Explosives - Nitramines

The nitramines are the most recently introduced class of organic nitrate explosives. The most prominent member of this class is RDX (research department explosive; hexahydro-1,3,5-trinitro-1,3,5 triazine, which is also known as cyclonite); HMX (high melting explosive; octahydro-1,3,5,7-tetranitro-1,3,5,7 tetrazocine), nitroguanidine, and tetryl are also significant nitramines.

In a class of explosives like nitramines, the higher density, bigger molecules will give more power because more realizable energy can be packed in the same space. Bigger molecules using the same proportion of elements are more dense because the formation of covalent bonds makes atoms come closer together than if they were just pushed together but from different molecules. HMX is a big ring molecule, same as RDX but with an extra CH2NNO2 unit. It has higher density (TMD 1.902) than RDX, 1.806, its det. vel is 9.11 km/sec vs. 8.70 for RDX. It is considered more powerful.

Pollution from manufacturing processes of the major energetic materials currently used in the U.S., 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX), 1,3,5,7-tetranitro-1,3,5,7 tetraazacyclooctane (HMX) was briefly evaluated. It was found that acetic acid was a major pollutant. It appeared that the British Process could be controlled to reduce the polluting effluents better than the Bachmann Process used in the U.S.

RDX [Cyclonite - Hexahydro-1,3,5-trinitro-1,3,5-triazine]

RDX stands for Royal Demolition eXplosive. It is also known as cyclonite or hexogen. RDX is currently the most important military high explosive in the US. Cyclotrimethylenetrinitramine, C3H6N606 (RDX), is second in strength to nitroglycerin among common explosive substances. When compressed to a specific gravity of 1.70, it has a confined detonation velocity of about 27,000 fps. RDX is used as an explosive, usually in mixtures with other explosives, oils, or waxes. It has a high degree of stability in storage and is considered the most powerful and brisant of the military high explosives. RDX is used as a base charge in detonators and in blasting caps. RDX can be used alone or with other explosives, including PETN.t RDX can be mixed with plasticizers to make C-4, and the most common explosive combining RDX and PETN is Semtex. RDX forms the base for the following common military explosives: Composition A, Composition B, Composition C, HBX, H-6 and Cyclotol. Composition A consists of RDX melted with wax; in Composition B, RDX is mixed with TNT; and Composition C contains RDX blended with a non-explosive plasticizer. Pure RDX is used in press-loaded projectiles. Cast loading is accomplished by blending RDX with a relatively low melting point substance.

RDX has both military and civilian applications. As a military explosive, RDX can be used alone as a base charge for detonators or mixed with another explosive such as TNT to form cyclotols, which produce a bursting charge for aerial bombs, mines, and torpedoes. Common military uses of RDX have been as an ingredient in plastic bonded explosives, or plastic explosives which have been used as explosive fill in almost all types of munition compounds. Civilian applications of RDX include use in fireworks, in demolition blocks, as a heating fuel for food rations, and as an occasional rodenticide. Combinations of RDX and HMX, another explosive, have been the chief ingredients in approximately 75 products.

RDX is an explosive nitramine compound. It is in the form of a white powder with a density of 1.806 g/cc. Nitrogen content of 37.84%. The chemical name for RDX is 1,3,5-trinitro-1,3,5-triazine. The chemical formula for RDX is C3H6N6O6 and the molecular weight is 222.117. Its melting point is 205�C. RDX has very low solubility in water and has an extremely low volatility. RDX does not sorb to soil very strongly and can move into the groundwater from soil. It can be broken down in air and water in a few hours, but breaks down more slowly in soil.

Although RDX [Royal Demolition Explosive or Research Department Explosive] was first prepared in 1899, its explosive properties were not appreciated until 1920. RDX was used widely during World War II because petroleum was not needed as a raw ingredient. During and since World War II, RDX has become the second-most-widely used high explosive in the military, exceeded only by TNT. As with most military explosives, RDX is rarely used alone; it is widely used as a component of plastic explosives, detonators, high explosives in artillery rounds, Claymore mines, and demolition kits. RDX has limited civilian use as a rat poison.

RDX can cause seizures in humans and animals when large amounts are inhaled or ingested. Nausea and vomiting have also been observed. The effects of long-term (365 days or longer), low-level exposure on the nervous system are not known. No other significant health effects have been reported in humans. Rats and mice that ate RDX for 3 months or more had decreased body weights and slight liver and kidney damage. It is not known whether RDX causes birth defects in humans. It did not cause birth defects in rabbits, but did result in smaller offspring in rats. It is not known whether RDX affects reproduction in humans. The EPA has determined that RDX is a possible human carcinogen (Class C). In one study, RDX caused liver tumors in mice that were exposed to it in the diet. However, carcinogenic effects were not noted in rat studies and no human data are available. RDX does not bioaccumulate in fish or in humans.

