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Carbon foams with channel like pores have been prepared by pyrolysis of a thermosetting resin system; bismaleimide (BMI) modified allyl novolac (BAN) as carbon precursor and polyvinyl acetyl fibers (PVAF) as an organic sacrificial template. For improving the cross-linking density and glass transition temperature, dicumyl peroxide (DCP) was chosen as a curing initiator and compared the results with that of the most commonly used Hexamethylenetetramine (HTMA). After pyrolysis at 1000 °C, the resulting PVAF/HTMA/BAN carbon foam developed excessive voids with linear lengths and widths up to 3 and 0.25 mm respectively. Excessive bubbling of discrete self-curable BMI resin molecular chains surrounded by phenolic hydroxyl groups created such excessive voids and gaps. The PVAF/DCP/BAN carbon foam exhibited no such voids and the shape of the pores replicated the shape of PVAF template. Channel like pores were orientated at random with a non-cylindrical, flat, or kidney bean shape cross section with a maximum dimension of 25–50 μm. Moreover, general characteristics were studied including density, porosity, open cell, pore-size distribution, thermal conductivity and flexural strength. Results have showed that the PVAF/DCP/BAN carbon foam possessed improved properties including density, thermal conductivity and flexural strength of 0.53 g cm −3 , 0.87 W m −1 K −1 and 19.12 MPa respectively. [ABSTRACT FROM AUTHOR]

A two-step process has been developed for silicon carbide (SiC) coated polyurethane mimetic SiC preform containing silicon nitride (Si 3 N 4 ) whiskers. SiC/Si 3 N 4 preforms were prepared by pyrolysis/siliconization treatment at 1600 °C, of powder compacts containing rigid polyurethane, novolac and Si, forming a porous body with in situ grown Si 3 N 4 whiskers. The properties were controlled by varying Si/C mole ratios such as 1–2.5. After densification using a chemical vapour infiltration, the resulting SiC/Si 3 N 4 /SiC composites showed excellent oxidation resistance, thermal conductivity of 4.32–6.62 Wm −1 K −1 , ablation rate of 2.38 × 10 −3 − 3.24 × 10 −3 g cm −2 s and a flexural strength 43.12–55.33 MPa for a final density of 1.39–1.62 gcm −3 . The presence of a Si 3 N 4 phase reduced the thermal expansion mismatch resulting in relatively small cracks and well-bonded layers even after ablation testing. This innovative two-step processing can provide opportunities for expanded design for using SiC/Si 3 N 4 /SiC composites being lightweight, inexpensive, homogeneous and isotropic for various high temperature applications. [ABSTRACT FROM AUTHOR]

A lightweight carbon foam, with a density of 0.57 g/cm 3 , was prepared from powdered precursors containing waste rigid-polyurethane (RPU), novolac resin and coal-tar pitch. The waste RPU being 50 wt.% was used as a major pore former bonded by novolac resin (33 wt.%) and pitch (17 wt.%). A variant of this process utilized waste-resole resin of prepreg manufacturing plant in place of the novolac resin. These mixtures subsequently underwent molding, curing and carbonization without using any protective gas. Both types of carbon foams were described in terms of porosity, thermal and mechanical properties, but the investigations mainly focused on ablation testing, post-ablation morphology and back-face temperature. Overall, both types of specimens showed improved properties whereas the short-carbon fibers in the resole resin reflected in a higher porosity of 71.87%, improved compressive strength of 26.79 MPa and a lower erosion rate of 0.164 mm/s. During the fire-test, the specimen did not burn and remained colder at the other end. Very encouraging results were obtained in terms of surface insulation capacity as reflected in a very low back-face temperature. During carbonization, the pyrolyzing gases were rich in N 2 and covering under coke-breeze eliminated the use of any external inert gas. [ABSTRACT FROM AUTHOR]

