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.
Researchers from the U.S. Army, along with university scientists, are implementing efforts to develop a hyperspectral/broadband and/or ultraviolet (UV) sensing technology for target discrimination. The Army’s primary goal is to advance the development of fast reliable broadband optics techniques that can quickly identify and ascertain an indication of the geometric shape/compositional structure of various materials encountered on the battlefield. Samples of a variety of cement-based, metal, and composite materials are assembled and investigated to determine each sample’s spectra optical reflectance and absorption properties after being exposed to varying optical wavelengths. The optical wavelengths are generated from deuterium, halogen, and white light sources. The light intensity ratios are used to create data points which allowed for the identification of unique characteristics of each sample material. Broadband visible and near infrared (NIR) sources (deuterium and halogen) are reflected off the samples and the spectrometric reflections were captured. Several light intensity ratios are used and compared to distinguish the samples and error bars are created. While the initial results indicated that the halogen source may be used to distinguish most of the sample materials (and perhaps stand-alone versions of the other wavelength sources may not be sufficient), combinations of wavelengths/laser diodes with broadband light sources were used to determine if the identification/characteristics of each sample could be achieved. Results outlined in this paper include the current progress made toward the development of broadband optics sensing methodologies and instrumentation for identifying and discriminating the geometric configurations/formations of various battlefield materials.
Nowadays, undergraduate research is recognized as an essential component of STEM discipline enhancing students learning outcome. As a result, governmental and non-governmental agencies have been allocating a substantial amount of funding and resources to support undergraduate students through scholarships and research activities. In addition to reinforcing the traditional classroom learning experience and providing the students with hands-on experience early on in their studies, undergraduate research is one of the key motivating factors to pursue graduate education and advance careers in STEM fields. In this paper, the positive impact of mentoring and engaging undergraduate students in paid research activities, and the project outcomes including awards and recognitions received by the students are discussed.
A sensitive Raman spectroscopy technique is used for detection and possible quantification of the propellant stabilizer, nmethyl nitroaniline (MNA), in solid rocket propellants used in multiple domestic missile systems. Over time, the energetic ingredients of the propellant will degrade and react with the stabilizer, causing issues with the propellant useful safe life. Currently, there are no non-destructive analytical techniques for which MNA can be detected in solid rocket fuel inside a missile. Therefore, after a certain amount of time, missiles in inventory must be disassembled and tested for reliability and safety. This methodology is labor intensive, costly, and time consuming so a less intrusive approach is warranted to determine a missile useful safe life. Raman spectroscopy provides a possible solution to this problem, where a small fiber optic probe line may be inserted into the rocket motor of the missiles, which can be tested within seconds without the need for dismantling the missiles. A 785 nm portable Raman analyzer is used for all measurements reported in this paper with integration times ranging from 10 to 60 s. It is found that Raman sensing is a viable option for detection of MNA in solid rocket fuels.
Stabilizers are added to nitrate ester-based rocket motor propellants to form a stable product. The products added to stabilize the propellants react with NOx and are gradually exhausted over a period of time. In this paper, we demonstrate the efficacy of Raman spectroscopy technique for nondestructive, inexpensive, and rapid evaluation and monitoring of the depletion of rocket motor propellant stabilizers. Preliminary results show that concentrations as low as 0.1% of both MNA and 2-NDPA dissolved in DMSO (Dimethyl sulfoxide) can easily be detected at 1 second integration time using a 785 nm wavelength Raman system. In addition, MNA concentrations between 0.37% and 0.54% are detected in propellant samples containing energetic constituents using a 60 second integration time.
The purpose of this research project is to demonstrate the application of Raman spectroscopy technique for characterization and identification of the distinct Raman signatures of construction materials. The results reported include the spectroscopic characterization of building materials using compact Raman system with 785 nm wavelength laser. The construction materials studied include polyblend sanded grout, fire barrier sealant, acrylic latex caulk plus and white silicone. It is found that, both fire barrier sealant and acrylic latex caulk plus has a prominent Raman band at 1082 cm-1, and three minor Raman signatures located at 275, 706 and 1436 cm-1. On the other hand, sand grout has three major Raman bands at 1265, 1368 and 1455 cm-1, and four minor peaks at 1573, 1683, 1762, and 1868 cm-1. White silicone, which is a widely used sealant material in construction industry, has two major Raman bands at 482 and 703 cm-1, and minor Raman characteristic bands at 783 and 1409 cm-1.
Pure extra virgin olive oil (EVOO) is mixed with cheaper edible oils and samples are kept inside clear glass containers, while a 785nm Raman system is used to take measurements as Raman probe is placed against glass container. Several types of oils at various concentrations of adulteration are used. Ratios of peak intensities are used to analyze raw data, which allows for quick, easy, and accurate analysis. While conventional Raman measurements of EVOO may take as long as 2 minutes, all measurements reported here are for integration times of 15s. It is found that adulteration of EVOO with cheaper oils is detectable at concentrations as low as 5% for all oils used in this study.
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