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UBC Theses and Dissertations

Process engineering and characterization of composite electrocoatings Chen, Michael Nai-Chia

Abstract

Electrocoating (E-coat) has conventionally been used primarily for corrosion protection purposes as a barrier coating beneath the primer of the automobile body. For E-coat to be used as a long term solution for outdoor equipment barrier protection, mechanical properties such as abrasion/wear, scratch and hardness must be improved. In this work we assess the possibility of such improvement of E-coatings by combining them with ceramic particles. The effects of ceramic filler particle size and concentration, along with deposition parameters and processing procedures on the properties of epoxy cathodic barrier coating have been investigated. The deposition voltage was varied from 100 to 300 volts with various filler (α-AI₂O₃) concentrations of 0 - 30 vol% and particle size of 0.3 - 5 μm. The effect of the filler was also tested in an electrochemical cell in order to foresee corrosion resistance variations due to different concentrations of filler in the coating. Other possible applications were also investigated to utilize the composite E-coat processing to create a functional coating with transducer like effects. The ceramic filler content was observed to improve mechanical properties such as hardness, scratch resistance and wear. Mechanical properties showed a decline at higher concentration of filler (> 10 vol%) due to lower resin content, which increased filler-to-filler interactions. The thickness of the deposited films increased with increased filler concentration and deposition voltage, with filler concentration having a greater effect on the deposited film thickness. Large filler particle size (3-5 μm) was observed to deteriorate the film's mechanical properties when compared to a smaller filler particle (0.3-0.5 μm). The filler-film interface showed homogeneous bonding and encapsulation of the filler particles, resulting in excellent adhesion of 68-82 MPa along with improved corrosion resistance with increased filler content in the film up to 10 vol% filler. A functional composite film was also deposited by adding piezoelectric ceramic powders within E-coatings. A hysteresis loop was observed during testing showing poling during deposition. Resonance and anti-resonance frequencies were found to be 3.90x10⁷ Hz and 3.80x10⁷ Hz respectively. This demonstrates that the composite E-coat process is a viable method of manufacturing low cost and large area coverage thin film sensors and actuators.

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