National Repository of Grey Literature 25 records found  1 - 10nextend  jump to record: Search took 0.00 seconds. 
Quantum-mechanical study of magnetic properties of superalloy nanocomposite phase Fe2AlTi
Slávik, Anton ; Miháliková, Ivana ; Friák, Martin ; Všianská, Monika ; Šob, Mojmír
The L21-structure Fe2AlTi intermetallic compound is one of the two phases identified in Fe-Al-Ti superalloy nanocomposites. Experimental data related to low-temperature magnetic properties of this Heusler compound indicate that magnetic moment is about 0.1 Bohr magneton per formula unit. In contrast, previous quantum-mechanical calculations predicted Fe2AlTi to have much higher magnetic moment, 0.9 Bohr magneton per formula unit. In order to solve this discrepancy between the theory and experiment we have performed a series of quantum-mechanical fix-spin-moment calculations and compared our results with those for non-magnetic state. It turns out that the total energy of the non-magnetic state is only by 10.73 meV/atom higher than that of the magnetic state. When applying Boltzmann statistics to this very small energy difference we predict that the non-magnetic state appears at non-zero temperatures with significant probabilities (for instance, 22.36 % at T = 100 K) and reduces the overall magnetic moment. As another mechanism lowering the magnetization we studied selected shape deformations, in particular trigonal shearing. Fe2AlTi exhibits a compression-tension asymmetry with respect to these strains and, for example, the strain 0.08 destabilizes the spin-polarized state, leaving the non-magnetic state as the only stable one.
First-principles study of interface energies in Fe-Al-based superalloy nanocomposites
Miháliková, Ivana ; Slávik, Anton ; Friák, Martin ; Všianská, Monika ; Koutná, N. ; Holec, David ; Šob, Mojmír
Fe-Al-based nanocomposites with a superalloy-type of microstructure constitute a very promising class of materials. They possess a great potential as an alternative to the currently used steel grades in high temperature applications. Intermetallics-containing nanocomposites, such as those with the Fe3Al compound being one of the phases, may open a way towards future automotive and energy-conversion technologies with lower fuel consumption and reduced environmental impact. We employ quantum-mechanical calculations to analyze relations between ordering tendencies of Al atoms in the disordered Fe-18.75at.%Al phase on one hand and thermodynamic, structural and magnetic properties of Fe-Al-based nanocomposites on the other. When comparing supercells modeling disordered Fe-Al phase with different atomic distribution of atoms we find out that the supercell without 1st and 2nd nearest neighbor Al-Al pairs has a lower energy than that mimicking a perfect disorder (a special quasi-random structure, SQS). Further, coherent interfaces with (001), (110) and (1-10) crystallographic orientations between Fe3Al compound and SQS Fe-Al phase have higher energies than those exhibiting atomic distribution without 1st and 2nd nearest neighbor Al-Al pairs.
Self-assembling hybrid nanomaterials
Rodzeń, Krzysztof ; Strachota, Adam (advisor) ; Svoboda, Jan (referee) ; Matějíček, Pavel (referee)
Organic-inorganic polymer hybrids containing butyl stannoxane dodecamer cages (Sn_POSS) as nano-building blocks were prepared and investigated. Sn_POSS was employed as a linear, crosslinking or non-bonding molecularly blended unit. For this purpose, it was synthesized with two acrylamido, primary- or secondary amino, or with two additional non- functional groups, which were attached via ionic-bonded sulfonate substituents. The nano- building block was then incorporated in matrices such as PS, PAOS, PETA, PEMA, PHEMA and PPO-based epoxies (the latter with different mesh sizes). Sn_POSS reinforces the studied matrixes by filler-filler interactions (self-assembly to nano-domains). Specific interactions of the ionic bonds of Sn_POSS with suitable pendant groups of the matrixes also can generate reinforcement and suppress filler aggregation. Moreover, the Sn_POSS can undergo several types of chemical reactions like heat-induced oligomerization, dissociation of the ionic substituents, acidolysis of the Sn-butyl bonds, as well as radical reactions of the latter. The influence of ionically bonded cages on the hybrids' morphology, as well as their ability of dissociation and short-distance migration in the polymer network at elevated temperature, was evaluated by TEM, IR and NMR analyses. The mechanical...
Nanoclusters coatings for biomedical applications
Divín, Radek ; Kylián, Ondřej (advisor) ; Hanuš, Jan (referee)
Title: Nanoclusters coatings for biomedical applications Author: Radek Divín Department: Department of Macromolecular Physics (110. 32-KMF) Supervisor: RNDr. Ondřej Kylián, Ph.D. Abstract: The copper nanocluster films were prepared with the aid of the gas cluster aggregation source based on the principle of material sputtering from the magnetron target to the relatively high pressure of the working gas (Ar). The nanocluster films prepared in this way were subsequently overlapped with the layer of plasma polymer deposited by RF magnetron sputtering from the nylon polymer target in the atmosphere of the working gas (Ar, 2 Pa). A repetition of this procedure enabled to prepare nanocomposite layers having a multilayer character. These layers were subsequently investigated with regard to their morphology, chemical composition, surface wettability and optical properties. The chemical composition of the surface layer formed by nanocomposite films was determined by the X-ray photoelectron spectroscopy (XPS). It turned out that the chemical surface composition of prepared nanocomposites was not markedly influenced by the presence of the Cu nanoclusters. The morphology of prepared films was studied by the scanning electron microscopy (SEM) and the atomic force microscopy (AFM), which showed that the resulting...
