RDX (Research Department Explosive orRoyal Demolition Explosive), orhexogen,[4] also known by other names, is anorganic compound with the formula (CH2N2O2)3. It is white, odorless, tasteless, and widely used as anexplosive.[5] Chemically, it is classified as anitroamine alongsideHMX, which is a more energetic explosive thanTNT. It was used widely inWorld War II and remains common inmilitary applications. It is lower performing and more toxic than modern replacements such asTKX-50.[6]
RDX is also less commonly known ascyclonite,hexogen (particularly in Russian, French and German-influenced languages),T4, and, chemically, ascyclotrimethylene trinitramine.[7] In the 1930s, theRoyal Arsenal,Woolwich, started investigating cyclonite to use against GermanU-boats that were being built with thicker hulls. The goal was to develop an explosive more energetic thanTNT. For security reasons, Britain termed cyclonite "Research Department Explosive" (R.D.X.).[8] The termRDX appeared in the United States in 1946.[9] The first public reference in the United Kingdom to the nameR.D.X. appeared in 1948; its authors were: the Managing Chemist,ROF Bridgwater; the Chemical Research and Development Department, Woolwich; and the Director ofRoyal Ordnance Factories, Explosives.[10]
Armourers prepare to load 1,000 lb (450 kg) Medium Capacity bombs into the bomb-bay of anAvro Lancaster B Mark III of No. 106 SquadronRAF atRAF Metheringham before a major night raid onFrankfurt. The stencilled lettering around the circumference of each bomb reads "RDX/TNT".
RDX is believed to have been used in many bomb plots, includingterrorist plots.
RDX is the base for a number of common military explosives:
Composition A: Granular explosive consisting of RDX and plasticizing wax, such as composition A-3 (91% RDX coated with 9% wax)[12] and composition A-5 (98.5 to 99.1% RDX coated with 0.95 to 1.54%stearic acid).[13]
Composition C: The original composition C was used in World War II, but there have been subsequent variations including C-2, C-3, andC-4. C-4 consists of RDX (91%); a plasticizer,dioctyl sebacate (5.3%); and a binder, which is usually polyisobutylene (2.1%); and a specially manufactured mineral oil (1.6%).[15]
DBX (Depth Bomb Explosive): Castable mixture consisting of 21% RDX, 21%ammonium nitrate, 40% TNT, and 18% powdered aluminium, developed during World War II, it was to be used in underwater munitions as a substitute forTorpex employing only half the amount of then-scarce RDX,[2][17] as the supply of RDX became more adequate, however, the mixture was shelved
Cyclotol: Castable mixture of RDX (50–80%) with TNT (20–50%) designated by the amount of RDX/TNT, such as Cyclotol 70/30
HBX: Castable mixtures of RDX, TNT, powdered aluminium, and D-2wax with calcium chloride
PBX: RDX is also used as a major component of manypolymer-bonded explosives (PBX); RDX-based PBXs typically consist of RDX and at least thirteen different polymer/co-polymer binders.[18] Examples of RDX-based PBX formulations include, but are not limited to: PBX-9007, PBX-9010, PBX-9205, PBX-9407, PBX-9604, PBXN-106, PBXN-3, PBXN-6, PBXN-10, PBXN-201, PBX-0280, PBX Type I, PBXC-116, PBXAF-108, etc.[citation needed]
Semtex (trade name): Plastic demolition explosive containing RDX andPETN as major energetic components[19]
Torpex: 42% RDX, 40% TNT, and 18% powdered aluminium; the mixture was designed during World War II and used mainly in underwater ordnance[20]
The conventional cheapnitration agent, called "mixed acid", cannot be used for RDX synthesis because concentrated sulfuric acid conventionally used to stimulate thenitronium ion formation decomposes hexamine into formaldehyde and ammonia.
