Quasi-stable temperature of the steady state of microwave heated hematite

• The existence of quasi-stable state temperature in microwave field was experimentally observed.
• The microwave heating behavior of hematite varies significantly with its initial temperature.
• Absorption properties of hematite at frequencies in the range 1–13.5 GHz were measured.
• The theory predicted the existence of quasi-stable state and these heating behavior.

Microwave heated materials often reach a quasi-stable temperature resulting in thermal runaway. To control steady state in microwave processing, it is important to predict the quasi-stable temperature of the steady state. We demonstrated that the microwave heating behavior of hematite varies significantly with its initial temperature. In microwave heating, hematite samples could not be heated from room temperature, whereas hematite samples preheated to 410 °C or higher was heated to a temperature of 1020 °C. The microwave heating behavior can be accurately predicted by considering the steady-state energy balance.