16 results on '"Marián Kucharík"'
Search Results
2. Rapid solidification of cryolite and cryolite–alumina melts
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Marián Kucharík, Jozef Vincenc Oboňa, Miroslav Boča, Michal Korenko, Magdaléna Kadlečíková, and Dušan Janičkovič
- Subjects
Infrared ,Annealing (metallurgy) ,Analytical chemistry ,Mineralogy ,General Chemistry ,Hall–Héroult process ,Cryolite ,Amorphous solid ,symbols.namesake ,chemistry.chemical_compound ,Cooling rate ,chemistry ,Metastability ,symbols ,Raman spectroscopy - Abstract
Rapid solidification processing (with a cooling rate in the interval 105–106 K s−1) was used to prepare deeply undercooled cryolite–alumina melts. These samples were analyzed by XRD, infrared, and Raman spectroscopy. Besides cryolite, the amorphous phase and a low amount of ι-Al2O3 were detected. Annealing of the quenched sample revealed the transformation of metastable amorphous phases into different products depending on the annealing conditions. The results obtained showed that all of the elements (Na, Al, O, and F) are probably present in the amorphous parts of the quenched samples.
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- 2009
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3. Phase Equilibria, Volume Properties, Surface Tension, and Viscosity of the (FLiNaK)eut + K2NbF7 Melts
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Marián Kucharík, Miroslav Boča, Roman Vasiljev, and Blanka Kubíková
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Surface tension ,Maximum bubble pressure method ,chemistry.chemical_compound ,Viscosity ,Volume (thermodynamics) ,chemistry ,General Chemical Engineering ,Torsion pendulum clock ,FLiNaK ,Thermodynamics ,Partial molar property ,General Chemistry ,Volume contraction - Abstract
Physicochemical properties of the system (FLiNaK) eut (1) + K 2 NbF 7 (2) were investigated. Phase equilibria were studied by a thermal analysis method. Density of the investigated system was measured by the Archimedean method. On the basis of these data, molar volumes were calculated for selected temperatures, and the partial molar volume of K 2 NbF 7 in (FLiNaK) eut was evaluated adopting the value V 2 /cm 3 ·mol -1 = (121.1 ± 0.4) at 1073 K, indicating volume contraction. Surface tension was measured by the maximal bubble pressure method, and viscosity was measured using the computerized torsion pendulum method.
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- 2009
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4. Nanotubes Made from Deeply Undercooled Cryolite/Alumina Melts
- Author
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Michal Korenko, Blanka Kubíková, Rosa Córdoba, Dušan Janičkovič, José María de Teresa, Marián Kucharík, and Jozef Vincenc Oboňa
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Diffraction ,chemistry.chemical_classification ,Base (chemistry) ,Chemistry ,Scanning electron microscope ,Organic Chemistry ,Analytical chemistry ,Infrared spectroscopy ,Biochemistry ,Catalysis ,Cryolite ,Inorganic Chemistry ,chemistry.chemical_compound ,Crystallography ,Cooling rate ,Drug Discovery ,X-ray crystallography ,Physical and Theoretical Chemistry ,Spectroscopy - Abstract
d ) Institute of Physics, Slovak Academy of Sciences, Dubravska cesta 9, SK-845 36 Bratislava e ) Instituto de Ciencia de Materiales de Aragon, CSIC-University of Zaragoza, ES-50009 Zaragoza The rapid-solidification processing (by a cooling rate of 105 -1 06 K/s) was used for the preparation of deeply undercooled cryolite/alumina (Na3AlF 6/Al2O3) melts. We found a mass of nanotubes on the surface of these undercooled melts. The nanotubes were preferentially located on the defect places of the surface with the following approximate dimensions: base � 100 � 100 nm, length � 1000 nm. The solidified samples with the nanotubes on the surface were analyzed by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and infrared spectroscopy (IR).
- Published
- 2008
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5. Thermal Analysis of the System Na3AlF6–NaVO3
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Marián Kucharík, V. Danielik, František Šimko, Roman Vasiljev, and Miroslav Boča
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chemistry.chemical_compound ,chemistry ,Aluminum electrolysis ,Metallurgy ,Thermodynamics ,Binary number ,General Chemistry ,Binary system ,Thermal analysis ,Cryolite ,Eutectic system ,Phase diagram - Abstract
The phase diagram of the system Na3AlF6–NaVO3 was determined by means of thermal analysis. The system is a simple binary eutectic one. The eutectic point was estimated at x(NaVO3) = 0.975 and teut = 617°C. The XRD patterns of samples after thermal analysis revealed the presence of cryolite and NaVO3 only supporting the above assumption of a simple eutectic binary system.
