4 research outputs found
Characterization of α- and β‑RDX Polymorphs in Crystalline Deposits on Stainless Steel Substrates
The highly energetic
material (HEM) hexahydro-1,3,5-trinitro-<i>s</i>-triazine,
also known as RDX, has two stable conformational
polymorphs at room temperature: α-RDX (molecular conformation
of −NO<sub>2</sub> groups: axial–axial–equatorial)
and β-RDX (molecular conformation of −NO<sub>2</sub> groups:
axial–axial–axial). Both polymorphs can be formed by
deposition on stainless steel substrates using spin coating methodology.
α-RDX is the most stable crystal form at room temperature and
ambient pressure. However, β-RDX, which has been reported to
be difficult to obtain in bulk form at room temperature, was readily
formed. Reflection–absorption infrared spectroscopy measurements
for RDX-coated stainless steel substrates provided spectral markers
that were used to distinguish between the conformational polymorphs
on large surface areas of the substrates. Raman microspectroscopy
was employed to examine small areas where the intensity was proportional
to the height of the structures of RDX. Spectral features were interpreted
and classified by using principal component analysis (PCA). The results
from these spectral analyses provided good correlation with the values
reported in the literature. Conditions to generate predominantly β-RDX
crystalline films as a function of the spin coating rotational speed
on these substrates were obtained. PCA was also applied to predict
percentages of polymorphs present in experimental samples. Applications
of the results obtained suggest the modification of existing vibrational
spectroscopy based spectral libraries for defense and security applications.
Understanding the effects of polymorphism in HEMs will result in the
attainment of higher confidence limits in the detection and identification
of explosives, especially at trace or near trace levels
Mechanism for the Uncatalyzed Cyclic Acetone-Peroxide Formation Reaction: An Experimental and Computational Study
In
this study, a mechanism for the uncatalyzed reaction between
acetone and hydrogen peroxide is postulated. The reaction leads to
the formation of the important homemade explosives collectively known
as cyclic acetone peroxides (CAP). The proposed mechanistic scheme
is based on Raman, GC-MS, and nuclear magnetic resonance measurements,
and it is supported by <i>ab initio</i> density functional
theory (DFT) calculations. The results demonstrate that the proposed
mechanism for the uncatalyzed formation reaction of CAP occurs in
three steps: monomer formation, polymerization of the 2-hydroperoxipropan-2-ol
monomer, and cyclization. The temporal decay of the intensities of
important assigned-bands is in excellent agreement with the proposed
mechanism. Previous reports also confirm that the polymerization step
is favored in comparison to other possible pathways