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Study of phytic acid-based organic conversion coatings on magnesium alloys
Zbíral, Roman ; Doskočil, Leoš (referee) ; Buchtík, Martin (advisor)
This thesis deals with organic conversion coatings based on phytic acid, on the magnesium alloys. In theoretical part it deals with corrosion properties of magnesium and magnesium alloys, usage of magnesium alloys for biomedicine applications. There are also summarized information’s about usage of phytic acid, it’s reactions with magnesium and magnesium alloys. At the end of theoretical part is search about phytic acid conversion coatings deposited on magnesium alloys. There are studied optimal conditions for application of phytic acid coatings such as pH, concentration, time of deposition, etc. Based on the knowledge from the theoretical part, a layer based on phytic acid was deposited on the surface of Mg alloy AZ31. The coating was evaluated in the experimental part in terms of its morphology and structure, chemical and corrosion behaviour. Scanning electron microscope (SEM) images showed the presence of microcracks in the dried coating. The chemical nature of the phytic acid-based conversion coating was investigated by energy dispersive spectroscopy (EDS) techniques in combination with Fourier transform infrared spectroscopy (FTIR). The electrochemical corrosion behaviour of Mg alloy AZ31 and coated Mg alloy was investigated by potentiodynamic polarization in Hank's solutions. Based on the obtained values of the corrosion potential and the corrosion current density, it can be stated that the applied layer of the conversion coating leads to an improvement of the corrosion properties. From the results of SEM analysis of samples after exposure in a corrosive environment, it was found that during potentiodynamic measurements no significant manifestation of corrosion attack was observed in coated samples, as was the case with Mg alloy AZ31.
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Effect of humic acid on the corrosion of carbon steel
Horák, Tomáš ; Buchtík, Martin (referee) ; Doskočil, Leoš (advisor)
Bachelor thesis deals with influence of humic acids on corrosion of ČSN 12020 steel. For this purpose, potentiodynamic tests and electrochemical impedance spectroscopy (EIS) in leaches of humic acids, isolated from South Moravian lignite were executed. Results suggest that corrosion is initially promoted by humic acids, but after a longer time (about 98 hours) an inhibitory effect is exerted due to the adsorption of humic acids on the corrosion products. Adsorption efficiency of humic acids on surface of corrosion products was about 30 %. Results also suggest that the presence of humic acids may influence the composition of corrosion products of the steel.
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Fluoride conversion coatings on composite Mg/MgO materials
Peroutka, Jakub ; Buchtík, Martin (referee) ; Hasoňová, Michaela (advisor)
Bachelor thesis deals with preparation of composite materials based on Mg/MgO and their subsequent coating with fluoride conversion coating. Materials based on Mg/MgO were prepared by powder metallurgy. The theoretical part contains of basic magnesium information, advantages and disadvantages of Mg and brief Mg preparation. In the next part there are summarized basic principles, advantages and disadvantages in powder metallurgy. The second theoretical part deals with basic properties of MgO, literary research which deals with description of MgO on chemical structure of different varieties of Mg alloys or composition materials based on Mg/MgO. The last part of theoretical part describes conversion coatings, brief description of chemical reaction kinetics and diffusion of fluoride conversion coating. The experimental part deals with preparation of composite materials based on Mg/MgO by powder metallurgy. The main goal of experimental part was description of possible effect of MgO content on the formation of fluoride conversion coating.
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Structural analysis of Fe48Cr28Ni16Mo4,5Si1,5C1,75 thermally-sprayed coatings on AZ91 magnesium alloy
Kobzinková, Eliška ; Doskočil, Leoš (referee) ; Buchtík, Martin (advisor)
The bachelor thesis deals with the analysis of thermally sprayed Fe48Cr28Ni16Mo4,5Si1,5C1,75 coatings on AZ91 magnesium alloy and evaluation of their structural and mechanical properties. The theoretical part deals with magnesium alloys, focusing on AZ91 alloy, thermal spray methods, specifically the High Velocity Oxygen Fuel method of depositing (HVOF), and Fe and Fe-Cr-Ni based materials. The theoretical part concludes with a review of current research in the field of Fe-based coatings deposited by the HVOF method. The experimental part is devoted to the structural analysis of AZ91 magnesium alloy and the Fe-based thermally sprayed coating deposited on this alloy. The microstructure was analyzed by light microscopy (LM) and scanning electron microscopy (SEM). Elemental and phase analysis was performed using energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The hardness of the coating and alloy was measured by the Vickers method. The application of thermally sprayed coating increased the surface hardness from 87 ± 10 HV0.3 (AZ91) to 536 ± 94 HV0.3.
