Subject polycrystalline powders

Refining of the particle size can be achieved by etching of bulk sample. For example, the nanosize zirconia powder doped with yttrium has been prepared by etching of yttrium containing polycrystalline BaZrOs or NaaZrOs [15]. Preliminary sintered ceramics of BaZrOs or Na2Zr03 doped with yttrium was subjected to hydrothermal treatment to eliminate the undesirable ions of Ba + or Na+ in nitric acid solution or supercritical water. The etching precipitate represents yttrium-stabilized zirconia nanopowder with particle size of 3-15 nm. 

The investigated polycrystalline AI2O3 sample was prepared from 99.6% pure alumina powder (Alcoa A16). The powder was first subjected to uniaxial press at 30 MPa, then isostatically pressed at 250 MPa and finaly sintered at 1600 °C for 3 h. After sintering, the sample surface was polished with 0.5 pm colloidal silica the final microstructure was found to be equiaxed and without appreciable crystallographic texture. 

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