Temperature dependence and shape effect in high-temperature microwave heating of nickel oxide powders

The temperature dependence of microwave absorption was investigated for Ni1-yO particles over the frequency range 2.0-13.5 GHz and temperature range 25-1000 degrees C. Using a coaxial transmission line method with a network analyzer, both the real and imaginary parts of the relative permittivity (epsilon'(r) and respectively) and permeability (mu'(r) and mu"(r) respectively) were measured; finding that both are largely dependent on the temperature at all frequencies. Furthermore, permeability loss factors related to shape effects were observed at high frequencies, indicating an increase in the microwave absorption properties. A modified form of Mie's theory was applied to discuss these effects, wherein a spherical model demonstrating a close fit to the shape effect data suggests a more complex microwave absorption behavior at increased temperature. (C) 2014 Elsevier B.V All rights reserved.