Lignite desiccation and cracking mechanism based on physical and molecular simulation

NMR experiments: In order to avoid the testing errors caused by the scattered phase while simultaneously reducing the overall testing time, the NMR experiment employs the Carr-Purcell-Meiboom-Gill (CPMG) sequence to obtain the transverse relaxation signals of the samples under examination (Sun et al., 2023). The specific parameters were set as follows: 90° and 180° pulse widths of 5.80 μs and 11.12 μs, respectively; a radio frequency delay of 0.002 ms; a sampling frequency of 200 KHz; an echo time of 0.1 ms; and a number of echoes of 10 000.Thermogravimetry experiments：Approximately 10 mg of water-saturated coal powder was placed in a crucible, and the temperature was then rapidly increased to 60 °C. This temperature was maintained until no further change in sample mass was observed. During this process, the curves of sample weight and weight loss rate versus time were recorded in detail.