Influence of Spray Drying Conditions on the Properties of Ammonium Dihydrogen Phosphate Fire-Extinguishing Particles

Abstract

Superfine spherical hollow ammonium dihydrogen phosphate (NH4H2PO4) fire-extinguishing particles are first produced by the spray-drying method. The particles prepared at drying gas inlet temperature ranging from 180°C to 220°C are composed of NH4H2PO4. When the proportion of FK-510 increases from 5 wt%to 10 wt%, the surfaces of the as-prepared particles become rougher, and the volume mean size of particles increases from 11.25 to 15.44 µm. When the proportion of FK-510 increases from 10 to 15 wt%, the amount of broken spherical hollow particles clearly decreases and the volume mean size of particles decreases from 15.44 to 13.5 µm. The flow rate and bulk density of the particles prepared from the solution containing the proportion of FK-510 ranging from 5 to 15 wt% decreases with an increase in the proportion of FK-510. When 15 wt% of FK-510 is added, diesel oil contact angle of particles markedly increases. In addition, water contact angle of particles decreases with an increase in the proportion of FK-510. XPS analysis suggests that the wettability of particles is attributed to the migration of FK-510 and silicone oil emulsion to the surface of particles during the spray-drying process. Diesel oil contact angles of particles agree with fluorine element concentrations on the surface of particles, while water contact angles of particles agree with silicon element concentrations.