Abstract The wettability of coal is an important parameter for representing the surface hydrophobicity and floatability of coal particle, and hence determines coal flotation behavior. The wettability of coal is primarily governed by the surface functional groups. However, the role of surface topography in the wettability of coal has not attracted enough attentions. This paper was to investigate the effect of roughness on the wettability of coal by measuring the contact angle between air bubble and flat coal surface. Besides, a new method to measure the contact angle is introduced. The shape of the bubble is fitted by both the circle and the ellipse. The lump coal particles were used as coal sample and polished by sand papers of different meshes to gain the specific flat coal surfaces of different roughness. The attachment time measurements and Wenzel theory were used to further explain why the surface roughness has significant effects on the contact angle of air bubble on coal surface. Throughout this paper, it was found that the wettability of coal was decreased with the increase of surface roughness. The water may be entrapped in the pores/cracks of rough coal surface which prevents the attachment between coal surface and bubble as well as the spreading of three-phrase contact line. Therefore, both the attachment time and contact angle were decreased with the increase of roughness.

中文翻译：

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不同粗糙度平坦煤面上气泡的接触角和诱导时间

摘要 煤的润湿性是表征煤颗粒表面疏水性和可浮性的重要参数，决定了煤的浮选行为。煤的润湿性主要由表面官能团控制。然而，表面形貌在煤润湿性中的作用尚未引起足够的重视。本文旨在通过测量气泡与平坦煤表面的接触角来研究粗糙度对煤润湿性的影响。此外，还介绍了一种测量接触角的新方法。气泡的形状由圆和椭圆拟合。以块煤颗粒为煤样，用不同目数的砂纸打磨，得到不同粗糙度的特定平坦煤面。附着时间测量和文泽尔理论被用来进一步解释为什么表面粗糙度对气泡在煤表面的接触角有显着影响。贯穿本文，发现煤的润湿性随着表面粗糙度的增加而降低。水分可能滞留在粗糙煤面的孔隙/裂缝中，从而阻碍煤面与气泡的附着以及三相接触线的扩展。因此，附着时间和接触角都随着粗糙度的增加而减少。水分可能滞留在粗糙煤面的孔隙/裂缝中，从而阻碍煤面与气泡的附着以及三相接触线的扩展。因此，附着时间和接触角都随着粗糙度的增加而减少。水分可能滞留在粗糙煤面的孔隙/裂缝中，从而阻碍煤面与气泡的附着以及三相接触线的扩展。因此，附着时间和接触角都随着粗糙度的增加而减少。