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

Abstract

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 (PSx-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.

Fabrication of porous mullite‐based ceramic bricks from Al‐rich water treatment sludge and kaolinitic‐based clay

“…[36], primarily consists of quartz and muscovite. It has been reported that gibbsite (Al(OH) 3 ) undergoes thermal dehydration and phase transformation between 500 and 900°C to form ρ‐Al 2 O 3 37,38 . Other researchers have found that gibbsite could produce porous Al 2 O 3 during heating 38 .…”

“…Mullite (3Al 2 O 3 ·2SiO 2 ) was identified as a significant crystalline phase and cristobalite as a minor crystalline phase. The intensity of the cristobalite is expected to reduce with the rise in sintering temperature 38 . Lithomargic clay‐WTS mixtures had sharper and well‐defined mullite peaks than WTS‐kaolin clay bricks.…”

“…The intensity of the cristobalite is expected to reduce with the rise in sintering temperature. 38 Lithomargic clay-WTS mixtures had sharper and well-defined mullite peaks than WTS-kaolin clay bricks. As mentioned, lithomargic clay consists of kaolinite and gibbsite phases.…”

“…It has been reported that gibbsite (Al(OH) 3 ) undergoes thermal dehydration and phase transformation between 500 and 900 • C to form ρ-Al 2 O 3 . 37,38 Other researchers have found that gibbsite could produce porous Al 2 O 3 during heating. 38 The structure of the porous Al 2 O 3 depends on the initial particle size of Al(OH) 3 .…”

“…37,38 Other researchers have found that gibbsite could produce porous Al 2 O 3 during heating. 38 The structure of the porous Al 2 O 3 depends on the initial particle size of Al(OH) 3 . The increase in porosity with increased WTS is therefore expected.…”