Evaluación de la aleación de aluminio AA 5052 (UNS A95052) para la fabricación de un desalinizador de tipo multiplaca

Abstract

Tesis para optar al título de Magister en Ciencia y Tecnología de Materiales

Nuclear desalination is a suitable alternative to face global fresh water shortage. Among the challenges associated to the fabrication of a nuclear desalinator, the materials selection must be performed adequately so that the plant will withstand the severe operating conditions. A wrought and non-heat treatable aluminium alloy, AA5052 (UNS A95052), with a content of ~2,5% of magnesium in solid solution has been chosen as a candidate for the plates of a multi-plate desalinator fully designed in CNEA according to the principles of multi-effect desalination. AA5052 possess several advantages for this application, including good thermal conductivity, low cost when compared to copper or titanium alloys, the non-toxicity of the alloys or its corrosion products, good wettability in seawater at high temperature and excellent corrosion resistance in chloride solutions at neutral pH. Nonetheless, the design includes an elastomeric gasket between the plates, which can promote the initiation of crevice corrosion on the metal surface when chlorides are present in bulk water. In order to guaranty the integrity of the plates during service, it is required to characterize localized corrosion under relevant temperature and chloride concentration ranges. Accordingly, a pitting and crevice corrosion study was carried out at 30°C, 60°C and 85°C in solutions with contents of 65.000 and 45.000 ppm of NaCl, in absence of oxygen and at neutral pH. Electrochemical parameters like corrosion, initiation and repassivation potentials were obtained by different sets of electrochemical tests, including evaluation of the potential at open circuit condition, cyclic potentiodynamic polarizations (CPP or PD) and multi-stage polarizations experiments like potentiodynamic-galvanostatic (or potentiostatic)-potentiodynamic (PD-GS-PD and PD-PS-PD). Localized corrosion cavities depth was studied by varying the anodic charge that was circulated through the sample and also, a possible contamination due to oxygen and heavy metal ions like Cu2+ in samples with an O-ring crevice former was simulated. Additionally, the localized acidification model was applied in order to estimate the solution composition inside the cavities. The extent of the localized corrosion damage and its morphology were determined by surface characterization techniques such as optical and scanning electron microscopy and profilometry. Based on the reported results, it can be inferred that the elastomeric gaskets will not represent an additional risk for the desalinator plate’s integrity.