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Potential of AZ series magnesium alloys for ureteral stent manufacturing
Trnková, Zuzana ; Buchtík, Martin (referee) ; Doskočil, Leoš (advisor)
This master's thesis focuses on investigating the potential of magnesium alloys AZ31 and AZ91 for the production of ureteral stents. Potentiodynamic polarization (PDP) and electrical impedance spectroscopy (EIS) methods were used for electrochemical testing. Surface and microscopic analysis were conducted using scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). Immersion tests were used to characterize the corrosion solution and surface of AZ31 and AZ91 alloys. Fourier transform infrared spectroscopy (FTIR) with ATR module was used to determine the corrosion products on the surface of the alloys. The results showed that the AZ series alloys have potential for ureteral stent manufacturing, with AZ31 appearing to be more suitable than AZ91 as it provides more stable corrosion protection in the long term and the corrosion products do not form large particles that could lead to undesirable encrustation. Urea has also been shown to have a negligible impact on corrosion of AZ31 and AZ91 at lower concentrations, but at higher concentrations a significant impact on corrosion has been observed (especially in the case of AZ31).
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Malonate and succinate as potential corrosion inhibitors of AZ31 magnesium alloy in 0.9% NaCl
Tkáčová, Karolína ; Buchtík, Martin (referee) ; Doskočil, Leoš (advisor)
The aim of this work was to evaluate the inhibitory effects of malonic acid, succinic acid and their mixture in a 0,15M NaCl solution at pH 7 on AZ31 magnesium alloy. The theoretical part focuses on magnesium, its alloys and alloying elements. It also discusses magnesium corrosion in aqueous environments and the influence of microstructure on corrosion. The final section is dedicated to corrosion inhibitors and small aliphatic acids. The practical part of this work involves potentiodynamic measurements, immersion tests, and subsequent analysis of alloy surfaces. The following concentrations of acids were chosen for studying inhibitory properties: 0.025M, 0.05M, 0.075M, and 0.1M, as well as various mixtures of both acids. Suppression of corrosion was observed in immersion tests for both acids individually and in their mixture. The best inhibitory results in both potentiodynamic polarization (PDP) analysis and immersion tests were achieved with a mixture of 0.025M malonic acid solution and 0.075M succinic acid solution.
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Preparation and characterization of layered double hydroxides on Mg substrates prepared by powder metalurgy
Kobzinková, Eliška ; Doskočil, Leoš (referee) ; Buchtík, Martin (advisor)
This thesis deals with the preparation and characterization of double-layered hydroxides (LDH) on Mg substrates prepared by powder metallurgy. The theoretical part deals with magnesium, magnesium powder metallurgy, and LDH coatings and methods of their preparation with a focus on MgAl-LDH. The theoretical part is concluded with a research study of current research in the field of preparation of LDH coatings on magnesium substrates and the influence of process parameters on the properties of coatings. The experimental part covers the process of optimization of MgAl-LDH on Mg samples prepared by powder metallurgy. In particular, the morphology and structure of the coatings and their elemental composition were evaluated. The evaluation was carried out using a scanning electron microscope (SEM) with an energy dispersive spectrometer (EDS). The optimized MgAl-LDH coatings were also evaluated for electrochemical corrosion properties by potentiodynamic tests in Hank's solution corrosion environment and phase analysis by X-ray diffraction (XRD).
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Preparation of yttrium-based coating to increase the corrosion resistance of AZ31 magnesium alloy
Kolařík, Václav ; Buchtík, Martin (referee) ; Doskočil, Leoš (advisor)
The subject of the bachelor thesis was the preparation and characterization (morphological and chemical) of coatings based on layered double hydroxides (LDH) with yttrium on AZ31 magnesium alloy to improve the corrosion resistance of the alloy. The coatings were prepared under mild and hydrothermal conditions and the synthesis was supported by thermodynamic assumptions. The corrosion resistance of the AZ31 alloy with coatings was described by potentiodynamic measurements and compared with the pure AZ31 alloy. This was followed by a description of the morphological and elemental composition through SEM-EDS analysis, and confirmation of the formation of the structures observed by this method was performed through FTIR analysis. The best coating prepared under mild conditions was a sample prepared at 90 °C for 24 h with a yttrium concentration of 0,05 M and under hydrothermal conditions it was a coating prepared at 120 °C for 30 h with a yttrium concentration of 0,075 M. SEM-EDS and FTIR analysis did not show the formation of MgY-LDH but the formation of Mg(OH)2. Yttrium was minorly represented in the coatings where it could be present, e.g. as Y(OH)3. Yttrium was shown to have a positive effect on the preparation of the coatings compared to the sample prepared without yttrium under the same reaction conditions.
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Soil solution - supramolecular architecture and stability of dissolved organic matter
Trubková, Eliška ; Doskočil, Leoš (referee) ; Enev, Vojtěch (advisor)
This final thesis is focused on the complex physico-chemical characterization of soil solutions, especially with a focus on the study of the stability and molecular architecture of dissolved organic matter. The subject of the study was six soil solutions obtained from lysimeters in the Závišín locality. Three soil solution samples were taken in December 2022 and the remaining three samples were taken one month later in January 2023, at horizons at 40, 60 and 80 cm below the soil surface. Characterization of soil solutions included measurements of their pH and conductivity. Mass and optical emission spectrometry with inductively coupled plasma was used to determine the concentration of cations. The determination of the total dissolved organic matter content was carried out according to the technical standard ČSN 75 7536 and the values of absorption coefficients were calculated using UV/Vis spectrometry. Functional groups and basic structures of soil solutions were identified based on the evaluated spectra from infrared spectrometry with Fourier transformation. The main contribution was fluorescence spectrometry, which was used to determine the fluorescence intensities of A–fulvic-like and C–humic-like fluorophores. Particle size was also measured using dynamic light scattering and zeta potential, which was a suitable indicator of the stability of selected soil solution samples. The obtained results very well characterized both individual soil solutions and dissolved organic matter.
