Nanotozlardan kolloidal yöntemler ile yüksek yoğunluklu seramiklerin üretimi

Utilizing nanopowders in production of fully dense materials with fine grain structures is highly advantageous, particularly where high mechanical properties are desired. Besides, recently developed techniques, such as 3D-printing of ceramics, may require high solids content suspensions. Despite the advantages of slurry based processing of oxide ceramics, production of nano-structured high density bodies is still a challenge. The main limitation in colloidal processing of nanopowders is their unexpectedly high suspension viscosities. High viscosities restrict the maximum achievable solids content, which, in turn, limit the structural integrity and the density of a green body when consolidated. Furthermore, because of the smaller interparticle distance in highly loaded suspensions, nanopowders tend to agglomerate fast, which creates another challenge in terms of the homogeneous distribution of powders in their suspensions and in green bodies. In this thesis, various approaches for nanopowder suspension formulations were discussed and their effect on the particle packing, green body formation and sintering process were investigated. Suspensions with solids content up to 35-40 vol% were obtained. When these suspensions are slip casted, the green body densities as high as 58% could be obtained. When sintered, the structures with relative densities up to 96% could be achieved and that can be further increased to 99% using α-Al2O3 seed powder during sintering. As a result, high density alumina ceramics could successfully be fabricated from nanopowders.