On the likelihood that underwater metal ignition is a vapor phase phenomenon

The hypothesis that the ignition of metals (particularly aluminum) under water occurs in the vapor phase is examined theoretically. An available two-phase stagnation flow film-boiling model is used to calculate the oxidizer (steam) flux toward the vaporizing metal surface. Combining this model with the fact that there is an upper limit to the magnitude of the metal vaporization rate at which the reaction regime must change from vapor to surface oxidation, as first discussed in the valuable paper by Turkdogan, Grieveson and Darken, leads to prediction of the critical metal temperature below which vapor phase oxidation is impossible. The predicted critical temperatures are compared with observed ignitions of metal spheres in free-fall in water and during violent metal-water interactions (steam explosions). It appears from the theory that observed underwater metal ignitions did not occur in the vapor phase