Naďa Pizúrová - Academia.edu (original) (raw)
Papers by Naďa Pizúrová
The application of an alternating magnetic field (0.54 T) was observed to lead to an improvement ... more The application of an alternating magnetic field (0.54 T) was observed to lead to an improvement in the fatigue endurance and an increase in Vickers microhardness and tensile strength of both EN8 steel and AA2014-T6 alloy. Fractography using scanning electron microscopy showed evidence of more ductile fracture features after treatment in contrast to untreated samples. The results of X-ray diffraction indicated formation of more compressive residual stresses following treatment; while examination by transmission electron microscopy showed evidence of fewer dislocations. In the case of the AA2014-T6 alloy; Guinier-Preston (GP) zones were also generated by the alternating magnetic field. However; the temperature increase during the treatment was too low to explain these observations. The results were attributed to the non-thermal effect of the alternating magnetic field treatment that led to depinning and movement of dislocations and secondary precipitation of copper.
Materials Science Forum, 2005
We are reporting the core-shell structured iron/graphite nanoparticles formed by annealing of a n... more We are reporting the core-shell structured iron/graphite nanoparticles formed by annealing of a nanopowder. The original Fe-C-N based nanopowder has been synthesized by the laser pyrolysis of gas phase reactants. TEM, XRD, Raman spectroscopy, Mössbauer spectroscopy and magnetic measurements were used for its characterization. Nanopowder was heated up to 800°C at ~ 1 Pa vacuum. Presence of iron nanoparticles with the mean diameter of 40 nm in the annealed state of the nanopowder was confirmed from the width of α-Fe X-ray diffraction lines and their core-shell structure was observed under TEM.
Surface and Interface Analysis, 2006
ABSTRACT We describe the Fe3C-based nanopowder obtained through the laser-induced pyrolysis of th... more ABSTRACT We describe the Fe3C-based nanopowder obtained through the laser-induced pyrolysis of the gas mixture of Fe(CO)5 and C2H4. This ferromagnetic nanopowder was characterized by XRD, HRTEM and magnetic measurements. Aggregated core-shell nanoparticles were identified in the nanopowder; Fe3C cores were coated with pyrolytic carbon. The mean coherence domain size estimated by the Scherrer formula was 18 nm. Basic magnetic characteristics were measured at 20 °C: HC = 42.0 kA m−1; σR = 31.2 A m2 kg−1; σS = 95.7 A m2 kg−1 (at 1200 kA m−1). The Curie temperature TC was 227 °C. Thermally induced phase transformations are discussed. Copyright © 2006 John Wiley & Sons, Ltd.
Metallurgical and Materials Transactions A, 2012
Thermal treatment of amorphous Fe 75 Ni 2 Si 8 B 13 C 2 alloy leads to crystallization of the sta... more Thermal treatment of amorphous Fe 75 Ni 2 Si 8 B 13 C 2 alloy leads to crystallization of the stable a-Fe(Si) and Fe 2 B as well as to the metastable Fe 3 B phase. The study of the mechanism of crystal growth of the a-Fe(Si) phase revealed that the mechanism of a-Fe(Si) growth changes from two dimensional in the early stage to one dimensional in the later stage of crystallization. The Fe 2 B phase was found to crystallize through two independent routes: from the amorphous phase and from the metastable Fe 3 B phase, which leads to a different mechanism of crystal growth for each route. Both routes exhibit a change in the mechanism of crystal growth: from two dimensional to one dimensional and from three dimensional to two dimensional, respectively. The respective mechanisms of crystal growth correlate well with the observed changes in preferential orientation of the crystallites of the Fe 2 B phase.
Intermetallics, 2014
Investigation of thermal stability of the alloy revealed stepwise crystallization process, manife... more Investigation of thermal stability of the alloy revealed stepwise crystallization process, manifested by two distinct complex exothermic peaks in dierential scanning calorimetry curves. Kinetic parameters of individual crystallization steps were found using the Kissinger and Vyazovkin methods. Structural characterization of thermally treated samples showed formation of dierent iron-based phases including α-Fe(Si), Fe2B, Fe16Nb6Si7 and Fe2Si and some metastable intermediary species. Morphology characterization of the surface and cross-section of the thermally treated samples showed granulated structure composed of several dierent phases and indicated occurrence of impingement eects during crystal growth. Value of estimated lifetime suggested very high stability against crystallization at room temperature and abrupt decrease of lifetime with temperature increase.
