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Abstract Utilizing the 600 ℃ 20 MN servo-controlled rock triaxial testing machine with high temperature and high pressure developed by the authors，the research of permeability of anthracite from Jincheng and gas coal from Xinglongzhuang coal mine with 400 mm long and 200 mm in diameter is carried out under in-situ stress with depth of 500 m and different temperatures，considering coefficient of horizontal pressure 1.2. The research results indicate that：(1) A critical temperature is found when the permeability of samples experienced changes with temperature from room temperature(RT) to 300 ℃，evidencing that the permeability of coal samples reaches the minimum value at this temperature stage. (2) A peak temperature is also found from 300 ℃ to 600 ℃，and the permeability at this temperature point reaches the maximum value at temperature over 300 ℃. (3) The process of coal samples¢ permeability changing can be divided into three stages by the critical temperature and peak temperature from RT to 600 ℃. The permeability decreased from RT to the critical temperature；it increases between the critical temperature and the peak temperature；above the peak temperature，it decreases as well. (4) The critical temperature and the peak temperature of permeability are related with coal rank. The critical temperature of anthracite is from 150 ℃ to 200 ℃ and the peak temperature is between 450 ℃ and 500 ℃；the range from 200 ℃ to 250 ℃ is the critical temperature of gas coal and the peak temperature does not emerge with the experimental temperature changing from RT to 400 ℃.
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Received: 13 November 2009
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