POLYMETALLOSILOXANE COATINGS DERIVED FROM 2-STEP, ACID-BASE CATALYZEDSOL PRECURSORS FOR CORROSION PROTECTION OF ALUMINUM SUBSTRATES

Fractal polymetallosiloxane (PMS) cluster films were fabricated on alu minum (Al) substrates by the hydrolysis-polycondensation-pyrolysis rou te of two-step, acid-base-catalyzed sol precursors consisting of N-[3- (triethoxysilyl)propyl]-4,5-dihydroimidazole, metal alkoxides, water, and methyl alcohol. Thin PMS coating films prepared by dipping Al into sol solution provided significant protection for Al against NaCl-indu ced corrosion. The important factors governing a good protective perfo rmance of PMS were as follows: (1) an increase in metal-O-Si linkages with increased treatment temperature; (2) a low degree of water wettab ility and spreadability; and (3) a specific microstructure geometry, i n which the cluster units consisting of symmetrically grown fractal po lymer branches were linked together. The third factor contributed to a decrease in stress generated by the shrinkage of films, thereby elimi nating crazing and peeling of the film.