The activation parameters for the temperature dependent irreversible loss of surface-enhanced Raman scattered (SERS) intensity from pyridine and chloride adsorbed at silver surfaces in an electrochemical environment have been determined. Laser-induced heating is introduced as a probe of the chemical nature of SERS-active sites. Surface temperatures are calculated from spectroscopic data. The activation energies associated with the destruction of SERS-active sites at a surface roughened by an illuminated oxidation-reduction cycle (ORC) are 12.8 ± 3.2 kcal/mole and 27.7 ± 3.1 kcal/mole for pyridine at two different types of sites on the Ag surface. Similarly, values for coadsorbed chloride are found to be 11.1 ± 2.4 kcal/mole and 24.5 ± 3.8 kcal/mole. An activation energy of 27.4 ± 1.9 kcal/mole is obtained for pyridine on a silver surface roughened by a nonilluminated ORC. Evidence for the desorption of pyridine and chloride is presented.

The method utilizes both cation and anion concentrator columns in parallel as a preconcentration system. The preconcentrator system is loaded using a reagent delivery module operated for a specific time at a preset flow rate. Total injection volumes of 2-5 ml are routinely used. Various chromatograms are discussed along with detailed information concerning detection limits for sodium and chloride, the system operating conditions, and the solutions to other pitfalls which have arisen during the course of this work.

Este trabalho tem por objetivo estudar a eficiência dos oxiânions molibdato (MoO4 2-) e tungstato (WO4 2-) na inibição da corrosão localizada em aços inoxidáveis austeníticos (347 e 304L) em sistemas de água com alto grau de pureza na presença de íons cloreto (Cl-). Para avaliar a ação dos oxiânions estudados foram empregadas técnicas eletroquímicas de monitoramento do potencial de circuito aberto (Eoc), espectroscopia de impedância eletroquímica (EIS), polarização cíclica (PC) e cronoamperometria (CA). Para caracterização superficial foram utilizadas microscopia óptica (MO) e microscopia eletrônica de varredura (SEM). Os ensaios foram realizados em meios contendo somente água pura desoxigenada e água pura desoxigenada contendo íons cloreto (50, 100, 200, 300 e 500 ppm) variando a concentração (0, 10-4, 10-3 e 10-2 M) dos inibidores molibdato e tungstato de sódio. Todos os experimentos foram realizados à temperatura ambiente e em condições hidrodinâmicas controladas, empregando o sistema de eletrodo de disco rotativo (RDE) com velocidade constante de1200 rpm. Os resultados mostraram que os aços inoxidáveis 347 e 304L permanecem passivos em água pura, uma vez que o meio não é agressivo. Entretanto, a adição de íons cloreto tornou-os susceptíveis à corrosão por pites, pois os cloretos atuam como desapassivadores, fragilizando o filme passivo que fornece proteção aos aços inoxidáveis. O aumento da concentração dos íons cloreto no eletrólito aumentou a sua agressividade para os dois aços estudados, sendo observado o precoce aparecimento da corrosão. No entanto, a adição dos inibidores molibdato e tungstato de sódio melhorou a qualidade da camada passiva, aumentando os valores de potencial de pite (Ep) e de módulo de impedância, mantendo a passividade dos aços num amplo intervalo de potenciais. Ensaios cronoamperométricos mostraram que na presença dos oxiânions os valores medidos de densidade de corrente de resposta para os aços inoxidáveis 347 e 304L foram acentuadamente menores em relação aos valores obtidos na ausência dos mesmos, confirmando que os inibidores utilizados atuam na melhora da camada passiva, diminuindo a sensibilidade aos cloretos e conseqüentemente aumentando a resistência contra a corrosão por pites dos aços. O estudo mostrou que os melhores resultados para ambos os aços foram obtidos na presença de 10-2 M de inibidor, tanto para o tungstato quanto para o molibdato, sendo este com eficiência levemente melhor. Além disso, o aço 304L sem partículas incrustadas de alumina mostrou-se menos susceptível aos ataques dos cloretos do que o aço 347. Nas amostras que tiveram a superfície tratada com lixas de abrasivo de alumina, essas partículas foram incrustadas nos aços e isso levou ao desaparecimento de um potencial de pite bem definido. Na presença de alta concentração de cloretos, essas partículas foram arrancadas pelo ataque às regiões deformadas mecanicamente, localizadas ao redor das partículas incrustadas e as propriedades do aço em si puderam ser verificadas. / The aim of this work is to study the efficiency of molibdate (MoO4 2-) and tungstate (WO4 2-) oxianions in the inhibition of the localized corrosion in austenitic stainless steels (347 and 304L) in high purity water systems in the presence of chloride ions (Cl-). In order to evaluate the action of the oxianions electrochemical techniques as open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), cyclic polarization (CP) and chronoamperometry (CA) were accomplished. For surface characterization optical microscopy (OM) and scanning electron microscopy (SEM) were used. The experiments were carried out in deoxygenated pure water and deoxygenated pure water containing chloride ions (50, 100, 200, 300 and 500 ppm) adding different concentrations (0, 10-4, 10-3 and 10-2 M) of molibdate and tungstate ions. All the experiments were performed at room temperature under controlled hydrodynamic conditions using a rotating disk electrode (RDE) at constant rotation speed of 1200 rpm. The results showed that 347 and 304L stainless steels remain passive in pure water, since the environment is not aggressive. However, in the presence of chloride ions they become susceptive to pitting corrosion, with chloride ions acting depassivity agents weakening the passive film that supplies protection to the stainless steels. The increase of chloride ions concentration in the electrolyte enhanced the aggressiveness for both steels evidenced by a precocious accurance of pitting corrosion. On the other hand, the addition of sodium molibdate and tungstate inhibitors improved the quality of the passive layer, increasing the pitting potentials (Ep) and the impedance modulus, improving the the passivity of steels a large of potential range. Chronoamperometric measurements showed that in the presence of oxianions response current density for 347 and 304L stainless steels was strongly diminished in relation to the values obtained in the absence of the inhibitors, confirming that the inhibitors act in the improvement of the passive layer, decreasing its sensitivity to chlorides and consequently increasing the steels resistance against pitting corrosion. Results showed that the best results for both steels were obtained in the presence of 10- 2 M tungstate or molibdate, being this latter with efficiency lightly better. Moreover, the 304L stainless steel showed to be less susceptive to pitting corrosion compared to 347 stainless steel. For stainless steel specimens previously treated with Al2O3 emery papers, Al2O3 particles become embedded in the steel surface and led to the indefinition of the pitting potential values. In the presence of high chloride concentrations, the mechanically affected region of steel in the surrounding of Al2O3 particles was attacked and Al2O3 particles were removed reveling the stainless steel own resistance to chlorides.

