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In this work, a facile microwave-assisted foaming and thermal imidization treatment method was proposed to fabricate flexible polyimide (PI)/rGO composite foams with anisotropic pore structures. The PI/rGO composite foams (PIF/rGO) were used as the starting derivatives to prepare carbon foams that demonstrated excellent anisotropic thermal insulation and electromagnetic interference (EMI) shielding applications. The directional growth of pore structures during the foaming period resulted in the formation of aligned ellipsoidal strip-like pore structure in the horizontal direction (i.e., perpendicular to the pore growth direction), which was attributed to the escape of foaming gases such as tetrahydrofuran, methanol and H 2 O. The homogeneous dispersion of rGO in the PI-derived carbon skeleton endowed corresponding carbon foams with excellent mechanical and thermal stability, high thermal insulation and electrical conductivity (σ) as well as absorption dominated EMI shielding performance. The σ and EMI shielding effectiveness (SE) of carbon foams showed an increasing trend with increasing rGO content. The σ, EMI SE and specific EMI SE of the carbon foams reached up to 33.0 S/m, 49.0 dB and 8792.8 dB/(g/cm2) in the horizontal direction, respectively. Therefore, this work provided a facile strategy to fabricate lightweight and anisotropic pore structure rGO-containing PIFs and carbonized derivatives, which demonstrated promising applications in high-end industrial fields. [Display omitted] • A facile strategy was proposed to prepare PIF/rGO and CF/rGO. • The directional growth of pores endowed foams with anisotropic properties. • The foams showed excellent mechanical and thermal insulation properties. • CF/rGO showed absorption-dominated EMI shielding performances. [ABSTRACT FROM AUTHOR]

Herein, five new La 2 Zr 2 O 7 based high-entropy ceramic materials, such as (La 0.2 Ce 0.2 Gd 0.2 Y 0.2 Er 0.2) 2 Zr 2 O 7 , (La 0.2 Ce 0.2 Gd 0.2 Er 0.2 Sm 0.2) 2 Zr 2 O 7 , (La 0.2 Gd 0.2 Y 0.2 Er 0.2 Sm 0.2) 2 Zr 2 O 7 , (La 0.2 Ce 0.2 Y 0.2 Er 0.2 Sm 0.2) 2 Zr 2 O 7 , (La 0.2 Ce 0.2 Gd 0.2 Y 0.2 Sm 0.2) 2 Zr 2 O 7), were synthesized using a sol-gel and high-temperature sintering (1000 °C) method. The spark plasma sintered (SPS) (La 0.2 Ce 0.2 Gd 0.2 Er 0.2 Sm 0.2) 2 Zr 2 O 7 pellet shows a low thermal conductivity of 1.33 W m-1 K-1 at 773 K, and it also exhibits better CaO–MgO–Al 2 O 3 –SiO 2 corrosion resistance than that of Y 2 O 3 stabilized ZrO 2. It shows that (La 0.2 Ce 0.2 Gd 0.2 Er 0.2 Sm 0.2) 2 Zr 2 O 7 has a promising application potential as a thermal barrier coating. [ABSTRACT FROM AUTHOR]

Flexible polyimide foams (PIFs) demonstrate a great potential for applications in the fields of thermal insulation, flame retardancy and irradiation tolerance. In this work, mechanically flexible PIFs with anisotropic pore structure were prepared by adopting the copolymerization strategy and microwave-assisted foaming process. The copolymerization reaction was conducted to synthesize polyester ammonium salt (PEAS) precursors using 3,3′,4,4′-benzophenone tetracarboxylic acid dianhydride (BTDA) as dianhydride, 4,4′-diaminodiphenyl ether (ODA) and 4,4′-diaminodiphenyl sulfone (DDS) as the copolymerized diamines; afterwards, PEAS powders with particle sizes ranging from 100 to 300 μm were obtained by drying, crushing and sieving treatments, which were used as the feedstock for "bottom-up" microwave-assisted foaming and thermal imidization process, thereby leading to the formation of PIFs with regular three-dimensional near-spherical pores in vertical direction (parallel to the pore growth direction) and the aligned ellipsoidal strip-like pore structure in horizontal direction. The directional growth of foam pores resulted in anisotropic mechanical flexibility and thermal insulation performance. Moreover, PIFs possessed excellent thermal stability and flame retardancy with the initial thermal degradation temperature higher than 545 °C and limited oxygen index up to 58.8%. The PIFs exhibited exceptional thermal insulation performance with thermal conductivity values ranging from 0.0276 to 0.0517 W/(m·K) between 25 and 300 °C. Additionally, the PIFs demonstrated excellent irradiation tolerance, with the mechanical and thermal stability retention rate being above 96% after the irradiation experiment (radiation dosage: 1.15 × 105 Gy) using 60Co source. Thus, lightweight PIFs with superior high temperature thermal insulation performance, flame retardancy and irradiation tolerance were successfully prepared, which showed potential applications in aerospace, medical and nuclear power sectors. [Display omitted] • PIFs were prepared by copolymerization and microwave-assisted foaming strategy. • The directional growth of foam pores endowed PIFs with anisotropic structure. • The mechanical and flame retardancy were enhanced by introducing DDS. • PIFs had excellent high temperature thermal insulation and irradiation tolerance. [ABSTRACT FROM AUTHOR]