ADHESION OF NANOPARTICLES WITHIN SPRAY-DRIED AGGLOMERATES

20-mu-m diameter spray-dried agglomerates made up of 21 0 nm zirconia particles have been individually tested by crushing between rigid plates using a modified nanoindenter. The results show that the agglomerates support considerable stress before deforming. Both the elastic and plastic deformations of the agglomerates have been observed, followed by ultimate failure through a cracking mechanism. A model has been proposed to account for the results based on van der Waals adhesion between particles within the agglomerate. This model has been realized in a macroscopic agglomerate of smooth adhesive rubber beads. The test method could distinguish variations in the properties of individual agglomerates in a batch, and could detect differences between batches made under different spray-drier conditions. Powders with weaker agglomerates were shown to give improved ceramics as a result of easier particle dispersion during mixing.