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.

Madagascar

Tourmaline from Madagascar

It’s been a while since I posted. Trip to Kansas, and my dog died, and June-July are absolutely the busiest time for tourism in Butte (I drive the Chamber of Commerce Trolley and lead historic walking tours in one of my other lives).

This post is for another country: Madagascar. Government edicts and other problems can dramatically impact mineral production and trade, and the coup in Madagascar in 2009, combined with the worldwide recession, certainly did not help the mineral industry there. Madagascar had been the world’s leading sapphire producer – but in 2008, the government banned export of rough gemstones. Why would they do that? Because of one specimen, the Heaven’s Gift Emerald. A 536-kg (1,182-pound) emerald in matrix, it was declared a national treasure worth $150 million; the government said its exportation was illegal, although courts ruled otherwise, and the ban on all exports was instituted and continued until mid-2009. By 2010 the gem industry was recovering – led in volume by tourmaline at 43,000 kg produced in Madagascar (compare 2,100 kg of sapphires).

Madagascar produces nearly 3% of the world’s titanium mineral concentrates (mostly ilmenite) but that ranks it #11. Australia and South Africa are the leaders, and the primary import sources for the US, which is 81% dependent on imports. The titanium dioxide pigment industry in the US is valued at about $3 billion, about the 7th most valuable mineral commodity in the US. Titanium dioxide finds its way into products from white sidewall tires to playing cards to Oreo cookies.

Cobalt, nickel, and increasing chromite mining are expected to improve Madagascar’s role in global mineral supplies in the next few years. Vanadium, uranium, and zircon mining may also impact the industry on the island as those reserves begin to be developed.

Photo: Tourmaline from Madagascar, credit: Laurie Minor-Penland (Smithsonian Institution), under CC by 2.0 license.

Sapphires

I recently completed an article on Montana sapphires for Distinctly Montana Magazine, focused on beautiful gems from Yogo Gulch. But sapphires have practical uses too.

Because rubies (red) and sapphires (famously blue, but also pink, yellow, green, purple, and even colorless) are nothing more than corundum, aluminum oxide, with some interesting trace elements (mostly titanium and iron), they are very hard—number nine on the Mohs Hardness Scale, second only to diamond. Consequently they find their way into watch and clock bearings, and those that don’t make the cut as gems are sometimes used as high-quality abrasives.

The first lasers, in 1960, used synthetic rubies to focus light into a coherent beam. Solid-state integrated circuits sometimes use sapphires formed into small thin wafers as their insulating substrate. Larger sheets built from synthetic sapphire sometimes make tough windows in armored vehicles, as well as mundane surfaces such as grocery-store barcode scanners where scratch resistance is valued. High quality watches may have sapphire crystal faces in addition to gem-like bearings inside.

Even though Auguste Verneuil invented a process for making synthetic sapphires in 1902, natural sapphires were used for non-jewel applications for decades after that. Today about 250 tons of synthetic sapphires supply the world annually with watch bearings, abrasives, and specialty uses. The US and Russia manufacture most synthetic stones, while Madagascar is the leading gem sapphire producer.

Watch for the article on Montana’s Yogo sapphires in the Summer issue of Distinctly Montana.

Image: The 182-carat Star of Bombay star sapphire, via Wikipedia.