In the 24th century, the windows of starships are made with transparent aluminum. (CBS via Getty Images)
In Star Trek IV: The Voyage Home, the crew of the USS Enterprise travels back in time to find a humpback whale and transport this back to the 24th Century. In the absence of the 23rd Century technology that the crew were used to working with, the tank needed to be made of six-inch thick poly(methyl methactylate), PMMA –or Plexiglas as it is more commonly known - in order to withstand the pressure of the 18,000 cubic feet of water required to comfortably transport such a creature.
In an attempt to acquire the Plexiglas required for free, Scotty and Bones trade the chemical composition of a material that could rival Plexiglas; the very same material used to make the windows of the USS Enterprise. Tougher than bulletproof glass, but made not of glass or polymers, this material was known as Transparent Aluminium. We frequently encounter aluminium in our everyday lives, from our crushable fizzy drinks cans to the foldable wrapping for our sandwiches. However, this is aluminium in its elemental, metallic form. As science fiction increasingly becomes science fact, is there is a way of making aluminium both optically transparent and tough in the 21st Century? Yes, there is!
The answer lies in compounds of aluminium. Aluminium oxide, Al2O3, can be found in nature in the form of Corundum, the crystalline phase of Al2O3 that exist as rubies and sapphires, depending on the colour given to the crystal by trace elemental impurities. These gemstones are tough and also transparent, but not colourless, which would admittedly give a rather rose-tinted view of the universe from inside the USS Enterprise, but would limit the uses of this so called Transparent Aluminium. Compounds are however a good starting point in the search for this futuristic material.
Spinel that's been formed into a dome shape. (Credit: U.S. Naval Laboratory)
Recently, two separate methods of making Transparent Aluminium that possesses both transparency and toughness have been announced. The first has been developed by the US Naval Laboratory, and is an aluminium compound that also contains magnesium. The magnesium aluminate, known as Spinel, is produced by pressing a nanopowder of the mineral at high pressure in a mould, and then heating the resultant product at high temperature, before polishing the product to remove the cloudy finish. The material can form any shape, simply by creating the appropriately sized mold.
ALON transparent aluminum in various sizes. (Credit: Surmet)
The second method creates a material that closely resembles the Transparent Aluminium ofStar Trek. Called aluminium oxynitride, it has a similar crystal structure to that of the magnesium aluminate. And you don't have to wait 200 years to get it, as it is now commercially available and sold under the trade name ALON in reference to the elements contained in the ceramic compound. ALON is 15% harder than magnesium aluminate and, combined with the high transparency of this material and relatively low density compared to traditional armour glass, could find uses in smartphone screens, bulletproof glass and aircraft cladding.
Proof once again that science fiction provides us with inspirational ideas that science can turn into a reality – and thankfully before the 24th Century!