Magnetically-triggered heating of Fe–Al powders

Powders of Fe and Al with a 3:2 atomic ratio were mechanically milled for either 1 or 2 h and subsequently subjected to an alternating magnetic field (AMF) to evaluate their heating. The microstructures of both the milled and heated powders were characterized using X-ray diffractometry, differential scanning calorimetry (DSC), scanning electron microscopy, and vibrating sample magnetometry. The results show that the milled powders consisted of fine intermixed Fe and Al layers. These were found to be susceptible to heating in an AMF, and underwent a significant heat output (21.3 kJ mol−1) around 400 °C, corresponding to the reaction between the Fe and Al layers to form B2-structured FeAl. The temperature increase depended on the square of the field strength and the frequency of the AMF. By using a Kissinger analysis of the exothermic peaks obtained in a DSC at different heating rates, the activation energy for the formation of FeAl was found to be 67 ± 10 kJ mol−1.