Aluminum powders added to solid propellants burn either as single particles or agglomerates. Combustion efficiency is very dependent on the final aluminum particle size injected into the chamber flowfield. This work has investigated experimentally the microscopic behavior of powdered aluminum particles during gradual heating in inert and oxidative atmospheres. Effects of surrounding gas composition, particle size, initial oxide layer thickness, and dilution by refractory compound on the particles behavior during heating have been studied. A novel model of a crucial stage in aluminum particles agglomeration based on estimation of mechanical stresses appearing in the oxide layer during particle heating has been suggested. Results of estimation confirm that disruption of oxide layer takes place during aluminum melting. This disruption results in the flow of a molten metal through cracks formed in the oxide layer and in the formation of large liquid drops. Results of theoretical calculations are in a good agreement with experimental data.