Investigation on the structure evolution of pre and post explosion of coal dust using X-ray diffraction

Abstract

To reveal the effects of coal dust explosion on its crystal structures evolution, the micro structure of six different rank of coal dust and its explosion solid products had been studied using 20 L explosion sphere vessel and X-ray diffraction (XRD) analyzer. The correlations between structural parameters and explosion severity had been analyzed detailed. Results show that coal dusts with higher volatile matter contents (Vdaf), lower vitrinite reflectance (Ro,max) and less ash contents (Aad) show stronger explosion severity. The effects of vitrinite reflectance (Ro,max) on the explosion severity parameters present the same role as the influence of volatile matter contents (Vdaf). Coal dusts with developed porous structure (SBET and VBJH) also present higher explosion reactivity. Interestingly, six selected coal samples present the strongest explosion severity at the same optimum explosion concentration (250 g/m3). For the different rank raw coal, the difference of the shape and intensity of 002 peak varies greatly. With the decreasing of coal ranks, the 002 band tends to be blunt and the peak intensity is relatively short. Quantitative analysis show that the lattice parameters (La, Lc, and Navg) of six coal samples are found to relatively increase with increasing vitrinite reflectance (Ro,max), whereas the d002 slightly decreases. The explosion treatments have significant effects on the ordering of coal aggregate structure. Compared with raw coal sample, the relative intensity of 002 bands at about 26° is reduced by the explosion treatments, which would increase the degree of graphitization of the explosion solid products. With the increasing of explosion pressure, the relative intensity of 002 peak would be gradually decreased. However, the shape of 002 peak for the explosion solid products tend to be more asymmetric and blunter than that at lower explosion conditions. Compared with the parent coals, the inter-layer spacing d002, Lc and Navg of all explosion products would be slightly reduced correspondingly. However, there is no clear rule for the evolution of La parameter. Moreover, calculated aromaticity (fa) of the coals ranges from 0.2208 to 0.6883, which is linear positively increased with the coal maturity by vitrinite reflectance.