Thermal Theory of Metal Particle Ignition

A set of equations of metal particles, oxidation kinetics, and thermal balance is considered. Critical conditions for ignition are investigated. It is shown that, in the general case, ignition is not necessarily connected with melting of oxide film and can occur as a result of self-accelera ting temperature increase by the thermal explosion mechanism. It is found when the Friedman-Macek theory is valid. Ignition of the titanium-nitrogen, aluminumoxygen, and tantalum-oxygen systems has been studied by heating a metallic wire with electrical current of constant power in a gas flow. The experiments permit checking the conclusions of the theory. I. Introduction A :CORDING to the ideas developed by Friedman and Macek, as well as by Mellor and Glassman,1'2 ignition of metal particles of aluminum type in gaseous oxidant occurs when an initial oxide film loses its protective properties, which usually takes place on melting. Heating of the particle up to the melting temperature of the oxide film T% is realized mainly at the cost of heat supplied from the outer source (hot gas) and partly as a result of self-heating from an oxidation reaction. Friedman and Macek have developed the theory of self-heating using the assumption that the rate of heat release depends on the temperature only. It has been shown that critical ignition temperature 7^crjt is close to T*, and the dependence of the T* — T0 crjt difference on the parameters was calculated. In the studies of the present author carried out together with B. I. Khaikin, V. N. Bloshenko, Yu. M. Grigorjev, Yu. A. Gal'chenko, A. P. Aldushin, and S. L. Khafatyan,38 a different and more general viewpoint was developed regarding the mechanism of metal ignition. The mathematical theory of the process was created and the theoretical conclusions were verified experimentally. This paper presents some results of these studies.