Carbon fiber-reinforced carbon aerogel composites (C/CAs) for thermal insulators were prepared by copyrolysis of resorcinol-formaldehyde (RF) aerogels reinforced by oxidized polyacrylonitrile (PAN) fiber felts. The RF aerogel composites were obtained by impregnating PAN fiber felts with RF sols, then aging, ethanol exchanging, and drying at ambient pressure. Upon carbonization, the PAN fibers shrink with the RF aerogels, thus reducing the difference of shrinkage rates between the fiber reinforcements and the aerogel matrices, and resulting in C/CAs without any obvious cracks. The three point bend strength of the C/CAs is 7.1 ± 1.7 MPa, and the thermal conductivity is 0.328 W m(-1) K(-1) at 300 °C in air. These composites can be used as high-temperature thermal insulators (in inert atmospheres or vacuum) or supports for phase change materials in thermal protection system.

Boron nitride (BN) aerogels are porous materials with a continuous three-dimensional network structure. They are attracting increasing attention for a wide range of applications. Here, we report the template-assisted synthesis of BN aerogels by catalyst-free, low-pressure chemical vapor deposition on graphene-carbon nanotube composite aerogels using borazine as the B and N sources with a relatively low temperature of 900 °C. The three-dimensional structure of the BN aerogels was achieved through the structural design of carbon aerogel templates. The BN aerogels have an ultrahigh specific surface area, ultralow density, excellent oil absorbing ability, and high temperature oxidation resistance. The specific surface area of BN aerogels can reach up to 1051 m2 g−1, 2-3 times larger than the reported BN aerogels. The mass density can be as low as 0.6 mg cm−3, much lower than that of air. The BN aerogels exhibit high hydrophobic properties and can absorb up to 160 times their weight in oil. This is much higher than porous BN nanosheets reported previously. The BN aerogels can be restored for reuse after oil absorption simply by burning them in air. This is because of their high temperature oxidation resistance and suggests broad utility as water treatment tools.

No abstract

No abstract

No abstract

No abstract

Zirconium carbide (ZrC) was synthesized by solution‐based processing using versatile starting reagents including zirconium oxychloride octahydrate (ZrOCl2·8H2O, ZOC), acetylacetone (Hacac), and phenolic resin. Polyzirconoxane (PZO), obtained by chelation of Hacac to zirconium, was used to combine with phenolic resin to form a precursor for ZrC. It generated ZrC at a relatively low temperature (1550°C) and in a low C/Zr molar ratio of 2 assuming that phenolic resin was the only carbon source. As a comparison, synthesis of ZrC only using ZOC and phenolic resin was also conducted. Besides, the pyrolysis of PZO was carried out and the transformation mechanism during the pyrolysis was studied, during which ZrC was obtained at 1550°C in flowing argon. The conversions from as‐synthesized preceramic precursors to ceramics were studied by means of FTIR, DSC‐TG, SEM, EDS, and XRD.

No abstract