RDX is a high explosive which is used in the manufacture of plastic explosives such as C-4 and Semtex. RDX is used to create C-4 and mixed with PETN to create Semtex. RDX is also used in combination with TNT to create Torpex.
RDX is known by many names, including:
- Cyclotrimethylene trinitramine
- Hexogen 5W
RDX is a white crystalline solid. It is most useful when mixed with plasticizers and binders to create malleable plastic explosives.
Pure RDX is very stable. It melts at 204 degrees celsius. However, it is dangerous when stored below -4 degrees celsius.
RDX is an extremely powerful explosive, with a velocity of detonation of 8,750 meters per second at a density of 1.76 grams/cm3.
RDX has a Figure of Insensitivity (FofI) of 80. FofI is an inverse scale; a higher numbers means a less sensitive explosive.
In Chemistry and Technology of Explosives, Vol. III, Urbanski documents five methods for the manufacture of RDX.
Here are the two most common methods of making RDX in a laboratory environment:
- Add 335 mL of 100% nitric acid, free of nitrogen oxides in a 500-mL beaker.
- Cool the nitric acid to below 30 degrees C.
- Add 75 g of hexamine in small portions, while stirring the mixture. NOTE: During the addition toxic fumes will be produced.
- During the addition the temperature must be kept between 20 degrees C and 30 degrees C.
- After the hexamine has dissolved, slowly heat the mixture to 55 degrees C while stirring.
- Keep the mixture between 50-55 degrees C for 5 minutes, keep stirring.
- Now cool the mixture to 20 degrees C then let sit for 20 minutes.
- Slowly dilute the mixture with four times its volume of cool water to precipitate the RDX from solution. Most of the RDX will precipitate in several hours; after 24 hours there will be no additional precipitation of RDX.
- Filter the RDX that precipitated from the mixture and add 1 L of 5% sodium bicarbonate solution to adjust the pH to neutral.
- Dry the pH balanced RDX at room temperature; after drying the RDX is ready to use.
- If RDX of higher purity is desired, recrystalize from acetone.
The Eberle Method
The precursors used in the Eberle Method (or E-method) are ammonium nitrate, acetic anhydride and paraformaldehyde. No nitric acid is needed for this method. The yield of this process is typically 60 – 65%, although it can be as high as 80% on small scale production. Boron fluoride is needed as a catalyst to reduce the quantity of by-products.
- Warm 260 ml of acetic anhydride to 60 – 65 degrees C and add 0,4% of Boron fluoride (BF3).
- Slowly add 105 g of ammonium nitrate while stirring. Remove the source of heat and keep the temperature 60 – 65 degrees C.
- Slowly add paraformaldehyde. NOTE: During the addition toxic and flammable fumes will be produced.
- After the reaction has stopped put the product in distilled water to precipitate the crystals of RDX.
Cast-cured PBXs containing insensitive RDX grades are intrinsically less sensitive to shock stimuli and have increased critical diameters.
Today’s HMX crystals Type B are sufficient for acceptable insensitive HE mixtures. Improvement of HMX crystals will result in additional insensitivity against shock stimuli. Shock insensitivity improvement is expected to be achieved by use of Insensitive RDX crystals only. In both cases an additional reduction of binder system seems to be possible to achieve sufficient insensitive pressable mixtures by Paste Process using organic solvents.
RDX fact sheet from the University of Iowa
RDX, a cyclic nitramine, releases a large amount of energy upon bulk decomposition, making this compound an important ingredient for various propellants and explosive materials. Over the last years the decomposition pathways of this compound have been the focus of both experimental and computational studies. Both these types of study face major problems when applied to fast-reacting explosive compounds like RDX.
A 150 lb/day sub-scale plant has been demonstrated for the recovery of HMX and RDX from LX-14 and Composition A-3, respectively. This recovery process involves solubilizing the binder through the use of an acid or hot water/surfactant, then separating the explosive from the binder solution by centrifugation. The recovered HMX and RDX are of high purity at a high yield and have melting points comparable to pure HMX and RDX. This technology will allow for the recovery of valuable explosives, which may be reused for commercial or military applications.
Intermolecular Potential for the Hexahydro-1,3,5-trinitro-1,3,5,-s- triazine (RDX) Crystal: A Crystal-Packing, Monte Carlo, and Molecular Dynamics Study
We have developed an intermolecular potential that describes the structure of the alpha-form of the hexahydro-1,3,5- trinitro,1,3,5-s-triazine (RDX) crystal. The potential is composed of pairwise atom-atom (6-exp) Buckingham interactions and charge-charge interactions. The parameters of the Buckingham repulsion-dispersion terms have been determined through a combination of nonlinear least-squares fitting to observed crystal structures and lattice energies and trial-and-error adjustment. Crystal-packing calculations were performed to determine the equilibrium crystallographic structure and lattice energy of the model. There are no significant differences in the geometrical structures and crystal energies resulting from minimization of the lattice energy with and without symmetry constraints. Further testing of the intermolecular potential has been done by performing symmetry-constrained isothermal-isobaric Monte Carlo simulations. The properties of the crystal (lattice dimensions, molecular orientation, and lattice energy) determined from Monte Carlo simulations at temperatures over the range 4.2-300 K indicate good agreement with experimental data. The intermolecular potential was also subjected to isothermal-isobaric molecular dynamics calculations at ambient pressure for temperatures ranging from 4.2 to 325 K. Crystal structures at 300 K are in outstanding agreement with experiment (within 2% of lattice diinensions, and almost no rotational and translational disorder of the molecules in the unit cell). The space-group symmetry was maintained throughout the simulations.