HOT SPOT MODELING OF THERMITE TYPE REACTIONS REGARDING PARTICLE SIZE AND COMPOSITION

摘要

Solid phase redox reactions are characterized by the exchange of oxygen between particles of metals and solid oxides. The reaction velocity is controlled by the fuel/oxidizer ratio and the particle size which influences the contact area and homogeneity of the dispersion. To model this type of reaction mainly thermodynamic approaches are in use which only allow limited conclusions to reaction velocity and physico-chemical reaction mechanisms. To describe particle reactions with heat and mass transfer a transient, 3-D model is developed using the heat flow and diffusion equation in combination with hot-spots both as energy sources and as material sources. An approach based on the Green's function is used to solve the equations. The advantage of the procedure is that the physical/chemical nature of the process is always obvious as well as occurring stability problems. In addition, complex geometrical 3-D configurations are accessible at transient conditions because of the effectiveness of the approach. To validate this modeling thermite-like mixtures of Zr with Fe2O3 have been prepared using different fuel/oxidizer ratios (lean, stoichiometric and fat) and particle sizes including nano-particles. The reaction temperature was determined using fast NIR-spectrometer assuming grey body spectra. The results are discussed in comparison to the modeling calculation.