<p>This study proposes a new environmentally benign fluorine-free mold flux that can control heat transfer by exploiting Mie scattering at the interface of dispersed metallic particles. To optimally replace the heat-transfer-control role of cuspidine (Ca₄Si₂O₇F₂) with dispersed metallic particles, the characteristics of the formation behavior of particles by carbothermic reduction of hematite were evaluated under varying Fe₂O₃ contents, free carbon contents, and CO₂ emission conditions, and the optimal condition was determined using two-dimensional particle image analysis. The effect of Fe₂O₃ size on particle-formation behavior was also quantified. Radiative and conductive heat transfer mechanisms were examined for samples prepared under selected conditions that produced particle distributions capable of inducing Mie scattering to control heat transfer through the liquid phase of the mold flux. To assess the radiative heat transfer, the extinction coefficient was calculated by the Lambert–Beer law using ultraiolet–visible (UV/VIS) and Fourier transform infrared (FT-IR) spectra. The thermal conductivity of glassy mold fluxes was measured using the laser flash technique. Finally, the feasibility of a new type of mold flux was demonstrated in terms of essential functions such as lubrication and heat-transfer control.</p> Graphical Abstract <p></p>