Micro-electrical characteristics of coals with different metamorphic grade

In order to further study the mechanism of the electromagnetic radiation of coal,the atomic force microscopy (AFM) was used to study the distribution rules of electric parameters such as micro-surface potential and charge den- sity of coal samples with different metamorphism grades. This research pushes the study in this field to a micro-nano scale. The results show that the coal surface shows weak electricity at the meso-or macro-level or electrical neutrality, but exhibits certain electrical characteristics at the nanoscale. The surface charge density of coal samples varies from 79. 95 μC / m2 to 312. 97 μC / m2 ,and the difference of which is obvious. The metamorphism grade has an important in- fluence on the electrical parameters of coal surface:with the increase of metamorphism grade,the negative surface po- tential of coal undergoes a slow change first and then rapidly,while the surface charge density shows a “ V” curve change that firstly decreases and then increases. It is of significance to study the micro-electrical characteristics of coal and rock for further revealing the electromagnetic radiation mechanism,gas adsorption and desorption processes,and even the physical properties of coal from the micro level.