RDX has been produced several ways, but the most common method of manufacture used in the United States is the continuous Bachmann process. The Bachmann process involves reacting hexamine with nitric acid, ammonium nitrate, glacial acetic acid, and acetic anhydride. The crude product is filtered and recrystallized to form RDX. The byproducts of RDX manufacture include nitrogen oxides, sulfur oxides, acid mists, and unreacted ingredients. A second process that has been used to manufacture RDX, the direct nitration of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), has not yielded a percentage of RDX as high as the percentage produced in the Bachmann process (Army 1978; Merck 1989).

Production of RDX peaked in the 1960s when it was ranked third in explosive production by volume in the United States. The average volume of RDX produced from 1969 to 1971 was 15 million pounds per month. However, production of RDX decreased to a yearly total of 16 million pounds for 1984.

RDX is not produced commercially in the United States. Production in the United States is limited to Army ammunition plants such as Holston Army ammunition plant in Kingsport, Tennessee, which has been operating at 10-20% capacity. Several Army ammunition plants, such as Louisiana (Shreveport, Louisiana), Lone Star (Texarkana, Texas), Iowa (Middletown, Iowa), and Milan (Milan, Tennessee), also handle and package RDX. Since the release of RDX is not required to be reported under SARA Section 313, there are no data on RDX in the Toxics Release Inventory (TRI 1993).

Waste-water treatment sludges resulting from the manufacture of RDX are classified as hazardous wastes and are subject to EPA regulations. Munitions such as RDX have been disposed of in the past by dumping in deep sea water. By-products of military explosives such as RDX have also been openly burned in many Army ammunition plants in the past. There are indications that in recent years as much as 80% of waste munitions and propellants have been disposed of by incineration. Wastes containing RDX have been incinerated by grinding the explosive wastes with a flying knife cutter and spraying the ground material with water to form a slurry. The types of incineration used to dispose of waste munitions containing RDX include rotary kiln incineration, fluidized bed incineration, and pyrolitic incineration. The primary disadvantage of open burning or incineration is that explosive contaminants are often released into the air, water, and soils.

Soldiers and other workers have been exposed to RDX during its manufacture, in the field, and through the contamination of the environment. The main occupational exposure to RDX during its manufacture is through the inhalation of fine dust particles. Ingestion may also be a possible route of exposure, but it is poorly absorbed through the dermis.

The greatest potential for occupational exposure to RDX occurs at ammunition plants with load, assemble and pack (LAP) operations, where workers involved with melt-pouring and maintenance operations have the greatest potential for exposures.

In 1962, five cases of convulsions or unconsciousness or both occurred at an RDX manufacturing plant in the United States. All five employees had convulsions during their work shifts or within a few hours after their shifts were over. These patients exhibited little or no prodrome, and the postictal phase lasted up to 24 hours. No abnormal laboratory or physical findings were noted.

Troops have also become intoxicated during field operations from exposure to composition C4 plastic explosive, which contains 91% RDX. These field exposures occurred because C4 was either chewed as an intoxicant or used as a fuel for cooking. Thus, the route of exposure was ingestion or inhalation. At least 40 American soldiers experienced convulsions due to RDX ingestion during the Vietnam War.

After acute exposure by inhalation or ingestion, there is a latent period of a few hours, followed by a general sequence of intoxication that begins with a prodromal period of irritability. Neurological symptoms predominate and include restlessness and hyperirritability; headache; weakness; dizziness; hyperactive reflexes; nausea and vomiting; prolonged and recurrent generalized convulsions; muscle twitching and soreness; and stupor, delirium, and disorientation.

Clinical findings in acute exposures may also include fever, tachycardia, hematuria, proteinuria, azotemia, mild anemia, neutrophilic leukocytosis, elevated AST, and electroencephalogram (EEG) abnormalities. These abnormal effects, transient and unreliable for diagnosis purposes, last at most a few days. In fact, all physical and laboratory tests may remain normal, even in the presence of seizures. EEGs made at the time of convulsions may show bilateral synchronous spike and wave complexes (2-3/sec) in the frontal areas with diffuse slow wave activity; normalization occurs within 1 to 3 months.

