Um eletrodo de carbono vítreo foi modificado pela deposição de uma camada de nanotubos de carbono de paredes múltiplas, funcionalizados e decorados com nanopartículas de ouro. Este eletrodo foi caracterizado por microscopia ótica, mostrando uma superfície homogeneamente recoberta. Além disto, a sua morfologia foi investigada por microscopia eletrônica de transmissão, onde observou-se a distribuição e o tamanho médio aproximado de 20 nm das nanopartículas de ouro. Estas nanopartículas metálicas também foram caracterizadas por espectroscopia de absorção na região do UV-vis, mostrando um máximo de absorção em aproximadamente 525nm, o que confirma o seu tamanho médio de 20 nm. Os eletrodos modificados foram caracterizados eletroquimicamente pelo seu comportamento voltamétrico em uma solução de H2SO4 0,1 mol L-1, com uma velocidade de varredura de 0,100 V s-1. Nestes experimentos, ficou evidente os picos de formação e redução do óxido de ouro em potenciais acima de 0,8 V vs Ag/AgCl. Ainda foi observado o bom funcionamento dos eletrodos pela resposta voltamétrica do par redox [Ru(NH3)6]Cl2 / [Ru(NH3)6]Cl3 em meio de KCl. O desempenho deste eletrodo modificado para a oxidação dos pesticidas carbaril, etil-paration, malation e carbendazim foi investigado por voltametria de onda quadrada em tampão fosfato pH 7, porém apenas o inseticida e fungicida carbendazim mostrou eletroatividade. Desta forma, os estudos posteriores se focaram neste pesticida. O voltamograma cíclico do carbendazim mostrou um pico de oxidação e, na varredura reversa, um pico bem menor de redução. Isto sugeriu um mecanismo EC e um esquema da reação de oxidação foi proposto. Com o perfil voltamétrico estabelecido, a voltametria de onda quadrada foi utilizada para a determinação da curva analítica para o pesticida. Com todos os parâmetros da voltametria de onda quadrada otimizados, uma dependência linear da corrente de pico de oxidação com a concentração de carbendazim foi obtida, com a equação: Ip = 0,1 + 4,30 [carbendazim], com r2 = 0,9911 (n = 5). Esta curva analítica mostrou que a metodologia apresenta um limite de detecção de 17 x 10-8 mol L-1. Esta metodologia foi empregada na determinação de carbendazim em amostras de suco de laranja contaminadas artificialmente. A utilização de um teste t, de Student, mostrou que os valores recuperados pela voltametria não apresentaram qualquer diferença significante em relação àqueles adicionados às amostras. Assim, esta metodologia foi validada para a utilização na análise de suco de laranja contaminado com carbendazim / A glassy carbon electrode was modified by depositing a layer of multi-walled carbon nanotubes, functionalized and decorated with gold nanoparticles. This electrode was characterized by optical microscopy, showing a evenly coated surface. In addition, the morphology was investigated by transmission electron microscopy, where the distribution and the average size of 20 nm of the gold nanoparticles were observed. These metal nanoparticles were also characterized by absorption spectroscopy in the UV-vis region showing an absorption maximum at approximately 525 nm, which confirms their average size of 20 nm. The modified electrodes were electrochemically characterized by its voltammetric behavior in a 0.1 mol L-1H2SO4 solution, with a scanning rate of 0.100 V s-1. In these experiments, it became clear the formation and reduction of gold oxide peaks at potentials above 0.8 V vs. Ag/AgCl. It was also observed the proper functioning of the electrodes for the voltammetric response of the redox couple [Ru(NH3)6]Cl2/[Ru(NH3)6]Cl3 in a KCl electrolyte. The performance of the modified electrode for the oxidation of the pesticides: carbaryl, ethyl-parathion, malathion and carbendazim was investigated by square wave voltammetry in phosphate buffer, pH 7, but only the insecticide and fungicide carbendazim showed electroactivity. Thus, future studies focused on this pesticide. The cyclic voltammogram of carbendazim in phosphate buffer showed an oxidation peak and in the reverse scan, a much smaller reduction one. It suggested an EC mechanism and an oxidation reaction scheme was proposed. With the voltammetric profile established, square wave voltammetry was used to determine the calibration curve for the pesticide. With all square wave voltammetric parameters optimized, a linear dependence of the oxidation peak current with the concentration of carbendazim was obtained, with equation: Ip = 0.1 ± 4.30 [carbendazim] with r2 = 0, 9911 (n = 5). This calibration curve showed that the method has a detection limit of 17 x 10-8mol L-1. This methodology was used in the determination of carbendazim in orange juice samples artificially contaminated. A t-test of Student showed that the amounts recovered by voltammetry showed no significant difference in relation to those added to the samples. Thus, this methodology has been validated for use in analysis of orange juice contaminated with carbendazim

Um eletrodo de carbono vítreo foi modificado pela deposição de uma camada de nanotubos de carbono de paredes múltiplas, funcionalizados e decorados com nanopartículas de ouro. Este eletrodo foi caracterizado por microscopia ótica, mostrando uma superfície homogeneamente recoberta. Além disto, a sua morfologia foi investigada por microscopia eletrônica de transmissão, onde observou-se a distribuição e o tamanho médio aproximado de 20 nm das nanopartículas de ouro. Estas nanopartículas metálicas também foram caracterizadas por espectroscopia de absorção na região do UV-vis, mostrando um máximo de absorção em aproximadamente 525nm, o que confirma o seu tamanho médio de 20 nm. Os eletrodos modificados foram caracterizados eletroquimicamente pelo seu comportamento voltamétrico em uma solução de H2SO4 0,1 mol L-1, com uma velocidade de varredura de 0,100 V s-1. Nestes experimentos, ficou evidente os picos de formação e redução do óxido de ouro em potenciais acima de 0,8 V vs Ag/AgCl. Ainda foi observado o bom funcionamento dos eletrodos pela resposta voltamétrica do par redox [Ru(NH3)6]Cl2 / [Ru(NH3)6]Cl3 em meio de KCl. O desempenho deste eletrodo modificado para a oxidação dos pesticidas carbaril, etil-paration, malation e carbendazim foi investigado por voltametria de onda quadrada em tampão fosfato pH 7, porém apenas o inseticida e fungicida carbendazim mostrou eletroatividade. Desta forma, os estudos posteriores se focaram neste pesticida. O voltamograma cíclico do carbendazim mostrou