Synthesis of yttria nanopowders for transparent yttria ceramics

This paper describes a precipitation process for synthesizing nanocrystalline yttria powder and sintering transparent yttria ceramics. Hydroxide precursor of Y2O3 with an approximate composition of Y2(OH)5NO3 · H2O was synthesized by using ammonia water as precipitant and yttrium nitrate as the starting salt. Employing appropriate striking method and optimum synthetic conditions, yttrium hydroxide with a card-house or spherical structure can be formed. It was found that normal striking derived powders have higher sinterability than reverse striking derived powders. The addition of a small amount of ammonia sulfate in the yttrium nitrate solution reduces the agglomeration and particle size of the produced yttria powders. Nanocrystalline yttria powders (60 nm in average size) was obtained by calcining the precursor at 1100 °C for 4 h. Transparent yttria ceramics were fabricated from the nano Y2O3 powders by vacuum sintering at 1700 °C for 4 h. In the wavelength of 1000 nm, the in-line transmittance reaches 52%.