Carlos Roberto Araújo

This study aims to investigate the effect of lime addition in cement mortar on corrosion resistance of carbon and galvanized steel reinforcements. Mixed mortars were studied containing three contents of lime (6.7, 13.3, and 26.3 wt.%). The water retention, incorporated air, and compression strength of reinforced mortars were determined. Immersion tests were performed using the reinforced mortars consisting of 12 cycles of immersion in a solution of 3.5% (wt./v) sodium chloride and drying in a stove at 60oC. Electrochemical impedance spectroscopy was used to monitoring reinforcement corrosion after cyclic tests. These measurements were repeated after 36 months of the cyclic immersion testing. After the cyclic immersion tests in a saline solution, the polarization resistance of carbon and galvanized steel reinforcement increased as the lime content in mortar increased, demonstrating the protective effect of lime. After 36 months, the polarization resistance of steels in mixed mortars with the highest lime content was the lowest. For the carbon and galvanized steel in cement and mixed mortars, the polarization resistance increased after 36 months of the cyclic test.

Zinc electrowinning is performed with the application of a current through insoluble electrodes (Pb - Ag), causing the electrolysis of zinc sulfate, with or without impurities, and zinc deposition on the cathode of aluminum. The impurities can reduce the current efficiency and increase the energy consumption in zinc electrolysis. In this work, the effect of nickel and magnesium on zinc electrodeposition was studied using the electrochemical techniques of galvanostatic deposition and cyclic voltammetry. Additions of nickel, magnesium or both cations in zinc sulfate electrolyte resulted in a marginal increase in current efficiency. Addition of nickel or magnesium polarizes the cathode; however, the extent of polarization in the presence of magnesium is more than that of nickel. Addition of magnesium to the zinc electrolyte caused zinc reduction at a more negative potential. The addition of nickel to the zinc electrolyte increased the current density of the anodic peaks, thus increasing the dissolution of zinc and hydrogenated phases. The addition of nickel to the zinc and magnesium solutions decreased the nucleation loop, facilitating zinc deposition.

Purpose – The purpose of this paper is to study the corrosion of the coupling of two different types of stainless steel, austenitic and ferritic, used in the fabrication of water reservoirs in the solar energy industry. Design/methodology/approach – Potentiodynamic polarization and gravimetric immersion tests were used to evaluate corrosion of the coupling of two different types of stainless steel, austenitic and ferritic. Findings – The galvanic corrosion was not significant in the case of the coupling of AISI 304 and 444 steels. The difference of the open circuit potentials obtained for the AISI 304 and AISI 444 steels was 28?mV for the polished samples. The galvanic current density (i g) was 55?nA/cm². The corrosion observed in the stainless steel couple was in the weld area. Research limitations/implications – The methodology used is adequate to evaluate generalized galvanic corrosion. The problem of the corrosion in the coupling of the stainless steels is a problem of localized corrosion and the observed 28?mV potential difference was lower than the dispersion of results usually obtained from readings of corrosion potentials in electrochemical cells. Practical implications – The use of two different types of steel in contact with each other may lead to galvanic corrosion, and the welding of steel pieces may lead to several corrosion problems. Since the boiler may be used in different countries, subject to a great diversity of water quality, corrosion may be a significant problem. Originality/value – Literature data of the AISI 444 steel corrosion behaviour are still scarce. The coupling of two different stainless steels (AISI 304 and 444) in the water reservoir manufacturing was a necessary requirement of the solar energy industry. The manufacturers of boilers must evaluate and quantify the corrosion processes, which occur in the equipment used in the solar energy industry. As the solar energy industry has matured in the last ten years, the corrosion of this equipment may be a significant problem in due course.

PDF | Avaliou-se o estado de sensitização de aços inoxidáveis ferríticos AISI: 430; 439; 444, e um do tipo modificado (P430). Variaram-se as condições de temperatura e tempo de permanência em um forno, e mediram-se os resultados empregando-se as técnicas de ensaios de corrosão intergranular, Prática W (Norma ASTM A 763 – 93), e técnicas não destrutivas, quantitativas, de reativação eletroquímica potenciocinética (polarização cíclica com duplo loop). A partir de temperatura de 900oC, empregaram-se tempos de 10 e 20 minutos, com resfriamentos em forno, ao ar, em água, óleo e nitrogênio líquido. Para caracterizar qualitativamente a precipitação de carbonetos, utilizou-se um microscópio ótico. Notou-se que em condições de resfriamentos mais lentos ocorreu maior grau de sensitização para os aços AISI 430 e P430, nos outros aços não detectou-se precipitação de carbonetos em contornos de grão.