Analysis of iron FC 250 microstructure under the effect of phosphoric acid corrosion

Abstract

The study of the prevention of metals corrosion by phosphoric acid has been increasing, due to its vast use in industrial processes such as the production of fertilizers and food products. About 5% of the profits of industrialized nations are spent to prevent corrosion. Several studies have been carried out to determine the corrosive behavior of cast iron in acidic and basic medium, but the resistance to corrosion in phosphoric acid has not yet been studied. The present work analyses the effects of phosphoric acid (H3PO4) on the corrosion of FC 250 cast iron, in its structure and properties, using mass loss analysis and scanning electron microscopy (SEM). The studies were performed after samples immersion in acid solutions with concentrations of 1, 2 and 3% of content for 86,400 and 424,800 s at room temperature and in a solution of 3% at 323,15 K and 373,15 K, for 21,600 and 43,200 s. The main losses were found in the percentage of 3%, at higher temperatures and lower immersion time. H3PO4 promotes the oxidation state in gray cast irons, which can compromise their structure and properties. The higher percentage of the acid causes greater mass losses, the temperature reacts in an analogous way and, in longer exposure times, the loss is sustained.