K. Vartanov THERMODYNAMIC THEORY OF SINTERING: GRANULAR SYSTEMS A thermodynamic theory of sintering of granular systems for modeling of such processes as compaction, coalescence of pores and clustering of granules is proposed. <...> For describing a thermodynamic state, generalized coordinates, a state function, and a constitutive equation are determined. <...> It is shown, that the second law of thermodynamics imposes restrictions on the state function and Helmgoltz’s free energy. <...> Keywords: Granular systems, Specific surface, Porosity, Sintering, State function, Constitutive equation, Helmgoltz’s free energy. <...> A sum of surfaces of the separate granules is always bigger then an internal surface of the granular system by an amount of a sum of the contact surfaces. <...> J. Frankel established the first physical theory the internal surface of the granular system is discussed below. <...> However, this theory could be applied for modeling of other processes, connected with changing of the internal surface. <...> For a condition T<TS the melting temperature) granular systems are ture of sintering (as rule TS ≈ 0,6.TM , where TS is the tempera, where TM indifferent and only for temperature, close to TS sintering, is activated. <...> A driving force of sintering is the reducing of the surface energy; it means that the granular system aspires to minimize the surface energy. <...> A probability for realizing any configuration of the system P(E) according to Gibbs’ relation is defined by , (1) where k is Boltzman’s constant, T is the absolute temperature. <...> The same result could be received by minimizing Hemgoltz’s free energy, which is proportional to , (2) 78 Проблемы машиностроения и автоматизации, № 4 – 2006 is of sintering in the paper: “Viscous flow of crystalline bodies under action of surface tension” [2], in which the cause of sintering and its driving force were defined as a superfluity of Gibbs’ surface energy. <...> From the result, that solid materials have a similar flow to the flow of viscous liquids at high temperatures, J. Frankel stated that surface forces can cause viscous flow in crystal materials; and sintering of crystal materials can be explained by that phenomenon. <...> Frenkel’s basic relation determines sintering kinetic , (3) tensor, V <...>