Contract for DU Replacement by Liquidmetal Extended last May 2006
'Safe' Alternative to Depleted Uranium Revealed
DAVID HAMBLING / New Scientist
Controversial anti-tank shells tipped with depleted uranium may be phased out if an alternative material proves its worth.
The US Army is expected to award a contract this week for the manufacture of prototype ammunition incorporating a "liquid metal" alloy. The new rounds could be in service within two years.
Campaigners have complained for years about the potential health effects of DU—it has been linked to everything from Gulf War syndrome to birth defects. But the health connection is disputed and the military defends its use of DU.
All the same, the US Army's Tank-automotive and Armaments Command is looking for alternatives in case political pressures force it to abandon DU.
DU has been the material of choice for anti-tank ammunition since the 1970s because it has twice the density of lead. And it has two key advantages over pure tungsten, which has a similar density.
Tungsten shells flatten on impact, forming a mushroom shape. But DU rounds self-sharpen as they deform because material breaks away in a way that preserves the shell's shape, a phenomenon known as "adiabatic shear banding". DU rounds are also pyrophoric—the fragments ignite in air, torching the interior of the target vehicle.
Now Liquidmetal Technologies, an R&D company based in Tampa, Florida, says it can get comparable performance from penetrators made of an exotic alloy of tungsten.
Normally, solid metals are a lattice of tiny crystals. The size of the crystals affects the properties of the material, which tends to fracture along the boundaries between them. Instead of such a metal, the company wants to use an amorphous alloy that has a random arrangement of atoms, as in a glass or liquid.
Amorphous tungsten alloy has many of the properties that make DU such an effective penetrator: it is self-sharpening and it should also be pyrophoric, says Steve Collier, former president of Liquidmetal's defense arm.
The new contract is for a test batch of 30-millimetre ammunition of the type used by American A-10 "tank buster" aircraft, which fired some 75 tonnes of DU during the recent Iraq conflict.
While many will welcome an alternative to DU, questions remain over the safety of tungsten. Fragments of tungsten embedded in flesh have been shown to cause tumours by Alexandra Miller and her colleagues at the Armed Forces Radiobiology Research Institute in Bethesda, Maryland. However, the toxicity of tungsten when inhaled is believed to be much lower than that of uranium or lead.
"Clearly, tungsten is not radioactive like DU, so there is no hazard from radioactivity," says Peter Collins, director of the Royal Society's Science Policy Group. But most casualties will be caused in battle, he says: "The most obvious health hazard from any of these things is being hit by one."