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Preparation of layered double hydroxides on Mg-hydroxyapatite-based substrates
Knoflíček, Milan ; Doskočil, Leoš (referee) ; Buchtík, Martin (advisor)
The aim of this bachelor thesis was the preparation and characterization of coatings based on layered double hydroxides (LDH) on Mg composite substrates prepared by powder metalurgy. Hydroxyapatite (HAp) was used as a filler. The deposition of MgAl-LDH coatings on the surface of composites was carried out in a reaction mixture containing Al(NO3)3 at pH 10 and a temperature of 95 °C. The morphology and structure of the samples were characterized using scanning electron microscopy (SEM). The elemental composition of both composites themselves and the prepared coatings were characterized by energy dispersive spectroscopy (EDS). Analysis of the structure of Mg-HAp composites revealed that the frequency of HAp agglomerates increased with increasing reinforcement concentration. The highest frequency of agglomerates was detected in samples containing 20 and 50 wt. % HAp filler, where unlike the other samples, a significant deterioration of corrosion properties was also observed. In contrast, the best corrosion resistance was shown by the sample with 1 wt. % of filler. Other samples with filler contents from 0 to 10 wt. % were relatively similar in terms of corrosion resistance. Potentiodynamic tests demonstrated that coated samples exhibited significantly higher corrosion resistance compared to the uncoated samples. A uniform layer of LDH was observed in the coated samples with HAp content up to and including 10 wt. %. The presence of cracks related to the presence of bulky HAp agglomerates was detected on samples with higher reinforcement content, i.e. 20 and 50 wt. % HAp. Lower coating adhesion was also observed at these locations. It was found that to achieve high quality of LDH coatings, the optimum amount of HAp reinforcement of mixed and subsequently pressed Mg-HAp composites is up to 5 wt. % HAp. Higher HAp content in the samples generally led to the formation of defects and deterioration of corrosion properties.
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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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