Fluoride coatings on magnesium prepared in melts

Táto práca sa zaoberá protikoróznou ochranou horčíkových zliatin AZ31, AZ61, AZ91 pomocou fluoridového konverzného povlaku pripraveného z taveniny Na[BF4]. V teoretickej časti sú popísané vlastnosti horčíkových zliatin, súčasné výsledky príprav fluoridových konverzných povlakov a rozbor dostupnej literatúry ohľadom vlastnosti soli Na[BF4] a jeho produktov rozkladu. Experimentálna časť bola rozdelená na dve hlavné časti. Prvá sa zaoberá koróznou odolnosťou ošetrených horčíkových zliatin (AZ31, AZ61, AZ91 a žíhanej AZ91) v tavenine Na[BF4]. Korózna odolnosť bola testovaná pomocou potenciodynamických skúšok a skúšok v koróznej komore. V druhej časti bol skúmaný mechanizmus prípravy fluoridového konverzného povlaku, pričom bolo preukázané, že bez prístupu vzduchu ako oxidačné činidlo v procese vystupuje bór, ktorý sa redukuje z BIII na B0, a tým umožňuje vznik fluoridového konverzného povlaku.This work deals with the corrosion protection of magnesium alloy AZ31, AZ61, AZ91 using fluoride conversion coating prepared from Na[BF4] melt. The theoretical part describes the properties of magnesium alloys, the recent results of fluoride conversion coatings preparation and analysis of the available literature about the properties of salt Na[BF4] and its decomposition products. The experimental part was devided into two main sections. The first deals with the corrosion resistance of the treated magnesium alloys (AZ31, AZ61, AZ91 and AZ91 annealed) in the Na[BF4] melt. Corrosion resistance was tested using potentiodynamic tests and tests in the corrosion chamber. In the second part, the mechanism has been studied for preparing fluoride conversion coating, where it was shown that in air-free atmosphere the oxidizing agent in the process is boron, which is reduced from BIII to B0, and thereby enables the fluoride conversion coating.

Propsective surface treatments of magnesium alloys

Cieľom tejto bakalárskej práce je zhrnutie poznatkov o metódach povrchových úprav na horčíkových zliatinách a preskúmanie ich efektívnosti voči korózii. Horčík na rozdiel od iných technicky využívaných kovov má najmenšiu odolnosť voči korózii, ktorá sa zvyšuje legovaním, alebo povrchovými úpravami. V úvodnej časti sú zhrnuté všeobecné poznatky o horčíku, jeho zliatinách AZ31, AZ91 a korózii. Rešeršná časť zahŕňa doterajšie výsledky výskumu ohľadom týchto zliatin, pričom dôraz je kladený na fluoridové konverzné povlaky a kompozitné povlaky na báze niklu, kde popisujeme ich prípravu a pozornosť sústreďujeme na ich ochranné vlastnosti pred koróznym napadnutím. Výstupom práce je kritické zhodnotenie pozitív a negatív protikoróznych ochranných vrstiev na Mg zliatinách a návrh vhodných experimentov k overeniu reprodukovateľnosti výsledkov publikovaných v literatúre.The aim of this bachelor thesis is to summarize the methods of surface treatment of magnesium alloys and discussion of theireffectiveness of corrosion protection. In contrast to other metallic material used in technical practice, magnesium alloys have the lowest corrosion resistance, which can be increased by alloying or by use of surface treatments. The introduction part of the thesis deals with general knowledge about magnesium, its alloys AZ31, AZ91 and their corrosion processes. The recherché includes actual results of research about these alloys. Emphasizedare fluoride conversion coatings and composite coatings based on nickel, where their preparation is described and attention is focused on their properties in the sense of corrosion protection. Concluding the work, we give a critical assessment of the pros and cons of corrosion protective coatings on Mg alloys. Finally, there are suggested some convenient experiments to prove the repeatability of results published in the recherché literature.

Determination of tin, chromium, cadmium and lead in canned fruits from the Czech market

The global production of metal cans is more than 300 billion cans. Benefits of metal packaging consist mainly from the great strenght, excellent barrier properties and good thermal conductivity. The main problem of used metal packaging are the corrosion processes. The corrosion of metal container causes dissolution of tin which is used as a protective layer of the steel shell of the can and other metallic elements used in the manufacture of cans. In this work 31 samples of canned fruit was analysed and the concentration of tin, chromium, cadmium and lead was determined in fruit and in syrup using ICP-OES and ICP-MS techniques. The results showed no difference between the concentration of analysed elements in fruit and in syrup. In none of the analyzed samples the permitted maximum concentration of tin 200 mg.kg-1 was exceeded. Maximum concentration of tin was measured in canned grepfruit (59.8 ±1.9 mg.kg-1). The age of cans had no significant effect on the concentration of tin in canned fruit. The concentration of tin in fruit packaged in cans with protective layer of lacquer was significantly lower than the concentration of tin in fruit packaged in cans without protective layer of lacquer. Concentration of chromium, cadmium and lead in the analysed samples was very low at the natural levels of occurrence of these metals in fruit and it was impossible to determine unequivocally that the measured concentrations of these metals in canned fruit originate from the corrosion of can. The corrosion of the tinplate was studied using scanning electron microscopy with an energy dispersive spectrometer. By analyzing the SEM pictures and EDS spectra, critical areas of tin plate corrosion were observed. Based on the measured results it can be concluded that the consumption of fresh canned fruit is not a major problem for the inhabitants of the Czech Republic in terms of intake of potentially hazardous metals

