In a remarkable case of science fiction becoming science fact, it seems scientists have been able to invent transparent aluminium.
The fantastically strong material was mentioned in Star Trek IV: The Voyage Home by Enterprise engineer Mr Scott.
With the crew of the Enterprise stuck in the 20th century, Scotty barters his knowledge of 24th century technology with an engineer in exchange for having a tank built.
It appears that now that the future has arrived. Sort of.
While scientists have not figured out a way of making metallic aluminium transparent, they have developed a transparent aluminium-based ceramic that is almost as strong.
The material, aluminium oxynitride, known as AION, is four times harder than fused silica glass, 85 per cent as hard as sapphire and stable up to a temperature of 1,200C.
At 1.6in thick it is strong enough to stop .50 calibre bullets which can easily penetrate more than twice that thickness of conventional laminated glass armour.
And, of course, you can see through it, making it sound incredibly similar to the stuff peddled by the Enterprise engineer.
Research into aluminium oxynitride powder has being going on since at least 1981, making it possible that the 1986 movie’s writers took their idea for transparent aluminium at least partly from early publicity about AION.
But these days the stuff can actually be mass produced. To make the material, aluminium oxynitride powder is packed into a rubber mould in the rough shape of the part wanted.
In a tank of hydraulic fluid, the mould is compressed to 15,000psi – a procedure known as isostatic pressing – until the powder is mashed into a grainy ‘green body’.
This grainy structure is then fused by heating at 2,000C for several days. The fused substance is cloudy, but can be given an optically clear finish by mechanical polishing.
The resulting material is expensive, and so is generally only used for high-performance applications, especially in the military.
Surmet Corporation in Massachusetts manufactures it under the brand name ALON for use in armoured windows, lenses for battlefield optics, and ‘seeker domes’, the clear round windows covering the sensors on missiles.