The effect of heat treatment on the corrosion resistance of electroless Ni-P coatings containing pure and Ce-doped hematites

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 %25 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%25 (%25W/%25W) 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 icorr smaller than their corresponding as-coated samples. Also, the most protective alloy after annealing at 400°C for 1 h is Ni-P-pure pseudocubic hematite alloy (its icorr was 2.7*10 -7). © 2009 by NACE International.

VIVO