Processing and Characterisation of Porous Mullite Via Synthetic Template Replica Method

Abstract

Porous Mullite ceramics finds numerous advanced engineering applications including aerospace, molten metal filtration, catalysis, refractory insulation, and hot gas filtration. The application of mullite for this purpose requires inclusion of continuous and homogeneous macro porosity with sufficient strength to withstand mechanical impacts and loads. Mullite is used as material due to its properties-such as low thermal expansion, high thermal shock resistance, and high creep resistance as well as excellent chemical inertness. In this work the porous mullite samples have been prepared using silicic acid (SiO2 .xH2O) and boehmite (AlO(OH)) as precursors. Solgel slurry was prepared with the addition of poly-vinyl alcohol (PVA 2 wt %) to follow the ‘sacrificial template method’ for the achievement of a regular shape. A polyurethane foam (PU) of 0.04 gm /cc density was used for this purpose. Batches were produced with different solid loading varying from 22.5 to 30 wt/wt% of powder and sintered at temperatures 1500-1600oC. The phase of synthesized shape was analysed by using the conventional X-Ray Diffraction technique (XRD) using K-α radiation (powder method).The presence of mullite as a desired phase was confirmed by XRD analysis. The morphology and microstructure of the samples were studied under field emission Scanning electron microscope (FE-SEM). From the observation of microscopy, the pore size and grain has been reported. Under the microstructure study mullite grains were observed along with both macro and micro pores. The physical properties like apparent porosity (A.P.), bulk density (B.D.), volumetric shrinkage (ΔV/V, %) relative density was measured by following the well-established method as applicable to specific experiment. Cold crushing Strength (C.C.S.) of all samples was also measured and the arithmetic average value has been reported. The apparent porosity of samples decreased as a function of solid loading from 22.5% to 30% sintered at two different temperatures (1500oC and 1600oC). The bulk density increased from 1.3 to 2 gm/cc for the samples with increasing solid content in the slurry. The Crushing strength increased from 1.7 MPa to 5.2 MPa as the solid content was increased from 22.5 to 30% for 1500oC and 2.8 MPa to 7.2 MPa for 1600oC.