Corning Gorilla Glass and its uses in portable

electronic devicesOliver Webb - 701

Requirements for a good screen coating• Resistant to shattering• Smooth to allow for easy and comfortable use• Hard surface meaning it doesn’t scratch easily• Highly transparent to avoid a blurred or dark image on the

screen• High chemical durability to avoid damage from spillages• Thin to allow capacitive touchscreens to remain responsive

Microstructure

• The microstructure of Gorilla Glass is greatly similar to that of Soda Lime (common) glass, the main difference is the layer of Potassium Nitrate ions on the exposed surface and a thin layer below it. The crystal structure remains the same in this layer, however, the molecules are overall larger. Corning do not provide any pictures showing the microstructure of their glass, but it is almost identical to that of the Alumina-zirconia-silica glass shown on the right.

Gorilla glass was developed by Corning as an alternative to plastic or regular glass screens on mobile phones, tablets, laptops, and TVs. The main purpose of gorilla glass was to stop the increasing chance of cracking your screen when your phone gets dropped. It is incredibly scratch resistant compared to normal glass that is made primarily from Silicon Dioxide (SiO2).

Its other desirable properties include: • A low friction surface• High Flexibility• Much better strength to mass ratio than regular glass

Figure B shows Gorilla Glass, notice how much less cracking there is compared to the soda lime glass in figure A.

Two heavy metal balls placed on a sheet of Gorilla Glass. If regular glass were used, it’d break due to its lower flexural strength.

Size and density compared to SiO2 Glass • The 4th and latest generation of Gorilla Glass is the

lightest and thinnest version to be manufactured yet. Its thickness on the just-released Samsung Galaxy A7 was only 0.4mm or 400 microns. It is incredibly difficult to get regular glass to this thickness without sacrificing strength and its already limited resistance to strain. It has a density of 2.42gcm-3. The density of SiO2 varies depending on other materials used but is generally somewhere between 2.4 and 2.8gcm-3

making it about the same density as gorilla glass. Although their densities are similar, Gorilla Glass achieves much greater strength and durability with the same volume of material.

Manufacturing process

• Gorilla Glass is made from an alkali-aluminosilicate which is created via ion exchange. This material is submerged in a molten alkaline potassium salt. To melt this salt temperatures of about 500°C (930°F) are required. When molten, the ions in the salt are able to move freely. Potassium ions are much larger than the sodium ions present in the material before it’s submerged. The larger potassium ions replace the sodium ions which means there is less empty space in the newly formed sheet of glass. By occupying more space, a layer of high residual compressive stress is created at the surface which is mostly what gives Gorilla Glass its highly useful and desirable properties. This is also combined with a process called “fusion forming”, a proprietary method used by Corning. This involves taking the high quality raw material, making it into molten glass at temperatures above 1000°C, pushing it through an isopipe (a specialised metal pipe that acts as a thermal insulator for the glass flowing through it), then letting it evenly flow over both sides of the specially shaped container they use. This allows Corning to make exceptionally thin glass with a very smooth finish which is essential for glass coatings on touchscreens.

Chemical Durability

• Sheets of Gorilla Glass were submerged in various solvents to measure how much mass was lost after different periods of time. As you can see from the table, even in very extreme conditions such as exposure to Hydrochloric acid at high temperature for a long period of time, only around 36% of mass was lost. Judging by how little effect these chemicals had on loss of mass, they shouldn’t become damaged under any normal conditions.

Hardness• A high measure of hardness means that a

material can withstand a lot of force before becoming scratched. As can be seen in the picture, even at a relatively high force of 4.00 newtons, no easily visible scratch has been made in the Gorilla Glass. However, in the two oher types of glass on show, large amounts of damage. There is noticeable fracturing, particularly in the regular Soda Lime glass. This shows that Gorilla Glass must be much harder and therefore much better suited to its intended purpose than other forms of glass. The value Corning give for its Vickers Hardness is 596 kgf/mm2 for the strengthened glass and 489 kgf/mm2 for the un-strengthened glass.

Summary

• Gorilla Glass meets all special requirements for its use. It is hard, chemically durable, thin, smooth and tough. These all make it ideal for use on mobile phones, tablets, and other electronics. Corning are continuing development on Gorilla Glass so that they can further improve on the revolutionary material they’ve already created.