engleski

The impact of chain length and terminal functional group on properties of self-assembled monolayers of phosphonic acids on bronze

Corrosion of metallic structures causes significant material loss and environment pollution. For that reason new ecologically acceptable corrosion protection techniques needs to be developed. The great potential for application in this field have self-assembled monolayers (SAMs) of long-chain organic acids that are formed by adsorption of acid on the surface of oxide-covered metal, resulting in acid-base reaction between metal oxide and acid. This reaction is followed by the self- organization of alkyl chains which creates a very thin and compact protective film on the metal surface thus preventing the penetration of water molecules and aggressive ions towards the metal surface. The aim of this work is to examine the possibility of bronze protection in simulated acid rain by SAMs of 6-phosphonohexanoic acid (PHA), 16-phosphonohexadecanoic acid (COOH-PA) and 12-aminododecylphosphonic acid (12-NH2PA). Furthermore, the impact of chain length and terminal functional group on arrangement and stability of obtained films are examined. In order to obtain a compact well-ordered monolayer which will provide long term protection, SAM preparation procedures consist of bronze pretreatment and phosphonic acid adsorption by dip-coating followed with drying period. Protective properties of phosphonic acid self-assembled layer are examined by linear polarization measurements and electrochemical impedance spectroscopy. These measurements are carried out in simulated acid rain (0.2 g/L NaNO3 + 0.2 g/L Na2SO4 + 0.2 g/L NaHCO3 at pH 5) which simulates the rain in urban atmosphere. The surface of modified samples is also examined by scanning electron microscopy and Fourier transform infrared spectroscopy in order to verify adsorption of phosphonic acid on metal and formation of an ordered organic layer.

corrosion protection, self-assembled monolayers, electrochemical impedance spectroscopy, FTIR

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