Nos dias de hoje um grande número de pesticidas é utilizado em colheitas, agricultura, transporte de sementes, entre outros. Esses pesticidas são moléculas orgânicas que apresentam em sua estrutura grupos funcionais capazes de formar ligações com íons metálicos, que de forma natural ou por intervenção humana, são encontradas no solo. Estas espécies entram em contato no meio ambiente, e assim, interagem formando ligações, dando forma aos chamados compostos de coordenação, ou complexos. A formação destes complexos pode alterar significativamente as propriedades dos pesticidas e dos íons metálicos, podendo acentuar seu caráter tóxico, sua persistência e degradação. Neste trabalho foram escolhidos dois pesticidas que são bons exemplos deste tipo de molécula. O fungicida Thiram, que apresenta em sua estrutura átomos de enxofre, e assim interage com uma gama de íons metálicos; e o herbicida picloram, que é um derivado piridínico, o qual apresenta um átomo de nitrogênio com pares de elétrons livres e capazes de formar ligações, e um grupamento ácido na posição dois do anel também capaz de interagir com íons metálicos. Com o intuito de se entender melhor como ocorre estas interações, realizou-se este trabalho onde observou-se a complexação dos pesticidas thiram e picloram com quatro íons metálicos previamente selecionados, zinco, cobre, cádmio e chumbo. Dessa forma, deu-se início a um estudo de complexação utilizando o método de Voltametria de Redissolução Anódica em modo de Pulso Diferencial, a fim de se avaliar a ocorrência desta complexação. Para isso, contamos com duas ferramentas muito utilizadas para a avaliação da capacidade complexante de amostras, os métodos de linearização de Scatchard e Langmuir. Com a técnica utilizada foram levantadas curvas de titulação de amostras contento os pesticidas, e a partir dos dados obtidos aplicou-se os cálculos de Langmuir e Scatchard para se obter dois parâmetros importantes, a constante de estabilidade condicional do complexo formado, K\', e a concentração de ligante que participa da reação de complexação em solução, [L]T. Os dados obtidos com ambos pesticidas foram satisfatórios, indicando a ocorrência de complexos. Porém, observou-se que essa interação é maior entre o fungicida thiram e os respectivos metais do que com o herbicida picloram. As constantes de estabilidade condicional para o fungicida thiram se encontram com Log de K\' entre 6 e 7, enquanto as mesmas para os complexos formados entre o herbicida picloram e os íons metálicos se encontram entre 5 e 6. Para se confirmar as medidas de voltametria de redissolução anódica, foram realizadas medidas de espectroscopia na região do ultravioleta visível, bem como medidas de voltametria cíclica e de pulso diferencial. / Nowadays, numerous pesticides are used in crops, agriculture, transport of seeds, among others. These pesticides are organic molecules that present functional groups in their structure which are capable of forming connections with metallic ions, which, whether naturally or by human intervention, are found in the soil. These species enter in contact in the environment, and thus, they interact forming connections, giving form to the so called compound of coordination, or complex. The formation of these complexes can alter significantly the properties of both the pesticides and the metallic ions, being able to enhance toxic character, persistence and degradation. In this work, two pesticides were chosen for being good examples of this type of molecule. The fungicide Thiram, which presents atoms of sulfur in its structure, and thus interact with a range of metallic ions; and the herbicide picloram, a derived pyridinic, which presents a nitrogen atom with pairs of free electrons and capable of forming binding, and an acid group in the position two of the ring, also capable of interacting with metallic ions. In order to better understand how these interactions occur, this work focused where the complexation of pesticides thiram and picloram was observed with four metallic ions previously selected, zinc, copper, cadmium and lead. Hence, a study of complexation was started using the method of Differential Pulse Anodic Stripping Voltammetry, in order to evaluate the occurrence of the complexation. For that, we counted on two tools very frequently used for the viii evaluation of the metal-binding capacity of samples, namely, the linearization methods of Scatchard and Langmuir. Titration curves of the samples containing the pesticide were obtained using the technique, and starting from the data, the calculations of Langmuir and Scatchard were applied in order to obtain two important parameters, stability conditional constant of the formed compound, K\', as well as the ligand concentration that participates in the reaction complexation in solution, [L]T. The data obtained with both pesticides were satisfactory, indicating the occurrence of complexes. However, it was observed that the interaction is larger between the fungicide thiram and the respective metals than with the herbicide picloram. The constants of conditional stability for the fungicide thiram are with LogK\' between 6 and 7, while the same ones for the compounds formed between the herbicide picloram and the metallic íons are between 5 and 6. To confirm the measures of anodic stripping voltammetry, spectroscopy measures were carried out in the area of the visible ultraviolet, as well as measures of cyclic voltammetry and of differential pulse.

