Burning Temperatures of Uranium and Zirconium in Air

The burning temperatures and oxidation rates for uranium and zirconium metals in air were investigated analytically. The calculations were based on the assumption that the metal-oxygen reaction is controlled by atmospheric diffusion. Reaction is assumed to be limited by the rate at which oxygen can diffuse through a nitrogen-rich boundary layer. Expressions for mass transfer were obtained by applying the Lewis relation to accepted heat transfer correlations. Calculations were made for the case of vertical plates (foils), horizontal cylinders (wires), and spheres in both natural and forced convection. Characteristic dimensions ranging from 0.02 to 10 cm and flow velocities up to 3162 cm/sec (70 mph) were considered. Computed burning temperatures were compared with experimental measurements of the maximum temperature reached by burning foils of uranium, zirconium, and a zirconium alloy containing 14.9 wt.% titanium in natural convection. Experimental temperatures with zirconium were higher than calculated values while uranium temperatures were somewhat below theoretical. The calculations, however, correctly described the variation of burning temperature with foil width and appear to be good evidence for the proposed model of burning.