![]() ![]() The enthalpy of sublimation ( Δ s u b H) is the energy change when a compound changes from the solid phase to the gas phase. The desorption of an adsorbed molecule is an elemental surface kinetics process and is a measure of the strength of the interaction between the surface and the adsorbed species. ![]() The desorption energy ( Δ d e s U) can be defined as the change in energy when a substance adsorbed on a surface is desorbed. The vapor pressure of a HEM and its interaction with any given surface can be characterized in terms of the desorption energy and the sublimation enthalpy. Aside from adhesion considerations, the residence time mainly depends on the vapor pressure of the compound and surface–HEM interactions. The concept is essential for the development of samples and standards for trace detection systems. The residence time of a highly energetic material (HEM) on a surface can be defined as the time that the material persists on the surface after its deposition. Finally, for TATP the enthalpies were statistically identical, but a non-linear behavior and a change of heat capacity values different from zero was found for both trace and bulk phases. In the case of DNT and TNT, bulk and traces enthalpies were statistically similar, but it is evidenced that at the level of traces a metastable phase was observed. This interaction energy was determined using grazing angle FTIR microscopy. Second, an interaction between the RDX and SS was found. First, the beta-RDX phase was present at trace levels, unlike the case of bulk amounts which consisted only of the alpha-RDX phase. The sublimation enthalpy of RDX was very different for traces than for bulk quantities, attributed to two main factors. These were compared with enthalpies of sublimation determined by thermal gravimetric analysis for bulk amounts and differences between them were found. The enthalpies of sublimation of traces of four highly energetic materials: triacetone triperoxide (TATP), 2,4-dinitrotoluene (DNT), 2,4,6-trinitrotoluene (TNT), and 1,3,5- trinitrohexahydro-s-triazine (RDX) deposited on SS substrates were determined by optical fiber coupled-grazing angle probe Fourier Transform Infrared (FTIR) Spectroscopy. This study presents evidence that the sublimation process of these traces on stainless steel (SS) surfaces is very different than in bulk quantities. The persistence on surfaces of these traces depends on the sublimation processes and the interactions with the surfaces. ![]() In the fields of Security and Defense, explosive traces must be analyzed at the sites of the terrorist events. ![]()
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |