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It has so far not been possible to fabricate a sol-gel-derived hafnia film with a uniform surface by spin-coating an aqueous hafnia sol on a stainless steel substrate. The reason is that the substrate repulses the sol because of the latter's high surface energy. To improve the wettability and coating properties of the sol on the substrate, the authors degreased the substrate in a strong basic solution with and without the application of a 2-A electric current prior to the spin-coating process. After the surface treatment, it was found by atomic force microscopy and temperature programmed desorption analysis, respectively, that the surface roughness and the amount of water adsorbed on the substrate surface increased. The water and hafnia sol droplet contact angles on the substrate deceased. Thus, the sols were wetted and spread well on the surface-treated substrates during the spin-coating process, resulting in sol-gel-derived hafnia films with uniform and flat surfaces.

The wettability and corrosion resistance of aluminum fins prepainted with a dual coating of cellulose on acrylic have been investigated.Formation of rust on aluminum fins in an indoor cooler was suppressed by painting with more than 0.5g/m2 thickness. Under exposure to corrosive environments, painted fins fitted to copper pipes in an outdoor cooler underwent severe galvanic corrosion. Accordingly, the corrosion resistance with acrylic painting of 1.5g/m2 was only twice as high as that of unpainted fins.The wettability of cellulose painted fins was excellent -5°-10° depending on the surfactant, and whether covering was complete or not. It was also confirmed that cellulose painting with good wettability reduced air pressure loss.