Techn ca]l Notes @ An X-Ray Study of Oxidized Uranium Surfaces

kinetics of u ran ium oxidation. A marked change in the appearance of the tracings occurs at about 400 ~ The diffraction max ima in the regions 28 = 55 ~ and 75 ~ which are broad and diffuse up to 400~ are quite sharp at 500 ~ and 600 ~ The max imum in the region 20 = 33 ~ shows a similar change be-tween 300 ~ and 400~ It is interest ing to note that a change in the ki-netics of oxidation of u ran ium occurs at 450 ~ (8). Below that temperature an accelerating oxidation rate was found, proport ional to (t ime) 5/4 whi le above 450 ~ a decelerat ing rate proport ional to (t ime) 5/ ~ holds. It is reasonable to ascribe this change in react ion kinetics to the changed character of the oxide. A l though some of the l ine broadening observed at the lower temperatures may be att r ibuted to small crystal l i te size, not all the changes in th