Koichi Kikuta

Microstructural development of Si 3 N 4 –SiC–Y 2 O 3 ceramics derived from polymeric precursors

[Si–Y–O–C–N] amorphous powders were synthesized by the pyrolysis at 1000 °C in N 2 of chemically modified perhydropolysilazane using n-decyl alcohol and yttrium tri-methoxide. [Si–Y–O–C–N] amorphous powders yielded a unique fibrous microstructure by heat treatment in N 2 at 1800 °C. The fibrous microstructure was composed of β–Si 3 N 4 whiskers of submicron in diameter and more than 10 μm in length. Fully dense Si 3 N 4 –SiC–Y 2 O 3 ceramics were also fabricated by heat treatment at 1800 °C followed by powder-vehicle hot pressing at 1700 °C. After these two-step processings, [Si–Y–O–C–N] amorphous powders yielded a unique fine-grained microstructure composed of submicron grains with high aspect ratio.

Microstructure characterization of one-directionally oriented ulexite

Microstructures of ulexite were investigated by CTEM and low electron dose HREM. It was found that the longitudinal grains in ulexite were oriented to c -direction to form a bundle structure. There were a number of small-angle grain boundaries and stacking faults inside a grain in the ulexite. Cleavage microcracks and stacking faults were mostly introduced on the {010} of the ulexite. The high-angle grain boundaries mainly consisted of high coincidence boundaries, which was confirmed by a comparison of observed contact angles and calculated degree of coincidence at the boundaries. The light transmittance properties of the ulexite would depend on the defects such as stacking fault, small-angle grain boundary, and high-angle grain boundary.