Recubrimientos protectores para plantas de concentración solar con almacenamiento térmicosíntesis, deposición y caracterización

Abstract

In the present work, the great potential of the ZrO₂ – 3%mol Y₂O₃ sol-gel coatings in the current concentrated solar power plants is demonstrated, appearing as solution to the outstanding corrosion problems in the thermal storage tanks and pipes in contact with molten salts. For the study, these coatings were firstly deposited by dip-coating into AISI 304 stainless steel and were optimized according to the thickness uniformity using a novel method based on electrical impedance measurements. Once optimized, the as-deposited coatings were tested in Solar Salt at 500 ºC, after which the conditions that provided the higher protective character to the system were selected. These conditions were then applied for coating P91 ferritic-martensitic steel, with a lower corrosion resistance compared to AISI 304 steel and higher industrial interest due to its low cost. The coated system was tested in contact with Solar Salt at 500 ºC with long-term exposure tests and the corrosion process was monitored by electrochemical impedance spectroscopy. Results proved the protective character of the coating, presenting a diffusion layer of about 5 μm consisting of Zr-Fe couples that reduce ionic diffusion and corrosion rate in the substrate (22 μm·año₋₁ vs 300 μm·año₋₁), thereby improving that accepted in the current thermosolar plants (64 μm·año₋₁). Finally, the results obtained by life cycle analysis demonstrated that the substitution of the currently used steels by the proposed P91/ZrO₂-Y₂O₃ system implies a large reduction in the environmental impact of the current concentrated solar power plants.