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.

Peanut Butter Jar--the inner seal

By Richard I. Gibson

This simple little thing should be familiar to most Americans. It’s an inner safety seal from a jar of peanut butter. Many packages have them nowadays, in our society that seeks to ensure absolute safety in all aspects of food. Such hermetic barriers do help prevent contamination, extend product life, and provide a tamper-evident seal.

What’s it made of?

You’d probably say aluminum foil, and you’d be right—partly. It’s a sheet of pulp paper to which is bonded three more layers adding up to about 3.5 mils (a mil is one one-thousandth of an inch) in thickness. Only about 1 mil is aluminum. Another half-mil is a polyester that gives the sheet rigidity and flexibility. The rest, 2 mils out of 3.5, is usually a resin like DuPont’s patented and trademarked Surlyn™.

Surlyn is an ethylene copolymer, more or less ethylene vinyl acetate. Such resins make for a clean and easy peel when removing the seal, and they are also added to plastic wrap to enhance clinginess. Ethylene vinyl acetate combines ethylene and vinyl acetate. No surprises there.

Ethylene is a gas, C2H4, produced from natural gas and crude oil in the petrochemical cracking process in a refinery. It’s the largest volume organic chemical produced in the world today. Vinyl acetate comes from the chemical reaction between ethylene and acetic acid, a reaction enhanced by the presence of palladium as a catalyst. Acetic acid, essentially vinegar, was produced historically by distillation of various wood products, but today its chemosynthesis is by combining methanol (wood alcohol, CH3OH) with carbon monoxide. That’s another reaction that demands catalysts, this time including some pretty unusual metals, such as ruthenium, osmium, and iridium.

All this stuff obviously comes from somewhere. The next time you tear the seal off a new jar of peanut butter, think of it this way: you’re discarding a bit of paper, probably from pulp mills in the U.S., and some aluminum, ultimately from ores imported into the U.S. from Jamaica, Guinea, and Brazil. Processing aluminum ore (bauxite) to yield the pure metal demands a long list of chemicals, as well as a lot of electricity—which in the US is generated primarily by burning coal and natural gas.

The hydrocarbons that became the polyester and ethylene and methanol came from a long list of nations before reaching a U.S. refinery or petrochemical plant—if the stuff had “country of origin” labels, you’d have to include 86 nations that supply the U.S. with raw hydrocarbons.

Those metal catalysts are not trivial, but make the chemical reactions possible and economically feasible. While the U.S. does produce some palladium (from the Stillwater mine in Montana), more than half the palladium the U.S. consumes is imported, mostly from Russia and South Africa. Most of the iridium and ruthenium produced worldwide is mined in South Africa.  

Yes, we have no aluminum (ore)

A friend questioned the quiz answer indicating that the U.S. is 100% dependent on imports for bauxite (photo, right), the only ore of aluminum. He knew that lots of minerals contain aluminum—it’s the third most abundant element in the earth’s crust, after oxygen and silicon. And the rock-forming minerals that contain aluminum are common, ranging from feldspars in granite to clays in fine-grained shale.

So why can’t the U.S. use those aluminum sources, rather than relying 100% on bauxite imports from Jamaica, Guinea, Brazil, Guyana, China, Sierra Leone, and Greece? The simple answer: It’s far too energy-demanding to get the aluminum out of any rock other than bauxite.

Despite aluminum’s abundance, aluminum metal was not isolated until 1825, by Danish chemist Hans Christian Oersted—the discoverer of the close relationship between electricity and magnetic fields. It was an electric current that allowed Oersted to produce impure metallic aluminum, but aluminum remained a rare and expensive curiosity for 60 years.

Charles Hall, a student at Oberlin College (Ohio) devised the first relatively cheap electrolytic aluminum manufacturing process in 1886—and the Aluminum Company of America treasured as “crown jewels” the small metal buttons Hall made.

Aluminum is bound tightly, usually with silicon, in common minerals. Only a few minerals lend themselves to the electrical disruption needed to free aluminum metal from the crystal lattices. Three aluminum hydroxide minerals, gibbsite, boehmite, and diaspore, are in that category, and they are the primary components of the rock bauxite. Bauxite forms by intense chemical weathering of aluminous minerals like feldspar in granite—in fact, Mother Nature does most of the work of producing aluminum, rearranging aluminum atoms to make bauxite’s hydroxides. Metallurgists seeking pure aluminum can process bauxite cheaply, while the aluminum in more common compounds like feldspar and clay is impossible to remove commercially.

In the United States, the only significant bauxite formed 90 million years ago in what is now Arkansas. Those deposits served as important ore sources from 1899 until competition from cheaper foreign markets and recycling ended production in 1990. The U.S. has no primary bauxite production today.

No bauxite doesn’t mean we don’t produce a lot of aluminum. With 30% recycling, together with processed imports, the United States in 2008 was a net aluminum exporter—a dramatic change from 2005 when metallic aluminum was imported (more than 40% of domestic consumption) along with 100% imported bauxite. U.S. aluminum smelters employ 55,000 workers in an industry whose metal production earns $7.9 billion each year.

As Jules Verne wrote, “Aluminum was once a precious metal.” Precious enough to cap the pyramid atop the Washington Monument in 1884, when aluminum’s price was $1 per ounce, the same as silver—at a time when a dollar bought nearly 500 pounds of coal, 150 bricks, or 15 pounds of flour.

Adapted and expanded from What Things Are Made Of, Chapter 4: You Are What You Eat. Bauxite image above from USGS via Wikipedia.