Permanent agglomerates in powdered nanoparticles: Formation and future prospects

In pace with the advancement in nanotechnology, different types of nanoparticles, have been largely produced and are now commercially available. Considering both transport and storage efficiencies, these nanoparticles are normally sold in powder form. Unfortunately, one of the major issues associated with nanopowders is that they tend to form hard agglomerates. These hard agglomerates are hardly segregated even external driving force (such as sonication) has been provided. Such kind of agglomerates is undesired as it reduces the surface area-to-volume ratio of the nanoparticles and thus limits their application performance. Formation of hard agglomerates has to do with the drying step, which is also the main step to convert nanosuspensions into dry powders. Thus, the present work aims to provide a comprehensive review of the occurrence and factors that lead to the hard agglomerates formation in nanopowders. In particular, the creation of interparticle necks upon sintering is reviewed. Approaches to avoid hard agglomerate formation; as well as dissolution of the interparticle necks are also considered here. Lastly, prospects of these nanopowders (if formation of hard agglomerates is unavoidable) in the future nano-research are discussed. (C) 2017 Elsevier B.V. All rights reserved.