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Growth and dislocation studies of β-HMX.

Gallagher HG, Sherwood JN, Vrcelj RM - Chem Cent J (2014)

Bottom Line: 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).The twin plane in β-HMX was identified as a (101) reflection plane.Graphical abstractEtch pits on the twinned (010) face of β-HMX.

View Article: PubMed Central - PubMed

Affiliation: WESTCHEM, Department of Pure and Applied Chemistry, University of Strathclyde, Thomas Graham Building, 295 Cathedral Street, Glasgow, G1 1XL UK.

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

No MeSH data available.


Related in: MedlinePlus

SHAPE calculations of the equilibrium form of HMX and the expected changes of gradually increasing the relative growth rates of the crystal faces growing in the {100} direction. (a) Predicted Donnay-Harker morphology of HMX; (b) prismatic; (c) tabular; (d) columnar.
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Fig10: SHAPE calculations of the equilibrium form of HMX and the expected changes of gradually increasing the relative growth rates of the crystal faces growing in the {100} direction. (a) Predicted Donnay-Harker morphology of HMX; (b) prismatic; (c) tabular; (d) columnar.

Mentions: Despite the variations in growth conditions all the crystals of β-HMX grown in this study exhibited the morphological forms {011}, {110}, (010) and (101) only. The law of Donnay and Harker [37] predicts that the predominant crystal forms have the smallest reticular areas and are associated with the largest interplanar spacings. This relatively simple approach is consistent with and explains many aspects of the observed morphology. The calculated reticular areas and interplanar spacings [38] are listed in Table 2. It can be seen that the four smallest reticular areas in order of decreasing morphological importance are {011}, {110}, (010) and (101), in agreement with the observed faces and estimated relative facial areas for typical crystals. The absence of further faces is explained by the considerably larger reticular areas for forms other than those observed. Calculation of the equilibrium form using the prediction programme SHAPE [39] using the Donnay-Harker approach yields the often observed equant prismatic form shown in Figure 10. In the present case however the crystal habit varied significantly with the method of growth.Table 2


Growth and dislocation studies of β-HMX.

Gallagher HG, Sherwood JN, Vrcelj RM - Chem Cent J (2014)

SHAPE calculations of the equilibrium form of HMX and the expected changes of gradually increasing the relative growth rates of the crystal faces growing in the {100} direction. (a) Predicted Donnay-Harker morphology of HMX; (b) prismatic; (c) tabular; (d) columnar.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4317510&req=5

Fig10: SHAPE calculations of the equilibrium form of HMX and the expected changes of gradually increasing the relative growth rates of the crystal faces growing in the {100} direction. (a) Predicted Donnay-Harker morphology of HMX; (b) prismatic; (c) tabular; (d) columnar.
Mentions: Despite the variations in growth conditions all the crystals of β-HMX grown in this study exhibited the morphological forms {011}, {110}, (010) and (101) only. The law of Donnay and Harker [37] predicts that the predominant crystal forms have the smallest reticular areas and are associated with the largest interplanar spacings. This relatively simple approach is consistent with and explains many aspects of the observed morphology. The calculated reticular areas and interplanar spacings [38] are listed in Table 2. It can be seen that the four smallest reticular areas in order of decreasing morphological importance are {011}, {110}, (010) and (101), in agreement with the observed faces and estimated relative facial areas for typical crystals. The absence of further faces is explained by the considerably larger reticular areas for forms other than those observed. Calculation of the equilibrium form using the prediction programme SHAPE [39] using the Donnay-Harker approach yields the often observed equant prismatic form shown in Figure 10. In the present case however the crystal habit varied significantly with the method of growth.Table 2

Bottom Line: 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).The twin plane in β-HMX was identified as a (101) reflection plane.Graphical abstractEtch pits on the twinned (010) face of β-HMX.

View Article: PubMed Central - PubMed

Affiliation: WESTCHEM, Department of Pure and Applied Chemistry, University of Strathclyde, Thomas Graham Building, 295 Cathedral Street, Glasgow, G1 1XL UK.

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

No MeSH data available.


Related in: MedlinePlus