SURFACE-TREATMENT OF RUSTED STEEL WITH PHOSPHORIC-ACID SOLUTIONS - A STUDY USING PHYSICOCHEMICAL METHODS

Although many papers have been published about the use of phosphoric a cid as a pretreatment for rusted steel surfaces, the main mechanisms i nvolved in its action are not yet well understood. In the present pape r the authors advance a further contribution towards a knowledge of th ose mechanisms through the results of experimental work in which they have used a variety of physicochemical methods including: energy dispe rsive spectroscopy associated with scanning electron microscopy (EDS/S EM), X-ray diffraction (XDR), infrared spectroscopy (IR/FTIR) and Moss bauer spectroscopy. The results obtained show that the nature of the ' conversion layers' formed depends strongly on the concentration of the phosphoric acid solutions used and on the prior exposure time of the steel surfaces. Mechanisms are proposed for their formation.