Ignition process of a heated iron block in high-pressure oxygen atmosphere

Ignition process of a heated iron rod in a high pressure oxygen atmosphere has been studied experimentally and theoretically. A mild steel rod 10 mm in diameter and 50 mm in length was used for experiments. The test pieces were heated in an argon atmosphere to prevent the oxidation reaction during the heating stage, and then ejected into the high-pressure oxygen atmosphere. When the heated iron rod was exposed in the oxygen, the surface temperature increased rapidly, reached a maximum, and then decreased gradually. If the ignition did not occur, the thick oxide layer was only formed on the surface. If ignition occurred, the convective burning spots appeared on the surface after a certain time from the exposure, increase in these areas, and then covered all of the surface, i.e., continuous combustion occurred. Theoretical results show that, if there is no convective flow in the melted oxide and metal layer formed on the surface, the oxide layer works only as a barrier for oxidation reaction between metal and oxygen, resulting in termination of the fast oxidation reaction. For the case of ignition, the Marangoni instability in the melted oxide and metal layer occurs after a certain time from the exposure. The occurrence of the convective flow in the melted layer formed on the heated iron block is responsible for the ignition.