HE evaiuation of the sinterability* of UOZ powders is complicated by variations in surface structure and particle size. An T evaluation of the surface characteristics of several UQ powders showed that (1) UOt powders from various sources have a wide variety of surface characteristics, (2) surface-area values measure the combined effects of both particle size and surface texture, and ( 3 ) the surface area and average diameter of UOn powders can be used as a measure of sinterability.* Density change during sintering.Mallinckrodt PU'R-grade and ceramic-grade UOZ powders and Hanford-depleted UO, powder were investigated. Carbon replicas of these powders were obtained, using techniques described by Marriott.' Average diameters were determined with a Fisher subsieve sizer, and surface areas by the Brunauer-Emmett-Teller2 nitrogen gas adsorption method. The UOn powders were compacted a t 15 tons per sq. in. into pellets 0.600 in. in diameter and about 1 in. in height and then sintered for 8 hours a t 1750°C. The per cent change in density during sintering was used as a measure of sinterability.The relations established between sinterability and surfacearea and average particle-size determinations are plotted in Figs. 1 and 2 and emphasize the requirement of both these determi-I J. Marriott, "Replica Technique for Particle Surfaces," Stephen Brunauer, P. H. Emmett, and Edward Teller, "Adsorption of Gases in Multimolecular Layers." J . A m . Chem. Brit J . APPl. Phys., 7 [lo] 373-74 (1956).SOC., 60,309-319 (1938).

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