RDX

What is RDX?

RDX, an initialism for Research Department Explosive, is an explosive nitroamine widely used in military and industrial applications. It is also known less commonly as cyclonite, hexogen (particularly in German and German-influenced languages), and T4. Its chemical name is cyclotrimethylenetrinitramine; variants include cyclotrimethylene-trinitramine and cyclotrimethylene trinitramine.
In its pure, synthesized state RDX is a white, crystalline solid. As an explosive, it is usually used in mixtures with other explosives and plasticizers, phlegmatizers or desensitizers. It is stable in storage and is considered one of the most powerful and brisant of the military high explosives.

Name

RDX is also known, but less commonly, as cyclonite, hexogen (particularly in German and German-influenced languages), T4 and chemically as cyclotrimethylenetrinitramine. Tenney L Davis, writing in the USA in 1943, stated it was generally known in the USA as cyclonite; the Germans called it Hexogen, the Italians T4. In the 1930s, the Royal Arsenal, Woolwich, started investigating cyclonite as an explosive to use against German U-boats that were being built with thicker hulls. Britain wanted an explosive that was more powerful than TNT. For security reasons, Britain termed cyclonite as "Research Department Explosive" (R. D. X.). The term RDX appeared in the United States in 1946, but the name RDX is given without explanation. The first public reference in the United Kingdom to the name RDX, or R.D.X. to use the official title, 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; again, it was referred to as simply RDX.

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. RDX is believed to have been used in many bomb plots including terrorist plots. The bombs used in the "Dambusters Raid" contained 6,600 pounds of Torpex.
RDX forms the base for a number of common military explosives:

• Composition A: Granular explosive consisting of RDX and plasticizing wax. Such as, composition A-5 (RDX coated with 1.5% stearic acid) and composition A-3 (91% RDX coated with 9% wax)
• Composition B: Castable mixtures of RDX and TNT
• 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 (91%), a plasticizer (which can be dioctyl adipate {DOA}, diethylhexyl, or dioctyl sebacate) (5.3%), a binder, which is usually polyisobutylene (2.1%), SAE 10 non-detergent motor oil (1.6%).
• Composition CH-6: 97.5% RDX, 1.5% calcium stearate, 0.5% polyisobutylene, and 0.5% graphite.
• Composition D:
• Cyclotol:
• 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
• Semtex: (Trade name): Plastic demolition explosives containing RDX and PETN as major energetic components
• Torpex: 42% RDX, 40% TNT and 18% powdered aluminium
• PBX: RDX is also used as a major component of many polymer-bonded explosives (PBX). RDX-based PBX's typically consist of RDX and a polymer/co-polymer binder. 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.
Outside of military applications, RDX is also used in controlled demolition to raze structures. The demolition of the Jamestown Bridge in the U.S. state of Rhode Island is one example where RDX shaped charges were used to remove the span.

Properties

The velocity of detonation of RDX at a density of 1.76 g/cm³ is 8750 m/s.
It is a colourless solid, of maximum theoretical density 1.82 g/cm³. It is obtained by reacting concentrated nitric acid with hexamine.

(CH2)6N4 + 10HNO3 → (CH2-N-NO2)3 + 3CH2(ONO2)2 + NH4NO3 + 3H2O

It is a heterocycle and has the molecular shape of a ring. It starts to decompose at about 170 °C and melts at 204 °C. Its structural formula is: hexahydro-1,3,5-trinitro-1,3,5-triazine or (CH2-N-NO2)3.

At room temperature, it is very stable. It burns rather than explodes and detonates only with a detonator, being unaffected even by small arms fire. It is less sensitive than pentaerythritol tetranitrate (PETN). However, it is very sensitive when crystallized, below −4 °C. Under normal conditions, RDX has a figure of insensitivity of exactly 80 (RDX defines the reference point.).

RDX sublimes in vacuum, which limits its use in pyrotechnic fasteners for spacecraft.
RDX when exploded in air has about 1.5 times the explosive power of TNT per unit weight and about 2.0 times per unit volume.

History

RDX was used by both sides in World War II. The U.S. produced about 15,000 long tons (15,000 t) per month during WW II and Germany about 7,000 long tons (7,100 t) per month. RDX had the major advantages of possessing greater explosive power than TNT used in the First World War, and requiring no additional raw materials for its manufacture.

Germany

The discovery of RDX dates from 1898 when Georg Friedrich Henning obtained a German patent (patent No. 104280) for its manufacture, by nitrating hexamine nitrate (hexamethylenetetramine nitrate) with concentrated nitric acid.

UK

In the United 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 the RGPF Waltham Abbey just outside London in 1939.

Canada

A different method of production to the Woolwich process, was found and used in Canada, possibly at the McGill University Department of Chemistry. This was based on reacting paraformaldehyde and ammonium nitrate in acetic anhydride.

UK, U.S. and Canadian production and development

At the beginning of the 1940s, the major U.S. explosive manufacturers, E. I. du Pont de Nemours & Company and Hercules had several decades of experience of manufacturing Trinitrotoluene (TNT) and had no wish to experiment with new explosives; a view also held by the U.S. Army Ordnance, who proposed to continue using TNT.

Bachmann process

The NDRC tasked three companies to develop pilot plants. They were the Western Cartridge Company, E. I. du Pont de Nemours & Company and Tennessee Eastman Company, part of Eastman Kodak.

Military compositions

The United Kingdom's intention in World War II was to use "desensitised" RDX: in the original Woolwich process RDX coated with beeswax, but changed to a RDX coated with petroleum-based product, based on the work carried out at Bruceton.

Terrorism

Ahmed Ressam, the al-Qaeda Millenium Bomber, used a small quantity of RDX as one of the components in the explosives that he prepared to bomb Los Angeles International Airport on New Year's Eve 1999/2000; the combined explosives could have produced a blast forty times greater than that of a devastating car bomb.