Wenting Wang

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.

Phenolic resin pyrolytic carbon is a key matrix phase in carbon-based refractories and carbon/carbon composites; however, its defect-rich glassy carbon structure exhibits poor oxidation resistance at elevated temperatures. In this work, we report a facile one-step thermal-treatment strategy using melamine as a nitrogen source to prepare nitrogen-modified phenolic resin pyrolytic carbon (NC). The structural evolution and oxidation behavior of samples carbonized at 500–800 °C were systematically investigated by XRD, SEM, TEM, FT-IR, Raman, XPS, BET, and TG-DSC. The results reveal that melamine-derived nitrogen exists in two distinct forms: at 500–700 °C, a carbon nitride-rich phase consistent with graphitic carbon nitride (g-C₃N₄) forms sheet- and belt-like structures on the carbon surface and partially fills the internal pores; at 800 °C, its long-range crystalline signature disappears, while pyridinic, pyrrolic, and graphitic nitrogen remain in the carbon framework. From 500 to 800 °C, the relative N 1s fraction of pyridinic N decreases from 72.33% to 44.38%, whereas graphitic N increases from 0.47% to 24.09%. Meanwhile, the pore structure evolves from a mesopore-dominated architecture with a limited accessible surface area at 500–600 °C to a micropore-rich structure at 700–800 °C. Relative to unmodified PR-800, NC-800 exhibits an approximately 30 °C higher onset oxidation temperature and an approximately 40 °C higher complete oxidation temperature, together with a lower maximum mass-loss rate and a delayed, broadened exothermic response. These results show that melamine-derived pore regulation and skeletal nitrogen doping jointly retard oxygen transport and suppress oxidation-active defect sites, providing a simple and potentially scalable route for improving the high-temperature oxidation resistance of phenolic resin pyrolytic carbon.

Phenolic resin is widely used as a binder in high-temperature industries; however, its pyrolysis generally yields isotropic glassy carbon, which strongly influences its high-temperature oxidation behavior. In this work, cupric tartrate was introduced as a catalyst precursor to investigate its effects on the thermal decomposition behavior, microstructural evolution, and oxidation behavior of the phenolic resin pyrolytic carbon. Upon heating, cupric tartrate decomposed at 250–320 °C into nanoscale Cu/Cu₂O composites, which were then converted into metallic Cu nanoparticles through reduction by gaseous products generated during the pyrolysis of phenolic resin. The in situ formed Cu nanoparticles were associated with the growth of tapered carbon nanofibers (CNFs), reaching maximum lengths of 30–50 μm at 700 °C. Based on the observed microstructural features and established literature reports, a dissolution–precipitation pathway is proposed to rationalize the formation of these CNFs. The presence of Cu-catalyzed CNFs correlates with enhanced structural ordering of the pyrolytic carbon, as reflected by reduced I_D/I_G ratios, and with an increased apparent oxidation activation energy in the selected fitting region (from 103.73 to 137.45 kJ/mol). Overall, this work demonstrates a facile strategy in which cupric tartrate serves as an effective catalyst precursor that generates Cu nanoparticles in situ; these nanoparticles then catalyze CNF growth from phenolic resin, enabling the construction of low-dimensional carbon nanostructures.