Hydrolysis of uranium mononitride

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 αU2N3+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.