3.1. CHEMICAL IDENTITY

Information regarding the chemical identity of white phosphorus is located in Table 3-1.

3.2. PHYSICAL AND CHEMICAL PROPERTIES

Information regarding the physical and chemical properties of white phosphorus and white phosphorus smoke is located in Table 3-2.

Elemental phosphorus exists in several allotropic forms (Van Wazer 1982). The best known and most important commercially is the a-white phosphorus whose properties are given in Table 3-2. Commercial white phosphorus is 99.9% pure, with a slight yellow color caused by traces of red phosphorus impurities. Hence, white phosphorus also is known as yellow phosphorus. When a-white phosphorus is cooled below -79.6^°C, P-white phosphorus forms. Other important solid allotropes of phosphorus are red and black phosphorus (Van Wazer 1982).

The U.S. Army uses at least two phosphorus-based smoke/obscurants for training and testing activities (Shinn et al. 1985). One such agent is white phosphorus/felt (WP/F), and the other is red phosphorus/butyl rubber (Spanggord et al. 1985). WP/F consists of 75-80% white phosphorus solidified into a cellulose (felt) matrix (20-25%). When WP/F is burnt, besides unburnt white phosphorus, the smoke consists primarily of oxidation and hydrolysis products of phosphorus. For example, when white phosphorus burns in air it produces oxides of phosphorus including phosphorus pentoxide (P₄O₁₀, and phosphorus trioxide (P₄0₆). These oxides react with moisture present in air to form a number of phosphorus-containing acids, such as orthophosphoric acid (H₃PO₄), pyrophosphoric acid (H₄P₂O₇), orthophosphorus acid (H₃PO₃), hypophosphorus acid (H₃PO₂), polyphosphoric acid of the general formula H_n+2P_nO_3n+1, where n=2-8, and a homologous series of linear and cyclic P₆-P₁₆ polyphosphates (Spanggord et al. 1983; Tolle et al. 1988). The composition of white phosphorus smoke will change with time (Spanggord et al. 1988). In the absence of stoichiometric quantities of oxygen, phosphine (PH₃) may form in WP/F smoke from the reaction of unreacted phosphorus with moisture in air (Spanggord et al. 1983).

TABLE 3-1

Chemical Identity of White Phosphorus.

TABLE 3-2

Physical and Chemical Properties of White Phosphorus.

Reactions of white phosphorus that lead to the formation of some typical products are listed below (Cotton and Wilkinson 1980; Spanggord et al. 1985).

Organic constituents that may be found in ppb levels in WP/F smoke include methane, ethylene, carbonyl sulfide, acetylene, 1,4-dicyanobenzene, 1,3-dicyanobenzene, 1,2-dicyanobenzene, acetonitrile, and acrylonitrile (Tolle et al. 1988). Since white phosphorus contains boron, silicon, calcium, aluminum, iron, and arsenic in excess of 10 ppm as impurities (Berkowitz et al. 1981), WP/F smoke also contains these elements and possibly their oxidation products. The physical properties of a few major compounds that may be important for determining the fate of WP/F smoke in the environment are given in Table 3-3.

Table 3-3

Physical Properties of Major Compounds in White Phosphorus Smoke.