Characteristics of Gas-Discharge Plasma-Chemical Reactor with Synthesis of Colloidal Solutions of Metal Oxide Nanoparticles

Shuaibov A, Minya A, Malinina A, Malinin A, Gomoki Z and Danilo V

Published on: 2019-06-20

Abstract

The article presents the electrical and optical characteristics of high-current discharges of nanosecond duration in the air between the electrodes of metal blades and the surface of solutions of copper and zinc salts in distilled water. The conditions for stable ignition of nanosecond discharges of atmospheric pressure, their spatial, electrical and optical characteristics are established. It has been shown that they are promising for the synthesis of colloidal solutions of nanostructures based on copper and zinc oxides in volumes of the order of 1 litre or more.

Keywords

Nanosecond discharge; Plasma; Air; Water; Solutions of copper and zinc salts; Nanostructures; Radiation spectrum; Oscillograms of voltage and current pulses; Energy input into the plasma

Introduction

Atmospheric pressure glow discharges in the air between metal and liquid electrodes are distinguished by the ease of implementation and control of plasma parameters, low cost of output materials, a large number of practical applications in plasma chemistry for the synthesis and conversion of chemical compounds in the discharge volume and on the surface of the liquid, in ecology for water and air purification, in medicine, agriculture, food industry for disinfection, sterilization due to the manifestation of bactericidal and fungicidal properties with contactless, wasteless local action at treatment and modification of surfaces of various materials for the synthesis of nanoparticles and spectral analysis of solutions. Experimental and theoretical studies of discharges with one or two liquid electrodes [1-3] carried out at present are insufficient to explain the entire set of phenomena occurring in its positive column, as well as in the near-electrode regions. Such discharges are unique as objects for a comprehensive study of physico-chemical phenomena from the standpoint of plasma chemistry, electrochemistry, radiation chemistry, gas discharge physics and emission electronics. Of course, the properties of such systems depend not only on the properties of the liquid and metal electrodes, but also on the gas phase. The amount of experimental data on plasma characteristics and parameters of nanosecond discharges in air at atmospheric pressure between the metal and liquid electrode is limited. In particular, the possibility of synthesizing colloidal solutions based on nanostructures of metal oxides in a macroscopic quantity (with a volume of more than 1 litre) and the characteristics of pulsed discharges between metallic and electrolytic (solutions of copper, zinc and iron salts in distilled water or ethyl alcohol) electrodes has not been clarified. Currently, there is considerable interest in plasma-solution technologies, which are already widely used for applying various coatings, purifying water and stimulating chemical reactions [4-6]. However, work in continuous mode with currents greater than 0.1 A causes heating of liquid electrodes, requires the inclusion of a liquid cooling system in a plasma-chemical reactor, and the density of electrons in such a plasma does not exceed 1012-1013 cm-3 [4,7,8]. Therefore, to increase the discharge current, the electron density and the electrolyte area that can be processed by the plasma, it is promising to translate the operation of gas discharge systems with electrolytic electrodes into a pulsed mode of operation [9-11].

A special place among discharges with liquid non-metallic electrodes is occupied by a nanosecond discharge between the tip-based electrode system and the liquid surface, which can be stably ignited in the air at atmospheric pressure without using pre-ionization systems [12]. Such a discharge is a powerful source of ultraviolet radiation and strong oxidants such as ozone, hydrogen atoms, oxygen, and hydroxyl radicals that penetrate the liquid electrode and can process a sufficiently large surface of the liquid. Compared to underwater nanosecond discharges, there is much less erosion of metal electrodes and a larger plasma volume. In [12], hig h efficiency of water purification from impurities was established when a nanosecond corona discharge was applied between the tip system and the solution surface. From a technological point of view, it may be promising to replace a large number of needles with a system of knife electrodes (blades), which contributes to an increase in the uniformity of such discharges. From the point of view of the possibility of synthesizing nano carbon, it is of interest to study the characteristics of a nanosecond discharge between a knife electrode and a solution of alcohol in water, and for the synthesis of colloidal solutions based on nanostructures of transition metal oxides of the discharge over the surface of solutions of corresponding salts in distilled water. This article presents the results of systematic studies of the characteristics of nanosecond discharges in air at atmospheric pressure between the edges of metal blades and the surface of solutions of copper and zinc salts in distilled water, which are promising for the synthesis of transition metal oxide nanostructures.

