Microwave sintering of fly ash samples with large amounts of unburned carbon and CaCO3 was examined in this study. To this end, CaCO3 was mixed with fly ash sintered body to fix CO2. The decomposition of CaCO3 was observed when the raw material was heated to 1000 °C using microwave irradiation; however, a sintered body containing aragonite was obtained when the raw material was heated to 1000 °C with added water. Further, carbides in the fly ash could be selectively heated by controlling the microwave irradiation. The microwave magnetic field created a temperature gradient of 100 °C in a narrow region of 2.7 μm or less in the sintered body, and it helped suppress the CaCO3 decomposition in the mixture during sintering. By storing water in the gas phase before spreading, CaCO3, which is difficult to sinter using conventional heating, can be sintered without decomposing.
Microwave sintering of fly ash samples with large amounts of unburned carbon and CaCO3 was examined in this study. To this end, CaCO3 was mixed with fly ash sintered body to fix CO2. The decomposition of CaCO3 was observed when the raw material was heated to 1000 ℃ using microwave irradiation; however, a sintered body containing aragonite was obtained when the raw material with water was heated to 1000°C. Further, carbides in the fly ash could be selectively heated by controlling the microwave irradiation. The microwave magnetic field created a temperature gradient of 100°C in a narrow region of 2.7 µm or less in the sintered body, and it helped suppress the CaCO3 decomposition of the mixture in sintering. By storing water in the gas phase, CaCO3, which is difficult to sinter with conventional heating, can be sintered without decomposing.
The ongoing development of high-temperature processes with the use of microwaves requires new microwave absorbers that are useful at these temperatures. In this study, we propose Al4SiC4 powders as important and efficient microwave absorbers. We investigated both the behavioural microwave heating and electrical permittivity characteristics of Al4SiC4 powders with various particle sizes at 2.45 GHz. The TE103 single-mode cavity indicated that Al4SiC4 powder samples yielded different heating behaviours and dielectric constants for each particle size compared with SiC. By microwave heating ∅50 mm × 5 mm disks of Al4SiC4 and SiC, we demonstrate that for specific sizes, Al4SiC4 can be heated at a higher temperature than SiC. Finally, the results of the two-dimensional two-colour thermometer show that an energy concentration appears at the interface of the microwave-heated Al4SiC4. These phenomena, which are inconsistent in individual physical property values, can be explained without contradicting microwave heating physics.
Acetylene black, activated carbon, and Ketjenblack were subjected to microwave heating up to 1000 °C under N2 atmosphere to rapidly convert them into graphene-like materials. Few carbon materials exhibit a favorable increase in the intensity of the G’ band with increasing temperature. Upon electric field heating of acetylene black to 1000 °C, the observed relative intensity ratios of D and G bands (or G’ and G band) were equivalent to those of reduced graphene oxide heated under identical conditions. In addition, microwave irradiation under different conditions, i.e., electric field or magnetic field heating, produced graphene of qualities different from those of the same carbon material conventionally treated at the same temperature. We propose that this difference arises from the different mesoscale temperature gradients. The conversion of inexpensive acetylene black and Ketjenblack into graphene-like materials within 2 min of microwave heating is a major achievement toward low-cost mass synthesis of graphene.
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