Nanoestructuras de alumina anódica porosa (AAP) têm sido tradicionalmente fabricadas por duas etapas de anodização a temperaturas relativamente baixas (de 0 até 5°C), e usadas como máscaras ideais para formação de vários materiais nanoestruturados. Neste sentido, o objetivo do trabalho foi estudar sistematicamente a formação e a fabricação de nanoestruturas de AAP autoorganizadas por uma só etapa de anodização e posterior aplicação na síntese de nanopartículas e nanofios metálicos. As nanoestruturas auto-organizadas de AAP foram obtidas por apenas uma etapa de anodização em ácido oxálico (H2C2O4) a temperatura ambiente; diferentemente dos processos convencionais onde são utilizados duas ou mais etapas de anodização. As características estruturais dos filmes de AAP foram moduladas através do controle dos parâmetros da concentração da solução, temperatura e potencial de polarização. O procedimento principal, para a obtenção de AAP auto-organizadas apenas por uma etapa de anodização, foi o pós-processamento de abertura dos poros através de um processo de corrosão química. Os resultados obtidos neste trabalho mostraram que o diâmetro médio dos poros apresentou uma dependência linear com a temperatura, potencial e tempo de corrosão química e foi constante em relação à concentração da solução eletrolítica. No entanto, a análise estrutural via microscopia eletrônica de varredura (MEV), mostrou que a circularidade e a ordem dos nanoporos sobre a superfície anodizada melhoraram com o aumento da concentração do eletrólito. A estrutura de AAP com um arranjo hexagonal de poros regularmente distribuídos foi obtida quando a anodização foi realizada em 0,3M de H2C2O4, a 45V e 20°C de temperatura seguido de uma corrosão química a temperatura de 17°C por 102 minutos. Adicionalmente foram obtidos nanopartículas e nanofios metálicos utilizando-se as nanoestruturas de AAP como moldes. Como os filmes de AAP são isolantes a obtenção das nanopartículas e nanofios foi realizado através de um processo de eletrodeposição de corrente alternada (CA). Os resultados deste trabalho mostraram que nanoestruturas de AAP autoorganizadas podem ser fabricadas por uma etapa de anodização controlando o tempo de corrosão química. Os resultados apresentados neste trabalho mostram-se vantajosos em relação aos reportados na literatura, já que normalmente as nanoestruturas de AAP são obtidas mediante processos de anodização em duas etapas e tempos longos de anodização. / Nanostructures of porous anodic alumina (PAA) have been traditionally manufactured by two steps anodization at relatively low temperatures (0 to 5°C) and used as templates suitable for the formation of various nanostructured materials. In this sense, the goal of this work was the fabrication of self-organized porous Anodic alumina nanostructures (AAP) by a one anodization step and subsequent application in the synthesis of metal nanowires and nanoparticles. The self-organized nanostructures of PAA were obtained by just one anodization step in oxalic acid (H2C2O4) at ambient temperature unlike to conventional processes where they are used two or more anodization steps. The structural characteristics of PAA films were modulated through control of the solution concentration, temperature and potential of polarization. The key procedure to obtain the periodic organized PAA by only one step anodization was the post-processing of pore opening through a process of corrosion chemistry. The results of this work showed that the average diameter of pores presented a linear dependence with temperature, time of chemical corrosion, polarization potential and it was constant relative to the concentration of the electrolyte solution. However, the structural analysis via scanning electron microscopy (SEM) showed that the roundness and the order of nanoporos over the anodized surface improved with the electrolyte concentration increasing. The PAA structure with a hexagonal arrangement of pores was obtained when the anodization was held in 0.3 M of H2C2O4, 45V, and 20°C of temperature followed by a chemical corrosion at 17°C of temperature for 102 minutes. Additionally it was obtained nano particles and nano metal wires using the PAA structures as molds. Since the PAA films are insulating, the nanoparticles and nanowire were obtained through an electrodeposition process using alternating current. The results of this work have shown that self-organized PAA nanostructures can be fabricated by one anodization step controlling the time of chemical etching process. The results presented in this work are advantageous in relation to reported in the literature, since normally the structures of PAA are obtained by two step anodization and for long anodization time.