Methods and Technique of the Experiment

A pulse-periodic nanosecond discharge above the surface of an aqueous solution of zinc chloride was implemented in a discharge cell with a system of electrodes: the “blade- blade” scheme, which is shown in (Figure 1) [13,14]. This electrode system is mounted on the top flange of the cell. The distance between the electrodes could be varied with the help of rotating electrodes.

In the experiment, the distance between the blades and the surface of the solution varied within 1 ... 5 mm. The level of the working liquid was maintained using a drip system. The working liquid was an aqueous solution of zinc chloride. A nanosecond power supply with a pulse repetition rate of 35 ... 1000 Hz and a bipolar voltage of 15 ... 40 kV was used to excite the discharge. Due to the rotation of the blades around the axis of attachment, the distance between them changed within 5 ... 80 mm. The cuvette is made of organic glass. The wall thickness was 8 mm, the internal dimensions of the cell were 100 × 100 × 100 (mm). The electrodes were made of metal blades, 0.1 mm thick. The discharge cell is located in a metal screen in order to reduce the influence of electromagnetic fields on the registration system of spectral characteristics. To study the characteristics of a nanosecond pulsed discharge over the surface of a liquid, an experimental setup was used, the block diagram of which is given in [15].

The circuit of the discharge module for ignition of the discharge in the system "metal blades-liquid surface" is shown in (Figure 2). The experimental conditions are described in more detail in [9,16]). A transverse nanosecond discharge over the surface of 

distilled water and solutions was ignited in a plexiglas cuvette between a metal blade system and a massive stainless steel electrode immersed in a liquid. The distance between the blades and the surface of the liquid ranged from 3 to 12 mm, and the distance between the flat metal electrode of stainless steel and the liquid surface was 4 mm. The electrode, which was installed in the air above the surface of the liquid, consisted of 15 stainless blades 0.1 mm thick. The distance between the blades was 1.5 mm. The working surface area of the electrode based on the blade system was 37 × 22 mm2. The metal electrode immersed in the liquid had dimensions 60 × 40 × 14 mm. Pulsed-periodic nanosecond discharge fired up in both discharge modules using a source of bipolar high-voltage nanosecond voltage pulses with a resonant recharge of the storage capacitor 1.54 nF and a hydrogen thyratron switch. When a pulsed power supply system was connected to electrodes with a full voltage pulse duration of 150 ns for a capacitive load consisting of a flat capacitor where the role of a dielectric is performed by a liquid, a set of high-voltage pulses of different polarity was formed.

The amplitude of the voltage pulses of single polarity at the output of the high-voltage modulator can vary in the range of 10-25 kV with the duration of an individual peak at the level of 10-15 ns. The amplitude of the main peak of the current pulse reached 100-170 A. The frequency of the next bursts of nanosecond bipolar voltage and current pulses could vary in the range of 35-1000 Hz. Plasma radiation was recorded in the spectral range λ = 196-663 nm using a 1200 lines / mm spectrometer with a diffraction grating. At the output of the spectrometer, a FEP-106 photomultiplier connected to a DC amplifier was used to record the radiation, the signal from which came to the analog-to-digital converter and then served for processing on a personal computer. Adjustment of the system was carried out in two stages. At the first stage, all elements of the system were installed on the optical 

axis, namely, the discharge cell, the lens and the slit of the monochromator. A helium-neon laser was used at this stage. The laser beam was focused at the middle of the slit and perpendicular to it. The discharge cell was located in such a way that the laser beam passed between the electrodes. The lens was located between the slit and the discharge cell so that the beam passes through its center. At the second stage, focusing was carried out using a discharge radiation lens on a monochromator slit. With the unit turned on, it was impossible to focus the discharge glow due to the danger of electric shock. Therefore, the simulation of the discharge plasma glow was carried out by an LED that was placed in the interelectrode gap. The exact focusing of the plasma radiation on the slit of the monochromator was carried out according to the intensity of the glow at a certain wavelength. To evaluate the energy input in the discharge plasma, oscillograms of current, voltage and luminescence were recorded using a 6-channel wideband oscilloscope 6LOR-04. The voltage pulses on the electrodes were fed through a capacitive divider to the first channel of the oscilloscope. Current pulses through the calibrated Rogowski coil were fed to the second channel of the oscilloscope.

