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HMX and RDX

Dateline: 02/08/99

By Alan Bruzel

Rocket fuels and explosives used in industrial, aerospace, and military applications all share common characteristics. They are reasonably stable (that is, they do not detonate during normal handling), but will explode violently with a high detonation velocity and pressure when initiated by a more sensitive, primary explosive such as lead azide or mercury fulminate.

RDX is a popular explosive used in oil exploration, rocket propellants, and armaments. (Its acronym has been variously ascribed to Research Department eXplosive, Royal Demolition eXplosive, or Royal Dutch eXplosive.) Its chemical name is cyclotrimethylenetrinitramine and it is synthesized by the nitration of hexamethylenetetramine (HA).

Interestingly, until the advent of sulfa drugs and other therapies, HA was used orally to treat urinary infections – in urine, it hydrolyzes into formaldehyde. World War II rapidly brought HA out of the clinic and into the munitions factory. Why? Because its nitration product, RDX, has more explosive power than TNT.

A side reaction of HA nitration yields cyclotetramethylenetetranitramine, abbreviated HMX (from High Melting eXplosive, Her Majesty's eXplosive, or His Majesty's eXplosive). HMX has one of the fastest detonation velocities known: 9,110 meters per second (20,380 miles per hour).

Powerful explosive forces such as these are effective in penetrating steel and concrete. Add to this the plasticity of RDX and HMX (within proper limits, they can be heated without exploding and cast into a variety of shapes), and one comprehends their potential uses. Military dynamite is 75% RDX, 15% TNT, and 10% plasticizers and desensitizers. The plastic explosive Composition C4 (known simply as C4, and the stock-in-trade of terrorists) is 91% RDX and 9% plasticizer. Exploding HMX provides the detonation waves that compress an atom bomb's uranium-235, thereby initiating the vast energies of nuclear fission. (Iraq has imported hundreds of tons of HMX.)

An inescapable truth is that military preparedness always requires newer and better explosives. In 1987, Arnold Nielson working at the US Naval Air Warfare Center Weapons Division at China Lake synthesized hexanitrohexaazaisowurtzitane (designated as CL-20). Like HMX and RDX, CL-20 is a cyclic nitramine stable to handling and amenable to casting into shaped charges, but is up to 20% more powerful than HMX. In a test using shaped charges (30 grams each) of CL-20 and PBXN-5 (the explosive used in armor-piercing 30mm ammunition fired by the M230 chain gun on the AH-64 Apache helicopter), the CL-20 was able to penetrate seven one-inch steel plates compared to PBXN-5's five plate penetration.

Recommended Web resources for additional information:

Advanced CL-20 Based Propellant Formulated by China Lake Team
From the China Lake site of the US Naval Air Warfare Center Weapons Division.

Cage Structure of CL-20
Molecular representation of CL-20. From R. J. Doyle Jr., Chemistry Division, US Naval Research Laboratory.

Elements of Fission Weapon Design
Use of HMX in the shock compression of uranium. From Engineering and Design of Nuclear Weapons, by Carey Sublette.

Hexanitrohexaazaisowurtzitane
Excerpt from The Rocketeer, published by the US Naval Air Warfare Center Weapons Division, China Lake.

HMX
Fact sheet from Agency for Toxic Substances and Disease Registry, US Department of Health and Human Services.

International Traffic in Arms Regulations
Includes the Military Explosives Section from the United States Munitions List.

Iraq's Shop-Till-You-Drop Nuclear Program
Article by David Albright and Mark Hibbs in the April 1992, Bulletin of the Atomic Scientists.

RDX
Fact sheet from Agency for Toxic Substances and Disease Registry, US Department of Health and Human Services.

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