화학공학소재연구정보센터
Journal of the American Ceramic Society, Vol.94, No.3, 938-944, 2011
Morphologically Textured Mullite in Sintered Tape-Cast Kaolin
A commercial Malaysian kaolin powder made into an aqueous slurry was cast into green tapes similar to 200 mu m in thickness using the doctor-blade technique. A kaolinite (001)(K(aolinite)) texture was found on the green tapes using X-ray diffractometry (XRD). Subsequent sintering at 1600 degrees C/1 h induces the preferred crystallographic orientations of (100)(M(ullite)), (110)(M), (120)(M), and (210)(M) in the mullite crystals thus formed by vitrification, as determined using electron backscatter diffraction. A nonunique orientation was observed on these crystals, suggesting that the texture is morphological with the c-axis, i.e., [001](M) lying parallel to the sample surface, rather than crystallographical. An additional preferred orientation on (100)(M), a forbidden reflection of the systematic absence from XRD is detected using pole figure. Kaolin is vitrified at 1600 degrees C into mullite when the texture is developed, and sintering is initially facilitated by an SiO(2)-Al(2)O(3) liquid formed at > 1260 degrees C, the eutectic temperature of metastable equilibrium. Further densification is promoted by additional particle rearrangement in an SiO(2)-mullite liquid formed at > 1587 degrees C, the stable equilibrium eutectic temperature. Alumina used as a substrate for the kaolin sintering does not play a significant role in developing the mullite morphological texture.