Touch-free flash sintering of titania: Coupling of reactor and induction currents

The first experiment on “touch-free” flash sintering, was reported in 2022, where it was shown that superposition of magnetic field could migrate the “flash” from a reactor held in Stage III of flash into a free-standing workpiece. The density of the workpiece increased with the magnetic field which was controlled by increasing the current through the induction coil. The coil was constructed from Kanthal wire which is nominally used for heating elements. Thus, the heat from the Kanthal wire raised the question of whether it or the magnetic field, was the cause of enhanced sintering. Here we present results with silver wire, which being one hundred times more conductive than Kanthal, can carry a much higher current without significant heating. The higher magnetic field obtained with silver led to nearly full density of the workpiece (> 98%). The results are presented in the form of a map with the current density ranging up to 200 mA/mm², and the induction current up to 70 A (at 60 Hz). These experiments serve to (i) allay the concern that heat from the induction coil was inducing flash in the workpiece and (ii) show the need for high induction currents to attain high density in magnetic field-assisted flash sintering experiments.