Influence of the heating method on the particle characteristics of copper oxide powders synthesized from copper nitrate aqueous solutions

The influence of the heating method and rate on the morphology of CuO powders synthesized from Cu(NO₃)₂·3H₂O aqueous solutions by denitration was investigated. The median diameter of the obtained powder was found to decrease as the heating rate increased, independent of the heating method. The microwave heating (MW) method remarkably reduced the particle size and enhanced the irregularity and disorder of the shape and surface of the particles, which were found to be more widely distributed. In contrast, the microwave hybrid heating (MHH) method (i.e., a combined usage of microwave and external heating) yielded the most spherical particles with the smoothest surface. It was also found that this heating method sharpened the particle size distribution and had higher energy efficiency than the MW method. Numerical simulations also indicated a difference in the energy efficiency between these two methods. The simulations also revealed that the MHH method could heat the whole reactor more uniformly with a lower microwave output. Moreover, the morphological difference of the powders obtained by these heating methods can be potentially explained by the difference in the simulated bulk temperature distribution and the intensity of the formed hot spot in the CuO particles caused by microwave irradiation.