Air‐Sensitive Material Synthesis via Liquid Metal Shielding

Air‐sensitive solid‐state reactions typically require complex encapsulation or inert atmospheres to prevent oxidation at elevated temperatures. Here we introduce a liquid metal shielding strategy that enables high‐temperature solid‐state reactions to be carried out under ambient conditions. Owing to its near‐room‐temperature melting point and low viscosity, liquid gallium forms a conformal and hermetic sealing barrier that prevents oxygen transport throughout thermal processing. We demonstrate the gram‐scale synthesis of nanocrystalline refractory borides including WB x , ReB 2 , ZrB 2 , and FeB, layered WS 2 , and bronze oxides (K x WO 3 ). Mechanistic investigations reveal that gallium primarily serves as a physical shield, while also modifying local redox chemistry and phase evolution in certain systems. While limitations exist for reactions producing large gas volumes or involving gallium‐soluble elements, this approach provides a practical encapsulating strategy for efficient, high‐temperature, air‐sensitive solid‐state synthesis. This methodology offers a powerful platform to expand the toolkit for advanced materials synthesis.