煤微观结构的X射线衍射原子分布函数分析

ANALYSIS ON MICROSTRUCTURE OF COAL BY X-RAY DIFFRACTION ATOMIC DISTRIBUTION FUNCTION

采用在非晶态结构研究中应用的Ｘ射线衍射原子分布函数法测试了四种不同煤化程度煤的碳原子平均径向分布，求出了碳原子间距、配位数、芳香度、聚合度和短程有序畴等结构信息，并与文献值进行了对比。结果表明，煤的碳原子间距及对应的配位数介于石墨和金刚石对应的数值之间；随着煤化程度的增加，芳香度、聚合度和短程有序畴增大，煤的石墨化程度增加。

X-ray diffraction experiments on four coal samples of different ranks were performed.The coherent portion of the diffraction pattern was calculated,normalized and corrected with suitable factors.Then the Atomic Distribution Function G(r)(=4πr[ρ(r)-ρ0]),RDF(r)(=4πr2ρ(r))and g(r)(=ρ(r)/ρ0)were deduced from the Fourier transformation of the intensity data. The mass densities of coal derived from G(r)curves were in agreement with those obtained by pycnometer methods.The carbon interatomic distances(r)in coal were defined by the positions of peaks on the g(r)curves.The distances between the first neighbouring atoms varied from 0.143nm to 0.148nm,i.e.from the distance observed in graphite(0.142nm)towards that in diamond (0.154nm).From these distances,the values of aromaticity(fa)of coal were calculated.The areas of the peaks on RDF (r)curves were propertional to the carbon atoms coordination numbers(N).From these statistical and approximate N values,the degree of polymerization(Ks)in coal were calculated.Finally the short range regular domains(Rs)were measured On g(r)Curves.The results showed that these microstructural parameters had a good correlation with the change of coal coalification,and the coal structure changed towards the graphitization with increasing coal ranks.