The evaporation and degradation of VX (O-ethyl S-[2-N,N-(diisopropylamino)ethyl] methylphosphonothioate) on silica sand and borosilicate glass were measured using vapor analysis and 31 P solid state magic angle spinning nuclear magnetic resonance (SSMAS NMR) spectroscopy. 31 P SSMAS NMR studies of VX degradation on crushed glass, air-dried sand, and oven-dried sand at a variety of temperatures showed that the final product was nontoxic ethyl methylphosphonic acid (EMPA), produced via the toxic diethyl dimethylpyrophosphonate intermediate. The reaction exhibited a lag time that depended upon the quantity of water and EMPA that were present in the initial sample of VX and was autocatalytic; EMPA was both the catalyst and product for the degradation of VX. 31 P SSMAS NMR studies of VX on moist sand at a variety of temperatures showed that the final product was nontoxic EMPA; observed intermediates were protonated VX, O-ethyl methylphosphonothioic acid, and toxic EA-2192 (S-[2-N,N-(diisopropylamino)ethyl methylphosphonothioic acid). The VX degradation mechanism differed on the moist and dry surfaces; the activation energies were 80 kJ/mol on moist sand and ∼46 kJ/mol on glass, air-dried, and oven-dried sand. The VX degradation rate was 5 to 9 times slower on moist sand than on air-dried sand. Analysis of the vapor emitted showed that the maximum vapor concentration coincided with the maximum surface area of the droplets, which was at ∼300 min. After four days, no further change in the concentration of vapor emitted was detected; approximately 9% of the incident VX drop on sand and ∼60% of the incident VX drop on glass had been recovered as VX vapor.

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The experimental measurement and modeling of liquid chemical agent spread and sorption on a porous substrate are described. Experimental results with the nerve agent O-ethyl S-(2-diisopropylaminoethyl) methylphosphonothiolate (VX) demonstrate that the wetted imprint volume increases, even after the sessile drop volume is exhausted. This indicates the wetted imprint is only partially saturated, and a multiphase flow problem formulation is needed to predict the VX fate in porous substrates. Three characteristics and their changes in time: (i) sessile volume remaining, (ii) wetted imprint area on the sand surface where the droplet is deposited, and (iii) VX penetration depth into sand, are computed numerically and compared to experimentally measured values. A very good qualitative and quantitative agreement was found between the numerical and experimental results. These numerical and experimental methods can be used to determine the spread and sorption of hazardous materials into a variety of substrates.

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