um pico de oxidação e, na varredura reversa, um pico bem menor de redução. Isto sugeriu um mecanismo EC e um esquema da reação de oxidação foi proposto. Com o perfil voltamétrico estabelecido, a voltametria de onda quadrada foi utilizada para a determinação da curva analítica para o pesticida. Com todos os parâmetros da voltametria de onda quadrada otimizados, uma dependência linear da corrente de pico de oxidação com a concentração de carbendazim foi obtida, com a equação: Ip = 0,1 + 4,30 [carbendazim], com r2 = 0,9911 (n = 5). Esta curva analítica mostrou que a metodologia apresenta um limite de detecção de 17 x 10-8 mol L-1. Esta metodologia foi empregada na determinação de carbendazim em amostras de suco de laranja contaminadas artificialmente. A utilização de um teste t, de Student, mostrou que os valores recuperados pela voltametria não apresentaram qualquer diferença significante em relação àqueles adicionados às amostras. Assim, esta metodologia foi validada para a utilização na análise de suco de laranja contaminado com carbendazim / A glassy carbon electrode was modified by depositing a layer of multi-walled carbon nanotubes, functionalized and decorated with gold nanoparticles. This electrode was characterized by optical microscopy, showing a evenly coated surface. In addition, the morphology was investigated by transmission electron microscopy, where the distribution and the average size of 20 nm of the gold nanoparticles were observed. These metal nanoparticles were also characterized by absorption spectroscopy in the UV-vis region showing an absorption maximum at approximately 525 nm, which confirms their average size of 20 nm. The modified electrodes were electrochemically characterized by its voltammetric behavior in a 0.1 mol L-1H2SO4 solution, with a scanning rate of 0.100 V s-1. In these experiments, it became clear the formation and reduction of gold oxide peaks at potentials above 0.8 V vs. Ag/AgCl. It was also observed the proper functioning of the electrodes for the voltammetric response of the redox couple [Ru(NH3)6]Cl2/[Ru(NH3)6]Cl3 in a KCl electrolyte. The performance of the modified electrode for the oxidation of the pesticides: carbaryl, ethyl-parathion, malathion and carbendazim was investigated by square wave voltammetry in phosphate buffer, pH 7, but only the insecticide and fungicide carbendazim showed electroactivity. Thus, future studies focused on this pesticide. The cyclic voltammogram of carbendazim in phosphate buffer showed an oxidation peak and in the reverse scan, a much smaller reduction one. It suggested an EC mechanism and an oxidation reaction scheme was proposed. With the voltammetric profile established, square wave voltammetry was used to determine the calibration curve for the pesticide. With all square wave voltammetric parameters optimized, a linear dependence of the oxidation peak current with the concentration of carbendazim was obtained, with equation: Ip = 0.1 ± 4.30 [carbendazim] with r2 = 0, 9911 (n = 5). This calibration curve showed that the method has a detection limit of 17 x 10-8mol L-1. This methodology was used in the determination of carbendazim in orange juice samples artificially contaminated. A t-test of Student showed that the amounts recovered by voltammetry showed no significant difference in relation to those added to the samples. Thus, this methodology has been validated for use in analysis of orange juice contaminated with carbendazim

Electrochemical assessment of the condition of the steel reinforced concrete structures is being carried out increasingly and more regularly, both in the laboratory and in the field. It is important to have enough information about the factors that may affect these measurements. In this way, results obtained from different tests can be interpreted in more reliable manner and the condition of the embedded reinforcing steel bars in concrete structures can be evaluated with more confidence. The main goals of this project were: • to determine the causes of the errors in electrochemical measurements that may mislead the researchers, • to determine factors that may affect the measurements, • to attempt to manifest better interpretation of the results, • to avoid the problematic pitfalls and overcome them as much as possible. To this end, two types of concrete specimens were prepared for performing gravimetric and electrochemical tests: beams with four pre-weighed sections of rebars, and prisms with a single rebar and with different variables (cracked in two directions, carbonated and different cover depth). These have been exposed to de-icing salt for more than 2.5 years. The condition of the rebar in the beams and prisms was evaluated over this period by (i) half-cell potential measurements, (ii) galvanostatic pulse measurements (using the GalvaPulse™ and the potentiostat), (iii) potentiostatic linear polarisation resistance measurements (LPR), (iv) electrochemical impedance spectroscopy (EIS) and (v) potentiodynamic cyclic polarisation. Also, specimens were prepared to determine the amount of required time for steel to passivate itself in pore solution and mortar. Results from corrosion measurements in the laboratory show that: • Steel bar in mortar and pore solution needs time for passivation: about 7 days for steel embedded in mortar and about 3 days for steel in simulated pore solution. • Data from gravimetric tests were compared with the values calculated from electrochemical tests and results show that, in the laboratory condition, values obtained from potentiostatic LPR technique are more realistic and closer the actual mass loss than those obtained by galvanostatic techniques. • It was observed that, in most cases, when the steel bars were corroding actively, the half-cell potential values were more negative than -350 mV vs. CSE, in agreement with ASTM guidelines. • When performing the half-cell potential measurements, it was found that it is essential provide sufficient time after wetting the surface to allow the potential to stabilise. A minimum of about 15-20 minutes was found to be required. • One of the most informative electrochemical tests is the cyclic polarisation technique. The half-cell potential, corrosion rate, susceptibility to pitting, severity of corrosion, protecting potential, concentration limitations and, with appropriate procedures, Tafel constants, can be obtained by this technique. However, it is essential to choose the appropriate scan rate for the particular system, otherwise the achieved data mislead the researcher. The appropriate scan rate can be determined by using the Bode plot obtained from the EIS experiment. • To measure the concrete resistance, the galvanostatic pulse technique and EIS are suggested. Wenner four probe technique measures only the surface resistance and is, therefore, very dependant on the surface condition and is not recommended. • The guard ring in the GalvaPulse™ instrument which is designed to limit the polarised area was found to be working in reverse and, in fact, it polarises the steel even more than when it is not used. It is recommended that the guard ring electrode not be used during the measurements. • Another limitation of the GalvaPulse™ is its lack of capability to measure the high corrosion rates. • It was found that the GalvaPulse™ pulse generator unit must be calibrated every month, or before each measurement, which ever is longer period. In addition to the experiments in the laboratory, four locations were chosen for field measurements in collaboration with the Ministry of Transportation of Ontario. These measurements show that: • The half-cell potential of galvanised steel in much more negative than that in the black steel. This emphasises the importance that the ASTM C876 recommended guideline should not be used for other types of reinforcing bars. • It is recommended that half-cell potential contour map rather than the absolute values of potential be used for condition analysis. However, it is found that these maps are not constant varying with time and ambient conditions. Based on this experience, it is recommended that half-cell potential measurements be made exactly at the same time and date in different years. The results might be closer and more readily interpretable. • The measured half cell potential is a function, not only of the state of corrosion, but also of environmental factors. The temperature and relative humidity of both the atmosphere and inside the concrete play a role. The permittivity of concrete is dependent on all these factors and needs to be taken into account. • To measure the corrosion current density in the field, galvanostatic and galvanodynamic LPR and galvanodynamic polarisation can be used. The potentiostatic LPR, potentiodynamic LPR and EIS techniques appear to be limited by the size of full-scale structures and are also very sensitive to extraneous electrical noise. Consequently, they cannot be performed in the field.

Electrochemical assessment of the condition of the steel reinforced concrete structures is being carried out increasingly and more regularly, both in the laboratory and in the field. It is important to have enough information about the factors that may affect these measurements. In this way, results obtained from different tests can be interpreted in more reliable manner and the condition of the embedded reinforcing steel bars in concrete structures can be evaluated with more confidence. The main goals of this project were: • to determine the causes of the errors in electrochemical measurements that may mislead the researchers, • to determine factors that may affect the measurements, • to attempt to manifest better interpretation of the results, • to avoid the problematic pitfalls and overcome them as much as possible. To this end, two types of concrete specimens were prepared for performing gravimetric and electrochemical tests: beams with four pre-weighed sections of rebars, and prisms with a single rebar and with different variables (cracked in two directions, carbonated and different cover depth). These have been exposed to de-icing salt for more than 2.5 years. The condition of the rebar in the beams and prisms was evaluated over this period by (i) half-cell potential measurements, (ii) galvanostatic pulse measurements (using the GalvaPulse™ and the potentiostat), (iii) potentiostatic linear polarisation resistance measurements (LPR), (iv) electrochemical impedance spectroscopy (EIS) and (v) potentiodynamic cyclic polarisation. Also, specimens were prepared to determine the amount of required time for steel to passivate itself in pore solution and mortar. Results from corrosion measurements in the laboratory show that: • Steel bar in mortar and pore solution needs time for passivation: about 7 days for steel embedded in mortar and about 3 days for steel in simulated pore solution. • Data from gravimetric tests were compared with the values calculated from electrochemical tests and results show that, in the laboratory condition, values obtained from potentiostatic LPR technique are more realistic and closer the actual mass loss than those obtained by galvanostatic techniques. • It was observed that, in most cases, when the steel bars were corroding actively, the half-cell potential values were more negative than -350 mV vs. CSE, in agreement with ASTM guidelines. • When performing the half-cell potential measurements, it was found that it is essential provide sufficient time after wetting the surface to allow the potential to stabilise. A minimum of about 15-20 minutes was found to be required. • One of the most informative electrochemical tests is the cyclic polarisation technique. The half-cell potential, corrosion rate, susceptibility to pitting, severity of corrosion, protecting potential, concentration limitations and, with appropriate procedures, Tafel constants, can be obtained by this technique. However, it is essential to choose the appropriate scan rate for the particular system, otherwise the achieved data mislead the researcher. The appropriate scan rate can be determined by using the Bode plot obtained from the EIS experiment. • To measure the concrete resistance, the galvanostatic pulse technique and EIS are suggested. Wenner four probe technique measures only the surface resistance and is, therefore, very dependant on the surface condition and is not recommended. • The guard ring in the GalvaPulse™ instrument which is designed to limit the polarised area was found to be working in reverse and, in fact, it polarises the steel even more than when it is not used. It is recommended that the guard ring electrode not be used during the measurements. • Another limitation of the GalvaPulse™ is its lack of capability to measure the high corrosion rates. • It was found that the GalvaPulse™ pulse generator unit must be calibrated every month, or before each measurement, which ever is longer period. In addition to the experiments in the laboratory, four locations were chosen for field measurements in collaboration with the Ministry of Transportation of Ontario. These measurements show that: • The half-cell potential of galvanised steel in much more negative than that in the black steel. This emphasises the importance that the ASTM C876 recommended guideline should not be used for other types of reinforcing bars. • It is recommended that half-cell potential contour map rather than the absolute values of potential be used for condition analysis. However, it is found that these maps are not constant varying with time and ambient conditions. Based on this experience, it is recommended that half-cell potential measurements be made exactly at the same time and date in different years. The results might be closer and more readily interpretable. • The measured half cell potential is a function, not only of the state of corrosion, but also of environmental factors. The temperature and relative humidity of both the atmosphere and inside the concrete play a role. The permittivity of concrete is dependent on all these factors and needs to be taken into account. • To measure the corrosion current density in the field, galvanostatic and galvanodynamic LPR and galvanodynamic polarisation can be used. The potentiostatic LPR, potentiodynamic LPR and EIS techniques appear to be limited by the size of full-scale structures and are also very sensitive to extraneous electrical noise. Consequently, they cannot be performed in the field.

The electrochemical enzymatic electrodes dominate the world market for blood glucose monitoring devices for controlling, as well as reducing the detrimental effects of diabetes. However, the enzymatic electrodes exhibit constraints restricting their reliance on the enzyme’s activity which can be influenced by the external, and the environmental factors such as temperature, pH, and humidity etc. However, the greater thickness of the enzyme layer hinders the performance of the glucose biosensors resulting in signal dampening or loss. In addition, the selectivity of the electrodes is affected by the interferents present in blood. Moreover, the invasive nature of the electrodes is a major problem considering the patient’s perspective. In contrast, recent research activities demonstrated that the electrochemical non-enzymatic electrodes possess huge potential for inexpensive and highly sensitive glucose monitoring devices, yet these electrodes are invasive in nature. Therefore, the purpose of this research was to fabricate electrochemical non-enzymatic non-invasive electrodes for sweat glucose monitoring devices. A very simple low-cost fabrication technique has been shown to make the facile, flexible, and inexpensive electrodes to detect sugar in sweat bio-analyte for a non-invasive glucose monitoring system using the native stable Cu oxides (CuNOx), Cu2O, layers grown on 35 µm thin Cu foils keeping under ambient conditions (25℃- and 760-mm Hg) for more than 2 years so that the oxide layers are full-grown, and fully stable. Moreover, the foils also annealed at various temperatures such as 160, 230, and 280℃ with new temperature profile for reducing the required time of growing stable oxides and producing oxides with larger crystallized structures with higher surface – to – volume ratio. The X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM) results supported that at 280℃ annealing temperature the surface, mostly, transformed into highly electrocatalytic CuO with larger grain sizes, crystallized structures, and the uniform layer of ~ 140 nm. The electrochemical characterization, and sensing performance of the electrodes have been done by cyclic voltammetry (CV), one of the excellent and well accepted electrochemical methods, with the 3 – electrode configuration of the potentiostat. The CuNOx sensors of having ~10 nm layer of stable Cu2O exhibited a sensitivity of 603.42 μA mM−1 cm−2, a linear range beyond the desired limit of 7.00 mM with excellent linearity (R2 = 0.9983) and a low limit of detection of 94.21 μM. In contrast, the new annealing profile has. the CuNOx sensors annealed at 280 ºC using new temperature profile provided twin calibration curves of linear ranges of 0.05 – 1.00 mM and 1.00 – 7.00 mM, that applicable for sweat and blood glucose sensing, respectively, and exhibited a sensitivity of 1795 μA mM−1 cm−2, a linear range up to the desired limit of 1.00 mM for sweat glucose sensing with excellent linearity (R2 = 0.9844), and a lower limit of detection of 135.39 μM. In addition, it has been shown that the peak electro-oxidation current of glucose sensing is linearly related with the squire root of the annealing temperature, √T. This can help to figure out the required applied annealing temperature for getting desired peak electro-oxidation current of glucose in a human health monitoring system. / Dissertation / Doctor of Philosophy (PhD)

This work investigated the protection of mechanism of organic coatings on steel exposed to 3% sodium chloride solution at 50°C, coupled with the use of electrochemical impedance spectroscopy (EIS) to monitor progress of corrosion and degradation of coating. Unlike Walter, EIS measurement was conducted at 50°C as well as after cooling, and measurements at intermediate temperatures have been used to characterize the dependence of the process involved. The proposition that corrosion rate is controlled by the ionic resistance of an organic coating has been tested. EIS results were fitted to a model circuit and changes in the film resistance and charge-transfer resistance with temperature were analyzed to deduce activation energies for the processes involved. Surprisingly, the calculated activation energy for coating resistance is significantly lower than the activation energy for the charge transfer resistance. This suggests that ion conduction in the coating, as apparent in an AC measurement, cannot be controlling the corrosion rate. Potentiostatic pulse tests on coated metal enable iR-corrected polarization curves to be plotted at different temperatures. From this, the activation energy determined from the corrosion currents also higher matches the higher activation energy value calculated from the charge transfer resistance. However, measurements of coating resistance on free films of the same coating also generate higher activation energy values, leaving two possible models that can account for the results.

O processo de deposição de uma fina camada de zinco sobre o aço carbono por imersão a quente e posterior tratamento térmico gera como produto o aço galvannealed. O baixo custo do zinco e o fácil processo de aplicação faz com que o maior consumo deste metal seja aplicado na proteção da superfície do aço carbono de um meio agressivo a que ele esteja exposto. Esta camada de zinco não pode ser muito espessa, pois limita a soldabilidade, dificulta o acabamento após pintura e limita a aderência de tintas à superfície. Essa condição da fina espessura da camada de zinco depositada sobre o aço carbono torna necessário o desenvolvimento de revestimentos com espessuras menores, com melhores propriedades de dureza, ductilidade e resistência à corrosão mais elevada. Sendo assim, a superfície de zinco tem de ser pré tratada com a fosfatização e cromatização antes que as tintas possam ser devidamente aplicadas. No entanto, estes processos de pré-tratamento vêm sendo questionados devido à sua toxidade e agressividade ao meio ambiente, levando o seu uso a ser menos frequente por meio do desenvolvimento de novos processos e compostos. Alguns destes compostos estudados são os inibidores de corrosão à base de silanóis, cujo desenvolvimento e aplicação busca a baixa toxicidade, a exigência de serem ecologicamente corretos e a alta eficiência. Quando exposto em meios ácidos, o processo de corrosão para o aço galvannealed pode ser acentuado e dessa maneira, o uso de soluções aquosas de silanos organofuncionais hidrolisados em pH ácido vem sendo promissor como promotores de aderência e como inibidores de corrosão. O número de estudos publicados para o uso de silanóis adicionados diretamente no meio agressivo para a formação de filmes adsorvidos no metal protegendo-o contra a corrosão ainda é baixo, devido seu caráter inovador. Neste estudo, caracterizou-se o uso do sulfossilanol obtido a partir da hidrólise em meio ácido (pH 4,0) do silano NXT (3 - octanoiltio - 1 - propiltrietoxisilano) como inibidor de corrosão para o aço galvannealed, zinco puro e aço carbono em meio ácido (pH 5,0) de NaCl 0,1 mol L-1. Escolheu-se o zinco puro e o aço carbono para estudo pois seus átomos de zinco e ferro são constituintes da liga Fe-Zn do aço galvannealed, de maneira a se observar a adsorção do sulfossilanol em diferentes superfícies. Por meio de técnicas eletroquímicas como a técnica de varredura por eletrodo vibratório (SVET), espectroscopia de impedância eletroquímica (EIE), curvas de polarização, medida da resistência de polarização linear (Rp) foi possível verificar que o sulfossilanol estudado atua como inibidor de corrosão para o aço galvannealed, se mostrando promissor para o zinco. Através deste estudo verificou-se que o inibidor de corrosão em questão atuou principalmente na inibição das regiões ricas em zinco, já que a avaliação isolada dos metais constituintes do aço galvannealed mostrou melhores resultados para o zinco do que para o ferro. A partir disto, estudou-se por meio de técnicas eletroquímicas em meio ácido (pH 5,0) de NaCl 0,1 mol L-1, outro inibidor de corrosão clássico para aço carbono contendo também o enxofre em sua molécula, o 2 - mercaptobenzotiazol (MBT) com o intuito de comparar a eficiência da inibição da corrosão para o aço galvannealed com um inibidor clássico para ferro e o sulfossilanol, já que o aço galvannealed possui áreas ricas em ferro. O estudo evidenciou que tanto o sulfossilanol, como o MBT são bons inibidores para o aço galvannealed, sendo o sulfossilanol um excelente inibidor para zinco e o MBT um excelente inibidor para o ferro. / The process of deposition of a thin layer of zinc on carbon steel by hot immersion and subsequent heat treatment generates as product the galvannealed steel. The low cost of zinc and the easy application process leads to high consumption of this metal for carbon steel surface protection from an aggressive medium. This layer of zinc cannot be too thick because it limits the weldability, hinders the finish after painting and limits the adhesion of paints to the surface. This condition of the thin thickness of the zinc layer deposited on the carbon steel requires the development of coatings having smaller thicknesses with better hardness, ductility and higher corrosion resistance properties. Thus, the zinc surface must be pre-treated with the phosphatization and chromatization before painting. However, these pretreatments processes have been questioned because of their toxicity and aggressiveness to the environment, making their use less frequent with the development of new processes and compounds. Some of these compounds studied are silane-based corrosion inhibitors, whose development and application seek the low toxicity, the requirement of being environmentally correct and the high corrosion inhibition efficiency. When exposed in acidic media, the corrosion process for galvannealed steel can be accentuated and, in this way, the use of aqueous solutions of hydrolyzed organofunctional silanes has been promising as adhesion promoters and as corrosion inhibitors. The number of published studies for the use of sulfur silanol added directly in the aggressive medium for the formation of adsorbed films in the metal protecting it against corrosion is still low due to its novelty. In this study, the use of the sulfur silanol obtained from acid hydrolysis (pH 4.0) of NXT (3-Octanoylthio-1 propyltriethoxysilane) silane as a corrosion inhibitor for galvannealed steel, metallic zinc and carbon steel (pH 5.0) in 0.1 mol L-1 NaCl. Zinc and carbon steel were also chosen for this study because they are constituents of the Fe-Zn alloy phases present in galvannealed steel. By means of electrochemical techniques such as the scanning vibrating electrode (SVET), electrochemical impedance spectroscopy (EIS), polarization curves and linear polarization resistance (Rp) measurements, it was possible to verify that the evaluated sulfur silanol acts as a corrosion inhibitor for galvannealed steel. In this study, it was also verified that the corrosion inhibitor in question acted mainly in the inhibition of zinc rich regions or phases, since the isolated study of the constituent metals of the galvannealed steel showed better results for pure zinc than for iron. From this, it was studied by means of electrochemical techniques in acidic environment (pH 5,0) of 0,1 mol L-1 NaCl, another classic corrosion inhibitor for carbon steel also containing the sulfur in its molecule, 2 - mercaptobenzothiazole (MBT) in order to compare the corrosion inhibition efficiency for galvannealed steel with a classical inhibitor for iron and sulfur silanol, since galvannealed steel has iron rich areas. The study showed that both sulfur silanol and MBT are good inhibitors for galvannealed steel, with sulfur silanol being an excellent inhibitor for zinc and MBT being an excellent inhibitor for iron.

The work within this thesis focuses on the study of alloy formation using an active liquid metal electrode for fundamental analysis and for the extraction and separation of the lanthanides and actinides in a pyroprocessing system. The electrochemical work herein is performed in a molten salt of lithium chloride and potassium chloride at its eutectic point (LKE). This salt is a likely candidate for pyroprocessing due to its relatively low melting point and resistance to degradation on exposure to high levels of radiation. The active electrode material under examination is bismuth due to its propensity to alloy with other elements, its relatively low melting point, high density and non-toxicity. The alloying processes studied are those of bismuth-lithium and bismuth-cerium. Lithium is the limiting reduction reaction defining the negative solvent limit in LKE. As a result, understanding the processes that would occur if the electrode were to be pushed to such negative potentials is of significant importance. Cerium is a commonly-used surrogate for plutonium, which is an element of relatively high concentration in waste nuclear fuel and is of significant interest to the nuclear international community in waste fuel recycling. This work examines the alloying processes in terms of which intermetallic compounds are formed and by what mechanisms. This is achieved through the use of co-deposition on a macro tungsten rod, employing a number of electrochemical techniques to extract pertinent information. Lithium electrodeposition and alloying with bismuth (at the negative solvent limit) was found to form BiLim alloy with increasing m at more reducing potentials, followed by the deposition of near pure lithium. Mixing of these two then gave rise to specific bismuth-lithium alloys and the apparent ejection of a lithium metal fog into the molten salt, which resulted in the chemical reduction of Bi3+ and the loss of the bismuth electrodeposition current. When electrodepositing cerium on, and alloying with, bismuth, the formation of intermetallic compounds is governed by potential with a maximum BiCem stoichiometry of m = 1 with equimolar Bi3+ and Ce3+. However, at concentrations of cerium greater than that of bismuth, alloys much richer in cerium were also deposited at more negative potentials. There is evidence that deposited cerium may also escape into solution and chemically react with Bi3+. In-house microelectrodes are also developed and used for this purpose, both through co-deposition and direct alloy formation on a liquid bismuth thin-film microelectrode. This work demonstrates that these devices provide a richness of information due to their highly beneficial microelectrode properties. A means of controllably depositing bismuth from an aqueous plating bath, without dendrite formation, on both platinum and tungsten microelectrodes was devised. This was followed by electrodeposition of bismuth films on these devices in LKE. Platinum was found to be an active electrode material, alloying with bismuth, while tungsten remained inert. Nonetheless, both electrode types produced characteristic microelectrode behaviour, which was successfully used to determine the diffusion coefficient of bismuth in LKE. A comparison of bismuth-cerium and cerium alloying on a thin film liquid bismuth microelectrode found that the latter indicated the formation of BiCe2 where only BiCe had been seen previously during co-deposition in an equivalent salt. This is thought to be due to the thin film liquid bismuth microelectrode configuration with enhanced Ce3+ mass transport. This response was also used to calculate the diffusion coefficient of cerium inside the bismuth film, which was found to be slightly slower than for Ce3+ in LKE.

