Raman spectroscopy as a tool for long‐term energetic material stability studies

Abstract

Raman spectroscopy is shown to be useful as a tool for long-term stability studies. The stability of a novel submicron-size g-polymorph form of the explosive HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) was monitored up to 1 year using Raman spectroscopy. The preparation and characterization of this submicron HMX has been previously discussed. It is important to know the long-term stability of this submicron g-polymorph material under ambient conditions for its eventual utilization. This submicron HMX material has been found to be stable both chemically and polymorphically (to the order of 1% impurity level), even though HMX normally converts to the b-polymorph at ambient conditions.

Design Considerations for a Portable Raman Probe Spectrometer for Field Forensics

“…Fast, noncontact field analysis of complex chemical stains or particles spread over surfaces of several square centimeters is the final goal of our work. The path for quantifying the chemical makeup of smaller particles <10 μm or 1.5 g/cm 3 • 4π/3 • {r 3 } ≤0.785 ng or finely suspended thinfilms at areal-dosages of ≤1 μg/cm 2 , while not fully achieved in this study, does look feasible. Sensitive quantification of trace explosive stains or barely visible particles, without the need to use confocal Raman spectroscopy, appears practical with our prototype system.…”

“…Shifting to shorter excitation wavelengths gains signal according to the "ν 4 " factor. (In fact, if a power-detecting element is used the appropriate expression is (ν 0 − ν k ) 4 whereas if a photoncounting device is used, the response term is ν 0 (ν 0 − ν k ) 3 where ν 0 is the laser frequency and ν k the vibrational mode frequency [15].) Shifting to shorter wavelengths, however, often induces molecular fluorescence whereby the laser light is absorbed and reemitted via an electronic transition that does not involve a change in the electronic spin quantum.…”

“…Often the analyte Raman spectra can be simply and quickly interpreted in terms of peak height and/or peak area comparisons with an appropriate database [2]. Component concentrations of plastic explosives, for example, appear to be treatable as simple linear superpositions of spectra, and quantifications can sometimes be done to about the 1% level of contamination with bulk samples [3]. As a consequence, identifying the provenance of materials, especially explosives, becomes more straightforward.…”

Comparison of Fresh and Aged TNT with Multiwavelength Raman Spectroscopy

“…To simulate thermal ageing, a bulk sample of each explosive was inserted into an aluminum block calorimeter and heated using an oil bath to 75 o C and maintained at that temperature for two weeks. This process is an abbreviated version of a typical ageing protocol for solid explosives (18,19) , in which samples are held at elevated temperatures (usually 50, 60, or 70 o C) for periods of 8-12 months. UV ageing was accomplished by exposing the samples for two weeks with a 15 Watt, 254 nm, Cole Parmer ultraviolet lamp at a distance of 12.7 cm.…”

Automated identification of components in a chemical mixture utilizing multi‐wavelength resonant‐Raman spectroscopy and a Pearson correlation algorithm

“…In some applications, classification of all of the constituents within a mixture of chemicals is necessary . Examples include forensics, detection of explosives, and recognition of pollutants in the environment . Raman spectroscopy is often used for this, and has been shown to be a rapid, non‐contact detection method, which offers the ability for a single detector to identify a variety of substances …”