Ceramic foams with open‐cell structures have attracted extensive attention due to their unique structure and superior properties. But these materials often exhibit the weakness of high sintered shrinkage and low strength at high porosity levels. In this work, novel ceramic foams with open‐cell structures have been obtained using Al powder by combining direct foaming and gelation freezing (DF–GF). The foams are assembled by hollow Al2O3 particles resulting from the Kirkendall effect, in which expanded particles overcome the shrinkage of sintering. The influence of sintering temperature on the microstructure and properties of foams are investigated. The Al2O3 foams show near‐zero‐shrinkage at 1773 K after undergoing the process of first expansion and then shrinkage. Compared to other conventional open‐cell foam, this foam displays relatively high compressive strength of 0.35–2.19 MPa at high porosity levels of 89.45%–94.45%, attributed to hierarchical pore structure and reaction bonding between Al and O2. This method from pore structure design provides a novel route for the preparation of controlled shrinkage and high‐compressive strength alumina foam with open‐cell toward potential application.

The brittleness of Si3N4 ceramics has always limited its wide application. In this paper, Si3N4 ceramics were prepared based on foam. Combining the unique honeycomb structure of the ceramic foams and the self‐toughening mechanism of Si3N4, the strengthening and toughening of Si3N4 ceramics can be further achieved by adjusting the microstructure of Si3N4 ceramic foams. The powder particles are self‐assembled by particle‐stabilized foaming to form a foam body with a honeycomb structure. It was pretreated at different temperatures (1450–1750°C). The microstructure evolution of foamed ceramics at different pretreatment temperatures and the conversion rate of α‐Si3N4 to β‐Si3N4 at different pretreatment temperatures were explored. Then the foamed ceramics with different microstructures are hot‐press sintered to prepare Si3N4 dense ceramics. The effects of different microstructures of foamed ceramics on the strength and toughness of Si3N4 ceramics were analyzed. The experimental results show that the relative density of Si3N4 ceramics prepared at a particle pretreatment temperature of 1500°C is 97.8%, and its flexural strength and fracture toughness are relatively the highest, which are 1089 ± 60 MPa and 12.9 ± 1.3 MPa m1/2, respectively. Compared with the traditional powder hot‐pressing sintering, the improvement is 21% and 33%, respectively. It is shown that this method of preparing Si3N4 ceramics based on foam has the potential to strengthen and toughen Si3N4 ceramics.

The growth of SiC nanowires (SiCNWs) plays a vital role that determines the microstructure and the dielectric and absorption properties. With SiCNW growth, regulating the growth space and atmosphere of the nanowire is an important method to determine its performance. In this article, we propose a novel approach to control the microstructure of SiCNWs. The SiC precursor prepares the high-porosity foams based on a particle-stablized foaming process. The growth and microstructure of SiCNWs are adjusted by controlling porosity and reaction conditions. Adjusting the foam porosity indirectly coordinates the atmosphere of individual pores and the growth space of the SiCNW mesh. Foam pore structure density and the reactive sintering temperature enable control over SiCNW mesh growth composition. The influence of the microstructure on dielectric and absorption properties of nanowires was studied. The SiCNW mesh composites exhibit a favorable electromagnetic absorption performance, and the minimum reflection loss (RL) is −19.1 dB. The effective bandwidth (RL < −5 dB) of the SiCNW mesh in the thickness range of 2.40–2.58 mm can cover the whole X-band. This provides a potential new direction in the investigation of absorption materials.

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