## 3 Results and Discussion
### Effect of Thermal Evolution on the XRD Microcrystalline Structure of Coal  
Figure 1 shows that both thermally evolved coal samples and normal coal samples show a typical graphite diffraction peak (002 peak) at around 20 = 25\({}^{\circ}\). Another graphite diffraction peak (100 peak) also appears at about 20 = 42\({}^{\circ}\). It indicates that each coal sample possesses some characteristics of crystals, with both disordered and ordered structures within them [44].  
Based on a previous study, the asymmetry of the 002 diffraction peak is attributed to the overlap of this peak by the amorphous carbon peak (\(\gamma\) peak) and the microcrystalline carbon peak (002 peak) [45; 46]. To delve further into the characteristics of the XRD microcrystalline structure parameters of the magmatic thermal evolution coal samples and normal coal samples, the raw data were subjected to denoising and fitted using Origin 2022b software for peak splitting [38]. The fitting results are presented in Figure 2, with DX 1# and DX 2# serving as illustrative examples.  
As can be seen in Figure 2, an obvious diffraction peak appears near the diffraction angle of 20 = 20\({}^{\circ}\) as an amorphous carbon peak (\(\gamma\) peak), which is caused by branched microcrystals of aliphatic hydrocarbon branched chains, various functional groups, and alicyclic hydrocarbons [39; 47]. A clear diffraction peak also appears near the diffraction angle of 20 = 26\({}^{\circ}\) as a graphite peak (002 peak), which correlates with the stacking between aromatic ring lamellae [48]. Based on the peak position, area, and FWHM parameters of the three peaks (002 peak and \(\gamma\) peak) obtained from the split-peak fitting profiles, the results of the quantitative calculation of the aromatic lamellae spacing (d\({}_{002}\)), aromaticity (\(f_{a}\)), average stacking heights (L\({}_{\text{c}}\)), and stacking layer number (N\({}_{\text{ave}}\)) combined with Equations (3)-(6) are shown in Table 2.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multicolumn{4}{c}{**Proximate Analysis (wt.\%)**} & \multicolumn{4}{c}{**Ultimate Analysis (wt.\%)**} & \multirow{2}{*}{**H/C**} & \multirow{2}{*}{**\(f_{a}\)**} & \multirow{2}{*}{**(R/C)\({}_{\text{u}}\)**} \\ \cline{2-2} \cline{4-2}  
evolved coal samples have a higher degree of aromatization. The combustion reactivity of thermally evolved coal samples may be weak relative to normal coal samples [29]. However, in the process of coal mine production, coal bodies affected by magmatic intrusion often have a high risk of spontaneous combustion. The factors affecting the spontaneous combustion of coal include not only the chemical and microcrystalline structure of the coal itself, but also other factors such as the pore structure, geologic endowment conditions, and moisture. Therefore, the effects of the above factors on the spontaneous combustion hazard of coal will be investigated in combination with other research methods in the following research work. In addition, DX 1# and HY 1# have higher N\({}_{\text{ave}}\) and L\({}_{\text{c}}\) values than DX 2# and HY 2#, respectively, which indicates that the magmatic thermally evolved coal samples affected by magma intrusion have larger microcrystalline structural units. The analysis indicates that the thermal evolution of magma leads to an increase in the volume of coal microcrystalline structural units, which promotes the aromatization process and the degree of condensation of the macromolecular structural units.