Experimental Study on the Thermal Damage Mechanisms of Aluminum-Particle Protective Film in Thermite

An important issue to study ignition of thermite is the investigation into the damage mechanism of aluminum particles protective film under heat. Experiments have found the following rules. When the aluminum powder was heated in air, its weight decreased at first and then increased. The electrical resistance of an aluminum powder column decreased with the increase of its temperature. The resistance dropped abruptly at approximate temperatures of 500 ℃ and 600 ℃, and finally its value reached to metal level. The aluminum particles were disrupted completely at temperature of 670 ℃. The thermite powder heated at temperature of 700 ℃ was condensed into solid state. The conclusion can be inferred from above experiments that the protective film of aluminum particles partly loses its effectiveness at about 500 ℃ and no longer has any effect after the melting point of aluminum.