Characterization of polyacrylic acid modified zinc phosphate crystal conversion coatings

Abstract

SYNOPSISRaman spectroscopy and atomic force microscopy have been used to investigate the composition and surface structure of polyacrylic acid modified zinc phosphate crystal conversion coatings on steel. Zinc phosphate coatings are used extensively to provide corrosion protection and to improve adherence of topcoatings to steel. Within the last few years it has been demonstrated that addition of high molecular weight polyacrylic acid (PAA) to the phosphating bath can significantly improve both resistance to corrosion and topcoat adherence. It has been reported that the addition of PAA reduces the size of crystallites, which leads to greater film ductility, and therefore to fewer sites for corrosive attack, and that organic molecular segments from the PAA are incorporated into the surface structure and provide additional adhesive bonding with polymeric topcoats. In this work Raman spectra show the compositions of both unmodified and PAA modified films to be zinc phosphate dihydrate, Zn3 ( PO,), -2H20. Atomic force microscopy ( AFM ) was used to measure the morphologies of single crystallite surfaces. Morphologies of the unmodified and modified films obtained by AFM are in general quite similar, but subtle differences are apparent.

Intercalation in Zinc-Layered Hydroxide: Zinc Hydroxyheptanoate Used as Protective Material on Zinc

“…Nowadays, the imperative respect of environmental rules concerning wastewater rejects implies the development of effective, low-cost, and environmentally friendly anticorrosion treatment as alternatives to the current formulations based on chromate or mineral oil. Several anionic compounds, more or less toxic, have been investigated to fulfill this requirement: phosphates, − phosphonates, benzoates, and amine derivatives. − …”