Characteristics of the nanosecond discharge above the surface of distilled water

Typical characteristics of a nanosecond high-current discharge between a metal blade system and the surface of distilled water in atmospheric pressure air, the discharge module circuit for which is shown in (Figure 1), are shown in (Figures 3 and 4). Using this discharge module, a method of ignition of a spatially uniform discharge was implemented in air at atmospheric pressure, including the supply of high-voltage pulses of nanosecond duration to a metal and liquid electrode, which was distinguished by the following way: to form air plasma enriched by water vapor that radiates in ultraviolet region of the spectrum and is the source of hydroxyl radicals, hydrogen atoms and oxygen was used bipolar nanosecond discharge system between the metal blades and the surface of the liquid, which allows to obtain a uniform sheet plasma from each blade. When applying nanosecond voltage pulses with an amplitude of ± (20-40) kV to the electrodes of the device, a discharge in the form of fifteen homogeneous plasma sheets was ignited between the tips of the blades and the surface of the water electrode. Plasma sheets were homogeneous with an interelectrode distance in the range of 3-12 mm. In (Figure 3) images of a nanosecond discharge with a water electrode in humid air of atmospheric pressure are given at various repetition frequencies of discharge pulses. With an increase in the pulse repetition rate from 35 to 1000 Hz, the homogeneity of the sheet plasma and the total intensity of its radiation increase. At frequencies in the range of 350–1000 Hz, a diffuse uniform discharge was also ignited in the intervals between the stainless steel blades, which improved the uniformity of the discharge as a whole.

In the conditions of nanosecond electric discharge above the surface of distilled water in humid air the chemically active  

particles that have a significant potential for oxidation are formed. These include the hydroxyl radicals (OH), hydrogen atoms (H) and oxygen (O). These radicals are formed in the plasma on the basis of moist air in the following reactions: ? + ?2O→ ? + ? + ??; ? + O2→ ? + ?(1D) + ?; ?(1D) + ?2O→ 2 O?.

The voltage pulse between the nanosecond discharge electrodes included positive and negative components with a duration of about 50 ns and an amplitude of 12-15 kV. An analysis of the temporal dependences of the current and voltage revealed that the amplitude of the discharge current is changes in the range from +150 A to –150 A with a leading edge duration of about 20 ns. The total current pulse duration is about 150 ns. The maximum value of the pulse electric power of the discharge reaches 2 MW, and the energy input in the pulse is in the range of 20-30 mJ.

In (Figure 4) the emission spectrum of a nanosecond discharge plasma is presented. The most intense were the spectral bands of the second positive system of the nitrogen molecule, the radiation of which is concentrated in the spectral range of 300-400 nm. Low-intensity bands of nitrogen oxide radicals were also observed in the spectral range of 200-300 nm. A more detailed identification of the emission bands in the spectrum in (Figure 4) is given in [10].

The spatial characteristics of the nanosecond discharge in the “blade-blade” electrode system installed above the surface of distilled water are shown in (Figure 5).

When the tip of the blades was removed from the surface of distilled water at a distance of 3 mm, a discharge was ignited in the air between the side edges of the blades (Figure 5). By increasing this distance to 10 mm, a nanosecond discharge started on the surface of distilled water, that is, the discharge between the blades closed above the surface of the distilled water. When using salt solution as a liquid, surface discharge was absent. The discharge in this case burned in the form of thin plasma sheets between the edges of the blades and the surface of the electrolyte along the entire length of the blades. A similar pattern was observed when the distance between the sharp edges and the water surface was increased to 80 mm. The discharge glow was blue-violet and filled almost the entire gap between the edges of the blades and the surface of the liquid. The electrical characteristics of nanosecond discharges in air at atmospheric pressure, which ignited between the blade system and the surface of distilled water (Figure 2), were close to the results for the blade-blade electrode system. For this discharge module, the maximum pulsed power of a nanosecond discharge reached 1.8 MW, and the discharge energy reached 30 mJ. With the distance between the blades d = 25 mm (Figure 1), the magnitude of the pulsed electric power of the discharge reached 2-4 MW (Figure 6). 

The maximum energy input into the discharge was achieved during the time interval from 70 to 120 nanoseconds from the beginning of the development of discharge processes. With increasing distance d in the sequence of 3 - 10 - 25 - 80 mm, the total energy input into the plasma changes in the sequence of 190 - 40 - 102 - 50 mJ. These results show that the maximum energy 

input into the discharge was achieved at d = 3 mm, when the discharge burns between the blades without touching the surface of the water. The energy input for the surface discharge is reduced by about four times (d = 10 mm). During the transition from the surface discharge to the discharge between the edges of the blades and the water surface, the energy input increased to a distance of d = 25 mm (102 mJ), and with a further increase in the distance between the blades (up to 80 mm), it decreased significantly (to 50 mJ).

