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Elektrická rezistivita podstechiometrického TiO2 vyrobeného plazmovým nástřikem
Ctibor, Pavel ; Sedláček, J. ; Neufuss, Karel
The work is concentrated on electric resistivity of plasma sprayed titania TiO2. Synthetic conventional TiO2 powder and powder prepared by agglomeration of nanopowder particles were sprayed and measured. Spraying was carried out using the water-stabilized plasma system (WSP®) and resistivity measurement was applied on TiO2 layers detached from the substrate. Variations in basic spray conditions – spray distance, feedindg distance and substrate preheating temperature were commented from the point of view of their influence on electric resistivity.
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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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Adhesion improvement of plasma sprayed coatings ceramics-metal
Brožek, Vlastimil ; Neufuss, Karel
The paper summarizes knowledge dealing with shape similarity of the profile of surfacial anchoring of iron borides onto steel substrates, devoted to covering by ceramic coating using thermal or plasma spraying. Boride interlayer improves the conditions for deposition of ceramic materials having different dilatation characteristics. By this way cermet coatings on steels designed for cyclic thermal load up to 1000°C could be carried out.
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Treatment of tungsten carbide in low temperature plasma
Brožek, Vlastimil ; Matějíček, Jiří ; Neufuss, Karel
Tungsten carbide powder was thermally processed in a water stabilized plasma, using the WSP plasma torch developed in the Institute of Plasma Physics, where the plasma temperatures can reach 30 000 K at the nozzle exit. Oxidation of the molten carbide was suppressed by a nitrogen atmosphere during deposition on substrates positioned immediately above liquid nitrogen level. Analyses of both the deposits and spheroidized particles in the 5 – 63 μm size range determined the W:W2C:WC ratios and mechanical properties.
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Plasma deposition of tungsten coatings
Brožek, Vlastimil ; Matějíček, Jiří ; Neufuss, Karel
Tungsten coatings on steel or ceramic substrates were prepared by water stabilized plasma generator WSP®. It operates on the Gerdien arc principle and produces plasma reaching temperatures up to 28000 K and velocities several Mach at the nozzle exit. Tungsten particles are melted and accelerated to velocities 30-70 m/s in the turbulent plasma that transports them to the substrate, where the particles rapidly solidify, forming characteristic splats and porous coatings. Protection of the molten 20-63 μm tungsten particles against oxidation by argon and acetylene shrouding was found to be inadequate. Therefore, a new method was tested, using hydrogen as a carrier gas in a special, house-built powder feeder. Another modification of the spraying process consisted of admixture of stoichiometric amount of tungsten monocarbide. During melting, it decomposes to W2C and carbon, which oxidizes and forms a protective cloud of carbon monoxide around the particles.
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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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Preparation and Properties of Spheroised Tungsten Powder
Brožek, V. ; Dufek, V. ; Neufuss, Karel ; Šarman, L.
In our series of experiments ball shaped tungsten particles were prepared.Tungsten microballs can be used in filters for chemical and metallurgical industry.Possible applications can be awaited in nuclear fusion reactors.Tungsten balls are tested also as special type of ammunition.Coarse tungsten powder of OSRAM Sylvania Inc provenience was screened into fractions 40-60ćm, 60-100ćm.
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