THE EFFECT OF POSTCURE ANNEALING ON THE PROTECTIVE PROPERTIES OF POLYIMIDES ON CHROMIUM SUBSTRATES

The effect of post-cure annealing on the protective properties of thin (2.6-2.8 mu m) polyimide films on chromium metallic substrates was in vestigated in aerated neutral 0.05, 0.5, and 5 M aqueous NaCl solution s at ambient temperature (approximate to 20 degrees C). The study was carried out using the technique of electrochemical impedance spectrosc opy to monitor film degradation as a function of immersion time in the test solutions. Results obtained indicate that when exposed to aqueou s NaCl solutions for extended periods, a majority of the nonannealed c oated substrates failed; however, the performance of the annealed samp les was significantly better. At face value, these results suggested i mproved protective properties of the polyimide due to annealing. Howev er, a more in-depth analysis of the data revealed that post-cure annea ling leads to the development of a thicker oxide on the chromium subst rate. The change in the oxide occurring during the post-cure annealing treatment contributes to the improved corrosion resistance of the pol yimide/Cr system.