Combustion wave structure during the MoSi2 synthesis by Mechanically-Activated Self-propagating High-temperature Synthesis (MASHS): In situ time-resolved investigations

In situ synchrotron time-resolved X-ray diffraction experiments coupled with an infrared imaging camera have been used to reveal the combustion wave structure during the production of MoSi2 by Mechanically Activated Self-propagating High-temperature Synthesis (MASHS). The fast combustion front exhibits a form described as an ‘equilibrium structure’ where the chemical reaction is the sole major driving force. In the MASHS process, oxide-free interfaces between Mo and Si nanocrystallites enhance the reaction Mo+2Si→MoSi2. Exhaustive time-resolved investigations show a possible solid-state process in the first second of the reaction within the combustion front. If preheating is added, the reaction rate is increased, whereas, the presence of α- and β-MoSi2 phases, produced during the ball milling (i.e. mechanical alloying), cause fluctuations in combustion rate. Therefore, an increasing of the mechanical pre-treatment duration leads to an unstable wave by acting directly on the thermal and matter transfer rates.