Sapphire glass is an application of synthetic sapphire generally produced by subjecting aluminium oxide powder under extreme heat and pressure. Further heat treatment removes internal stresses before processing into thin sheets. The resulting output is a transparent material that is more durable than standard glass. Take note that a synthetic sapphire has the same physical properties of naturally-occurring sapphire.
The extraordinary durability of sapphire glass makes it an ideal material for consumer electronic devices that use digital output displays such as smartphones and tablet computers. In fact, Apple initially had a plan of equipping the iPhone 5S, iPhone 6, and iPad Mini 3 with sapphire glass screens. These products however came with a Gorilla Glass screens instead.
Advantages of sapphire glass
Despite the fact that sapphires are blue in colour, a sapphire glass is highly transparent to wavelengths of light between 150 nanometres and 5500 nanometres. This range gives the material a very wide optical transmission band from ultraviolet to near-infrared.
It is worth mentioning that the human eye can only discern wavelengths between 380 nanometres and 750 nanometre. In other words, a sapphire glass passes the most basic requirement of an ideal screen: light should pass through it and an individual should clearly see through it.
But the real advantage of sapphire glass lies in its extraordinary hardness. The material is nearly twice as hard as a standard glass and it is nearly as hard as a diamond. For a quick reference, the sapphire has a value of 9 while diamond has a value of 10 under the Mohs scale of mineral hardness. This means that a sapphire glass is almost resistant to scratch unless it will come in direct and hard abrasive contact with a diamond.
A sapphire glass is not only hard but also strong. Because it shares similar properties with naturally-occurring sapphire, it has a compressive strength of 2000 mega Pascals. This makes the material about 10 times stronger than stainless deal.
Resistance to thermal shock is another advantage of sapphire glass. A sapphire has an extremely high melting point of 2030 °C.
Just imagine having consumer electronic devices equipped with a sapphire glass screen. These devices would certainly have longer lifespans. Consumers can use their smartphones or tablet computers without worrying too much about unexpected drops or scratches.
Disadvantages of sapphire glass
Despite the aforementioned advantages of sapphire glass, it has several disadvantages that make it impractical for use in consumer electronic devices. An interview with material scientists Richard Lehman and Dr. Helen Chan by Tim Bajarin of Time magazine highlighted these drawbacks.
For starters, despite an established manufacturing process, a sapphire glass is this difficult to produce in large quantities considering the associated cost. Lehman said that a standard glass costs a nickel per square inch to manufacture while a sapphire glass costs several dollars per square inch. This production cost would drive the price of smartphones or tablet devices with sapphire glasses high.
There are also environmental issues associated with producing synthetic sapphire. Dr. Chan noted that it would take more than 2030 °C to melt sapphire. This would consume tremendous amount of energy resulting in high energy cost. It is also possible that a sapphire glass has higher carbon footprint than standard glass.
It is important to highlight the fact that consumer electronic devices such as smartphones and tablets have short lifespans. Users would purchase these devices and keep them for about one to two years before replacing them with newer models. Manufacturers are also introducing newer editions of smartphones and tablets ever year.
The market for smartphones and tablets has become highly competitive—leaning towards yearly innovations and iterations. Equipping these devices with an expensive material could be impractical for most consumers. From the perspective of manufacturers, they would end up choosing between the two: either to keep the price low while upgrading pertinent hardware specifications and maintaining form factor standards or to keep the price high due to advanced hardware specifications and a more durable form factor.
Conclusion: Advantages and disadvantages of sapphire glass
The advantages of sapphire glass make it an ideal screen material for consumer electronic devices. Consumers are looking for devices that could stand day-to-day use amid unexpected overuse.
However, because of the aforementioned disadvantages, it would be impractical to equip smartphones or tablet devices with this material without raising their overall price. Take note also that these devices have shorter lifespan than other products.
Equipping popular consumer electronic devices with sapphire glass screens would definitely raise their price high due to higher manufacturing costs. Will it be worth it? The answer depends on the preference of consumers. It is possible that manufacturers could choose this material for their exclusive luxury smartphones.
Nonetheless, considering the popularity of high-end smartphones from Apple and Samsung, among others, it would be impractical to use sapphire glass screens.
It is therefore not surprising that to this date, sapphire glass materials are popular in products with lengthier lifespans to include glasses or crystals of watches, windows or armoured-vehicles, bullet-proof glass, and screens or visors in military body armour suits, among others.
Further details of the interview of Bajarin are in the article “Why Sapphire is not the Future of Smartphone” published in 26 January 2015 in Time magazine.