Papers by Author: Svetlana Stelmakh

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Authors: Bogdan F. Palosz, Ewa Grzanka, Svetlana Stelmakh, Stanislaw Gierlotka, Roman Pielaszek, Ulrich Bismayer, H.-P. Weber, Th. Proffen, W. Palosz
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Authors: Bogdan F. Palosz, Stanislaw Gierlotka, Ewa Grzanka, K. Akimow, Roman Pielaszek, Piotr Biczyk, A. Grzegorczyk, Svetlana Stelmakh, Ulrich Bismayer, J.F. Janik
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Authors: Bogdan F. Palosz, Svetlana Stelmakh, Stanislaw Gierlotka, M. Aloszyna, Roman Pielaszek, P. Zinn, Th. Peun, Ulrich Bismayer, D.G. Keil
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Authors: Roman Pielaszek, Svetlana Stelmakh, Stanislaw Gierlotka, Bogdan F. Palosz, Dirk Kurtenbach, Ulrich Bismayer
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Authors: Roman Pielaszek, Stanislaw Gierlotka, Svetlana Stelmakh, Ewa Grzanka, Bogdan F. Palosz
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Authors: Anna Swiderska-Sroda, J.A. Kozubowski, A. Maranda-Niedbala, Ewa Grzanka, Bogdan F. Palosz, A. Presz, Stanislaw Gierlotka, Svetlana Stelmakh, Grzegorz Kalisz, Nathalie Herlin-Boime, C. Lathe
Abstract: SiC-Zn nanocomposites with about 20% volume fraction of metal were fabricated by infiltration process under the pressure of 2-8 GPa and at the temperature of 400_1000oC. SiC nanopowders used in the experiments formed loosely agglomerated chains of single crystal nanoparticles. The dimension of the agglomerates was in the micrometer range, the mean grain size was up to tens of nanometers. Microstructural investigations of the nanocomposites were performed at a different resolution levels using scanning, transmission electron microscopy and atomic force microscopy techniques (SEM, TEM, AFM, respectively). SEM observations indicate a presence of nano-dispersed, uniform (on the micrometer scale) mixture of two phases. TEM observations show that distribution of SiC and Zn nanocrystallites is uniform on the nanometer scale. High-resolution TEM images demonstrate an existence of thin (on the order of tens of Angstroms) Zn layers separating SiC grains. AFM images of the mechanically polished samples show a smooth surface with the roughness on the order of the SiC grain size (10-30 nm). After ion etching of some samples the AFM topographs show surface irregularities: periodically spaced hillocks 50-100 nm in height. The size of the SiC grains remains equal to that of the initial powder crystallites. The size of the Zn grains varies in the range of 20-100 nm depending on the initial SiC grain size and the composite fabrication conditions.
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Authors: Grzegorz Kalisz, Anna Swiderska-Sroda, Stanislaw Gierlotka, Ewa Grzanka, Bogdan F. Palosz, Svetlana Stelmakh
Abstract: Thermal surface purification in an inert gas flow and densification processes of SiC and diamond nanocrystalline powders with specific surface in the range of 60 – 300 m2/g and average grain sizes from 5 to 15 nm in diameter were examined. Termogravimetric Analysis (TGA) linked with mass spectrometry of outgassing products show that surface impurities desorb at up to 450°C. Further heating above 450°C leads to oxidation of the powder surface. Small Angle X-Ray Scattering (SAXS) and gas porosimetry (ASAP) was applied to investigate densification of the nanocrystalline powders. Compaction under 1GPa or higher pressure was found necessary for obtaining the ceramic matrix with porosity in the nanometer range.
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Authors: Anna Swiderska-Sroda, Grzegorz Kalisz, Ewa Grzanka, Stanislaw Gierlotka, Svetlana Stelmakh, Nathalie Herlin-Boime, Bogdan F. Palosz
Abstract: Two-nanophase SiC-Zn composites were synthesized under pressure up to 8 GPa at up to 1000oC using an high-pressure infiltration method. The advantage of this technique is that in a single, continuous process the ceramic nanopowder is compressed to form the matrix with nanopores; the nanopores are filled with a liquid secondary phase, (here Zn), which crystallizes as nano-scale grains. The key limitation is that the pores in the infiltrated preform have to stay open during the entire process. For this reason only powders of very hard ceramic materials can be used as a matrix. Two types of SiC nanopowders with average crystallite size of 10 nm and 60 nm and average particle size of 30 nm and 100 nm, respectively were used. The measurements of porosity of the green compacts prepared from these powders, pressed at 2.5 GPa and 8 GPa at room temperature, indicated that open porosity was maintained. The nanocomposites obtained show a “nano-nano” type microstructure with a uniform mixture of SiC and Zn phases. The volume fraction of Zn is 20 % independent of the process conditions and initial powder morphology. The process parameters and powder granularity influenced the crystal size of the secondary phase. The average grain size of Zn varied from 20 to 85 nm and was smaller in the composites obtained with the finer matrix, under higher pressure and at lower temperature. The microhardness HV02 of SiCZn nanocomposites varied from 6 to 22 GPa and increased with an increase of pressure and temperature of the infiltration process, and was significantly larger for the finer grained composites.
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Authors: Bogdan F. Palosz, Svetlana Stelmakh, Stanislaw Gierlotka
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Authors: Stanislaw Gierlotka, Bogdan F. Palosz, Roman Pielaszek, Svetlana Stelmakh, Stephen Doyle, Thomas Wroblewski
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