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Ceramo-metallic materials of the Ti-B-C and Ti-B-N systems
Brožek, V. ; Doležal, J. ; Novák, M. ; Ctibor, Pavel ; Kolman, Blahoslav Jan
Products prepared by the sintering of titanium and boron carbide powder and by the sintering of titanium and boron nitride powder were studied. The sintering was performed at 2,000 °C under the pressure of 6 GPa in a high-pressure apparatus of BELT-type with sufficient holding time to reach thermodynamic equilibrium. The results of chemical and phase composition analyses were compared with thermodynamic prediction of possible reactions in the system. We proved the preferential formation of borides TiB and TiB2 prior to the carbides or nitrides formation. The products, which may be considered Ti-(TiB,TiB2)-TiN or Ti-(TiB,TiB2)-TiC cermets, were analysed in order to determine their microstructure, phase and chemical composition and their influence on mechanical properties such as hardness or elastic modulus. This work precedes similar study which will be performed using the same powders processed by plasma spraying, which enables to stabilize high-temperature phases by rapid cooling.
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Složení a struktura plazmově stříkaných prášků chromové ocele
Schneeweiss, O. ; Voleník, Karel ; Kolman, Blahoslav Jan
Chromium steel powder (13% Cr) was sprayed by a water stabilized plasma gun. The changes of composition and structure occurring during two plasma spraying stages were studied. To characterize the main features of the first (in-flight) stage product, the molten powder particles flying in the plasma stream were trapped and quenched in liquid nitrogen. At the second stage, the particles were allowed to hit a solid substrate and to form a coating. The composition of the feedstock powder and the samples resulting from both plasma spraying stages were determined by chemical methods and X-ray microanalysis. Significant Cr-depletion was due mainly to selective oxidation of chromium at the in-flight stage. At the second stage, the composition changes were less important. Some details of the structure, in particular the distribution of Cr-atoms in the nearest neighbourhood of a Fe-atom, were assessed employing the results of Mössbauer spectroscopy.
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Porcelanite - a rare material of polished stone artefacts
Šrein, Vladimír ; Šťastný, Martin ; Šreinová, B. ; Langrová, Anna ; Kolman, Blahoslav Jan
Contact metamorphism is effected by heat supply at the contacts of rocks with magmatites. This process produces porcelanite, vitrification of sandstones and burning of coal seans, among other things. In detail mineralogical study we determined calcic feldspar and pyroxenes as a major minerals with titanite, calcite, zeolite, analcime and others.
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