RESUMEN
The kinetics of hexogen coating with polyurethane-based hydroxyl-terminated polybutadiene (HTPB) using infrared spectrometry was investigated. The kinetics model was evaluated through reaction steps: (1) hydroxyl and isocyanate to produce urethane, (2) urethane and isocyanate to produce allophanate, and (3) nitro and isocyanate to produce diazene oxide and carbon dioxide. HTPB, ethyl acetate, TDI (toluene diisocyanate), and hexogen were mixed for 60 min at 40 °C. The sample was withdrawn and analyzed with infrared spectroscopy every ten minutes at reference wavelengths of 2270 (the specific absorption for isocyanate groups) and 1768 cm-1 (the specific absorption for N=N groups). The solvent was vaporized; then, the coated hexogen was cured in the oven for 7 days at 60 °C. The effect of temperature on the coating kinetics was studied by adjusting the reaction temperature at 40, 50, and 60 °C. This procedure was repeated with IPDI (isophorone diisocyanate) as a curing agent. The reaction rate constant, k3, was calculated from an independent graphic based on increasing diazene oxide concentration every ten minutes. The reaction rate constants, k1 and k2, were numerically calculated using the Newton-Raphson and Runge-Kutta methods based on decreasing isocyanate concentrations. The activation energy of those steps was 1178, 1021, and 912 kJ mole-1. The reaction rate of hexogen coating with IPDI was slightly faster than with TDI.
RESUMEN
In Aerodynamic Breakup Droplet ionization (ABDI) mass spectrometry the dimer/monomer (I2/I1) and trimer/dimer (I3/I2) ratios are considered for compounds ionized in various ways. The following test compounds were selected: morphine (gives protonated ion, (M+H)+); hexogen, RDX (forms adducts with anion of chlorine or nitrate ion); and trinitrotoluene, TNT (gives deprotonated ion, (M-H)-). The test compounds were dissolved in water, acetonitrile or ethanol. It is shown that in the ABDI mass spectra of a number of compounds (protonated morphine ions in water and RDX adducts with chlorine in acetonitrile), the ratios I2/I1 and I3/I2 linearly depend on the analyte concentration in the solution. This is evident throughout the range of measured concentrations, when monomers and dimers are simultaneously visible in the mass spectrum. The phenomenon can be roughly explained by the dimerization of analyte molecules in singly charged parent drops during ABDI ionization. The linearity of the I2/I1 and I3/I2 on the concentration can be used for estimation of the analyte concentration in a sample without using an internal or external standard. This can be useful for routine analysis when standards are not commercially available or very expensive.