|
Effect of Number of ECAP Passes on Creep Behaviour and Microstructure of Pure Aluminium and Al-Sc Alloy
Král, Petr ; Dvořák, Jiří ; Kvapilová, Marie ; Svoboda, Milan ; Sklenička, Václav
Experiments were conducted to determine an effect of equal-channel angular pressing (ECAP) on the creep behaviour and the microstructure of pure aluminium and an Al-Sc alloy. The coarse-grained materials in their as-received states were subjected to ECAP at room temperature using a die, which had a 90° angle between the channels. Experiments show that ECAP reduced the average grain sizes of ~1µm and ~0.3µm for pure Al and Al-Sc. The grain sizes after 8 ECAP passes and subsequent creep exposure are ~12µm and ~2µm for Al and Al-Sc alloy, respectively. The fracture analysis and morphology of creep fracture surfaces of an Al-Sc alloy revealed the formation of shear bands which were orientated along the direction of the last ECAP pass. The application of ECAP method causes a substantial continuous decrease in the creep resistance of Al and Al-Sc alloy with increasing numbers of ECAP passes which can be explained by increasing contribution of grain boundary sliding to the total creep strain.
|
|
Creep behaviour of Al-0.2%Sc alloy processed by ECAP Method
Dvořák, Jiří ; Král, Petr ; Kvapilová, Marie ; Sklenička, Václav
An Al-0.2wt.%Sc aluminium alloy was subjected to equal-channel angular pressing (ECAP) at room temperature to refine its coarse – grain size corresponding to its as-received state. For this purpose the ECAP die was used which had a 90° angle between the die channels. By application of this method at room temperature an ultrafine-grained microstructure was achieved with the grain size of ~ 0.3mm after 8 ECAP passes by route BC. Following creep tests in tension were performed at 473 K and at applied stresses ranging from 10 to 50 MPa on ECAP material and, for comparison purposes, on unpressed one. The results indicate, that the creep resistance of ECAP material is markedly lower after 8 passes in comparison with creep behaviour of coarse – grained one. The detrimental effect of ECAP on the creep resistance is probably caused by increasing contribution of grain boundary sliding to the overall creep deformation.
|
|
Types of floor covering and floors from castle Rokštejn
Martinisková, Monika ; Měřínský, Zdeněk (advisor) ; Fleková, Klára (referee)
This thesis deals with medieval ceramic floor tiles from castle Rokštejn. On this site were found various kinds of ceramic floor tiles that are divided to groups by their size or theme. Thesis deals with another kinds of floor covering. Also is mentioned developement of castle Rokštejn. In thesis is also mentioned developement of medieval ceramic floor tiles in Czech Republic and in anothers countries in Europe.
|
|
Sol-gel synthesis of ternary ZnxTiyOz nanostructures for applications in solar cell technologies and photonics
Mrázek, Jan ; Nižňanský, Daniel (advisor) ; Pinkas, Jiří (referee) ; Pollert, Emil (referee)
The presented study deals with the sol-gel synthesis of nanocrystalline ternary phases of the general formula ZnxTiyOz, their characterization and potential application in photonics. Achieved results brings new fundamental knowledge about the processes leading to the formation of ZnxTiyOz nanocrystals from amorphous xerogels and gives novel information about structural and opto-electrical properties of prepared materials. Based on the presented results, most of all up-to-date reported ZnxTiyOz compounds with tailored nanocrystalline size and structure can be prepared as powders or thin films. Two sol-gel approaches based on the cluster process and direct heteronucleation were employed to prepare initial sol. Sols were optionally doped by Eu3+ ions to evaluate the effects of rare earth element to crystallization properties of formed compounds. In the first part of our study crystallization properties and structural evolution of thermally treated xerogels were analyzed. As a result a versatile method allowing the preparation of inverse spinel Zn2TiO4, cubic defect spinel ZnTiO3 and rhombohedral ZnTiO3 with tailored nanocrystal sizes was established. Initial composition and thermal annealing allow us to prepare selected ternary phase with tailored nanocrystal size ranging from tens of nanometers up to...
|
|
Redistribuce napětí a její vliv na precipitaci v mikrostruktuře
Holec, David ; Dlouhý, Antonín
The present study considers two mechanisms that can contribute to the local redistribution of stresses in the microstructure of engineering alloys. The first model takes into account the anisotropy of thermal expansion coefficients and predicts a stress state generated close to a boundary between two differently oriented grains after a temperature change. The second model addresses a stress distribution in a polycrystalline aggregate characterized by anisotropic elastic constants and subjected to the isothermal aging under the assistance of external stress. The influence of local stress states on the selective precipitation of the Ni4Ti3 crystallographic variants in the microstructure of the NiTi shape memory alloy is demonstrated.