Electromagnetic interference (EMI) shielding effectiveness of the carbon foam containing different amounts of silicon carbide nanowires (SiC NWs) was determined over X-band (8.2–12.4 GHz). Carbon foam was prepared from powdered precursors containing polyurethane, novolac and pitch. In situ SiC NWs were grown inside the porous body by using different weight ratios of silicon powder ranging from zero to 20 wt% and pyrolyzing at 1500 °C under argon atmosphere. Decorated nanowires led to a different cellular structure compared to pristine carbon foam and improved the absorptivity of EM radiations due to a very high level of dielectric loss (loss tangent of 3.1 at 12.4 GHz). A maximum EMI specific shielding effectiveness of ~79.50 dB cm 3 /g (at 8.2 GHz) was achieved in the carbon foam containing the highest amount of SiC NWs, which was more than two times higher than that of the pristine carbon foam. Presence of NWs with stacking faults, heterostructure interfaces and long tortuous paths in the carbon foam caused a strong dielectric loss and induced higher dielectric permittivity. The study shows that by controlling the amount of SiC NWs, it is possible to improve multiple properties while achieving lightweight material for stealth technology. [ABSTRACT FROM AUTHOR]

A novel method for the processing of carbon foam has been developed by using a powder mixture containing polyurethane foam and novolac resin hereafter called PN. Various additives like Si, Al, FeCl 3 , activated carbon (AC), short-carbon fibers (SCF) were mixed individually or in combination, carbonized under coal and analyzed for density, microstructure and compressive strength. The pore morphology changed significantly by using different kinds of additives. SCFs were effectively mixed and bonded within the pore walls. Si converted in situ into silicon carbide and a jungle of kinked and twisted nanowires all around the pores. CNTs with amorphous carbon beads were observed throughout the pore surfaces when 10 wt% FeCl 3 was added. Al increased the compressive strength when used upto 6 wt%. [ABSTRACT FROM AUTHOR]

Microwave absorption materials (MAMs) play a crucial role in mitigating electromagnetic pollution and enhancing communication technology. MXenes, a family of two-dimensional materials, have emerged as promising candidates for MAMs due to their unique layered structure, large surface area, abundant defects, and high electrical conductivity. However, the poor impedance matching of MXene poses a challenge for effective absorption. This review comprehensively discusses strategies for optimizing MXene-based MAMs through microstructure and macrostructure design. In two-dimensional microstructures, strong absorption is primarily achieved by self-transformation MXene and introducing other components to expand layer spacing and enhance dielectric/magnetic losses. In 3D microstructures, MXene serves as a framework and additive to create diverse geometrical frameworks such as porous, hollow, and hierarchical structures, optimizing electromagnetic properties. Additionally, MXene-based aerogels, foams, and films developed through 3D macrostructural design offer greater flexibility for performance tuning and multifunctional design. Therefore, this review may provide guidance for the structural design of MXene-based MAMs. [Display omitted] [ABSTRACT FROM AUTHOR]

Highlights • The biomimetic films are prepared through replication of shark skin and SI-ATRP. • The biomimetic films have excellent superhydrophobicity. • The biomimetic films have self-healing property of superhydrophobicity. • Drag reduction rate of the biomimetic PDMS films surface can reach up to 21.7%. Abstract Nature has provided a lot of important inspirations for human beings to create artificial methods to mimic the excellent performance of biological systems. Based on the shark skin pattern microstructure, the low surface energy and stimuli-responsive behavior of the poly(2-perfluorooctylethyl methacrylate) (PFMA) brush, a biomimetic PDMS film with superhydrophobic, self-healing and drag reduction properties was prepared by first replication of shark skin surface on PDMS film, followed by treatment with surface-initiated atom transfer radical polymerization (SI-ATRP) of FMA. The PFMA brushes can self-assemble into different hierarchical structures in ethanol or DMF, which make the biomimetic PDMS films show different contact angles. Having been damaged by finger-wipe with and without water respectively, the water repellency of the biomimetic PDMS films decreased. However, the surfaces recovered superhydrophobic property just by immersing the destroyed PDMS films into DMF which is good solvent for PFMA. The SEM images and XPS results demonstrated the changes of structure and chemical compositions of the biomimetic PDMS films surface in damage and self-healing processes. Rotational viscometer result showed the drag reduction rate of the biomimetic PDMS films surface can reach up to 21.7%. This research is expected to supply a novel method of controlling polymer brushes' self-assembly to prepare superhydrophobic and self-healing films. [ABSTRACT FROM AUTHOR]