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

Abstract

Excessive sintering shrinkage leads to severe deformation and cracking, affecting the microstructure and properties of porous ceramics. Therefore, reducing sintering shrinkage and achieving near‐net‐size forming is one of the effective ways to prepare high‐performance porous ceramics. Herein, low‐shrinkage porous mullite ceramics were prepared by foam‐gelcasting using kyanite as raw material and aluminum fluoride (AlF3) as additive, through volume expansion from phase transition and gas generated from the reaction. The effects of AlF3 content on the shrinkage, porosity, compressive strength, and thermal conductivity of mullite‐based porous ceramics were investigated. The results showed that with the increase of content, the sintering shrinkage decreased, the porosity increased, and mullite whiskers were produced. Porous mullite ceramics with 30 wt% AlF3 content exhibited a whisker structure with the lowest shrinkage of 3.5%, porosity of 85.2%, compressive strength of 3.06 ± 0.51 MPa, and thermal conductivity of 0.23 W/(m·K) at room temperature. The temperature difference between the front and back sides of the sample reached 710°C under high temperature fire resistance test. The low sintering shrinkage preparation process effectively reduces the subsequent processing cost, which is significant for the preparation of high‐performance porous ceramics.

Ultrastrong and High Thermal Insulating Porous High‐Entropy Ceramics up to 2000 °C

“…When the total porosity of 9PHEB samples is further tailored to ≈40% (specifically, 40.3% ± 2.2%, with a closed porosity of 29.0% ± 8.1%, Figure S5, Supporting Information), the mechanical strength increases up to 507 ± 35 MPa (Figure 4a; and Figure S6c,d, Supporting Information). As can be found in Figure 4c; and Table S3 (Supporting Information), the 9PHEB materials possess significantly higher mechanical strength compared to the reported porous ceramics, [ 3,15,8,30–53 ] demonstrating an exceptional load‐bearing capability. Therefore, the ultrahigh compressive strength achieved in our 9PHEB samples should benefit from the following reasons: First, as proved in Figure 2d–f, the samples are characterized by ultrafine pores at the microscale, which are firmly connected by abundant well‐sintered necks (with high‐quality and strong interface between grains at the nanoscale).…”

“…With the increase of temperature to 2000 °C (Figure 4d), the strength of the samples is slightly reduced (102 MPa at 10% strain and 692 MPa at 49% strain); additionally, the stress-strain curve becomes smoother (the zigzag has disappeared), demonstrating Weibull distribution regarding the compressive strength of tested samples at a porosity range of 45-55%. c) Strength versus porosity of the 9HEB samples compared to the reported porous ceramics, such as SiC, [3,15,[30][31][32][33] mullite, [34][35][36][37][38] Si 3 N 4 -SiC, [39] Si 3 N 4 , [40] Al 2 O 3 , [41] SiO 2 , [42,43] ZrB 2 -SiC, [44,45] 𝛾-Y 2 Si 2 O 7 , [46,47] ZrC, [48,50] ZrC-SiC, [49] HfC, [50] AlN, [51] SiOC, [52] Anorthite, [53] and ZrO 2 -Al 2 O 3 . [8] d) In situ compressive stress-strain curves of the samples at elevated temperatures.…”

“…b)Weibull distribution regarding the compressive strength of tested samples at a porosity range of 45-55%. c) Strength versus porosity of the 9HEB samples compared to the reported porous ceramics, such as SiC,[3,15,[30][31][32][33] mullite,[34][35][36][37][38] Si 3 N 4 -SiC,[39] Si 3 N 4 ,[40] Al 2 O 3 ,[41] SiO 2 ,[42,43] ZrB 2 -SiC,[44,45] 𝛾-Y 2 Si 2 O 7 ,[46,47] ZrC,[48,50] ZrC-SiC,[49] HfC,[50] AlN,[51] SiOC,[52] Anorthite,[53] and ZrO 2 -Al 2 O 3 [8]. d) In situ compressive stress-strain curves of the samples at elevated temperatures.…”

Manipulating mechanical properties of CaTiO3:Eu3+ flexible fiber membrane by fiber design

“…Compared to flexible organic and organic-inorganic composite functional materials, flexible inorganic functional materials have gained significant attention due to their exceptional properties, such as high melting point, low thermal conductivity, excellent chemical corrosion resistance, favorable electrical properties, and impressive wear resistance. [1][2][3][4][5][6][7][8] Currently, flexible inorganic functional materials can be broadly classified into three categories: one-dimensional (1D) materials, two-dimensional (2D) materials, and threedimensional (3D) materials. 1D materials, exemplified by fibers, are typically synthesized using hydrothermal methods.…”