The influence of the anion type on the anticorrosive behaviour of inorganic phosphates

M. DEYÁ; G. BLUSTEIN; R. ROMAGNOLI; B. DEL AMO

Santiago, Chile

Congreso; LATINCORR2003. 5to Congreso de Corrosión de la NACE Región Latinoamerica y 8vo Congreso Iberoamericano de Corrosión y Protección; 2003

The objective of this work was to study the efficiency of the anticorrosive pigments obtained by substituing the phosphate anion in zinc phosphate by other anions suc as tripolyphosphate and pyrophosphate. The procedure to prepare the pigments is outline and their anticorrosive properties werew evaluated followint the electrochemical behaviour of a steel electrode in pigments suspension. In a second stage, solvent borne paints with 30% by volume (v/v) of the pigment with respect of the total pigment content and a PVC/CPVC (pigment volume concentration/critical pigment volume concentration) ratio was 0.8 were formulated. Two resins were chosen as film forming material: an alkyd and an epoxy one. The performance of the resulting anticorrosive paints was assessed by accelerated (salt spray and humidity chamvers) and electrochemical tests (corrosion potential, ionic resistance and polarisation resistance). It was demonstrated that the substitution of the phosphate anion by tripolyphosphate or pyrophosphate anions may give rise to effective anticorrosive pigments for paints. The essays performed with pigments suspensions suggested that zinc pyrophosphate has the best anticorrosive properties. The anticorrosive behaviour of the pigments in paints were found to depend on the resin employed to formulate the coatings. Good correlation was obtained between accelerated and electrochemical tests.