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- 2007
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6. Surface Tension of the System NaF –AlF3–Al2O3 and Surface Adsorption of Al2O3
- Author
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Roman Vasiljev and Marián Kucharík
- Subjects
Surface tension ,Surface (mathematics) ,Maximum bubble pressure method ,chemistry.chemical_compound ,Adsorption ,Concentration dependence ,Chemistry ,Inorganic chemistry ,Analytical chemistry ,General Physics and Astronomy ,Physical and Theoretical Chemistry ,Mathematical Physics ,Cryolite - Abstract
Part of the molten system NaF-AlF3-Al2O3 was studied by surface tension measurements, which were performed at cryolite ratios (CR) between 1.5 and 3 [CR = n(NaF)/n(AlF3)]. The maximal bubble pressure method was applied. The surface adsorption of alumina (Al2O3) was also calculated. The obtained results were discussed in terms of the anionic composition of the melt. The addition of AlF3 to melt with CR= 3 decreases the surface tension, as AlF3 is surface-active in molten Na3AlF6. The concentration dependence of the surface tension and the surface adsorption of alumina in the title system are influenced by the formation of surface-active oxofluoroaluminates. An increase of the difference between the surface tension of NaF-AlF3 mixtures and the surface tension of pure alumina was observed with decreasing cryolite ratio.
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- 2006
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7. Density and Surface Tension of the System KF–K2TaF7–Ta2O5
- Author
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Miroslav Boča, Zuzana Ivanová, Marián Kucharík, Roman Vasiljev, M. Chrenková, and Jarmila Cibulkova
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Surface tension ,Maximum bubble pressure method ,Ternary numeral system ,Molar volume ,chemistry ,Tantalum ,Thermodynamics ,chemistry.chemical_element ,Partial molar property ,Binary system ,Physical and Theoretical Chemistry ,Ternary operation - Abstract
The density of the system KF–K2TaF7–Ta2O5 was measured by the Archimedean method and the surface tension by the maximum bubble pressure method in the composition range up to 20 mol% Ta2O5. The density in the system KF–K2TaF7–Ta2O5 increases from KF through K2TaF7 to Ta2O5 and the surface tension increases from K2TaF7 through KF to Ta2O5. Based on the measured density values, the molar volumes of the binary and ternary melts at 860 °C, 900 °C and 950 °C were calculated as well as the partial molar volumes of particular components in different binaries. The small negative deviation from ideal behaviour in the binary system KF–K2TaF7 was identified by the calculation of the molar excess volume. The formation of complex anions [TaF8]3− is expected in this binary system. The surface tension decreases monotonically from KF to K2TaF7 in the binary system KF–K2TaF7. In the next two binaries KF–Ta2O5 and K2TaF7–Ta2O5 decrease of the surface tension was observed with the initial addition of Ta2O5 followed by the increase of the surface tension by further addition of Ta2O5. Based on measured data it was concluded that in binaries KF–Ta2O5 and K2TaF7–Ta2O5 the surface active component is Ta2O5 and in the binary KF–K2TaF7 the surface active component is K2TaF7. Mathematical description of the concentration dependence of the molar volume and surface tension of the measured ternary system was done by the polynomial function at 860°C, 900°C, and at 950°C.