Influence of the Composition of the Hank’s Balanced Salt Solution on the Corrosion Behavior of AZ31 and AZ61 Magnesium Alloys

namic tests and electrochemical impedance spectroscopy. The influence of the solution composition and material surface finish was examined also through the analysis of corrosion products created on the samples’ surface after electrochemical measurements in terms of scanning electron microscopy using energy-dispersive spectroscopy. Obtained data revealed the differences in the response of the magnesium alloys to enriched Hank’s Balanced Salt Solution—HBSS+ (with Mg2+ and Ca2+ ions) and Hank’s Balanced Salt Solution—HBSS (without Mg2+ and Ca2+ ions). Both examined alloys exhibited better corrosion resistance from the thermodynamic and kinetic point of view in the enriched HBSS+. AZ61 magnesium alloy reached higher values of polarization resistance than AZ31 magnesium alloy in both the used corrosion solutions. Phosphate-based corrosion products were characteristic for the AZ31 and AZ61 alloys tested in the HBSS (without Mg2+ and Ca2+ ions). The combination of phosphate-based corrosion products and clusters of MgO and Mg(OH)2 was typical for the surface of samples tested in the enriched HBSS+ (with Mg2+ and Ca2+ ions). Pitting corrosion attack was observed only in the case of enriched HBSS+

PEO of AZ31 Mg Alloy: Effect of Electrolyte Phosphate Content and Current Density

In this work, the quality of coatings prepared by plasma electrolytic oxidation (PEO) on an AZ31 magnesium alloy were evaluated. This was done by studying the effects of the chemical composition of phosphate-based process electrolytes in combination with different applied current densities on coating thickness, porosity, micro-cracking and corrosion resistance in 0.1 M NaCl. Both processing parameters were studied in four different levels. Mid-term corrosion resistance in 0.1 M NaCl was examined by electrochemical impedance spectroscopy and based on this, corrosion mechanisms were hypothesized. Results of performed experiments showed that the chosen processing parameters and electrolyte composition significantly influenced the morphology and corrosion performance of the prepared PEO coatings. The PEO coating prepared in an electrolyte with 12 g/L Na3PO4 center dot 12H(2)O and using an applied current density 0.05 A/cm(2) reached the highest value of polarization resistance. This was more than 11 times higher when compared to the uncoated counterpart

Preparation and Characterization of Fluoride Conversion Coatings on Biodegradable Magnesium Alloys

Predložená práca sa zaoberá nekonvenčnou technológiou prípravy fluoridového konverzného povlaku na horčíkových zliatinách typu AZ31, AZ61, ZE10 a ZE41, a to vložením zliatin do roztavenej soli Na[BF4]. V práci je posudzovaný vplyv technologických parametrov prípravy (teplota a čas) na kvalitu vzniknutého fluoridového konverzného povlaku, a to z hľadiska morfológie, chemického zloženia a jeho dosiahnutej hrúbky, kedy boli využité metódy svetelnej a elektrónovej mikroskopie. Vybrané vzorky bez a s fluoridovým konverzným povlakom boli podrobené krátkodobým a dlhodobým koróznym skúškam v roztoku simulovaných telesných tekutín pri teplote 37 ± 2 °C. Na vyhodnotenie krátkodobých skúšok boli využité potenciodynamické skúšky, konkrétne metóda lineárnej polarizácie a pre dlhodobé experimenty bola využitá metóda elektrochemickej impedančnej spektroskopie, či ponorové skúšky. Na základe dosiahnutých výsledkov bol definovaný vplyv parametrov prípravy povlaku na charakter vytvoreného fluoridového konverzného povlaku. Ďalšia časť práce je zameraná na popis možného mechanizmu vzniku a kinetiky rastu nekonvenčného fluoridového konverzného povlaku na vybranej horčíkovej zliatine AZ61. V tejto časti práce bola ďalej detailne vykonaná analýza mikroštruktúry a chemického zloženia fluoridového konverzného povlaku s využitím fokusovaného iónového zväzku, transmisnej elektrónovej mikroskopie a röntgenovej fotoelektrónovej spektroskopie.The submitted work is aimed at the unconventional fluoride conversation coating preparation on the AZ31, AZ61, ZE10 and ZE41 magnesium alloys by their immersion in Na[BF4] molten salt. The influence of the preparation parameters (such as temperature and time) on the quality of the fluoride conversion coating is investigated. Methods of light and scanning electron microscopy were used for the evaluation of morphology, chemical composition and thickness of the coating. Short and long-term corrosion tests were executed to analyze the corrosion performance in simulated body fluid solution at 37 ± 2 °C with and without the fluoride conversion coating. The short-term behavior was evaluated by potentiodynamic tests, namely by the linear polarization. Long-term performance was assessed by electrochemical impedance spectroscopy or immersion tests. The coating preparation parameters influence on the character of the formed fluoride conversion coating was defined based on the obtained results. The next part of the thesis deals with the description of the possible mechanism of formation and kinetics of growth of the unconventional fluoride conversion coating on the selected AZ61 magnesium alloy. In this part, further detailed analyses were carried out to investigate the microstructure and chemical composition of the fluoride conversion coating using focused ion beam, transmission electron microscopy and X-ray photoelectron spectroscopy.