Comparing the results from this study with the heating characteristics of Fe2O3 and Fe3O4
obtained by Walkiewicz in Table 4.1, we can also observe similar differences in the heating
behavior of Fe2O3 and Fe3O4 when exposed simultaneously to E and H microwave fields in a
multimode cavity. From Table 4.1, Fe3O4 shows an extremely high heating rate of more than
400 C per minute, reaching a maximum temperature of 1258 C in less than 3 minutes,
while Fe2O3 is only minimally heated to 134 C in 7 minutes.
4.2.3 Sintering Behavior and Mechanisms
Veltl et al. reported the presence of a microwave effect due to enhancement of the material
transport between particles during the sintering of bronze powder and steel bearing balls in a
multimode cavity [16]. It was suggested that the high frequency electric field acting between
the particles generates plasma which promotes mass transport into the contact areas between
particles by generating fine particles below 1 micron in size [16]. Figures 4.5 and 4.6 are
reproduced from the study.
In conventional sintering, the particles have to be in contact with each other in order for
diffusion, and the subsequent reduction of surface energy, to occur. In microwave sintering,