Gorilla House: Smartphone Tech Will Lighten Your Greenhouse – Technologue

Gorilla Glass. It makes your smartphone screen scratch-resistant and tough, and now it’s being used in the Ford GT windshield and the BMW i8 bulkhead window. What is it, and what makes it different from the plain green stuff glazing other cars? To find out, I rang up Doug Harshbarger, Corning Automotive Glass Products’ business director, who explained that there are two big differences: chemistry and the manufacturing process.

Plain “soda-lime” glass is composed primarily of silicon dioxide. Gorilla Glass is a “technical glass,” an aluminosilicate formulation that includes aluminum, magnesium, and sodium. Plain green glass is typically formed by pulling a hot sheet of glass across a bed of molten tin. Liquid Gorilla Glass is poured into an elevated trough with a V-shaped bottom. It overflows this trough, flowing down both sides and fusing together as it leaves the point of the V. With nothing touching either surface, the optical purity exceeds that of float glass. Gorilla’s strength comes from then dipping the glass sheet in a 750-degree bath of molten potassium salt, where sodium ions flow out of the glass and get replaced by larger potassium ions. This size difference crowds the surface of the glass, creating surface compression that increases scratch and impact resistance.

Ironically, a similar formulation of technical glass got its start as Chemcor, a thinner, ultra-tough windshield glass Corning couldn’t sell. (American Motors’ 1970 AMX and Javelin were the only cars that used it.) It was shelved until Steve Jobs came shopping for a tough, thin smartphone/tablet glass in 2007. Now Gorilla Glass is attracting automakers on its weight-saving merits with the bonus that every lost pound lowers the center of gravity.

 A similar formulation was shelved until Steve Jobs came shopping for a touch, thin smartphone/tablet glass in 2007.

The BMW i8 and Ford GT bulkhead window applications both use two thin layers of Gorilla Glass sandwiching an acoustic-absorbing polyvinyl butyrate layer. But for most other applications an all-Gorilla solution is too thin to be structural, so Corning proposes laminating a thin weight-saving layer of Gorilla Glass to a thicker layer of soda-lime glass. It still ends up 40 percent lighter and two to three times tougher, structurally. And contrary to what you’d expect, the Gorilla Glass goes on the inside.

It’s more effective there because allowing some flex when an object impacts a windshield reduces damage, and the outer soda-lime layer is inherently more flexible. The inner layer of Gorilla Glass then acts like the steel reinforcement in concrete to limit this flex without breaking. Hence more objects are able to bounce off without pitting or cracking than would be the case with a thicker, more rigid windshield—even a structural thick/thin all-Gorilla one. Thinner glass naturally improves head-up display performance, reducing the amount of “wedge” required in the laminate layer to prevent image ghosting. It also defrosts more quickly, and so far Gorilla Glass is performing as well as or better than plain glass in crash testing. One complication for windshields and other glazing with compound curvatures: Whereas plain glass can be laminated and then formed to the desired shape, the Gorilla Glass must be shaped then chemically strengthened in the salt bath before being laminated. (Many side-glass applications use simple cylindrical curvature, to which treated flat sheets of Gorilla Glass can easily be laminated.)

What about cost? Harshbarger pegs Gorilla’s cost-per-pound-saved at $2-$4, similar to the aluminum-versus-steel cost penalty. But that’s for upgrading laminated plain glass to laminated Gorilla Glass. The penalty is greater if compared against simple, cheap, tempered side glass, but in that case Gorilla also delivers a sound-reduction bonus. Rear-seat riders, rejoice; this may be the only justification for fitting acoustic glass aft of the ears of the person making the payments.

Read more Technologue columns here:

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• Another Batter Swings at the Compression-Ignition Gas Engine
• What the Bentley Mulsanne and Acura NSX Have in Common
• Road Hard (If Not Put Down Wet): Rethinking Concrete Science

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