The application and characterization of protective polymer layers on electrochemically passivated zirconium and titanium.

摘要

Previous work from this laboratory has shown that electrochemical passivation of zirconium and titanium increases the thickness of their passive oxide layers, offering superior protection towards corrosion while causing the metals to exhibit a wide range of bright and attractive reproducible colours depending on the thickness of the oxide layers. This technique has opened many new windows for application of these metals from bicycle and eyeglass frames to colour-coded engine parts, however superior protection from abrasion and weathering is required for their successful performance. Presented are the application and characterization of two types of commercial polymer clearcoat layers to electrochemically passivated zirconium and titanium surfaces; an acrylic automobile clearcoat and an epoxy marine clearcoat. It was found that on average the thicknesses of the automobile and marine clearcoats on the passivated metal substrates were approximately 3.5 mum and 8.0 mum respectively. The colours exhibited by the passive layers were found to change slightly upon application of the clearcoats, becoming slightly whiter. The clearcoat layers were found to be free of cracks and blisters, and generally decrease the surface roughnesses of the passivated zirconium and titanium surfaces. The wetting properties of the passivated zirconium and titanium surfaces were found to decrease upon application of both clearcoats, with the water contact angle increasing to approximately 91° when coated in automobile clearcoat and approximately 83° when coated in marine clearcoat. Also, the wetting properties of uncoated zirconium were found to decrease upon passivation, with the water contact angle increasing from approximately 27° for the etched surface to 62.5° on average when passivated at 30 V and to 66.3° on average when passivated at 60 V. The automobile clearcoat was found to adhere flawlessly to the passivated zirconium and titanium substrates, though the marine clearcoat did not perform as well, likely due to its higher viscosity upon application and a surfactant content poorly-suited towards the zirconium and titanium surfaces studied here. The commercial clearcoats applied in this thesis have shown the potential to increase protection of the passive layers on zirconium and titanium from physical and chemical damage while maintaining their attractive visual properties.