440 High Dense Mullite Ceramics at Low Temperature: Rheological and Sintering Control

Friday, November 6, 2009: 2:00 PM
Pancho Villa (Camino Real Hotel)
Jesus Rocha , Department of Chemistry, Guanajuato University, Guanajuato, Gto., Mexico
Satoshi Sugita , Department of Chemistry, Guanajuato University, Guanajuato, Gto., Mexico
Keizo Uematsu , Department of Materials Science and Technology, Nagaoka University of Technology, Nagaoka, Niigata
Usually, mullite shows abnormal grain growth above eutectic temperature (~1590°C), and its affects the mechanic properties of sintered products. Recently, yttria powder (Y2O3) was used as dopant in sintering of alumina and mullite, in order to reduce sintering temperature and to control grain growth of mullite and alumina ceramics.

To improve the densification behavior of the sintered ceramic compacts, it is necessary to achieve green bodies with uniform and sufficiently high green density. However, a hetero-flocculation occurs in yttria – mullite precursor slurry due to the difference of isoelectric points, and consequently flocculated suspensions produces defects in casted bodies.

In this work, rheologies of yttria – mullite water suspensions could be controlled adding ammonium polyacrylate dispersant. Effects of polyacrylate on rheology of suspensions were studied in 40 v/v % ceramic slurry with different concentration of dispersant, and stable Newtonian flow suspension could be prepared at 0.6 w/w % relation dispersant and solid.

Furthermore, effect of yttria on densification of mullite was investigated in the rage of 0 – 3 w/w % of yttria/mullite. The green bodies were obtained after slip casting of slurry. The conformed solids were dried.  Finally, high dense mullite ceramic bodies have been achieved at low temperature, finding optimum condition in which 1 w/w % yttria added sample was sintered at 1425°C for 3 hours, achieving the 99 % theoretical density.