| 초록 |
Mullite interlocking needle-like microstructures offer an efficient filtering effect. The properties of such need-like microstructures include high thermal and chemical stability. However, mullite ceramics processed by ordinary sintering conditions yield alumina-rich and silica-rich phases in the grain boundaries which lead to degradation of mechanical properties. The aim of this study is to produce a needle-like mullite matrix with silica free grain boundaries using a two-step sintering procedure. Mullite composite samples were prepared from high purity Al(OH)3, SiO2, AlF3 and yttria stabilized ZrO2 powders by a two step sintering procedure between 900 ˚C and 1450 ˚C. Effect of ZrO2 on mechanical properties of mullite was explained in terms of SEM images of the fractured SEM microstructures and phases obtained on XRD patterns. Equi-axed needle-like microstructures with bending strengths of 10.8 MPa to 12.7 MPa were obtained in 5 wt% samples. However, irregular microstructures and bending strengths which ranged from 4.4 MPa to 8.7 MPa were obtained in 10 wt% and 15 wt% samples. At low sintering temperatures mullite and zircon were detected as the major phases, but with increase in sintering temperatures zirconia and mullite phases were dominant. Apparent porosities of up to 62% make these mullite-zirconia composites suitable candidates in filtering applications. |
