Flame-spreading process over thin aluminum sheets in oxygen-enriched environments

An experimental study of flame-spreading process over thin aluminum (99 % A l and 1 % Mn) sheets was investigated in oxygen-enriched environments. The objective of this study was to determine the dependency of flame-spreading rate over aluminum sheets as a function of initial chamber pressure, sample thickness, oxygen purity, oxygen flow condition, and sample orientation. T he reaction mechanism of aluminum in oxygen was also studied by examining t he recovered partially-burned sample using a scanning electron microscope ( SEM) coupled with an energy dispersive spectrometer (EDS). The dame-spreadi ng rate over aluminum sheets was measured by an array of fast-response lead -selenide (Pb-Se) IR photodetectors. The initial chamber pressure was varie d from 0.1 to 6.3 MPa. Two grades of oxygen gas were used with purities of 99.996 % and 99.75 %. In terms of the effect of pressure on the flame-sprea ding rate, as the initial chamber pressure was increased, the dame-spreadin g rate was found to increase to a maximum, decrease to a minimum, and then increase again. Based upon the comparison of flame-spreading rates in horiz ontal, upward, and downward orientation, the dame-spreading process over al uminum sheets was found to be dominated by the solid-phase heat conduction mechanism. The continuous oxygen dow showed a strong influence on the flame -spreading behavior, and it was demonstrated that the flame can be blown of f when the counter-current flow velocity exceeds a critical value. The flam e-spreading rates under high-purity (similar to 99.996 %) oxygen environmen ts were found to be significantly greater than those in commercial grade (s imilar to 99.75 %) oxygen. In addition, the oxygen content in the white cer amic-type nodules formed on the burned edge of the recovered partially-burn ed sample is much higher than that on the unburned surface. These imply tha t there exist heterogeneous reactions between aluminum and either oxygen or gaseous aluminum sub-oxides on the burning surface.