«Production engineering of bulk nanomaterials and articles»
To manufacture bulk nanostructured ceramics from nanopowder it is necessary to prevent grain growth at consolidation. However, to achieve full density of nanostructured ceramics a lot of technology tasks have to be solved: application of nanoparticles with narrow size distribution, special approaches for compacting, sintering and densification of ceramics, etc.
Important stage of the nanoceramics production is powder compacting due to essential fabrication difficulties related to shaping of homogeneous non sintered compacts without gradients of density and stresses. The green compact homogeneity is a very important parameter that determines the possibility to avoid warping, pores and cracks at sintering, to reduce sintering temperatures and durations, and finally to preserve a homogenous nanoscale structure in the fully dense ceramics.
Conventional methods of dry powder compaction, being applied to nanopowders, encounter an obstacle due to high agglomeration forces as well as high interparticle and particle-die wall frictional forces. These features give rise to local density differences and internal stress gradients within the green body especially with complex shape followed by differences in the local sintering rates and differential shrinkage, and eventually, to the ceramics warping. The uniform compaction of nanopowders especially via dry compaction is yet a challenge. It is known to use the liquid-based techniques to overcome the mentioned difficulties, but this approach includes application of many chemicals agents during the powder processing which make these techniques non-friendly to the environment and can contaminate the final product or cause the residual porosity due to burning-out. The course examines aspects of developed the techniques allowing uniform dry packing of powders into green compacts having complex shapes. These green compacts were characterized by homogeneous microstructure and density. This was achieved by application of different physically action (powerful ultrasonic, spark-plasma, etc.) on the nanopowders during the compaction.