Characteristics of a nanosecond high-current discharge with an electrode based on solutions of zinc and copper salts in distilled water

Consider the characteristics of a nanosecond discharge over a surface solution of zinc and copper sulphates in distilled water, which is ignited in the discharge module, which is shown in (Figure 2), when the discharge was ignited between the blade system and the electrolyte surface. The ignition of a nanosecond discharge over the surface of a 10% zinc sulphate solution in distilled water was performed using a power supply from a nitrogen laser with a longitudinal discharge “LGI-21”, which allowed operating at pulse repetition frequencies of 10, 25, 50, 100 Hz. At the frequencies of the voltage pulse f = 10; 25 Hz discharge looked like a set of sufficiently uniform plasma sheets, the number of which was equal to the number of metal blades on the electrode, which was placed in atmospheric pressure air, and with increasing frequency, the appearance of individual streamers was observed against the background of the plasma sheet. Increasing the thickness of the liquid layer above the immersed electrode made it difficult for the nanosecond discharge to become streamer. The amplitude of the voltage pulse was about 30 kV. Its duration was 14 ns. The current amplitude was 180 A, and the pulse duration was somewhat delayed to 30 ns. After the beginning of the voltage rise, almost immediately (after 2 ns) a current appeared, reflected in the voltage oscillogram with a slight jump at the time point of 2 ns (Figure 7).

The voltage pulse consisted of two regions: positive and negative. The amplitude of the first voltage pulse is determined by the initial resistance of the discharge gap, consisting of an air layer and a liquid layer, which in turn acts as a ballast resistance limiting a 

sharp increase in current. This in turn affects the formation of the discharge: the greater the thickness of the liquid layer and the lower its electrical conductivity, the smaller the amplitude of the current. An increase in the air gap caused a decrease in the current amplitude. The system of electrodes "blades - electrolyte surface" behaved like a capacitor of a certain capacitance, which accumulated charge during the first voltage pulse. In (Figure 7) the time dependences of the current and pulsed power input into the plasma are also shown.

Consider the optical characteristics of this discharge. Each individual experiment to study the spectral characteristics of the plasma lasted from 30 to 60 minutes. After the third minute, intense ozone occurred in the discharge cell, which was identified by a specific odor. In experiments with a 10% aqueous solution of zinc sulphate ZnSO4 on the bottom electrode– a plane with stainless steel a precipitate of white-gray color was dropped (precipitation of zinc oxide nanostructures is described in a literature on similar solution). In the emission spectrum of a nanosecond discharge above the surface of a 10% solution of zinc sulphate in distilled water (Figure 8), radiation of molecules and radicals N2, NO, OH, H2 and atoms N, Fe, Zn, S was observed. The results of the identification of the plasma emission spectrum are shown in (Table 1). 

The interpretation of the spectra for the zinc sulphate solution was rather complicated, since the radiation from the expective atoms and molecules (N2, NO, OH, H2, N, Fe, Zn, S) in the studied range in many cases was superimposed within the error of determining the radiation wavelength. The appearance in the spectrum of the 

emission lines of an iron atom can be explained by sputtering the blade material during the discharge process onto the surface of a more electrically conductive liquid than distilled water, where they have not been observed. A number of spectral emission lines of zinc and sulfur atoms is explained by the dissociation of the ZnSO4 components in the discharge. With a high-current nanosecond discharge, chemically active particles are formed over the surface of the solution of copper sulphate in distilled water in humid air, which have a significant potential for oxidation. 

These include the hydroxyl radicals (OH), hydrogen atoms (H) and oxygen (O). Some of the OH and O radicals penetrate into the solution and, upon interaction with copper, form copper oxide molecules. The combination of individual copper oxide molecules among themselves in the nucleation processes leads to the formation of copper oxide nanostructures of various sizes, which enter the solution. Over time, the largest copper oxide nanoparticles (with a diameter of more than 1 μm) precipitate as a solid-state dispersion fraction, and copper oxide nanoparticles with a diameter of 10-50 nm remain in the colloidal solution. After evaporation of water and filtration of solid micro particles of large diameter, it is possible to obtain a fine solid nanopowder of copper oxide in a macroscopic amount. 

