Low-voltage Spark Discharge Research Articles

Experimental evaluation of methodologies for single transient cavitation bubble generation in liquids

Single bubble dynamics are of fundamental importance for understanding the underlying mechanisms in liquid–vapor transition phenomenon known as cavitation. In the past years, numerous studies were published and results were extrapolated from one technique to another and further on to “real-world” cavitation. In the present paper, we highlight the issues of using various experimental approaches to study the cavitation bubble phenomenon and its effects. We scrutinize the transients bubble generation mechanisms behind tension-based and energy deposition-based techniques and overview the physics behind the bubble production. Four vapor bubble generation methods, which are most commonly used in single bubble research, are directly compared in this study: the pulsed laser technique, a high- and low-voltage spark discharge and the tube arrest method. Important modifications to the experimental techniques are implemented, demonstrating improvement of the bubble production range, control and repeatability. Results are compared to other similar techniques from the literature, and an extensive report on the topic is given in the scope of this work. Simple-to-implement techniques are presented and categorized herein, in order to help with future experimental design. Repeatability and sphericity of the produced bubbles are examined, as well as a comprehensive overview on the subject, listing the bubble production range and highlighting the attributes and limitation for the transient cavitation bubble techniques.Graphic abstract

Spark-generated bubble near an elastic sphere

The interaction between a spark-generated bubble and an elastic sphere is investigated. A spark-generated bubble is created at various distances horizontally away from a suspended elastic sphere made of silicone rubber or super absorbent polymer (of shear modulus of elasticity G of between 5 and 312kPa), using a low-voltage spark discharge method. We observe pronounced deformation and elongation of the elastic sphere when the spark-bubble is generated very close to a sphere. This happens when the elastic sphere has a small modulus of elasticity and a small size ratio R’ between the bubble and the elastic sphere (i.e. the bubble and the sphere have similar radii). Numerical simulations are also conducted using a Boundary Element Method (BEM) model coupled with a Finite Element Method (FEM) solver. The simulation results compare well with the experimental data. The numerical model is then extended to study the effects of elasticity and experimental parameters, such as the dimensionless stand-off distance H’, and size ratio R’, on the degree of deformation of the elastic cell and the dynamics of the bubble.

Synthesis of Hollow Carbon Nano-Onions Using the Pulsed Plasma in Liquid

We synthesized carbon nano-onions (CNOs) using a low-voltage spark discharge in a liquid and studied the effects of liquid type and pulse duration. By the pulsed electric discharge between two graphite rods of 120 mm length and 6 mm diameter submerged into a 200 ml toluene or ethanol, hollow CNOs with diameters ranging from 10 to 30 nm were produced. CNOs produced using toluene grew more carbon shells than does the sample produced using ethanol. The sample that was synthesized using pulsed plasma with pulse duration of 5 μs showed more carbon shells (10-30) than the sample prepared by 12 μs (2 to 10). High performance liquid chromatography (HPLC) and high resolution transmission electron microscopy analyses confirmed that the sample produced at 12 μs pulsed plasma contains fullerene C60, while the sample prepared at 5 μs does not.

Magnetite Nanoparticles Synthesized Using Pulsed Plasma in Liquid

Iron oxide nanoparticles have attracted much attention over the last few years owing to their fundamental importance and technological applications. In this work, spherical ferromagnetic Fe3O4 nanoparticles with an average diameter of 19 nm were synthesized by a simple and one-step method, pulsed plasma in liquid. Pulsed plasma, induced by a low-voltage spark discharge, was submerged in a dielectric liquid at a voltage of 200 V, a current of 6 A, a frequency of 60 Hz, and a single discharge duration of 10 µs. Water with different concentrations of 1-hexadecylpyridinium bromide (CPyB) was applied as a liquid, and several experiments made evident that the surfactant concentration affects the phase compositions of the produced materials. The purity of the magnetite phase in the sample increased (from 65 to 98%) with increasing CPyB concentration (from 0.10 to 0.84 g) in 200 ml of water. The crystal structure of magnetite (Fe3O4) nanoparticles with the Fd3̄m space group and a lattice parameter of a = 0.8393 nm was evident from X-ray diffraction results. Magnetite nanoparticles were investigated further by high-resolution transmission electron microscopy/energy-dispersive spectroscopy and thermogravimetrical analysis, and using a vibrating sample magnetometer.

Onion-like carbon-encapsulated Co, Ni, and Fe magnetic nanoparticles with low cytotoxicity synthesized by a pulsed plasma in a liquid

We synthesized onion-like carbon-encapsulated Co, Ni, and Fe (Co–C, Ni–C, and Fe–C) magnetic nanoparticles with low cytotoxicity using pulsed plasma in a liquid. The pulsed plasma is induced by a low-voltage spark discharge submerged in a dielectric liquid. The face-centered cubic Co and Ni, and body-centered cubic Fe core nanoparticles showed good crystalline structures with an average size between 20 and 30nm were encapsulated in onion-like carbon coatings with a thickness of 2–10nm. Vibrating-sample magnetometer measurements revealed the ferromagnetic properties of as-synthesized samples at room temperature (Co–C=360Oe, Fe–C=380Oe, and Ni–C=211Oe). Raman-spectroscopy analysis found onion-like carbon shells composed of well-organized graphitic structures. Thermal gravimetric analysis showed a high stability of the as-synthesized samples under thermal treatment and oxidation. Cytotoxicity measurements showed higher cancer cell viability than samples synthesized by different methods.

