THE WETTING BEHAVIOR OF SEVERAL ORGANIC LIQUIDS IN WATER ON COAL SURFACES

Several organic liquids were used to probe the surface chemical charac teristics of five coal types ranging in rank from brown to low-volatil e bituminous in the presence of water. The liquids were hexane, cycloh exane, diiodomethane, toluene, o-xylene, chloroform, dichloromethane, oleic acid, chloroform and hexan-1-ol. The advancing and receding cont act angles formed at the coal-water-liquid junction were measured and it was found that a critical interfacial tension existed, below which the organic liquid wetting properties were equivalent. Above the criti cal interfacial tension, the wettability of the coal by the organic li quid increased as the polarity of the liquid increased, giving a measu re of the efficiency with which the water wetting film could be expell ed from the coal surface. At a fixed interfacial tension, the advancin g and receding contact angles decreased as the rank of the coal increa sed.