The initiation of pitting corrosion on AISI 316 stainless steel has been examined from a phenomenological viewpoint with emphasis on the role of the metal in this complex, interaction. A modified potentiodynamic technique was used to prepare specimens corresponding with a series of different points on the anodic polarisation curve for the material in 0.05 M sulphuric acid alone and with additions of 0.1 M sodium chloride solutions-. The specimens were subsequently examined using standard metallographic, techniques. It was found that suitable pit nuclei, called 'pit sites', are manifest as a result of the initial interaction of the metal with the solution at the rest potential, (ER), i.e., at potentials far below the potential range in which catastrophic pitting processes normally occur. It was further found that these pit sites were manifest even in the absence of chloride ions for which there is no subsequent catastrophic pitting process, Estimation of pit site density (NA) for the different stages of the E-i curve and the use of a simple stereological model permit a statistical interpretation of the localisation of the phenomenon to particular areas of the metal surface. The statistical argument is extended to show that the breakdown potential for chloride media is associated with the development of a catastrophic condition which does not apply if chloride ions are absent and it is deduced that the breakdown potential is essentially indeterminate.

Hard anodising on aluminium and its alloys has been widely practised for many years in order to improve the resistance of the otherwise poor wear characteristics of aluminium. In recent years there has been an increasing interest in other treatments and coatings, on both aluminium and other base metals. The aim of this investigation is to explain the tribological performance and wear mechanism(s) of an uncoated aluminium alloy, four anodic coated alloys, and also an electroless nickel alloy. All of the coatings are produced on three different aluminium alloys. The thickness of the anodic films is 30-35 micron, as this thickness falls within the range commonly used by industry. In an endeavour to explain the role of coating thickness on wear life, electroless nickel alloy has been produced in a range of thicknesses of 10, 20 and 30 micron. To evaluate abrasive and adhesive wear, the samples were rubbed against a single point diamond and steel ball, respectively, in a reciprocating movement at room temperature and 65-75% relative humidity, under a wide range of load and sliding distance. Some tests continued to run until a breakdown of the coatings occurred, whilst other tests were interrupted at intermediate stages. This enabled the initiation and propagation of failure mechanisms to be studied. Abrasive wear was performed under dry conditions, whereas, adhesive wear was evaluated under both dry and lubricated conditions. Wear of these coatings was proportional to the applied load and sliding distance, but there was no direct relationship between wear and hardness. The tribological performance of these coatings appears to be dictated by a) the composition of the substrate, b) the chemical and physical nature of the coatings and c) the test conditions. Under boundary lubricated conditions there was a considerable increase in the wear life of the coatings. A three dimensional surface texture is superior to a machined surface, in controlling contact conditions. There is an approximate linear relationship between coating thickness and wear life for electroless nickel alloys. These coatings predominantly fail by adhesion, plastic deformation and brittle fracture. A microscopic model for fracture of brittle materials, under both static and dynamic conditions for abrasive and adhesive wear correlates very well with the behaviour of these coatings. Analytical interpretation of adhesive wear was made by separately calculating the coefficient of wear "K" of the counterbodies. This information enables an improved understanding of the wear test itself to be added to the model of the wear mechanisms involved.

Magister Scientiae - MSc / An electrolytic cell was designed and constructed for the preparation of TiO2 nanotubes. Conditions of anodic oxidation were established to reproducibly prepare TiO2 nanotubes of average length 35-50 μm vertically orientated relative to the plain of a pure titanium metal sheet. A non-aqueous solution of ethylene glycol containing small percentage of ammonium fluoride was used as the electrolyte with an applied voltage of 60 V. The morphology and dimensions of the nanotube arrays were studied by scanning (SEM) and transmission (TEM) electron microscopy. The effect of calcination under different conditions of temperature and atmosphere (nitrogen, argon and air) were assessed by both X-ray diffraction (XRD) and cyclic voltammetry (CV). Cyclic voltammetry studies were made possible by construction of a specially designed titanium electrode upon which the nanotubes were prepared. CV studies established a positive correlation between crystallinity and conductivity of the nanotubes. Doping of the nanotubes with nitrogen and carbon was established by elemental analysis, X-ray photoelectron spectroscopy (XPS) and Rutherford back scattering (RBS). The effect of nonmetal doping on the band gap of the TiO2 nanotubes was investigated by diffuse reflectance spectroscopy (DRS). / South Africa

