Interaction of Diisopropyl methyl Phosphonate (DIMP) with magnesium oxide at elevated temperatures

Diisopropyl Methyl Phosphonate (DIMP) is a liquid widely considered a surrogate for chemical warfare agents (CWA). Respectively, its interactions with different surfaces must be understood to predict the fate of CWA in various scenarios involving their release. Magnesium oxide (MgO) is a combustion product of metallized energetic materials and can serve as a model material for other common oxides. Thus, its interaction with DIMP is of both fundamental and practical interest. In this work, powders of MgO produced by different methods and having different surface areas and crystallite sizes were exposed to liquid DIMP and heated above the DIMP boiling point in a thermal analyzer. The residue remaining on the surface of different powders was quantified and examined using infrared spectroscopy. It was found that the mass of the residue scaled with the specific surface area determined based on the MgO crystallite sizes. The results suggest that the residue consists of P-CH₃ molecular groups with the phosphorus attached to multiple surface oxygen anions. The residue was found to be discontinuous on smaller crystallites, but it could form a continuous monolayer on larger crystallites. The presence of Mg(OH)₂ prevented interactions between DIMP and the solid surface.