REACTION OF HYDROGEN WITH URANIUM 1601the hydride and during dehydriding may be responsible for tl~e apparent slow decomposition rate described above. ConclusionThe hyriding of uranium powder was found to follow a two-thirds order rate in 13.3 kPa of hydrogen but increased to a first-order rate as the hydrogen pressure was increased to 26.6 kPa. Comparison of the phase boundary with the progressive conversion reaction models showed little difference between the two. The progressive conversion model did fit all of the data from 0 to 100% reaction. Increasing the temperature reduced the hydriding rate, which can be predicted using a model with adsorption as the rate-controlling step. This resulted in an apparent negative activation energy of --1.59 kcal/mole. Repeated hydriding/dehydriding cycles increased the surface area of the sample and also the reaction rate for the first five cycIes. Subsequent cycling had little effect on the surface area. Dehydriding was found to be zero order with an activation energy of 9.5 kcal/mole over the temperature range 200~176 ABSTRACT In view of a possible application for the chemical vapor deposition of Gd~Fe5012 the equilibria GdCl~(s) ~-1.5LfCle(g) ----GdI4Cll~(g), L = A.I, Fe

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Volumen 50, Fasciculus 8 (1967) -No. 231-232 2215 dest. Wasser gewaschen und im Vakuum bei 130" (14 Std.) getrocknet: 1,2 g violettbraunes Pulver. I m Dunnschichtchromatogramm (Alox, Athanol als Entwickler) einheitlich.

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