Experimental and teaching application of coal microstructure and its gas adsorption properties
[Objective]There are many associated energy sources in the coal mining process,and gas is one of them.However,gas explosion accidents have always been one of the most influential accidents in coal mining,which seriously hinders safe and efficient underground mining.Coal is a porous medium with many pores and fissures,and these microscopic pores and fissures will affect its adsorption and desorption properties of gas.Therefore,it is of great significance to study the microstructure of coal and its adsorption properties for gas extraction and disaster prevention.[Methods]Based on this,the obtained coal samples were first broken and screened,and then the microscopic structures of coal samples with magnification scales of 30,10,2 μm and 500 nm were investigated by scanning electron microscopy.The element distribution law was obtained by surface scanning of the microscopic morphology images of coal samples at the 100 μm scale using an energy spectrometer.Then,the isothermal gas adsorption experiment of coal particles under different pressures was conducted using a high-temperature and high-pressure adsorption instrument.The change characteristics of the gas adsorption amount of coal samples over time were analyzed and verified with the empirical formula of gas adsorption/desorption.Finally,the application of the experiment content in the experimental teaching reform was discussed.[Results]The results show that there are a lot of pores,coal matrix,and minerals on the surface of the coal sample,and the observed phenomena are different under different magnification scales.The shape of the pores is round at 500 nm,the pore size is approximately 500 nm,and a lot of debris is attached to the surface.The overall element distribution of the coal sample is dominated by C and O,and its weight percentage and atomic percentage can reach more than 90%.However,the element distribution is different at different locations,and there are a lot of Al,Si,and other elements in some locations,which suggests that some minerals may be contained in this location.Under different pressures,the gas adsorption capacity increases rapidly at first and then slowly until it becomes stable.Under stable conditions,the gas limit adsorption capacity and adsorption pressure increase linearly.The experimental data fit well with a Langmuir-type empirical formula with the NTH power of t,and the correlation coefficients are all above 0.99,proving the correctness of the empirical formula.The constants A and B are proportional to the adsorption pressure,representing that the gas adsorption amount and gas adsorption rate under the limit time are proportional to the adsorption pressure.[Conclusions]By guiding students to understand the internal microstructure of coal and characterizing it,students'hands-on ability is exercised,and their understanding of the properties of coal porous media is deepened.Integrating experimental content into experimental teaching can significantly increase students'interest.The test of student satisfaction shows that students'satisfaction is above 95%,which greatly improves the experimental teaching results.This method is significant in enriching the content of students'experimental courses and reforming the experimental teaching system.
scanning electron microscopymicrostructureelement distributiongas adsorptionexperimental teaching
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