SUPER- AND QUASIPLASTICITY OF CERAMIC NANOCOMPOSITES IN CaO-MgO-ZrO_2 SYSTEM DERIVED FROM NATURAL DOLOMITE

摘要

Nano-grained CaO/MgO and related composites have been synthesized from the mixed carbonate mineral, dolomite, CaMg(CO_3)_2 by pyrolytic reactive sintering. Dense CaO/MgO in situ nanocomposite was produced by hot-pressing the pure dolomite powder. CaO and MgO mutually inhibited each other grain growth. Effects of LiF doping on decomposition and sintering of dolomite were studied. The LiF-doped dolomite decomposed in two steps, while the pure dolomite decomposed in almost one step. In addition, the lowering of the decomposition temperature was observed for the LiF-doped case. The CaO/MgO nanocomposite with a small amount of LiF showed superplastic-like deformation at high temperatures. A preliminary machining test revealed that the CaZrO_3/MgO in situ nanocomposite, which was synthesized from dolomite/zirconia mixed powder, was machinable at room temperature accompanying quasiplastic deformation.