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Bratislava, Slovakia

Prnova A.,Slovak Academy of Sciences | Galusek D.,Slovak Academy of Sciences | Hnatko M.,Slovak Academy of Sciences | Kozankova J.,Glass and Cement | Vavra I.,Slovak Academy of Sciences
Ceramics - Silikaty | Year: 2011

In the work we describe the use of Al2O3-Y 2O3 glass microspheres with high alumina contents prepared by flame synthesis as a precursor for materials with binary eutectic microstructure and high hardness. XRD amorphous microspheres with eutectic composition in a pseudobinary system Al2O3-Y 3Al5O12 (YAG) were prepared by feeding a crystalline powder precursor of respective composition into methane-oxygen flame. The microspheres with the mean diameter ≈10 μm were hot-pressed in vacuum under various conditions (temperatures 840-1600°C, pressure 30 or 40 MPa, isothermal dwell 0-120 min). Hot pressing at 1600°C without isothermal dwell yielded fully dense bulk materials with fine two phase microstructure with Al2O3 and YAG phases percolating at submicrometre level and with hardness 15 GPa. Extension of the isothermal dwell resulted in undesirable coarsening of the resulting microstructure. Source


Prnova A.,Slovak Academy of Sciences | Domanicka A.,Slovak Academy of Sciences | Klement R.,Slovak Academy of Sciences | Kraxner J.,Slovak Academy of Sciences | And 5 more authors.
Optical Materials | Year: 2011

The undoped, and Nd-, Er-doped low silica high alumina yttrium aluminosilicate (YAS) glasses were prepared by flame synthesis in the form of transparent glass microbeads with diameters ranging from a few to several tens of micrometers. The silica content ranged between 5 and 20 mol.%. The prepared glass microbeads were characterized by optical microscopy, SEM XRD, FT-IR and UV-VIS-NIR spectroscopy. The glass forming ability of glasses, expressed in terms of the difference between the glass transition temperature, Tg, and the onset of crystallization, Tx, improved with increasing silica content. Doping of YAS15 glass with neodymium or erbium at the level of 1-5 mol.% leads to decrease of both the Tg and Tx. However, the glass forming ability was not affected. The UV-VIS-NIR reflectance spectra in the spectral range from 300 to 1800 nm shows characteristic absorptions, due to the optically active Nd3+ and Er3+ ions in the host glass. © 2011 Elsevier B.V. All rights reserved. Source


Jezo L.,PCLA | Palou M.,Glass and Cement | Kozankova J.,Glass and Cement | Ifka T.,Glass and Cement
Journal of Thermal Analysis and Calorimetry | Year: 2010

Isothermal conduction calorimetry, differential thermal analysis (DTA)-thermogravimetric analysis (TG) analysis, and SEM observations have proved the activation effect of Ca(OH)2 released from the C3S hydration upon blast furnace slag (BFS). Five sample mixtures of BFS and C 3S and two samples of pure BFS and C3S were submitted to reaction with water inside the calorimeter at room temperature. The values of hydration heat were recorded up to 7 days. Samples were stored in humidity during 28 days and then were submitted to DTA-TG and SEM analysis. The effect of Ca(OH)2 upon heat evolution of sample mixtures has been quantified and its influence upon the formation of new hydrates and microstructure of pastes was evidenced. © 2010 Akadémiai Kiadó, Budapest, Hungary. Source

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