Формирование микроканальной структуры искрового разряда в воздухе в промежутке острие-плоскость"

The formation of the microchannel structure of a spark discharge in the gap spike (cathode)-plane of 1.5 mm length in the air of atmospheric pressure was studied by the method of shadow photography. The images with the concurrent descent of microchannel diameter sand the number of microchannel increase in the cathode region on the time interval of 5 ns were recorded. The obtained data are explained in the frames of the microstructure formation mechanism at the expense of the front instability of the ionization wave. The parameters characterizing the process of the microstructure formation are estimated, and they agree with the experimental data.

Микроволновая диагностика разрядов в искусственном облаке заряженных водяных капель

The microwave diagnostics of discharges occurring in an artificial cloud of charged water droplets created in an open air simulating the environment of thunderclouds is implemented. An artificial cloud with a droplet size of about 1 microns is opaque in the visible range, so intra-cloud discharges are not available for investigation by traditional methods in the spark discharge physics based on the registration of visible discharge radiation. Microwaves pass through such a cloud without noticeable attenuation, they interact only with the plasma of discharges occurring in the cloud. The probing microwave radiation had a wavelength of 8 mm. The attenuation of microwaves passed through the cloud was measured with temporary resolution of about 10 ns. The temporal characteristics of intra-cloud discharges were investigated.

A Study of Fabricating Nano-W Colloid by Discharge Energy Enhancement of the micro-EDM System

This study enhanced the discharge energy of an existing micro-electric discharge machining (EDM) system to provide the system with the ability to prepare nano-tungsten (nano-W) colloid. The energy- enhanced EDM system, referred to as the upgraded-micro-EDM system, enables spark discharge using tungsten wires immersed in deionized water to produce nano-W colloids. Compared with the chemical preparation method, the processing environment for preparing colloids will not have nanoparticle escape in this study. Among the nano-W colloids prepared using the upgraded-micro-EDM system and an industrial EDM system, the colloid prepared by the upgraded-micro-EDM system exhibited more favorable absorbance, suspensibility, and particle size. The colloid prepared by the upgraded-micro-EDM system with the pulse on time and off time of 10–10 µs had an absorbance of 0.277 at the wavelength of 315 nm, ζ potential of −64.9 mV, and an average particle size of 164.9 nm. Transmission electron microscope imaging revealed the minimum particle size of approximately 11 nm, and the X-ray diffractometer spectrum verified that the colloid contained only \({\text{W}}_{2.00}\) and W nanoparticles. Relative to industrial EDM applications for nano-W colloid preparation, the upgraded system boasts lower costs and smaller size, and produces nano-W colloid with superior performance. These advantages contribute to the competitiveness of electrical spark discharge method in the preparation of high-quality nano-W colloids.

Synthesis of gold nanoparticles by the spark discharge method for visible plasmonics

This work demonstrates synthesis of metal Au nanoparticles with a plasmon resonance in the visible optical region by the spark discharge method in atmosphere of argon of purity 6.0. With raising of sintering temperature from 25 to 950 °C, the morphology of synthesized Au nanoparticles changed from agglomerates to individual particles with decreasing the median size from 270 to 90 nm according to aerosol spectrometer. While by transmission electron microscopy primary nanoparticles with a gold crystalline structure with sizes in range from 5 to 120 nm were observed. Synthesized nanoparticles ensembles had broad absorption peaks with maximum in the visible optical region with peak positions approximately at 490 nm. High temperature sintered particles had a spherical shape and an additional absorption peak at approximately 640 nm.

Investigation of laser and thermal sintering processes of silver nanoparticles agglomerates synthesized by spark discharge

Changes in the shape and size of silver nanoparticles (NPs) during their laser and thermal sintering have been studied experimentally and theoretically. Aerosol silver NPs forming dendrid-like agglomerates 180 nm in size were synthesized by spark discharge and exposed to laser radiation and high temperature of 750 °C. The shape and size of the NPs were investigated depending on the power of the laser radiation and the temperature of the gas. It is estimated that, at a power density of laser radiation of the order of 103-104 W/cm2, the formation of spherical NPs with an average size of 140 nm is expected. Such particles turn out to be similar to NPs thermally heated in a gas flow at 750 °C for 6 seconds.