UBC Theses and Dissertations
Composite sol-gel alumina ceramic/siloxane coatings Li, Gesheng
This thesis relates to the novel, relatively low temperature process (160-300°C) for preparation of chemically bonded composite sol-gel (CB-CSG) coatings. This "warm" temperature process (160-300°C) overcomes some drawbacks of the conventional composite sol-gel process, in particular minimization of stresses due to differential thermal expansion coefficient between the coating and the substrate. The biggest contribution o f this research involves use of siloxane bond coat between the CBCSG coating and the mild steel substrate, which relaxes residual stress in the coating, as well as protects the substrate from damage (corrosion) during the chemical bonding process. A method of multi-gun spraying to uniformly distribute the phosphates throughout the coating during the chemical bonding process is also an original contribution of this Thesis. The resulting coatings are free of surface cracks, have medium hardness (6.0GPa), moderate adhesion (42.0MPa) and good scratch resistance (17.0kgf). Electrochemical analysis shows that the multi-layer coating composed of the siloxane bond coat and the CB-CSG "top coat" forms a physical barrier against wet corrosion.
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