Pore characteristics and phase compositions of porous corundum-mullite ceramics prepared from kaolinite gangue and Al(OH)₃ with different amount of CaCO₃ addition

Abstract

Porous corundum-mullite ceramics were prepared from Al(OH)₃ and kaolinite gangue with different CaCO₃ amount through an in-situ decomposition pore-forming technique. The effect of the amount of CaCO₃ added (ACA) on the phase compositions and pore characteristics was investigated through X-ray diffractometer (XRD), scanning electron microscopy (SEM), and mercury porosimetry measurements, etc. It’s interesting that the granular mullite crystals are in the Al(OH)₃ pseudomorphs but the needle-like mullite crystals are in the gangue pseudomorphs, and found that the ACA slightly affects the apparent porosity (AP), but strongly affects the formation of liquid phase, and then affects the secondary mullitization, microstructure, pore size distribution and crystal morphology. With an increase in ACA from 0 to 2.36 wt %, the increasing liquid phase make the rate of secondary mullitization increase markedly; when the ACA is 2.36 wt %, the secondary mullitization reaches the maximum; with a further increase of ACA to 3.54 wt %, the secondary mullitization decreases due to the formation of anorthite. With an increase in ACA from 0 to 3.54 wt %, the APs are in the range of 40.7–42.3%, whereas, the average pore size increases from 0.326 to 2.750 µm, and the crystal sizes of mullite in both pseudomorphs increase evidently.