Strong Adhesion of Dust Particles

Fundamental mechanisms in flue gas conditioning. Final report

“…quickly dissipated by grounded surfaces or humidity; greater than van der Waals forces only if particles exposed to corona charging (Visser, 1974); a small factor for particles 1 to 10 pm diameter unless > lo5 charges are on particles (Keller, 1973) 10 times stronger than van der W a a l s force, but charges quickly cancel at distance (Hobbel, 1988); initial layer(s) of adsorbed water may form hydrogen bonds that can contribute 99 % of the total adhesive force (van Oss, 1988) increases adhesion due to van der Waals forces by as much as 5 times up to several layers of adsorption (Visser, 1974); chemisorbed vapors are usually a monolayer thick, whereas physisorbed vapors, less tightly bound, can be many layers thick (Hench, 1971;Rietma, 1984) stronger than van der Waals forces, depending on tensile strength of the adsorbed film and the solid/liquid contact angle (Luckham, 1989); develop above a critical humidity dissolving a water-soluble salt and then evaporating the water can leave a solid bond lo4 times stronger than before the salt was dissolved (Williams and Nosker, 1983) In the particle size regime of coal fly ash, van der Waals forces are generally considered the most fundamental of the interparticle forces. Other forces are usually subsidiary; that is, they become important after the van der Waals forces have attracted particles close enough together for the shorter-range forces to participate in the adhesion.…”