Calcination of ammonium polyuranate at temperatures between 350 and 600°, with a rate of temperature increase of 1°/min., yielded amorphous UO3 having surface area of about 30 m.2/g. More rapid increase of temperature gave mixtures of amorphous UO3+β‐UO3 with no reproducible surface area. To obtain pure amorphous UO3, the mixtures were hydrated in water or in steam and then dehydrated. During hydration, the surface area decreased and the decrease continued during subsequent calcination, to give a final surface area between 3 and 5 m.2/g.
IMRI,!? et al.-SEDIMENTATION ANALYSIS OF UO, PARTICLES over the other repulsive and attractive forces between the particles. The adhesion of the deposit is then much greater than when it depends only on the London-van der Waals attractive forces between the original particles.The size distribution is determined of UO, particles with a specific surface area of 1 to 6 m.2/g., prepared from U,O, by reduction in hydrogen and calcined a t temperatures between 610" and 1000". Of the U,O, and UO,, 90% by wt. was within the particle size range 4 to 90 p. The narrowest spectrum 4 -5 6 p-was found in the product of calcination a t 700" which was-in comparison with all the other samples-easiest to sinter. After being pressed at 2.5 tons/cm.2 and sintered at 1600" the pellets attained a density of 96% of the theoretical. The object of the work was to find a connexion between the physical, physico-chemical and sintering properties of UO,.
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