Revista de Ciências e Engenharia de Materiais

Slow diffusion at room temperature over long periods of time (centuries and millennia) rewrites the different heat treatments suffered by a steel. With the precipitation of iron carbides, it redraws all those places in the steel where there have been some kind of marks of the thermal treatments suffered: twins, grain limits, etc. These iron carbides draw perfectly these places. In this work this fact has been visualized in one of the iron nails that appeared in a tomb from the 1st century A.D. in the Northern Necropolis of Cordoba in the Roman Baetica. It is one of the many steel artifacts that allow us to see these metallurgical phenomena that we could not easily reproduce today. The metallographic techniques used have been the Conventional Optical Microscopy and the Scanning Electron Microscope.

Although, corrosion of pipelines conveying petroleum crude-oil and gas is an electrochemical process, it however, involves several chemical reactions occurring in the bulk solution, prior to the surface of the metal. The occurrence of these chemical reactions can alter significantly the rate of the electrochemical processes at the metal’s surface; especially when as a result of high local concentrations of reacting species, the solubility limit of the product formed (iron carbonate or/and iron sulphide) is exceeded and the precipitation of inhibiting surface films occurs on the metal’s surface. Thus, this paper investigated the effects of the chemical reactions on the rate of corrosion of steel pipes conveying petroleum crude-oil and gas with the presence of hydrogen sulphide (H2S) and carbon dioxide (CO2). The results affirmed what were reported in the literature that corrosion of steel pipes is as a result of the formation of acidic solution due to the transportation of hydrogen sulphide (H2S), carbon dioxide (CO2) and water along with the crude oil and gas. In addition, it also ascertained that corrosion severity depends on the pH of the solution, and the higher the pH value, the less severe the corrosion. In other words, corrosion occurs at a faster rate in acidic pH, compared to neutral and alkaline pH. It further established that H2S corrosion is more severe than that of CO2, and also, pipeline corrosion could be catastrophic leading to failures of pipelines and environmental pollution, etc. due to open cracks formed.

This research aims to study the feasibility of nickel recovery from spent electroplating solution via hydrometallurgy and electrochemical treatment. The spent nickel-plating solution obtained as an industrial waste was found to contain nickel of 89.4 g/l, which was still in high quantity sufficient for prospective recovery. In this research, precipitation of nickel from the spent electro plating solution was first carried out to separate other unwanted impurities. The remained nickel precipitate was then leached by using 1 M or 2 M H2SO4 for 24 h. at a solid/liquid ratio of 100 g/l. The leached solution was then adjusted to obtain pH 2 prior to electrowinning. It was found that the maximum weight of nickel cathode is 5.07 g or at 90.7% recovery of 97.46% purity can be achieved in a condition using 1 M H2SO4 and electrical potential 3.7 V.

Metal containing waste sludge from electronic industrial has been rapidly accumulating due to the surge of global demands for electronic components. This study looks into the feasibility of recycling copper from galvanic waste through hydrometallurgy combining with electrometallurgy process. The parameters of copper selective leaching including types of leaching solution, acid concentrations, and liquid-solid ratios were systematically studied. The optimum selective leaching conditions were 1 M and 2 M sulfuric acid with 24 h leaching duration, 100/1000 g/cc solid-liquid ratio offering copper leach recovery of 42,540 and 45,850 mg/l, respectively. Copper purification was successfully obtained from electrolytic refining process. The effects of electrolysis voltage to the amount and purity of copper cathode were studied. It was found that the optimum parameters for copper purification were using 2 M sulfuric acid with electrolytic voltage of 2.2 V. Under these conditions, the recovery of pure copper was raised up to 92%.

Inhibitory effect of water hyacinth extract on mild steel corrosion in acidified seawater was investigated by weight loss and gasometric techniques. Values of inhibition efficiency calculated from weight loss and gasometric techniques are in good agreement Inhibition efficiency was found to increase with increasing concentration of the extract. The effect of temperature, immersion time, and acid concentration on the corrosion behaviour of mild steel in the presence of extract were also studied. Temperature studies revealed an increase in activation energies and decrease in inhibition efficiency with rise in temperature. The adsorption of the inhibitor molecules on metal surface was in accordance with Langmuir adsorption isotherm. Kinetic treatment of the data obtained with or without plant extract indicates first-order electrochemical reactions. FT-IR analysis was carried out on the protective film formed on the surface of the metal to establish the formation of metal-ligand bond. The results obtained showed that water hyacinth extract could serve as an effective inhibitor of the corrosion of mild steel in acidified water.

Bamboo and Sisal fibers are among the most common used reinforcement materials in the fabrication of new natural fiber based composite materials. In this work, an attempt is made to fabricate, characterize and analyze the mechanical property of hybrid sisal/bamboo fibers reinforced epoxy matrix composite. The fibers were manually extracted from sisal and bamboo plants. After extraction, bamboo and sisal fibers were chemically treated with 8% and 5% sodium hydroxide respectively, to remove the extra lignin and hemicelluloses so that the bond and interfacial, shear strength of the fibres can be improved. The experiment was conducted based on Taguchi experimental method by considering weight fraction of hybrid sisal/bamboo fibers, fibers orientation and curing temperature as basic parameters which affect product strength. Hand lay-up and compression techniques were employed in the fabrication of the experimental composite. The tensile and flexural strength tests of the experimental hybrid sisal/bamboo fiber reinforced epoxy matrix composites were determined by taking samples as per the ASTM standard. The result revealed that, the bamboo–sisal fiber reinforced epoxy composites fabricated with 25/25% weight fraction of sisal to bamboo fibers, fibers stacked unidirectional and cured at 25°C demonstrate a high tensile and bending strength.