Engineering Cf /ZrB2 -SiC-Y2 O3 for Thermal Structures of Hypersonic Vehicles with Excellent Long-Term Ultrahigh Temperature Ablation Resistance.

Ultrahigh temperature ceramic matrix composites (UHTCMCs) are critical for the development of high Mach reusable hypersonic vehicles. Although various materials are utilized as the thermal components of hypersonic vehicles, it is still challenging to meet the ultrahigh temperature ablation-resistant and reusability. Herein, the Y2 O3 reinforced Cf /ZrB2 -SiC composites are designed, which demonstrates near-zero damage under long-term ablation at temperatures up to 2500 °C for ten cycles. Notably, the linear ablation rate of the composites (0.33 µm s-1 ) is over 24 times better than that of the conventional Cf /C-ZrC at 2500 °C (8.0 µm s-1 ). Moreover, the long-term multi-cycle ablation mechanisms of the composites are investigated with the assistance of DFT calculations. Especially, the size effect and the content of the Zr-based crystals in the oxide layer fundamentally affect the stability of the oxide layer and the ablation properties. The ideal component and structure of the oxide layer for multi-cycle ablation condition are put forward, which can be obtained by controlling the Y2 O3 /ZrB2 mole ratio and establishing Y-Si-O - t-Zr0.9 Y0.1 O1.95 core-shell nano structure. This work proposes a new strategy for improving the long-term multi-cycle ablation resistance of UHTCMCs.

Incorporating Cobalt Nanoparticles in Nitrogen-Doped Mesoporous Carbon Spheres through Composite Micelle Assembly for High-Performance Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries have exhibited tremendous potential among the various secondary batteries benefitting from their large energy density, low expense, and enhanced security. However, the commercial use for Li-S batteries is immensely limited by the insulation of S, noticeable volume expansion from S to Li2S2/Li2S, and the undesired shuttle effect of lithium polysulfides (LiPs). Herein, a composite sulfur host has been prepared by in situ incorporations of cobalt nanoparticles (NPs) into nitrogen-doped mesoporous carbon spheres (Co/N-PCSs) through the composite micelle assembly strategy. The resultant functional Co/N-PCSs not only possess uniform spherical morphology with large open mesopores, high surface area, and pore volume but also have small Co NPs homogeneously inlaid into the pore walls of carbon frameworks. Both the experimental and theoretical calculation results demonstrate that the formed cobalt NPs can efficiently accelerate the lithium-ion diffusion reaction and greatly entrap the soluble intermediate LiPs. Benefiting from the well-designed structure, the Co/N-PCSs@S cathode with a S loading of 73.82 wt % delivers superior electrochemical performance, including long cycling stability (60% for the residual capacity at 1 A g-1 within 300 cycles) and excellent rate performance (∼512 mAh g-1 at 6 A g-1). This design strategy of implanting metal NPs in mesoporous carbon can be inspiring in energy storage applications.

Synthesis and characterization of nano-crystalized HfC based on an aqueous solution-derived precursor.

Nano-crystalized HfC was successfully synthesized based on an aqueous solution-derived precursor using hafnium tetrachloride and sucrose as raw materials. The precursor can be converted to pure phase HfC after pyrolysis at ∼600 °C and subsequent carbothermal reduction reaction at ∼1600 °C, with a ceramic yield of around 46.3%. Reaction mechanisms of the synthesis process are revealed based on FT-IR, TG-DSC, TEM analysis and thermodynamic calculations, etc. The obtained HfC nanoparticles possess an equiaxial shape with an average particle size of ∼73 nm. Oxygen content of the as-synthesized HfC powders is as low as 0.64 wt%, which exists in the form of an amorphous Hf-O-C thin layer covering the surface of the HfC particles. This feasible and promising method for HfC particle synthesis is believed to be suitable for the fabrication of continuous fibers reinforced HfC ceramic matrix composites.