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Complete characterization and comparison of lacquer / Ni-P / AZ91 and lacquer / AZ91 systems
Šomanová, Pavlína ; Doskočil, Leoš (referee) ; Buchtík, Martin (advisor)
The aim of this bachelor thesis was to compare the influence of Ni-P coating and varnish on the corrosion properties and chemical – physical properties (adhesion) of the magnesium alloy AZ91. The theoretical part contains the information about the alloy AZ91 itself and its microstructure, following by discussion about Ni-P coating, its properties, the process of the electroless deposition and composition it the nickel bath. Next chapter focuses on information about varnishes, its function and the process of its application on the surface of the substrate. Theoretical part closes with the summary of current research in the field of Ni-P coatings applied on magnesium alloys. The experimental part focuses on analysis of the microstructure of AZ91 alloy. The microstructure of the Ni-P coating and of the system Mg alloy/Ni-P coating/varnish was 4 examined by scanning electron microscope (SEM) and inverted microscope. During the next phase was thickness and hardness measured and composition measured by EDS analysis. The factor of the heat treatment of the samples and its impact on the final microstructure, hardness and corrosion resistance was taken in account. Finally, several samples were modified with the layer of the varnish and its thickness and the influence on the corrosion resistance ware measured. Samples were tested with electromechanical impedance spectroscopy (EIS), the corossion resistance were tested by neutral salt spray (NSS) and adhesive test was performed. The results showed, that Ni-P coating and the layer of varnish had positive impact on the corrosion resistance and the hardness of AZ91. The corrosion resistance of the samples modified with heat treatment was much lower, because of the contracting, which causes creation of the cracks. Also, the layer of varnish had positive effect on anticorrosion properties of tested AZ91 alloy.
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Hydrothermal synthesis and characterization of calcium phosphate-based coatings on AZ31 magnesium alloy
Knoflíčková, Lenka ; Doskočil, Leoš (referee) ; Buchtík, Martin (advisor)
The aim of this diploma thesis was to summarize all necessary knowledge needed for preparation of a quality CaP coating on AZ31 wrought magnesium alloys, and to implement its optimization for use in simulated body fluids. The theoretical part discusses biomaterials and their classification. Subsequently, the potential of magnesium alloys, their corrosion, and the possibility of surface treatment for in vivo applications are described in detail. The theoretical part concludes with the mechanism of deposition of CaP coatings on magnesium alloys and methods to evaluate their corrosion resistance. The experimental part includes the process of optimization of Mg alloy pretreatment and optimization of CaP coatings preparation, where the quality evaluation criteria were the appearance of the coating and its electrochemical and corrosion properties. These were evaluated by potentiodynamic tests. The microstructure and the chemical composition of deposited coating were observed and measured by optical and scanning electron microscopy. Long-term corrosion tests using electrochemical impedance spectroscopy (EIS) were performed on the optimized CaP coatings and these results were then compared with the corrosion properties of the uncoated AZ31 alloy.
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Characterization of the thermally-sprayed metal-ceramic WC-CoCr coating on the AZ91 magnesium alloy
Knoflíčková, Lenka ; Wasserbauer, Jaromír (referee) ; Buchtík, Martin (advisor)
The aim of this bachelor thesis is to evaluate metal-ceramic coating WC-CoCr on magnesium alloy AZ91 to terms of microstructure, chemical and phase structure and mechanical properties. Deposition was made by HVOF (High Velocity Oxy-Fuel). The theoretical part is devoted to magnesium alloys focusing on alloy AZ91. Further there is said about methods of heat spraying. Where this part is focused on metal-ceramic WC-CoCr coatings made by HVOF method. The theoretical part is ended by current research, that is focused on characterization of WC-CoCr on magnesium alloys. Experimental part is about characterization of microstructure of alloy AZ91, WC-CoCr powder and WC-CoCr coating on magnesium alloy AZ91 with optical, SEM and XRD analysis. With heat spraying was observed that phase W2C was made by decay of phase WC in coating which leaded to dissolve of WC in matrix. For measuring of mechanical properties was used measurement by Vickers (hardness test). As result of WC-CoCr coating on surface of magnesium alloy AZ91 was increase of average hardness from 71 ± 5 HV0,3 to 1116 ± 109 HV0,3.