|
|
Standard bioassay of the efficacy of entomoparazitic nematodes
TRNKOVÁ, Zuzana
The efficacy of three entomopathogenic nematodes (EPN) of family Steinernematidae was tested in different laboratory conditions in this study. The virulence of Steinernema arenarium, S. carpocapsae and S. feltiae was evaluated to fourth-instar larvae of Galleria mellonella and Tenebrio molitor. Standard temperature (25°C) and humidity (12,5 %) was used in bioassay No I. Trial No II focused on impact of temperature 10, 15 and 25°C on effectivity of S. feltiae and S. carpocapsae. Bioassay No III examined the influence of lower humidity and in consequence rehydration on virulence nematodes.
|
|
Application of UHPLC with various types of detection in the field of environmental and food analysis.
Rejman, David ; Jáč, Pavel (referee) ; Nováková, Lucie (advisor)
The use of UHPLC with various types of detection in the field of environmental and food analysis Abstract The aim of this work was to inform about possible use of UHPLC instrumentation in connection with various types of detection when chromatographic separating of substances in the field of environmental and food analysis is performed. The next aim was to search and study a number of articles referring to UHPLC methodology, which are at present available in the internet databases ScienceDirect and Web of Science. On the basis of the information from the articles there is a graphic summary in this work relating to the number of found articles and the groups of analysed substances within years. In the introduction of the work van Deemter's, Gidding's and Knox's theories about the efficiency of the chromatographic system are mentioned. These theories are substantial for understanding the principle of chromatographic separation. Following chapters deal with the problems of the development of chromatography in the last decades, especially concerning the length and type of analytical columns, the size of filling particles or the temperature and pressure in the chromatographic system. Now thanks to the development, the columns dimensions are 50 x 1 mm and are filled with particles less than 2 μm in diameter and...
|
|
Effect of manual lymph drainage on the healing of muscle
Krajsová, Barbora ; Hnátová, Iva (referee) ; Dudová, Agnieszka (advisor)
Title of work: Effect of manual lymph drainage on the healing of muscle Objective: The aim of this thesis is to assess the impact and effect of manual lymph drainage on wound rupture of the muscle. Method: Development and comparison of six case studies of patients diagnosed with muscle rupture. Three patients were treated with manual lymphatic drainage, the remaining three patients were treated with rest therapy. The effect of treatment was documented using diagnostic ultrasound. All patients were performed one frame muscle rupture after myocardial muscle injury and second inspection, after three weeks of the treatment. Size rupture were compared before and after treatment. Results: After comparing six case histories of patients diagnosed with muscle rupture was found that for the first group that was treated with manual lymphatic drainage has been reduced swelling, hematoma, and thus muscle rupture. Conclusion: The effect of manual lymph drainage in the group of probands was noticeable. However, such results shouldn't be generally applicable due to the small number of probands.
|
|
Interaction of adsorbates with passivated Si surfaces studied by STM
Matvija, Peter ; Kocán, Pavel (advisor)
The scanning tunneling microscopy is used to study the morphology of Tl adlayer in various stages of Tl desorption from the Si(111) surface and to study behaviour of various adsorbates on the Si(111)/Tl-(1 × 1). The utilization of thallium layer for passivation of the Si(111) was examined closely for various adsorbates. Manganese, aluminium, indium and tin layers which were directly deposited onto the Si(111)-(7 × 7) were compared with the layers prepared by deposition of adsorbate onto the passivating layer after the subsequent thermal desorption of Tl (after annealing at ≈ 400◦ C). Examined adsorbates exhibited signs of extremely high diffusivity and weak bond with the surface Si(111)/Tl- (1 × 1). The passivating layer was stable against the adsorbates.The application of thallium in the role of surfactant caused lowering of temperature and coverage needed for the preparation of reconstructions which were observed on the surfaces prepared by the direct deposition of adsorbate. 1
|
|
VAT ledger statement
Křempek, Vojtěch ; Zídková, Hana (advisor) ; Tecl, Jan (referee)
This thesis deals with the VAT ledger statement. The main objective is to quantify company's costs caused by the implementation and operation of the VAT ledger statement. Other goals are to compare these costs according to the size of taxpayers and to map practical problems associated with the process of completing the statement. The first part explains the system of carousel fraud and outlines possible ways to fight it. It also provides the basic information on the statement. The second part focuses on the main issues caused by this newly established institute of VAT ledger statement. In the third chapter there are quantified establishing and ongoing costs associated with the VAT ledger statement.
|
guest ::
