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Anticorrosive polyurethane coating compositions were compounded using novel zinc-free nanosized phosphates: aluminum ammonium phosphates (AAP) or calcium aluminum ammonium phosphates (CAAP). For comparison, a nanosized strontium phosphate (SP), AAP/SP mixtures, and a microsized zinc phosphate (ZP) were tested. Paints containing ammonium-modified phosphates exhibited similar or a slightly higher viscosity than systems with SP or ZP. Nevertheless, coatings with the AAP or CAAP reached significantly better gloss and adhesion to a steel substrate as well as a slightly higher hardness. Results of a salt spray test showed that anticorrosive properties of the coatings containing AAP/SP mixtures were markedly better in relation to the systems containing solely AAP, CAAP, SP, or ZP. Electrochemical tests revealed the best barrier/anticorrosive features for AAP (electrochemical impedance spectroscopy and potentiodynamic polarization) or SP and CAAP (a novel electrochemical noise technique).

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