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Evaluation of the effect of chelating agents on the properties of phosphate coatings on AZ31 magnesium alloy prepared by hydrothermal method
Molva, Vojtěch ; Doskočil, Leoš (referee) ; Buchtík, Martin (advisor)
The aim of this bachelor thesis was to evaluate the influence of chelating agents on the properties of CaP coatings deposited on the AZ31 magnesium alloy by hydrothermal method. The theoretical part deals with magnesium and its alloys useful not only in biomedicine. Subsequently, the possibilities of surface treatments in the field of biomedical applications are described, with a focus on calcium phosphate (CaP) coatings. The theoretical part further discusses these coatings and the influence of selected chelating agents on the formation of CaP coatings. The theoretical part is concluded with a review of the experiments already carried out for the preparation of CaP coatings on Mg alloys. The experimental part includes the preparation and analysis of the protective Mg(OH)2 layer necessary for the deposition of CaP coatings. Within the experimental part, the influence of chelating agents (Chelaton III, citric acid, magnesium gluconate hydrate) at concentrations of 5, 50, and 500 mM at different pH of the reaction mixture on the structure, morphology, composition, and quality of the prepared CaP coatings was studied. The morphology, structure, and composition of the deposited coatings were investigated by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Based on these analyses, an assessment of the quality of the coatings was performed. In terms of coating quality, the coating prepared with the addition of 50 mM of Chelaton III at pH 7 and with the addition of 5 mM of magnesium gluconate hydrate at pH 5 appeared to be the best. The corrosion resistance was investigated by potentiodynamic tests in 0.15M NaCl, always with the sample from each batch that showed the best quality. The corrosion potential (Ecorr) and current corrosion density (icorr) values were determined from the polarization curves using the Tafel extrapolation method. Based on the measurements made, the most corrosion-resistant coated sample was the one with the addition of 5 mM magnesium gluconate hydrate at pH 5.
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Effect of complexing agents on the preparation of phosphate coatings on AZ31 magnesium alloy
Wolanský, Petr ; Buchtík, Martin (referee) ; Doskočil, Leoš (advisor)
The bachelor thesis deals with the characterization of the effect of complexing agents on the preparation of phosphate (CaP) coatings deposited on AZ31 magnesium alloy. The theoretical part presents the basic characterization of magnesium alloys with emphasis on AZ31 and their corrosion properties. Furthermore, attention is paid to CaP coatings, their preparation with a focus on the chosen hydrothermal synthesis and the influence of complexing agents on the preparation of CaP coatings. In the experimental part the preparation of CaP coatings on AZ31 alloy with Mg(OH)2 interlayer is presented. Surface analysis of CaP coatings was performed using scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS). Chemical analysis of CaP coatings was performed using Fourier transform infrared spectroscopy. To assess the corrosion resistance of the coatings, potentiodynamic tests were performed in 0.15M NaCl. For all the selected reagents, the best corrosion properties were obtained at the lowest concentrations, while the lowest value of icorr was observed for the sample with 0.0175M EDTA, this value corresponded to the icorr of the pretreated Mg(OH)2 sample. The preparation of CaP coatings resulted in better corrosion properties than that of pure AZ31 alloy. In all samples, the presence of hydroxyapatite (HA) as the main phase in the coating was identified. From the results obtained, it can be clearly determined that the presence of complexing agents and their concentrations affect the morphology of CaP coatings and can alter the corrosion resistance. It seems that the corrosion resistance was mainly due to the Mg(OH)2 interlayer rather than the prepared CaP coatings, which could provide higher biocompatibility of the materials.
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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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