Modern syntheses employ hexahydro triacyl triazine as it avoids formation of HMX.[24]
RDX was used by both sides in World War II. The US produced about 15,000 long tons (15,000 t) per month during WWII and Germany about 7,100 tonnes (7,000 long tons) per month.[25] RDX had the major advantages of possessing greater explosive force thanTNT and required no additional raw materials for its manufacture. Thus, it was also extensively used inWorld War I[25]
RDX was reported in 1898 by Georg Friedrich Henning (1863-1945), who obtained aGermanpatent[26] for its manufacture by nitrolysis of hexamine (hexamethylenetetramine) with concentrated nitric acid.[27] In this patent, only the medical properties of RDX were mentioned.[27]
During WWI, Heinrich Brunswig (1865-1946) at the private military-industrial laboratoryZentralstelle für wissenschaftlich-technische Untersuchungen [de] (Center for Scientific-Technical Research) inNeubabelsberg studied the compound more closely and in June 1916 filed two patent applications, one for its use insmokeless propellants[28] and another for its use as an explosive, noting its excellent characteristics.[29][30] The German military hadn't considered its adoption during the war due to the expense of production[31] but started investigating its use in 1920, referring to it as hexogen.[32]
Research and development findings were not published further until Edmund von Herz,[33] described as an Austrian and later a German citizen, rediscovered the explosive properties of RDX[31] and applied for an Austrian patent in 1919, obtaining a British one in 1921[34] and an American one in 1922.[35] All patents described the synthesis of the compound by nitrating hexamethylenetetramine.[34][35] The British patent claims included the manufacture of RDX by nitration, its use with or without other explosives, its use as a bursting charge and as an initiator.[34] The US patent claim was for the use of a hollow explosive device containing RDX and a detonator cap containing it.[35] Herz was also the first to identify the cyclic nature of the molecule.[31]
In the 1930s, Germany developed improved production methods.[32]
During World War II, Germany used the code names W Salt, SH Salt, K-method, the E-method, and the KA-method. These names represented the identities of the developers of the various chemical routes to RDX. The W-method was developed by Wolfram in 1934 and gave RDX the code name "W-Salz". It usedsulfamic acid, formaldehyde, and nitric acid.[36] SH-Salz (SH salt) was from Schnurr, who developed a batch-process in 1937–38 based on nitrolysis of hexamine.[37] The K-method, from Knöffler, involved addition of ammonium nitrate to the hexamine/nitric acid process.[38] The E-method, developed by Ebele, proved to be identical to the Ross and Schiessler process described below.[39] The KA-method, also developed by Knöffler, turned out to be identical to the Bachmann process described below.[40]
The explosive shells fired by theMK 108 cannon and the warhead of theR4M rocket, both used inLuftwaffe fighter aircraft as offensive armament, both used hexogen as their explosive base.[41]
In theUnited Kingdom (UK), RDX was manufactured from 1933 by the research department in a pilot plant at the Royal Arsenal in Woolwich,London, a larger pilot plant being built at theRGPF Waltham Abbey just outside London in 1939.[42][43] In 1939 a twin-unit industrial-scale plant was designed to be installed at a new 700-acre (280 ha) site, ROF Bridgwater, away from London and production of RDX started at Bridgwater on one unit in August 1941.[42][44] The ROF Bridgwater plant brought in ammonia and methanol as raw materials: the methanol was converted to formaldehyde and some of the ammonia converted to nitric acid, which was concentrated for RDX production.[10] The rest of the ammonia was reacted with formaldehyde to produce hexamine. The hexamine plant was supplied byImperial Chemical Industries. It incorporated some features based on data obtained from the United States (US).[10] RDX was produced by continually adding hexamine and concentrated nitric acid to a cooled mixture of hexamine and nitric acid in the nitrator.[10] The RDX was purified and processed for its intended use; recovery and reuse of some methanol and nitric acid also was carried out.[10] The hexamine-nitration and RDX purification plants were duplicated (i.e. twin-unit) to provide some insurance against loss of production due to fire, explosion, or air attack.[42]
The United Kingdom andBritish Empire were fighting without allies againstNazi Germany until the middle of 1941 and had to beself-sufficient. At that time (1941), the UK had the capacity to produce 70 long tons (71 t) (160,000 lb) of RDX per week; bothCanada, an allied country and self-governing dominion within the British Empire, and the US were looked upon to supply ammunition and explosives, including RDX.[45] By 1942, theRoyal Air Force's annual requirement was forecast to be 52,000 long tons (53,000 t) of RDX, much of which came from North America (Canada and the US).[44]
