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

Abstract

ZrSiO₄ 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 ZrSiO₄ no other phases were identified in the fired samples added with ZrSiO₄, implying that at the firing temperature, ZrSiO₄ neither decomposed, nor reacted with mullite. In the microstructures of these samples, mullite/ZrSiO₄ grains were evenly distributed, and the overall pore sizes were reduced. The addition of ZrSiO₄ showed little effect on porosity and bulk density of fired samples, which were respectively around 77% and 0.7g.cm-3. However, it led to the enhanced mechanical strength, and more importantly, the reduced thermal conductivity, especially at high temperatures. When 8 wt% ZrSiO₄ 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 W.m-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.

Keywords

• microstructure
• pore size distribution
• thermal conductivity
• mechanical property