Chemical and Physical Effects of Fluoride on the Corrosion of Austenitic Stainless Steel in Polluted Phosphoric Acid

Abstract

The effect of fluoride ions was investigated on the austenitic stainless steel in a typical solution of phosphoric acid that is used in industrial process, for clear understanding the damage that caused by corrosion to special alloying material Uranus B6 at temperature of 80 °C. For that the electrochemical and spectroscopy methods were used like potentiodynamic and electrochemical impedance spectroscopy, X-ray diffraction and UV–visible–IR reflection, Scanning electron microscopy and energy-dispersive spectroscopy analysis (SEM–EDX). The electrochemical methods show the drastic effect of fluoride on the passivation parameters, especially icrit, ipass and Epit caused by decreasing the alloy elements in the surface alloy, specially the molybdenum. Moreover, the spectroscopy results reflect that fluoride has two axes of interaction with the surface alloy; chemical interaction that was appeared by the dissolution mechanism, which it increases the dissolution of the base alloy atom and the alloying elements and this result was improved by the UV–visible–IR and EDX analysis. And the physical effect was demonstrated by X-ray diffraction, which is showing a deformation of the crystalline structure of surface alloy; and different pit types were detected by SEM. And the suggestion of the effect of fluoride on the nickel percent in the passive film and also on the molybdenum and copper has been proposed as a mechanism to explain these results.