A conversion electron Mössbauer investigation of the phosphating of iron surfaces

Abstract

Conversion electron Mössbauer spectroscopy has been used to establish the formation of iron(II) phosphate octahydrate on the surface of metallic iron following treatment by various phosphating processes. Heating in air dehydrates the surface phase, whereas bulk samples of the powdered iron(II) phosphate octahydrate are readily converted to an iron(III) species even under anaerobic conditions. Phosphating processes which produce heavier surface coatings lead to the inclusion of hydrolysed iron(III) species in the iron(II) phosphate surface phase. Exposure of the surface phases to water vapour gives partial oxidation of the iron(II) phosphate to an iron(III) hydrate.