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 U02, ammonia and hydrogen (UNS2H20 +U02+NH3+ ~H z ) , whereas others yield a solid product containing significant amounts of ~U2N3+~and dissolved nitrogen. The difference is ascribed to particle texture: when the release of ammonia is inhibited it reacts further with UN to form aU2N3. The overall activation energy of hydrolysis is 21 kcal/mole. Experiments with single crystals of UN, hydrolyzed at higher temperatures, show that an epitaxially oriented sandwich structure of O L U ~N ~ and U02 is formed on the surface of the crystal, exactly as during oxidation.1 Some experiments on the hydrolysis of UC single crystals are also described. This surface f i l m protects UN from hydrolysis at low temperatures.
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