The Microstructure of TATB‐Based Explosive Formulations During Temperature Cycling Using Ultra‐Small‐Angle X‐Ray Scattering

Abstract

TATB (1,3,5 triamino‐2,4,6‐trinitrobenzene), an extremely insensitive explosive, is used both in polymer‐bound explosives (PBXs) and as an ultra‐fine pressed powder (UFTATB). Many TATB‐based explosives, including LX‐17, a mixture of TATB and Kel‐F 800 binder, experience an irreversible expansion with temperature cycling known as ratchet growth. Additional voids, with sizes hundreds of nanometers to a few micrometers, account for much of the volume expansion. Measuring these voids is important feedback for hot‐spot theory and for determining the relationship between void size distributions and detonation properties. Also, understanding mechanisms for ratchet growth allows future choice of explosive/binder mixtures to minimize these types of changes, further extending PBX shelf life. This paper presents the void size distributions of LX‐17, UFTATB, and PBXs using commercially available Cytop M, Cytop A, and Hyflon AD60 binders during temperature cycling between −55 and 70 °C. These void size distributions are derived from ultra‐small‐angle X‐ray scattering (USAXS), a technique sensitive to structures from about 2 nm to about 2 μm. Structures with these sizes do not appreciably change in UFTATB. Compared to TATB/Kel‐F 800, Cytop M and Cytop A show relatively small increases in void volume from 0.9 to 1.3% and 0.6 to 1.1%, respectively, while Hyflon fails to prevent irreversible volume expansion (1.2–4.6%). Computational mesoscale models combined with experimental results indicate both high glass transition temperature as well as TATB binder adhesion and wetting are important to minimize ratchet growth.

Effects of crystal quality and preferred orientation on the irreversible growth of compact TATB cylindrical explosives

“…13 However, we have significantly decreased the irreversible volume growth of pure TATB cylinders by improvement of crystal quality, and the anisotropy of irreversible dimension growth by control of preferred orientation. When these strategies are applied into TATB-based PBXs, the PBXs should display less irreversible growth and less deformation.…”

“…Willey et al 13,14 found that the cavity quantity and size of multi-crystal TATB-based PBX cylinder increased after thermal cycling. Willey 13,14 and Sun 15 thought that additional interstices between TATB powders originated from the thermal cycling should be responsible for the irreversible growth of TATB-based PBX. TATB crystal quality should have much effect on additional interstice production, and further affect the irreversible growth of TATB-based PBX.…”

Tailoring the irreversible thermal expansion of 1,3,5‐triamino‐2,4,6‐trinitrobenzene crystals by bioinspired polydopamine coating

“…The ratchet growth leads to void size distributions in PBXs tending towards both larger size and higher void concentration . In addition, ratchet growth affects initiation and detonation properties, including shock sensitivity and detonation velocity . Consequently, the irreversible thermal expansion harms the safety and reliability of the weapon system …”

“…The coefficient of thermal expansion (CTE) of “fine particle size” dry‐aminated TATB is 10% higher than that of 50 μm dry‐aminated TATB (in the lower temperature range). Furthermore, TATB/binder adhesion and wetting are both important to minimize ratchet growth as indicated by computational mesoscale models combined with experimental results . Besides, the production scale of solution crystallization is difficult to amplify for engineering applications, due to the extraordinary low solubility of TATB in common solvents, such as dimethyl sulfoxide.…”

Structural Characterization of RDX‐Based Explosive Nanocomposites

“…In the case of coated HE's, the voids are not accessible as they are sealed by the binder, consequently, the above mentioned techniques are not applicable. For such materials, several alternative method may be employed, including X-ray [8][9][10] and neutron [11,12] scattering, which allow probing "closed" voids with sizes ranging from ca. 2 nm to hundreds of micrometers [13], X-ray Microscopy (XRM) [14], and Scanning Electron Microscopy (SEM) imaging of sectioned specimens, which, in the case of specimens with nanoscale features, can be performed by Focused Ion Beam (FIB) milling [15].…”