Ultrathin films deposited by means of magnetron sputtering and their characterization
Petr, Martin ; Kylián, Ondřej (advisor) ; Straňák, Vítězslav (referee) ; Tichý, Milan (referee)
Presented work is focused on the deposition and characterization of thin and ultrathin plasma polymer films, then also on the preparation of nanocomposites metal/plasma polymer. The characterization of plasma polymer films was partly done in-situ without exposing the samples to the atmosphere. The thickness of prepared films was measured by spectral ellipsometry, the chemical composition was measured by XPS. The morphology and optical properties of deposited films were measured ex-situ. It is shown that during the initial stages of growth the properties of plasma polymer films depend on their thickness and also on the material of the substrate. Many interesting applications were explored for prepared nanocomposites metal/plasma polymer. They can be used as superhydrophobic coatings, gradient coatings, substrates for Raman spectroscopy or as antibacterial coatings. Moreover, special optical properties of prepared nanocomposites were studied in detail. Presented work has an experimental character.
Study of electric properties of nanocomposit material
Ovsík, Jiří ; Rozsívalová, Zdenka (referee) ; Polsterová, Helena (advisor)
This work deals with the electrical properties of nanocomposite materials. Samples for the experiment are made of epoxy resin as matrix and titanium dioxide TiO2 as nanofillers in varying percentage performance. Measurements are temperature dependent components of the permittivity, dissipation factor and resistivity. Furthermore, the internal resistivity is observed with regard to the percentage performance of a sample of nanoparticles.
Structure and Properties of Collagen/HAP Nanocomposite Networks
Kopuletá, Ema ; Lehocký,, Marián (referee) ; Amler,, Evžen (referee) ; Jančář, Josef (advisor)
Polymerní biomateriály jsou jedním ze současných populárních témat vzhledem k možnosti potenciální aplikace v tkáňovém inženýrství a řízeného dávkování léčiv v organismech. Kolagen je jako jeden z nejčastěji se vyskytujících proteinů zvláště zajímavý díky svým rozmanitým vlastnostem bez imunoreakce organismu příjemce. Tato práce je zaměřena na samouspořádávací procesy, kinetiku, obecné zákonitosti řídící proces samouspořádání a mechanické vlastnosti kolagenních roztoků. Dále je zkoumán efekt hydroxyapatitových nanočástic na samouspořádávání kolagenu a mechanické vlastnosti výsledných nanokompozitních hydrogelů. Jsou objasněny možné mechanismy interakcí mezi kolagenem I a hydroxyapatitem spolu s popisem vývoje struktury a vlastností na různých úrovních struktury. Byly měřeny a molekulárně interpretovány závislosti viskoelastických veličin na smykové rychlosti spolu s viskoelastickým chováním. Dále byla studována struktura kolagenních scaffoldů a určen vliv HAP a síťování. Závěrem byly diskutovány výsledky v souvislosti s jejich aplikovatelností v tkáňovém inženýrství chrupavek tvrdých tkání a v regenerativní medicíně.
Study of electric properties of nanocomposites
Libra, Miroslav ; Rozsívalová, Zdenka (referee) ; Polsterová, Helena (advisor)
The present master´s thesis deals with the electrical properties of nanocomposite materials. Samples for the experiment are made epoxi resin and oxides TiO2 and Al2O3 as nanofillers in different percent performace. The samples nanocomposites are measured temperature dependence of the resistivity inside, dissipation factor and relative permittivity. It discusses the effect of the filler on the resulting electrical properties of the polymer.
Study of electrical properties of nanocomposites
Ovsík, Jiří ; Rozsívalová, Zdenka (referee) ; Polsterová, Helena (advisor)
The present work deals with the electrical properties of nanocomposite materials. Samples for the experiment are made of epoxy resin as a matrix and oxides TiO2, Al2O3, WO3, SiO2 as nanofillers in 0.5 and 1 percent performance. The experimental samples are measured in temperature and frequency dependence of relative permittivity, dissipation factor, rezistivity and are broken down by the influence of filler on the electrical properties of the polymer. Attention is also paid to the mechanical properties of nanocomposites.
The influence of nanoparticles on isothermal crystallization rate of isotactic polypropylene
Miškolci, Michal ; Jančář, Josef (referee) ; Bálková, Radka (advisor)
This diploma thesis deals with the study of isothermal crystallization of nanocomposite materials based on isotactic polypropylene (iPP) and nanosilica, depending on the volume fraction (0, 2, 4 and 6 %) and type of silica and the crystallization temperature. Fumed silica and four types of silica with different surface treatment were used as filler. The crystallization performed at temperatures 136, 138, 140 and 142 °C has been studied in-situ using polarized optical microscope and the crystallization rate was evaluated from the growing radius of spherulites. It can be stated that particles of silica have been inbuilt into the spherulites due to the linear growth of spherulites of all composite materials. The most significant increase of the crystallization rate of iPP was caused by fumed silica, the most significant decrease was caused by silica TS-720 at volume fraction 4 %. The crystallization rate (G) has been slightly increased with the increasing volume fraction of filler at 136 °C, the G slightly decreased at 138 °C and there was no trend of G for two higher temperatures. Also, it was not possible to exactly evaluate the influence of the surface treatments. The reason is the most probably uneven (non-homogenous) distribution of nanosilica as revealed thermogravimetric analysis. The crystallization kinetics was evaluated according to the Lauritzen-Hoffmann theory. The morphological part of the study showed that iPP was in ? and ß-structure and spherulites of ? phase were of the type I, II and mixed.

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