Sapphire vs. Gorilla Glass: Anticipating the winner

Gonzo’s take on Sapphire cleverly dodges past the central point, which is, technicality. Not that I know a great deal about it, but I’m sure there are more like me who would like to read about it. Hopefully, Gonzo will post something soon that addresses the technology and technicality behind sapphire, so I’d like to put my two cents on Gorilla Glass to help you make a better comparison later.

This may or may not be a bad news for people looking for exotic things in their watches; to some, sapphire is more exotic than Gorilla. Why? Sapphire got something that Gorilla glass does not, so let’s start with their compositions.

Gorilla Glass is simply a chemically toughened glass that underwent an ion-exchange process. To simplify further, a glass sheet is put into a 400oC bath of potassium salts (molten). This initiates an ion exchange; sodium ions on glass are replaced with the larger potassium ions from the salt. The potassium ions, upon condensing, come up tougher than the sodium, bringing higher compressive stress.

Sapphire, on the other hand, is crystallized aluminium oxide, just like Corundum, another name for which is RUBY (when red). Corundum; however, is a natural occurrence, a mineral and often with impurities that bar its transparency but imparts excellent colors. The difference is, here the alumina is crystallized in the lab, artificially.

While Sapphire ranks 2 and scores 9 on the Mohs scale of hardness of naturally occurring minerals on the planet, Gorilla Glass scores 6.8. Even a mineral like Quartz is a step above. The catch is: Mohs scale of mineral hardness tests the ability of one substance to scratch another, so while it indicates scratch resistance better, it doesn’t gauge shatter resistance.

Let’s hear it from the horse’s mouth. The Director of the Center for Advanced Ceramic Technology (Kazuo Inamori School of Engineering; Alfred University) Mr. Matthew Hall gave the lowdown: “Chemically strengthened glass can be excellent, but sapphire is better in terms of hardness, strength, and toughness. The fracture toughness of sapphire should be around 4 times greater than Gorilla Glass – about 3 MPa-m0.5 versus 0.7 MPa-m0.5, respectively.” [Ref:  Quora.com]

I can hear the question coming: “Is it in real life or in lab tests?” A very pertinent question, that is; for at the end of the day, it all boils down to the real life hardships the glass will face.

As a matter of fact, you have to make both winners. Sapphire resists scratches more than Gorilla Glass but sapphire shatters easier than GG, which can withstand a sudden impact 2.5 times more. But then again, scratches invite fractures in future and therefore, shattering; so less scratches on the GG means it is less less likely to shatter. With that said, here comes the final factors, which is the cost and weight. Gorilla Glass costs a-tenth of sapphire and its density of 2.54 g/cm3 is less than sapphire’s 3.98 g/cm3.

So is it possible to blend sapphire and GG together? Yes, there are ways to fuse sapphire and GG layers together; it creates a laminate which got the best of both – Sapphire’s durability and GG’s flexibility. Their RI (refractive index) are close (sapphire’s 1.76 compared to GG’s 1.5) but the difference in light transmission is quite huge. Here, GG has a disadvantage; it can result in a shorter battery life or a longer charging time. This doesn’t; however, affect the display and perhaps this is the only USP of GG to gain some competitive advantage.

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