O processo de deposição de uma fina camada de zinco sobre o aço carbono por imersão a quente e posterior tratamento térmico gera como produto o aço galvannealed. O baixo custo do zinco e o fácil processo de aplicação faz com que o maior consumo deste metal seja aplicado na proteção da superfície do aço carbono de um meio agressivo a que ele esteja exposto. Esta camada de zinco não pode ser muito espessa, pois limita a soldabilidade, dificulta o acabamento após pintura e limita a aderência de tintas à superfície. Essa condição da fina espessura da camada de zinco depositada sobre o aço carbono torna necessário o desenvolvimento de revestimentos com espessuras menores, com melhores propriedades de dureza, ductilidade e resistência à corrosão mais elevada. Sendo assim, a superfície de zinco tem de ser pré tratada com a fosfatização e cromatização antes que as tintas possam ser devidamente aplicadas. No entanto, estes processos de pré-tratamento vêm sendo questionados devido à sua toxidade e agressividade ao meio ambiente, levando o seu uso a ser menos frequente por meio do desenvolvimento de novos processos e compostos. Alguns destes compostos estudados são os inibidores de corrosão à base de silanóis, cujo desenvolvimento e aplicação busca a baixa toxicidade, a exigência de serem ecologicamente corretos e a alta eficiência. Quando exposto em meios ácidos, o processo de corrosão para o aço galvannealed pode ser acentuado e dessa maneira, o uso de soluções aquosas de silanos organofuncionais hidrolisados em pH ácido vem sendo promissor como promotores de aderência e como inibidores de corrosão. O número de estudos publicados para o uso de silanóis adicionados diretamente no meio agressivo para a formação de filmes adsorvidos no metal protegendo-o contra a corrosão ainda é baixo, devido seu caráter inovador. Neste estudo, caracterizou-se o uso do sulfossilanol obtido a partir da hidrólise em meio ácido (pH 4,0) do silano NXT (3 - octanoiltio - 1 - propiltrietoxisilano) como inibidor de corrosão para o aço galvannealed, zinco puro e aço carbono em meio ácido (pH 5,0) de NaCl 0,1 mol L-1. Escolheu-se o zinco puro e o aço carbono para estudo pois seus átomos de zinco e ferro são constituintes da liga Fe-Zn do aço galvannealed, de maneira a se observar a adsorção do sulfossilanol em diferentes superfícies. Por meio de técnicas eletroquímicas como a técnica de varredura por eletrodo vibratório (SVET), espectroscopia de impedância eletroquímica (EIE), curvas de polarização, medida da resistência de polarização linear (Rp) foi possível verificar que o sulfossilanol estudado atua como inibidor de corrosão para o aço galvannealed, se mostrando promissor para o zinco. Através deste estudo verificou-se que o inibidor de corrosão em questão atuou principalmente na inibição das regiões ricas em zinco, já que a avaliação isolada dos metais constituintes do aço galvannealed mostrou melhores resultados para o zinco do que para o ferro. A partir disto, estudou-se por meio de técnicas eletroquímicas em meio ácido (pH 5,0) de NaCl 0,1 mol L-1, outro inibidor de corrosão clássico para aço carbono contendo também o enxofre em sua molécula, o 2 - mercaptobenzotiazol (MBT) com o intuito de comparar a eficiência da inibição da corrosão para o aço galvannealed com um inibidor clássico para ferro e o sulfossilanol, já que o aço galvannealed possui áreas ricas em ferro. O estudo evidenciou que tanto o sulfossilanol, como o MBT são bons inibidores para o aço galvannealed, sendo o sulfossilanol um excelente inibidor para zinco e o MBT um excelente inibidor para o ferro. / The process of deposition of a thin layer of zinc on carbon steel by hot immersion and subsequent heat treatment generates as product the galvannealed steel. The low cost of zinc and the easy application process leads to high consumption of this metal for carbon steel surface protection from an aggressive medium. This layer of zinc cannot be too thick because it limits the weldability, hinders the finish after painting and limits the adhesion of paints to the surface. This condition of the thin thickness of the zinc layer deposited on the carbon steel requires the development of coatings having smaller thicknesses with better hardness, ductility and higher corrosion resistance properties. Thus, the zinc surface must be pre-treated with the phosphatization and chromatization before painting. However, these pretreatments processes have been questioned because of their toxicity and aggressiveness to the environment, making their use less frequent with the development of new processes and compounds. Some of these compounds studied are silane-based corrosion inhibitors, whose development and application seek the low toxicity, the requirement of being environmentally correct and the high corrosion inhibition efficiency. When exposed in acidic media, the corrosion process for galvannealed steel can be accentuated and, in this way, the use of aqueous solutions of hydrolyzed organofunctional silanes has been promising as adhesion promoters and as corrosion inhibitors. The number of published studies for the use of sulfur silanol added directly in the aggressive medium for the formation of adsorbed films in the metal protecting it against corrosion is still low due to its novelty. In this study, the use of the sulfur silanol obtained from acid hydrolysis (pH 4.0) of NXT (3-Octanoylthio-1 propyltriethoxysilane) silane as a corrosion inhibitor for galvannealed steel, metallic zinc and carbon steel (pH 5.0) in 0.1 mol L-1 NaCl. Zinc and carbon steel were also chosen for this study because they are constituents of the Fe-Zn alloy phases present in galvannealed steel. By means of electrochemical techniques such as the scanning vibrating electrode (SVET), electrochemical impedance spectroscopy (EIS), polarization curves and linear polarization resistance (Rp) measurements, it was possible to verify that the evaluated sulfur silanol acts as a corrosion inhibitor for galvannealed steel. In this study, it was also verified that the corrosion inhibitor in question acted mainly in the inhibition of zinc rich regions or phases, since the isolated study of the constituent metals of the galvannealed steel showed better results for pure zinc than for iron. From this, it was studied by means of electrochemical techniques in acidic environment (pH 5,0) of 0,1 mol L-1 NaCl, another classic corrosion inhibitor for carbon steel also containing the sulfur in its molecule, 2 - mercaptobenzothiazole (MBT) in order to compare the corrosion inhibition efficiency for galvannealed steel with a classical inhibitor for iron and sulfur silanol, since galvannealed steel has iron rich areas. The study showed that both sulfur silanol and MBT are good inhibitors for galvannealed steel, with sulfur silanol being an excellent inhibitor for zinc and MBT being an excellent inhibitor for iron.

