SMOKE PRODUCTION
Two basic processes are used to create smoke clouds: the con- densation of vaporized material and the dispersion of solid or liquid particles. Materials can either be released slowly via a pyrotechnic reaction or they can instantaneously be scattered using an explosive material. Technically, a dispersion of fine solid particles in air is termed a smoke, while liquid particles in air create a fog. A smoke is created by particles, while larger suspended particles create a dust.
A variety of events that will lead to smoke production can occur in the pyrotechnic flame. Incomplete burning of an organic fuel will produce a black, sooty flame (mainly atomic carbon). A highly-oxidized fuel such as a sugar is not likely to produce carbon. Materials such as naphthalene (C10H 8) and anthracene ( C 1,,H 10 ) - volatile solids with high carbon content - are good candidates for soot production. Several mixtures that will produce black smokes are listed in the table.
Black Smoke Compositions
The heat from the reaction between an oxidizer and fuel can vaporize a volatile ingredient, with no chemical change occurring in the vaporized material. The vaporized component, which was part of the original mixture, then condenses as fine, solid particles upon leaving the reaction zone and a smoke is created. Organic dyes, ammonium chloride, and sulfur can be used to create smokes using this method.
Alternately, the pyrotechnic reaction can occur in a separate container, and the heat that is produced volatilizes a smoke-forming component contained in an adjacent compartment. The vaporization and dispersion of heavy oils to create white smoke uses this technique.
Finally, a product of a pyrotechnic reaction may vaporize from the reaction zone and subsequently condense as fine particles in air, creating a smoke. Potassium chloride (boiling point 1407°C) produces smoke in many potassium chlorate and potassium perchlorate compositions, although smoke is usually not a goal sought from these mixtures.
A good white smoke can be obtained by the formation of zinc chloride, ZnC12, from a reaction between zinc metal and a chlorinated organic compound (the chlorine-containing species serves as the oxidizer). Reaction products that strongly attract moisture (such as ZnCl2 ) will have an enhanced smoke effect in humid atmospheres. The burning of elemental phosphorus, producing phosphorus oxides, creates dense white smoke as the oxides attract moisture to form acids such as phosphoric acid, H3PO2.