Note on Correlation of Surface Characteristics of Uranium Dioxide Powders with Their Sintering Behavior

Abstract

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).

Some Preparative Methods and Physical Characteristics of Uranium Dioxide Powders.

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RANIUM dioxide has become of considerable importance as a nuclear fuel in the field of atomic power. Published data on the surface area, density, porosity, crystallite size, microstructure, and sinterability of this compound show wide variations (2,3,5,(17)(18)(19)23). Considerable evidence shows that characteristics of powders, such as uranium oxides, are determined largely by their preparative history.

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