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Sixth generation (6G) wireless networks operating in terahertz frequency region are significant solutions to the increasing number of telecommunication devices and the demand for faster data transmission. However, few dielectric materials exhibiting an ultralow relative dielectric constant (εr), loss tangent (tanδ), and high mechanical strength are found suited for 6G telecommunication. In this study, we developed lightweight ceramic foams by directly sintering glass hollow spheres. The effects of sintering temperatures on their mechanical performance, and terahertz optical and dielectric properties were systematically investigated. The final compositions of ceramic foams contain glass, cristobalite, quartz, and wollastonite. The crystalline content increases with increasing sintering temperature. The ceramic foams sintered at low temperatures of 700–850°C exhibit a high porosity ranging from 74.6% to 87.3%, ultralow εr ranging from 1.41 to 1.83, and tanδ of ∼0.011 at 0.5 THz, as well as high compressive strength ranging from 10.1 to 27.4 MPa, which could be promising materials for 6G telecommunication. [ABSTRACT FROM AUTHOR]

The weak compressive strength of dried ceramic foams is a disadvantage of fabricating ultralight ceramic foams, especially for the ceramic foams with porosity exceeding 95%. In this study, dried alumina foams were enhanced by agar and PVA-freezing-thawing using sodium dodecyl sulfate as surfactant. It is found that the two additives have no negative influence on adsorption of sodium dodecyl sulfate on alumina particles as well as the hydrophobic character of alumina particles. Stable alumina particle-stabilized foams were prepared with less than 0.5 wt% agar and 1.0 wt% PVA. High additive concentration above the critical values weakens stability of wet foams, which is probably due to the aggregate of alumina particles caused by long-chain molecules connecting. The compressive strength of dried alumina foams has a significant improvement with the employment of agar and PVA-freezing-thawing. The dried foams prepared with 1wt% PVA assisted by freezing-thawing has porosity of 97.1% and compressive strength of 0.16 MPa, which could maintain integrity of dried foams without destruction in the fabricating process. [ABSTRACT FROM AUTHOR]

Ultralight ceramics with striking mechanical properties and improved pore connectivity could have wide applications in areas ranging from catalyst support to hot gas filtration. However, creating such materials has proven to be a challenging target. This work demonstrated a novel methodology to prepare porous MgAl 2 O 4 ceramics by calcining gelled MgO–Al 2 O 3 –SiO 2 particle-stabilized foams. The striking green strength of dried foams can be achieved as a consequence of MgO hydration and subsequent formation of gelled Mg(OH) 2 and MgO–SiO 2 –H 2 O skeleton. The decomposition of colloidal substance at elevated temperature resulted in the formation of small pores on the cell wall, thus forming the hierarchical porous architecture and improving the pore connectivity. The highly porous MgAl 2 O 4 ceramics fired at 1600°C possessed the integrated properties of ultrahigh porosity (87.0%), improved pore connectivity and satisfactory compressive strength (7.93 MPa), showing great potential to be used in multiple industrial fields. [ABSTRACT FROM AUTHOR]