- Published
- 2006
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8. Structural and thermodynamic aspects in the molybdenum melts of the system KF–K2MoO4–SiO2
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Miroslav Boča, Roman Vasiljev, Helena Pálková, Vladimír Daněk, Marián Kucharík, and M. Chrenková
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Maximum bubble pressure method ,Ternary numeral system ,Chemistry ,Thermodynamics ,Partial molar property ,Condensed Matter Physics ,Mole fraction ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,Molar volume ,Materials Chemistry ,Physical and Theoretical Chemistry ,Ternary operation ,Spectroscopy ,Phase diagram ,Eutectic system - Abstract
The complex physico-chemical analysis of the system KF–K2MoO4–SiO2, based on the phase diagram, density, surface tension and viscosity measurements, was performed. The phase diagrams of the binary systems as well as that of the ternary system in the range up to 50% SiO2 were measured using the thermal analysis method. The results proved the presence of the congruently melting compound K3FMoO4 at 751 °C in the binary melt KF–K2MoO4. The strong positive deviation from ideal behaviour of the ternary system KF–K2MoO4–SiO2 was ascribed to the formation of heteropolyanions [SiMo12O40]4− in the melt. In the investigated concentration range of the ternary system, no eutectic point has been found. It lies most probably beyond the investigated part of the system. The probable inaccuracy in the calculated ternary phase diagram is 5.9 °C. The density of the melts of the system KF–K2MoO4–SiO2 was measured using the Archimedean method. Based on the obtained density data the molar volume, partial molar volume and excess molar volume of the melts were calculated in order to consider the possible chemical interactions of components. The degree of thermal dissociation of the additive compound K3FMoO4 was calculated based on both the thermodynamic analysis of the phase diagram and the volume properties of the investigated system. It was found that the degree of the thermal dissociation of K3FMoO4 at the melting point attains the value αo=0.81. The dissociation enthalpy, calculated on the basis of the density values is ΔH(dis, K3FMoO4)=18.8 kJ mol−1. The surface tension of the molten system KF–K2MoO4–SiO2 has been determined using the maximum bubble pressure method. Based on the obtained data the concentration dependence of the surface tension and of the surface tension excess of the investigated system was calculated. The viscosity of melts of the system KF–K2MoO4–SiO2 has been measured using the computerised torsional pendulum method. The sum of viscosities of pure components in logarithm values multiplied by their mole fraction was used as an ‘additive’ behaviour. A multiple linear regression analysis was performed to obtain coefficients of the modified Redlich–Kister's type equation. Binary and ternary interactions of the particular components were found. X-ray powder diffraction patterns and IR spectra of the certain quenched powdered samples of both binary and ternary mixtures were recorded. By both techniques the presence of starting compounds and the presence of another compounds, as well, was detected. Some of these compounds were recognized based on the known data. The remaining data were attributed to the possible expected compounds.
- Published
- 2004
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9. Preparation and Analysis of Na2Al2O2F4
- Author
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V. Daněk, F. Šimko, M. Chrenková, and Marián Kucharík
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Materials science ,General Materials Science ,Nanotechnology ,Condensed Matter Physics ,Atomic and Molecular Physics, and Optics - Published
- 2003
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10. Solubility of AlPO4 and NaVO3 in NaF−AlF3 Melts
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Roman Vasiljev and Marián Kucharík
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Primary (chemistry) ,General Chemical Engineering ,Inorganic chemistry ,General Chemistry ,Sodium metavanadate ,Cryolite ,law.invention ,chemistry.chemical_compound ,chemistry ,law ,Aluminium phosphate ,Crystallization ,Solubility ,Molten salt ,Thermal analysis - Abstract
The temperatures of primary crystallization of cryolite in systems NaF−AlF3−AlPO4 and NaF−AlF3−NaVO3 were determined by thermal analysis. The measurements were performed at cryolite ratios (CR) equal to 2.5 and 2 [CR = n(NaF)/n(AlF3)]. It is evident that AlPO4 decreases the temperature of primary crystallization of cryolite more than NaVO3 at both selected cryolite ratios.
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- 2008
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11. Structure of K2TaF7at 993 K: the combined use of synchrotron powder data and solid-state DFT calculations
- Author
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Marián Kucharík, Ľubomír Smrčok, Michela Brunelli, and Miroslav Boča
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Chemistry ,Rietveld refinement ,Tantalum ,chemistry.chemical_element ,Energy minimization ,General Biochemistry, Genetics and Molecular Biology ,Synchrotron ,law.invention ,Crystallography ,law ,Atom ,Fluorine ,Physical chemistry ,Density functional theory ,Powder diffraction - Abstract
The structure of dipotassium tantalum heptafluoride, K2TaF7, was optimized by energy minimization in the solid state using a plane-waves DFT (density functional theory) computation for which the lattice parameters were obtained by the Le Bail technique from synchrotron X-ray powder diffraction data collected at 993 K. Owing to the sample's corrosiveness, it had to be loaded in a thin-walled Pt capillary. It was found that the structure corresponds to that of the β-K2TaF7phase. The Ta atoms in the TaF7−polyhedra are sevenfold coordinated by fluorine atoms positioned within 1.977–2.007 Å. The K atoms are surrounded by eleven (K1) or eight (K2) fluorine atoms. Every F atom in the structure is surrounded by three K atoms. The F...K contact distances vary from 2.57 to 3.32 Å. It is suggested that solid-state DFT methods may, in many cases, provide an alternative tool to standard Rietveld refinements for structure determination.
