Coal surface structure and gas adsorption under direct current electric field treatment

The direct current electric field was used as a physical field. An experimental apparatus affecting the gas ad- sorption in coal with voltage weakening was utilized. The experiment on the gas adsorption in coal under the voltage treatment had been conducted. The coal surface structures of the experimental samples were measured by XPS. The species and the relative contents of the C element with oxygen functional groups in the coal surface structure were ana- lyzed. The law between the coal gas adsorption under the voltage and the C element with oxygen functional groups was studied. The experimental results were as follows:the gas adsorption in coal could be weakened under the voltage treat- ment. Under the electric field of 80 kHz / 1 kV,80 kHz / 3 kV and 80 kHz / 5 kV,the oxygen functional group of the C element on the coal surface structure was modified, the relative content of C—C / C—H reduced from 47． 22% to 24． 95% ,and the new oxygen functional groups were C—O,C O and COO—. The relative contents of the third oxy- gen functional groups increased and the maximum contents were 54. 44% ,13. 89% and 7. 39% ,respectively. With the decrease of the relative content of C—C / C—H,the saturated adsorption capacity reduced with a linear law and the adsorption constant reduced with an exponential law. The coal pore structure parameters including the total pore area, the median pore size (volume),the median pore size (area) and the mean pore size were increased under the electric field.