STRUCTURES OF NANOCRYSTALLINE MGO, ZNO AND WO3 PREPARED BY GAS EVAPORATION AND IN-SITU COMPACTION

Nanocrystalline magnesium oxide (n-MgO), zinc oxide (n-ZnO) and tungst en oxide (n-WO3) were prepared by gas evaporation and successive in si tu compacting. Nanometer-sized amorphous aluminum oxide particles were also prepared by gas evaporation. The structures of the nanometer-siz ed particles and the nanocrystalline ceramics, and their sintering beh aviors were investigated by high-resolution transmission electron micr oscopy. It was found that the structural features of the as-compacted n-MgO, n-ZnO and n-WO3 are the same; they have similar porous structur es. These nanocrystalline ceramics were prepared by the bonding of nan ometer-sized grains at room temperature without neck growth. The sinte ring behavior in these ceramics is, however, different with respect to densification and neck growth. Substantial densification can be reali zed in n-ZnO by increasing the annealing temperature up to 800 degrees C. On the other hand, voids remained in n-MgO and n-WO3 after anneali ng at the same temperature. The process of neck growth in n-MgO and n- ZnO is different from that in n-WO3. No amorphous layer forms during t he annealing in n-MgO and n-ZnO, while amorphous necks form at 600 deg rees C and then crystallize at 800 degrees C in n-WO3.