RDX in the wastewater from manufacturing and loading operations has also contaminated the environment. Although contamination has appeared in soil and groundwater near some ammunition plants, RDX's low solubility in water has limited its migration in most cases.

Although intensive research with animals has revealed some effects, few effects of chronic human exposure to RDX have been reported. Investigations into the mutagenicity and carcinogenicity of RDX have yielded conflicting results. RDX does not appear to be a mutagen, based on negative results in the Ames tests, the dominant lethal test, and the unscheduled deoxyribonucleic acid synthesis assay. RDX has not been found to be carcinogenic in gavage studies performed on rats, but increased hepatocellular carcinoma and adenoma were noted in females of one strain of mice. Due to this finding, the U.S. Environmental Protection Agency has classified RDX as a possible human carcinogen.

Reproductive effects have been noted in rabbits and rats. A study performed on rabbits showed teratogenic effects at 2 mg/kg/day (10% of the dose that caused maternal toxicity). Similarly, a teratology study performed on pregnant rats exposed to RDX resulted in offspring with lower body weights and shorter body lengths than were found in the control group. These researchers therefore recommended that human females of childbearing age be protected from exposure to RDX.

Despite the low toxicity of RDX, exposure should be maintained at the lowest levels possible due to its possible carcinogenicity. General medical surveillance examinations can be conducted (such as liver and kidney function tests), but specific testing for the effects of low level occupational exposure does not appear to be warranted, given the absence of abnormal results even in those patients with RDX-induced seizures. Surveillance for both males and females should also include a screening questionnaire for reproductive history. Pregnant women should avoid exposure to RDX.

HMX [Octogen - Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine ]

High Melting Explosive [HMX] is the highest-energy solid explosive produced on a large scale in the United States. It is also known as Octogen and cyclotetramethylene-tetranitramine, as well as other names. HMX explodes violently at high temperatures (534�F and above). Because of this property, HMX is used exclusively for military purposes to implode fissionable material in nuclear devices, as a component of plastic-bonded explosives, as a component of rocket propellant, and as a high explosive burster charge. The use of HMX as a propellant and in maximum-performance explosives is increasing.

HMX was discovered as a by-product in the production of RDX. Although it is almost as sensitive and powerful as RDX, it is seldom used alone in military applications but is normally mixed with another compound, such as TNT. In the Navy, HMX is used as an ingredient in plastic-bonded explosives.

HMX is produced by the nitration of hexamine with ammonium nitrate and nitric acid in an acetic acid/acetic anhydride solvent at 44�C. The raw materials are mixed in a two-step process and the product is purified by recrystallization. This is a modification of the Bachmann Process used to produce RDX, another explosive. The yield of HMX is about 55-60%, with RDX as an impurity. RDX produced by the Bachmann Process usually contains about 8-12% HMX as an acceptable byproduct.

HMX is currently produced at only one facility in the United States, the Holston Army Ammunition Plant in Kingsport, Tennessee. The amount of HMX made and used in the United States at present is not known, but it is believed to be greater than 30 million pounds [15,000 tons] per year between 1969 and 1971. No estimates of current production volume were located, but it is estimated that its use is increasing. Processing may occur at load, assemble, and pack (LAP) facilities operated by the military. There were 10 facilities engaged in LAP operations in the United States in 1976

No information was located regarding import or export of HMX in the United States. Export of this chemical is regulated by the U.S. State Department.

Wastes from explosive manufacturing processes are classified as hazardous wastes by EPA. Generators of these wastes must conform to EPA regulations for treatment, storage, and disposal. The waste water treatment sludges from processing of explosives are listed as hazardous wastes by EPA based only on reactivity. Waste water treatment may involve filtering through activated charcoal, photolytic degradation, and biodegradation. Rotary kiln or fluidized bed incineration methods are acceptable disposal methods for HMX-containing wastes. At the Holston facility, waste waters are generated from the manufacturing areas and piped to an industrial water treatment plant on site. Following neutralization and nutrient addition, sludge is aerobically digested and dewatered. It was estimated that the facility generates a maximum of 3,800 tons (7.6 million pounds) of treated, dewatered sludge annually. Based on demonstration by Holston that this sludge is nonhazardous, the EPA proposed granting a petition to exclude the sludge from hazardous waste control. HMX is not listed on the Toxics Release Inventory (TRI) database, because it is not a chemical for which companies are required to report discharges to environmental media.