A different method of production to the Woolwich process was found and used in Canada, possibly at theMcGill University department of chemistry. This was based on reacting paraformaldehyde and ammonium nitrate inacetic anhydride.[46] A UK patent application was made by Robert Walter Schiessler (Pennsylvania State University) and James Hamilton Ross (McGill, Canada) in May 1942; the UK patent was issued in December 1947.[47] Gilman states that the same method of production had been independently discovered by Ebele in Germany prior to Schiessler and Ross, but that this was not known by the Allies.[27][46] Urbański provides details of five methods of production, and he refers to this method as the (German) E-method.[39]
At the beginning of the 1940s, the major US explosive manufacturers,E. I. du Pont de Nemours & Company andHercules, had several decades of experience of manufacturing trinitrotoluene (TNT) and had no wish to experiment with new explosives. US Army Ordnance held the same viewpoint and wanted to continue using TNT.[48] RDX had been tested byPicatinny Arsenal in 1929, and it was regarded as too expensive and too sensitive.[45] The Navy proposed to continue usingammonium picrate.[48] In contrast, theNational Defense Research Committee (NDRC), who had visited The Royal Arsenal, Woolwich, thought new explosives were necessary.[48]James B. Conant, chairman of Division B, wished to involve academic research into this area. Conant therefore set up an experimental explosives research laboratory at theBureau of Mines,Bruceton, Pennsylvania, usingOffice of Scientific Research and Development (OSRD) funding.[45]
In 1941, the UK'sTizard Mission visited the US Army and Navy departments and part of the information handed over included details of the "Woolwich" method of manufacture of RDX and its stabilisation by mixing it withbeeswax.[45] The UK was asking that the US and Canada, combined, supply 220 short tons (200 t) (440,000 lb) of RDX per day.[45] A decision was taken byWilliam H. P. Blandy, chief of theBureau of Ordnance, to adopt RDX for use in mines andtorpedoes.[45] Given the immediate need for RDX, the US Army Ordnance, at Blandy's request, built a plant that copied the equipment and process used at Woolwich. The result was theWabash River Ordnance Works run by E. I. du Pont de Nemours & Company.[49] At that time, this works had the largest nitric acid plant in the world.[45] The Woolwich process was expensive: it needed 11 pounds (5.0 kg) ofstrong nitric acid for every pound of RDX produced.[50]
By early 1941, the NDRC was researching new processes.[50] The Woolwich or direct nitration process has at least two serious disadvantages: (1) it used large amounts of nitric acid and (2) at least one-half of the formaldehyde is lost. One mole of hexamethylenetetramine could produce at most one mole of RDX.[51] At least three laboratories with no previous explosive experience were instructed to develop better production methods for RDX; they were based atCornell,Michigan, andPennsylvania State universities.[45][a]Werner Emmanuel Bachmann, from Michigan, successfully developed the "combination process" by combining the Ross and Schiessler process used in Canada (aka the German E-method) with direct nitration.[40][45] The combination process required large quantities of acetic anhydride instead of nitric acid in the old British "Woolwich process". Ideally, the combination process could produce two moles of RDX from each mole of hexamethylenetetramine.[51]
The expanded production of RDX could not continue to rely on the use of natural beeswax to desensitize the explosive as in the original British composition (RDX/BWK-91/9). A substitute stabilizer based on petroleum was developed at the Bruceton Explosives Research Laboratory in Pennsylvania, with the resulting explosive designated Composition A-3.[45][52]
The National Defence Research Committee (NDRC) instructed three companies to develop pilot plants. They were the Western Cartridge Company, E. I. du Pont de Nemours & Company, andTennessee Eastman Company, part of Eastman Kodak.[45] At the Eastman Chemical Company (TEC), a leading manufacturer of acetic anhydride, Werner Emmanuel Bachmann developed a continuous-flow process for RDX utilizing an ammonium nitrate/nitric acid mixture as a nitrating agent in a medium of acetic acid and acetic anhydride. RDX was crucial to the war effort and the current batch-production process was too slow. In February 1942, TEC began producing small amounts of RDX at its Wexler Bend pilot plant, which led to the US government authorizing TEC to design and buildHolston Ordnance Works (H.O.W.) in June 1942. By April 1943, RDX was being manufactured there.[53] At the end of 1944, the Holston plant and the Wabash River Ordnance Works, which used the Woolwich process, were producing 25,000 short tons (23,000 t) (50 million pounds) of Composition B per month.[54]
