  Thermodynamic characteristics of the radiation of condensed combustion
products presented in the form of agglomerates of metal-oxide nanoparticles
demonstrate deviations from the classical Planck's law. We propose to interpret
these deviations in terms of the non-additive entropy of the photon system
interacting with the heterogeneous combustion products, which makes it possible
to use the non-extensive Tsallis thermodynamics for their description. It is
assumed that the non-additive character of the radiation entropy in
heterogeneous plasma can be explained by the influence of long-range
interactions and non-equilibrium physicochemical processes. An expression is
obtained for the energy-dependent distribution of the photon density, based on
the phenomenological parameter of non-extensiveness $q$ which, in the first
approximation, does not depend on the energy. In this case, the "non-extensive"
Planck's law can be reduced to the "usual" Planck distribution by introducing
the "effective temperature" that exceeds the real temperature. Numerical
modelling has shown that the spectral density of photons, the position and
magnitude of its maximum depend on the value of the parameter $q$, which can be
used for its experimental determination and revelation of its physical nature
and origin.
