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. 2021 Jul 28;11(1):15398.
doi: 10.1038/s41598-021-94943-6.

Variation features of unfrozen water content of water-saturated coal under low freezing temperature

Bo Li  1   2   3 , Laisheng Huang  4 , Xiaoquan Lv  4 , Yongjie Ren  4
Affiliations
Free PMC article

Variation features of unfrozen water content of water-saturated coal under low freezing temperature

Bo Li et al. Sci Rep. .
Free PMC article

Abstract

To determine the unfrozen water content variation characteristics of coal from the low temperature freezing based on the good linear relationship between the amplitude of the nuclear magnetic resonance (NMR) signal and movable water, pulsed NMR technology was used to test water-saturated coal samples and analyze the relationship between the unfrozen water content, the temperature and pore pressure during freeze-thaw from a microscopic perspective. Experimental results show that the swelling stress of the ice destroys the original pore structure during the freezing process, causing the melting point of the pore ice to change, so the unfrozen water content during the melting process presents a hysteresis phenomenon. When phase equilibrium has been established in the freezing process, the unfrozen water is mainly the film water on the pore surface and pore water in pores with pore radius below 10 nm. At this time, the freezing point of the water in the system decreases exponentially as the temperature increases. The micropores of the coal samples from the Jiulishan Coalmine are well-developed, and the macropores and fractures are relatively small, with most pores having a pore radius between 0.1 and 10 nm. The pore water freezing point gradually decreases with the pore radius. When the pore radius decreases to 10 nm, the freezing point of pore water starts to decrease sharply with the decreasing pore radius. When the pore radius reaches 1.54 nm, the pore water freezing point changes as fast as 600 ℃/nm.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
System diagram of NMR experiment.
Figure 2
Figure 2
Variation of FID signal strength of coal samples with temperature.
Figure 3
Figure 3
Unfrozen water content—temperature curve during freezing of coal samples.
Figure 4
Figure 4
Three-phase graph of water.
Figure 5
Figure 5
Relationship between unfrozen water content and temperature during coal sample freeze–thaw.
Figure 6
Figure 6
Relationship between unfrozen water content and temperature of coal sample C during freeze–thaw.
Figure 7
Figure 7
Pore radius distribution of coal sample.
Figure 8
Figure 8
T2 distribution curve of coal sample A during freeze–thaw.
Figure 9
Figure 9
Relationship between pore radius and pore water freezing point.
See this image and copyright information in PMC

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