Temperature-Dependent Structural Evolution of Coal-Based Graphite During Synthetic Graphitization Process

A series of synthetic coal-based graphite (SCG) samples were prepared from anthracite, with heating temperatures ranging from 1400 to 2900 °C, and the structural evolution during graphitization was investigated. The overall graphitization process can be divided into three phases based on the parameters of XRD and Raman spectroscopy: (1) The carbonization phase (below 1400 °C) with disordered carbon structure: A carbon-rich process occurs in this period; however, the disordered structure with turbulent lattice fringes remains, as evidenced by the values of d₀₀₂, FWHM (002), and I_D1/I_G of the sample heated at 1400 °C, which are 0.3590 nm, 4.64° (2θ), and 1.21, respectively. (2) The initial graphitization phase (1400–2300 °C) with more aligned and equidistant layers lattice fringes shown in TEM images: The platelets of microcrystalline graphite are dominated with less than 3 μm in length. The parameter variations of d₀₀₂, FWHM (002), and I_D1/I_G are significant, which are 0.3389–0.3590 nm, 0.64–4.64° (2θ), and 0.27–1.21, respectively. (3) The “flake-like” graphitization phase (2300–2900 °C) with perfect straight three-dimensional (3D) lattice fringes: The platelets of graphite are generally >5 μm in length. A robust edge-to-edge coalescence process occurs at this stage, leading to the formation of large 3D-ordered graphite crystals. However, the variation of d₀₀₂, FWHM (002), and I_D1/I_G are stable and narrow ranges, which are 0.3373–0.3389 nm, 0.41–0.64° (2θ), and 0.06–0.27, respectively. The temperature of 2300 °C is a mutation point in the structural transformation during the synthetic graphitization process, at which the underlying mechanism of molecular dynamics for carbon atom reorganization needs to be further studied. This study provides valuable insight for precisely managing structural conversion in future synthetic coal-based graphitization processes.