The behaviour of zinc stearate (0-4 W/o) during blending with $UO_2$ powder has been studied by monitoring changes of apparent density. Apparent density increased by the development of thin surface films on the $UO_2$ particles at low Zinc stearate contents but decreased by the formation of thick layers and free Zinc stearate at high contents.
Pressure/density data were obtained from double acting compaction of cylindrical $UO_2$ green pellets containing admixed zinc stearate with and without die-wall lubrication to determine the relative significance of interparticle friction, particle/die-wall friction and compaction inhibition. Compaction pressure losses associated with interparticle friction were lower than those caused by die-wall lubrication which also caused undesirable compaction inhibition.
The influence of admixed zinc stearate on the sintered density, shrinkage and microstructure after sintering of $UO_2$ pellets has also been studied. The sintered density and shrinkage decreased with increasing lubricant contents. Many larger pores were shown in the microstructure of sintered pellet with higher lubricant contents.