Study On Mechanism Of Surface Potential Signals Generation Based On Microstructure And Composition Of Coal Rock

The occurrence of coal rock dynamic disasters seriously restricts mine safety production.As an emerging monitoring method of coal rock dynamic disasters,surface potential method has attracted the attention of many scholars.At present,there are few studies on the mechanism of coal rock microstructure and composition on the surface potential signals generation.In this paper,an experimental system for uniaxial compression surface potential signals acquisition of coal rock is constructed.Using the loading system,the uniaxial compression failure tests of graphite,raw coal,granite and sandstone are carried out.The surface potential signals generated by the fracture process are collected.The generated surface potential signals are processed using the critical slowing theory.The surface potentials of coal rock are tested and by Atomic Force Microscope KPFM mode to study the charging characteristics of coal rock surfaces.The microscopic morphology observation and energy spectrum analysis of the fractured coal rock surface are carried out by the Scanning Electron Microscopy.The relationships between the microstructure and composition of coal rock and the mechanism of surface potential signals generation are discussed.Through analysis,the following main conclusions are drawn.(1)The autocorrelation coefficient and the variance curve which characterize the critical slowing characteristics of the surface potential signals of coal rock have sudden increases in the sample failure.Compared with the autocorrelation coefficient,the variance curve produces less false signals.(2)The surface of coal rock exhibits a certain charge characteristic at the nanoscale level.The charge characteristics of the nanoscale of coal rock provide a certain charge basis for the generation of surface potential signals.(3)From the perspective of the surface potential signals generated by the failure mode of coal rock micro-morphology structure,the surface potential signals of graphite are mainly caused by friction and slip.The surface potential signals of raw coal are mainly caused by crack propagation.For granite and sandstone,the free charges generated by the rapid expansion of cracks and the frictional electrification are largely involved in the generation of surface potential signals.(4)The higher the quartz crystal content in the coal rock,the stronger the piezoelectric effect during the loading,and the larger the corresponding surface potential signals increase.For the coal rock with uniform distribution of quartz crystals,the growth of surface potential signals is relatively stable.(5)The surface potential signals generated by different lithologic coal rocks can be divided into three stages.The dominant mechanisms for generating surface potential signals at different stages of different lithologic coal rocks are different.At I stage,the surface potential signals of coal rock are mainly caused by micro-rupture and frictional slip caused by the compaction and closure of the inner original pores.At stage II,for graphite and raw coal,the surface potential signals at this stage are related to small scale frictions and rupture occurring inside.For granite and sandstone,the surface potential signals generated are dominated by the piezoelectric effect of quartz crystal.At stage III,the surface potential signals of coal rock are mainly generated by the internal rapid crack propagation and friction.The research results have important theoretical and practical significance for establishing the complete theoretical system of coal rock surface potential signals and developing and improving the early warning technology of coal rock dynamic disaster potential signals.