Surface deposition characteristics of water-based SiO2 nanofluids on coal

Abstract

Water-based SiO2 nanofluids, a type of wetting agent for water injection of coal seams, have been well recognized by many scholars due to being environment-friendly and having a stable modification effect. The key of the modification effect of water-based SiO2 nanofluids on coal seam is the deposition behavior of nanofluids on coal surface. Based on this issue, this research conducted real-time monitoring of the morphological evolution characteristics and deposition images of water-based SiO2 nanofluid droplets with different concentrations on coal surface. Moreover, the deposition behavior of water-based SiO2 nanofluids on coal surface was microscopically expounded. The results indicate that the initial contact angle between the nanofluid droplets and coal surface is small, and the spreading degree of water-based SiO2 nanofluids is better than that of deionized water. With the increase of time, the contact angles between water-based SiO2 nanofluid droplets and coal surface tend to linearly decrease. However, the relative length of contact line features flattening at first and then a sharp decline. As the nanoparticles are completely precipitated, water-based SiO2 nanofluid droplets form a deposition pattern with a coffee ring structure on coal surface. In addition, as the particle concentration increases, the relative width of the coffee ring increases stepwise. The particle aggregate on the middle of the deposition pattern gradually connects to coalesce and forms a relatively uniform and flat deposition layer. Based on the research results aforementioned, this research divided the deposition behavior of the water-based SiO2 nanofluid droplets on coal surface into initial stage, the contact angle dominance change, the contact angle and line co-dominance change and complete deposition. Among which, the duration of the angle dominance change stage is longest. With the increase of the particle concentration, the proportion of the angle dominance change stage increases. The research can fill the gap of the research on the deposition behavior of nanofluids on coal surface, which lays a foundation for further research of coal seam water injection using nanofluids.