No description available.

No description available.

No description available.

Nanometer thick layers of clay and polymer were formed on mica, silicon, and aluminum 2024-T3 alloy using alternating solutions of positively and negatively charged polymer and clay, respectively. Atomic force microscopy was used to observe the morphology of the composite films on mica and silicon. It was found that solution concentrations of clay above 0.02 weight percent lead to the uncontrolled deposition of clay platelets on the substrate's surface. By using solution concentrations of clay above 0.02 weight percent and ultrasonic agitation together it is possible to deposit a uniform monolayer of clay platelets on a mica substrate in £ 20 seconds. Ultrasonic agitation also produced crude patterns of montmorillonite platelets. Thin films of poly(diallydimethylammonium chloride) (PDDA) were made using concentrations ³ 2 weight percent of PDDA. It was found that the PDDA formed several unusual morphologies. Spherulites of PDDA were observed with AFM and the glass transition temperature of high molecular weight PDDA was measured using differential scanning calorimetry (DSC). Circular regions of positive charge were discovered on silicon wafers provided by three different sources. These areas of charge have never been reported in literature, but can easily be detected by placing wafers into solutions containing negatively or positively charged solutions of clay or polymer, respectively. The exact nature of these charged regions is unknown, but it is hypothesized that impurities on silicon wafers create the circular regions of positive charge. ISAM films made of a polyamide salt and a synthetic clay, Laponite RD®, demonstrated significant corrosion resistance on 2024-T3 Al alloys after 168 hours of salt spray testing. The ISAM films offered corrosion protection only if there was a significant layer of underlying surface oxide present, however. It was found that ISAM deposited films of polyarylic acid (PAA) and polyallylamine hydrochloride (PAH) may offer some corrosion resistance on 2024-T3 Al alloys, but these films' corrosion resistance is severely hampered by the presence of Cl- in the PAH solution. Funding from this project was gratefully received from the Materials Science and Engineering Department at Virginia Tech; Luna Innovations Inc; the American Chemical Society / Petroleum Research Fund #34412-G5 and the Environmental Protection Agency Contract #68-D-00-244. / Master of Science

This diploma thesis deals with evaluation of efficiency of protection conversion coatings created by passivation metals and alloys in passivation baths without chromium compounds. The theoretical part is initially concerned with question of electrochemical corrosion of metals, consequently there are mentioned different methods of corrosion protection. The main section of theoretical part of this thesis deals with chromate conversion coatings, description of their protective efficiency (including their unique self-healing effect) and then with account of new chromate-free conversion coatings occurring as chromate alternatives, whose usage is constrained because of their content of hexavalent chromium, which is highly toxic, oxidizing and also carcinogenic and thereby very dangerous for human body and the environment. Experimental part of this thesis is concerned with evaluation of efficiency of particular conversion coating which is quite commonly use in some applications as chromate alternative. It is chromate-free conversion coating which is created by passivation of metals or alloys in passivation bath Pragokor BP, which contains zirconium fluorocomplexes and is without any chromium or other toxic or ecologically unhealthy compounds. The influence of sealing of the coating in preparation Pragokor Seal Al and also other surface treatments such as application of conservation wax WAXENG or cold application of zinc coating were tested too. Efficiency of mentioned surface treatments was then evaluated on aluminum and steel by laboratory accelerated and atmospheric corrosion testing.

The diploma thesis deals with preparation of fluoride conversion coatings and evaluation of electrochemical corrosion characteristics of magnesium alloys ZE10 and ZE41 in SBF solution. The main aim of the work is to increase the corrosion resistance of the investigated magnesium alloys using fluoride conversion coatings. The influence of the conditions of the preparation of the conversion coatings on their morphology and the corrosion resistance of the coated alloys will be studied. The electrochemical corrosion characteristics of the magnesium alloys with conversion coatings will be evaluated by potentiodynamic and electrochemical impedance spectroscopy.

