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The obscurant portion of the grenades consists of a 95:5 mixture of red phosphorus and styrene-butadiene rubber (butyl rubber) in the presence of methylene chloride, which is later removed by low temperature drying (Lundy and Eaton 1994). Analysis of samples for methylene chloride found none present (Brazell et al. 1984). The purpose of the butyl rubber is to reduce the cloud-pillar effect found with pure red phosphorus. This mixture of red phosphorus and butyl rubber (RP-BR) also contains two other compounds. The red phosphorus is coated with about 1.25% (by weight) of insulating oil, and approximately 1% talc or silica is added to break up and improve uniformity of the pattern.
Red phosphorus is also the major ingredient in mortar rounds used to generate smoke. In that use, it is combined with sodium nitrate and an epoxy binder in a ratio of 80:14:6 parts by weight, respectively.
Physical and Chemical Properties
The red allotropic form of elemental phosphorus is intermediate to the black and white varieties in reactivity. Red phosphorus reacts slowly with oxygen and water vapor and can evolve phosphine gas, which is highly toxic. The reaction is extremely slow at normal temperatures and humidities and is not considered to be a factor in the deployment of phosphorus munitions in military operations. However, this reaction can be catalyzed by metal ions (e.g., iron and copper), which can markedly increase the oxidation rate. The physical and chemical properties of red phosphorus are listed below:
