RDX and HMX

RDX was first prepared in 1899 by the German, Henning for medicinal use. Its value as an explosive was not recognized until 1920 by Herz. 

Herz succeeded in preparing RDX by direct nitration of hexamine, but the yields were low and the process was expensive and unattractive for large scale production. Hale, at Picatinny Arsenal in 1925, developed a process for manufacturing RDX which produced yields of 68%. However, no further substantial improvements were made in the manufacture of RDX until 1940 when Meissner developed a continuous method for the manufacture of RDX, and Ross and Schiessler from Canada developed a process which did not require the use of hexamine as a starting material. At the same time, Bachmann developed a manufacturing process for RDX (1.5) from hexamine which gave the greatest yield. 

Bachmann s products were known as Type B RDX and contained a constant impurity level of 8-12%. The explosive properties of this impurity were later utilized and the explosive HMX, also known as Octogen, was developed. The Bachmann process was adopted in Canada during World War II, and later in the USA by the Tennes-see-Eastman Company. This manufacturing process was more economical and also led to the discovery of several new explosives. A manufacturing route for the synthesis of pure RDX (no impurities) was developed by Brockman, and this became known as Type A RDX. 

Research and development continued throughout World War II to develop new and more powerful explosives and explosive compositions. Torpex (TNT/RDX/aluminium) and cyclotetramethylenetetranit-ramine, known as Octogen [(HMX) (C4H8N8Og)], became available at 

---

RDX and HMX are rather more recalcitrant, especially under aerobic conditions, but there are promising indications that biodegradation can occur under some conditions, especially composting (67). Several strains of bacteria able to use RDX (and Triazine) as a sole source of nitrogen for growth have recentiy been isolated, and this is an area where rapid progress is being made. 

Both RDX and HMX are stable, crystalline soHds, somewhat less sensitive to impact than PETN. Both may be handled with no physiological effect if appropriate precautions are taken to assure cleanliness of operations. Both RDX and HMX detonate to form mostiy gaseous, low molecular weight products and some intermediate formation of soHd carbons. The calculated molar detonation products of RDX are 3.00 H2O, 3.00 N2, 1.49 CO2, and 0.02 CO. RDX has been stored for as long as 10 months at 85°C without perceptible deterioration. 

Both RDX and HMX are substantially desensitized by mixing with TNT to form cyclotols (RDX) and octols (HMX) or by coating with waxes, synthetic polymers, and elastomeric biaders. Most of the RDX made ia the United States is converted to Composition B (60% RDX, 40% TNT, 1 part wax added). Composition A5 (RDX 98.5/stearic acid 1.5) and composition C4 (RDX91/nonexplosive plasticizer) account for the next largest uses. HMX is used as a propellant and ia maximum-performance plastic bonded explosives such as PBX 9401 and PBX N5 and the octols (147—150). 

Ma.nufa.cture. The two most common processes for making RDX and HMX use hexamethylenetetramine (hexamine) as starting material. The Woolwich or direct nitrolysis process used ia the United Kingdom proceeds according to ... 

Oxidizers. The characteristics of the oxidizer affect the baUistic and mechanical properties of a composite propellant as well as the processibihty. Oxidizers are selected to provide the best combination of available oxygen, high density, low heat of formation, and maximum gas volume in reaction with binders. Increases in oxidizer content increase the density, the adiabatic flame temperature, and the specific impulse of a propellant up to a maximum. The most commonly used inorganic oxidizer in both composite and nitroceUulose-based rocket propellant is ammonium perchlorate. The primary combustion products of an ammonium perchlorate propellant and a polymeric binder containing C, H, and O are CO2, H2, O2, and HCl. Ammonium nitrate has been used in slow burning propellants, and where a smokeless exhaust is requited. Nitramines such as RDX and HMX have also been used where maximum energy is essential. 

Tracer Studies on the Nitro lysis of Hexamine to RDX and HMX. The formation of RDX and/or HMX molecules from the nitration or nitrolysis of Hexamethylenetetramine (Hexamine) is a complex process and has been postulated to take place via two separate paths. One involves the selective cleavage of the Hexamine molecule to the appropriate cyclic nitramine (RDX, HMX or both) depending on the specific... 

Thyagarajan and Majumdar (Ref 18) have studied the condensations of urethanes with formaldehyde under various exptl conditions and accomplished the selective synthesis of either six-membered 1,3,5-triazines or eight-membered 1,3,5,7-tetrazocines. These are nonnitrated analogs of RDX and HMX respectively. Their results are summarized in Fig 4... 

A linear relationship between Chapman-Jouguet pressure and density was confirmed for Cyclotol and Octol (Ref 28). Despite the near-equal performance of RDX and HMX at equal densities there appears to be no economical way of making the density of RDX equal to the cast density of HMX. Dinitrobenzene (DNB) has been evaluated as an economical or emergency substitute for TNT but charges prepared with DNB gave somewhat poorer performance than... 

Development work by the US Navy has included attempts to use expls other than RDX and HMX viz, HNS and TACOT (Tetranitro-1,2,5,6-tetraazadibenzocyclooctatetrene) together with binders such as RTV silicon rubbers. As reported by Stott (Ref 43) such work was not fruitful because of the low deton vel and d of the developed compns... 

