Academic literature on the topic 'Kinetika krystalizace'

Abstract The work presents the test results of the crystallisation and cooling of magnesium alloys: AM60 and AZ91, with the use of the TDA method. The tested alloys were cast into ceramic shells heated up to 180°C, produced according to the technology of the shell production in the investment casting method. The TDA method was applied to record and characterize the thermal effect resulting from the phase transformations occurring during the crystallisation of magnesium alloys. The kinetics and dynamics of the thermal processes of the crystallisation of AM60 and AZ91 in the ceramic shells were determined. Metallographic tests were performed with the use of an optical microscope as well as scanning microscopy, together with the EDS chemical analysis of the phases present in the tested casts. A comparison of these test results with the thermal effect recorded by way of the TDA method was made.

Růst krystalů zásadně ovlivňuje morfologii a tím také mechanické vlastnosti semikrystalických polymerů. Tato PhD práce přináší alternativní pohled na popis kinetiky krystalizace v polyolefinech plněných slabě interagujícími částicemi. V nanokompozitních materiálech vysoký specifický povrch plniva i při nízkých plněních zásadně ovlivňuje dynamiku řetězců. V blízkosti povrchu plniva začíná hrát významnou roli zpomalená reptace způsobená jak vzájemnými interakcemi plnivo-polymer tak prostorovým omezením mezi nanočásticemi. Růst krystalů byl zkoumán pomocí polarizovaného optického mikroskopu vybaveného horkým stolkem. Výsledky byly korelovány s teoretickými modely a rozsáhlými počítačovými simulacemi na molekulární úrovni. Pozorovaný pokles rychlosti růstu sférolitů v závislosti na obsahu plniva a molekulové hmotnosti matrice je interpretován na základě imobilizační teorie, tedy, zpomalení reptačního pohybu.

The aim of submitted diploma thesis is the study of non-isothermal crystallization kinetics of polylactide (PLA) with selected agents (1 %) and observation of the emerging crystalline structure under polarizing optical microscope. The agents were talc, a mixture of organic salts with the addition of amorphous SiO2 (HPN 68L) and zinc stearate (HPN 20E) and LAK-301 (potassium salt of 5-dimethylsulfoisophtalate), which is a nucleating agent developer for PLA. The PLA matrix served as a reference. Non-isothermal crystallization took place on a differential scanning calorimeter at cooling rates () 0,3; 0,5; 0,7; 1; 1,5; 2 °C/min After non-isothermal crystallization, the crystalline fraction (Xc) od PLA was evaluated from X-ray diffraction analysis, and the supramolecular structure was observed after chemical degradative etching using confocal laser scanning microscope. The crystallization kinetics were evaluated by the methods of Jeziorny and Mo and the activation energy of the crystallization was determined according to the Friedmann method. All prepared materials were amorphous (Xc 40 % for up to 1,5 °C/min). However, for LAK-301, Xc decreased to 30 % already at the = 2 °C/min and it can be assumed that with increasing its nucleation activity will decrease. A spherulitic structure was observed in all samples, but the number and size of spherulites decreased with increasing and the appearance varied according to the type of agent. Both kinetic models proved to be unsuitable for materials with low Xc and the highest because the rate of crystallization did not change. With the Jeziorny method, it was possible to evaluate the kinetics only for the relative crystallinity Xt = 29–50 % and with the Mo method it was not possible to evaluate the data for the highest for PLA matrix and sample with HPN 68L. The samples with LAK-301 and HPN 68L showed the lowest activation energy.

This Ph.D. thesis addresses the structure-function relationship of the multimeric oxidoreductase WrbA with the principal aim being the explanation of the unusual kinetics of this enzyme in molecular terms, and thus getting an insight about its physiological role in bacteria. WrbA is a multimeric enzyme with FMN as a co-factor, catalyzing the oxidation of NADH by a two electrons transfer. Structure and function analysis of WrbA places this enzyme between bacterial flavodoxins and eukaryotic oxidoreductases in terms of its evolutionary relationship. The kinetic activity of WrbA was studied under varying conditions such as temperature, pH etc, and its kinetic mechanism was evaluated from parameters KM and Vmax and confirmed by product inhibition pattern experiments. Crystallization and proteolytic experiments also underpin the functional importance of the multimeric nature of WrbA and aid the understanding of the physiological role of this enzyme in molecular terms.

Texture of igneous rocks, which includes size, shape and spatial distribution of grains, represents the final record of kinetic and mechanical processes operating during ascent and final emplacement of a magma. However, traditional geochemical approaches cannot assess and verify the physical processes of magma solidification, in particular, crystal nucleation and growth, textural coarsening, or mechanical crystal-melt interactions. In this work, I apply stereological methods to quantitatively characterize the textures and to interpret the crystallization history of granitic rocks in the Western Krušné hory/Erzgebirge and Vogtland. The Western Krušné hory/Erzgebirge granites consist of three suites: biotite granites (Kirchberg), muscovite-biotite microgranites (Walfischkopf), and topaz-zinnwaldite alkali- feldspar granites (Eibenstock), which consist of eight intrusive units and two aplite dyke sets. The entire granite sequence exhibits an extreme and nearly continuous differentiation range, but in detail the evolutionary trends of each suite are independent, and individual intrusive units are also clearly compositionally separated. The granites consist of 29-43 vol.% quartz, 20-30 vol. % plagioclase, 22-31 vol. % K-feldspar, 2-9 vol. % biotite, <2 vol. % muscovite, and minor topaz and apatite. All...