Mechanisms of Autoignition of Finely Divided Steel

Abstract

Autoignition of direct reduced iron (DRI) that leads to severe warming or even to uncontrollable metal fires has always been linked with the presence of moisture, being particularly severe in the presence of sea water. This is of considerable concern in view of the regular transportation of DRI across the oceans. In spite of the very high specific surface area and high reactivity of DRI, oxidation reactions cannot alone proceed to autoignition in the absence of water. Reactions involved in aqueous corrosion appear to be a necessary precursor for autoignition. But there has been no satisfactory explanation of how aqueous corrosion reactions that must terminate at 100°C, can initiate high temperature oxidation reactions. It has also been reported that, although most DRI cargos and piles show some warming, autoignition to an uncontrollable situation or a metal fire is observed only in case of relatively large or deep piles. The present work suggests that while thermal insulation is necessary, the size of the...