About the blog: What Things Are Made Of


The United States relies on imports for dozens of commodities in everyday use. Often enough, that reliance is 100%. In this book I aim to provide awareness of the hidden geology and mineralogy behind common things, and to develop an appreciation for the global resource distribution that underpins our society. While concerns about oil import reliance are in the news every day, our needs for other minerals are comparable and are typically unknown even to technologically aware Americans.

Wednesday, December 4, 2013

Transparent Aluminum

By Richard I. Gibson

Do you recall the walls that encased the humpback whales transported forward in time by the U.S.S. Enterprise in Star Trek IV, thereby saving humanity? Scotty was challenged to come up with transparent aluminum to make that gigantic aquarium.

Welcome to the future.

Sapphire glass, second to diamond in hardness, and shatter- and scratch resistant, is in use in some smartphone camera lenses, some LED lights, high-end watch covers and some store barcode scanners. It’s in the screen of one pricey ($3,000) smartphone touchscreen made by Vertu. This material made the news lately when speculations arose that Apple’s iPhone 6 would carry a sapphire glass screen, but although Apple reportedly is building an Arizona alumina processing facility, recent news reports suggest the material may be to expensive for screens.

Sapphire glass is not glass, because glass is amorphous and this material is crystalline. It’s made by processing aluminum oxide (alumina) under high heat and pressure with a specific optical orientation, and the result is essentially high-purity corundum, Al2O3, which is called sapphire when blue (and clear and many other shades) and ruby when red. Corning® Glass makes Gorilla® Glass, the component in more than a billion smartphone screens, but they do not see sapphire glass as competition because of the high cost. They estimate that it takes 100 times the energy to make sapphire glass as their Gorilla Glass and at least ten times the total dollar cost.

Sapphire glass is not made from natural gem sapphires, but is created synthetically using high-purity alumina. The alumina has to come from somewhere, of course, and it is mined. Although aluminum is one of the most common elements in the earth’s crust, minerals and rocks that contain it in a form that allows its efficient extraction are unusual. Virtually all alumina is produced by processing the aluminous rock bauxite, and China leads the world in alumina production; China and Australia together make 58% of the world’s alumina. The United States is 100% dependent on imports of alumina, mostly from Australia, 34%; Suriname, 22%; Brazil, 17%; and Jamaica, 14%.

References: USGS Mineral Commodity Summaries; Minerals Yearbook; linked news reports. Smartphone photo public domain via Wikipedia.

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