Using Simultaneous SHG and XRD Capabilities to Examine Phase Transitions of HMX and TATB Page: 3 of 8
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Using simultaneous SHG and XRD capabilities to examine phase
transitions of HMX and TATB*
C. K. Saw, J. Zaug, D. Farber and C. Ruddle
Lawrence Livermore National Laboratory, P.O. Box 808, 7000 East Avenue, Livermore, CA
94550
Abstract: Simultaneous SHG (second harmonic generation) and XRD (x-ray diffraction)
capabilities have been developed at SSRL (Stanford Synchrotron Radiation laboratory) to examine
the phase behavior of energetic materials, for example, HMX (octahydro-1,3,5,7-tetranitro-I1,3,5,7-
tetrazocine) and TATB (1,3,5-triamino-2,4,6 trinitrobenzene). This unique capability provides
information on the evolution at the molecular level (centro and non-centrosymmetric) on material
stability, phase transformation or decomposition reactions, which are important to continue
refinement of computational predictions of material properties. This paper reports x-ray diffraction
experiments on both HMX and TATB with increasing temperature and on simultaneous SHG and
XRD experiments at fixed temperature. Our results indicate that, for HMX, the 3 to S
transformation occurs over a range of temperature which do not correlate to the previously reported
fast rise in SHG signal close to 170*C as a phase transformation. No phase transition is observed for
TATB, even though, previous paper shows an increase in the SHG signal.
INTRODUCTIONUnderstanding of the phase transformations and
kinetics of energetic materials are of importance to
development of stable explosives. This is
demonstrated by differences in burnt rates and
drop height sensitivity of 1 and S phases. Detailed
understanding of the 3-)S transformation is still a
point of discussion. Recently, a number of papers
have been published which discuss the unusual
observation of SHG during the transformation of
p3-* phase HMX [1] and TATB [2]. The
appearance of SHG signifies the presence of non-
centrosymmetric crystal structure from that of
centrosymmetric. For HMX, several heating rates
were used and it was reported that a fast rise in
SHG signals have been observed as the
temperature approaches that of the 0-+8 transition
at about 170*C. This observation of change in SHG
is taken to be the transformation of p0-+ phase. In
TATB, it was argued that a mixture of
polymorphic forms existed at all times and the
SHG is due to a non-centrosymmetric form. It wasalso reported that an abrupt increase in SHG signal
is caused by the transformation of 03-+ phase and
on continuing heating, a reduction of SHG can be
observed which is assigned decomposition.
In the thermal analysis study of HMX, Herrmann
et. al. [3] reported on high temperature x-ray
diffraction experiment of HMX utilizing chromium
Ka radiation. For both P and S phases, the volumes
are observed to increase with increasing
temperature and decrease with decreasing
temperature. It is also interesting to note that the
volume shrinkage is observed for p phase right
before the conversion to the S phase. Clearly, this
result is important from the application point of
view.
To further understand the behavior of these phases
and phase kinetics of both the HMX and TATB,
our group at the Lawrence Livermore National
Laboratory focuses on performing simultaneous
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Saw, C. K.; Zaug, J.; Farber, D. & Ruddle, C. Using Simultaneous SHG and XRD Capabilities to Examine Phase Transitions of HMX and TATB, article, June 19, 2001; Livermore, California. (https://digital.library.unt.edu/ark:/67531/metadc1406367/m1/3/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.