Determination of urea nitrate and guanidine nitrate vapor pressures by isothermal thermogravimetry

Abstract

Since the bombing of Pan Am Flight 103 over Lockerbie, Scotland in 1988, detection of military explosives has received much attention. Only in the last few years has detection of improvised explosives become a priority. Many detection methods require that the particulate or vapor be available. Elsewhere we have reported the vapor pressures of peroxide explosives triacetone triperoxide (TATP), diacetone diperoxide (DADP), and 2,4,6-trinitrotoluene (TNT). Herein we examine the vapor signatures of the nitrate salts of urea and guanidine (UN and GN, respectively), and compare them to ammonium nitrate (AN) and TATP using an isothermal thermo-gravimetric method. The vapor signatures of the nitrate salts are assumed to be the vapor pressures of the neutral parent base and nitric acid. Studies were performed at elevated temperatures (80-120 °C for UN, 205-2258°C for GN, 100-160°C for AN, and 40-59 °C for TATP), enthalpies of sublimation calculated and vapor pressures extrapolated to room temperature. Reported vapor pressure values (in Pa) are as follows: GN 2.66 × 10 -18 ≪ UN 3.94 × 10 -5 < AN × 5.98 × 10 -4 ≪ TATP 24.8. © 2010 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim.