National Repository of Grey Literature 8 records found  Search took 0.00 seconds. 
Electric probe measurements in the anode area of a DC arc plasma torch at low pressure
Ondáč, Peter ; Mašláni, Alan ; Hrabovský, Milan
We measured radial profiles of the electric field, plasma electrical potential and electron temperature in the hot anode area of a hybrid water-argon DC arc plasma torch with an external anode. The measurements were made under different values of the ambient pressure, during the restrike mode with a constricted anode arc attachment or during a supersonic mode with a diffuse anode arc attachment. The results provide first experimental data on plasma electrical potential in that anode area.
Preparation of spheroidized and nano-structural spinels by the SPPS method
Brožek, Vlastimil ; Lukáč, František ; Medřický, Jan ; Mušálek, Radek ; Mašláni, Alan ; Mastný, L. ; Brodil, R.
Solution Precursor Plasma Spraying (SPPS) method, using hybrid water-stabilised plasma torch (WSP®-H), is presented in this study. Precursor, in a form of a solution of inorganic salts, is injected into the plasma jet, where the temperature can reach up to 25 000 K and a series of reactions lead to the formation of spherical sub-micrometric sized particles. The complete process of evaporating the liquid, crystallization, thermic decomposition, melting and recrystallization takes place in few milliseconds before the particles solidify. Melted nanoparticles can be either directly collected in order to obtain ultrafine powders or deposited onto a substrate to form micro-splats and continuous polycrystalline, and often partially amorphous, coatings. The possibility of continuous and discontinuous changes of stoichiometric composition in tetrahedral and octahedral configurations were analysed for the deposits of MgAl2O4, CoAl2O4 and CoFe2O4 spinels. Furthermore, thin colourful coatings of ruby and modified cobalt oxides were deposited onto ceramic and metallic substrates.
Measuring of Mean Plasma Electrical Conductivity in Anode Area of Plasma Torches with an External Anode
Ondáč, Peter ; Mašláni, Alan ; Hrabovský, Milan
We developed a non-intrusive direct procedure of measuring an average electrical conductivity of a plasma volume in hot anode areas of those plasma torches. For our measurements, we used a high-speed camera, a high-voltage probe, and a hybrid water–argon plasma torch. The measurements were made for various values of ambient pressure, arc electric current, and argon flow rate. The measured plasma conductivity is in agreement with a model, camera observations and indirectly also with spectroscopy measurements. The procedure provides missing experimental data on the average plasma electrical conductivity and estimates average plasma temperature in the anode areas. The procedure can be theoretically used in every plasma torch where the anode arc attachment movement can be observed during a restrike process\n
Arc–Anode Attachment Area in DC Arc Plasma Torch at Low Pressure
Ondáč, Peter ; Mašláni, Alan ; Hrabovský, Milan
Studying the processes in the anode attachment area of a DC arc plasma torch helps to extend the lifetime of the anode, stabilize the plasma flow for plasma spraying and better understand the movement of the anode attachment. In this work, such processes were studied at low pressure, by a non-disturbing method, using a high-speed camera and a high voltage probe. We also found pressure ranges, in which the following transitions were observed: the constricted/diffuse anode attachment, and subsonic/supersonic plasma jet\n
Investigation of Anode Attachment Area in Water/Argon Stabilized Plasma Arc
Ondáč, Peter ; Mašláni, Alan ; Hrabovský, Milan
Arc-anode attachment in a DC plasma arc stabilized by water vortex and argon, influences power distribution in the plasma, lifetime of the anode and also flow structure of the plasma jet. A movement of the attachment and the surrounding plasma has been directly observed by using a high-speed camera (max. 1,080,000 fps). The observations were compared with cathode–anode voltage measurements (sample rate 80 MHz). More than one attachment was observed in one frame with exposure time 0.25 μs or 0.29 μs. We have directly measured average velocities of the attachments and hydrodynamic waves above them, as well as the characteristic dwell times and dwell frequencies of the attachments
Experimental investigation of electric arc behavior during cutting of stainless steel
Kavka, Tetyana ; Mašláni, Alan ; Konrád, Miloš ; Tossens, S.
The present work is devoted to experimental investigation of electric arc behaviour during cutting of stainless steel. The goal of this work is to define influence of arc voltage fluctuations and anode attachment behaviour on the cutting performance. In most cases the anode attachment was verz luminous and was observed far from the main arc column close to the plate top. The cut material exhibited stronger surface roughness at the anode attachment location. The measured voltage traces showed a so-called restrike mode of oscillations of different frequencies and amplitudes.
Měření excitačních a ionizačních teplot v expandujícím proudu H2O-Ar plazmatu
Sember, Viktor ; Mašláni, Alan
Optical emission spectroscopy is used to determine the temperature in a plasma jet expanding from the H2O-Ar dc arc torch into a chamber maintained at a pressure of 10 kPa. The excitation and rotational temperatures are derived from relative intensities of argon atomic and ionic lines, and from the UV OH band at 306.357 nm, respectively. The ionization temperature is obtained from the intensity ratio of argon ionic and atomic lines, using electron number density calculated from the Stark broadening of hydrogen H line. The structure of the plasma jet is characterized by isocontours of electron number density and intensity of atomic and ionic lines. In the expansion region, the ionic excitation temperature is found close to the ionization temperature and much higher than the excitation temperature of argon atoms, which is close to the rotational temperature of OH radical. In the normal shock region, all the measured temperatures tend to be equal.
Studium expandujícího proudu termického plazmatu s využitím molekulových spekter
Mašláni, Alan ; Sember, Viktor
Thermal plasmas generated by plasma torches are well-known for their high temperatures and high enthalpies. Therefore optical emission spectroscopy is appropriate diagnostic method because of strong emission of radiation corresponding to the visible light. The decay of excited atoms, ions and molecules causes emission of the light at characteristic wavelengths. Except spectral lines of atoms and ions, also some molecular bands can be seen in the spectra of the plasma jet. Especially expanding thermal plasma jet operated under low pressure conditions offers possibility of observing molecular transitions. Pressure lower than atmospheric may cause the presence of supersonic flow and departures from thermodynamic equilibrium. Spectra of OH radical have been investigated using computer code LIFBASE, which contains a lot of data regarding spectra of diatomic molecules. Radial profiles of rotational and vibrational temperatures have been found in several regions of the jet.

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