Влияние предыонизации на микроканальную структуру искрового разряда в воздухе в промежутке острие-плоскость

The initial phase of a spark discharge in the gap between the pin (cathode) and a plane 1.5 mm long in atmospheric pressure air under conditions of preliminary photoionization by an auxiliary discharge was investigated by the method of shadow photography. In the absence of preionization, the discharge from the first nanoseconds after breakdown is an aggregate of a large number of micron-diameter channels. It was found that the electron concentration resulting from preionization, estimated at 108  109 cm-3, increases the degree of uniformity of the discharge channel in the near-cathode region; however, in the near-anode region, the channel remains microstructured. Within the framework of the mechanism of microstructure formation due to the instability of the ionization wave front, a criterion for the formation of a uniform discharge is obtained and an explanation of the results obtained is presented.

Dynamics of macro- and micro-bubbles induced by nanosecond discharge in liquid water

Gaseous micro-bubbles dispersed in liquid water represent perturbations of the homogeneity of the liquid and influence the onset of electrical discharge in the bulk liquid. In this study, we systematically examined shadowgraph images to analyse the gaseous structures occurring in response to nanosecond micro-discharges produced in deionised water. The images revealed the dynamics of resolved bubbles and unresolved sub-micrometric structures starting from nanoseconds after the onset of discharge. We provide absolute counts and the radii distributions of micro-bubbles that occur near the anode needle and show how this depends on the amplitude and repetition frequency of the applied high-voltage pulses, when the latter varies between 0.1 and 100 Hz. A systematic statistical analysis showed that the probability of producing bubble-assisted nanosecond discharge in the liquid phase rapidly increases with the discharge repetition rate (>0.5 Hz). Although the cavitation bubble formed around the anode disintegrates and disappears from the anode region within the first millisecond, the sub-micrometric structures remain for tens of milliseconds, and fragmented micro-bubbles survive even for hundreds of milliseconds. Our findings impose strict limitations on the experimental setups used to investigate the mechanisms of direct discharge in liquid water.

Deposition of Al2O3 coatings in Ar-O2 low-pressure discharge plasma under a high dissociation degree of O2

The deposition of Al2O3 coating with a corundum structure was done by anodic evaporation in a low-pressure arc with a self-heated hollow cathode. The conditions were created for increasing the energy of plasma electrons and a corresponding increase in the frequency of O2 dissociation by contraction of the discharge in the anode region. The discharge was maintained in a combined mode with a constant current (70 – 100 A), on which current pulses (100 μs, 1 kHz) with adjustable amplitude (up to 220 A) were superimposed. This mode ensured a change in the degree of O2 dissociation in the range of 0.3 – 0.5 at constant average discharge current and Al evaporation rate. It is shown that an increase in the degree of O2 dissociation leads to an increase in the rate of coating deposition by a factor of 1.3 and promotion of the preferred (300) orientation of crystallites. The effect is due to the features of the adsorption of molecular and atomic oxygen on the Al2O3.

Exploration of collagen cavitation based on peptide electrolysis

Electrochemical modification of animal skin is a new material preparation method and new direction of research exploration. In this study, under the action of the electric field using NaCl as the supporting electrolyte, the effect of electrolysis on Glycyl-glycine(GlyGl), gelatin(Gel) and Three-dimensional rawhide collagen(3DC) were determined. The amino group of GlyGl is quickly eliminated within the anode region by electrolysis isolated by an anion exchange membrane. Using the same method, it was found that the molecular weight of Gel and the isoelectric point of the Gel decreased, and the viscosity and transparency of the Gel solution obviously changed. The electrolytic dissolution and structural changes of 3DC were further investigated. The results of TOC and TN showed that the organic matter in 3DC was dissolved by electrolysis, and the tissue cavitation was obvious. A new approach for the preparation of collagen-based multi-pore biomaterials by electrochemical method was explored.

Nanometer-thin pure boron CVD layers as material barrier to Au or Cu metallization of Si

Metallization layers of aluminum, gold, or copper are shown to be protected from interactions with silicon substrates by thin boron layers grown by chemical-vapor deposition (CVD) at 450 °C. A 3-nm-thick B-layer was studied in detail. It formed the p+-anode region of PureB diodes that have a metallurgic junction depth of zero on n-type Si. The metals were deposited by electron-beam-assisted physical vapor deposition (EBPVD) at room temperature and annealed at temperatures up to 500 °C. In all cases, the B-layer was an effective material barrier between the metal and Si, as verified by practically unchanged PureB diode I–V characteristics and microscopy inspections of the deposited layers. For this result, it was required that the Si surface be clean before B-deposition. Any Si surface contamination was otherwise seen to impede a complete B-coverage giving, sometimes Schottky-like, current increases. For Au, room-temperature interactions with the Si through such pinholes in the B-layer were excessive after the 500 °C anneal.

Study of anode spot transient processes of a high-current vacuum arc with high-speed spectroscopy and videorecording

The processes of plasma formation in the anode region of a high-current vacuum arc discharge are of high actuality in terms of improving the switching characteristics of vacuum circuit breaker. In present paper the dynamics of the radiation spectrum of anode region was recorded with the system that allows time scanning of a spectrum. In parallel, there was high-speed videorecording. The obtained data clearly show changes in the charge composition of the anode spot plasma in the process of changing discharge forms.