Reaction of Molten/Burning Aluminum with Liquid Oxygen

Aluminum packings and trays are used in the cryogenic distillation of air. During the sixth International Symposium on Flammability and Sensitivity of Materials in Oxygen Enriched Atmospheres, we presented test results under simulated operating conditions of aluminum packings in oxygen atmosphere. Flammability tests were also performed on aluminum tray samples and heat exchangers. During these tests, a violent energy release (VER) was observed when aluminum samples were ignited and a LOX pool was present. It was established that this phenomenon was not relevant for the operating conditions of cryogenic air separation plants, but the conditions necessary to obtain/explain this VER were not clear. The VER's were attributed to molten/burning aluminum coming into contact with LOX. In this paper we have analyzed, from the tests already performed, the conditions/parameters necessary for this phenomenon to occur. Further tests were also performed involving aluminum rods, in order to get a better understanding of this phenomenon. The results show that the necessary conditions to obtain a pressure wave: ♦ do not depend on the geometry of the sample (packings, trays, heat exchangers, rods) ♦ are the simultaneous presence of a vaporizable liquid (LOX) and a very hot molten material (liquid aluminum T > 1900 K or liquid alumina) ♦ are the rapid contact and mixing of these two liquids so as to get a quick vaporization of LOX.

These conditions are very similar to those encountered in Molten fuel/coolant, interactions which have been widely studied for nuclear reactor safety. An analogy between the two types of reactions is proposed to enhance the understanding of the physical phenomena involved in Aluminum/LOX reactions.