Stabilizing additives are added to solid rocket propellant systems to slow the break-down of energetic nitrogen-based compounds utilized in solid rocket propellants. Over time this results in a reduction of stabilizers and an increase of inert compounds, which decrease propellant performance. Raman spectroscopic techniques can detect changes in chemical concentrations due to the strong spectrum that these compounds demonstrate. In this study, two wavelengths, 532 nm, and 785nm are used to analyze the Raman spectra of samples to characterize the changes to compounds over time. Computational techniques are demonstrated to mitigate fluorescence and improve the signal-to-noise ratio of chemical peaks specific to stabilizer compounds. Fluorescence in the 532 nm Raman spectrum is examined as a method for characterizing propellant compounds, as 2-Nitrodiphenylamine (2-NDPA) traditionally has more fluorescence than Nmethyl- 4-nitroaniline (MNA), and the 532 nm Raman system traditionally detects more fluorescence than the 785 nm Raman system. Detection of the stabilizer, MNA, in concentrations ranging from 0.38% to 0.75% is demonstrated. Raman spectroscopy is shown to provide a rapid method for analyzing high and low concentrations of stabilizer compounds to determine the remaining viability of the propellant.
The primary objective of this effort is to demonstrate the efficacy of the Raman spectroscopy technique for detecting and evaluating the health of propellant stabilizers commonly used in missiles stored under a range of ambient conditions. Tincured silicone rubber doped with a commonly used propellant stabilizer N-methyl-4-nitroaniline (MNA) and ammonium nitrates used in explosives has been investigated using 532 nm and 785 nm wavelength laser Raman systems. The detected propellants’ Raman peak intensity ratios are used to analyze the results. Calibration curves with error bars are created using more than 30 data runs. The results indicate both systems are suitable to detect fractions of these chemicals as low as 0.2 percent within a few seconds of integration time. The calibration curves created for all the samples measured show a consistent linear increase to the ratio indicating the reliability of the measurements.
Energetic nitrogen-based compounds utilized in solid rocket propellants break down under typical environmental conditions. The breakdown of these energetic propellant compounds requires stabilizing additives to absorb excess acids that form. These chemical changes result in a reduction of stabilizers and an increase of inert compounds over time which decrease propellant performance. Vibrational spectroscopic techniques such as Raman can detect changes in chemical concentrations due to the strong spectrum that these compounds demonstrate. In this study two wavelengths, 532 nm and 783 nm, are used to analyze the Raman spectra of propellant samples to characterize the changes to compounds over time. Computational techniques are demonstrated to mitigate fluorescence and single out the ratio of chemical peaks specific to stabilizer compounds. In addition, fluorescence in the 532 nm spectrum is examined as a method for characterizing propellant compounds, as 2NDPA traditionally has more fluorescence than MNA, and the 532 nm Raman system traditionally detects more fluorescence than the 785 nm Raman system. Detection of the stabilizer MNA in concentrations of greater than .70% and lower than .40% are demonstrated. Raman spectroscopy is shown to provide a rapid method for analyzing high and low concentrations of stabilizer compounds to determine the remaining viability of propellant.
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