Cerium acetate-modified aminopropylsilane triol: A precursor of corrosion-preventing coating for aluminum-finned condensers

A poly-acetamide-acetoxyl methyl-propylsiloxane (PAAMPS) polymer containing a cerium (Ce) oxide derivative was synthesized through three spontaneous reactions: condensation, amidation, and acetoxylation. The PAAMPS synthesizing took place between the Ce acetate dopant and aminopropylsilane triol (APST) as the film-forming precursor aqueous solution at 150 degrees C. PAAMPS was evaluated for use as a corrosion-preventing coating for air-cooled condensers consisting of two metal components: aluminum fins and carbon steel tube. The key factors to ensuring the maximum performance of the PAAMPS/Ce oxide coating system in mitigating the corrosion of both aluminum and steel included (1) minimizing the content of non-reacted water-soluble APST and Ce acetate remaining in the coating, (2) lowering the susceptibility of the coating's surface to moisture, (3) precipitating a passive Ce3+ oxide (Ce2O3) film insensitive to Cl dissolution over the metal's surfaces, and (4) possessing excellent adhesion to the metal's surfaces. The combination of these factors considerably decreased the rate of the cathodic oxygen reduction reaction at the corrosion site of the metals. In fact, the corrosion rate, measured in milli-inches per year (mpy), of bare steel was reduced more than one order of magnitude by applying this coating. Correspondingly, the coating extended the useful lifetime of steel exposed in a salt-fog chamber at 35 degrees C from only similar to 10 hr to similar to 768 hr. Furthermore, this coating system far better protected an aluminum substrate from the corrosion than it did one of steel. Even a very thin nanoscale coating film deposited on the aluminum's surfaces reduced the corrosion rate, (mpy), by nearly two orders of magnitude over that of the bare aluminum. Also, the salt-spray resistance of aluminum panels covered by this nanoscale film was strikingly,extended to more than 1440 hr, compared with similar to 40 hr for bare aluminum.