Citric acid augmented flashlamp cleaning of corroded steel surfaces

Abstract

Due in large part to its environmental acceptability, solutions of citric acid are used to effectively attack and dissolve rust while maintaining the integrity of the base metal. However, the need for high temperatures and solution additives poses constraints. We have recently demonstrated an improved method of rust removal that synergistically employs the high intensity light output of a flashlamp together with a thin layer of citric acid solution. Such a combination will remove rust from steel surfaces as effectively as conventional citric acid cleaning, but at an increased rate. The short, intense burst of radiation in conjunction with the chelating properties of the citric acid acts to explosively remove surface oxide layers. Microscopic surface analysis (scanning electron microscopy and X-ray diffractometry) reveals conversion of red hematite to black magnetite during the irradiation process. Subsequent applications of the treatment serve to completely remove the magnetite leaving a clean metal surface. Optical radiation cleaning of steel surfaces offers several advantages: ambient temperature citric acid solutions are used in small quantities, organic surface contaminants are removed in the process, and an increased resistance of the cleaned surface towards flash rusting. Details of the flashcleaning process and examples of treated surfaces will be presented in this paper.