Nitrite, N-nitrosamines and the explosives RDX and HMX yield reddish-violet j chromatogram zones on a pale pink-colored background. 

Hawthorne SB, AJM Lagadec, D Kalderis, AV Lilke, DJ Miller (2000) Pilot-scale destruction of TNT, RDX, and HMX on contaminated soils using subcritical water. Environ Sci Technol 34 3224-3228. 

Sullivan, J.H., Jr. Putnam, H.D. Keirn, M.A. Pruitt, B.C., Jr. Nichols, J.C. McClave, J.T. "A Summary and Evaluation of Aquatic Environmental Data in Relation to Establishing Water Quality Criteria for Munitions-unique Compounds. Part 4 RDX and HMX," Final Report, Contract DAMD 17-77-C-7027., Water and Air Research, Inc.,... 

This nitrimine, the nominal monomer of the cyclic nitramine high explosives RDX and HMX, may be involved in their detonation and can be formed from them by pyrolysis. 

The military explosives RDX and HMX are manufactured from the 3 components using the Bachman process. Some of the possible mixtures may lead to fires in open vessels and explosions under confinement, and the exothermic and other effects (some calculated by the CHETAH program) for a wide range of mixtures are presented as ternary diagrams. It was also found that acetic anhydride layered onto solutions of ammonium nitrate in nitric acid exploded, owing to formation of acetyl nitrate. 

Numerous experimental studies have investigated the atomistic details of HE decomposition by examining the net products after thermal (low-pressure) decomposition (see, for example, Ref. 54). For RDX and HMX, the rate limiting reaction is most likely NO2 dissociation and a plethora of final products in the decomposition process have been isolated. Several theoretical studies have also... 

Several color reactions were reported for heterocycbc nitramines RDX and HMX [43, 44, 53, 58]. These nitramines release formaldehyde when treated with concentrated sulfuric acid. Therefore, the use of 1,8-dihhydroxynaphthalene-3,6-disulfonic acid (chromotropic acid) in concentrated sulfuric acid — a known reagent for the detection of formaldehyde [4] — produced the expected violet-pink color. The reaction is hardly specific other compounds that release formaldehyde under similar conditions will react in the same way. 

Another non-specific color reagent for RDX and HMX is a solution of thymol in concentrated sulfuric acid [3, 56, 59]. It produces a typical red color. Positive results are also obtained with non-explosive compounds such as sugars and aldehydes. 

Although RDX and HMX are adequate for military applications, they are by no means perfect. The risk of premature detonation increases when such explosives are used in shells for high calibre guns due to the higher set-back force. Also of concern is the risk of catastrophic... 

Nitrolysis is a term originally used for the rupture of a N-C bond leading to the formation of the N-NO2 group. A prime example is the nitrolysis of the N-CH2 bonds of hexamine to form the important military explosives RDX and HMX. Nitrolysis is the most important route available to polynitramine energetic materials. 

The decomposition reactions of RDX and HMX are stoichiometrically balanced-when it is assumed that CO, rather than COj, is formed as a combustion product ... 

The physicochemical properties of explosives are fundamentally equivalent to those of propellants. Explosives are also made of energetic materials such as nitropolymers and composite materials composed of crystalline particles and polymeric materials. TNT, RDX, and HMX are typical energetic crystalline materials used as explosives. Furthermore, when ammonium nitrate (AN) particles are mixed with an oil, an energetic explosive named ANFO (ammonium nitrate fuel oil) is formed. AN with water is also an explosive, named slurry explosive, used in industrial and civil engineering. A difference between the materials used as explosives and propellants is not readily evident. Propellants can be detonated when they are subjected to excess heat energy or mechanical shock. Explosives can be deflagrated steadily without a detonation wave when they are gently heated without mechanical shock. 

The combustion wave structure of RDX composite propellants is homogeneous and the temperature in the solid phase and in the gas phase increases relatively smoothly as compared with AP composite propellants. The temperature increases rapidly on and just above the burning surface (in the dark zone near the burning surface) and so the temperature gradient at the burning surface is high. The temperature in the dark zone increases slowly. However, the temperature increases rapidly once more at the luminous flame front. The combustion wave structure of RDX and HMX composite propellants composed of nitramines and hydrocarbon polymers is thus very similar to that of double-base propellants composed of nitrate esters.[1 1... 

The flame stand-off distance, L4, defined in Eq. (3.70), decreases with increasing pressure, and the pressure exponent of the flame stand-off distance, d, ranges from -1.9 to -2.3 for RDX and HMX propellants. The overall order of the reaction in the dark zone is determined to be m = 2.5-2.8. This is approximately equal to the overall order of the reaction in the dark zone in the case of double-base propellants, m = 2.5, which would suggest close similarity of the reaction pathways in the dark zone for nitramine composite propellants and double-base propellants. 

Since rocket propellants are composed of oxidizers and fuels, the specific impulseis essenhally determined by the stoichiometry of these chemical ingredients. Ni-tramines such as RDX and HMX are high-energy materials and no oxidizers or fuels are required to gain further increased specific impulse. AP composite propellants composed of AP particles and a polymeric binder are formulated so as to make the mixture ratio as close as possible to their stoichiometric ratio. As shown in Fig. 4.14, the maximum is obtained at about p(0.89), with the remaining fraction being HTPB used as a fuel component. 

---