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Corrosion of carbon steel pipelines in sweet environments has been extensively researched on oil and natural gas exploration and production in order to obtain efficient corrosion mitigation methods. Although the consequences of corrosion are known, the cause and mechanism by which a certain phenomenon occurs are still not well understood. Sweet corrosion is mainly caused by the carbon dioxide dissolved in the water contained in the oil. It can manifest itself in different ways and one of which is the formation of a scale on the inner walls of the pipelines, which determines the evolution of corrosion process. This paper discusses the effects of partial pressure of carbon dioxide, dissolved hydrogen sulfide, dissolved oxygen and water chemistry on scale formation. Particular attention is paid to the nature and stability of the aqueous species formed during the corrosion process, as well as the thermodynamic and kinetic aspects lead to the scale formation on the carbon steel surface. The main objective is to enhance the understanding of the conditions of formation and precipitation of siderite and mackinawite and their effects on corrosion processes involving low carbon steels.

A possibilidade de determinação eletroanalítica de cafeína com ultramicroeletrodo de fibra de carbono (CF-UME), utilizando voltametria de varredura rápida, foi avaliada. Os CF-UMEs foram submetidos a pré-tratamentos eletroquímicos. Parâmetros como o número de ciclos para cálculo da média, velocidade de varredura, intervalo de potencial e o tipo de pré-tratamento superficial foram otimizados. Sob condições otimizadas, foi possível alcançar intervalo linear de resposta entre 10,0 e 200 mmol L-1 , obtendo limites de detecção de 3,33 mmol L-1. O método foi aplicado à determinação de cafeína em amostras comerciais de fármacos, com erros entre 1,0 e 3,5% em relação ao valor do rótulo e valores de adição e recuperação de 97-114%. Caffeine determination using a fast-scan voltammetric procedure at a carbon fiber ultramicroelectrode (CF-UME) is described. The CF-UME was submitted to electrochemical pretreatment. Parameters such as number of acquisition cycles, scan rate, potential window, and the electrochemical surface pretreatment were optimized. Using the optimized conditions, it was possible to achieve a LDR from 10.0 up to 200 mmol L-1 , with a LOD of 3.33 mmol L-1. The method has been applied in the determination of caffeine in commercial samples, with errors of 1.0-3.5% in relation to the label values and recoveries of 97-114% within the linear range.

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