Ceramic aerogels with low dielectric are attractive due to its lightweight and ultralow thermal conductivity, while it can withstand complex mechanical loads and thermal shock for the randoms/windows of aerospace. In this work, Si₃N₄ nanowires are assembled as basic building blocks to fabricate the nanostructure-based ultralight ceramic aerogels by freeze-drying and subsequent heat treatment method. The SiO₂ shell is formed on the surface of Si₃N₄ nanowire core and the Si₃N₄/SiO₂ interface is applied to improve the mechanical and thermal insulation performance. Thanks to the core-shell structure of Si₃N₄@SiO₂ nanowire and the ultra-high porosity, the as-obtained Si₃N₄@SiO₂ nanowire (SSN) aerogels display robust mechanical and thermal stability, the compress strength up to 27.1 KPa, and the compress strength up to 4.6 KPa even after heat treatment up to 1300 °C for 9000 s. The compress strength retention rate is 58% for SSN aerogel after oxidation for 9000 s. The SSN aerogel also features low thermal conductivity of 0.029 W·m^-1·K^-1 at room temperature. Furthermore, the dielectric property of SSN aerogel is low (an ultra-low real permittivity (ε′) of 1.02-1.04, the dielectric loss of 2 ´ 10^-3). This robust material system is ideal for thermal insulation for the randoms/windows of aerospace. 

Carbon fiber reinforced dual-matrix composites (CHM) including carbon fiber reinforced hydroxyapatite-polymer matrix composites (CHM_P) and carbon fiber reinforced hydroxyapatite-pyrolytic carbon matrix composites (CHM_C) have great potential application in the field of artificial hip joints, where a combination of high mechanical strength and excellent biotribological property are required. In this work, the graphene-silicon nitride nanowires (Graphene-Si₃N₄nws) interlocking interfacial enhancement were designed and constructed into CHM for boosting the mechanical and biotribological properties. The graphene and Si₃N₄nws interact with each other and construct interlocking interfacial enhancement. Benefiting from the Graphene-Si₃N₄nws synergistic effect and interlocking enhancement mechanism, the mechanical and biotribological properties of CHM were promoted. Compared with CHM_P, the shear and compressive strengths of Graphene-Si₃N₄nws reinforced CHM_P were increased by 80.0% and 61.5%, respectively. The friction coefficient and wear rate were reduced by 52.8% and 52.9%, respectively. Compared with CHM_C, the shear and compressive strengths of Graphene-Si₃N₄nws reinforced CHM_C were increased by 145.4% and 64.2%. The friction coefficient and wear rate were decreased by 52.3% and 73.6%. Our work provides a promising methodology for preparing Graphene-Si₃N₄nws reinforced CHM with more reliable mechanical and biotribological properties for use in artificial hip joints.

Mimicking the structure of natural bone collagen fibers/hydroxyapatite (HA) to synthesize large size of HA for accelerated bone repair remains a challenge. Herein, silicon nitride nanowires (SN)-graphene (GE) was designed by the chemical vapor deposition, forming SN-GE (SG) similar to collagen fibers. Then, the large size HA was assembled onto SG by pulsed electrochemical deposition, the SG/HA (SGH) mimics the collagen fibers/HA structure of bone. The introduction of SG induces HA to large size grow in the form of coral-like. HA can be grown on a large size inextricably with the existence of GE modified layers. On the one hand, the upright GE sheets effectively increases the surface roughness which enhances the nucleation site of HA. On the other hand, the CO provides chemical bonding and induces HA nucleation. Compared with SN/HA(SH), the porosity of SGH decreased by 71%. The average diameter of the SGH is (9.76 ± 0.25) μm. Compared with SH, the diameter of SGH is 22 times larger than the diameter of SH. Indicating that SG induces large size growth of HA. Our work can provide a general strategy for the efficient preparation of biological scaffolds with large size HA that can be used in bone tissue engineering.

Stealth materials with high dependability at elevated temperatures and outstanding mechanical properties are urgently needed for practical applications. As one-dimensional ultrahigh temperature ceramic (UHTC) materials, zirconium carbide whiskers (ZrCw) have attracted a great deal of attention due to their desirable mechanical and ablation resistance performance in high-temperature environments. We have successfully synthesized ZrCw using a carbothermal reduction technique without the introduction of metal catalytic in this paper. ZrCw shows a typically prismatic structure with the diameter of 1–2 μm and the aspect ratio of up to 250. The growth of ZrCw is controlled by a solid-liquid-solid (SLS) and vapor-solid (VS) compound mechanism in conjunction with the auxiliary action of mesophase Na₃ZrF₇. The ZrCw/paraffin hybrids achieve the minimum reflection loss (R_L(min)) of −25.77 dB at 13.28 GHz under the thickness of 1.25 mm, and reach an effective absorption bandwidth (EAB) of 3.04 GHz (14.96–18.00 GHz) with a thickness of only 1.0 mm. This work presents a promising approach for large-scale producing high-purity whiskers, and verifies that ZrCw has extensive application prospects in the field of stealth materials.

Extensive attention has been drawn to the development of carbon-matrix composites for application in the aerospace and military industry, where a combination of high mechanical strength and excellent frictional properties are required. Herein, carbon-matrix composites reinforced by Si₃N₄ nanowires@pyrolytic carbon nanolayers (Si₃N_4nws@PyC_nls) coupled with hydroxyapatite nanosheets is reported. The Si₃N_4nws@PyC_nls (SP) with coaxial structure could increase the surface roughness of Si₃N_4nws and promote the stress transfer to the carbon matrix, whereas the porous hydroxyapatite nanosheets favor the infiltration of the carbon matrix and promote the interfacial bonding between the SP and carbon matrix. The carbon matrix composites reinforced by SP coupled with hydroxyapatite nanosheets (Si₃N_4nws@PyC_nls-HA-C) exhibit excellent mechanical strength. Compare with the conventional Si₃N_4nws reinforced carbon composites, Si₃N_4nws@PyC_nls-HA-C (SPHC) have 162% and 249% improvement in flexural strength and elastic modulus, respectively. Moreover, the friction coefficient and wear rate decreased by 53% and 23%, respectively. This study provides a co-reinforcement strategy generated by SP coupled with hydroxyapatite nanosheets for effective improvement of mechanical and frictional properties of carbon matrix composites that are used for aerospace and military industry applications.