Effects of composition and temperature on porosity and pore size distribution of porous ceramics prepared from Al(OH)3 and kaolinite gangue

Porous corundum-mullite ceramics were made from Al(OH)3 and kaolinite gangue by the in situ decomposition pore-forming technique. The porosity of the sample increases with increasing Al(OH)3 content in the raw mixture of Al(OH)3 powder and kaolinite gangue. With increasing temperature from 1300 to 1500 °C the porosity of the sample changes a little because of mullite formation. However, when the sintering temperature increases from 1500 to 1600 °C the porosity decreases rapidly. The pores in the samples consist of two groups. One is composed of micropores with maximum diameter of 100 nm. This kind of pores are located in the pseudomorphs of Al(OH)3 and kaolinite gangue. They are derived from the decomposition of Al(OH)3 and kaolinite, and from burning of carbon and organic substance in the gangue. The other is composed of pores with maximum diameter of 1000 nm. They are located among the pseudomorphs of Al(OH)3 and kaolinite gangue. With increase of the Al(OH)3 content in the starting powder mixture the % volume of micropores (pore diameter 250 nm) increases, while it decreases with the increase of the sintering temperature.