The Bachmann process yields both RDX andHMX, with the major product determined by the specific reaction conditions.[55]
The United Kingdom's intention in World War II was to use "desensitised" RDX. In the original Woolwich process, RDX wasphlegmatized with beeswax, but laterparaffin wax was used, based on the work carried out at Bruceton. In the event the UK was unable to obtain sufficient RDX to meet its needs, some of the shortfall was met by substitutingamatol, a mixture of ammonium nitrate and TNT.[44]
Karl Dönitz was reputed to have claimed that "an aircraft can no more kill a U-boat than a crow can kill amole".[56] Nonetheless, by May 1942Wellington bombers began to deploydepth charges containing Torpex, a mixture of RDX, TNT, and aluminium, which had up to 50 percent more destructive power than TNT-filled depth charges.[56] Considerable quantities of the RDX–TNT mixture were produced at the Holston Ordnance Works, withTennessee Eastman developing an automated mixing and cooling process based around the use of stainless steelconveyor belts.[57]
In July 2012, the Kenyan government arrested two Iranian nationals and charged them with illegal possession of 15 kilograms (33 pounds) of RDX. According to theKenyan Police, the Iranians planned to use the RDX for "attacks on Israeli, US, UK and Saudi Arabian targets".[70]
RDX has a high nitrogen content and a high oxygen to carbon ratio, (O:C ratio), both of which indicate its explosive potential for formation of N2 and CO2.
It starts to decompose at approximately 170 °C and melts at 204 °C. Atroom temperature, it is very stable. It burns rather than explodes. It detonates only with adetonator, being unaffected even bysmall arms fire. This property makes it a useful military explosive. It is less sensitive than pentaerythritol tetranitrate (PETN). Under normal conditions, RDX has a Figure of Insensitivity of exactly 80 (RDX defines the reference point).[76][page needed]
RDXsublimes invacuum, which restricts or prevents its use in some applications.[77]
RDX, when exploded in air, has about 1.5 times the explosive energy of TNT per unit weight and about 2.0 times per unit volume.[57][78]
RDX is insoluble in water, with solubility 0.05975 g/L at temperature of 25 °C.[79]
The substance's toxicity has been studied for many years.[80] RDX has caused convulsions (seizures) in military field personnel ingesting it, and inmunition workers inhaling its dust during manufacture. At least one fatality was attributed to RDX toxicity in a European munitions manufacturing plant.[81]
During theVietnam War, at least 40 American soldiers were hospitalized withcomposition C-4 (which is 91% RDX) intoxication from December 1968 to December 1969. C-4 was frequently used by soldiers as a fuel to heat food, and the food was generally mixed by the same knife that was used to cut C-4 into small pieces prior to burning. Soldiers were exposed to C-4 either due to inhaling the fumes, or due to ingestion, made possible by many small particles adhering to the knife having been deposited into the cooked food. The symptom complex involved nausea, vomiting, generalized seizures, and prolongedpostictal confusion and amnesia; which indicatedtoxic encephalopathy.[82]
Oral toxicity of RDX depends on its physical form; in rats, the LD50 was found to be 100 mg/kg for finely powdered RDX, and 300 mg/kg for coarse, granular RDX.[81] A case has been reported of a human child hospitalized instatus epilepticus following the ingestion of 84.82 mg/kg dose of RDX (or 1.23 g for the patient's body weight of 14.5 kg) in the "plastic explosive" form.[83]
The substance has low to moderate toxicity with apossible human carcinogen classification.[84][85][86] Further research is ongoing, however, and this classification may be revised by theUnited States Environmental Protection Agency (EPA).[87][88] Remediating RDX-contaminated water supplies has proven to be successful.[89] It is known to be a kidney toxin in humans and highly toxic to earthworms and plants, thus army testing ranges where RDX was used heavily may need to undergo environmental remediation.[90] Concerns have been raised by research published in late 2017 indicating that the issue has not been addressed correctly by U.S. officials.[91]
FOX-7 is considered to be approximately a 1-to-1 replacement for RDX in almost all applications.[97][98]TKX-50 is considered to be a high-performance replacement.[99]
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^DE 299028, "Verfahren zur Herstellung von Sprengstoffen und Detonationsüberträgern", published October 15, 1919, issued June 15, 1916, assigned to Zentralstelle für wissenschaftlich-technische Untersuchungen GmbH
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