Film-Forming Property and Oxygen Barrier Characteristic of Gel-Stabilized Foam Used for Controlling Spontaneous Combustion of Coal

In order to prolong the extinguishment period of foam, gel-stabilized foam with special film-forming properties and oxygen barrier characteristics was developed in this paper. The film formed from gel-stabilized foam would stop coal from coming into contact with oxygen and retarded the oxidation process and self-heating behavior of coal. Effects of composition concentrations including the thickening agent (TA) and crosslinking agent (CA) on film-forming properties were investigated by analyzing the film morphology formed from gel-stabilized foam. The results showed that increasing the TA concentration from 2 to 4 g/L would enhance the foam stability obviously, and the gel-stabilized foam after adding 4 g/L TA would form the fragmentized coverage film with some obvious holes. Furthermore, adding the CA into gel-stabilized foam would be beneficial to form a whole film to cover coal, and the film structure became more complete when the CA was increased from 1 to 3 g/L. In addition, when foam was composed of 3 g/L CA and 4 g/L TA, it could form an unbroken film mainly ascribed to the strong chemical reaction between the TA and CA in foam. Experimental and theoretical analysis indicated that the forming process of the film mainly included gravity drainage of foam, connection of surface layers, and formation of a frame structure. The oxygen barrier characteristic test and FTIR analysis showed the excellent coverage ability of gel-stabilized foam, and it would form a layer of coverage film to prevent the combination of coal and oxygen. The excellent coverage ability of the film could be evidenced by more weak changes in contents of aliphatic hydrocarbons and oxygen-containing functional groups for coal covered by gel-stabilized foam, compared to other coal samples. The study provided a novel technology to control the oxidation process of coal.