Caractéristiques du revêtement obtenu par prépassivation de l'acier galvanisé^*

Coating characteristics obtained by prepassivation of galvanized steel^(*)

¹ Compagnie Royale Asturienne des Mines
² Groupe d'Etude de la Corrosion de Lille

Abstract

In the hot water production and distribution installations, galvanized steel may be protected against localized corrosion by a hydrated zinc pyrophosphate coating, Zn₂P₂O₇, 3H₂O. This insoluble compound is formed out of galvanizing zinc,, partly oxidized by hydrogen ions, and pyrophosphate ions P₂O₇2— freed by hydrolysis of hexametaphosphate PO₃—. Such a surface treatment favours the subsequent obtaining of a faultless natural passivating layer and thus decreases considerably the susceptibility to pitting corrosion in presence of cupric ions.