HMX or octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine is an explosive polynitramine. The chemical formula is C4H8N8O8 and molecular weight is 296.20. It is a colorless solid with a melting point of 276 to 286�C. HMX is made by the nitration of hexamine with ammonium nitrate and nitric acid in an acetic acid/acetic anhydride solvent. A small amount of HMX is also formed in making cyclotrimethylene-trinitramine (RDX), another explosive similar in structure to HMX.

It dissolves slightly in water. Only a very small amount of HMX will evaporate into the air; however, it can occur in air attached to suspended particles or dust. The taste and smell of HMX are not known.

HMX is a manmade chemical and does not occur naturally in the environment. It is made from other chemicals known as hexamine, ammonium nitrate, nitric acid, and acetic acid. A small amount of HMX is also formed in making cyclotrimethylene-trinitramine (RDX), another explosive similar in structure to HMX.

HMX is only slightly soluble in water. It has low volatility and thus only a small amount of HMX will evaporate into the air; however, it can occur in air attached to suspended particles or dust. In surface water, HMX does not evaporate or bind to sediments to any large extent. Sunlight breaks down most of the HMX in surface water into other compounds, usually in a matter of days to weeks. HMX is likely to move from soil into groundwater, particularly in sandy soils.

Exposure to HMX can occur during the manufacture and filling of munitions or through the environmental contamination of groundwater and soil. HMX, like RDX, is manufactured using the continuous Bachman process. Although its solubility in water is very low, HMX can be present in particulate form in water effluent from manufacturing, LAP, and demilitarization operations.

Information on the adverse health effects of HMX is limited. In one study on humans, no adverse effects were reported in workers exposed to HMX in air. However, the concentrations of HMX in the workplace air were not reported in this study, and only a small number of workers and effects were investigated.

Studies in rats, mice, and rabbits indicate that HMX may be harmful to the liver and central nervous system if it is swallowed or contacts the skin. The lowest dose producing any effects in animals was 100 milligrams per kilogram of body weight per day (mg/kg/day) orally and 165 mg/kg/day on the skin. Limited evidence suggests that even a single exposure to these dose levels harmed rabbits. The mechanism by which HMX causes adverse effects on the liver and nervous system is not understood.

The reproductive and developmental effects of HMX have not been well studied in humans or animals. At present, the information needed to determine if HMX causes cancer is insufficient. Due to the lack of information, EPA has determined that HMX is not classifiable as to its human carcinogenicity.

The data on the effects on human health of exposure to HMX are very limited. HMX causes CNS effects similar to those of RDX, but at considerably higher doses. In one study, volunteers submitted to patch testing, which produced skin irritation. Another study of a cohort of 93 workers at an ammunition plant found no hematological, hepatic, autoimmune, or renal diseases. However, the study did not quantify the levels of exposure to HMX.

HMX exposure has been investigated in several studies on animals. Overall, the toxicity appears to be quite low. HMX is poorly absorbed by ingestion. When applied to the dermis, it induces mild skin irritation but not delayed contact sensitization. Various acute and subchronic neurobehavioral effects have been reported in rabbits and rodents, including ataxia, sedation, hyperkinesia, and convulsions. The chronic effects of HMX that have been documented through animal studies include decreased hemoglobin, increased serum alkaline phosphatase, and decreased albumin. Pathological changes were also observed in the animals' livers and kidneys. No data are available concerning the possible reproductive, developmental, or carcinogenic effects of HMX.

CL-20 / HNIW

CL-20 [2,4,6,8,10,12-hexanitrohexaazaisowurtzitane (HNIW) ] is a new nitramine explosive that is 20 percent more powerful that HMX. CL20 was a breakthrough in energetic materials with higher performance, minimum signature, and reduced-hazard characteristics. CL-20 has numerous military and commercial applications. The trend today is to explore the possibilities that HNIW can provide to munitions;from high performance gun propellants , shaped charges etc. The only limitation is the cost of its production. Even there had been practical methods to nitrate the special reactant (acetyl Isowurtzitane derivatives) with mixed acid, but the effort of debenzylation of the condensation products of glyoxal and benzylamine still requires the expensive palladium catalyst. Therefore it will take some time before it can reach the level of comparatively lower cost needed to make HMX.

CL-20 exists in four crystalline forms, stable at different temperatures. Only the e and the � form are used in ex-ploitation. CL-20 has better detonation properties than octogen, higher den-sity and detonation rate but lower impact and friction sensitivity (of the PETN class). The CL-20 melting point is lower than in octogen, 240�C approximately.

