Experimental Study on Fractal Characteristics of Surface Roughness of Briquettes and their Effect on Wettability of Coal Samples

To quantify the influence of surface roughness and its fractal characteristics on the wettability of the samples, coal samples of five particle sizes were selected to produce different cylindrically shaped coal samples in the laboratory, and four grinding methods were used to obtain the coal samples having different roughness values. Three different wetting solutions were utilized to conduct the wetting tests on the coal samples having different roughness values. Theoretical analysis and laboratory studies were carried out to investigate the influence of roughness on wetting parameters. The fractal characteristics of the coal samples with different surface roughness values were analyzed by electron microscopy, and the mechanism of the effect of roughness on wetting performance was analyzed in conjunction with parameters. The results showed that as the surface roughness of the coal samples gradually increased, the fractal dimension increased, the specific surface area of the coal samples increased, the actual contact area of the solid–liquid interface was found to be larger than the apparent contact area, and the adhesion tension and the adhesion work of the wetting solution on the surface of the coal samples increased. The chance of forming a continuous liquid film on the surface of coal samples decreased, more pores were found filled by the wetting solution, resulting in the decrease in contact angle of the liquid on the surface of the coal samples. When the roughness values of the coal samples were in the range of 7–11 μm, the fractal dimension increased rapidly, while the contact angle decreased rapidly.