Open Access Research Article Issue
Preparation of SiC coated graphite composite powders by nitriding combustion synthesis
Journal of Advanced Ceramics 2023, 12 (10): 1930-1945
Published: 19 October 2023
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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.

Open Access Research Article Issue
Continuous SiC skeleton reinforced highly oriented graphite flake composites with high strength and specific thermal conductivity
Journal of Advanced Ceramics 2022, 11 (3): 403-413
Published: 11 February 2022
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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.

Open Access Research Article Issue
Synthesis of nearly spherical AlN particles by an in-situ nitriding combustion route
Journal of Advanced Ceramics 2021, 10 (2): 291-300
Published: 24 February 2021
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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.

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