Investigation of Structural Characteristics of Thermally Metamorphosed Coal by FTIR Spectroscopy and X-ray Diffraction

The structural parameters of nine coal samples from a contact metamorphic zone were studied by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The FTIR spectra parameters composed of CH2/CH3, f(a), H-al/H-ar, and (R/C)(u) indicate distinguishing features, including increase of aromaticity and the loss of aliphatic and oxygen-containing groups with thermally metamorphic evolution of coal. The XRD analysis shows that magmatic intrusion potentially caused rapid changes of structures in coal. With the decrease of distances from the intrusion rocks, the average lateral sizes (L-a), stacking heights (L-c), and interlayer spacing (d(002)) of the crystallite structures of coal range from 22.90 to 37.70 angstrom, 12.90 to 23.30 angstrom, and 3.80 to 3.50 angstrom, respectively. Exponential correlations are observed between structural parameters (f(a), d(002), L-a, L-c, H-al/H, (R/C)(u), and A(ar)/A(al)) and C/H of the coal, suggesting that the structures of coal are controlled by the degree of contact metamorphism.