Microwave heating characteristics of bulk metallic materials and role of oxides

In the present work, microwave heating characteristics of a few selected bulk metallic materials were studied in the ambient environment using 1400 W input microwave power at 2.45GHz. Interactions of microwaves with the three target metallic materialsaluminum, copper and stainless steel and their effects were elucidated using the time-temperature profiles monitored during microwave hybrid heating. Metal oxides formed at different stages of the exposure were characterized using scanning electron microscopy and other X-ray-based techniques; role of the oxides in the heating behavior has been explained. The results revealed that heating of the target materials get influenced by the metallic oxides formed on the exposed surfaces of the metallic materials. The oxide layer reduces heat transfer between the susceptor and metallic material at initial stages of heating; however, it assists microwave absorption in the metallic materials depending upon its electromagnetic properties at elevated temperatures during irradiation. The oxide particles act as tiny susceptors initially, which, however, turn into secondary sources of conventional heating in the target material during hybrid heating.