FOAM-GELCASTING PREPARATION OF Zr Si O₄ MODIFIED POROUS MULLITE CERAMICS

ZrSiO 4 modified mullite-based porous ceramics were fabricated at 1400 C by using a foam-gelcasting method from industrial grade powder materials. Except for mullite and ZrSiO 4 no other phases were identified in the fired samples added with ZrSiO 4 , implying that at the firing temperature, ZrSiO 4 neither decomposed, nor reacted with mullite. In the microstructures of these samples, mullite/ZrSiO 4 grains were evenly distributed, and the overall pore sizes were reduced. The addition of ZrSiO 4 showed little effect on porosity and bulk density of fired samples, which were respectively around 77 % and 0.7 gcm -3 . However, it led to the enhanced mechanical strength, and more importantly, the reduced thermal conductivity, especially at high temperatures. When 8 wt. % ZrSiO 4 was added, flexural and compressive strengths increased respectively to 3.63 and 7.35 MPa, whereas thermal conductivity at 200 and 1000 C was reduced to 0.160 and 0.277 Wm -1 K -1 , respectively, which was mainly attributed to the shading effect, decreased size of "large" spherical pores, and more centralized and homogenized pore size distribution.