Temperature-Dependent Evolution of Coke Structure and Growth Mechanisms of SiC Whiskers Synthesized from Coke and Silicon Powder Under Graphite-Burial Conditions

Silicon carbide (SiC) whiskers are effective reinforcements for carbon-containing refractories; however, their application is restricted by the inherently low reactivity of graphite, which is commonly used as an internal carbon source. In this study, low-cost coke and silicon powder were used as the carbon and silicon sources to synthesize SiC whiskers via a graphite-burial heat treatment process. The structural evolution of coke and the reaction behavior of the coke–Si system at different temperatures were systematically characterized. The results reveal that coke exhibits a TG-DSC mass loss of 16.01% and undergoes progressive structural rearrangement and enhanced short-range ordering at 1200–1400 °C while retaining a predominantly turbostratic carbon structure and morphological stability. At 1100–1200 °C, SiC whiskers form predominantly within pores, and this distribution is consistent with a gas-phase-assisted VS-type growth pathway; the normalized crystalline SiC fractions remain relatively low (~4–11%). A pronounced enhancement of SiC formation occurs at 1300 °C, where the crystalline Si phase becomes undetectable by XRD and abundant SiC whiskers spread from localized pore regions to the matrix surface. The enhanced whisker formation at 1300–1400 °C is attributed to accelerated reaction and mass-transfer processes at elevated temperatures. The synthesized whiskers consist of crystalline β-SiC, and those formed at 1400 °C exhibit high-density stacking faults and pronounced radial coarsening, with representative diameters of approximately 35–80 nm in the TEM images. The structural evolution of coke from a defect-rich state toward a more ordered turbostratic structure occurs concurrently with the temperature-dependent evolution of SiC nucleation and growth and may contribute to the availability of reaction sites and transport pathways, establishing coke as a promising carbon source for the in-situ synthesis of SiC whiskers in refractory applications.