CL20, a high-energy explosive compound, is a polyazapolycyclic caged polynitramine. The combustion and detonation characteristics of CL20 can be improved if it is formed into nanoparticles of uniform size. A new, promising process for particulation of materials utilizes environmentally benign compressed gases as either solvents or anti-solvents. Predictive models are required to describe the solubility and phase behavior of supercritical solutions of CL20 and supercritical carbon dioxide and for process simulation and development. Here, the solubility of CL20 in supercritical carbon dioxide was evaluated using the Peng-Robinson cubic equation of state. Critical properties, vapor pressure, and other required thermodynamic properties were estimated using a variety of available estimation techniques. A Fortran program to predict the solubility of CL20 was developed. The program was validated using available literature data for the solubility of naphthalene and of biphenyl in supercritical carbon dioxide. The applicability of the estimation techniques employed for the critical properties for CL20 was established using these same techniques to estimate the critical properties of comparable compounds, including RDX and HMX. Solubility data for RDX in supercritical carbon dioxide reported in the literature were also used to establish the validity of the estimation approach. Solubility was predicted over the temperature range of 305.15 to 368.15 K and over the pressure range of 74 to 150 atm. In general, as the temperature increases, the solubility decreases, while as the pressure increases, the solubility increases.

Fortunately, shortly after Dr. Arnold Nielson first synthesized Hexanitrohexaazaisowurtzitane [hexa-nitro-hexa-aza-iso-wurtzi-tane] in 1987 it was designated "CL-20," and talking and writing about this "most significant energetic ingredient in 50 years" was made much easier. And there has been alot of writing and discussion about the development of CL-20. Nielson's original discovery astonished the scientific community because he constructed the CL-20 cage using a single chemical reaction and, in the process, established a new type of amine glyoxal chemistry.

It was soon realized that CL-20 had greater energy output than existing (in-use) energetic ingredients while having an acceptable level of insensitivity to shock and other external stimuli. This fit in nicely with the Navy's 1989 decree for development of "insensitive munitions," capable of withstanding unplanned exposure to external forces. Further, CL-20-based formulations were clean burning, with less signature and which also met requirements spawned by the government's then new-found emphasis of its role in preserving the natural environment.

Seeing potential for the new molecule, early members of the team set about purifying and characterizing new polymorphic forms and scaling up to produce usable quantities. In 1993 some 48 members of the Research, Ordnance Systems and Range departments received a Team Award for their CL-20 efforts. Still more have been involved since then.

On June 19, 1996, NAWCWD and Thiokol Corporation of Ogden, Utah, entered into a Cooperative Research and Development Agreement (CRADA), the ultimate goal of which is to test a warhead containing a CL-20-based explosive that will demonstrate performance significantly above that of existing explosives. Under the terms of the three-year agreement NAWCWD will provide the personnel, facilities, equipment and materials necessary to characterize CL-20; formulate, test and evaluate CL-20-based explosives; and test and evaluate subscale warheads. Thiokol will provide the personnel, facilities, equipment and materials necessary, and will provide 250 lbs. Of epsilon (polymorph) CL-20 for this effort, to support preparation of subscale samples and other tasks.

cost reduction is a major benefit expected to be gained from this CRADA. By successfully completing this CRADA and demonstrating the potential of CL-20, demand for the material will go up. With increased demand, and improved production processes for high-grade product that will also come from this CRADA, availability will go up. When that happens cost will go down. When Arnold Nielson first synthesized a few grams of CL-20, the extrapolated cost to produce a pound by that method would have been several thousand dollars. Thiokil has refined the production process to the point that customers were paying around $400 a pound in the mid-1990s, which was a considerable reduction. The hope at that time was to quarter that cost and get it down to around $100 a pound.

As NAWCWD has been characterizing and refining the CL-20 molecule, other entities, including Thiokol, have been working on the CL-20 molecule produced from their own processes. Thiokol with continuous assistance and collaboration from China Lake researchers has scaled up its process to the point that it can now produce 1,000-plus pound batches of the ingredient. It has also been commercially marketing the basic ingredient as well as end-product formulations for explosives, gun propellants and, to a lesser degree, rocket propellants.

While there have been other new ingredients over the years, none of them have been successfully scaled up to mass productionlevels. Thiokol has made the jump to mass production of CL-20. That's why many have called CL-20 the mostsignificant energetic ingredient in the past 50 years. It offers great potential to meet the performance, insensitive munitions and environmental requirements for future weapons systems. CL-20-based shaped charges are already being used in the oil well industry. Other commercial applications he expects to see include specialty demolition, because CL-20 has good properties for use as a "cutter." And it will likely be used in high-rate detonating cord.