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Sorption of charged organic compounds on humic acids
Krist, Tomáš ; Doskočil, Leoš (referee) ; Enev, Vojtěch (advisor)
Bachelor thesis deals with a sorption properties and physical-chemical characterization of humic acids before and after the adsorption. Sorption experiments with a methylene blue and a rhodamin 6G were performed. Adsorption isotherms were obtain via UV/VIS spectrometry. The Langmuir isotherm was used to evaluate the experimental data. Standard of HA isolated from Leonardite was characterized by an elemental and thermogravimetric analysis, by a Fourier-transform infrared spectroscopy, a surface area analysis and also by a potentiometric titration.
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Use of thin layer chromatography for fractionation of humic substances isolated from oxyhumolite
Hegrová, Nela ; Doskočil, Leoš (referee) ; Enev, Vojtěch (advisor)
The main goal of this thesis was to optimize the fractionation of humic substances (HS) using the method of Thin-layer chromatography, so that it can be used for physico-chemical characterization of the obtained individual organic fractions. Due to the high content of HS in the natural oxyhumolite matrix this oxidized brown coal was selected as a source of these biocolloid compounds which were isolated according to the international IHSS procedure. The sample of native oxyhumolite and oxyhumolite after extraction was characterized by thermal techniques such as thermogravimetric (TGA) and elemental analysis (EA). The above-mentioned oxyhumolite samples were further analyzed by Fourier transform infrared spectroscopy, mainly for deeper understanding of their structure in terms of an organic matrix containing HS. Characterization of isolated HSs was performed by the following thermochemical and spectrometric techniques, elemental analysis, thermogravimetry, ultraviolet and visible electromagnetic absorption (UV/Vis) molecular spectroscopy, Fourier transform infrared spectroscopy and steady-state fluorescence spectroscopy. Molecular absorption spectroscopy (UV/Vis) and steady-state fluorescence spectroscopy were used for physicochemical characterization of individual organic fractions.
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Study of Lignite Organic Matter
Doskočil, Leoš ; Maršálek, Roman (referee) ; Havelcová, Martina (referee) ; Pekař, Miloslav (advisor)
This work deals with the study of organic matter in the South Moravian lignite using the available physico-chemical methods and the results obtained are eventually considered for non-energy applications of lignite. Lignite organic matter was studied by degradation methods, which included CuO oxidation, thermochemolysis with TMAH and DFRC method. Special attention was paid to the lignite oxidation with hydrogen peroxide, which was carried out under different reaction conditions (time and temperature). Thermal degradation was performed in an inert atmosphere in order to observation of chemical change of lignite (including lignite after extraction with chloroform, demineralised lignite, remineralised lignete) during pyrolysis by means of various methods, especially TG-FTIR for analysis of gaseous products and FTIR for analysis the residual lignite after pyrolysis. Further, water-soluble fractions from lignite were characterized, particularly in terms of the content of organic substances.
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Surface pre-treatment of structural aluminum alloys for bonded joints
Pikner, Jan ; Doskočil, Leoš (referee) ; Wasserbauer, Jaromír (advisor)
This thesis deals with pre-treatment of surface of aluminium alloys. The theoretical part focuses on the properties of aluminium and its alloys, on methods of surface treatment and the possibilities of quality assessment of pre-treated surface. The experimental part deals with finding of a proper method of pre-treatment. The quality of surface pre-treatment is assessed by observation by SEM with EDS and by single lap shear tests of adhesive joints. According to evaluated results, the optimalised methods are qualitatively and financially compared with the commercial method.
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Characterization of humic substances isolated from natural waste treated by vermicomposting process
Marková, Kamila ; Doskočil, Leoš (referee) ; Enev, Vojtěch (advisor)
This bachelor thesis deals with the study of humic substances isolated from vermicompost natural waste through spectrometric methods. The aim of this thesis is to study physicochemical properties of the humic substances through modern instrumental techniques such as molecular absorption spectroscopy in the ultraviolet and visible regions of electromagnetic radiation (UV/Vis), infrared spectroscopy with Fourier transformationn (FTIR), elemental analysis (EA), thermogravimetric analysis (TGA) and inductively coupled plasma emission (ICP OES). A research focused on basic information about the humic substances was developed in the theoretical part. A description about their distribution or structure was made and also their utilization in medicine, industry or ecology. Then, methods, which are used for study of the humic substances, were described as well. An essential part of the thesis was isolation of humic and fulvic acid from the vermicompost natural waste. Absorption coefficients were calculated from the measured UV/VIS spectrum which served to following characterization of HK and FK. FTIR spectrum was used to determination of functional groups of studied HL. An area of biogenic elements was specified using the elementary analysis. Total amount of studied trace elements was determined with with the help of ICP-OES.
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