Surface and Interface Analysis, 2006
We describe the Fe3C-based nanopowder obtained through the laser-induced pyrolysis of the gas mix... more We describe the Fe3C-based nanopowder obtained through the laser-induced pyrolysis of the gas mixture of Fe(CO)5 and C2H4. This ferromagnetic nanopowder was characterized by XRD, HRTEM and magnetic measurements. Aggregated core-shell nanoparticles were identified in the nanopowder; Fe3C cores were coated with pyrolytic carbon. The mean coherence domain size estimated by the Scherrer formula was 18 nm. Basic magnetic characteristics were measured at 20 °C: HC = 42.0 kA m−1; σR = 31.2 A m2 kg−1; σS = 95.7 A m2 kg−1 (at 1200 kA m−1). The Curie temperature TC was 227 °C. Thermally induced phase transformations are discussed. Copyright © 2006 John Wiley & Sons, Ltd.
The Journal of Physical Chemistry C
IOP Conference Series: Materials Science and Engineering
Three Fe-Al-based alloys, a binary with 22 at. % of Al, a ternary with 22 at. % of Al and 7 at. %... more Three Fe-Al-based alloys, a binary with 22 at. % of Al, a ternary with 22 at. % of Al and 7 at. % of Ti and a quaternary with 22 at. % of Al, 4 at. % of Ti and 4 at. % of Nb prepared by arc melting to small button type ingots were studied by small punch test and small punch creep test in order to obtain the high temperature tensile and creep properties. Evaluation of the results shows a significantly improved strength at high temperatures and creep resistance of the ternary and quaternary alloys compared to the binary alloy. The observation of the punched discs fracture surfaces related to the initial microstructure also helps to better understanding of the deformation and fracture behavior of these alloys at high temperatures.
Proceedings
Gas microsensors based on columnar zinc oxide structures (rods and needles) with different aspect... more Gas microsensors based on columnar zinc oxide structures (rods and needles) with different aspect ratios and wetting properties are developed via aerosol-assisted chemical vapor deposition. The correlation between their wetting properties and degree of humidity-interference in gas sensing is presented. Gas sensing tests of these systems to hydrogen demonstrate noticeable lower humidity-interference for the columnar zinc oxide structures in the form of needles provided of higher hydrophobicity, as opposed to those in the form of rods, suggesting that a tuning of the wetting properties in metal oxides could allow for the humidity-resilient detection of gaseous analytes.
Colloid and Polymer Science
Crystals
We combine theoretical and experimental tools to study elastic properties of Fe-Al-Ti superalloys... more We combine theoretical and experimental tools to study elastic properties of Fe-Al-Ti superalloys. Focusing on samples with chemical composition Fe 71 Al 22 Ti 7 , we use transmission electron microscopy (TEM) to detect their two-phase superalloy nano-structure (consisting of cuboids embedded into a matrix). The chemical composition of both phases, Fe 66 . 2 Al 23 . 3 Ti 10 . 5 for cuboids and Fe 81 Al 19 (with about 1% or less of Ti) for the matrix, was determined from an Energy-Dispersive X-ray Spectroscopy (EDS) analysis. The phase of cuboids is found to be a rather strongly off-stoichiometric (Fe-rich and Ti-poor) variant of Heusler Fe 2 TiAl intermetallic compound with the L2 1 structure. The phase of the matrix is a solid solution of Al atoms in a ferromagnetic body-centered cubic (bcc) Fe. Quantum-mechanical calculations were employed to obtain an insight into elastic properties of the two phases. Three distributions of chemical species were simulated for the phase of cuboids...
