Jorge Luiz Rosa

Corrosion behavior of niobium, tantalum and their alloys in hot hydrochloric and phosphoric acid solutions

Abstract The corrosion resistance of niobium, tantalum and Nb–20, 40, 60 and 80 wt% Ta alloys in 5, 10, 15 and 20 wt% HCl and 20, 40, 60 and 80 wt% H 3 PO 4 solutions at boiling point, 150°C and 200°C is evaluated using the mass-loss technique. The corrosion rates of all materials increase with acid concentration and temperature. At boiling point the corrosion rates diminish with time but for long exposure time, they tend to stabilize due to the formation of superficial oxides. The corrosion resistance increases with tantalum content. The iso-corrosion curves of niobium, tantalum and Nb–Ta alloys in 5–20 wt% HCl and 20–80 wt% H 3 PO 4 up to 200°C are drawn from interpolation of the measured corrosion rates.

Corrosion behavior of HA-316L SS biocomposites in aqueous solutions

316L stainless steel and Hydroxyapatite (5, 20 and 50 wt. (%) HA)-316L stainless steel composites were fabricated by mechanical alloying technique, pressing and sintering from 316L and HA powders. The corrosion behavior of both sintered 316L and HA-316L composites was evaluated by electrochemical techniques in simulated body fluid (Ringers solution) and in 0.1M HCl solution which simulates occluded cell corrosion conditions. The results indicate that 316L stainless steel and HA-316L composites are passive in Ringers solution and active in HCl solution. All materials are highly corrosion resistant in Ringers solution with corrosion current density in the order of 10-6 A cm-2 or less. Both 316L stainless steel and 5% HA-316L composite present good corrosion resistance in HCl with corrosion current density in the order of 10-5 A cm-2. The corrosion resistance decreases with increasing HA content in both solutions.

Formation of titania nanotube arrays by anodisation: DOE approach

Abstract Self-organised TiO2 nanotubes were obtained on titanium by anodisation in Glycerol-H2O DI (50-50 v/v) electrolyte containing NH4F. A design of experiments (DOE) based on a 2k factorial design with four replicates at the center point was used in order to study the influence of voltage, anodisation time and fluoride concentration and their possible interactions on the obtainment of titania nanotubes. The statistical analysis showed that voltage is the only significant factor. The best condition according to the response surface analysis is the centre point (1%NH4F, 20 V, 2 h). Electrochemical tests performed in Ringer’s solution showed that TiO2 nanotubes coated titanium is less corrosion resistant than as received titanium.

Análise morfológica da corrosão por pites em aço inoxidável austenítico AISI 310S submetido à exposição em névoa salina

This paper aims to study evolution of increase, distribution and classification of pits in 310S austenitic stainless steels obtained in the state as-received and heat-treated under different exposure times in saline. This work applicability has been based on a technique development for morphologic characterization of localized corrosion associated with description aspects of shapes, size and population-specific parameters. Methodology has been consisted in the following steps: specimens preparation, corrosion tests via salt spray in different conditions, microstructural analysis, pits profiles analysis and images analysis, digital processing and image analysis in order to characterize the pits distribution, morphology and size. Results obtained in digital processing and profiles image analysis have been subjected to statistical analysis using median as parameter in the alloy as received and treated.The alloy as received displays the following morphology: hemispheric pits> transition region A> transition region B> irregular> conic. The pits amount in the treated alloy at each exposure time is: transition region B> hemispherical> transition region A> conic> irregular.

Production and Characterization of Copper-Niobium Composite Electrocoatings

Copper-niobium composite electrocoatings were obtained by co-electrodeposition in acidic copper sulfate bath containing suspended niobium particles. The amount of incorporated particles was evaluated using a Central Composite Design (CCD) with three factors of control (cathodic current density, stirring rate and particle concentration in the bath) at three levels each. A great influence of particle concentration was observed. The stirring rate also had influence but to a lower extent and the cathodic current density was the least significant factor. The combination, both cathodic current density and particle concentration at the highest levels and stirring rate at the lowest level, led to the highest amount of incorporated particles. The behavior was not linear between the high and low levels for all factors. The roughness of the composites was higher than the pure copper coatings and increased with increasing current density. The microhardness of the composite layers was higher than that of pure copper deposits obtained under the same conditions due to copper matrix grain refinement and increased with the increase of both current density and incorporated particle volume fraction.