Synthesis of Nitrogen Oxides in a Subthreshold Microwave Discharge in Air and in Air Mixtures with Methane

Plasma Physics Reports - A subthreshold discharge excited by a microwave beam in air at pressures close to atmospheric is studied as a plasmachemical method of nitrogen oxide (NOx) production. It...     

Initiation of solid-phase chemical reactions in powder mixtures by microwave discharges

The initiation of exothermic chemical reactions in powder (metal-dielectric) mixtures by irradiating them with a high-power microwave beam is investigated. The initial stage of microwave breakdown is accompanied by the emission in the atomic lines of the metal component of the mixture (Ti, Mo, Sn, Al, etc.). The subsequent microwave discharge generates a continuous optical spectrum, the temperature of the effective Planckian radiator being 2000–3000 K. A prolonged radiation of the mixture after the end of the microwave pulse is caused by the energy release in chemical reactions.     

Long-lived plasmoids generated by surface microwave discharges in chemically active gases

The generation of long-lived microplasmoids is observed during the irradiation of a metal-dielectric surface with a high-power microwave beam in a chemically active gas mixture (H₂ + O₂; CH₄ + O₂). The lifetime of these plasmoids substantially exceeds the characteristic recombination and cooling times of plasmoids arising at the target surface in a chemically inactive medium.     

Ignition of a combustible gas mixture by a high-current electric discharge in a closed volume

Results are presented from experimental studies and numerical calculations of the ignition of a stoichiometric CH₄: O₂ gas mixture by a high-current gliding discharge. It is shown that this type of discharge generates an axially propagating thermal wave (precursor) that penetrates into the gas medium and leads to fast gas heating. This process is followed by an almost simultaneous ignition of the gas mixture over the entire reactor volume.     

A Subthreshold High-Pressure Discharge Excited by a Microwave Beam: Physical Basics and Applications

A new form of discharge excited by a microwave beam in a high-pressure (up to atmospheric and higher) gas in free space and in a closed chamber is discussed. For the first time, the discharge was implemented by means of a gyrotron with a pulse power of 200 ≤ P ≤ 600 kW, a pulse duration of 0.5 ≤ τ ≤ 20 ms, and a wavelength of λ = 0.4 cm. Under deeply subthreshold conditions in atmospheric-pressure air, a plasma column with a length of L = 50 cm was generated by a microwave beam formed with the help of a quasi-optical transmission line. With the use of the MIG-3 gyrotron complex with the above parameters, generation of a plasma column with a length of several meters is possible in principle. The parameters and structure of the formation of the plasma investigated make it possible to class it as a self-non-self-sustained (SNSS) discharge, discovered and described for the first time at the Prokhorov General Physics Institute, Russian Academy of Sciences. One of the important applications of this type of discharge is plasmachemical cleaning of the urban air environment of hazardous contaminants.     

Application of microwave discharge for the synthesis of TiB2 and BN nano- and microcrystals in a mixture of Ti-B powders in a nitrogen atmosphere

Synthesis of titanium diboride and boron nitride nano- and microcrystals by means of a pulsed microwave discharge in a mixture of Ti-B powders in a nitrogen atmosphere is considered. For this purpose, a new type of reactor with a free surface of the powder mixture was used. The reactor design permits free expansion of the reaction products into the reactor volume and their deposition on the reactor walls. Conditions for the synthesis of TiB₂ and BN compounds were studied as functions of the energy input in the discharge, the powder component ratio, the rate of the nitrogen flow through the reactor, and the structure and phase composition of the compounds deposited on the reactor walls. The synthesis of boron nitride and titanium diboride in crystal structures is proven. An important role in the process of synthesis is played by the heating of the mixture due to the titanium diboride synthesis reaction, its behavior in the bulk of the reactor, and the titanium concentration in the powder mixture. It is also found that, as the number of discharges in the bulk of the reactor increases, a dust cloud forms. The luminescence of this cloud indicates that the initiated discharge proceeds not only on the powder surface and in the powder bulk, but also in the reactor volume.     

Characteristics of a Subthreshold Microwave Discharge in a Wave Beam in Air and the Efficiency of the Plasma-Chemical Reactor

Plasma Physics Reports - An analysis of a set of experiments on studying subthreshold microwave self/non-self-sustained (SNSS) discharges made it possible to estimate the volume of the active zone...     

Parameters of microwave discharge plasmas in powder mixtures

A study is made of the optical emission spectra of a plasma produced under the action of a microwave beam with a field amplitude of about 3 kV/cm on a metal-dielectric mixture at atmospheric pressure. In the initial stage of the discharge, the plasma is localized in microscale sites at the target surface, the characteristic size of the glowing regions in the target plane being less than 1 mm. In this stage, the target material is evaporated and atomic spectral lines with excitation energies of up to 6–8 eV are emitted. The population temperature of the excited levels, which was determined from the intensity ratios of atomic spectral lines, can be interpreted as the temperature of the atmospheric-pressure plasma. The temperatures determined from different pairs of lines belonging to the same or different elements (Cu, Mo, Li, Fe) fall within the range 7000–9000 K. In the later stage of the discharge, when the characteristic plasma size reaches a few centimeters, no atomic lines are present in the spectrum, which corresponds to a Planckian continuum with a temperature of 2400–3200 K.     

Microwave cellular discharge in fine powder mixtures

The excitation of microwave discharges in fine semiconductor powders and powder mixtures of metals and dielectrics is studied. The plasma is produced due to local sparks generated in microsecond microwave pulses. The time delay in the onset of a discharge amounts to several milliseconds for intensities on the order of 10 kW/cm². As the discharge develops, both microwave absorption and the discharge glow intensity increase. Intense nonuniform heating of the powder is observed.     

Discharge in a Subthreshold Microwave Beam as an Effective Means for Mercaptan Decomposition

Plasma Physics Reports - A subthreshold microwave discharge in atmospheric-pressure air is used to process mixtures of mercaptans (thiols) with air and with air and methane. It is found that, at...