Experimental studies of a high-current nanosecond discharge over the surface of solutions of copper sulfate (CuSO4) salt in distilled 

water were carried out with a salt content in distilled water in the range of 1-20%. The experiments were carried out at distances between the electrolyte surface and the blades of 4, 7, and 10 mm. The thickness of the liquid layer above the immersed metal electrode was 4 mm. The discharge glow in air at atmospheric pressure over the surface of 10% electrolyte with an interelectrode distance of 7 mm was blue-violet with sufficiently uniform filling almost the entire discharge gap (Figure 9). The peak voltage value reached 40-50 kV, and the current 75 A. The magnitude of the pulsed electric power of the nanosecond discharge reached 2 MW, and the energy input in one discharge pulse in the plasma was ~ 78 mJ (Figure 10). The pulsed electrical power of a nanosecond discharge was obtained by graphically multiplying oscillograms of voltage and current, and the energy per pulse was obtained by graphically integrating the pulsed power over time. The voltage and current pulses consisted of two sections: positive and negative, and their total duration was 50–100 ns. In (Figure 11) the plasma emission spectrum of a nanosecond discharge above the surface of the CuSO4 salt solution is given, with an interelectrode distance of 7 mm and a thickness of the electrolyte layer above the immersed metal electrode - 4 mm, with a current pulse frequency of f = 80 Hz.

In the emission spectrum of the discharge plasma, the spectral bands of the second positive system of nitrogen molecules were the most intense, the radiation of which was concentrated in the spectral range 300-400 nm. Low-intensity bands of nitrogen oxide radicals were also observed in the spectral range of 200–300 nm. Separate spectral lines of copper and sulfur atoms were observed from the products of destruction of copper sulfate salt in the emission spectrum of the plasma, which indicates that the electrolyte is rather efficiently evaporated and individual fragments of dissolved salt are introduced into the discharge plasma. The results of the detailed identification of the spectral lines and bands, which were emitted by nanosecond discharge plasma on the electrolyte surface are shown in (Table 2).

After the discharge cell was working for 2-3 hours at a frequency of 100-150 Hz, the electrolyte changed color from blue to green, which indicated the complete conversion of copper and anion cations (SO4) - in aqueous solution into a colloidal solution based on copper oxide nanoparticles (Figure 12). The green color of the solution corresponds to the maximum emission of plasmon resonance of copper oxide nanoparticles. This allows us to propose a method of synthesizing copper oxide nanostructures in a nanosecond discharge with an electrolytic electrode in atmospheric pressure air between a metal electrode and a surface of copper sulfate solution in distilled water [11], which can be used in nanotechnology to synthesize colloidal solutions based on copper oxide nanostructures and to obtain solid finely dispersed powders of copper oxide in a macroscopic quantity. 

The uniqueness of the properties of nanomaterials and the wide possibilities of their use encourage researchers not only to study the materials themselves, but also to search for new methods for their synthesis. Among the new effective ways of forming nanostructures, the place belongs to the method based on an electric discharge in liquids. The advantages of this plasma method include the ability to adjust the parameters of the synthesized particles by varying the discharge modes, a sufficiently high performance with the ability to scale the synthesis process, a relatively simple reactor design and a simple process of preparing output materials. Considerably less information, from the point of view of technologies for the synthesis of nanostructures, is about pulsed nanosecond discharges above the surface of solutions of metal salts (Cu, Zn, etc.). The high rates of nanosecond corona discharge water purification are primarily due to the presence of a strong electric field in the discharge gap, the intensity of which significantly exceeds the threshold value at which most of the plasma-chemical reactions useful for treating water in the air begin to occur. However, in the case of an electric discharge of direct current, the path that the streamer passes before its decay makes up only 10–20% of the entire length of the discharge gap and cannot reach the surface of the liquid. This disadvantage can be avoided by moving from glow discharges with a liquid cathode to a nanosecond discharge with an electrolytic electrode.

One of the elements of the experimental setup is the discharge cell shown in (Figure 1), in which a pulse-periodic nanosecond discharge flowed over the surface of an aqueous solution of zinc chloride, which passed between the electrode system “blade- liquid surface- blade” or “blade- blade”. In the experiment, the distance between the blades and the surface of the solution varied within 2 ... 5 mm. The level of the working liquid was maintained using a drip system. The working liquid was a solution of zinc chloride in distilled water. To excite a pulsed discharge, a nanosecond power supply unit with a pulse repetition rate of 35 ... 1000 Hz and a voltage of 25 ... 40 kV was used. Due to the rotation of the blades around the axis of attachment, the distance between them changed within 5 ... 80 mm.

