Evaluation of microwave absorption properties of CNT-containing alumina composites and its application as a heating medium for microwave-heated particle synthesis

Abstract

We investigated the dielectric and exothermic properties and thermal durability of carbon nanotube (CNT)-containing alumina composites. Experiments were conducted to synthesize nickel oxide (NiO) powder from aqueous Ni(NO₃)₂・6H₂O via microwave denitration in the presence of a heating jacket as a microwave susceptor. The heating jackets were fabricated using the CNT-containing alumina composites. As the CNT content in the composite increased, the apparent dielectric loss also increased, reaching a maximum value. Thereafter, the apparent dielectric loss decreased with increasing CNT content in the composite, indicating that the exothermic properties of the composites depend on the CNT content. The aerosol coating had a negligible effect on the dielectric and exothermic properties of the composites. However, composites with an aerosol coating demonstrated superior thermal durability. The heating jacket not containing CNT did not effectively serve as a susceptor. However, the heating jacket containing CNTs effectively served as a susceptor and facilitated the microwave denitration reaction to proceed, yielding crystalline NiO particles. The heating jacket enabled the temperature of aqueous Ni(NO₃) ₂・6H₂O in the flask to continue increasing up to 500 ℃ via heat conduction. In conclusion, CNT-containing alumina composites are potential materials for use as susceptors in hybrid heating.