Method for preparation of fine TATB (2–5 μm) and its evaluation in plastic bonded explosive (PBX) formulations

doi:10.1016/j.jhazmat.2006.05.031

Journal of Hazardous Materials

Volume 137, Issue 3, 11 October 2006, Pages 1848-1852

https://doi.org/10.1016/j.jhazmat.2006.05.031 Get rights and content

Abstract

There is a need of fine 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) (2–5 μm) for various high explosive formulations to achieve desired mechanical strength, ease in processing and finally, provide better performance of end product. The reprecipitation method for TATB has been developed using concentrated sulfuric acid as a solvent. The reprecipitation parameters of TATB were optimized to achieve required fine TATB of particle size ∼2–5 μm. The characteristic properties of fine TATB thus obtained have been confirmed by FTIR, DSC and TG-FTIR. The spectroscopic and thermal data obtained for fine TATB were compared with standard coarse TATB and found chemically unchanged during particle size reduction. In the present study, the preparation of fine TATB was also attempted using ultrasonication method. The fine (2–5 μm) TATB has been introduced to study in the bimodal high explosive formulations. High explosive formulations based on coarse (55 μm) and fine TATB (∼2–5 μm) with 10% polyurethane were studied. It was observed that properties like bulk density (1.70 g/cm³), mechanical strength/compressed strength (115.9 mg/cm²), %elongation (6.36) were improved for fine TATB in comparison with coarse TATB (∼55 μm) alone in high explosive formulations.

Introduction

The most important insensitive high explosives (IHEs) for use in modern nuclear warheads is 1,3,5-triamino-2,4,6-trinitrobenzene (TATB), because its resistance to heat and physical shock is greater than that of any other known material of comparable energy [1]. The Department of Defence, U.S., is also studying the possible use of TATB as nuclear stockpile and an insensitive booster material, because even with its safety characteristics, a given amount of that explosive has more power than an equivalent volume of 2,4,6-trinitrotoluene (TNT). The high stability of TATB favors its use in military and civil applications where insensitive type explosives are required [2]. In addition to its application as HE, TATB is used to produce the important intermediate benzenehexamine. Benzenehexamine has been used in the preparation of ferromagnetic organic salts and in the synthesis of new heterocyclic molecules [3].

In addition to its military uses, TATB has been proposed for use as a reagent in the manufacture of components for liquid crystal computer displays [4]. There is also interest in employing the explosive in the civilian sector for deep oil well explorations, where heat insensitive explosives are required. Other potential applications include the use of TATB as the booster or main charge explosive for down-hole oil perforation at elevated temperature surrounding. However, one major problem with the utility of TATB is the resistance to initiation as required.

TATB was prepared by amination of 1,3,5-trichloro-2,4,6-trinitrobenzene (TCTNB) in toluene with anhydrous ammonia gas in a pressurized reactor [5]. TATB thus produced has particle size of 50 μm or larger and is suitable for most application. However, fine-grained TATB is desirable for ease of initiation. However, there is a need of fine particle TATB (<10 μm) for several high explosive formulations under development at HEMRL to achieve the ease in processing and desired mechanical strength and performance of the end product. Plastic bonded explosive (PBX) 9502 has been formulated as a insensitive high explosive comprised of 95% TATB and 5 wt% Kel-F800™ binder. Several studies on PBX 9502 have shown significant differences between the mechanical properties and postulated that the differences were related to various aspects of TATB particles size and distribution [6]. Coarse TATB based formulation generally provides brittle PBX, which can sustain damage in normal handling and succumb to extreme temperature suing or thermal stocks, while too soft a PBX may be susceptible to creep and lack dimensional stability or strength to achieve safe and stable PBXs. HEMRL is presently studying the bimodal (containing fine and coarse particle size TATB) charge explosives based on TATB.

Ultrasound [7] is sound of a frequency that is beyond human hearing, i.e., above 16 kHz. Applying ultrasound to crystallizing systems offers a significant potential for modifying and improving both the processes and products. Although ultrasonic has been used for years in research and diagnostics, its use in chemical processes has undergone development in the recent years. This is because high-intensity systems have become available that can deliver power ultrasound on industrially relevant scales. The use of ultrasound in promoting chemical reactions has been widely investigated and been developed recently as an intensification technology, driven by requirements for environmentally clean processing crystallization intuitively appears to be an obvious area in which ultrasonic irradiation could be beneficial. When ultrasound is applied to liquids of either a homogeneous or heterogeneous system, acoustic cavitations results. That is, the formation, expansion and implosive collapse of micro bubbles generated during the high frequency oscillation of liquid molecules. The work was therefore under taken to develop the technique for the reduction of particle size of TATB from 55 to 2–5 μm range using reprecipitation as well as sonocrystallization methods. The paper discusses the details of process for the preparation of fine TATB, its characterization and thermolysis. The fine TATB based PBX formulations are also discussed.

Section snippets

Structure and solubility of TATB

The structure of TATB (Fig. 1) contains unusual features. X-ray diffraction pattern of crystalline TATB reveals that C single bond C bond orders are approximately 1.2 and the amine CN and NO bond orders are nearly 1.5. The molecule is nearly planer and has extensive system of hydrogen bonds [8] and intermolecular interactions as shown in Fig. 1 contributing to its exceptional thermal stability and low solubility except in concentrated sulfuric acid.

Solubility of TATB in “super acids” such as chlorosulfonic

Materials and methods

AR grade sulfuric acid was used in this process. The IR spectra (FTIR-1600 spectrophotometer) were recorded on a Perkin-Elmer using KBr matrix. The DSC studies was carried out on a Perkin-Elmer DSC-7 instrument operating at a heating rate of 10 °C/min in nitrogen (40 ml/min) atmosphere and the mass of the sample used was less than 1 mg. The thermal properties of TATB were studied by simultaneous thermogravimetry (TG)/differential thermal analysis (DTA) and the mass of the sample used was 0.5 mg

Results and discussion

TATB dissolved in sulfuric acid and it is quickly solvated and protonated as shown in Fig. 2. The degree of protonation and solvation is proportional to the concentration of the sulfuric acid and thus, TATB is precipitated by diluting the solution with water.

For the characterizations of fine particles, the results from FTIR, DSC, DTA and TGA experiments were quite useful. The same methods were also used to characterize coarse TATB particles in order to find out if any chemical changes are

Conclusion

A simple and efficient laboratory method for reduction of coarse TATB from 55 to 5 μm at 150 g batch level is successfully established and can be further scaled up to pilot plant scale with available infrastructure. No any chemical change occurs in the process of making fine particles of TATB from the coarse one as described in this report.

High explosive formulations based on coarse (55 μm) and fine TATB (∼2–5 μm) with 10% polyurethane were studied. Bimodal formulation of TATB has been selected and

Acknowledgement

Authors are grateful to Director, HEMRL for his encouragement and valuable suggestions in this work.

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Method for preparation of fine TATB (2–5 μm) and its evaluation in plastic bonded explosive (PBX) formulations