Iron benzoate as environmentally-friendly pigment for paint technology: corrosion and fouling control

G. BLUSTEIN, M. GARCÍA, M. PÉREZ, R. ROMAGNOLI, B. DEL AMO, M. E. STUPAK

Rio de Janeiro, Brasil

Congreso; 13th INTERNATIONAL CONGRESS ON MARINE CORROSION AND FOULING; 2006

Traditionally, paints designed to protect metallic structures from corrosion and fouling have been formulated with high toxic pigments. For instance, lead or hexavalent chromium are used for anticorrosive paints and organotin compounds for antifouling paints. Although these active pigments are highly effective inhibitors, their use has been declining because they contaminate the environment and, at the same time, represent a risk to human health. International regulations concerning the protection of both the environment and industrial workers have prompted paint manufacturers and end users to desire replacements for these pigments. The anticorrosive properties of soluble benzoate compounds were known from many years ago and were studied employing sodium benzoate and benzoic acid in different media, included those containing chloride. The employment of soluble benzoate compounds in paint technology is limited by its high lixiviation which takes to the loss of the protective properties of the paint. However, it is possible to prepare insoluble iron benzoate to incorporate within paint film.  One of the goals of this investigation was to study the inhibitive properties of iron benzoate-based paints in simulated marine corrosion condition (3% NaCl solution). The pigment anticorrosive properties were investigated by way of electrochemical techniques in pigment suspensions. In a second stage, anticorrosive paints containing iron benzoate were formulated and their performance was evaluated by accelerated (salt fog chamber) and electrochemical (corrosion potential and ionic resistance) tests. On the other hand, the effect of iron benzoate in the laboratory and in the sea as probable antifouling agent was studied. Iron benzoate pigment in seawater is hydrolyzed and consequently it produces a pH decrease. In this sense, the effects of the pH on nauplii and the anion benzoate dissolved in seawater and leached from an antifouling paint were evaluated. Although anion benzoate has an intense narcotic effect on Balanus amphitrite nauplii, the results clearly demonstrated that the combined action of this compound and a pH decrease produce a pronounced antifouling activity, i.e. the synergic effect is greater than separate effects. Field trials confirmed laboratory assays; paints containing iron benzoate were effective in inhibiting organism settlement. Results show that iron benzoate pigment has successful anticorrosive and antifouling properties; the high levels of inhibitory activities suggest a potential for novel active ingredient in paint formulations.