Browsing by Author "Kejzlar, Pavel"
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- ItemA comparative study between chemically modified and copper nanoparticle immobilized Nylon 6 films to explore their efficiency in fighting against two types of pathogenic bacteria(2020-01-05) Swar, Sumita; Máková, Veronika; Horáková, Jana; Kejzlar, Pavel; Parma, Petr; Stibor, IvanHospital-acquired infections (HAI) caused by pathogenic bacteria such as Pseudomonas aeruginosa and Staphylococcus aureus adversely affect public health due to their colonization and subsequent formation of a biofilm on medical devices. Various functionalized polymers including polyamides are commonly used in the biomedical industry aiming to resist bacterial infection as well as to ensure cytocompatibility of the used materials. The present study is focused on the extension of our previous work that developed a new approach to immobilize mPEG on an amine-activated Nylon 6 surface. Herein, we compare functionalized samples of Nylon 6 together with samples additionally containing copper nanoparticles (Cu NPs, size 40-60 nm) physisorbed on a modified surface. Modified samples were analyzed via different techniques including water contact angle measurements, atomic force microscopy and scanning electron microscopy associated with energy dispersive Xray spectroscopy. The copper functionalized samples showed high antibacterial efficacy against Gram-positive Staphylococcus aureus and Gram-negative Pseudomonas aeruginosa. Moreover, most of the prepared samples were cytocompatible.
- ItemBarkhausen Noise Emission in Hard-Milled Surfaces(2019-02-22) Neslušan, Miroslav; Mičietová, Anna; Hadzima, Branislav; Mičieta, Branislav; Kejzlar, Pavel; Čapek, Jiří; Uríček, Juraj; Pastorek, FilipThis paper reports on an investigation treating a hard-milled surface as a surface undergoing severe plastic deformation at elevated temperatures. This surface exhibits remarkable magnetic anisotropy (expressed in term of Barkhausen noise). This paper also shows that Barkhausen noise emission in a hard-milled surface is a function of tool wear and the corresponding microstructure transformations initiated in the tool/machined surface interface. The paper discusses the specific character of Barkhausen noise bursts and the unusually high magnitude of Barkhausen noise pulses, especially at a low degree of tool wear. The main causes can be seen in specific structures and the corresponding domain configurations formed during rapid cooling following surface heating. Domains are not randomly but preferentially oriented in the direction of the cutting speed. Barkhausen noise signals (measured in two perpendicular directions such as cutting speed and feed direction) indicate that the mechanism of Bloch wall motion during cyclic magnetization in hard-milled surfaces differs from surfaces produced by grinding cycles or the raw surface after heat treatment.
- ItemINFLUENCE OF HEAT TREATMENT ON Al-Si COATING CHEMICAL COMPOSITION(TANGER LTD, KELTICKOVA 62, SLEZSKA, OSTRAVA 710 00, CZECH REPUBLIC, 2018) Petr-Soini, Jaroslav; Kejzlar, Pavel; Kučera, Vojtěch; Janovec, Jiří; Kolaříková, MarieThis paper addresses structural changes of Al-Si coating depending on various heat treatment parameters. Al-Si coated martensitic steel is one of the most commonly used materials in automotive industry for structural parts. Describing transformation of Al-Si coating is necessary in order to understand the phenomena affecting the welding and adhesive bonding stability. Three various heat treatment cycles were used in order to prepare specimens which were later evaluated by scanning electron microscopy, X-ray diffraction and tensile testing. Changes of the phase composition of the coating and mechanical properties of the base material are discussed in the paper.
- ItemMICROSTRUCTURE AND TEXTURE EVOLUTION DURING COLD DRAWING OF SEAMLESS STEEL TUBE(TANGER LTD, KELTICKOVA 62, SLEZSKA, OSTRAVA 710 00, CZECH REPUBLIC, 2018) Parilak, L'udovit; Burik, Peter; Bella, Peter; Mojzis, Milan; Kejzlar, PavelCold drawing of steel tubes is the manufacturing process characterized by anisotropic material flow during drawing. In this paper, the microstructural of the E235 hot rolled steel tube after normalizing and cold drawing were characterized by optical microscopy, EBSD (Electron BackScatter Diffraction) analysis performed on scanning electron microscope. The input feedstock with dimensions of circle divide 31.8 mm x 2.6 mm (O.D x W.T.) was cold drawn in one drawing passes with fixed plug to the final dimensions of circle divide 25.0 mm x 1.5 mm. The development of grain texture in 3 different regions was analyzed on a longitudinal section of the tube. The stress state in the tube material during drawing was calculated by finite element software and the development of the texture depending on the stress state in three different directions using cylindrical coordinates with respect to the drawing direction was evaluated.
- ItemStruktura a vysokoteplotní mechanické vlastnosti ternárních intermetalických slitin na bázi Fe-Al-Zr(Technická Univerzita v Liberci, ) Kejzlar, Pavel
- ItemThe Preparation of Iron Oxide Nanoparticles by a Self-combustion Method(J. E. Purkyne University in Usti nad Labem, 2019) Seibert, Ondřej; Grégr, Jan; Kejzlar, PavelThis paper deals with problematic of preparation of iron oxide nanoparticles according to a self-combustion method.Iron oxide nanoparticles can be used e.g. for catalysators and gas sensors or in MRI. The Self-combustion method is based on rapid chemical reaction between a fuel and iron oxide precursor. Glycine, urea and citric acid were used as fuels and iron nitrate nonahydrate was used as an iron oxide precursor. The self-combustion method doesn't require any special equipment, is environment-friendly due to minimize pollution and the results are easily reproducible. The shape, size, and phase of resulting particles were investigated studied using scanning electron microscopy and energy-dispersiveanalysis.
- ItemVliv tepelného zpracování na stabilitu fází v aliminidech železa typu Pyroferalu Fe42-45AlxC0.7Siat.(Technická Univerzita v Liberci, 2009) Kejzlar, Pavel; Vodičková, VěraDiploma work contains summary of knowledge about iron aluminides type FeAl, describes effect of carbon and silicon on alloy. It further deals with effect of heat treatment on structure of alloys type Pyroferal with contain of carbon 3,7 to 4,9 atomic %. Prismatic specimens of four alloys were prepared using melting and casting in laboratory vacuum furnace. Rolling of samples was done on laboratory kvarto finisher Institute modeling and proceedings of forming process VSB-TUO after heating on 1230°C in casual electric resistance furnace without protective atmosphere. It was{\dots}. three types of annealing (800°C/8hours/oil, 1100°C/24hours/oil, 1150°C/200hours/air) and then was investigated and described structure of scratch patterns using light optical microscopy, measuring of microhardness, scanning electron microscopy and energy-dispersive X-Ray analyze and X-Ray diffraction.