This diploma thesis discusses the gas sensor preparation via anodic oxidation. It names sensor types, deals with the sensing principle of electrochemical sensors in detail and submits sensor parameters. It describes preparation technology and characterization technology methods. In the experimental part, it focuses on both the measurement methodology and the electrochemical oxygen sensor covered with titanium dioxide nanocolumns fabrication. Not the least it discusses acquired research results.

Les alcaloïdes de la pipéridine sont des composés présents à la fois dans le règne animal et végétal. L'approche générale que nous avons développée au cours de ce travail de thèse est basée sur l'utilisation de différents -aminonitriles qui ont été préparés soit par réduction de sels de pyridinium chiraux soit par cyanation anodique d'amines tertiaires dérivées de l'-phényl-éthylamine. Dans le premier cas, la modification de la réaction de Fry nous a permis de préparer les deux énantiomères de la coniine qui constitue l'agent toxique de la grande cigüe (Conium maculatum). En combinant cette méthode avec la métallation de Beak, nous avons pu accéder à la (+)-solénopsine A qui est l'un des constituants du venin des fourmis tropicales Solenopsis invicta. La seconde méthode qui utilise la voie électrochimique, a permis de synthétiser la (+)-myrtine qui est une indolizidine isolée de Vaccinium myrtillis et l'alcaloïde (+)-241D qui est extrait de sécrétions cutanée des grenouilles tropicales Dendrobates speciosus. Enfin, une nouvelle synthèse de la (–)-perhydrohistrionicotoxine (isolée de Dendrobates histrionicus) a été mise au point et cette dernière est basée sur l'alkylation diastéréosélective d'un α-aminonitrile chiral non racémique préparé par voie électrochimique. / Piperidine alkaloids are found in both animal and vegetal kingdoms. In this work, we have developed the synthesis and the utilization of several -aminonitrile systems which have been prepared either from the reduction of chiral non racemic pyridinium salts or from the anodic cyanation of piperidine ring system. In the first case, the modification of the Fry cyanation allowed the synthesis of both enantiomers of coniine which is the toxic component of hemlock (conium maculatum). By virtue of the Beak's lithiation–alkylation procedure, we have been able to synthesize the trans 2,6-piperidine (+)-solenopsin A which is one of the constituents of the venom of fire ant solenopsis invicta. As an alternative process, the anodic cyanation of piperidone derivatives allowed us to prepare the quinolizidine alkaloid (+)-myrtine (vaccinum myrtillis) and the all cis-2,4,6-piperidine alkaloid (+)-241D which is extracted from the skin of brightly colored neotropical frog dendrobates speciosus. Our final synthetic approach has been devoted to the stereoselective construction of spiropiperidine (–)-perhydrohistrionicotoxin whose tertiary chiral center was elaborated through the diastereoselective alkylation of an α-aminonitrile system which has been prepared by electrochemical means.

