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.
The oxidation of uranium mononitride UN has been investigated and some comparative measurements carried out on uranium monocarbide UC. Powdered UN, of surface area 0*2-0.4m2/g, oxidizes isothermally at a measurable rate in the temperature range 230-270°C. The reaction kinetics are independent of oxygen pressure (50-760 torr) and the apparent activation energy is 30-32 kcal/mole. Complete oxidation leads to an amorphous product of composition uo3 . NO.2-0.4 * The paper is a condensed version of UKAEA Reports AERE R-4600 and AERE R-4985. 3591 * Our thanks are due to Dr. D. L. Keller and Mr. R. W. Endebrock of the Battelle Memoria Institute for supplying the ingot of UN and to Mr. B. L. Eyre of the Metallurgy Division, Hanvell, for the UC single crystals.
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