ON THE DETERMINATION OF SURFACE FREE ENERGY OF COAL BY MEANS OF THE DERIVATOGRAPH

The calculations of the dispersion γC^d and nondispersion (polar γC^p components of surface free energy of coal on the basis of adsorption measurements of nonpolar (n-heptane) and polar (methanol, propanol, water) liquid vapours a 20°C are presented. Average values ( γC^d = 45.1 mJ/m² and γC^p = 13.2 mJ/m²) are in good agreement with literature data calculated on the basis of separate and independent measurements. The heterogeneous nature of coal surface has been confirmed from derivatographic measurements.