Diploma thesis deals with the technology of surface modifications of magnesium alloys. Basic knowledge from the field of the corrosion of metal materials. The division corrosion according to way of attack and corrosion environment, etc. There is an enumeration of ways of the corrosion defence. Questions of surface modifications with an emphasis on passivation by conversion coating and its analysis. Characteristics of magnesium and its alloys. Magnesium alloys with lithium, possibilities of its passivation and the verification of corrosion resistance. Enumeration of the used devices, chemicals and materials. characteristics of the used alloys. creation of the corrosion resistance standard. Research in passivation on the alloy containing 12 percent of lithium. The verification of the corrosion test usability based on the suggestion of the background research results. The test results for passivated as well as untreated samples and the reference material (steel). Aplication of chromate-free passivation and corrosion test on the alloy containing 12 percent of lithium.

No description available.

Durch elektrochemische Impedanzspektroskopie während der anodischen Oxidation von Aluminium werden in der vorliegenden Arbeit die elektrochemischen Vorgänge während der Oxidbildung quantitativ und zeitabhängig untersucht. Es wird ein Modell vorgeschlagen und diskutiert, welches das Impedanzverhalten während der anodischen Oxidation in Schwefel-, Oxal- und Phosphorsäure über einen großen Bereich von Konzentrationen und Stromdichten abbilden kann. Aus den gewonnenen Ergebnissen werden die kapazitive Wirkung der Sperrschicht am Porengrund, der Eintritt von Ladungsträgern in die Sperrschicht, der Ionentransport durch die Sperrschicht sowie die Oxidbildungsreaktion selbst als wesentlich für das Impedanzverhalten identifiziert. Die ermittelten Zusammenhänge und Konstanten können als Grundlage für Modellvorstellungen dienen, welche das Verhalten elektrischer Prozessgrößen und die Ausbildung der charakteristischen Oxidstruktur bei der anodischen Oxidation von Aluminium verknüpfen. / In the present work, the electrochemical subprocesses of the oxide formation on aluminium by anodic oxidation are investigated using electrochemical impedance spectroscopy. The time dependence of the impedance behaviour and the quantitative relations between the process parameters and the impedance behaviour are considered. A model for the representation of the electrochemical behaviour during the anodic oxidation in sulphuric, oxalic and phosphoric acid is proposed and discussed for a wide range of anion concentrations and current densities. On the basis of the obtained results, the capacitive effect of the barrier layer, the charge transfer resistance of the barrier layer, the ion transport within the barrier layer and the oxide formation are identified as the dominating effects for the impedance behaviour. The established relations can serve as a basis for models, which interrelate both the electrochemical behaviour and the geometrical formation of the characteristic pore structure.

Durch elektrochemische Impedanzspektroskopie während der anodischen Oxidation von Aluminium werden in der vorliegenden Arbeit die elektrochemischen Vorgänge während der Oxidbildung quantitativ und zeitabhängig untersucht. Es wird ein Modell vorgeschlagen und diskutiert, welches das Impedanzverhalten während der anodischen Oxidation in Schwefel-, Oxal- und Phosphorsäure über einen großen Bereich von Konzentrationen und Stromdichten abbilden kann. Aus den gewonnenen Ergebnissen werden die kapazitive Wirkung der Sperrschicht am Porengrund, der Eintritt von Ladungsträgern in die Sperrschicht, der Ionentransport durch die Sperrschicht sowie die Oxidbildungsreaktion selbst als wesentlich für das Impedanzverhalten identifiziert. Die ermittelten Zusammenhänge und Konstanten können als Grundlage für Modellvorstellungen dienen, welche das Verhalten elektrischer Prozessgrößen und die Ausbildung der charakteristischen Oxidstruktur bei der anodischen Oxidation von Aluminium verknüpfen. / In the present work, the electrochemical subprocesses of the oxide formation on aluminium by anodic oxidation are investigated using electrochemical impedance spectroscopy. The time dependence of the impedance behaviour and the quantitative relations between the process parameters and the impedance behaviour are considered. A model for the representation of the electrochemical behaviour during the anodic oxidation in sulphuric, oxalic and phosphoric acid is proposed and discussed for a wide range of anion concentrations and current densities. On the basis of the obtained results, the capacitive effect of the barrier layer, the charge transfer resistance of the barrier layer, the ion transport within the barrier layer and the oxide formation are identified as the dominating effects for the impedance behaviour. The established relations can serve as a basis for models, which interrelate both the electrochemical behaviour and the geometrical formation of the characteristic pore structure.