The Effect of Post‐Cure Annealing on the Protective Properties of Polyimides on Chromium Substrates

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Abstract
The effect of post‐cure annealing on the protective properties of thin (2.6–2.8 μm) polyimide films on chromium metallic substrates was investigated in aerated neutral 0.05, 0.5, and 5 M aqueous NaCl solutions at ambient temperature (≈20°C). The study was carried out using the technique of electrochemical impedance spectroscopy to monitor film degradation as a function of immersion time in the test solutions. Results obtained indicate that when exposed to aqueous NaCl solutions for extended periods, a majority of the nonannealed coated substrates failed; however, the performance of the annealed samples was significantly better. At face value, these results suggested improved protective properties of the polyimide due to annealing. However, a more in‐depth analysis of the data revealed that post‐cure annealing leads to the development of a thicker oxide on the chromium substrate. The change in the oxide occurring during the post‐cure annealing treatment contributes to the improved corrosion resistance of the polyimide/Cr system.

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