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- 2008
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12. Rapid solidification processing in molten salts chemistry: X-ray analysis of deeply undercooled cryolite-alumina melts
- Author
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Dušan Janičkovič, Michal Korenko, and Marián Kucharík
- Subjects
chemistry.chemical_compound ,Cooling rate ,Annealing (metallurgy) ,Chemistry ,General Chemical Engineering ,Metallurgy ,Materials Chemistry ,General Chemistry ,X ray analysis ,Biochemistry ,Industrial and Manufacturing Engineering ,Cryolite - Abstract
Rapid solidification processing (cooling rate from the interval 105–106 K s−1) was used to prepare deeply undercooled cryolite-alumina melts. Such prepared samples were analyzed by the XRD method. Besides cryolite, XRD patterns belonging to ι-Al2O3 were recorded. The influence of annealing on the XRD patterns of deeply undercooled melts was also investigated.
- Published
- 2008
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13. Silver as Anode in Cryolite—Alumina-Based Melts
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Pierre Taxil, Marián Kucharík, Laurent Cassayre, Pierre Chamelot, Institut National Polytechnique de Toulouse - Toulouse INP (FRANCE), Université Toulouse III - Paul Sabatier - UT3 (FRANCE), Slovak Academy of Sciences - SAS (SLOVAKIA), and Centre National de la Recherche Scientifique - CNRS (FRANCE)
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Low-temperature electrolyte ,Electrolysis ,Cryolite- Alumina ,Chemistry ,General Chemical Engineering ,Inorganic chemistry ,Oxygen evolution ,General Chemistry ,Electrolyte ,Electrochemistry ,Biochemistry ,Redox ,Industrial and Manufacturing Engineering ,Cryolite ,Silver electrode ,Anode ,law.invention ,chemistry.chemical_compound ,law ,Materials Chemistry ,Melting point ,Génie chimique - Abstract
The anodic behaviour of silver was investigated in cryolite—alumina-based melt. Silver has a lower melting point (ca. 960°C) than the other metals considered as possible inert materials for aluminium electrolysis. The working temperature used in aluminium industry is approximately 960°C, depending on the melt composition. Therefore, the stability of silver during the anodic process was tested at 870°C in an acidic electrolyte consisting of 65.5 mass % Na3AlF6 + 22.9 mass % AlF3 + 5.7 mass % CaF2 + 3.9 mass % LiF + 2 mass % Al2O3 with the melting point ca. 850°C. The electrolyte without alumina was prepared as well, with the melting point ca. 860°C. The resulting cryolite ratio (CR = n(NaF)/n(AlF3)) for both electrolytes was equal to 1.6. The behaviour of the silver anode was studied by voltammetry measurements. The electrochemical study showed that an oxidation reaction occurred at a potential below the oxygen evolution potential. Silver was not found to be stable under oxygen evolution. The degradation of the silver anode was apparent after electrolysis.
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- 2007
14. Notes on notation of sodium oxofluoroaluminate anions
- Author
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Miroslav Boča and Marián Kucharík
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General Chemical Engineering ,Sodium ,Inorganic chemistry ,chemistry.chemical_element ,Thermodynamics ,General Chemistry ,Notation ,Biochemistry ,Industrial and Manufacturing Engineering ,Cryolite ,chemistry.chemical_compound ,chemistry ,Materials Chemistry ,Order of magnitude ,Equilibrium constant - Abstract
The chemical notation of the reaction products in the system NaF—AlF3—Al2O3 was reevaluated and its modifications were suggested. Based on these modifications, the equilibrium constants of selected reactions were calculated. Some of the equilibrium constants differed by one or two orders of magnitude from the values of the corresponding original equilibrium constants.
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- 2007
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15. Rapid solidification of cryolite and cryolite–alumina melts.
- Author
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Marián Kucharík, Michal Korenko, Dušan Janičkovič, Magdaléna Kadlečíková, Miroslav Boča, and Jozef Oboňa
- Abstract
Abstract Rapid solidification processing (with a cooling rate in the interval 105–106 K s−1) was used to prepare deeply undercooled cryolite–alumina melts. These samples were analyzed by XRD, infrared, and Raman spectroscopy. Besides cryolite, the amorphous phase and a low amount of ι-Al2O3 were detected. Annealing of the quenched sample revealed the transformation of metastable amorphous phases into different products depending on the annealing conditions. The results obtained showed that all of the elements (Na, Al, O, and F) are probably present in the amorphous parts of the quenched samples. Graphical Abstract [ABSTRACT FROM AUTHOR]
- Published
- 2010
16. Solubility of AlPO4and NaVO3in NaF−AlF3Melts.
- Author
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Marián Kucharík and Roman Vasiljev
- Published
- 2008
- Full Text
- View/download PDF
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