Doroshenko Y. Formation of nanodispersed condensed phase in laminar dust flames of metal particles

The thesis is devoted to theoretical and experimental study of the flame burning of metal powder with nano-sized oxide formation and is aimed at identifying mutual influence of combustion and chemical condensation in a dust flame, which determines the dispersion of the oxide. Nonstationary physical and mathematical model of combustion of gas suspensions of small metal particles, which takes into account the metal burning, condensation centers formation, and particle growth of end-oxide was developed. The dynamic of these processes on the example of aluminum was analyzed. According to the analysis of calculated data the analytical dependences of oxide particle size on the concentration of metal and oxygen in a gas suspension were set and explain. This dependences well agrees with existing experimental data. For the conditions of a large excess of oxidizer in the gas mixture a simplified theoretical model, which has provided analytic dependence of the final size of the oxide particles from the macro parameters of the flame was formulated. The effect of the presence (content) in a gas suspension impurities which are easily ionized (K2CO3) to disperse composition of the combustion products of aluminum was experimentally investigated and it was found that the dependence of the average particle size of Al2O3 on impurity content has a minimum. To explain the reasons of the extreme form of this dependence the conditions of ionization equilibrium of two-phase system - metal and oxide particles in the gas - at a maximum temperature in the combustion zone of aluminum flame were evaluated and the effect of changes in the potassium atoms concentration in the combustion zone of the flame on the properties of plasmas and possible mechanisms of Al2O3 particle growth in it were analyzed.