É crescente a preocupação mundial com a durabilidade e o atendimento da vida útil de projeto estabelecida pelas normativas para estruturas de concreto armado. Desta maneira, torna-se fundamental a utilização de modelos representativos dos processos de degradação para uma correta previsão da vida útil deste tipo de estrutura. Isto posto, esta pesquisa teve como objetivo a validação, com base em dados de exposição natural, do modelo para a previsão da vida útil de estruturas de concreto armado proposto por Andrade (2001). Para esta validação foram coletados dados na literatura referentes à penetração de cloretos em estruturas de concreto e foram obtidos dados experimentais da concentração de cloretos em prismas de concreto e argamassa moldados com cimento CP II – F, CP III, CP IV e CP V – ARI, com relações a/c de 0,45, 0,55 e 0,65, expostos por um período de 3, 2 e 1 ano, respectivamente, em ambiente protegido e desprotegido da chuva em zona de atmosfera marinha, na cidade de Vitória. Também foram avaliados os perfis de cloretos de blocos de concreto moldados com cimento CP IV, CP V, CP V + 5% SA e CP V + 10% SA e relações a/c de 0,45, 0,55 e 0,65, que permaneceram expostos por 9 anos na cidade de Tramandaí. Paralelamente, foram avaliadas a influência do tipo de cimento, da relação a/c, da condição de exposição (protegido e desprotegido da chuva) e da adição de sílica ativa na penetração de cloretos em matrizes cimentícias, bem como a diferença desta penetração em concretos e argamassas moldados com os mesmos materiais e relações a/c. Para isto foram retiradas, dos prismas e blocos de concreto e argamassa, amostras sob a forma pulverulenta, para posterior determinação da concentração de cloretos utilizando o equipamento CL - 2000 da NDT James Instruments. Os resultados obtidos indicaram que o tipo de cimento que determinou maiores concentrações de cloretos foi o CP III; que prismas de concreto tendem a apresentar concentrações superiores aos de argamassa, em função da existência da zona de transição entre a pasta e o agregado graúdo. No tocante à corrosão de armaduras desencadeada por cloretos, o ambiente desprotegido mostrou-se mais danoso; a utilização de teores de sílica ativa em percentuais de 5 e 10% é eficiente na redução do ingresso de cloretos; baixas relações a/c apresentaram concentrações superficiais mais elevadas, em contrapartida, a medida que a profundidade em relação à superfície do concreto aumenta, há uma redução nestes teores. Por fim, em relação à validação do modelo de Andrade (2001) constatou-se que, para os dados com pequenos tempos de exposição, o modelo apresentou níveis de resposta similares à penetração de cloretos in situ, com bons resultados dentro de um faixa de variação de 35%, associados a diferenças máximas de apenas 4,6 mm entre os valores observados e calculados. Para os dados com tempos de exposição superiores, as diferenças foram expressivas, indicando a necessidade de um ajuste no sentido de melhor descrever o crescimento da concentração superficial ao longo do tempo. / International concern about durability and service life design established by regulations is growing. Therefore, the use of representative models of degradation processes for a correct prediction of service life of reinforced concrete structures become fundamental. Moreover, this research aimed to validate, based on natural exposure data, the model for the prediction of service life of reinforced concrete structures proposed by Andrade (2001). For this validation, data were collected in the literature regarding the chloride penetration in concrete structures and experimental data were obtained in concrete and mortar prisms molded with cement CP II – F, CP III, CP IV and CP V, with w/b ratios of 0,45, 0,55 and 0,65, exposed for a period of 3, 2 and 1 year, respectively, in a rainfall protected and unprotected environment in a marine atmosphere zone, in the city of Vitória. The profiles of concrete blocks molded with cement CP IV, CP V, CP V + 5% SA and CP V + 10% SA, and w/b ratios of 0,45, 0,55 and 0,65, who remained exposed for 9 years in the city of Tramandaí, were also evaluated. At the same time, were evaluated the influence: of the cement type, the w/b ratio, the exposure condition (protected and unprotected from rainfall) and the addition of silica fume in chloride penetration in cementitious matrixes, as well as the difference of this penetration in concretes and mortars molded with the same materials and w/b ratios. For this purpose, pulverulent samples were removed from the prisms and blocks of concrete and mortar for further determination of chloride concentration using the CL – 2000 equipment of the NDT James Instruments. The results indicated the type of cement with highest chloride concentrations was CP III; that concrete prisms tend to have higher concentration than mortar, due to the exist of the transition zone between the past and the coarse aggregate; with regard to corrosion triggered by chlorides the unprotected environment is more damaging; the use of silica fume in percentages of 5 and 10% is efficient to reduce the chloride ingress; low w/b ratios showed higher surface concentration, in contrast, as the depth in relation to the concrete surface increases, there is a reduction in theses contents. Finally, in relation to the validation of Andrade´s model (2001), it was found that, for data with small exposure times, the model showed similar response levels to chloride penetration in situ, with good results within a range of variation of 35%, associated with maximum differences of only 4,6 mm between the observed and calculated values. For the data with longer exposure times, the differences were expressive, indicating the need for an adjustment in order to best describe the growth of the surface concentration over time.

