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1. Polymer derived SiOC and SiCN ceramics for electrochemical energy storage: A perspective

   https://doi.org/10.1002/ces2.10108  

   Mujib, Shakir Bin; Singh, Gurpreet (January 2022, International Journal of Ceramic Engineering & Science)
2. Hybrid HfC‐SiCN matrix for improved oxidation resistance of carbon fiber–reinforced mini‐composites

   https://doi.org/10.1002/ces2.10209  

   Mujib, Shakir_Bin; Rasheed, Mohammed; Arunachalam, Saravanan_R; Singh, Gurpreet (February 2024, International Journal of Ceramic Engineering & Science)

   Abstract Hafnium carbide (HfC) is an ultrahigh‐temperature ceramic with high melting point, chemical stability, hardness, and wear resistance. However, its low fracture toughness and poor thermal shock resistance limit its structural applications in extreme environments. In this study, co‐curing of liquid precursors was carried out prior to complete pyrolysis of individual polymeric precursors. First, HfC preceramic polymer precursor was cured, followed by silicon carbonitride (SiCN) precursor curing on a 2D carbon fiber (CF) cloth using the drop‐coating process. The infiltrated CFs were pyrolyzed at 800°C to achieve CF/HfC‐SiCN ceramic mini‐composites. The cross‐linked precursor‐to‐ceramic yield was observed to be as high as 65% when the procedure was carried out in an inert environment. Although stable up to 1200°C, CF/HfC‐SiCN samples demonstrated susceptibility to oxidation at 1500°C in ambient air. The oxidation of HfC in the presence of SiC leads to the formation of a hafnium‐containing silicate (Hf_xSi_yO_z) along with hafnia (HfO₂). This compound of silicate and hafnia limits oxygen diffusion better than SiO₂and HfO₂individually. The incorporation of SiCN in HfC ceramic led to improved phase stability compared to a neat HfC system. The results of this study also show that the use of liquid‐phase precursors for HfC and SiCN in the polymer‐infiltrated pyrolysis method is a promising approach to fabricating high‐temperature structural ceramic matrix composites with good oxidation resistance. 

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3. Thermal properties of field‐assisted‐sintered SiCN–Y ₂ O ₃ composites

   https://doi.org/10.1111/ijac.14265  

   Zhang, Zhao; Li, Quan; Maiti, Sanat Chandra; Shen, Xingchen; He, Jian; Peng, Fei; Bordia, Ranjendra K. (March 2023, International Journal of Applied Ceramic Technology)

   Abstract Polymer‐derived amorphous SiCN has excellent high‐temperature stability and properties. To reduce the shrinkage during pyrolysis and to improve the high‐temperature oxidation resistance, Y₂O₃was added as a filler. In this study, polymer‐derived SiCN–Y₂O₃composites were fabricated by mixing a polymeric precursor of SiCN with Y₂O₃submicron powders in different ratios. The mixtures were cross‐linked and pyrolyzed in argon. SiCN–Y₂O₃composites were processed using field‐assisted sintering technology at 1350°C for 5 min under vacuum. Dense SiCN–Y₂O₃composite pellets were successfully made with relative density higher than 98% and homogeneous microstructure. Due to low temperature and short time of the heat‐treatment, the grain growth of Y₂O₃was substantially inhibited. The Y₂O₃grain size was ∼1 μm after sintering. The composites’ heat capacity, thermal diffusivity, and thermal expansion coefficients were characterized as a function of temperature. The thermal conductivity of the composites ceramics decreased as the amount of amorphous SiCN increased and the coefficient of thermal expansion (CTE) of the composites increased with Y₂O₃content. However, the thermal conductivity and CTE did not follow the rule of mixture. This is likely due to the partial oxidation of SiCN and the resultant impurity phases such as Y₂SiO₅, Y₂Si₂O₇, and Y_4.67(SiO₄)₃O. 

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