How Gorilla Glass Works

A piece of Corning's Gorilla Glass undergoes a flexibility test in the lab.
Courtesy Corning Incorporated

You might say we're in the early days of the gadget age. A couple of decades ago, personal computers weren't portable and cell phones were rare luxuries. Today, a quick glance at the electronics store tells you all you need to know. Gadgets are our playthings and our playthings are portable.

But electronics have improved in other ways, too. Processor speeds have risen dramatically, following Moore's Law. Screen resolution is sharper and more vibrant than ever. And some companies spend almost as much time on aesthetics as they do engineering. But there's one improvement that you can't really see: Glass is getting stronger.


The manufacturing company Corning has developed a product it calls Gorilla Glass. The company designed the glass for our electronic lifestyles. As we carry around computers, tablets, smartphones, MP3 players and other devices, we risk damaging them through everyday use. Corning's Gorilla Glass stands up to abuse with scratch- and impact-resistant qualities. And Corning's approach allows the glass to be incredibly thin, meaning it won't interfere with capacitance touch screens or add significant weight to a device.

What's Corning's secret? What's so special about Gorilla Glass that sets it apart from other kinds of glass? The answer involves incredible temperatures, a special trough, robots and a molten salt bath. The finished product is a thin piece of glass that can withstand a lot of punishment.


The Fusion Draw

A dip in a special salt bath is what gives Gorilla Glass its damage-resistant properties.
Courtesy Corning Incorporated

While you might think of glass in its manufactured form, the truth is it's a material we find in nature. Certain rocks and minerals become glass after coming into contact with high temperatures. This occurs naturally along lava flows and places where lightning has hit the ground.

Humans have been creating glass for millennia. Furnaces capable of generating incredible heat melt the right type of rocks down into what we call a glass melt. At this stage, you can shape the glass in many ways, including using a tube to push air into the mass. We call this technique glass blowing.


Commercial glass tends to come from three main sources. The first is sand, which we refer to chemically as silicon dioxide. That's the type of material Corning uses in its manufacturing process. The other two types of materials in commercial glass include limestone and sodium carbonate.

Corning takes the silicon dioxide (SiO2) and combines it with other chemicals before melting it down into a glass melt. The resulting glass is aluminosilicate -- that means the glass contains aluminum, silicon and oxygen. The glass also contains sodium (Na) ions, which become important in the next phase of manufacturing.

Corning pours the molten glass into a V-shaped trough but doesn't stop at filling the trough to the top. The company continues to add molten glass until the glass begins to overflow the sides of the trough. Automated robotic arms draw the sheets of glass from the edge of the trough. Each sheet is just over half a millimeter thick.

If you were to use this glass for a screen on your electronic devices, you'd end up with a very clear covering. But it's not damage-resistant like Gorilla Glass -- it's just aluminosilicate glass. To give Gorilla Glass its ability to withstand scratches and cracks, Corning gives these sheets of glass a little bath.


The Ion Exchange

You can find Gorilla Glass in many products, including Samsung's Galaxy Tab device.
Coiurtesy Corning Incorporated

The real secret behind Gorilla Glass involves a chemical process called an ion exchange. An ion is an atom that has either gained or lost an electron and so carries a net charge. Electrons are negatively-charged sub-atomic particles. An ion's net charge is negative if it has an extra electron or positive if it lost an electron. Elements in their atomic form have a neutral charge because the number of electrons matches the number of protons, which are positively charged.

So what do ions have to do with glass? The aluminosilicate glass from the first phase of the manufacturing process contains sodium ions. Corning dips these sheets of glass into a bath of potassium ions. If you look at the periodic table of elements, you'll see that sodium is just above potassium. Dmitri Mendeleev, the man responsible for creating the periodic table, arranged elements by atomic weight and grouped elements possessing similar qualities together. Both sodium and potassium belong to a group known as active metals. These are metals that react strongly with other substances.


