高煤级煤石墨化轨迹阶段性的XRD和Raman光谱表征

为了研究石墨化过程中煤的分子结构有序化轨迹，选取湖南、陕西19个不同变形-变质程度高煤级煤为研究对象，采用工业分析、元素分析、X射线衍射分析（XRD）和拉曼光谱分析（Raman）等手段，结合分峰拟合的数学方法，对系列样品分子结构参数（XRD结构参数，如石墨化度、延展度L_a、堆砌度L_c及面网间距d₀₀₂等；Raman参数，如P_G，P₁，R₁，R₂等）进行了统计与计算。研究结果表明：煤化作用阶段H/C随变质程度增加而逐渐减小，但在石墨化阶段以物理变化为主，其趋势变缓或不显著；XRD参数d₀₀₂，L_a，L_c，N及L_a/L_c等随变质程度呈现非线性连续（阶跃性）变化，拐点大致对应R_m=7.0%，d₀₀₂=0.338 nm，拐点之前L_a，L_c及N变化较小（或平稳增大），拐点之后石墨晶体结构快速形成，微晶尺寸增大，拼叠作用开始并逐渐增强；L_a/L_c变化亦反映石墨化过程由缩合作用向拼叠作用转变。高煤级煤石墨化轨迹可按有序化增加的三阶段模型来表述，无定形碳（无烟煤）至变无烟煤阶段，G峰位、峰位差P₁变化显著，I_D1/I_G在表达无序程度时不服从TK关系；变无烟煤至半石墨阶段，即从石墨化开始结构演化轨迹呈现不同方向，R₁随着有序的增加呈现截然相反的轨迹，部分石墨组分演化服从TK关系，R₂在石墨化度为45%时呈现截然相反的轨迹；石墨阶段温、压作用导致微晶尺寸急剧增加（或阶跃），I_D1/I_G减小服从TK关系。当不同石墨化程度的新生组分共存时，d₀₀₂不足以代表样品最大的演化程度，但其作为平均度量来标度高煤级煤石墨化过程中结构演化特征仍为较优的选择，且(002)和(γ)峰半峰宽能较好地区分石墨化煤的变质类型，H/C，I_D1/I_G亦随d₀₀₂演化轨迹不同，需利用d₀₀₂＜0.344 0 nm，R₁＜2.0，H/C＜0.12等综合指标判别石墨化的开始。由此可以看出，采用XRD和Raman光谱分析技术可以表征高煤级煤石墨化轨迹阶段性以及结构的差异性。

XRD and Raman Spectroscopy Characterization of Graphitization Trajectories of High-Rank Coal

In order to the interpretation of ordering and crystallinity of natural graphitized coal, nineteen kinds of different deformation-metamorphism degree high-rank coal from Hunan Province and Shaanxi Province were studied with proximate and ultimate analysis, X-ray diffraction (XRD), Raman spectrum and curve-fitting analysis. The graphitization, crystal size (L_a and L_c), interplanar spacing (d₀₀₂) were calculated with XRD. The parameters of P_G (G band position), P₁ (G and D1 band separation), R₁=I_D1/I_G, the peak height ratio, R₂=A_D1/(A_G+A_D1), peak area ratio were calculated with Raman. The results showed that the H/C decreases gradually with the increase of metamorphic degree during the coalification stage, but during the graphitization stage, the change was primarily physical, and the trend was slow or not significant. The parameters of d₀₀₂, L_a, L_c, N and L_a/L_c had shown that the crystalline structure of natural graphitized coal presented nonlinear continuous (step) change with metamorphism degree. The inflection point corresponds roughly to R_m=7.0% and d₀₀₂=0.338 nm. Before the inflection point, L_a, L_c and N changed little (or increase steadily), and the graphite crystal structure formed rapidly after the inflection point, the stacking effect begins and gradually increases, as the crystallite size increases. L_a/L_c variation reflected that the graphitization process changed from condensation to overlap. The graphitization trajectory of high-rank coal can be given in a three-stage model of orderly increase. During the stage from amorphous carbon (anthracite) to meta-anthracite, the parameters of P_G and P₁ changed significantly, and I_D1/I_G did not obey the TK relation when expressing the degree of disorder. During the stage from meta-anthracite to semi-graphitization showed different directions, R₁ presented an opposite trajectory with the increase of order, the evolution of some graphite components followed the TK relation, and R₂ showed a completely contradictory trajectory when the graphitization degree was 45%. The temperature and pressure in the graphite stage led to a sharp increase in crystal size (step evolution), and the decrease of I_D1/I_G obeying the TK relation. As neogenesis-associated components in different graphitized coals, d₀₀₂ cannot reflect the largest metamorphic degree of graphitized coal. However, it was still a superior choice to consider d₀₀₂ as an average scaling of the graphitized coals in the process of graphitization. Moreover, full width at half maximum of the (002) and (γ) band are reliable indicators for distinguishing and classifying of metamorphism type of nature graphitized coals. H/C, and I_D1/I_G also evolved over d₀₀₂ trajectory was altered, needed to use d₀₀₂＜0.344 nm, R₁＜2.0, H/C＜0.12 and other comprehensive indicators to identify the beginning of graphitization. From this, it could be seen that XRD and Raman spectral analysis techniques could be used to characterize the graphitization track stages and structural differences of high rank coal.