Agglomeration of particles stored in a box

Metallic nanoparticles are an essential part of advanced rocket fuels. Because of difficulties caused by hard ignition, incomplete reaction, and large size of combustion residues metallic particles with conventional particle sizes are unfavorable. However, the application of nanosized metallic particles does not show these disadvantages, in contrast, the application of nanosized metallic particles increases burning rates and reduces the two-phase specific impulse losses associated with solid combustion residues. On the other side, nanosized metallic particles are problematic, too. Nanoparticles, especially metallic ones, have a tendency to agglomerate. The formation of agglomerates leads to a reduction of the total surface of the particles and, therefore, to a reduction of the surface energy. This paper is limited to the process of agglomeration. As agglomeration is a random process, meaningful results are possible only using statistical methods. For this paper, a model with random selection of the particles based on Markow chains was applied. To evaluate the stability of the agglomerated product, the entropy was calculated. The results show that, with increasing agglomeration, the entropy increases exponentially. The thermodynamically better criterion is the free enthalpy; however, in lack of adequate materials data, this criterion could not be applied. Therefore, in general, the consideration presented in this paper are not specific for the addition of a specific metal.