Importance of stearates in the fabrication of uo₂ and (u, pu)o₂ pellets

Eighteen qualities of metallic soaps have been studied, either as lubricants or as additives for the fabrication of UO₂ and (U, Pu)O₂ pellets. Compounds of the same family, such as zinc stearates, differ in their effectiveness as lubricants. This property is strongly dependent on the particle size of the powder and its purity. The behaviour of the dry lubricants when used as admixtures in UO₂ and also when employed for the direct lubrication of the pelletizing tools is discussed. The efficiency of metallic soaps as additives to lower the density of the sintered pellets is related to the nature of the metallic ion. Thus, zinc stearate has little influence on the fired density of UO₂, whereas barium stearate and other barium compounds are very effective. Barium inhibits sintering, but zinc, which is eliminated at low temperature, does not diminish the sinterability of the oxide powders. In the latter case, the decrease in density is caused by thermal decomposition of the organic molecule.