Experimental study on the microstructure change and evolution law of sandstone under different temperatures
The combination of high ground stress in deep coal seams and high temperature thermal stress in underground gasification will cause rock damage and destroy the stability of the coal seam surrounding the rock.This research investigated the relationship between temperature(25 ℃,200 ℃,400 ℃,600 ℃,800 ℃,and 1 000 ℃)with the microstructure and mineral composition of sandstone through the application of scanning electron microscopy,X-ray diffraction,and CT scanning.The results suggests that the temperature has a significant impact on sandstone microstructure because an increase in the temperature can improve the total porosity.The porosity of sandstone at 1 000℃ is the maximum and the minimum at 25 C.The number of pores of different sizes decreases with the increase in the temperature.However,the number of tiny pores at 1 000 ℃ is the most,and the number of pores at other sizes at 25 ℃ is the most.After heating,the sandstone begins to produce microcracks.When the temperature exceeds 600 ℃,the number of microcracks increases significantly,and the length,width and density of microcracks further expand with the increase in the temperature.The diffraction intensity and mineral composition of the sandstone vary with the temperature.When the temperature is higher than 600 ℃,the diffraction intensity of various mineral compositions takes a turning point.When the temperature exceeds 400 ℃,a physical and chemical reaction occurs in the mineral composition of sandstone,and a transformation occurs between crystals.With the increase in temperature,the quartz mineral content gradually increases,and the feldspar mineral gradually decreases.The critical temperature of the specimen's apparent morphology change was 400 ℃.
rock mechanicssandstonethermal damagemicroscopic structuremineral compositionpore structure
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