Permeation of saline solution in Al2O3–13 wt.% TiO2 coatings elaborated by atmospheric plasma spraying

The evolution of brine permeation in alumina–titania coatings elaborated by atmospheric plasma spray was studied using Electrochemical Impedance Spectroscopy (EIS). Two Al2O3–13 wt.% TiO2 micrometer-sized (5–25 and 15–40 μm) powders were sprayed onto aluminum substrates by a PTF4 torch 7 mm in anode-nozzle internal diameter, using a mixture of Ar–H2 (45–15 slpm) as plasma forming gas and applying a current intensity of 500 A. The electrochemical results obtained were related to structural defects of coatings (pores and cracks) determined by image analyses of their polished cross section. During the first hours of immersion the chlorine solution permeates into the coatings. However, after about 340 h the brine was stopped. The resistance to polarization (Rp) valuesʹ of coated samples are higher than those exhibited by the uncoated substrate, which indicates that these coatings could be potentially used to modify and protect the aluminum surface exposed to marine environment or other saline solutions. The protective capacity of coating obtained from finer feedstock powder is higher than that of coating sprayed from coarse powders, thanks to its lower porosity and crack content.