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Publicação
Corrosão do cobre em amostras de solo de diferentes graus de agressividade
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Resumo(s)
Este trabalho teve como objectivo o estudo da corrosão do cobre numa amostra de um solo do território nacional, um litossolo, de baixa agressividade, não modificado e modificado com adição de cloretos (500 a 8000 ppm). O grau de agressividade das amostras de solo foi avaliado com base no índice de Steinrath, tendo-se obtido amostras com índices entre -5 e -12. Velocidades médias de corrosão, para o cobre exposto nas amostras de solo acima referidas, durante um período de 3 meses, situaram-se entre 0,85 e 93,90 mg dm-2 dia-1 (3,50 e 385 μm ano-1) respectivamente, no solo original e no modificado com maior concentração de cloretos (8000 ppm). A superfície das amostras depois de retiradas do solo foi observada a olho nú e ao microscópio óptico, visualizando-se produtos de cor vermelho acastanhado em todas as amostras, e compostos de cor verde azulado nas amostras expostas em solos com maior concentração de cloretos. Observou-se corrosão localizada em todas as amostras. As imagens de MEV confirmaram o ataque localizado e os espectros de EDX permitiram a identificação dos seguintes elementos: Cu, Cl, O, Si e C, podendo estes dois últimos elementos ser atribuídos a resíduos dos produtos de polimento (SiC) e do solo (SiO2); os primeiros três poderão ser atribuídos aos produtos de corrosão (óxidos e cloretos). Contudo, por difracção de raios-X de pós foi possível identificar apenas o óxido cuproso (Cu2O) e o óxido de silício (SiO2). De modo análogo ao que foi feito com o solo preparam-se soluções de cloretos (0,01 a 0,5 M), utilizando como solvente a água lavagem do solo. Os estudos de voltametria cíclica e de polarização anódica realizados com as referidas soluções, permitiram concluir sobre a influência da concentração de cloretos e do pH nos parâmetros característicos da corrosão do cobre, nomeadamente, E(i=0), Eb, ΔEpass e Rp.
The aim of this work is the study of the corrosion of copper in a Portuguese soil, a Litosoil soil of low aggressivity. Non-modified and modified soil samples, by addition of different chloride concentrations (500 to 800 ppm), were employed. The aggressivity of the modified and non-modified soil samples was determined following Steinrath; levels of aggressivity between −5 and −12 were obtained. Corrosion rates varying from 0.85 to 93.90 mg dm-2 day-1 (3.50 to 385 μm year-1), for copper exposed, during 3 months, to the non-modified soil and to the soil modified by the highest chloride concentration (800 ppm), respectively, has been obtained. The corroded surfaces were observed by naked eye and optical microscope. Brownish red products were visible on all samples; bluish green products were also observed on copper samples exposed to the modified soil containing the highest chloride concentration. Localized instead of uniform corrosion was observed. The SEM images confirmed localized corrosion. EDS spectra led to the identification of Cu, Cl, O, Si and C, the presence of Si and C is maybe due to residues of polishing material (SiC) and soil (SiO2); Cu, Cl and O are the components of the corrosion compounds (oxides and chlorides). However, only cuprous oxide (Cu2O) and silicon oxide (SiO2) were identified by X-Ray powder diffraction. Electrochemical studies were also performed in solutions obtained from soil washing; the solutions were modified in the same way as the soil samples. Cyclic voltammetry and anodic polarization were employed to study the influence of both chloride concentration and pH on copper corrosion parameters, namely, E(i=0), Eb, ΔEpass and Rp.
The aim of this work is the study of the corrosion of copper in a Portuguese soil, a Litosoil soil of low aggressivity. Non-modified and modified soil samples, by addition of different chloride concentrations (500 to 800 ppm), were employed. The aggressivity of the modified and non-modified soil samples was determined following Steinrath; levels of aggressivity between −5 and −12 were obtained. Corrosion rates varying from 0.85 to 93.90 mg dm-2 day-1 (3.50 to 385 μm year-1), for copper exposed, during 3 months, to the non-modified soil and to the soil modified by the highest chloride concentration (800 ppm), respectively, has been obtained. The corroded surfaces were observed by naked eye and optical microscope. Brownish red products were visible on all samples; bluish green products were also observed on copper samples exposed to the modified soil containing the highest chloride concentration. Localized instead of uniform corrosion was observed. The SEM images confirmed localized corrosion. EDS spectra led to the identification of Cu, Cl, O, Si and C, the presence of Si and C is maybe due to residues of polishing material (SiC) and soil (SiO2); Cu, Cl and O are the components of the corrosion compounds (oxides and chlorides). However, only cuprous oxide (Cu2O) and silicon oxide (SiO2) were identified by X-Ray powder diffraction. Electrochemical studies were also performed in solutions obtained from soil washing; the solutions were modified in the same way as the soil samples. Cyclic voltammetry and anodic polarization were employed to study the influence of both chloride concentration and pH on copper corrosion parameters, namely, E(i=0), Eb, ΔEpass and Rp.
Descrição
Tese de mestrado, Química Tecnológica, Universidade de Lisboa, Faculdade de Ciências, 2010
Palavras-chave
Litossolo Corrosão do cobre Índice de Steinrath Gravimetria MEV/EDX Polarização anódica Parâmetros electroquímicos Teses de mestrado - 2010