Teor crítico de cloretos para iniciação da corrosão do aço no betão: influência do estado de superfície da armadura

Trabalho Final de Mestrado para obtenção do grau de Mestre em Engenharia Química e Biológica - Processos QuímicosA corrosão das armaduras no betão é a principal causa de degradação do betão armado em ambiente marítimo. Com o presente trabalho pretende-se contribuir para o conhecimento da influência do estado de superfície do aço das armaduras no teor crítico de cloretos (CCrit). Para tal recorreu-se a estudos eletroquímicos (Polarização Potenciodinâmica e Técnica do Eletrodo Vibrante de Varrimento – SVET) em soluções simulativas do líquido intersticial do betão, com diferentes concentrações de cloretos e por análise da superfície das amostras de aço com vários acabamentos/estados de superfície através da observação em microscopia ótica (MO) e em microscopia eletrónica de varrimento, associada a microanálise por dispersão de raios-X (MEV/EDS). Os ensaios eletroquímicos foram realizados numa solução que simula a solução existente nos poros do betão (SPS), de pH ~ 13.5 e 11.6, com diferentes concentrações de cloretos. Nos estudos de polarização potenciodinâmica utilizou -seum varrimento de potencial entre -0.2 V, em relação ao EOC, e +0.6 V, em relação ao Eref, a uma velocidade de 0.5 mV/s , em amostras de aço montadas em resina epoxídica e com diferentes estados de superfície: “tal e qual” (T), espelhada (D), polida (P500) e pré-oxidada (DH). Verificou-se, da polarização potenciodinâmica, que, a pH ~ 13.5, o estado de superfície do aço influencia a resistência à corrosão por picada, sendo esta sequenciada por > > 500> . Verificou-se também que a resistência do aço à corrosão por picada é inferior quando o pH da SPS diminui de 13.5 para 11.6.Por SVET, verificou-se que a formação de zonas ativas é quase imediata para teores de cloretos elevados (5 e 7%) e a diminuição de correntes anódicas com o tempo para teores inferiores pode ser explicada com a repassivação do aço, enquanto que nas zonas catódicas a diminuição da corrente pode ser atribuída à precipitação de produtos de corrosão. Por MEV/EDS e MO verificou-se que a corrosão se inicia, frequentemente, na zona de interface aço-resina, visto que nessa zona existem fendas e vazios, condições favoráveis à ocorrência de corrosão intersticial.Abstract: The reinforcement corrosion in concrete is the main cause of degradation of reinforced concrete for marine environment. This work is intended as a contribution to the understanding of some aspects of the steel surface finishing to determine the threshold chloride level (Cth), so we resorted to the electrochemical studies (potentiodynamic polarization and Scanning Vibrating Electrode - SVET ) in simulative pore solution andthe surface analysis of steel samples with various surface finishes and chloride concentrations by observation under an optical microscope (OM) and scanningelectron microscopy associated with microanalysis X-ray dispersion (SEM/EDS). The electrochemical tests were performed in a simulative concrete pore solution (SPS),at pH ~ 13.5 and 11.6, with different chloride concentrations. Electrochemical studies were conducted on steel samples with a potential scanning between -0.2 V vs EOCto +0.6 V vs Eref.with a rate of 0.5 mV/s, which were impregnated in epoxy resin with different surface states: as received (T), polished (D), grinded (P500) and pre-oxidized (DH). It was found, through the potentiodynamic polarization curves, that, at pH of 13.5,the chloride content above which c an initiate the formation of pit is sequenced by D > DH > P500 > T. It was also found that the steel's resistance to pitting corrosion is lower when the pH of the SPS decreased from 13.5 to 11.6. From the SVET technique, it was found that the formation of active areas is almostimmediate and the decrease in anode current with time can be explained with therepassivation, while the cathode areas are affected with precipitation of corrosion products and thus causing the same result. From SEM/EDS and OM was found that corrosion frequently begins in steel-resin interface, attributed to the existence in that zone of cracks and voids, favoring conditions to the occurrence of crevice corrosion

Cosmic Rays near Proxima Centauri b

Cosmic rays are an important factor of space weather determining radiation conditions near the Earth and it seems to be essential to clarify radiation conditions near extrasolar planets too. Last year a terrestrial planet candidate was discovered in an orbit around Proxima Centauri. Here we present our estimates on parameters of stellar wind from the Parker model, possible fluxes and fluencies of galactic and stellar cosmic rays based on the available data of the Proxima Centauri activity and its magnetic field. We found that galactic cosmic rays will be practically absent near Proxima b up to energies of 1 TeV due to the modulation by the stellar wind. Stellar cosmic rays may be accelerated in Proxima Centauri events, which are able to permanently maintain density of stellar cosmic rays in the astrosphere comparable to low energy cosmic ray density in the heliosphere. Maximal proton intensities in extreme Proxima events should be by 3–4 orders more than in solar events

Chloride threshold value to initiate reinforcement corrosion in simulated concrete pore solutions: The influence of surface finishing and pH

The influence of steel surface finishing and pH of simulated concrete pore solutions (SCPS) on the chloride threshold value (CTV) was evaluated. Steel samples were analysed, with four different finishes: as received (T), diamond-polished (D), polished (P500) and pre-oxidized (DH). The studies were performed in SCPS with pH values of 11.6 and 13.5, and of different chloride concentrations. The electrochemical behaviour of the samples was assessed using open circuit potential, potentiodynamic polarization curves and scanning vibrating electrode techniques. The surface of the steel samples was observed by optical microscopy and SEM/EDS. The results showed that the samples were ranked D > DH > P500 > T for the CTV after which pitting corrosion occurs. The highest chloride threshold value was found in D samples.info:eu-repo/semantics/acceptedVersio