In the present paper, the analysis of thermal modes of solid phase synthesis in the volume of mechanically activated powder mixtures was conducted. As a basic model, the Carter-Valensi model of solid phase interaction in powder systems was used. This model was considered from point of view of non-isothermal kinetics for the first time. Using the maximum temperature method, the critical ignition conditions of the mixture and the conditions of thermal explosion degeneration were determined. The corresponding diagrams of critical parameters were obtained and the parametric regions of thermal explosion existence were defined. The results presented allows solving the technologically important problem of demarcation of fast (thermal explosion) and slow (isothermal sintering) synthesis modes. Thus, it becomes possible to control the chemical activity of a heterogeneous reaction purposefully.