RDX
RDX, or hexogen, also known by other names, is an organic compound with the formula 3. It is white, odorless, tasteless, and widely used as an explosive. Chemically, it is classified as a nitroamine alongside HMX, which is a more energetic explosive than trinitrotoluene. It was used widely in World War II and remains common in military applications. It is lower performing and more toxic than modern replacements like TKX-50.
RDX is often used in mixtures with other explosives and plasticizers or phlegmatizers ; it is the explosive agent in C-4 plastic explosive and a key ingredient in Semtex. It is stable in storage and is considered one of the most energetic and brisant of the military high explosives, with a relative effectiveness factor of 1.60.
Name
RDX is also less commonly known as cyclonite, hexogen, T4, and, chemically, as cyclotrimethylene trinitramine. In the 1930s, the Royal Arsenal, Woolwich, started investigating cyclonite to use against German U-boats that were being built with thicker hulls. The goal was to develop an explosive more energetic than TNT. For security reasons, Britain termed cyclonite "Research Department Explosive". The term RDX appeared in the United States in 1946. The first public reference in the United Kingdom to the name R.D.X. appeared in 1948; its authors were: the Managing Chemist, ROF Bridgwater; the Chemical Research and Development Department, Woolwich; and the Director of Royal Ordnance Factories, Explosives.Usage
RDX was widely used during World War II, often in explosive mixtures with TNT such as Torpex, Composition B, Cyclotols, and H6. RDX was used in one of the first plastic explosives. The bouncing bomb depth charges used in the "Dambusters Raid" each contained of Torpex; The Tallboy and Grand Slam bombs designed by Barnes Wallis also used Torpex.RDX is believed to have been used in many bomb plots, including terrorist 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 and composition A-5.
- Composition B: Castable mixtures of 59.5% RDX and 39.4% TNT with 1% wax as desensitizer.
- Composition C: The original composition C was used in World War II, but there have been subsequent variations including C-2, C-3, and C-4. C-4 consists of RDX ; a plasticizer, dioctyl sebacate ; and a binder, which is usually polyisobutylene ; and a specially manufactured mineral oil.
- Composition CH-6: 97.5% RDX, 1.5% calcium stearate, 0.5% polyisobutylene, and 0.5% graphite
- DBX : 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 for Torpex employing only half the amount of then-scarce RDX, as the supply of RDX became more adequate, however, the mixture was shelved
- Cyclotol: Castable mixture of RDX with TNT designated by the amount of RDX/TNT, such as Cyclotol 70/30
- HBX: Castable mixtures of RDX, TNT, powdered aluminium, and D-2 wax with calcium chloride
- H-6: Castable mixture of RDX, TNT, powdered aluminum, and paraffin wax
- PBX: RDX is also used as a major component of many polymer-bonded explosives ; RDX-based PBXs typically consist of RDX and at least thirteen different polymer/co-polymer binders. 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.
- Semtex : Plastic demolition explosive containing RDX and PETN as major energetic components
- Torpex: 42% RDX, 40% TNT, and 18% powdered aluminium; the mixture was designed during World War II and used mainly in underwater ordnance
Synthesis
RDX is classified by chemists as a hexahydro-1,3,5-triazine derivative. In laboratory settings it is obtained by treating hexamine with white fuming nitric acid.This nitrolysis reaction also produces methylene dinitrate, ammonium nitrate, and water as by-products. The overall reaction is:
The conventional cheap nitration agent, called "mixed acid", cannot be used for RDX synthesis because concentrated sulfuric acid conventionally used to stimulate the nitronium ion formation decomposes hexamine into formaldehyde and ammonia.
Modern syntheses employ hexahydro triacyl triazine as it avoids formation of HMX.
History
RDX was used by both sides in World War II. The US produced about per month during WWII and Germany about per month. RDX had the major advantages of possessing greater explosive force than TNT and required no additional raw materials for its manufacture. Thus, it was also extensively used in World War IGermany
RDX was reported in 1898 by Georg Friedrich Henning, who obtained a German patent for its manufacture by nitrolysis of hexamine with concentrated nitric acid. In this patent, only the medical properties of RDX were mentioned.During WWI, Heinrich Brunswig at the private military-industrial laboratory in Neubabelsberg studied the compound more closely and in June 1916 filed two patent applications, one for its use in smokeless propellants and another for its use as an explosive, noting its excellent characteristics. The German military hadn't considered its adoption during the war due to the expense of production but started investigating its use in 1920, referring to it as hexogen.
Research and development findings were not published further until Edmund von Herz, described as an Austrian and later a German citizen, rediscovered the explosive properties of RDX and applied for an Austrian patent in 1919, obtaining a British one in 1921 and an American one in 1922. All patents described the synthesis of the compound by nitrating hexamethylenetetramine. 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. The US patent claim was for the use of a hollow explosive device containing RDX and a detonator cap containing it. Herz was also the first to identify the cyclic nature of the molecule.
In the 1930s, Germany developed improved production methods.
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 used sulfamic acid, formaldehyde, and nitric acid. SH-Salz was from Schnurr, who developed a batch-process in 1937–38 based on nitrolysis of hexamine. The K-method, from Knöffler, involved addition of ammonium nitrate to the hexamine/nitric acid process. The E-method, developed by Ebele, proved to be identical to the Ross and Schiessler process described below. The KA-method, also developed by Knöffler, turned out to be identical to the Bachmann process described below.
The explosive shells fired by the MK 108 cannon and the warhead of the R4M rocket, both used in Luftwaffe fighter aircraft as offensive armament, both used hexogen as their explosive base.
UK
In the United Kingdom, 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 the RGPF Waltham Abbey just outside London in 1939. In 1939 a twin-unit industrial-scale plant was designed to be installed at a new site, ROF Bridgwater, away from London and production of RDX started at Bridgwater on one unit in August 1941. 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. The rest of the ammonia was reacted with formaldehyde to produce hexamine. The hexamine plant was supplied by Imperial Chemical Industries. It incorporated some features based on data obtained from the United States. RDX was produced by continually adding hexamine and concentrated nitric acid to a cooled mixture of hexamine and nitric acid in the nitrator. The RDX was purified and processed for its intended use; recovery and reuse of some methanol and nitric acid also was carried out. The hexamine-nitration and RDX purification plants were duplicated to provide some insurance against loss of production due to fire, explosion, or air attack.The United Kingdom and British Empire were fighting without allies against Nazi Germany until the middle of 1941 and had to be self-sufficient. At that time, the UK had the capacity to produce of RDX per week; both Canada, an allied country and self-governing dominion within the British Empire, and the US were looked upon to supply ammunition and explosives, including RDX. By 1942, the Royal Air Force's annual requirement was forecast to be of RDX, much of which came from North America.