Si nanoparticles with diameters in the 3–8 nm range. The Raman peaks of the samples were shifted to the lower wave numbers in comparison to this of bulk crystalline silicon indicating the existence of tiny particles. The optical absorption spectrum of the nanoparticles was measured in the violet–visible (UV–Vis) spectral region. By measuring of the band gap we could estimate the average size of the prepared particles. The silicon nanoparticles synthesized exhibited a photoluminescence (PL) band in the violet-blue region with a double peak at around 417 and 439 nm. It can be attributed to oxide-related defects on the surface of silicon nanoparticles, which can act as the radiative centers for the electron-hole pair recombination.     

Synthesis and Characterization of Multi-layered Core/Shell Particles by Sequential Emulsion Polymerization

A series of core/shell particles were prepared by sequential emulsion polymerization. The core/shell particles consisting of poly(methyl methacrylate) core grafted with using rubbery layer [poly(butyl acrylate)co-(styrene)] and then glassy layer [poly(methyl methacrylate)-co-(ethyl acrylate)] were prepared. The conditions which led to controlled particle size and morphology were discussed. A highly cross-linked structure was formed in both the cores and the shells by using a cross-linking agent, which could prevent the migration of hydrophobic shells to the inside of the particles. The core/shell particles were characterized by Fourier-transform infrared spectroscopy, solid state ¹³C-NMR. Thermogravimetric analysis (TGA) and differential scanning calorimeter (DSC) were used to determine the thermal stability and glass transition temperature of the core/shell particles, respectively. Results of the particle size analysis indicate that particle sizes were decreased when there is a rubbery layer as outer layer (0.44 μm) whereas it increases when there is a glassy layer as outer layer (324 μm). Scanning electron microscopy (SEM) also confirms the multi-layers formation in the polymer.     

Electrochemical performance of surfactant-processed LiFePO4 as a cathode material for lithium-ion rechargeable batteries

This study focuses on the effect of addition of surfactant as a dispersing agent during vibratory ball milling of LiFePO₄ (LFP) precursor materials on the electrochemical performance of solid-state reaction synthesized LFP for lithium-ion battery cathode material. LFP particles formed after calcinations of ball milled LFP precursors (Li₂CO₃, FeC₂O₄, and NH₄H₂PO₄) showed better size uniformity, morphology control, and reduced particle size when anionic surfactant (Avanel S-150) was used. The specific surface area of LFP particles increased by approximately twofold on addition of surfactant during milling. These particles showed significantly enhanced cyclic performance during charge/discharge due to a reduced polarization of electrode material. Electrodes fabricated from LFP particles by conventional milling process showed a 22 % decrease in capacity after 50 cycles, whereas the performance of electrode prepared by surfactant processed LFP showed only 3 % loss in capacity. The LFP particles were characterized using XRD, FE-SEM, particle size distribution, density measurement, and BET-specific surface area measurement. Electrochemical impedance spectra and galvanostatic charge/discharge test were performed for the electrochemical performance using coin-type cell.     

Experimental study on parameters of dust plasma in SiH4/C2H4/Ar discharges

Measurements of dust plasma parameters were carried out in the discharges of （SiH4/C2H4/Ar） mixtures. Dust particles were formed in the capacitively coupled radio-frequency discharge of these reactive mixtures in a cylindrical chamber. Langmuir probe was employed for diagnosing and measuring the important plasma parameters such as electron density and electron temperature. The results showed that the electron density dropped, and in contrast the electron temperature rose when the dust particles formed. The curves of the electron density and temperature versus the RF power and pressure were presented and analysed. Further, it was found that the wriations of electron temperature and the size of dust void with the RF power followed the similar trends. These trends might be useful for understanding more about the characteristics of dusty voids.     

Revealing of water surface pollution with liquid marbles

Floating of “liquid marbles” on the surface of water contaminated with organic compounds was studied. Marbles were obtained with spreading of hydrophobic polyvinylidene fluoride particles on the surface of water droplets. Marbles floated stably on the water surface, whereas they were destroyed on the water surfaces contaminated with silicon oil and kerosene. Limiting conditions of floating were studied experimentally with the water/alcohol mixtures.     

