The effects of pressure on the crushing strength of UAS pellets, produ
ced by a laboratory pressing machine were investigated. Physico-chemic
al properties of UAS pellets were studied by Electron Microscope (EMS)
, X-ray, Infra-Red Derivatography with a view to identifying the reaso
ns for improvement in physico-mechanical properties. It was proved tha
t there are some structural changes in UAS pellets due to application
of pressure and because of this a higher crushing strength could be ob
tained. As a result of pelletization the average crystallites size is
lower. Secondly, the main chemical groups are the same, but there are
some evidences that a new co-ordination between NH2 and SO4 structures
is occurring. So the higher crushing strength is due not only to the
mechanical compacting but also to the chemical co-ordination. The addi
tion of ZnO accelerates those changes.