Effect of Hematites on Corrosion Resistance at High Temperatures of Ni-P-Hematites “Electroless” Coatings

    AISI-316 L stainless steal was coated by “electroless” technique with nickel (Ni)-phosphorus (P)-hematites alloy from a bath containing sodium hypophosphite and succinic acid as complexing agent. The anticorrosive effect of presence of hematites in the Ni-P matrix (these oxides were synthesized pure and in presence of 30 % cerium (Ce)) were analyzed. Corrosion parameters such as corrosion current density and corrosion potential were obtained for the as-coated and annealed Ni-P and Ni-P-pure and doped-hematites coatings from Tafel polarization curves in aerated 3,5% (%W/%W) NaCl solution. The annealing was made at 400°C in convection oven. The images of transmission electron microscopy (TEM) of hematites and the images of scanning electron microscopy (SEM) of several coatings were also studied. It was demonstrated by Tafel Curves that annealed samples have i_corr smaller than their corresponding as-coated samples. Also, that Ni-P-pure pseudocubic hematite is the coating most protective after annealing at 400ºC for 1 h.