ONE of the most important accomplishments made by weapons laboratories' chemists in the past two decades has been the formulation of powerful conventional high explosives that are remarkably insensitive to high temperatures, shock, and impact. These insensitive high explosives (IHEs) significantly improve the safety and survivability of munitions, weapons, and personnel. The Department of Energy's most important IHE for use in modern nuclear warheads is TATB (triamino-trinitrobenzene) because its resistance to heat and physical shock is greater than that of any other known material of comparable energy.|
The Department of Energy currently maintains an estimated five-year supply of TATB for its Stockpile Stewardship and Management Program (see the August 1996 Science & Technology Review, pp. 6-15), which is designed to ensure the safety, security, and reliability of the U.S. nuclear stockpile. The Department of Defense is also studying the possible use of TATB as an insensitive booster material, because even with its safety characteristics, a given amount of that explosive has more power than an equivalent volume of TNT.
In addition to its military uses, TATB has been proposed for use as a reagent in the manufacturing of components for liquid crystal computer displays. There is also interest in employing the explosive in the civilian sector for deep oil well explorations where heat-insensitive explosives are required.|
Despite its broad potential, the high cost of manufacturing TATB has limited its use. Several years ago, TATB produced on an industrial scale in the U.S. was priced at $90 to $250 per kilogram. Today it is available to customers outside DOE for about $200 per kilogram. In response to a need for a more economical product, chemists at Lawrence Livermore have developed a flexible and convenient means of synthesizing TATB as well as DATB (diamino-trinitrobenzene), a closely related but less well known IHE developed by the U.S. Navy. The initial phase of this work was funded by the Department of Defense (U.S. Navy) to explore the chemical conversion of surplus energetic materials to higher value products as an alternative to detonation.
The Lawrence Livermore process--also called the VNS (vicarious nucleophilic substitution) process--should be able to produce TATB for less than $90 a kilogram on an industrial scale in about 40% less manufacturing time. The process also offers significant advantages over the current method of synthesis in environmental friendliness, for example, by avoiding chlorinated starting materials. What's more, the process uses either inexpensive, commercially available chemicals or surplus energetic materials from both the former Soviet Union (UDMH, a rocket propellant) and the U.S. (Explosive D, a high explosive).
By using UDMH (uns-dimethylhydrazine) and Explosive D (ammonium picrate), this process disposes of energetic materials left over as a legacy of the Cold War in an environmentally responsible manner. It allows the use of surplus energetic materials as unique feedstocks to make more valuable materials such as higher value explosives or other products. Indeed, the new chemistry is also applicable to the synthesis of chemicals that are important intermediates in the preparation of numerous pharmaceutical and agricultural chemicals.
Current Process Produces Impurities|
The currently accepted method for manufacturing TATB in the U.S. involves a reaction sequence that starts with the relatively expensive and domestically unavailable chlorinated compound TCB (trichlorobenzene). Elevated temperatures of 150°C are required for two of the reaction steps leading to TATB. The major impurity produced is ammonium chloride; in addition there are low levels of chlorinated reaction side-products.
The VNS process is more environmentally friendly than the current synthesis. It employs mild reaction conditions and eliminates the need for chlorinated starting materials. The latter characteristic is especially important in light of the growing movement to eliminate chlorinated compounds from the industrial sector altogether because of their possible adverse environmental effects.
The VNS process depends on two key materials, TMHI (trimethylhydrazinium iodide) and picramide (trinitroaniline), which can be obtained from either inexpensive starting compounds or surplus energetic materials available from demilitarization activities. TMHI can be prepared directly from hydrazine and methyl iodide, or it can be synthesized by reacting UDMH with methyl iodide. Some 30,000 metric tons of UDMH rocket propellant are located in the former Soviet Union, where they await disposal in a safe and environmentally responsible manner.
Two U.S. companies have received congressional funding to demilitarize UDMH in Russia using a chemical process that produces lower value products (ammonia and dimethylamine). In contrast, the VNS process converts UVMH to TMHI, which will be used for the production of higher value products such as TATB.
TMHI reacts with picramide in the presence of a strong base to give TATB at a yield of over 95%. Picramide may be obtained from low-cost, domestically available nitroaniline. Or, as in the synthesis of TMHI, picramide may be synthesized from a surplus munition, in this case, Explosive D. Several million kilograms of Explosive D are available for disposal in the U.S.
New Process to Increase TATB Availability|
The availability of relatively inexpensive TATB using the improved synthesis will facilitate its use, both for military and civilian applications. At the same time, the VNS process provides a new avenue for disposing of large quantities of energetic materials that are a legacy of the Cold War. The process reflects a new perspective within both the Department of Defense and the Department of Energy--treating surplus energetic materials as assets to be recycled whenever possible.
This new approach to the synthesis of TATB and other insensitive energetic materials is still in the development stage. Over the next year, the synthesis will progress from the 10-gram scale at the Laboratory's state-of-the-art High Explosives Applications Facility to the kilogram-pilot-plant scale at Site 300. During this stage, the necessary performance and sensitivity tests will be conducted to qualify the synthesis in terms of ease of use, purity, particle size, and cost. The process will also be evaluated for environmental friendliness and waste reduction. At the conclusion of the study, the technology will be ready for transfer to an industrial partner for commercial scale-up.
Key Words: insensitive high explosives (IHE), stockpile stewardship, TATB (triamino-trinitrobenzene).
For further information contact Phil Pagoria (510) 423-0747 (firstname.lastname@example.org), Alexander Mitchell (510) 422-7994 (email@example.com), or Robert Schmidt (510) 423-6887 (firstname.lastname@example.org).