ALON: Transparent Aluminum Armor

Bullet-resistant glass has some clear drawbacks, namely, that it doesn't bar all bullets and that piling on the protective but heavy material merely slows the vehicle in question. So what can save the lives of soldiers and civilians under fire?

Researchers think the answer may be transparent aluminum armor, a finely polished ceramic alloy that's both lighter and stronger than traditional bullet-resistant glass.

Known commercially as ALON, transparent aluminum armor is made of aluminum oxynitride, a combination of aluminum, oxygen and nitrogen. Before it can end up as a hard transparent armor plate, it begins as a powder. This powder is then molded, subjected to high heat and baked, just as any other ceramic is baked. Once baked, the powder liquefies and then quickly cools into a solid, which leaves the molecules loosely arranged, as if still in liquid form. The resulting rigid crystalline structure of the molecules provides a level of strength and scratch resistance that's comparable to rugged sapphire. Additional polishing strengthens the aluminum alloy and also makes it extremely clear.

Now, just as bullet-resistant glass is made of three layers (two panes of glass and a middle pane of polycarbonate), so too is transparent aluminum armor. The three layers, consist of the following:

An outer layer that's exposed to gunfire and made of baked aluminum oxynitride
A middle layer of glass
A rear layer of polymer backing

Not only can the aluminum armor deflect rounds from small-caliber weapons and still be more clearly transparent than bullet-resistant glass that's been shot, it also passes a much more important test -- it resists .50-caliber armor-piercing bullets and anti-aircraft weapons that typically use .30-caliber rounds. This is an impressive feat, especially since it's half the weight and thickness of traditional transparent armor.

Such a material could save lives and be incorporated in a wide range of vehicles -- everything from lightly armored trucks to low-flying planes, such as the C-130 Hercules or the A-10 Thunderbolt II that are vulnerable to ground fire.

Sounds great. So how come it's not being applied to armored vehicles and aircraft yet? Find out in the next section.

Star Trek Trivia

If you have to transport live humpback whales in a starship off the Earth, around the sun and several centuries through time, what kind of aquarium will do the trick? Why, one made of transparent aluminum, of course. But if you're a character in "Star Trek IV: The Voyage Home," and your spaceship is stuck in the 20th century, 6-inch (15-cm) thick Plexiglas will have to do. But how will you get enough Plexiglas to safely hold 18,000 cubic feet of water on very short notice? Well, you just trade the intergalactic recipe for transparent aluminum to the 20th-century Plexiglas-producing industrialist who would one day invent it [source: imdb].