Nanosintering
Nanosintering is the sintering of nanometer size powders. For certain nanomaterial applications, sintering of powders while retaining grain sizes in the nanometer range becomes a critical processing step. Fully dense specimens with nanosize features are most important for structural, magnetic, electric or electronic applications.
The focus in the consolidation of out-of-equilibrium powders has been the retention of the metastable condition of the initial structures. The inevitable coarsening tendency and small specimen size produced by nanopowder densification generats at least some controversies on nanomaterial properties.
The sintering process of powder materials with particle in the nanometer range reveals thermodynamic and kinetic aspects of metastable powder densification, methods for full densification of metastable powders and their ability to maintain the metastability features. Specific features related to cold compaction, pore size, distribution, and their effects on sintering and grain coarsening, sintering mechanisms, and scaling laws are also applicable to nanopowder sintering.
Densification of out-of-equilibrium powders presents challenges related to the specific need to retain the metastability of initial microstructures in addition to usual pore elimination into a uniformly dense and sound part.
Studies of nanopowder densification have lead to a better understanding of numerous sintering issues such as powder agglomeration, surface condition or contamination, pore role in sintering and grain growth.
The resultant control of synthesis (e. g., non-agglomerated nanopowders) and processing has enabled fabrication of fully dense nanocrystalline parts particularly ceramic, even by conventional sintering.
Although some distinct differences in the densification of nano- versus micron-grained powders seem to emerge and a better understanding of nanosintering has been accomplished, the specific effect of densification variables on final density and properties of nanomaterials is still an area of fruitful future research.
More fundamentally, there is a tremendous need for specific materials data in the nanoregime, such as diffusion coefficients and surface energies.
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