In-situ growth of mullite whiskers and their effect on the microstructure and properties of porous mullite ceramics with an open/closed pore structure

Open-cell mullite ceramic foams derived from porous geopolymer precursors with tailored porosity

“…However, the amount of the sillimanite phase is too small to be detected by the XRD. Figure 10(j) reports the measured EDS profile of the mullite; it shows the presence and contents of Si, O, Al, Fe, and Ti elements [108,109], which is consistent with the chemical composition of the raw materials. It should be noted that no Na was found in the sample, indicating that the ion-exchange process was successful.…”

Low sintering shrinkage porous mullite ceramics with high strength and low thermal conductivity via foam‐gelcasting

“…Figure 7(F) shows a highresolution image of the mullite whisker with a lattice stripe spacing of 0.289 nm, which corresponds to the (001) crystal plane of mullite, indicating that the whisker grows along the [001] direction, which is consistent with other reported results. 29,31,33 Figure 8 shows the transmission electron micrographs of the pore wall structure of porous ceramics with 30 wt% AlF 3 content. As can be seen in Figure 8(A), the porous ceramic pore wall shows a clear grain morphology, and three different regions can be seen by EDS surface scanning: region A, which is rich in Al, O, and Si; region B, which does not contain Al but has a brighter contrast; and region C, which does not contain Al and has a darker contrast.…”

“…The thermal conductivity gradually decreases with increasing AlF 3 content, Comparison of the properties of porous mullite ceramics is listed in Table 2. 14,15,28,29,[38][39][40][41][42][43] It can be found that porous mullite ceramics prepared from sapphire with aluminum fluoride additives have relatively high porosity and have a low linear shrinkage rate. The compressive strength and thermal conductivity are not much different from those of other porous ceramics.…”

“…The researchers found that AlF 3 can be used as an additive that not only reacts with free silica to form alumina, which in turn continues to react to form mullite but also produces gaseous substances that catalyze the formation of mullite whiskers, achieving whisker enhancement and improving the performance of porous ceramics. [28][29][30][31][32][33] In this study, low sintering shrinkage porous mullite ceramics were prepared by the foam-gelcasting method using kyanite as raw material and AlF 3 as additive, through volume expansion from phase transition and gas generated from the reaction. The effects of AlF 3 addition on the shrinkage, phase composition, porosity, compressive strength, and thermal conductivity of porous mullite ceramics were investigated (if not specified, shrinkage in the text indicates sintering shrinkage).…”

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

“…Porous ceramics, including silicon carbide, corundum, titanate, and mullite, have been widely applied in many fields (gas/liquid filters, catalytic supports, heat insulation materials) due to their excellent properties, such as high-temperature resistance, corrosion resistance, and high-pressure resistance. [1][2][3][4] Among them, porous mullite has been considered as an exceptionally important material owing to its superior performance of low density, low thermal expansion coefficient, low thermal conductivity (3-6 W⋅m −1 ⋅K −1 ), excellent thermal shock resistance, and favorable mechanical properties [5][6][7][8] and has always attracted attention from researchers.…”