Interaction of Hydrated and Dehydrated MgO with Disopropyl Methyl Phosphonate (DIMP) at Elevated Temperatures

Condensed combustion products of reactive materials generated in a blast can serve to accelerate decomposition of toxic liquids, such as sarin, a chemical weapon agent (CWA). In particular, destruction of aerosols of CWA droplets can be augmented by inducing their interaction with a metal oxide smoke. The smoke particles are expected to adsorb and catalyze the decomposition of CWA. The mechanisms and rates of such adsorption and decomposition reactions are poorly understood and are expected to be different for various oxides. Experimental studies commonly use surrogates of CWA. Diisopropyl methyl phosphonate (DIMP), an organophosphorus compound often used as a surrogate of sarin, was used in this work. Its interaction with fine MgO powders representing a smoke produced by magnesium-bearing metal fuels, was studied experimentally. Different MgO powders were explored. In addition to two commercial (-325 mesh and nano-sized) MgO powders, several custom MgO powders synthesized from Mg(NO3)2*6H2O and C2H5NO2 (1:1 and 1:2 mole ratios) were used. Commercial MgO powders were found to be partially hydrated. To remove the hydroxide, all MgO powders were heated to 450 C in a furnace of a thermo-gravimetric (TG) analyzer in a mixed argon/oxygen flow. Further, as-received, as-prepared, and de-hydrated MgO powders were mixed with liquid DIMP in 0.7 ml open alumina crucibles. The DIMP/MgO mixtures were also heated to 450 C using the TG analyzer in a flow of mixed argon and oxygen. As expected, a first major mass loss step occurred while the liquid DIMP was evaporating. It ended before the boiling point of DIMP was reached. The residual mass represented DIMP adsorbed to the powder both physically and chemically. That mass was slowly reduced upon further heating for some samples. Certain residual mass was still retained by all powders even after their exposure to 450 C. A distinct second mass loss step was observed starting at ~250 C for the dehydrated commercial MgO powders, but not for the as-received and custom prepared powders. In separate experiments, all MgO powders were intentionally hydrated by mixing them with water. They were then dehydrated by heating them to 450 C in Ar/O2 environment. For all such hydrated and dehydrated powders exposed to DIMP and subsequently heated in TG, the second mass loss step was observed. This second mass loss step is qualitatively similar to that reported recently to occur when DIMP interacted with gamma alumina. The MgO powders exposed to DIMP and to the TG heating program were recovered and examined using FTIR-ATR analyzer. Clear signatures of DIMP molecule fragments adsorbed to MgO were observed. Such signatures were stronger for the dehydrated powders, which were initially hydrated. The results and possible mechanisms responsible for the adsorption and decomposition of DIMP by MgO surfaces will be discussed in this talk.