The characteristics of the discharge (with different placement of electrodes, namely with the interelectrode distance of 3, 10, and 80 mm) above the surface (10% and 20%) of solutions of zinc chloride salt in distilled water were investigated. The layout of the electrodes is the same as for the discharge above the surface of distilled water. At an interelectrode distance of 3 mm, a spark discharge was realized between the blades in the air gap. The discharges above distilled water and the aqueous solution of salt did not practically differ. At an interelectrode distance of 10 mm, the discharge above distilled water spread in the form of a spark over the surface of the water, whereas the spark above the aqueous salt solution was not observed, but there was a thin streamer channel between the blades and the surface of the solution along the entire length of the blades. A similar streamer looked like a place with an interelectrode distance of 80 mm above the surfaces of both distilled water and above the surface of the zinc chloride solution. The discharge glow had a blue-violet tone and filled almost the entire gap between the blades and the surface of the liquid. In this case, the passage of electric current occurred in the following way: from the blade into the liquid through the near-surface air layer (3 mm), then into the liquid and again through the 

Each individual experiment to study the spectral characteristics lasted from 30 to 60 minutes. The study of plasma emission spectra was carried out using a radiation detection system based on an MDR-2 monochromator and an FEU-106 photomultiplier in the spectral range 196 ... 663 nm. The emission spectrum of the plasma of a nanosecond discharge after a 3 mm air gap was almost identical for cases with distilled water and a solution of zinc chloride salt, with a salt concentration of less than 10%. The high-voltage nanosecond modulator used for the ignition of the discharge allowed a fixed change in the pulse repetition rate with fixed values of 35, 80, 150, 350, 1000 Hz.

A multichannel oscilloscope was used to record the oscillogram of the discharge and the voltage across the discharge gap. Oscillograms were recorded for electrode cases based on distilled water and zinc chloride solutions at various interelectrode distances and, as a result, at various discharge flow conditions. The oscillograms of the current and voltage (Figures 13 and 14) of the discharge were used to determine the pulsed power of the discharge and the electrical energy that was applied to the plasma. The amplitude of the first voltage pulse is determined by the initial resistance of the discharge gap, consisting of a layer of air and liquid. An increase in the size of the air gap caused a decrease in the current amplitude. The beginning of the current pulse began on the fall of the first voltage pulse. The presence of sharp drops on the voltage pulse can be explained by the presence of streamers, which arose as a result of the ionization of the discharge gap during the first pulse.

Analysis of the current and voltage for the discharge over the surface of the zinc chloride solution in the streamer mode at an electrode spacing of 80 mm found that the current has an amplitude of 170 A, the duration of the first half pulse was about 40 ns. The total duration of the current pulse was 60 ns. 

The peak value of the pulsed power of the discharge reached in the main part of the voltage and current pulses - 4 MW, and the energy input into the plasma per pulse reached ~ 0.13 J. Analysis of current waveforms in distilled water and in aqueous solution of zinc chloride showed that the current in the discharge above the surface of the latter increases. 

Conclusion

  1. It is shown that a nanosecond discharge in air at atmospheric pressure and an electrode system of the “blade- water surface (alcohol)” type without using pre-ionization allows to obtain a sufficiently uniform discharge and treat the surface of a non-metallic liquid electrode with it. The conditions for the ignition of a stable nanosecond surface discharge above the surface of distilled water in the blade – blade electrode system without the use of a reverse current lead are established. Measurements of the electrical and optical characteristics of these discharges have shown that they can be used in surface water treatment systems of a relatively large area.
  2. The study of the spatial characteristics of a nanosecond discharge over the surface of zinc sulphate solutions in distilled water implies that it ignites in the form of a sufficiently homogeneous set of wide plasma channels; current amplitude reaches 180 A, current pulse duration is 15 ns; the amplitude of the voltage pulse reached about 30 kV, and the maximum pulsed energy input in the main part of the voltage and current pulses reached 5 MW at an energy of this input of ~ 21 mJ; studies of survey emission spectra of plasma above the electrolyte surface under gas-static conditions have found that the radiation of nitrogen and nitric oxide molecules dominates in the UV range of the spectrum, as well as individual spectral lines of metal blades (anode - materials - steel), sulfur, zinc and a number of spectral lines and bands in visible range .
  3. It has been established that the method of synthesizing copper (zinc) oxide nanostructures in a nanosecond discharge between a blade system and an electrolyte involves applying high-voltage pulses of nanosecond duration to metallic and liquid electrodes and it is different in the following: bipolar high-current nanosecond is used to synthesize copper oxide (zinc) nanostructures between the metal blade system and the surface of copper or zinc sulfate solutions in distilled water, what allows to obtain a uniform sheet plasma from each blade, which is intensely active in the ultraviolet region of the spectrum and is a source of hydroxyl radicals under the action of which the blue color copper sulphate solution is transformed into a colloidal solution of green color copper oxide nanoparticles; when working with zinc salts the solution and the precipitate were white-gray, which is characteristic for zinc oxide nanostructures.

