Tuesday, September 20, 2011

Gorilla Glass - Smash it if you can

There’s a battle going on about who’s the toughest of them all. Is it the Gorilla or the Dragon?

In case there is any misunderstanding, we’re talking about the glass used in smartphones. It’s not enough that a phone display has to be the brightest, the clearest and the biggest nowadays. It must also be the toughest to withstand accidental scratches to the display.

Gorilla Glass vs Dragontrail

The company currently dominating this category of toughness is Corning, who makes Gorilla Glass. Phones from Samsung, HTC, Motorola and of course, Apple, all use this toughened material for their phones’ screen.

But now there’s a new animal in the picture. The new glass is called Dragontrail and it is manufactured by Asahi Glass Co. of Japan. Just like the Gorilla Glass, the Dragontrail is also very tough, scratch-proof and smooth.

The manufacturer claimed that their chemically-strengthened aluminium silicate glass is six times stronger than conventional glass, stronger than window soda-lime glass and has pristine finish, Besides being scratch proof, a millimetre-thin sample can take the weight of 60 kilos before breaking.

Gorilla Glass rules the jungle for the time being, as the Dragontrail currently has only 25% for cover glasses. However, Asahi Glass Co is expecting this to increase to 30% by 2012. With the expanding market for smartphones set to increase at an exponential rate, the winner of this battle stands to reap great rewards from a strong market share.

Why is Gorilla Glass so strong?

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 then dips these sheets of glass into a bath of potassium ions. 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 that 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 and as such, 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.

[Source: Howstuffsworks.com]

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