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Chemical aspects of antiballistic cermets preparation
Brožek, Vlastimil ; Kubatík, Tomáš František ; Chráska, Tomáš ; Mušálek, Radek ; Janata, Marek ; Mastný, L.
The paper aims to demonstrate the possibilities of metal-ceramic material deposition on different types of metal or ceramic substrates using plasma deposition. A number of self-supporting components and the preparation of metal-braced composites are described and the results of plasma depositions of two particular extremely hard ceramic materials, boride and nitride of titanium are presented. The plasma deposition of these material is performed in technological conditions which prevent undesirable high-temperature oxidation. The paper describes deposition conditions that may lead to materials suited to create anti-ballistic protection and complicated shapes or improve parameters of surface layers of present anti-ballistic ceramics.
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Properties of Novel Hybrid Water-Gas DC Arc Plasma Torch
Chráska, Tomáš ; Hrabovský, Milan ; Glanc, Aleš ; Mušálek, Radek ; Medřický, Jan
A new type of plasma torch with combined stabilization of electric arc by water vortex and gas flow is presented. This hybrid water/gas stabilization offers the possibility of adjusting plasma jet parameters within a wide range from high-enthalpy low-density plasmas typical for liquid stabilized torches to lower enthalpy higher density plasmas generated in gas stabilized torches. Moreover, gas flow in the cathode part protects a cathode tip and thus a consumable graphite cathode used in water-only stabilized plasma torches could be replaced by a fixed tungsten cathode. Examples of hybrid WSP torch utilization for high temperature application are given.
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Preparation of multiphase materials with spark plasma sintering
Mušálek, Radek ; Dlabáček, Zdeněk ; Vilémová, Monika ; Pala, Zdeněk ; Matějíček, Jiří ; Chráska, Tomáš
Spark plasma sintering (SPS), also called Field Assisted Sintering Technique (FAST), represents a novel method of preparation of sintered materials from powders. The main advantage of the SPS method is a high achievable heat rate (>200 °C/min) and high sintering temperatures (up to 2200 °C in our laboratory). Combination of high heating rate, rather high pressures (up to 80 MPa) and electric field fluctuations leads to an effective sintering and significant reduction of sintering time for both coarse-grained and nanocrystalline powders. Composite materials may be easily obtained by mixing or layering of different powders. The paper will introduce several examples of multiphase materials sintered by SPS at our institute and the establishment of procedures for routine testing of sub-sized specimens.
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Production of nanoparticles utilizing water stabilized plasma
Bertolissi, Gabriele ; Brožek, Vlastimil ; Chráska, Tomáš ; Mušálek, Radek ; Neufuss, Karel ; Mastný, L. ; Sofer, Z.
Water stabilized plasma torch (WSP®) generates plasma jet with max. plasma velocity in the nozzle exit 7000m/s and temperature of 25000-30000 K. Reactants injected into the plasma jet undergo complicated radical reactions. Interaction of plasma with injected reactants depends on energy settings of the WSP plasma torch and lasts from 5 to 10 ms. Droplets of inorganic compound solution are fed to the plasma jet by pressurized spray nozzle device. Compounds of AgI,AlIII,TiIV,PtIV,VV, and CrVI undergo decomposition in the extremely high plasma temperature and the decomposed products are collected in liquid separators. Size of the produced nanoparticles in unsettled fraction is from 10 to 200 nm and depends primarily on concentration of inputting aerosol particles. In the case of 15 seconds reaction time and use of saturated solutions at 20°C, one can obtain colloidal solutions with silver, platinum, alumina, titania, vanadia, and chromia nanoparticles in concentrations of 3 to 180mg
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Objemové nanokrystalické materiály na bázi oxidu hlinitého a zirkoničitého
Chráska, Tomáš ; Klementová, Mariana
An alternative method to produce bulk nanocrystalline materials is to produce amorphous material by rapid solidification and then by controlled crystallization introduce nanocrystalline structure. One technique capable of achieving rapid solidification in materials is plasma spraying. Feedstock material for plasma spraying was composed of about 15 wt.% of SiO2 in addition to the near eutectic ratio of Al2O3 and ZrO2 compounds. Amorphous coatings and free standing parts from this material prepared by water stabilized plasma torch (WSP) exhibit very low porosity and high hardness. When heat treated, the as-sprayed material crystallizes just above 950ºC with an associated volume shrinkage of 1.8%. The volume shrinkage does not cause material breakup. Short heat treatment of the as-sprayed material produces a very fine nanocomposite structure within each splat. Each splat contains nanocrystallites with average size as small as 13 nm.
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Objemový nanokrystalický keramický materiál připravený plazmovým stříkáním
Chráska, Tomáš ; Neufuss, Karel ; Rohan, Pavel ; Dubský, Jiří
Ceramic material based on alumina-zirconia mixture have been successfully plasma sprayed by water stabilized plasma torch (WSP®). The material is composed of three main compounds Al2O3, ZrO2, and SiO2 where the ratio of Al2O3 – ZrO2 compounds is close to the ratio in their respective eutectic alloy. The material is a refractory and exhibits very high hardness, abrasion resistance, and chemical resistance. Cast tiles of the original material were ground and sieved to obtain the right powder cut size for plasma spraying by WSP®. Both thick coatings and free standing parts with very low open porosity were easily achieved by WSP®. The feedstock powder is mostly crystalline whereas the as?sprayed material is mostly amorphous with some unmelted crystalline particles present. Electron microscopy and X-ray diffraction were employed to determine microstructure, crystallinity, and phase content of the bulk samples as well as individual splats.
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Plazmové stříkání nanokeramiky - oxidu hlinitého a zirkoničitého
Chráska, Tomáš ; Neufuss, Karel ; Nohava, Jiří ; Dubský, Jiří
A novel material has been plasma sprayed by water stabilized plasma torch (WSP®) in order to achieve nanocrystalline microstructure. The new material is composed of three main compounds, namely corundum (alpha Al2O3), baddeleyite (monoclinic ZrO2), and glassy phase (SiO2). The ratio of Al2O3 – ZrO2 compounds is close to that of their respective eutectic alloy. Both dense coatings and free standing parts were produced with the new material, which sprays very well by WSP®. Spraying parameters were varied and molten particles were monitored in flight. The coatings exhibit very low porosity and high hardness. The as-sprayed material is mostly amorphous with some nanocrystalline grains of aluminum and zirconium oxide present. The microstructure of the newly sprayed material was studied by electron microscopy (SEM, TEM) and was found to be very complex. Upon annealing, the as-sprayed material fully crystallizes at around 950ºC. Selected mechanical properties were measured as well.
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Utilization of plasma spraying for production of nanocrystalline ceramic materials
Chráska, Tomáš
The technique of plasma spraying is now being investigated as an apt candidate for production of nanocrystalline materials.In the conventional plasma spraying (PS) process,powder particles injected into a high temperature plasma jet are quickly melted and propelled onto a substrate where they spread upon impact and rapidly solidify.Due to the rapid solidification, the conventional PS.
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