Hydrolysis of uranium mononitride

Abstract

An experimental study has been made of the hydrolysis of UN in water vapour+argon mixtures of controlled composition. The kinetics of reaction are followed gravimetrically and by estimation of the ammonia liberated. For powdered UN the reaction proceeds rapidly above ∼340°C. Some specimens hydrolyze completely to UO₂, ammonia and hydrogen (UN+2H₂O →UO₂+NH₃+½H₂), whereas others yield a solid product containing significant amounts of αU₂N_3+x and dissolved nitrogen. The difference is ascribed to particle texture: when the release of ammonia is inhibited it reacts further with UN to form αU₂N₃. The overall activation energy of hydrolysis is 21 kcal/mole. Experiments with single crystals of UN, hydrolyzed at higher temperatures, show that an expitaxially oriented sandwich structure of αU₂N₃ and UO₂ is formed on the surface of the crystal, exactly as during oxidation.¹ This surface film protects UN from hydrolysis at low temperatures. Some experiments on the hydrolysis of UC single crystals are also described.