Journal of Non-Crystalline Solids
Key Engineering Materials
The local mechanical properties of Fe78Al22 alloy were studied using nanoindentation techniques. ... more The local mechanical properties of Fe78Al22 alloy were studied using nanoindentation techniques. Sharp Berkovich indenter was used to perform load-controlled nanoindentation experiments on the studied sample. Hardness and elastic modulus maps were created on the basis of the indentation tests carried out in different grains. The focus of the work was to study the dependence of mechanical properties on the grain orientation. The results were in good agreement with quantum-mechanical calculations of anisotropic elastic properties of the studied alloy. It was explained that the maximum detected elastic modulus values are likely for grains with [111] crystallographic orientations which we theoretically identified as the hard ones.
ACS applied materials & interfaces, Jan 7, 2016
We present a new method for vapor deposition of columnar ZnO structures in the form of rods on va... more We present a new method for vapor deposition of columnar ZnO structures in the form of rods on various substrates without the need for substrate modification with catalyst seed particles and at relatively low temperatures compared to other vapor deposition methods. These structures are used for the photodegradation of stearic acid (C18H36O2) and the photoactivated detection of gases such as carbon monoxide (CO), ethanol (C2H6O), toluene (C7H8), and nitrogen dioxide (NO2) at room temperature, showing improved selectivity compared to tests performed in themoactivated mode.
ABSTRACT The aim of the present work is to study how the volume (lattice parameters) changes of b... more ABSTRACT The aim of the present work is to study how the volume (lattice parameters) changes of barium titanate, induced by a phase transition, which occurs by temperature sweeps, influence magnetic behavior of cobalt ferrite in their composites via inverse magnetostrictive (Villari) effect. Structure, phase composition, and magnetic properties were investigated using X-ray diffraction, Mössbauer spectroscopy, and temperature dependence of magnetization. The tetragonal-to-orthorhombic phase transition in barium titanate occurring at ~280 K on cooling can be observed in the zero-field cooled magnetization curve. The other phase transitions, i.e., tetragonal-to-cubic transition at ~390 K and orthorhombic-to-rhombohedral transition at ~178 K, were detected neither by magnetic nor by Mössbauer measurements.
The application of an alternating magnetic field (0.54 T) was observed to lead to an improvement ... more The application of an alternating magnetic field (0.54 T) was observed to lead to an improvement in the fatigue endurance and an increase in Vickers microhardness and tensile strength of both EN8 steel and AA2014-T6 alloy. Fractography using scanning electron microscopy showed evidence of more ductile fracture features after treatment in contrast to untreated samples. The results of X-ray diffraction indicated formation of more compressive residual stresses following treatment; while examination by transmission electron microscopy showed evidence of fewer dislocations. In the case of the AA2014-T6 alloy; Guinier-Preston (GP) zones were also generated by the alternating magnetic field. However; the temperature increase during the treatment was too low to explain these observations. The results were attributed to the non-thermal effect of the alternating magnetic field treatment that led to depinning and movement of dislocations and secondary precipitation of copper.
Materials Science Forum, 2005
We are reporting the core-shell structured iron/graphite nanoparticles formed by annealing of a n... more We are reporting the core-shell structured iron/graphite nanoparticles formed by annealing of a nanopowder. The original Fe-C-N based nanopowder has been synthesized by the laser pyrolysis of gas phase reactants. TEM, XRD, Raman spectroscopy, Mössbauer spectroscopy and magnetic measurements were used for its characterization. Nanopowder was heated up to 800°C at ~ 1 Pa vacuum. Presence of iron nanoparticles with the mean diameter of 40 nm in the annealed state of the nanopowder was confirmed from the width of α-Fe X-ray diffraction lines and their core-shell structure was observed under TEM.
