Fabrication and properties of porous anorthite/mullite ceramics with both high porosity and high strength

Abstract

Porous anorthite/mullite ceramics with both high porosity and high strength have been successfully fabricated by foam-gelcasting and pressureless sintering technology, using α-Al 2 O 3 , SiO 2 , and CaCO 3 as starting materials and MnO 2 as sintering aids. The porous mullite ceramics prepared in this study had 83.3% porosity and 0.3 W/m·K thermal conductivity, exhibited compressive strength value as high as 6.1 MPa. The samples fabricated with mullite content of 30 mol% possessed 79.4% porosity and 5.9 MPa compressive strength showed thermal conductivity as low as 0.19 W/m·K. With the addition of MnO 2 , the properties of the prepared materials varied slightly when mullite content changed in a large scale. The results showed that the addition of MnO 2 promoted the reaction, affected sintering and grain growth, and contributed to high strength and low-thermal conductivity. K E Y W O R D Sanorthite, compressive strength, mullite, porosity, porous ceramics

Microstructure and properties of porous anorthite/mullite whiskers ceramics with high porosity

“…The reagents used in this method and the whole process for preparing the green bodies by this method were similar as those in our other studies. 7,11,12 The detailed process was not described here. The difference was the mullite whiskers were predispersed in anhydrous alcohol by a mechanical stirrer for 30 minutes and dried before being mixed with other ceramic powders to prepare slurry.…”

“…This result was very different from the phenomenon reported in previous study. 11 When porous anorthite/mullite ceramics were prepared by an in situ synthesis method, mullite content had obvious effect on the porosity (78.6%-83.3%) of the samples which mainly due to the effects on sintering shrinkage. 11 Compared with the trend of porosity, the change in bulk density was relatively obvious.…”

“…11 When porous anorthite/mullite ceramics were prepared by an in situ synthesis method, mullite content had obvious effect on the porosity (78.6%-83.3%) of the samples which mainly due to the effects on sintering shrinkage. 11 Compared with the trend of porosity, the change in bulk density was relatively obvious. With the increase in mullite whiskers content from 0 to 60 mol%, the bulk density enlarged from 0.23 ± 0.004 g/cm 3 to 0.27 ± 0.004 g/cm 3 .…”

“…The addition reinforced materials were usually adopted to improving strength. [9][10][11] Compared with mullite particles, mullite whiskers (mullite w ) showed better reinforcement effect and have been successfully used in many porous ceramics. [12][13][14][15] For example, porous Al 2 TiO 5 ceramics reinforced by in situ formation of mullite whiskers has been prepared by Xu et al 13 and the results showed that the interlocking structure formed in the pores of the prepared materials was beneficial to improve the strength.…”

“…And the more mullite was added, the more thermal conductivity increases. 11,21 In our previous work, when mullite w were used to prepare porous composite ceramics, the effects of mullite w content were relatively weak, 12 but the relevant mechanism was not clear and worth further discussion. Yi et al 15 thought the staggered whisker network structure formed between mullite microspheres refined the pore size, reduced the thermal conductivity, and enhanced the thermal insulation properties.…”