Single-step synthesis of SrMoO₄ particles from SrSO₄ and their anti-corrosive activity

By Diaz-Algara, J.; Rendón-Angeles, J.C.; Matamoros-Veloza, Z.; Yanagisawa, K.; Rodriguez-Galicia, J.L. & Rivera-Cobo, J.M.
Published in Journal of Alloys and Compounds NULL 2014

Abstract

The transformation of three different sizes (<38–165 μm) of SrSO₄ mineral powder into SrMoO₄ scheelite-type tetragonal particles was investigated via conventional hydrothermal treatments under both static and stirring conditions (20 rpm) at 100–250 °C and varying reaction intervals (0.08–48 h) in alkaline solutions saturated with MoO₄²⁻. A partial SrSO₄ transformation was found to proceed in mild to concentrated alkaline NaOH solutions (0.1–2.5 M), the complete transformation of SrSO₄ to SrMoO₄ was observed to proceed at temperatures lower than 200 °C over 48 h in a static 5 M NaOH solution, but this process was accelerated when the autoclave was stirred at 20 rpm during the treatment, which led to the production of uncontaminated SrMoO₄ particles at 200 °C within 6 h. The resultant SrMoO₄ particles had octahedral bipyramidal morphology and particle sizes between 1 and 5 μm; these particles exhibited a noticeable agglomeration at the intermediate and final stages of the reaction due to the formation of agglomerates with an average size of 60 μm. However, stirring of the mixture in the autoclave markedly reduced the growth of the bulky agglomerations of SrMoO₄ particles. A coupled process involving the bulk dissolution of the SrSO₄ powder and, subsequently, the massive precipitation of SrMoO₄ in an alkaline solution (5 M NaOH) saturated with MoO₄²⁻ ions was utilised to crystallise the SrMoO₄ particles. Kinetic studies demonstrated that the activation energy required for the formation of the octahedral shaped SrMoO₄ particles was 25.8 kJ mol⁻¹ in the system without agitation; in contrast, the activation energy decreased to 12.8 kJ mol⁻¹ when the transformation was stirred. In a subsequent investigation, the ionic permeability resistance of a commercial paint applied to a AISI 1020 steel substrate was improved by adding a 2.0 wt.% of the transformed SrMoO₄ particles to the paint.

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