Surface and Interface Analysis, 2006
ABSTRACT We describe the Fe3C-based nanopowder obtained through the laser-induced pyrolysis of th... more ABSTRACT We describe the Fe3C-based nanopowder obtained through the laser-induced pyrolysis of the gas mixture of Fe(CO)5 and C2H4. This ferromagnetic nanopowder was characterized by XRD, HRTEM and magnetic measurements. Aggregated core-shell nanoparticles were identified in the nanopowder; Fe3C cores were coated with pyrolytic carbon. The mean coherence domain size estimated by the Scherrer formula was 18 nm. Basic magnetic characteristics were measured at 20 °C: HC = 42.0 kA m−1; σR = 31.2 A m2 kg−1; σS = 95.7 A m2 kg−1 (at 1200 kA m−1). The Curie temperature TC was 227 °C. Thermally induced phase transformations are discussed. Copyright © 2006 John Wiley & Sons, Ltd.
Metallurgical and Materials Transactions A, 2012
Thermal treatment of amorphous Fe 75 Ni 2 Si 8 B 13 C 2 alloy leads to crystallization of the sta... more Thermal treatment of amorphous Fe 75 Ni 2 Si 8 B 13 C 2 alloy leads to crystallization of the stable a-Fe(Si) and Fe 2 B as well as to the metastable Fe 3 B phase. The study of the mechanism of crystal growth of the a-Fe(Si) phase revealed that the mechanism of a-Fe(Si) growth changes from two dimensional in the early stage to one dimensional in the later stage of crystallization. The Fe 2 B phase was found to crystallize through two independent routes: from the amorphous phase and from the metastable Fe 3 B phase, which leads to a different mechanism of crystal growth for each route. Both routes exhibit a change in the mechanism of crystal growth: from two dimensional to one dimensional and from three dimensional to two dimensional, respectively. The respective mechanisms of crystal growth correlate well with the observed changes in preferential orientation of the crystallites of the Fe 2 B phase.
Intermetallics, 2014
Investigation of thermal stability of the alloy revealed stepwise crystallization process, manife... more Investigation of thermal stability of the alloy revealed stepwise crystallization process, manifested by two distinct complex exothermic peaks in dierential scanning calorimetry curves. Kinetic parameters of individual crystallization steps were found using the Kissinger and Vyazovkin methods. Structural characterization of thermally treated samples showed formation of dierent iron-based phases including α-Fe(Si), Fe2B, Fe16Nb6Si7 and Fe2Si and some metastable intermediary species. Morphology characterization of the surface and cross-section of the thermally treated samples showed granulated structure composed of several dierent phases and indicated occurrence of impingement eects during crystal growth. Value of estimated lifetime suggested very high stability against crystallization at room temperature and abrupt decrease of lifetime with temperature increase.
Surface and Interface Analysis, 2006
We describe the Fe3C-based nanopowder obtained through the laser-induced pyrolysis of the gas mix... more We describe the Fe3C-based nanopowder obtained through the laser-induced pyrolysis of the gas mixture of Fe(CO)5 and C2H4. This ferromagnetic nanopowder was characterized by XRD, HRTEM and magnetic measurements. Aggregated core-shell nanoparticles were identified in the nanopowder; Fe3C cores were coated with pyrolytic carbon. The mean coherence domain size estimated by the Scherrer formula was 18 nm. Basic magnetic characteristics were measured at 20 °C: HC = 42.0 kA m−1; σR = 31.2 A m2 kg−1; σS = 95.7 A m2 kg−1 (at 1200 kA m−1). The Curie temperature TC was 227 °C. Thermally induced phase transformations are discussed. Copyright © 2006 John Wiley & Sons, Ltd.
The Journal of Physical Chemistry C
IOP Conference Series: Materials Science and Engineering
Three Fe-Al-based alloys, a binary with 22 at. % of Al, a ternary with 22 at. % of Al and 7 at. %... more Three Fe-Al-based alloys, a binary with 22 at. % of Al, a ternary with 22 at. % of Al and 7 at. % of Ti and a quaternary with 22 at. % of Al, 4 at. % of Ti and 4 at. % of Nb prepared by arc melting to small button type ingots were studied by small punch test and small punch creep test in order to obtain the high temperature tensile and creep properties. Evaluation of the results shows a significantly improved strength at high temperatures and creep resistance of the ternary and quaternary alloys compared to the binary alloy. The observation of the punched discs fracture surfaces related to the initial microstructure also helps to better understanding of the deformation and fracture behavior of these alloys at high temperatures.
