Construction of chitosan-derived porous nest-like C/SnO2 materials for microwave absorption.

Electromagnetic waves have an irreplaceable role as information carriers in civil and radar stealth fields, but they also lead to electromagnetic pollution and electromagnetic leakage. Therefore, electromagnetic wave absorbing materials that can reduce electromagnetic radiation have come into being. Especially, SnO2 has made a wave among many wave-absorbing materials as an easily tunable dielectric material, but it hardly has both broadband and powerful absorption properties. Here, the nested porous C/SnO2 composites derived from nitrogen-doped chitosan is obtained by freeze-drying and supplemented with carbonization treatment. The chitosan creates a nested cross-linked conductive network that can make part of the contribution to conduction loss. The amino groups contained in the molecule either help promote in situ nitrogen doping and trigger dipole polarization. The multiphase dissimilar interface between the nested carbon layer and the inner clad SnO2 formation is the major inducer of interfacial polarization. It reached intense absorption of -48.8 dB and bandwidth of 5.2 GHz at 3.46 mm. The interfacial polarization is confirmed to be the main force of dielectric loss by simulating the electromagnetic field distribution. In addition, the RCS simulation data assure the prospect of enticing applications of C/SnO2 composites in the field of radar stealth.

Pomegranate plasma heterostructure regulated 1D biomass derived microtube networks for lightweight broadband microwave absorber.

The excessive aggregation of magnetic metal particles and the resulting skin effect tend to cause a serious imbalance in impedance matching, which hinders its application in aerospace and military wave absorption fields. Obviously, effective dispersion configuration and network construction are two practical measures to develop broadband lightweight absorbers. Based on the recycling theme, pomegranate plasma heterostructure regulated one-dimensional (1D) biomass derived microtube networks are achieved through the conversion and utilization of waste Platanus ball fibers. The metal-organic framework strategy successfully avoids the hard agglomeration of metal particles. The pomegranate seed-like heterostructure effectively modulated the impedance of carbon microtubes, resulting in coordinated dielectric and magnetic losses. Such composites exhibited an effective absorbing bandwidth of 6.08 GHz and a minimum reflection loss of -29.8 dB. This work provides a new approach for constructing sustainable ultralight electromagnetic wave absorbers using plasmon modification and a 1D built-up network structure.

ZrB2-Based "Brick-and-Mortar" Composites Achieving the Synergy of Superior Damage Tolerance and Ablation Resistance.

The intrinsic brittleness and poor damage tolerance of ultrahigh-temperature ceramics are the key obstacles to their engineering applications as nonablative thermal protection materials. Biomimetic layered or "brick-and-mortar" hybrid composites composed of alternative strong/weak interfaces exhibit excellent strength and high toughness; however, the commonly used interfacial materials are weak and have poor thermal stability and ablation resistance, which strictly limit their use in high-temperature and oxidative environments. In this work, ZrB2-based "brick-and-mortar" hybrid ceramics were constructed with a hierarchical biomimetic design to improve the fracture resistance and damage tolerance. ZrB2-20vol %SiC ceramics containing 30 vol % reduced graphene oxide nanosheets were used as the weak interface to increase crack growth resistance without destroying the excellent ablation resistance. Finally, the ZrB2-based "brick-and-mortar" composites achieve the synergy of superior damage tolerance and ablation resistance.