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In order to study the surface electric potential signals during the coal adsorbing gas, designed the experiment system of the coal adsorbing gas and tested the electric potential signal generated during the coal adsorbing gas under different gas pressure. Experiment results show that surface potential signals can be generated in the process of adsorbing gas, and they increases gradually along with the growth of adsorption time. For the same coal samples, different gas pressure from the coal surface potential signal to the first adsorption gas pressure of coal potential signal has a memory effect in the process of absorption. When the adsorption gas pressure is higher than the first adsorption gas pressure, the coal induces stronger surface potential signals. And when the adsorption gas pressure is lower than the first adsorption gas pressure, the coal induce weaker surface potential signals. The main reasons why surface potential signals can be generated from coal adsorbing gas are that the gas seepage in coal pores produces flow potential and free charge is generated when the gas damages micro cracks and crack of coal. [ABSTRACT FROM AUTHOR]

An investigation was conducted on the characteristics of surface current induced by coal under uniaxial compression. An interpretation of the mechanisms governing the electrical behavior of the coal structures under uniaxial stress tests was presented in this paper. The experimental results show that the current signal is generated during the deformation and fracture process of coal samples. When the load is applied, the electric current makes its initial appearance and increases rapidly after a considerable time lag at 8C, until after the stress reaches a value δc ≈0.75δmax where δmax is the maximum applied stress before sample fracture. There is a good correlativity between the current and the load, and the correlation coefficient between them can reach up to 0.8 to 0.9. The current peaks occur under sudden loading and unloading. It suggests that the current is closely related to the loading. The status of coal loading level may be determined by the current signal. The intensive study on coal surface current can provide a way for monitoring the stability of coal and rock. [ABSTRACT FROM AUTHOR]

The experiment was made on the rules of surface potential of coal or rock during friction process. The mechanism producing surface potential of coal or rock friction was discussed initially. The results show that surface potential can be produced during coal or rock friction process, and it has a better corresponding relationship with load. The coal or rock friction process can be divided into two stages: static friction stage and kinetic friction stage. The surface potential signal in kinetic friction stage was stronger than that in static friction stage. During rock friction process, the polarity of surface potential signal was basically bidirectional mutation, and the polarity of surface potential on both sides of friction surface had obvious symmetry. While the polarity of surface potential signal was basically unidirectional mutation in coal friction process, and the polarity of surface potential on both sides of friction surface was not in significant symmetry. The changes of surface potential during coal or rock friction process can be explained by mechanism of electricity produced by friction, thermionic emission and field electron emission. [ABSTRACT FROM AUTHOR]

In order to study the relationship between surface potential distribution and destruction localization of the coal sample, the distribution law of strain field and surface potential of coal samples were tested under load. The relationship between surface potential field and strain localization & fracture of coal samples was studied and analyzed. Results show that the coal samples show obvious strain localization characteristics in deformation and failure process, the strain localization concentrated area is the severe damage and fracture part of coal samples, and the strain localization zones is usually the fracture location of coal samples. The distribution character of surface potential field of coal samples during deformation and fracture is similar to the strain field, the potential field will be centralized in the damage localization area, the connection between the points of high potential and low potential reflects the rupture section of coal samples. [ABSTRACT FROM AUTHOR]

In order to analyze the failure mechanism of coal under the load, multi-fractal characteristics of surface potential of coal sample under uniaxial compression was studied. The surface potential was analyzed using multi-fractal theory to calculate the multi-fractal spectrum. The change rules of characteristic parameters of multi-fractal spectrum with the loading process were studied. The results show that the surface potential represents multi-fractal feature, and keeps scale invariance in the wide range. The shape of the multi-fractal spectrum of different size specimens shows right hook. The characteristic parameters of multi-fractal spectrum, Δα and Δf, vary with the process of deformation and fracture of coal sample with load. The changes of trend that Δα and Δf increase in a long time, then decrease rapidly can be used as a precursory factor of coal-rock failure to forecast the instability of the samples. The results are helpful to understand the inherent law in the coal specimen failure process and forecast the dynamic disaster using the potential. [ABSTRACT FROM AUTHOR]

Acoustic emission signals generated in process of methane sorption and seepage in coal were observed, and the dynamic characteristic of damage evolution and the seepage process were analyzed based on the characteristic of acoustic emission. The experiments indicated that the strength of acoustic emission decreased with the adsorbed methane increase. And the acoustic emission showed paroxysmal in time domain. The results give implication that the methane seepage in coal layer by layer. In its seepage process, methane shows destructive seepage while the gas pressure gradient was bigger than the threshold value. Then, pressure of the seepage face decreased and the methane shows undestructive seepage. Sorption process tends to equilibrium with the gas pressure increase. [ABSTRACT FROM AUTHOR]