Growth and dislocation studies of β-HMX

Gallagher, Hugh G. and Sherwood, John N. and Vrcelj, Ranko M. (2014) Growth and dislocation studies of β-HMX. Chemistry Central, 8 (1). p. 75. ISSN 1752-153X

Full content URL: http://dx.doi.org/10.1186/s13065-014-0075-y

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Abstract

Background: The defect structure of organic materials is important as it plays a major role in their crystal growth
properties. It also can play a subcritical role in “hot-spot” detonation processes of energetics and one such
energetic is cyclotetramethylene-tetranitramine, in the commonly used beta form (β-HMX).
Results: The as-grown crystals grown by evaporation from acetone show prismatic, tabular and columnar habits, all
with {011}, {110}, (010) and (101) faces. Etching on (010) surfaces revealed three different types of etch pits, two of
which could be identified with either pure screw or pure edge dislocations, the third is shown to be an artifact of
the twinning process that this material undergoes. Examination of the {011} and {110} surfaces show only one type
of etch pit on each surface; however their natural asymmetry precludes the easy identification of their Burgers
vector or dislocation type. Etching of cleaved {011} surfaces demonstrates that the etch pits can be associated with
line dislocations. All dislocations appear randomly on the crystal surfaces and do not form alignments characteristic
of mechanical deformation by dislocation slip.
Conclusions: Crystals of β-HMX grown from acetone show good morphological agreement with that predicted by
modelling, with three distinct crystal habits observed depending upon the supersaturation of the growth solution.
Prismatic habit was favoured at low supersaturation, while tabular and columnar crystals were predominant at
higher super saturations. The twin plane in β-HMX was identified as a (101) reflection plane. The low plasticity of
β-HMX is shown by the lack of etch pit alignments corresponding to mechanically induced dislocation arrays.
On untwinned {010} faces, two types of dislocations exist, pure edge dislocations with b = [010] and pure screw
dislocations with b = [010]. On twinned (010) faces, a third dislocation type exists and it is proposed that these pits
are associated with pure screw dislocations with b = [010].

Keywords:Crystal growth, Dislocations, Etching, Energetics, HMX, JCOpen
Subjects:F Physical Sciences > F131 Crystallography
F Physical Sciences > F170 Physical Chemistry
F Physical Sciences > F190 Chemistry not elsewhere classified
F Physical Sciences > F130 Structural Chemistry
Divisions:College of Science > School of Pharmacy
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ID Code:16729
Deposited On:18 Feb 2015 11:40

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