Authors: A.A. Markov, I.A. Filimonov, K.S. Martirosyan
Affilation: University of Texas at Brownsville, United States
Pages: 689 - 692
Keywords: complex oxide nanoparticles, multiscale modeling, carbon combustion, porous media
Recently a novel, simple and energy efficient synthesis of nanoparticles of complex oxides referred to as Carbon Combustion Synthesis of Oxides, (CCSO) was developed. In CCSO the exothermic oxidation of nanoscale carbon generates a thermal reaction wave that propagates through the solid reactant mixture converting it to the desired oxide products. The carbon used in the CCSO is not incorporated in the product and is emitted from the sample as a CO2. The high rate of CO2 release helps to form a highly porous and friable product, having a particle size in range 50-800nm. This phenomenon results from a vortex gas flow in the reaction zone fed by the carbon dioxide co-flow and oxygen counter-flow filtration. It is characterized by alternate (stratified) macroscopic regions of large particles and low gas pressure. In contrast to the classical problems of filtration combustion it deals with the Navie-Stokes equation rather than with the Darcy law or Euler equation on the macroscopic level. This is a more general description which in combination with a non-uniform and self-organizing porosity of the combusting sample leads numerically first to a weak spin instability of the CCSO front and then to fingering at the latest combustion stages.