Due to their small particle size, light scattering in nanomaterials with particle sizes below ca. 40nm is very small. Therefore, new materials for optoceramics based on nanosized particles of zirconia, alumina-coated zirconia, alumina, and alumina doped with some additives are very promising. These materials were synthesized using the Karlsruhe Microwave Plasma Process [1,2]. The focus of this work is the synthesis and the characterization with respect to particle size and phase composition.
Zirconia based nanopowders with particle sizes below ca. 10nm crystallize in the cubic phase . In case of the bare zirconia particles, the monoclinic phase is observed for larger particles (>10nm). Coating the zirconia nanoparticles with alumina prevents mainly the formation of the monoclinic zirconia phase. The alumina coating is amorphous. Similar like the alumina coating, alumina nanoparticles are amorphous; sometimes, small amounts of the cubic gamma-phase are observed.
Alumina nanoparticles were doped with chromia, ferric ironoxide and magnesia in concentrations up to about 6mol-%. Magnesia and chromia exhibited no influence on phase formation and color of the alumina powders. Additions of ferric ironoxide lead to a slightly yellow coloring of the alumina powders. Amounts larger than 6mol-% ferric ironoxide seem to favor the formation of the cubic gamma-phase.
Greenbodys from these nanopowders are translucent or transparent. Additionally, the transformation temperature to the stable alpha-phase of alumina can be reduced significantly by dopants .
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