Sodium is higher on the periodic table than potassium, which means an atom of sodium is smaller than an atom of potassium. You might think that at the atomic scale size doesn't matter but it turns out that's not the case! If you could take the sodium ions out of the aluminosilicate glass and replace them with larger potassium ions, the sheet of glass would experience compression.

Imagine you have a net. The line in the net is flexible but taut -- there's not a lot of give. In each hole of the net there's a golf ball held into place. Now imagine that you replace all the golf balls with baseballs. That's similar to what's happening on an atomic level with an ion exchange.

So how does it work? To replace sodium with potassium, you first must break the ionic bond sodium has with the glass. That's why the potassium salt bath is so hot -- Corning says the bath reaches a temperature of 400 degrees Celsius (752 degrees Fahrenheit). At this temperature, the energy (heat) breaks down sodium's ionic bond to the aluminosilicate. But one of the qualities lower active metals have is that they can maintain an ionic bond at higher temperatures than the lighter active metals. Potassium weighs more than sodium -- that 400 degrees Celsius (752 degrees Fahrenheit) isn't enough to keep potassium ions and the aluminosilicate apart.

After a nice hot dip in the potassium bath, the aluminosilicate emerges compressed by potassium ions. The compression creates a protective layer on the glass and gives it strength that normal glass doesn't have. And the environmentally conscious can rest easy -- Gorilla Glass is recyclable.


Gorillas in the Glass

The ion exchange process isn't new and Corning's Gorilla Glass isn't the only chemically strengthened glass on the market. But Corning has demonstrated the strength of its glass in venues like the Consumer Electronics Show where the company invited people to test come up and see how much pressure it would take to break a piece of its glass. Untreated glass would break relatively easily. Standard chemically strengthened glass would put up more resistance but would also break given enough pressure. Gorilla Glass was much more resistant to damage.

How does Gorilla Glass get into products? Corning partners with manufacturers and provides Gorilla Glass as part of the product's manufacturing process. The average consumer can't go out and buy a sheet of Gorilla Glass to fit on top of an existing device. In that sense, Corning is an original equipment manufacturer (OEM). The finished product will contain Corning's glass but the finished product will have another company's brand on it.


Corning isn't allowed to reveal all the products that use its Gorilla Glass. But among the products the company has announced are the Sony BRAVIA line of television sets, the Samsung Galaxy Tab tablet device and the Dell Streak. While smartphone manufacturers may look into Gorilla Glass to help their products resist the wear and tear that comes with moving a portable device around, television manufacturers are considering it to make their products more durable.

Because Corning's fusion draw process creates thin sheets of glass that don't inhibit applications like capacitance touch screens, you may see a lot more smartphones and tablets that include Gorilla Glass in their construction. Corning's manufacturing process and the explosion in popularity of portable devices may be timed just right to propel the company to success.

For more transparency on touch-screen displays and other related topics, look on the next page.


Lots More Information

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More Great Links

  • Calvez, L., et al. "Strengthening of chalco-halide glasses by ion exchange." Journal of Non-oxide and Photonic Glasses. Vol. 1, No 1, 2009, pp. 30-37.
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  • Hogan, Patrick M. "Method of glass strengthening by ion exchange." U.S. Patent 4,218,230. Aug. 19, 1980. (Feb. 8, 2011)
  • Kiwi Web. "Dmitri Mendeleev." 2008. (Feb. 10, 2011)
  • Sadoway, Donald. "3.091 Introduction to Solid State Chemistry." MIT OpenCourseWare. Fall 2004. (Feb. 10, 2011)
  • Ulanoff, Lance. "Why is Gorilla Glass So Strong?" PCMag. Jan. 12, 2011. (Feb. 9, 2011),2817,2375657,00.asp
  • University of Illinois at Urbana-Champaign. "Q&A: Ask the Van - Active Metals." Department of Physics. July 13, 2006. (Feb 11, 2011)
  • Wierzchowski, Scott. "Chemistry of Ion Exchanges." Rensselaer. November 1995. (Feb 10, 2011)