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Nanostructured materials based on metal oxides - structure and thermal stability
Václavů, Tereza ; Kužel, Radomír (advisor) ; Čapková, Pavla (referee) ; Klementová, Mariana (referee)
Title: Nanostructured materials based on metal oxides - structure and thermal stability Author: Tereza Václavů Department: Department of Condensed Matter Physics Supervisor: prof. RNDr. Radomír Kužel, CSc. Abstract: The structure and temperature stability of two nanocrystalline ma- terials were studied. First, titanate nanotubes prepared by hydrothermal synthesis were studied from room temperature up to 1000 ◦ C in air and helium atmospheres and in vacuum with the aid of in situ X-ray diffraction (XRD) and calorimetry combined with electron microscopy. The nanotubes exhibit different behavior and structure transformations during heating in different atmospheres. A difference between vacuum and He atmosphere was observed; also a different final product was observed after annealing: In air, the nanorods disintegrated to nanoparticles, whereas in vacuum nanowires formed. The second material studied was a nanocrystalline particle system with an iron core protected against oxidation by an oxide layer. The structure of these nanoparticles was determined by XRD and Mossbauer spectroscopy. The tem- perature stability and induced transformations of these samples were studied by in situ XRD and X-ray small-angle scattering (SAXS). The long-time stability of the structure of these nanoparticles was studied as well;...
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Preparation of Cu3(Si0.5Ge0.5) Nanoplatelets
Dřínek, Vladislav ; Fajgar, Radek ; Palatinus, Lukáš ; Klementová, Mariana ; Novotný, F.
The nanoplatelets possess composition corresponding to Cu3(Si0.5Ge0.5). The 3D collection of electron diffraction patterns has shown that the rooom-temperature structure of the nanoplatelets corresponds to the ?-Cu3Si phase. Evaluation of the diffraction pattern shows that the structure has trigonal symmetry with long period incommensurate modulation. it can be approximately described in a 36-fold superstructure with trigonal unit cell and cell dimensions a=b=16.1A6, c=21.8A6.
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Objemové nanokrystalické materiály na bázi oxidu hlinitého a zirkoničitého
Chráska, Tomáš ; Klementová, Mariana
An alternative method to produce bulk nanocrystalline materials is to produce amorphous material by rapid solidification and then by controlled crystallization introduce nanocrystalline structure. One technique capable of achieving rapid solidification in materials is plasma spraying. Feedstock material for plasma spraying was composed of about 15 wt.% of SiO2 in addition to the near eutectic ratio of Al2O3 and ZrO2 compounds. Amorphous coatings and free standing parts from this material prepared by water stabilized plasma torch (WSP) exhibit very low porosity and high hardness. When heat treated, the as-sprayed material crystallizes just above 950ºC with an associated volume shrinkage of 1.8%. The volume shrinkage does not cause material breakup. Short heat treatment of the as-sprayed material produces a very fine nanocomposite structure within each splat. Each splat contains nanocrystallites with average size as small as 13 nm.
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Strukturní vlastnosti nanometrických železných částic
David, Bohumil ; Schneeweiss, Oldřich ; Pizúrová, Naděžda ; Klementová, Mariana ; Morjan, I.
Fe-based nanoparticles were prepared by the laser pyrolysis method using a cross-flow reactor in which the laser orthogonally irradiates the gas mixture of Fe(CO)5, C2H2, and C2H4. Ethylene serves as the CO2 laser radiation absorber. The as-synthesized powder was characterised by HRTEM, XRD, Raman spectroscopy, Mössbauer spectroscopy, and magnetic measurements. As observed under TEM, the as-synthesized powder consisted of nanoparticles smaller then 10 nm embedded in a pyrolytic carbon matrix. The XRD pattern exhibited three broad peaks: the first peak is assigned to pyrolytic carbon, the second peak is assigned to maghemite/magnetite, and the third peak belongs to α-Fe particles. The particle size d 2 nm was obtained for α-Fe from the Scherrer formula. The presence of α-Fe and maghemite/magnetite phases was also observed in the Mössbauer spectrum measured at 4 K.
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