Neste trabalho foi realizado um estudo estatístico do desempenho analítico das técnicas eletroquímicas Voltametria de pulso diferencial (VPD), Voltametria de onda quadrada (VOQ) e Voltametria de múltiplas ondas quadradas (VMOQ) para a redução do herbicida paraquat em ultramicroeletrodo de ouro (UME-Au) e sua análise e quantificação em águas puras e naturais. Os estudos da redução eletroquímica do paraquat foram realizados em eletrólito de suporte Na2SO4 0,1 mol L-1 em pH = 5,5. Os resultados mostraram a presença de dois picos de redução bem definidos , com o pico 1 em -0,64 V e o pico 2 em -0,94 V vs Ag/AgCl 3,0 mol L-1. Para as análises foi utilizado o pico 1 que é referente a uma reação em solução, onde a superfície eletródica serve apenas como intermediadora na transferência eletrônica. Utilizando-se os parâmetros experimentais e voltamétricos otimizados, curvas de trabalho foram construídas em eletrólito de suporte preparado com água ultrapurificada. Para a VPD, VOQ e VMOQ, os limites de detecção encontrados utilizando-se o método descrito em Miller & Miller e considerando-se o pico 1 foram: 55,35 ± 0,18 µg L-1 , 37,50 ± 0,32 µg L-1 e 21,42 ± 0,51 µg L-1, respectivamente. A metodologia foi aplicada em amostras de águas coletadas no Rio Mogi-Guaçu na cidade de São Carlos-SP. A variação da inclinação das curvas de trabalho obtida nas análises destas amostras foi praticamente insignificante em relação àquela obtida utilizando-se o eletrólito de suporte preparado com água ultrapurificada para as três técnicas utilizadas, mostrando pouca interferência da matéria orgânica presente nas amostras de águas naturais. Os menores valores de concentração mensuráveis de paraquat nas amostras de águas naturais foram inferiores ao valor máximo de resíduos permitido pela legislação brasileira para águas residuárias (100 µg L-1), mostrando a viabilidade na aplicação da metodologia proposta. Os cálculos dos limites de detecção e quantificação, a avaliação dos erros experimentais e os limites de confiança foram realizados a partir do procedimento estatístico descrito em Miller & Miller. Os valores de limites de detecção encontrados apresentam um significado físico e realístico para esta grandeza, já que foram determinados por interpolação nas curvas analíticas, construídas a partir da relação entre as concentrações do pesticida e os sinais obtidos. Estes mesmos limites foram calculados utilizando-se o método recomendado pela IUPAC e os valores encontrados foram 29,43 µg L-1 para VPD, 3,63 µg L-1 para VOQ e 0,37 µg L-1 para VMOQ. Estes resultados mostram diferenças de até 2 ordens de grandeza de uma técnica para outra, que se não forem bem avaliados podem levar o analista a conclusões equivocadas. / Statisctic studies of the analytical performance of Differential pulse voltammetry (DPV), Square wave voltammetry (SWV) and Multiple square wave voltammetry (MSWV) electrochemical techniques was performed for the electrochemical reduction of the paraquat herbicide on an gold ultramicroelectrode (Au-UME), aiming its analysis and quantification in pure and natural waters. The electrochemical reduction of paraquat was studied in 0.1 mol L-1 Na2SO4 support electrolyte in pH = 5.5 . The electrochemical responses showed two well-defined reduction peaks with potentials of -0.64 and -0.94 V vs Ag/AgCl 3.0 mol L-1 for peaks 1 and 2, respectively. The mathematical treatment was performed with data from peak 1, which is associated with a reversible solution reaction, where the electrode surface acts only as the electron transfer mediator. Working curves were obtained using the optimized experimental parameters in support electrolyte prepared with high purity water. To DPV, SWV and MSWV, the detection limits found for the peak currents associated to peak 1 were: 55.35 ± 0.18 µg L-1, 37.50 ± 0.32 µg L-1 and 21.42 ± 0.51 µg L-1, respectively. An analogous analytical procedure was applied in water samples collected in Mogi-Guaçu River, in São Carlos County, state of São Paulo. The variation in slope values, between curves obtained from pure water and those from river waters were practically depreciable for the three analytical methods, showing that the organic components and others contaminants present in natural waters caused only a minor interference in the measurements. The lower measurable values for paraquat in water samples were smaller than the allowed maximum of residue established by the Brazilian legislation for waste waters (100 µg L-1), indicating the developed methodology as convenient to such application. Calculations of detection and quantification limits, the evaluation of experimental errors and the limits of confidence were performed by the statistical procedure reported by Miller & Miller. The obtained detection limits values present a true physical significance, in a realistic order of magnitude, as they were determined by interpolation of the experimental analytical curves. The same analytical curves were submitted to the IUPAC methodology yielding the values of 29.43, 3.63 and 0.37 µg L-1 para DPV, SWV and MSWV, respectively, for pure water measurements. These results showed a difference up to two orders of magnitude from those obtained by the statistical methodology and may promote false conclusions, if not properly evaluated.