Growth and dislocation studies of β-HMX

Abstract

BackgroundThe 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).ResultsThe 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.ConclusionsCrystals 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].Graphical abstractEtch pits on the twinned (010) face of β-HMX.

Experimental study of anisotropic constitutive behavior of β-HMX crystals via nanoindentation and small-scale dynamic impact

“…However, both works did not indicate specific orientations for the values. A VHN range of 0.3-0.36 GPa, presented by Gallagher et al [2] for indentations made on the (010), {011}, and {110} planes, fall lower comparatively.…”

“…HMX occurs in four polymorphic forms, α, β, δ and ε. Of these, the most thermodynamically stable phase is β-HMX [2]. Thermal stability of the β-HMX crystalline phase makes it a good candidate to characterize effect of anisotropy on HMX material behavior.…”

Prediction of Growth Habit of β-Cyclotetramethylene-tetranitramine Crystals by the First-Principles Models

“…28 The bonding structures for all of the F-faces of β-HMX are represented in Figure 5. For the spiral growth model, the ϕ i kink,cryst was obtained by analyzing the PBCs, and the ϕ i kink was approximated by eqs 18,19, and 20, after which the ρ i was calculated by eq 8. At given a e,i , ϕ i kink , T, and σ, the l c was calculated by eq 4 and then τ S could be estimated by eqs 5 and 7.…”

The growth and perfection of β-cyclotetramethylene-tetranitramine (HMX) studied by laboratory and synchrotron X-ray topography

“…Previously, a dislocation etching technique [27] was used to investigate crystal defects and to define the likely mechanical deformation systems of this material, in particular for crystals with a defect density too high for x-ray methods. Pure edge and pure screw dislocations with Burgers vector b = [010] were suggested to be the most prominent emergent dislocations.…”