OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 25 No. 3 2023 container with the reaction mixture. The ignition temperature Tign and the maximum combustion temperature Tmax were processed from the recorded reaction mixture temperature curve. The reactor was removed from the furnace after equalization of temperatures of the outer reactor surface and the powders mixture. Equalization happened in about 2–4 minutes after the temperature peak appearance. Then the reactor was cooled in air. Part of the reacted powder mixtures were annealed in vacuum of 0.01 Pa with variation of the temperature and annealing duration. Mechanically activated powder mixtures, products of combustion and subsequent annealing were studied using the equipment of the Shared Use Center “Nanotech” of the ISPMS SB RAS by X-ray phase analysis (DRON-7 diffractometer, Burevestnik, Russia). The phases were identified based on the results of X-ray diffraction analysis using the ASTM X-ray database, and the primary results were processed using the RENEX and PDWIN software programs. Results and discussion Fig. 3 shows thermographs of MA reaction mixtures of two compositions at an average rate of 85 ± 5 deg/min and the time derivatives of temperature (the rate of increase in mixture temperature). There is an abrupt increase in temperature at 500–530 °C as a result of self-ignition, that is, the reaction occurs in the thermal explosion (TE) mode (fig. 3a, b). The duration of heating to self-ignition was 6–7 minutes. The rate of temperature elevation after ignition and the peak value for the 2Fe + Ti mixture turned out to be much higher (fig. 3a, c) than for the equiatomic mixture (fig. 3b, d). The reason is twice the negative value of the enthalpy of formation of the Fe2Ti compound compared to that for FeTi: -87.45 and -40.58 kcal/mol, respectively [20]. а b c d Fig. 3. Heating thermographs (a, b) and rate of temperature change (c, d) of mechanically activated powder mixtures: 2Fe + Ti (a, c) and Fe + Ti (b, d): 1 – the sample temperature; 2 – temperature of the outer surface of the reactor
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