The mental imagery of denting, bending and crushing a transparent glass-like material and having it react the same way aluminium would is immensely satisfying for some reason
Transparent ceramics made with aluminum
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Re: Transparent ceramics made with aluminum
#32The mental imagery of denting, bending and crushing a transparent glass-like material and having it react the same way aluminium would is immensely satisfying for some reason
Yup, but it won't happen with "transparent aluminum", it behaves more like a ceramic does, so don't expect to indulge your bending and denting urges on it.
Re: Transparent ceramics made with aluminum
#33Metal will never be transparent. Metal means metal bonds which means free electrons. Free electrons are opaque to visible light.
I'd never realised the two were connected. What's a good learning reference for bandgap physics? It's something I've never quite understood properly.
You don't need bandgaps to understand why conductors (other than thin films of ITO) don't transmit light. You derive it from Maxwell's equations and the fact that in a conductor, current density = conductivity * electric field. Griffiths' Introduction to Electrodynamics is the standard undergraduate textbook on electromagnetism, and explains this reasonably well. For bandgaps, Ashcroft and Mermin's Introduction to Solid State Physics is what I'm reading from right now, but you don't need it to understand why metals (conductors) don't transmit light.
Re: Transparent ceramics made with aluminum
#34Metal will never be transparent. Metal means metal bonds which means free electrons. Free electrons are opaque to visible light.
I don't think in quite understand. You mean they don't let photons to pass through? In which case do electrons in orbit? Or nuclei for example? Or does this need advanced physics knowledge?
On a quantum level, when a photon encounters a material you have to ask whether the material is able to absorb a photon with that wavelength. When electrons are bound to a specific atom (or are in specific molecular bonds) then there are only certain energy levels possible: that's one of the core features of quantum systems, and it's the reason that each material has its own characteristic "absorption spectrum" (or emission spectrum: same idea). Photons whose wavelength corresponds to an energy that doesn't very closely match what's necessary to raise an electron from one specific level to another will just pass on through. (Nuclei are in bound states with discrete energy levels, too, so they work the same way.)
But one of the essential features of a metal is that the atoms all share a bunch of electrons that are free to move around more or less any way they'd like throughout the material. Because the electrons aren't trapped in one specific bound state, they have an essentially continuous range of energies available to them (just speed up or slow down a little to change your energy), so they are able to absorb photons of any wavelength at all.
[Now, to actually understand why you get reflection rather than stopping with absorption would take me a little more work to figure out how to explain. My instinct keeps being to go back to the classical explanations at that point, but I wanted to focus on quantum here to address your question about electrons in orbit.]
Re: Transparent ceramics made with aluminum
#35Metal will never be transparent. Metal means metal bonds which means free electrons. Free electrons are opaque to visible light.
If the film is thin enough metal is transparent. See for instance 50/50 mirrors and gold plated windows.
Of course you can now argue that if the photons hit the metal they will not pass through, but that's not how it works: the photons will excite an electron to a higher orbit and it may drop back to a lower orbit on the other side of the film making the metal appear transparent or it may reflect.
edit: saiya-jin I can't reply to your comment but yes, the direction is preserved. The same happens with a mirror, the photons ejected will be ejected at the correct angle even though the photoelectric effect has absorbed the photons. That's why metals reflect the way they do!
https://www.scientificamerican.com/article/how-do-mirrors-re...
The small fraction of photons that is absorbed will heat up the mirror.
Re: Transparent ceramics made with aluminum
#36Earlier quoted context omitted.
According to wikipedia's AlON page it has a knoop hardness of ~1800 which from my understanding of things (I may have misread sources or be mistaken, I'm not a material scientist or even amateur) looks to be about equivalent to sapphire glass and much higher than gorilla glass (~600). edit: in fact while I skipped the intro it states specifically that AlON has ~85% the hardness of sapphire, which more or less checks…
I believe hardness is actually a bad thing in terms of replacing gorilla glass in phones. It increases the likelihood of shattering when dropped, and is the main reason for sapphire not being adopted.
The Corning product is an extremely interesting material, the hardness varies with the depth leading to scratch resistance and a reasonably high level of resistance against shattering.
Re: Transparent ceramics made with aluminum
#37On a completely separate note, what was the deal with the need for transparent aluminum in Star Trek IV?
Looking at the footage, they easily could have made the tank bigger if they just used all of the space available and didn't need to be able to "see" them from outside their tank. All they would have needed the aluminum for is to keep water out of where water shouldn't go and regular aluminum (or other material) would have worked just as well.
Re: Transparent ceramics made with aluminum
#38On a completely separate note, what was the deal with the need for transparent aluminum in Star Trek IV? Looking at the footage, they easily could have made the tank bigger if they just used all of the space available and didn't need to be able to "see" them from outside their tank. All they would have needed the aluminum for is to keep water out of where water shouldn't go and regular aluminum (or other material) wo…
Maybe its stronger than regular
Re: Transparent ceramics made with aluminum
#39On a completely separate note, what was the deal with the need for transparent aluminum in Star Trek IV? Looking at the footage, they easily could have made the tank bigger if they just used all of the space available and didn't need to be able to "see" them from outside their tank. All they would have needed the aluminum for is to keep water out of where water shouldn't go and regular aluminum (or other material) wo…
Aluminum corrodes a bit in sea water although it didn't need to last that long.
Re: Transparent ceramics made with aluminum
#40Earlier quoted context omitted.
I'd never realised the two were connected. What's a good learning reference for bandgap physics? It's something I've never quite understood properly.
You don't need bandgaps to understand why conductors (other than thin films of ITO) don't transmit light. You derive it from Maxwell's equations and the fact that in a conductor, current density = conductivity * electric field. Griffiths' Introduction to Electrodynamics is the standard undergraduate textbook on electromagnetism, and explains this reasonably well. For bandgaps, Ashcroft and Mermin's Introduction to So…
Ashcroft and Mermin is only an 'introduction' in the graduate student sense of 'introduction'. I don't think you can make sense of it without previous grounding in both quantum mechanics and solid state physics.