Ultrastrong Hierarchical Porous Materials via Colloidal Assembly and Oxidation of Metal Particles

Abstract

Porous materials are useful as lightweight structures, bone substitutes, and thermal insulators, but exhibit poor mechanical properties compared to their dense counterparts. Biological materials such as bone and bamboo are able to circumvent this trade‐off between porosity and mechanical performance by combining pores at multiple length scales. Inspired by these biological architectures, a manufacturing platform that allows for the fabrication of Al2O3 foams and Al2O3/Al composites with hierarchical porosity and enhanced mechanical properties is developed. Macroscale pores are formed through the assembly of aluminum particles around templating air bubbles in wet foams, whereas the thermal oxidation of the metal particles above 800 °C generates porosity at the micrometer scale. After elucidating the mechanism of pore formation under different sintering conditions at the microscale, the mechanical performance of the resulting hierarchical foams using compression experiments and finite element simulations is evaluated. Porous materials manufactured via this simple approach are found to reach unparalleled mechanical properties with near‐zero sintering shrinkage and minimum loss in mechanical strength. The ability to produce macroscopic objects with ultrahigh strength at porosities up to 95% makes this an attractive manufacturing technology for the fabrication of high‐performance lightweight structures or advanced thermal and acoustic insulators.

A Robust Hierarchical MXene/Ni/Aluminosilicate Glass Composite for High‐Performance Microwave Absorption

“…As shown in Figure 6 a , the zeolite derived AS glass has a compressive strength higher than 80 MPa, which is robust enough for most applications. The compressive strength is much better than many lightweight MACs [ 33 , 34 ] and even some porous ceramics, [ 35 ] considering the high porosity in the AS glass. The addition of Ti 3 C 2 T x nanosheets and Ni NPs seems to have no obvious influence on the compressive strength, indicating the load bearing capacity under compression is mainly determined by the porosity rather than microstructures.…”

Additive Manufacturing of Resilient SiC Nanowire Aerogels

“…Additive manufacturing, also referred to as three-dimensional (3D) printing, shines light on the fabrication of aerogels with fairly complex macroscopic and microscopic structures. − 3D printing can build materials with designed structures with high precision and high speed, which thus provides convenience in customizing the macroscopic geometries and microstructure of aerogels. − Direct ink writing (DIW) is an extrusion-based 3D printing method that can be used to fabricate both closed and open porous structures with pore size precision ranging from millimeter to micrometer scales. − Through modification of the inks with different materials, polyurethane, graphene, − and silica aerogels , with modified mechanical properties and functions have been printed. For example, through the organization of hierarchical load-bearing networks constructed by emulsified/foamed ceramic inks, the mechanical efficiency of the porous structures can also be enhanced even at high porosities of 94% .…”

Porous ceramics with near‐zero shrinkage and low thermal conductivity from hazardous secondary aluminum dross

“…As heating reaches up to 800℃, the relative content of metallic Al and AlN decreases but remains to the main phase, while that of α‐Al 2 O 3 as well as MgAl 2 O 4 increases, indicating the oxidation of metallic Al and AlN to generate α‐Al 2 O 3 , according to Equations (2)–(4) during Stage II. Owing to the density difference between Al of 2.70 g/cm 3 , AlN of 3.26 g/cm 3 , and Al 2 O 3 of 3.98 g/cm 3 , volume expansion of 28% and 1.89% could appear 55,56 . When the temperature continues to rise to 1000℃, α‐Al 2 O 3 and MgAl 2 O 4 are dominant, leaving very little amount of metallic AlN and Al, which have not completely reacted with oxygen.…”

“…As heating reaches up to 800°C, the relative content of metallic Al and AlN decreases but remains to the main phase, while that of α- 3 , and Al 2 O 3 of 3.98 g/cm 3 , volume expansion of 28% and 1.89% could appear. 55,56 When the temperature continues to rise to 1000°C, α-Al 2 O 3 and MgAl 2 O 4 are dominant, leaving very little amount of metallic AlN and Al, which have not completely reacted with oxygen. There are two endothermic peaks at 570°C and 1015°C, which may result from the generation of N 2 and NO.…”