Wide-aperture plasma jet source based on low-voltage spark discharge with ferroelectric electrode

Low-voltage vacuum spark discharge initiated at a storage capacitor voltage of 75–600 V using a metal grid cathode situated on the front surface of a polarized ferroelectric (FE) electrode has been experimentally studied. The discharge was initiated when a control voltage pulse with an amplitude of 1 kV and a duration of 100 ns at only negative polarity was applied to the rear FE surface (irrespective of the direction of its polarization vector). Optical measurements showed that the emitting surface area on the cathode increases approximately in proportion to the discharge voltage. According to the collector measurements, the ion plasma flux has slow and fast components, the velocities of which remain almost constant when the discharge current amplitude varies in a wide interval.

Nanorods of Metallic Bismuth and Antimony by the Impulse Plasma in Liquid

A new synthesis method of nanomaterials using the impulse plasma in liquid by the low voltage spark discharge is presented. The bismuth and antimony nanopowders were for the first synthesized by electric discharge method in liquid. The impulse plasma in liquid enables us to quench from plasma state, by which we can synthesize nanomaterials, nanorods, etc. In addition, the applied power is 100 times smaller than those of arc discharge. The possibility of obtaining nanorods of metallic bismuth and antimony by the impulse plasma in liquid between two electrodes from corresponding metal is presented.

Synthesis Method of Nanomaterials by Pulsed Plasma in Liquid

A new synthesis method of nanomaterials using pulsed plasma in liquid by the low voltage spark discharge is presented. The fullerene C60 and TiO nanopowder were for the first time synthesized by electric discharge method in liquid. The purity of C60 was >99%, which is much higher than those by the conventional arc plasma in inert gas methods (less than 80% C60 and 20% C70 and other fullerenes). Copper nanoparticles prepared by this method were smaller than those by arc method by a factor of >5. The pulsed plasma in liquid enables us to quench from plasma state, by which we can synthesize nanomaterials, metastable materials, etc. In addition, the applied power is 100 times smaller than those of arc discharge.

Dynamics of the continuum radiation of a low-voltage spark-discharge plasma

We have measured the absolute continuum-intensity reproducibility, wavelength distribution, and radial and time dependences of the continuum radiation intensity for a multicomponent plasma formed by a low-voltage spark discharge. The data are analyzed theoretically. Limiting characteristics of the discharge for analytical spectroscopy, as determined by the continuum, are also discussed.

発光分光用低圧火花放電を噴霧源とする固体金属試料のICP発光分光分析

A low voltage spark discharge has been investigated as an aerosol generator of metal samples for ICP emission spectrometry. Fine particles of aluminum alloys could be produced by low voltage spark discharge in argon atmosphere, and more intense specral lines could be observed by introduction of the aerosol into the ICP plasma, compared with low voltage spark excitaition. A calibration curve of high silicon concentration, which was difficult to dissolve into solution, was obtained when a series of reference samples were available.

Effect of Pores in Sample Electrode Prepared by Powder Metallurgy on Emission Spectrochemical Analysis. II.

A high voltage spark discharge was used to study and reduce the effect of pores in the sample electrodes (pure metals; Fe, Cu, Ni, Al and alloys), which were prepared by powder metallurgy, on the intensity of spectral lines. According to the experimental results, the effect of pores on the intensity varied with the discharge current. In case of the discharge of large current, the more the pores in the sample, the stronger the intensity, while in case of the discharge of small current, the weaker the intensity. No variation of the Fe I and Ni I lines intensity with the pore amount in Fe-Ni alloys was found under a dicharge condition of moderate current (4.6 A). Generally speaking, the effect of pores can be reduced by using the high voltage spark discharge instead of the low voltage spark discharge.

Effect of low-voltage spark discharge parameters on the spectral line intensities of sulfur and halogens

The influence of various circuit parameters on the spectral line intensities of sulfur and the halogens when excited in a low-voltage spark discharge have been investigated. The intensities were maximum for a discharge current of 6–8 A and a 1.0–1.5 mm spark gap. In ac spark discharges the maximum intensities occurred with capacitances of 20–50μF and an inductance of 15μH for primary circuit resistance of 200 ohm, and with 50–100μF and 30–60μH for 400 ohm. The intensities attained with dc sparks were higher than those with ac sparks. The intensity increased if the specimen served as the cathode and, in this case, occurred with capacitances of 100–800μF and inductances of 30–60μH for an ignition frequency of 12 sec−1.

Effect of Heat Treatment in Spectrochemical Analysis of Steels

By using a quantometer, Si-Mn steels differing in metallurgical history, that is quenched, tempered and untreated, are excited by low voltage spark discharge (C=12μF, L=50μIH, R=5Ω, V=940V) and by high voltage spark discharge (C=0.007μF, L=0, R=residual, V=15kV).Effect of heat treatment on the result of analysis is significant for alloying elements Si and Mn, but not for impurity elements Ni, Cr and Cu.With low voltage spark discharge, quenched samples give analytical values higher than tempered and untreated samples;with high voltage spark discharge, the result is reversed.