Low-Temperature Hydrothermal Synthesis of PbUO4

Abstract

Lead uranate (PbUO₄) is a ternary uranium (VI) oxide with significant relevance to actinide ceramic materials, often prepared via traditional high-temperature solid-state or flux-based synthesis methods. Herein, a low-temperature hydrothermal route to phase-pure orthorhombic PbUO₄ is demonstrated. PbUO₄ was synthesized via reaction of synthetic metaschoepite (UO₃·nH₂O) with Pb(NO₃)₂ under hydrothermal conditions at temperatures as low as 150°C–180°C. Systematic variation of solution pH, temperature, and reaction time shows that PbUO₄ formation is strongly pH-dependent, with lower pH favoring layered Pb-U oxide hydrate intermediates and higher pH (≈4.5) enabling direct PbUO₄ crystallization over a broad temperature window. Powder x-ray diffraction confirms phase purity, while optical and scanning electron microscopies reveal distinct, tunable PbUO₄ morphologies ranging from prism-like to block-like crystals. Thermogravimetric analysis shows that hydrothermally synthesized PbUO₄ is stable in air to temperatures exceeding 1000°C. These results establish hydrothermal synthesis as a low-energy route to PbUO₄ and highlight solution chemistry as a key parameter for controlling ternary uranium oxide ceramic formation.