Stabilisation of Red Phosphorus to Prevent Moisture Absorptionand Suppression of Phosphine Release

Abstract

Red phosphorus (RP) is an essential ingredient to generate smoke for multi-spectralobscuration and is receiving wide attention throughout the world for military applications.However, oxidation of phosphorus occurs in moist air resulting in the formation of variousphosphorus acids and subsequently the evolution of the toxic gas, phosphine (PH3), even inthe sealed systems. Entrapped moisture leads to deterioration of the stores. The commercial-RPat ambient temperature and 95 per cent  RH conditions indicates 15 per cent  moisture absorptionand 13 per cent acidity development with the generation of more than 100 ppm of phosphinegas. Efforts were made to overcome this problem by suppressing acid formation. The technologyadopted was: (i) use of stabiliser, and (ii) doping stabiliser-coated particles with polymericsubstance. The aim to use metal oxide as stabiliser was to neutralise the phosphorus acids,which are catalysing the phosphine generation. MgO due to its basic nature seems to be fasterthan amphoteric Al2O3, in removing the acid from site of reaction, thus suppressing the phosphinerelease effectively. Though MgCO3 as stabiliser suppresses moisture absorption and aciditydevelopment, phosphine release is not controlled effectively. Study of RP coated with thesematerials independently and monitoring them at different RH conditions indicated superiorityof MgO in suppressing acidity and phosphine formation.