No presente trabalho analisa-se o comportamento do aço de reforço ante à corrosão, com o uso dos inibidores: nitrito de sódio, fosfato de sódio e etalonamina, na água de poros contaminada com cloreto, e no concreto com a finalidade de analisar seus resultados e seus mecanismos diferenciados. Para cumprir este objetivo o presente trabalho divide-se em duas etapas: uma primeira etapa baseada em simular sinteticamente a água de poro de um concreto, cuja solução é KOH 28g/l+NaOH 4g/l. Essa água de poro é simulada em ambiente marinho, cuja solução é KOH 28g/l + NaOH 4g/l+NaCl 35g/l, e a esta solução referência incorporamse os inibidores (20g/l da cada um). Realizaram-se ensaios de espectroscopia de impedância eletroquímica (EIE) (após 3 e 72 horas de imersão) e curvas de polarização (após 72 horas de imersão) com vistas a obter respostas da cinética da corrosão ante a cada solução. Obteve-se o melhor comportamento para a água de poros. No caso da água de poro contaminada por cloretos, o melhor comportamento se obteve para o inibidor nitrito de sódio. Na segunda etapa adotou-se apenas o inibidor nitrito de sódio, pois estatisticamente as eficiências dos três inibidores foram muito similares. Analisou-se o nitrito de sódio em amostras reais de concreto armado contaminado com cloreto de sódio. Para isso se elegeram dois tipos de cimentos (CP IV e CP V) e três relações água-cimento (a/c-0.4, a/c-0.5, a/c- 0.65). Para simular o ambiente marinho, realizaram-se ensaios acelerados de cloretos. Comparam-se métodos de análises simuladas sinteticamente e reais, concluindo-se em ambos meios, embora fossem um solido e outro líquido o inibidor Nitrito de Sódio aumento a sua eficiência com os ciclos de exposição. / In this paper it is analyzed the behavior of reinforcing steel against corrosion using inhibitors: sodium nitrate, sodium phosphate and ethanolamine in water contaminated with chlorides pore and concrete, in order to analyzing the results and different mechanisms. To meet the objective of this work, it was divided into two stages, a first stage based on synthetically simulate the pore water of a concrete, through the following solution KOH 28g/l+NaOH 4g/l, this same solution simulated pore water to a marine environment it would be KOH 28g/l + NaOH 4g/l+NaCl 35g/l, it is then incorporated into both reference solutions inhibitors in a proportion, (20g/l de cada um). Assays were performed electrochemical impedance spectroscopy (EIE) (last 3 hours and 72 hours of immersion) and polarization curves (last 72 hours of immersion) in order to obtain responses corrosion kinetics in each solution. the best performance was obtained in the pore water. In the case of water contaminated with chlorides pore, the best performance was obtained in the presence of sodium nitrite inhibitor. In the second step was performed only with the inhibitor sodium nitrate, as statistically efficiencies of the three inhibitors were similar. Sodium nitrate was analyzed in real samples of reinforced concrete contaminated with chlorides of sodium. So they were chosen two types of cement CP- IV and CP-V, cement water three relationships 0.4, a/c-0.5, a/c- 0.65. In this case to simulate the marine environment, accelerated tests were performed chloride. They were compared the methods of analysis, simulated synthetically and simulated in real concrete.

La corrosion des aciers est l’une des principales causes de dégradation des ouvrages en béton armé, notamment en façade maritime. Cette dégradation est due à la diffusion d’ions chlorures qui peut se produire dans les ouvrages immergés dans l’eau de mer, ceux subissant des cycles de marnage et également ceux soumis aux embruns marins. La corrosion peut être également due au processus de carbonatation du béton, responsable de la baisse du pH et par conséquent de la dépassivation des aciers. Cette thèse propose un modèle physico-chimique pour décrire la penetration des agents agressifs dans la première phase de la corrosion des aciers. Cette phase dite « incubation » correspond à la phase pendant laquelle le transfert des espèces agressives se produit dans le béton. Afin d’identifier clairement les paramètres de transport de ce modèle macroscopique une démarche multi-échelle est mise en oeuvre pour rendre compte de la diffusion dans les bétons. Cette démarche repose sur une description détaillée de la microstructure du béton (constituants et morphologie) par des méthodes de changement d’échelle. Cette approche se veut la plus exhaustive possible avec la prise en compte explicite de l’influence du rapport eau sur liant de la pâte de ciment, des propriétés des granulats et de la zone de transition entre la pâte et les granulats. Après identification de tous les paramètres d’entrée, le modèle physico-chimique macroscopique est utilisé pour évaluer la durée de vie d’un béton soumis au couplage carbonatation -chlorures en milieu insaturé. Suite à une validation du modèle par comparaison à des résultats expérimentaux, plusieurs applications de ce modèle sont présentées. / The corrosion of steels is one of the principal causes of degradation of reinforced concrete structures, especially in front of the sea. This degradation is due to the diffusion of chloride ions that can occur in the structures immersed in the seawater, those undergoing tidal cycles and also those subjected to the sea spray. The corrosion can also be due to the carbonation process of the concrete, which is responsible for decreasing of the pH and consequently the depassivation of the steels. This thesis proposes a physicochemical model to describe the penetration of aggressive agents in the first period of steel corrosion. This so-called « incubation » period corresponds to the period during which the transfer of aggressive species occurs in the concrete. In order to clearly identify the transport parameters of thismacroscopic model, a multi-scale approach is implemented to consider the diffusion in concretes. This approach is based on taking into account the detailed description of the microstructure of the concrete (constituents and morphology) by upscaling methods. This multi-scale approach is intended to be the most comprehensive with the consideration of the influence of the water-to-binder ratio of the cement paste, the properties of the aggregates and the transition zone between the cement paste and the aggregates. After identifying all the input parameters, the macroscopic physico-chemical model is used to evaluate the service life of a concrete subjected to coupling carbonation -chlorides in unsaturated medium. Following a validation of the model compared to experimental results, several applications of this model are presented.

