IMPEDANCE SPECTROSCOPY OF FOSSIL COAL INCLUDING CRACKS. II. THE MOISTURE SATURATED SAMPLE
The influence of the moist coal cracking on the complex resistance (impedance) is studied theoretically with using the model of effective medium. It is shown that the cracks with the volume moisture contained promote to increasing of the coal dc conductance. At the same time, dry (gas-filled) cracks render the influence of two kinds: on the one hand, they obstruct the passage of direct current by producing the additional active resistance; on the other hand, they play the role of ac capacitors, by passing the displacement currents due to the polarization effects. In the model of randomly oriented cracks, the contribution of the cracks to the imaginary part of the ac impedance on the sample is found. Subject to aforesaid, the analytical expressions for the complex impedance of a water-saturated coal and the tangent of loss angle are obtained. It is shown that using the Nyquist diagram, one can obtain a simple equation for finding the coefficient of coal cracking. The solving of this equation allows an evident expression for the cracking coefficient through the characteristics of coal measured by the methods of impedance spectroscopy. The evaluation of the cracking coefficient for coals of an average metamorphism stage is carried out.