Green Molten Salt-Assisted Co-Deposition Synthesis of CeB₆ Powders

This study reports a novel and green molten salt electrolysis route for the synthesis of cerium hexaboride (CeB₆) powders using oxide-based salts. The cerium and boron atoms were co-deposited on different cathode substrates (e.g., Grade 2 titanium and AISI 1018 steel), and the influence of key process parameters (e.g., electrolyte temperatures, applied current density, and electrolyte compositions) on the morphology, phase composition, and stoichiometry of the obtained powders was systematically investigated. Structural characterizations were carried out using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy. The results demonstrated that the cathode material plays a crucial role in governing the Ce/B stoichiometry of co-deposited CeB₆, which is attributed to differences in the reduction and diffusion behavior of boron and cerium species within the Helmholtz layer. The operating temperature showed a slight influence on particle size, exhibiting that once the molten electrolyte provides sufficient ionic mobility, subsequent temperature increases do not considerably affect the growth characteristics of CeB₆ particles. Similarly, the applied current density showed a negligible effect, indicating that the electrolysis process was predominantly controlled by thermodynamic factors. SEM observations revealed the characteristic cubic morphology of CeB₆, while Raman spectroscopy confirmed the formation of CeB₆ through agreement with its vibrational modes. The suggested co-deposition mechanism, confirmed by experimental phase evolution, explains how interfacial chemistry in the oxide melt influences the production pathway of CeB₆. The optimal synthesis conditions were determined as an electrolyte composition of 94% Na₂B₄O₇ + 5% CeO₂ + 1% CaF₂ at 900°C at a current density of 200 mA/cm² on a Grade 2 titanium cathode. This environmentally friendly molten salt electrolysis approach offers a promising and scalable pathway for the sustainable production of rare-earth hexaboride powders.