Gorilla Glass is a protective glass produced by Corning. It is widely used in mobile devices such as smartphones. How widely? During the nine years since it first became available (the last version, Gorilla Glass 4 has been around two years or so), the glass has been used in about 4.5 billion devices, 1800 product models and 40 major brands. Shipments currently amount to around one billion devices per year. The company is now offering a technological update to this highly successful product called Gorilla Glass 5. The most significant improvement is the enhanced resistance of the glass to shattering on impact.
The need for the improvement derives from the obvious: everyone drops their smartphone. Engineers at Corning investigated the matter and determined that, when a smartphone is dropped, the average drop distance is about 1.0 meter. Laboratory tests conducted at Corning indicated that, in a smartphone, Gorilla Glass 5 will survive a 1.6 meter drop on its face about 80% of the time. This constitutes an improvement by a factor of 1.8 over the performance of Gorilla Glass 4 in a similar test.
The improvement is due to both a change in the composition of the materials from which the glass is composed as well as the chemicals used to strengthen the glass.
The process of making Gorilla Glass starts with the selection of the raw materials which are then blended and melted. Next, the molten glass is fed into a trough called an isopipe. The isopipe is filled with the molten glass until it overflows, doing so evenly over both sides. The flowing glass then rejoins at the bottom of the trough where it is drawn down to form a microns thick, continuous sheet of flat glass. Great care is taken to assure that there are no flaws in the surfaces of the glass sheet.
Depending on requirements, Gorilla Glass can be produced in thicknesses ranging from 0.4 mm to 2 mm. (that’s the same process that Corning uses for its mainstream display glass – Man. Ed.)
Making the Glass Stronger
Gorilla Glass is then chemically strengthened through a process called ion exchange. In the ion exchange process, the glass sheet is placed in a hot bath of molten salt at a temperature of approximately 400 oC. Under these conditions, smaller sodium ions leave the glass to be replaced by larger potassium ions from the salt bath. Since the large ions take up more space, they are compacted when the glass cools. The result is production of a layer near the surface of the glass that is under compressive stress. The specific composition of Gorilla Glass is such that the potassium ions are able to diffuse deeply into the glass. The result is a layer under compressive stress that extends quite deeply into the glass. This compressed layer creates a surface that has enhanced resistance to damage.
Other aspects of Gorilla Glass 5 are little changed with respect to version four. Most significantly, scratch resistance is unchanged. It might be mentioned that the means the company uses to test scratch resistance is both quite realistic and slightly amusing. The smartphone is put into a purse and the purse is tossed about in the barrel of a tumbling apparatus.
Corning represents Gorilla Glass as well suited for use as a cover sheet for touch screens. “It is tough enough to handle the surface pressures intrinsic to these devices, and exceptionally thin to enable more sensitive and accurate responses.”
A video discussing Gorilla Glass 5 can be found at the end of this article.
Gorilla Glass 5 is now commercially available. The company expects Gorilla Glass 5 to start appearing in commercial products later this quarter.
At this time, Corning has chosen to continue supplying versions 3 and 4 of Gorilla Glass to customers and to do so at a reduced price. The expectation is that the company will discontinue these earlier versions of Gorilla Glass in the near future. -Arthur Berman
