基于SAXS的不同变质程度煤纳米级孔隙结构特征研究

为揭示不同变质程度煤岩纳米级孔隙特征，运用小角X射线散射方法(SAXS)，采集镜质体反射率R_max在0.31%~6.24%的15个样品，基于散射数据获取的煤岩孔隙率、孔径分布、比表面积和分形维数，讨论了煤化过程对煤岩纳米孔隙(0.3~100 nm)结构的影响，并用低温CO₂和N₂吸附DFT模型结果对孔径分布进行了验证。结果表明:在R_max < 0.5 %时，煤岩孔隙率和比表面积随着变质程度的增加而增加，微孔(< 2 nm)含量增长较少，介孔(2~50 nm)和大孔(50~100 nm)含量大幅增加，煤岩表面逐渐光滑；在R_max=0.5%~1.4%时，孔隙率和比表面积减小，各类孔隙含量均减少，煤岩表面逐渐光滑；在R_max=1.4%~4.0%时，煤岩孔隙率和比表面积增大，微孔含量大幅增加，介孔和大孔含量近乎稳定，煤岩表面逐渐粗糙；在R_max > 4.0%后，煤岩孔隙率和比表面积缓慢增加，微孔增长幅度变缓，煤岩表面逐渐光滑。SAXS在0.3~100 nm孔径分布(本次实验范围)中用球形形状因子与低温CO₂和N₂吸附结果契合度较高，煤中纳米级孔隙率及比表面积主要由微孔贡献。 

SAXS-based nano-scale pore structure characteristics of coals with different metamorphic degrees

In order to reveal the characteristics of nano-scale pores in coals with different metamorphic degrees, the small-angle X-ray scattering method (SAXS) is used to obtain the porosity, pore size distribution, specific surface area and fractal dimension of 15 samples whose vitrinite reflectance R_max is 0.31%-6.24%, and the low temperature CO₂ and N₂ adsorption DFT model results are used to verify the pore size distribution. The results show: during coalification process, when R_max is < 0.5%, the porosity and the specific surface area of coal increase with the increase of metamorphic degree, the micropores(< 2 nm) content increases seldomly, the mesoporous(2-50 nm) and microporous(50-100 nm) content increase greatly, and the surface of coal is gradually smooth. When R_max=0.5%-1.4%, the porosity and the specific surface area decrease, and each type of pore content is reduced, and the surface of coal is gradually smooth. When R_max=1.4%-4.0%, the porosity and specific surface area of coal rock increase, the microporous content increases, and the mesoporous and microporous content are nearly stable, and the surface of the coal is gradually rough. When R_max > 4.0%, the porosity and specific surface area of coal increase, the microporous growth is slow, and the surface of coal is gradually smooth.