Characteristics and mechanism of microwave-induced discharge of spherical bio-char with graphite addition

The enhancement of efficiency converting microwave energy into heat has become great concern on industrial application of microwave heating. Microwave discharge can generate more hot spots, exhibiting more intense thermal effect than microwave heating alone. Microwave discharge can be achieved by a variety of carbon-based dielectrics like bio-char, whose performances are highly dependent on graphite degree of the carbon-based dielectrics. Therefore, graphite addition into bio-char by mechanical mixing is promising to improve the discharge performance. However, there are few studies on characteristics of microwave-induced discharge by spherical biochar with graphite addition, and kinetic analysis of microwave discharge is lacking. Moreover, the mechanism of microwave-induced discharge of spherical carbon-based dielectrics has not been fully clarified. As a result, the work firstly studied characteristics of microwave-induced discharge of spherical bio-char with graphite addition. The other focus of this work was to explore mechanism of microwave-induced discharge through electric field simulation. The results revealed the average discharge intensity of spherical graphite in the first 20 min was 38.2 % higher than that of spherical bio-char. Microwave-induced discharge of bio-char with graphite addition had synergistic effect at the initial stage. It was obtained apparent activation energies of microwave-induced discharge of bio-char and graphite were 237.08 W.g(-1 )and 48.42 W.g(-1), respectively. The formation of electric field polarization focuses offered active sites for microwave discharge. The work is of significance for fundamental research about microwave-induced discharge of carbon-based dielectrics.