Huge amounts of fly ash are generated as waste from coal-burning power plants around the world. By silanizing and thereby making its surface hydrophobic, the practically negative-value waste can be utilized as a low-cost surface coating agent to transform various water-wet solid surfaces to water-repelling hydrophobic ones. A thin film of water, on whose air/water interface the silanized fly ash particles are adsorbed, spreads rapidly on a water-wet solid surface, allowing a uniform deposition of silanized particles for easy and low-cost modification of wettability of a solid surface. The spreading rate of the silanized particle-laden thin water film can be quantified with the well-characterized phenomenon of surface pressure-driven “film-climbing” on water-wet wall (photo below, left). The concentration of the silane used for silanization was adjusted to control the particle’s hydrophobicity, which was characterized by the measurement of air/water/solid contact angle on various water-wet solid substrates deposited with silanized fly ash particles (photo below, right). By nano-milling fly ash to nano size, the effect of particle size on generating the hydrophobic, water-repelling surface was studied. With the thermal treatment of particles, the effect of carbon content of fly ash on hydrophobic surface generation was also investigated.

Use of silanized fly ash as a low-cost coating agent to make water-wet surfaces highly hydrophobic

2019 Spring National Meeting

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