| || Stabilisation of Red Phosphorus to Prevent Moisture Absorption and Suppression of Phosphine Release
Author : Somayajulu, M. R.;Gautam, G. K.;Rao, A. Subhananda
Source : Defence Science Journal ; Vol:57(6) ; 2007 ; pp 817-824
Subject : 620.261 Explosives ;623.4 Armaments and Ballistics
Keywords : Smoke;Red phosphorus;Multi-spectral obscuration;Phosphorus acids;Phosphine;Stabiliser
Abstract : Red phosphorus (RP) is an essential ingredient to generate smoke for multi-spectral obscuration and is receiving wide attention throughout the world for military applications. However, oxidation of phosphorus occurs in moist air resulting in the formation of various phosphorus acids and subsequently the evolution of the toxic gas, phosphine (PH3), even in the sealed systems. Entrapped moisture leads to deterioration of the stores. The commercial-RP at ambient temperature and 95 per cent RH conditions indicates 15 per cent moisture absorption and 13 per cent acidity development with the generation of more than 100 ppm of phosphine gas. Efforts were made to overcome this problem by suppressing acid formation. The technology adopted was: (i) use of stabiliser, and (ii) doping stabiliser-coated particles with polymeric substance. 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 faster than amphoteric Al2O3, in removing the acid from site of reaction, thus suppressing the phosphine release effectively. Though MgCO3 as stabiliser suppresses moisture absorption and acidity development, phosphine release is not controlled effectively. Study of RP coated with these materials independently and monitoring them at different RH conditions indicated superiority of MgO in suppressing acidity and phosphine formation.
| || Radiometric Screening of Red Phosphorus Smoke for its Obscuration Characteristics
Author : Gautam,G.K.;Joshi,A.D.;Joshi,S.A.;Arya,P.R.;Somayajulu, M.R.
Source : Defence Science Journal ; Vol:56(3) ; 2006 ; pp 377-381
Subject : 623.459 Chemical Weapons;623.459 War Gases
Keywords : Smoke screen;Pyrotechnic compositions;Red phosphorus;Obscuration characteristics;Radiometric screening
Abstract : Red phosphorus and potassium nitrate-based compositions exhibit favorable smoke screen formation with high obscuration characteristics at low oxidiser content. The rapid vaporisation of excess red phosphorus at higher flame temperature leads to quick aerodispersion. The obscuration characteristics are due to formation of P2O5 and subsequent reaction with moisture/ humidity in the atmosphere. Obscuration increases with increasing humidity. Extinction coefficient, the shadow cast per unit mass of the composition, is higher in visible and comparatively lower in far infrared.