Synthesis and evaluation of high thermal conductivity magnetic heat storage inorganic microcapsules simultaneously containing gallium and magnetic nanoparticles by sol-gel method

The authors propose microcapsules encapsulating multiple substances as a multifunctional refrigerant that can transport a large amount of heat due to latent heat while being driven self-excitedly by the application of a magnetic field. In this study, a fully inorganic functional microcapsule was synthesized that simultaneously encapsulates magnetic particles and gallium as a phase-change material and has a silica-coated outer shell. Magnetic particles synthesized by the coprecipitation method were mixed with liquid gallium and dispersed ultrasonically to make the core material. The core material was coated with a silica film using the sol-gel method. SEM and EDS observations confirmed that capsules containing iron and gallium were synthesized. The 1 wt% dispersion of the capsule had a 9.5 % increase in thermal conductivity and, like the metallic nanofluid, had excellent properties as a refrigerant. When latent heat was measured, two peaks of 14.2 and 18.4 °C were detected for the supercooling temperature, indicating that it can be used repeatedly with smaller values than in previous studies. The magnetization hysteresis shows that the material has ferromagnetic properties, responding quickly to a magnetic field and dispersing as the field is released.