Maria das Mercês Reis de Castro

Effect of nickel and magnesium on zinc electrowinning using sulfate solutions

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.

Atmospheric corrosion of materials used in the civil construction industry

Purpose – The purpose of this study was to select an atmospheric corrosion evaluation methodology and to establish a range of relative corrosion penetration and/or progress values, which could be used as reference in the selection of materials for the civil construction industry.Design/methodology/approach – Salt spray, field tests, accelerated cyclic tests and accelerated field tests were used to evaluate atmospheric corrosion resistance of civil construction materials. The cyclic accelerated test and the field test with saline solution spray were found to be appropriate for atmospheric corrosion resistance evaluation.Findings – The corrosion resistance of aluminium killed mild steel, aluminium killed copper added steel, and electrogalvanized steels, all phosphatized and painted, were evaluated by field and accelerated corrosion tests. Of the materials studied, aluminium killed mild steel showed the least resistance to atmospheric corrosion. The use of aluminium killed copper added steel is recommended f...

Strategies for corrosion inhibition of slurry pipelines prior to commissioning

A practice used to prevent corrosion in buried slurry pipelines is the hibernation of pipelines with an aqueous solution containing corrosion inhibitors before beginning the mining operation. The aim of this work is to evaluate the corrosion resistance of API 5L X70 steel used in the slurry pipelines in hibernation solution containing sodium sulphite, sodium hydroxide and glutaraldehyde in a synthetic river water. The electrochemical techniques used are the Tafel analysis and electrochemical impedance spectroscopy. The synergistic effect of the components of hibernation solution on the corrosion resistance of the API 5L X70 steel was evaluated. A lower corrosion resistance was obtained for the API steel in aqueous solution of sodium sulphite, and in solution of sodium sulphite with glutaraldehyde. The hibernation solution was efficient in inhibiting steel corrosion but the highest corrosion inhibition efficiency was obtained with the glutaraldehyde aqueous solution.

Cyclic corrosion tests of organometallic coated fuel tanks

Purpose – The purpose of this study is to evaluate the quality of organometallic coatings of automotive fuel tanks. Galvannealed steels and galvannealed steels coated with organometallic layers were analyzed using accelerated corrosion tests. Design/methodology/approach – The characterization of galvannealed and organometallic coatings was done by mass (layer removal and weighing) and layer thickness (glow discharge optical emission spectroscopy and scanning electron microscopy), chemical composition (energy dispersive spectroscopy) and surface morphology (scanning electron microscopy). The accelerated corrosion tests were performed in accordance with SAE J2334 and GMW 14872 standards. Findings – The samples tested using the GMW 14872 standard were more deteriorated as compared to the samples submitted to the SAE J2334 test because of the higher degree of aggressiveness of the GMW 14872 test. Despite the presence of white rust, the corrosion resistance of organometallic-coated steel samples was higher as ...

Optimal hydrated lime concentration in asphalt binder to improve photo degradation resistance

The effect of short-term oxidation, evaluated by using a Rolling Thin Film Oven Test, and the effect of weathering aging on the oxidation process of hydrated lime modified asphalts were studied. Hydrated lime (HL) has been known as an additive for asphalt mixtures and is now considered as a binder additive that increases asphalt mixture durability. HL was added to the binder in contents of 5, 10, 20, and 30 wt.%. The HL modified binders were aged by using the Rolling Thin Film Oven Test and weathering tests with xenon radiation. A storage stability test by measuring the softening points of HL modified binders was performed. The Thin Layer Chromatography with Flame Ionization Detection (TLC-FID) analysis was used to determine the fractions of resins, aromatics, asphaltenes and saturates of the binders. The aging of HL modified binders was evaluated by using Fourier transform infrared spectroscopy. According to the stability test, a hydrated lime concentration value close to 20 wt.% is the critical point at which there is a risk of segregation of the asphalt binder and hydrated lime during transportation and storage. For the sample weathering aged for 250 hours, a decrease of saturated and aromatic fractions, furthermore an increase in asphaltenes were observed for all samples. Results have shown that additions of 10 wt.% of hydrated lime in asphalt binders resulted in a higher photodegradation resistance among the other asphalt mixtures considering the carbonyl index, stability test and colloidal instability test results.

Corrosion behavior of experimental nickel-bearing carbon steels evaluated using field and electrochemical tests

The aim of this study was to evaluate the corrosion resistance of Ni-bearing carbon steels used in outdoor structures from short-term experimental techniques and compare with the long-term field test data. The carbon steels studied were two experimental steels, produced in a pilot plant, and alloyed with nickel, copper, silicon and molybdenum (Ni-Cu-Si and Ni-Cu-Mo-Si steels), one carbon steel and one commercial Cr-Cu-Si alloyed steel. The atmospheric corrosion resistance of low alloyed carbon steels was evaluated by using field tests for eight years in a marine station, and their electrochemical behavior was studied in laboratory using the electrochemical impedance spectroscopy in aqueous electrolytes containing chlorides. The Ni-Cu-Si and Ni-Cu-Mo-Si steels showed the lowest corrosion rates which decreased as the time increased after eight years of exposure in marine atmosphere. The classification of the low alloyed steels considering the corrosion resistance using electrochemical tests in 10% m/v NaCl solution was similar to rating using field tests in a marine station.

RESISTÊNCIA À CORROSÃO DOS AÇOS AISI 317L E SAF 2304 EM MEIO DE GLICERINA ACIDIFICADA CONTENDO CLORETOS

O biodiesel, obtido a partir de um ester e um alcool na presenca de um catalisador, e produzido pela reacao de transesterificacao e tem como coproduto a glicerina. A producao de biodiesel da Petrobras Biocombustiveis tem, em uma de suas etapas, a lavagem dos produtos para remocao do catalisador basico, metilato de sodio, por meio da reacao de neutralizacao com acido cloridrico. Devido a essa pratica, a glicerina obtida e acidificada e contem residuos de cloretos, o que leva a corrosao localizada dos acos utilizados em determinados pontos do processo de producao. Diante da escassez de trabalhos que abordem a corrosao de acos inoxidaveis em glicerina acidificada contendo cloretos, o presente trabalho avaliou, nesse meio, a resistencia a corrosao do aco inoxidavel austenitico 317L, do aco lean duplex 2304 laminado a quente e do aco lean duplex 2304 laminado a frio. Os acos austeniticos sao compostos pela fase austenita e apresentam boa resistencia a corrosao em ambientes contendo cloretos. Ja os acos lean duplex sao acos de baixa liga com menor teor de molibdenio e alto teor de cromo. Alem disso, possuem duas fases: a austenita e a ferrita. Todas as medidas foram conduzidas a 64oC±1oC, visando simular as condicoes de operacao da empresa. Para o estudo em questao, foram utilizadas as tecnicas de potencial de circuito aberto (OCP), polarizacao potenciodinâmica na direcao anodica, microscopia eletronica de varredura (MEV), espectroscopia de energia dispersiva (EDS) e microscopia de forca atomica (AFM). As analises mostraram que o aco AISI 317L foi menos resistente que o SAF 2304 nas condicoes estudadas. Ainda, a resistencia a corrosao do lean duplex laminado a quente foi similar a do laminado a frio, nas condicoes analisadas.