References

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Figures

Figure 1: The structure of the discharge cell with rotating electrodes: 1 - a cuvette made of organic glass; 2 - adjusting electrode screws; 3-lese; 4 - distilled water or solutions of salts of copper or zinc.

Figure 2. The structure of the discharge cell: 1 - cuvette, 2 - screws for installation of the interelectrode distance, 3 - electrode mount, 4 - blade system, 5 - metal electrode immersed in water, 6 - distilled water or salt solutions, 7 - quartz window, 8 - metal screen.

Figure 3: Images of a nanosecond discharge with an electrode based on distilled water (view from end A and side B) for different repetition rates of voltage pulses with a distance between the tips of the blades and the water surface is d = 7.5 mm and water thickness above the solid metal electrode is h = 4 mm.

Figure 4: The emission spectrum of the plasma nanosecond discharge between the blade system and the surface of distilled water in the air.

Figure 5: The spatial characteristics of nanosecond discharges in the blade-blade electrode system, which were ignited above the surface of distilled water.

Figure 6: The electrical characteristics of the nanosecond discharge above the surface of distilled water in the “blade-blade” electrode system with the distance between the blades d = 25 mm.

Figure 7: The temporal dependences of voltage (a), current (b) and pulsed power (c) of a corona discharge over the surface of a 10% aqueous solution of zinc sulphate.

Figure 8: The emission spectrum of a nanosecond discharge above the surface of a 10% zinc sulphate ZnSO4 solution in distilled water with an electrode spacing of 7.5 mm and a liquid layer thickness of 4 mm.

Figure 9: Image of a nanosecond discharge with an electrode based on a 20% solution of copper sulfate in air at atmospheric pressure.

Figure 10: The pulsed power of a nanosecond discharge with an electrode based on 20% CuSO4.

Figure 11: The emission spectrum of a nanosecond discharge with an electrode based on 20% CuSO4.

Figure 12: Images of solutions of copper sulfate in distilled water before and after plasma treatment of a nanosecond discharge in air at atmospheric pressure.

Figure 13: Oscillograms of voltage, current and pulsed power of the discharge above the surface of a 10% solution of zinc chloride with a distance between the electrodes of 10 mm.

Figure 14: Oscillograms of voltage, current and pulsed power of the discharge above the surface of a 10% solution of zinc chloride with a distance between the electrodes of 80 mm.

 

 

Tables

Table 1: Results of interpretation the emission spectrum of a nanosecond discharge on the surface of a 10% aqueous solution of zinc sulphate.

364,17 nm N2

371,05 nm N2

375,54 nm N2

380,09 nm NO

385,75 nm N2

388,62 nm Fe

393,03 nm Fe

406,14 nm NO

411,32 nm Zn

417,71 nm H2

423,43 nm N2

446,26 nm NO

455,98 nm Fe

484,86 nm N2

491,52 nm Fe (491,49 nm N)

516,49 nm Zn

522,68 nm OH (522,71 ?? Fe )

552,40 nm Fe

561,25 nm H2 (561,43 nm S)

Table 2: The results of the identification of the most intense spectral lines and emission bands of the plasma spectrum of a nanosecond discharge with an electrolytic electrode based on a 20% solution of copper sulphate.

~200-230 nm NO

297,68 nm N2

315,93 nm N2

337,13 nm N2

358,21 nm N2

375,54 nm N2

380,49 nm N2

399,5 nm NII

444,7 nm NII

~450-490 nm S I

502,57 nm NII

521,82 nm Cu I

570,02 nm Cu I

594,12 nm Cu I