用激光解吸附电离飞行时间质谱法检测悬浮土壤颗粒物

在自行研制的气溶胶飞行时间激光质谱仪(ATOFLMS)上实时探测单个悬浮土壤颗粒的粒径和化学成分。利用双束连续激光对单个粒子的空气动力学粒径进行测量,并用266 nm的Nd∶YAG激光器对气溶胶单粒子进行解吸附电离作用,产物离子通过飞行时间质谱仪的无场漂移区后完成单粒子化学成分的检测。本实验中使用了4个不同地区的土壤样本,在实验室内对分析的样本进行预处理和再悬浮,通过导管引入ATOFLMS进行测量,得到大量单粒子的粒径和质谱数据。发现在众多的单粒子的阳离子质谱中,金属成分以地壳元素(Fe, K, Al, Ca)为主,在其他阳离子质谱中包含了Mg和Na等。对悬浮土壤粒子的粒径进行实时检测的结果表明这些粒子多以粗粒子为主, 粒径主要集中在1～2 μm。实验结果表明该仪器在大气气溶胶环境监测及相关研究领域具有重要的实用价值。     

Influence of Liquid Medium on Optical Characteristics of the Si Nanoparticles Prepared by Submerged Electrical Spark Discharge

We have measured the size, structure, and optical properties for two sets of nanoparticles synthesized via electrical-spark discharge between two plane silicon electrodes immersed in deionized water (DI) and 97 % ethanol. The nanoparticles were characterized by X-ray diffraction (XRD), ultraviolet (UV)-visible absorption spectrometry, Raman spectrometry, transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FTIR). The size and optical features of the nanoparticles were studied as functions of nature of the liquid. Nearly spherical, single-crystal, and morphologically similar Si nanoparticles with diameters in the 3–8 and 6–13 nm ranges were formed in the colloidal solutions of water and ethanol, with estimated indirect bandgaps of approximately 1.5 and 1.3 eV, respectively. In both cases, the Raman peaks were blue shifted with respect to those of bulk silicon, a result consistent with the small diameters of the particles. The silicon nanoparticles synthesized in water exhibited strong emission in the violet-blue range, with a double peak near 417 and 439 nm. For those synthesized in ethanol, blue-green emission centered at 463 nm was detected.     

Preparation of magnetic nanoparticles by pulsed plasma chemical vapor synthesis

FePt nanoparticle is expected as a candidate for the magnetic material of the high density recording media. We attempted to synthesize FePt alloy nanoparticles using 13.56 MHz glow discharge plasma with the pulse operation of a square-wave on/off cycle of plasma discharge to control the size of nanoparticles. Vapors of metal organics, Biscyclopentadienyl iron (ferrocene) for Fe and (Methylcyclopentadienyl) trimethyl platinum for Pt, were introduced into the capacitively coupled flow-through plasma chamber, which consisted of shower head RF electrode and grounded mesh electrode. Synthesis experiments were conducted at room temperature under the conditions of pressure 0.27 Pa, source gas concentration 0.005 Pa, gas residence time 0.5 s and plasma powers 60 watts. Pulse width for plasma duration was chosen from 0.5 to 30 s and plasma off period was 4 s to each pulse operation. Visual observations during the particle growth showed plasma emission in the bulk region was increased with the particle growth. These were theoretically explained by using the model for both transient particle charging in the plasma and single particle behavior in the stationary plasma as well as assuming the similarity between the negative charged particle and negative gas containing plasma. Synthesized nanoparticles were directly collected onto TEM grid, which was placed just below the grounded mesh electrode in the plasma reactor downstream. TEM pictures showed two kinds of particles in size, one of which was nanometer size and isolated with crystal structures and the other appeared agglomerate of nanometer size particles. The size of agglomerated particle was controlled in the 10–120 nm range by varying the plasma-on time from 0.5 to 30 s, although the nanometer size particles did not change. The composition of FePt alloy particles could be altered by adjusting the source gas feed ratio. Also magnetization of FePt nanoparticles was measured by use of SQUID (superconducting quantum interference device) magnetometry measurements. As-synthesized FePt nanoparticles did not exhibit loop-shape characteristic, which indicated superpamagnetic property. Annealed nanoparticles with the composition of Fe₅₈Pt₄₂ at 650°C in atmospheric hydrogen showed clear hysterisis loop with the coercivity as large as 10 KOe.     

Influence of particle size on the breaking of aluminum particle shells

Rupturing the alumina shell (shell-breaking) is a prerequisite for releasing energy from aluminum powder. Thermal stress overload in a high-temperature environment is an important factor in the rupture of the alumina shell. COMSOL Multiphysics was used to simulate and analyze the shell-breaking response of micron-scale aluminum particles with different particle sizes at 650 ℃ in vacuum. The simulation results show that the thermal stability time and shell-breaking response time of 10 μm-100 μm aluminum particles are 0.15 μs-11.44 μs and 0.08 μs-3.94 μs, respectively. They also reveal the direct causes of shell breaking for aluminum particles with different particle sizes. When the particle size is less than 80 μm, the shell-breaking response is a direct result of compressive stress overload. When the particle size is between 80 μm and 100 μm, the shell-breaking response is a direct result of tensile stress overload. This article provides useful guidance for research into the energy release of aluminum powder.