Optimization of Zirconium Carbide Production via Molten Salt Synthesis

Zirconium carbide (ZrC) exhibits many exceptional material properties, making it a suitable material for use in advanced applications that require thermal and chemical stability under extreme conditions. Conventional industrial synthesis methods are energy-intensive and inefficient in atom utilization, highlighting the need for alternative, scalable synthetic methods. Here the molten salt synthesis (MSS) of high-purity ZrC from zirconium dioxide (ZrO2) and carbon black (C) has been systematically investigated by exploring the effect of metal chloride salts and reducing agents at 850 °C. ZrC formation was assessed through phase analysis of powder X-ray diffraction (XRD), carbon analysis via flame combustion, and product morphology as observed by scanning electron microscopy (SEM). Salts facilitate cracking of the Zr–O bond through the activity of free chloride ions in the molten salt solution, where reactive chlorides destabilize the ZrO2 starting material. Reducing metals and metal hydrides are consumed throughout the course of the reaction to form stable metal oxides, assisting in product formation. We examine product stability coupled with entropic contributions and rationalize experimental observations regarding reaction completion by thermodynamic and radioanalytical methods. Phase-pure high-yield zirconium carbide production is demonstrated by this simple one-pot method, allowing for improved scalability and reduced costs compared to current state-of-the-art methods. Factors that affect cracking of oxide starting materials and the overall thermodynamics of product formation can be applied beyond the zirconium system, paving the way for future efforts on the molten salt synthesis of lanthanide and actinide nonoxide ceramics from oxide starting materials.