The fabrication of porous mullite ceramics based on the different sizes of aluminum hydroxide

In this research, for studying the influence of size and heat treatment temperature of initial Al(OH) 3 on the physical properties of porous mullite ceramics, porous mullite ceramics were prepared by in situ reaction sintering of amorphous silica and treated Al(OH) 3 . The transition phases χ-Al 2 O 3 , к-Al 2 O 3 , and stable phase α-Al 2 O 3 can be obtained in turn when the treatment temperature of raw Al(OH) 3 is 500, 1000, and 1500°C, respectively. The coarser the raw Al(OH) 3 , the higher the strength of porous mullite ceramics. When the sintering temperature is 1500°C, the bending strengths of PS500-C, PS1000-C, and PS1500-C (PS x -C represents that the specimen was prepared by the coarse grade Al(OH) 3, which was previously treated at x °C) are 40.3 ± 2.1, 54.9 ± 5.2, and 64.8 ± 4.8 MPa, respectively. In addition, although the activated Al 2 O 3 can decrease the formation temperature (∼100°C) of porous mullite ceramics, the strength and density of porous mullite ceramics prepared by activated Al 2 O 3 will decrease at the same sintering temperature. It is believed that the increase of defects and pores during the phase transformation should be responsible for this phenomenon.