Sacrificial metallic coatings have been used in the past, for protecting steel in industrial and urban developments. It has been suggested that thermally sprayed aluminium coatings, immersed in marine environments, are also capable of protecting steel by providing galvanic protection. Researchers have also speculated that the growth of inert oxide products, on top of the coating as well as inside pores and cracks, could enhance even further its protective “shielding” properties. In addition, the self-healing abilities of the coatings, in case of mechanically induce damage, are still a matter of debate. This research project takes a critical look at these assumptions, focusing on the electrochemical response of aluminium metal sprayed (AMS) coatings immersed in 0.6 M NaCl and 0.6 M Na2SO4 solutions, in order to investigate how the presence of chlorides can alter the corrosion behaviour of these coatings. For such, a thin aluminium protective coating was deposited over two different panels (aluminium 1050 and low carbon steel), by the steel making company Fairfield-Mabey, using electric arc thermal spraying (TS). Subsequently, the coated panels were sectioned into smaller specimens, and with the aid of a SEM/EDS, and XRD, observations and analysis were conducted in their surfaces and cross sections, in order to determine the morphology, quality of deposition, and chemical composition of the coatings. Internal porosity/oxide growth after immersion, was studied using 3-D X-ray tomography scanning. Furthermore, the electrochemical behaviour of the coatings (intact and scribed) was also investigated, initially by analyzing the evolution of the open circuit potential in time, when immersed in chloride rich and chloride free environments. Additionally, the anodic polarization behaviour of the substrate and coatings were simultaneously analyzed, by connecting a zero resistance ammeter (ZRA) with the W.E. terminal of a potentiostat. To conclude, EIS and Rp vs. time plots were made in order to corroborate the data obtained from other tests. Results show that although the coating can generate superficial and internal corrosion products, these oxides are not isolating in nature nor will enhance its protective properties. On the other hand, the corrosion potential behaviour of the coatings revealed that AMS coatings have a more active than the substrate; regardless of the environment in which they were immersed or their substrate. Nevertheless, it was also observed that AMS coatings deposited onto steel will corrode faster than their substrates, and for that matter capable of offering corrosion protection, exclusively if chlorides are present in the solution.

No description available.

A utilização de filmes de polímeros intrinsecamente condutores (PIC) na proteção contra a corrosão tem se mostrado uma alternativa atraente como prérevestimento, pois estes materiais possuem a característica de proporcionar ou induzir o efeito de proteção anódica em metais passiváveis, de modo a desacelerar o processo corrosivo. Neste trabalho foi estudada a possibilidade de obtenção de filmes de PIC sobre aço carbono SAE1006 por eletrossíntese, utilizando os monômeros anilina e 5-amino-1-naftol em meio aquoso KNO3 alcalino. Através da caracterização dos filmes poliméricos, observou-se que os filmes são compactos, homogêneos, uniformes e delgados. Ensaios de eletroatividade mostraram que ambos os filmes possuem pares redox polímero-metal na faixa de potencial em que o substrato metálico é passivável, logo, os filmes são eletroativos. Este comportamento ficou evidente quando as amostras com filmes de PIC foram expostas a soluções ácidas de HCl e H2SO4. O estudo do comportamento eletroquímico via polarização potenciodinâmica mostrou a elevação do potencial de corrosão do aço, confirmando os resultados da eletroatividade. Após caracterização dos filmes de PIC, os corpos de prova foram revestidos com tintas nitrocelulósica, poliuretânica e epoxídica. Os ensaios de aderência mostraram que os filmes de polianilina e poli(5-amino-1-naftol) tem excelente aderência com o substrato metálico e com a tinta. A partir dos ensaios de polarização potenciodinâmica e espectroscopia de impedância eletroquímica em solução de NaCl, observou-se que os filmes PIC apresentaram bom desempenho quando comparados às amostras somente desengraxadas e fosfatizadas. / The use of intrinsically conducting polymers films (ICP) for corrosion protection have proved to be an attractive alternative as pre-coating, because these materials have the characteristic of providing or inducing the effect of anodic protection in passivable metals aimed at slowing down the corrosion process. This scientific research investigated the possibility of achieving ICP films on SAE1006 carbon steel surface through electrochemical synthesis using the aniline and 5-amino-1-naphthol monomers in alkaline medium, KNO3. Through the characterization of the polymeric films it was found were observed that the primers are compact, homogeneous, uniform and somewhat thick. Electroactivity trials have shown that both films have redox polymer-metal pairs in the potential range where the steel substrate is passivable, therefore the films have conductivity. This behavior was evident when samples with ICP films were exposed to HCl and H2SO4 acid solutions. The study of the electrochemical behavior through potentialdynamic polarization has shown an increase in steel potential corrosion, thus corroborating the electroactivity results. After the characterization of ICP films, samples were coated with nitrocellulose, polyurethane and epoxy paints. The adherence trials have shown that the polyaniline and poly(5-amino-1-naphfthol) films have an excellent adherence to paint as well as to steel substrate. From the polarization potentialdynamics testings and electrochemical impedance spectroscopy in NaCl solution, it was found that the ICP films have positive results when compared with without films samples and phosphatized samples.