Graphite materials are promising aerospace structural materials owing to their low density, high thermal conductivity, and high temperature stability. However, the poor mechanical properties and inferior ablation resistance of graphite materials limit their application in advanced space vehicles. To address this problem, three-dimensional zirconium carbide (3D ZrC) skeleton-reinforced graphite composites (mesocarbon microbeads, MCMBs) were designed and fabricated by combination of molten salt coating and spark plasma sintering (SPS). The effects of ZrC content on the mechanical and ablation properties were investigated in detail. With the ZrC content of 45 vol%, the bending strength and fracture toughness of the MCMB@ZrC composite were 112 MPa and 1.72 MPa·m^1/2, respectively. After ablation at 2.4 MW·m⁻² for 60 s, the MCMB@ZrC composites with 30 vol% ZrC exhibited the best ablation performance and remained intact after ablation, with linear and mass ablation rates of 2.13 μm·s⁻¹ and 4.24 mg·s⁻¹, respectively. The 3D ZrC skeleton with moderate content provides effective support for the graphite matrix and thermal protection during the ablation process to a certain extent.

Ceramic-coated graphite powders are considered as effective raw materials to fabricate three-dimensional continuous ceramic skeleton-reinforced graphite matrix composites which can overcome their inherent poor densification and improve their mechanical and antioxidation properties. However, the morphology and thickness regulation of ceramic coatings on graphite particles are still a great challenge. Herein, SiC-coated graphite (graphite@SiC) powders were prepared by nitriding combustion synthesis using Si and graphited mesocarbon microbead (MCMB) as raw powders with polytetrafluoroethylene (PTFE) as a promoter. The effects of the PTFE content and the Si/MCMB molar ratio on the phase composition and coating morphology were investigated. The phase transition and microstructure evolution of a combustion synthesis (CS) process were revealed by a gas-released quenching experiment. When the Si/MCMB molar ratio was 1 : 3 and the PTFE content was 10 wt%, the thickness of the SiC coating synthesized under 2 MPa N₂ reached 1.14 μm. The corresponding sintered graphite@SiC composite had relative density of 99.2% and flexural strength of 231 MPa, accompanied by a significant improvement in high-temperature antioxidation properties. The as-synthesized graphite@SiC powders with good sinterability and antioxidation properties show great promise for applications in the nuclear industry and other extreme fields.

Highly oriented graphite-based composites have attracted great attention because of their high thermal conductivity (TC), but the low mechanical properties caused by the inhomogeneous distribution and discontinuity of reinforcements restrict the wide applications. Herein, continuous SiC ceramic skeleton reinforced highly oriented graphite flake (SiC/GF) composites were successfully prepared by combining vacuum filtration and spark plasma sintering. The effect of SiC concentration on the microstructure, flexural strength, and thermophysical properties of the composites was investigated. The GF grains in the composites exhibited high orientation with a Lotgering factor of > 88% when the SiC concentration was ≤ 30 wt%, and the SiC skeleton became continuous with the SiC concentration reaching 20 wt%. The formation of continuous SiC skeleton improved the flexural strength of the composites effectively while keeping the TC in a high level. Especially, the composites with 30 wt% SiC exhibited the flexural strength up to 105 MPa, and the specific TC reaching 0.118 W·m²·K^-1·kg^-1. The composites with excellent flexural strength and thermophysical properties showed significant promise for thermal management applications.

Spherical AlN powders with micrometer size have attracted great attention owing to their good fluidity and dispersity. However, the industrial preparation methods usually require high temperature and long soaking time, which lead to the high cost and limit the wide application of the products. Herein, nearly spherical AlN particles with the average size of 2.5 μm were successfully synthesized via an in-situ combustion synthesis method. The effect of N₂ pressure, NH₄Cl content, and Al particle size on the combustion reaction procedure, phase composition, and microstructure of the products was systematically investigated. The results showed that the decreased N₂ pressure, increased NH₄Cl content, and Al particle size led to the decreasing of combustion temperature and speed, which further affected the morphology of the products. As a result, low N₂ pressure (0.2 MPa), a small amount of NH₄Cl (0.5 wt%), and fine Al particles (~2.5 μm) contributed to a moderate combustion temperature and facilitated the formation of nearly spherical AlN particles. In addition, based on the gas-releasing assisted quenching experiments and thermo-kinetic analysis, a two-step growth mechanism for the nearly spherical AlN particles was rationally proposed. The present method shows the advantages of low cost and high efficiency for preparing nearly spherical AlN particles, which can be used as raw materials for electronic substrates and fillers for packaging materials.