The structure of the pore space of coal in bump-prone and burst-prone seams and the form of the moisture filling this space

Abstract

To make a detailed study of the sorption pore space of the coal, we can use the method of sorption of vapor. For bodies permeated by a network of pores and capillaries, the form of the adsorption isotherms depends directly on the transverse dimensions of the capillaries (i.e., on their effective radius r/sub eff/). In most cases the adsorption isotherms of porous materials are of the so-called S shape (or approximate to it), with hysteresis over some range of relative vapor pressures p/p/sub s/. In adsorbents with fine pores (r/sub eff/ less than or equal to 10 A), or, on the other hand, in nonporous ones (and also in very coarsely porous ones), there may be no hysteresis. The first steep rise in the isotherm corresponds to monomolecular adsorption in which the first layer of gas molecules forms dipoles tightly bound to the surface. On further rise in pressure the adsorption continues to increase, because new adsorbed layers continue to form until the adsorbed gas (vapor) begins to condense on the surface or in the capillaries as an ordinary liquid. Therefore the second steep rise in the isotherm, characterized by hysteresis, is attributed to capillary condensation in the pores ofmore » the adsorbent. Capillary condensation begins on the polymolecular film; its start coincides with the start of hysteresis. In the region of capillary condensation, the relative pressure p/p/sub s/ above the meniscus of a liquid (gas)in the capillaries is related by Thomson's equation to the characteristics of the liquid (gas) in the capillary and the corresponding radius of the capillary r. With water vapor as the adsorbate, the relative vapor pressure is attained by means of the different relative air humidities above sulfuric acid solutions of various concentrations. Coal samples from various mines were examined and correlated with rock burst occurrences.« less