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Porovnání vlastností obloukových výbojů s hybridní a vodní vírovou stabilizovací
Jeništa, Jiří ; Bartlová, M. ; Aubrecht, V.
The paper deals with numerical modeling of the plasma torch electric arcs with water vortex stabilization and combined stabilization of arc by argon flow and water vortex. The axisymmetric model includes the arc discharge area between the near-cathode region and the outlet nozzle of the plasma torch. Thermal, electrical and fluid-dynamic characteristics as well as power losses of such arc has been studied for the range of currents 150-500 A. It was proved that addition of argon increases the plasma velocity but does not influence substantially the plasma temperature. The energy losses transferred radially from the arc by conduction and radiation range from 65 to 30 % of the input power. The amount of reabsorbed radiation, calculated by the partial characteristics method, divided to the total divergence of radiation flux is 35-26 % for hybrid torch and 25-16 % for water torch. The calculated velocities and temperatures show good agreement with experiments.
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Plazmové nástřiky ve zvýšeném gravitačním poli
Brožek, Vlastimil
Porosity – and thus density – of plasma sprayed materials can be influenced by kinetic parameters of the particles flying in the plasma jet. These parameters can be improved by increased gravity field. In an analogy to centrifugal casting, we have verified the possibility of plasma deposition on substrates placed on the inside perimeter of a centrifuge. A WSP® plasma generator with a 100 kW power was used. The calculated gravity acceleration was 307 ms-2, corresponding to a 30 MPa pressure on the substrate. Alternative method of ceramics densification, HIPping at 150 MPa, reduces porosity to below 5%. In our case, porosity of an alumina deposit was reduced from 8.74% to 7.82%.
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Interakce vodíkového plazmatu s ferity
Hofman, R. ; Vacík, M. ; Brožek, Vlastimil ; Eliáš, M. ; Janča, J.
Ferrites are a well-known ferroelectric materials based on metal oxides with different oxidation levels. They found thanks its advisable properties a broad field of exercise, especially in electronics. In our work we made an effort to amplify this field of exercise. An intention of our work was explaining how the ferrites behave in strongly reducing atmosphere realized in hydrogen plasma. The emphasis was laid on readiness and selectivity of reduction. And further we are interested in morphology and granulometry of obtained products and last but not least in mechanical properties, especially of obtained ceramics composite with metal matrix ( MMC
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Plazmochemická redukce a karbidace ilmenitu
Janča, J. ; Eliáš, M. ; Brožek, Vlastimil
Plasma spraying is a thermal spraying method applied mostly to produce coatings and functionally graded materials. Plasma spraying of ilmenite free-standing parts and coatings on metallic substrates has been mastered at IPP Praha. This report concerns compact ilmenite parts undergoing a reduction in hydrogen plasma, inductively and capacitive generated. In accordance with theoretical predictions, metallic iron was selectively reduced from ilmenite, while any form of hydrogen present in the plasma did not reduce titania. After the reduction, the products did not change their dimensions and shape, apart from a minute contraction (whose extent is now being measured). The thermal expansion coefficient of ilmenite is 9,98.10-6 K-1 in the 100-750°C range; for our products, it is slightly lower. The goal of further research is to find conditions to obtain anatase structure of the titania in the formed composite.
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Impregnace keramických membrán anatasem
Vacík, M. ; Hofman, R. ; Mastný, L. ; Šrank, Z. ; Brožek, Vlastimil
Catalytic properties of anatase have been known for a certain time but its practical usage has been hindered by technological limits of preparation of either compact massive intermediate products of various shapes which are necessary as a component of catalytic reactors or nanosized anatase powder. Our aim was to prepare ceramic membrane which would contain catalytic form of titanium oxide - i.e. anatase in its entire volume or on its surface only. Ceramic membranes of any shape (mostly tabular or piped) may be prepared by hot spattering technology. If plasma torch is used we call this process plasma spraying. The advantage of plasma spraying is in chance to provide semi-finished membranes with high dimension accuracy with defined radius of voids and/or as functionally graded materials, i.e. with changing concentration of some ceramic, metallic or combined components. The pores developed in membranes can be readily filled up with substances that allow modification of its properties. In this area, the possibility to impregnate membrane ceramic intermediates with other functional components, e.g. photocatalytic forms of titanium oxide, arises as well.
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Tribological Behaviour of Plasma Sprayed Al2O3 and Cr2O3 Coatings
Řidký, V. ; Dubský, Jiří ; Cejp, J.
Plasma sprayed ceramics coatings are well known for their wear resistance.Plasma sprayed alumina and chromia oxide coatings are widely used to improve the resistance of metallic components against various types of wear and corrosion[1,2].However, the particular structure of plasma-sprayed coatings(high porosity,cracks,nehomogenity etc.) affects their mechanical properties.
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