Research On Structural Damage Characteristics Of Coal Under The A Ction Of Surfactant

The structural characteristics of coal were dense structure,complex pore structure and poor permeability.There were often faced with gas explosions,coal and gas outbursts,gas poisoning,ground pressure and other mine disasters in the coal mining process.Surfactant can form a directional tight adsorption layer on the coal surface to change the physical and mechanical properties of the coal surface.In order to reduce or avoid the occurrence of mine disasters and to extract gas from dense coal seams,the structural damage characteristics of coal under the action of surfactants were studied.The Fuxin long flame coal was used as the research object,and the sodium dodecyl sulfate(SDS),the cetyltrimethylammonium bromide(CTAB)and the nonylphenol ethoxylate(NP-40)were used to carry out modification experiments for coal.The contact angle test,mercury injection test,permeability test,and uniaxial compression test were used to determine the changes in parameters such as the contact angle,pore structure,permeability,and mechanical strength of the coal before and after surfactant modification.The diffraction and fourier transform infrared spectroscopy experiments were used to determine the micromorphology,mineral composition,and functional group changes of coal before and after surfactant modification.Based on the first-principles and quantum chemical density functional theory,the modification mechanism of surfactant on coal was proposed.The structural damage mechanics model of loaded coal under the action of surfactant was established.The rationality of damage mechanics model was verified based on the results of uniaxial compression experiments.The main conclusions were as follows:(1)The optimum modification conditions of SDS,CTAB and NP-40 were determined by the modification experiment of the surfactant on the coal.The modification experiment was based on the contact angle,and the modification effect was SDS>CTAB>NP-40>distilled water.(2)After modification by SDS,CTAB and NP-40,both the porosity and permeability of the coal were increased,the peak strength and elastic modulus of the coal were decreased,and the peak strain of the coal were increased.The relationship between the modification conditions and mechanical parameters was analyzed,and it was found that the peak strength and the modification conditions satisfy a nonlinear relationship,the peak strain and the modification conditions satisfy a nonlinear relationship,and the elastic modulus and each modification condition satisfy an exponential relationship,and the correlation coefficients were all greater than 0.900,that is,R2>0.900.(3)After modification by SDS,CTAB and NP-40,the coal structure was loose,the pores and fractures were connected well,the carbonate minerals and sulfides in the coal were dissolved,and the silicate minerals were recrystallized.The microcrystal structure integrity of coal macromolecules was poor,and the ordering order was poor.The functional groups and various bridge bonds in coal macromolecules were abundant,and the content of hydroxyl,aliphatic hydrocarbon,aromatic hydrocarbon and oxygen-containing functional groups were increased.(4)Based on the first-principles and density functional theory,the modification mechanism of surfactant on coal was proposed,that is,the surfactant was adsorbed on the coal by.intermolecular force(electrostatic force,van der Waals force,π electron polarization),and secondary pores and cracks were formed on the surface and inside of the coal,and cracks were formed.The cracks change with the modification conditions of the surfactant.The number and width of cracks continue to increase until the crack penetrates the entire coal,which caused damage to the overall structure of the coal.(6)The total damage mechanics model of the loaded coal under the action of surfactant was established.The structural damage characteristics of the coal were analyzed from the essential characteristics of the damage mechanics.That is,the structural damage of the coal after the modification of the surfactant can be seen as two parts,one part was the damage caused by the surfactant to the coal,and the other part was the damage caused by the load of the coal,and the two parts complement each other.The damage caused by surfactants to the coal body structure can be seen as a microscopic cause in the macroscopic performance,that is,the surfactant adsorbed on the coal and caused micro-structure damage.As the modification conditions changed,the micro-structural damage gradually increased,and macro damage occurred when it reached a certain level,which was manifested as the failure of the coal structure.There are 76 pictures,32 tables and 215 references in this paper.