On the versatility and distinctiveness in the use of microwave energy for the ignition of low exothermic Ni–Ti intermetallics combustion synthesis

Microwave energy has been employed in the present work in order to reach ignition of the combustion synthesis in the binary Ni–Ti system without the need of any separate additional pre-heating step. Indeed, the latter is known to be necessary with more conventional ignition strategies, due to the low exothermic character of the reaction between elemental Ni and Ti powders. On the opposite, the unique microwaves heating mechanism allows directly transferring electromagnetic energy in the reactive specimen that absorbs and transforms it into the heat necessary to reach ignition of the exothermic reaction. According to the electromagnetic field distribution inside the microwave single mode applicator employed, it was possible to realize both Thermal Explosion (TE) and Self-propagating High-temperature Synthesis (SHS) ways of combustion. Moreover, the use of a single mode applicator also allowed separately investigating the effect of electric and magnetic fields strengths, at the 2450 MHz microwave frequency, on the combustion characteristics. This significantly affected the microstructure as well as the phase evolution in the synthesized products