Nano- to micro-pore characterization by synchrotron radiation SAXS and nano-CT for bituminous coals

doi:10.1007/s11707-021-0889-6

Front. Earth Sci.

2021, Vol. 15

Issue (2) : 189-201 https://doi.org/10.1007/s11707-021-0889-6

RESEARCH ARTICLE

Nano- to micro-pore characterization by synchrotron radiation SAXS and nano-CT for bituminous coals

Yixin ZHAO^1,²(

), Chujian HAN², Yingfeng SUN^3,⁴, Nima Noraei DANESH^1,², Tong LIU^1,², Yirui GAO^1,²

¹. Beijing Key Laboratory for Precise Mining of Intergrown Energy and Resources, China University of Mining and Technology (Beijing), Beijing 100083, China
². School of Energy and Mining Engineering, China University of Mining and Technology (Beijing), Beijing 100083, China
³. School of Civil and Resource Engineering, University of Science and Technology Beijing, Beijing 100083, China
⁴. Key Laboratory of Deep Earth Science and Engineering (Ministry of Education), Sichuan University, Chengdu 610065, China

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Abstract

Considering the complementarity of synchrotron radiation SAXS and nano-CT in the pore structure detection range, synchrotron radiation SAXS and nano-CT methods were combined to characterize the nano- to micro-pore structure of two bituminous coal samples. In mesopores, the pore size distribution curves exhibit unimodal distribution and the average pore diameters are similar due to the affinity of metamorphic grades of the two samples. In macropores, the sample with higher mineral matter content, especially clay mineral content, has a much higher number of pores. The fractal dimensions representing the pore surface irregularity and the pore structure heterogeneity were also characterized by synchrotron radiation SAXS and nano-CT. The fractal dimensions estimated by both methods for different pore sizes show consistency and the sample with smaller average pore diameters has a more complex pore structure within the full tested range.

Keywords synchrotron radiation SAXS nano-CT pore size distribution fractal coal

Corresponding Author(s): Yixin ZHAO

Online First Date: 08 May 2021 Issue Date: 26 October 2021

Cite this article:

Yixin ZHAO,Chujian HAN,Yingfeng SUN, et al. Nano- to micro-pore characterization by synchrotron radiation SAXS and nano-CT for bituminous coals[J]. Front. Earth Sci., 2021, 15(2): 189-201.

URL:

https://academic.hep.com.cn/fesci/EN/10.1007/s11707-021-0889-6
https://academic.hep.com.cn/fesci/EN/Y2021/V15/I2/189

Tab.1 Results of vitrinite reflectance of coal samples

Tab.2 Results of maceral compositions of coal samples

Fig.1 Instruments used in synchrotron radiation nano-CT imaging. (a) Sample turntable with pin, (b) Instrument for mounting gold particle on the sample (Sun et al., 2019).

Fig.2 Nano-CT image processing. (a) and (d) present 3D reconstruction images and REV selection, (b) and (e) present REV images before median filtration, and (c) and (f) present REV images after median filtration.

Fig.3 Distribution of REVs’ gray values. (a) No. 1-REV, (b) No. 2-REV.

Fig.4 Curves of scattering intensity I and scattering vector q. (a) Sample No. 1, (b) Sample No. 2.

Fig.5 Porod deviation and calibrated curves. (a) Sample No. 1, (b) Sample No. 2.

Fig.6 Guinier curves.

Fig.7 PSD curves based on SAXS.

Fig.8 Segmentation of matrix and pore structure of coal. (a) and (d) present all components of No. 1-REV and No. 2-REV, (b) and (e) present the matrix component of No. 1-REV and No. 2-REV, and (c) and (f) present the pore structure component of No. 1-REV and No. 2-REV.

Fig.9 The equivalent network model of coal samples’ REV. (a) and (h) present the pore and throat network model, (b) and (i) present the pore network model, (c) and (j) present the throat network model, (d) and (k) present the pore diameter statistics, (e) and (l) present the pore coordination number statistics, (f) and (m) present the throat length statistics, and (g) and (n) present the throat diameter statistics.

Fig.10 Double logarithmic curves of scattering intensity I and scattering vector q. (a) Sample No. 1, (b) Sample No. 2.

Tab.3 Results of fractal dimensions of two samples based on SAXS and nano-CT

Fig.11 2D fractal dimension of coal samples.

Fig.12 Slices with minimum and maximum 2D fractal dimensions in two samples’ REV. S1-Slice with the minimum D_2D value of No. 1-REV, S2-Slice with the maximum D_2D value of No. 1-REV, S3-Slice with the minimum D_2D value of No. 2-REV, and S4-Slice with the maximum D_2D value of No. 2-REV.

Fig.13 The relationship between the relative standard deviation of sub-blocks’ porosity and the number of sub-blocks (Sun, 2018b).

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