Why don't they make Cell Phone screens out of Sapphire

[BlackTigers]

They could make a lot of things better and cheaper, but then stuff wouldn't break and people wouldn't buy anything new - businesses would just cease after initial production.

See:kalishnakov.

 

[shortylickens]

I just put a otterbox on mine :/

I like Otterboxes but they make the phone too damn big. Especially the Defender series. But I got one for my mom anyway cuz her last blackberry got squeezed too much and the screen popped out. 300 bucks down the tube (bought it unlocked from Amazon, no warranty).

 

[Fenixgoon]

I think hardness is more about resisting scratches.

Taking a hammer (with a chisel) is exactly how you 'cut' a diamond.

Fern

hardness is basically resistance to deformation, and can be correlated to strength. This is usually measured with a small indenter applying a compressive load. In the case of ceramics, they are stable in compression but unstable in tension. This is a readily observed phenomena.

Toughness is resistance to the extension of a crack from a sharp notch. generally speaking, cracks open and are propagated by tensile stresses. The first formulation by Griffith was basically that the critical energy required was equal to twice the free surface energy per unit area (since extending a crack would create two new surfaces - one upper and lower). This is a very small amount of energy, relatively speaking, since ceramics are unstable in tension and have virtually no mechanism for deformation or damage tolerance. This ultimately means that they have very low toughness values. Metals, on the other hand, can deform via dislocation motion (called slip) which allows them to be shaped (undergo plastic deformation), to be stable in tension and yield, and to resist crack extension quite extensively. Ceramics might have a toughness of 30, while metals can easily have toughnesses of 100 or more (note: strength and toughness tend to be inversely related)

Wish I had my fracture mechanics book handy to give a little bit more technically correct description of Griffith energy as a driving force for crack extension

Furthermore, there are probably certain crystal directions where diamond, or any other ceramic, is more prone to cleavage and other planes where it is less prone. obviously you would want to cut on the planes that cleave the easiest

 

[StrangerGuy]

IIRC brittleness (tendency to break into pieces) is usually inversely proportional to hardness (ability to resist scratches and indentations).

 

[SsupernovaE]

hardness is basically resistance to deformation, and can be correlated to strength. This is usually measured with a small indenter applying a compressive load. In the case of ceramics, they are stable in compression but unstable in tension. This is a readily observed phenomena.

Toughness is resistance to the extension of a crack from a sharp notch. generally speaking, cracks open and are propagated by tensile stresses. The first formulation by Griffith was basically that the critical energy required was equal to twice the free surface energy per unit area (since extending a crack would create two new surfaces - one upper and lower). This is a very small amount of energy, relatively speaking, since ceramics are unstable in tension and have virtually no mechanism for deformation or damage tolerance. This ultimately means that they have very low toughness values. Metals, on the other hand, can deform via dislocation motion (called slip) which allows them to be shaped (undergo plastic deformation), to be stable in tension and yield, and to resist crack extension quite extensively. Ceramics might have a toughness of 30, while metals can easily have toughnesses of 100 or more (note: strength and toughness tend to be inversely related)

Wish I had my fracture mechanics book handy to give a little bit more technically correct description of Griffith energy as a driving force for crack extension

Furthermore, there are probably certain crystal directions where diamond, or any other ceramic, is more prone to cleavage and other planes where it is less prone. obviously you would want to cut on the planes that cleave the easiest

Materials science is so damn interesting. Most people don't realize that materials engineers were the ones doing much of the groundbreaking work on the Apollo program.

 

[edro]

Sapphire is aluminum oxide?
<head asplodes>

 

[CZroe]

All my sapphire watch lenses get scratched.

 

[zephyrprime]

The real question is why we don't use plastic? I know sony was once upon a time working on glass coated plastic but that research doesn't seem to have gone anywhere.

 

[Mark R]

Sapphire is aluminum oxide?
<head asplodes>

Correct. It really is transparent alumina.

 

[vetiver]

When displays were made in the US, the US display industry knew a lot about materials. With the transition to LCDs, the US became only a display purchaser with little materials expertise in the industry. Sapphire is unsuitable as a cover glass because of its 1.77 index of refraction. LCD performance outdoors is marginal due to the high level of reflections off the glass. Going to a material with an even higher index would make the display completely unreadable in many situations. And no, Gorilla Glass is a glass, it is not sapphire which is a crystal, two completely different classes of material.

 

[Howard]

North Korea should do it first.

 

[ImpulsE69]

I like borosilicate glass.

I see what you did there... :hmm:

 

[Ichinisan]

When displays were made in the US, the US display industry knew a lot about materials. With the transition to LCDs, the US became only a display purchaser with little materials expertise in the industry. Sapphire is unsuitable as a cover glass because of its 1.77 index of refraction. LCD performance outdoors is marginal due to the high level of reflections off the glass. Going to a material with an even higher index would make the display completely unreadable in many situations. And no, Gorilla Glass is a glass, it is not sapphire which is a crystal, two completely different classes of material.

Sounds like you know your stuff.

Welcome to Anandtech forums.

 

[Sukhoi]

Sounds like you know your stuff.

Welcome to Anandtech forums.

Yet he/she's banned after that post lol. Confusing.

 

[destrekor]

Yet he/she's banned after that post lol. Confusing.

HE KNEW TOO MUCH! He had to be silenced!
:ninja:

Probably multiple accounts/previously banned.

 

[Midwayman]

Doesn't the iphone 5 use it for the camera lens cover? I thought that's why it was getting the weird fringing on bright lights?

 

[Ichinisan]

Yet he/she's banned after that post lol. Confusing.

Having a subject entered on a reply does fit the profile of a spammer, but also someone unfamiliar with vbulletin forums.

I wonder why Dr. P edited my post? Probably clicked "edit" on the wrong one accidentally.

 

[OverVolt]

The real question is why we don't use plastic? I know sony was once upon a time working on glass coated plastic but that research doesn't seem to have gone anywhere.

The glass they are creating is basically glass-plastic hybrids.

 

[Fenixgoon]

I learned something Hardness doesn't mean unbreakable. Even diamonds will crack, chip, and break if hit with force. Apparently you can take a hammer and smash a diamond.

hardness != toughness.

two extremely different properties

Sapphire is aluminum oxide?
<head asplodes>

more specifically, sapphire is aluminum oxide doped with iron and titanium.

ruby is aluminum oxide doped with chromium.

emerald is aluminum oxide doped with chromium and vanadium

a pure, single crystal of aluminum oxide is quite transparent