Graduation date: 1995

Concrete marine structures are typically exposed to harsh marine environments where the ingress of chloride ions can lead to corrosion of steel reinforcing bars, reducing both strength and service life; therefore, concrete must be proportioned to resist these environments. Current recommendations for concrete mixtures and plastic shrinkage cracking both reduce the resistance to chloride ingress. The main objective of this thesis was to understand the benefits of fiber addition to concrete exposed to chlorides and quantify those benefits, which would lead to a concrete mixture suitable for marine structures in freeze thaw environments. The research program tested two different fibers in a total of nine concrete mixtures. The results demonstrated that fiber addition at dosages up to 0.33 % by volume resulted in significant reduction or elimination of plastic shrinkage cracking and the chloride tests determined that the ternary FRC mixtures had the best resistance to chloride diffusion.

This work concerns the microstructure of CSS-grown CdTe layers used for CdTe/CdS solar cells. Particular attention is given to how the development of microstructure on annealing with CdCl(_2) may correlate with increases in efficiency. By annealing pressed pellets of bulk CdTe powder, it is shown that microstructural change does occur on heating the material, enhanced by the inclusion of CdCl(_2) flux. However, the temperature required to cause significant effects is demonstrated to be higher than that at which heavy oxidation takes place. The dynamics of this oxidation are also examined. To investigate microstructural evolution in thin-films of CdTe, bi-layers of CdTe and CdS are examined by bevelling, thus revealing the microstructure to within ~1 µm of the interface. This allows optical microscopy and subsequent image analysis of grain structure. The work shows that the grain- size, which is well described by the Rayleigh distribution, varies linearly throughout the layer, but is invariant under CdCl(_2) treatment. Electrical measurements on these bi-layers, however, showed increased efficiency, as is widely reported. This demonstrates that the efficiency of these devices is not dictated by the bulk microstructure. Further, the region within 1 µm of the interface, of similar bi-layers to above, is examined by plan-view TEM. This reveals five-fold grain-growth on CdCl(_2) treatment. Moreover, these grains show a considerably smaller grain size than expected from extrapolating the linear trend in the bulk. These observations are explained in terms of the pinning of the CdTe grain size to the underlying CdS, and the small grain size this causes. A simple model was proposed for a link between the grain-growth to the efficiency improvement. The study also examines the behaviour of defects within grains upon CdCl(_2) treatment provided the first direct evidence of recovery on CdCl(_2) treatment in this system. Finally, a computer model is presented to describe the evolution of microstructure during growth. This is shown to be capable of reproducing the observed variation in grain size, but its strict physical accuracy is questioned.

19 Dec 2004. / Published through the Information Bridge: DOE Scientific and Technical Information. "IS-T 2515" Roman Vladimirovich Rozhkov. 12/19/2004. Report is also available in paper and microfiche from NTIS.