Proceedings
Gas microsensors based on columnar zinc oxide structures (rods and needles) with different aspect... more Gas microsensors based on columnar zinc oxide structures (rods and needles) with different aspect ratios and wetting properties are developed via aerosol-assisted chemical vapor deposition. The correlation between their wetting properties and degree of humidity-interference in gas sensing is presented. Gas sensing tests of these systems to hydrogen demonstrate noticeable lower humidity-interference for the columnar zinc oxide structures in the form of needles provided of higher hydrophobicity, as opposed to those in the form of rods, suggesting that a tuning of the wetting properties in metal oxides could allow for the humidity-resilient detection of gaseous analytes.
Colloid and Polymer Science
Crystals
We combine theoretical and experimental tools to study elastic properties of Fe-Al-Ti superalloys... more We combine theoretical and experimental tools to study elastic properties of Fe-Al-Ti superalloys. Focusing on samples with chemical composition Fe 71 Al 22 Ti 7 , we use transmission electron microscopy (TEM) to detect their two-phase superalloy nano-structure (consisting of cuboids embedded into a matrix). The chemical composition of both phases, Fe 66 . 2 Al 23 . 3 Ti 10 . 5 for cuboids and Fe 81 Al 19 (with about 1% or less of Ti) for the matrix, was determined from an Energy-Dispersive X-ray Spectroscopy (EDS) analysis. The phase of cuboids is found to be a rather strongly off-stoichiometric (Fe-rich and Ti-poor) variant of Heusler Fe 2 TiAl intermetallic compound with the L2 1 structure. The phase of the matrix is a solid solution of Al atoms in a ferromagnetic body-centered cubic (bcc) Fe. Quantum-mechanical calculations were employed to obtain an insight into elastic properties of the two phases. Three distributions of chemical species were simulated for the phase of cuboids...
Journal of Non-Crystalline Solids
Key Engineering Materials
The local mechanical properties of Fe78Al22 alloy were studied using nanoindentation techniques. ... more The local mechanical properties of Fe78Al22 alloy were studied using nanoindentation techniques. Sharp Berkovich indenter was used to perform load-controlled nanoindentation experiments on the studied sample. Hardness and elastic modulus maps were created on the basis of the indentation tests carried out in different grains. The focus of the work was to study the dependence of mechanical properties on the grain orientation. The results were in good agreement with quantum-mechanical calculations of anisotropic elastic properties of the studied alloy. It was explained that the maximum detected elastic modulus values are likely for grains with [111] crystallographic orientations which we theoretically identified as the hard ones.
ACS applied materials & interfaces, Jan 7, 2016
We present a new method for vapor deposition of columnar ZnO structures in the form of rods on va... more We present a new method for vapor deposition of columnar ZnO structures in the form of rods on various substrates without the need for substrate modification with catalyst seed particles and at relatively low temperatures compared to other vapor deposition methods. These structures are used for the photodegradation of stearic acid (C18H36O2) and the photoactivated detection of gases such as carbon monoxide (CO), ethanol (C2H6O), toluene (C7H8), and nitrogen dioxide (NO2) at room temperature, showing improved selectivity compared to tests performed in themoactivated mode.
ABSTRACT The aim of the present work is to study how the volume (lattice parameters) changes of b... more ABSTRACT The aim of the present work is to study how the volume (lattice parameters) changes of barium titanate, induced by a phase transition, which occurs by temperature sweeps, influence magnetic behavior of cobalt ferrite in their composites via inverse magnetostrictive (Villari) effect. Structure, phase composition, and magnetic properties were investigated using X-ray diffraction, Mössbauer spectroscopy, and temperature dependence of magnetization. The tetragonal-to-orthorhombic phase transition in barium titanate occurring at ~280 K on cooling can be observed in the zero-field cooled magnetization curve. The other phase transitions, i.e., tetragonal-to-cubic transition at ~390 K and orthorhombic-to-rhombohedral transition at ~178 K, were detected neither by magnetic nor by Mössbauer measurements.