No I have not been watching Star Trek or anything like that but I was seriously wondering why a transparent metal does not exist? What are the specific limitations? I seem to remember something about the the degree of ‘refraction’ being a factor that can not be manipulated but I am not sure…Anyone want to enlighten me?
A metal has free electrons. In fact the electrons in metals can be considered as independent from the ‘bulk’ matter (although they give it most of the bulk properties). Free electrons will react to electromagnetical waves.
If you consider the fact that light can be seen as little more than a rapidly alternating electrical field, it’s clear that free electrons will interact with the field. In fact, they will move along with the field, which in turn will give rise to a new field. That’s why metals are reflective, (if polished flat and without oxides). (This comes out brilliantly if one tries to solve Maxwells equations in an interface with vacuum/perfect conductor.)
One would be led to believe that there can be no transparent conductors, but that’s not 100% true. There are other details to consider, such as band gap, fermi levels etc, but for now, sufice it to say that there are materials that are transparent to (visible) light, but can conduct electricity. In those cases the electrons aren’t fully free, and we’re more talking about semi-conductors.
I thought one of the features of a metal was reflectiveness?
According to University of Illinois, Urbana/Champaign Materials Science and Engineering department
The “opaque” and “lustrous” part of it woudl seem to rule out transparent metals, but I don’t know if that’s an essential part of the definition.
So what exactly is a metal?
I’m not sure if it’s the definition, but one characteristic feature of metals is that the outer electrons are free to move around in what’s normally called an electron cloud. See my post above as to why this rules out transparency.
Agreed with all. However, there are get-outs being developed that use mesoporosity or stacked metal-dielectric layers.
Got any articles newer than that? Those are from 1999.
Not that I can find. I had those bookmarked from a while back, but a very quick skim of Google didn’t find anything current.
Does it have to be a metal? What about a clear plastic that was about as strong? Or is there even such a thing in development?
I think the main problem with getting a plastic or glass as strong as metal has to do with it’s tensile strength. Compressive strength wise glass should be as strong as metal.
Oops! I see raygirvan already covered this with the mesoporosity link. Never mind. . .
Well, if you’re an astronomer, it’s easy – they call every element heavier than helium a metal. (And, in extreme environments such as the interior of Jupiter, hydrogen can become metallic as well.)
The way in which light interacts with a material depends on the frequency of the light (most commony displayed in rainbows and prisms). This is the same for metals. It just so happens that simple metals reflect the frequencies of light that are in our visible region. Alkali metals are transparent to UV frequencies. Germanium is transparent in the IR range. (Kittel, Introduction to Solid State Physics )
If they are feasible - they’re going to be very very tweaked and engineered. I’m having a bit of a knee-jerk ‘nope. not possible. it wouldn’t be a metal then’ reaction but I’m not sure I can back it up just yet.
As I’ve noted in past threads, there already are transparent metals. But it depends upon how elastic your definition of “visible” is. The alkli metals are definitely metals – lustrous, silvery-looking, highly conducting They’re also low melting and very soft and highl reactive, but we’ll ignore that. They’re all also transparent in the ultraviolet (UV), with the “cutoff” varying with atomic number/density. One of them has a transparency range that hovers on the edge of the visible. ut with the proper equipment, you can “se” through this stuff.
Silicon and germanium are semiconductors. Not metals, of course, but they look all shiny. They’re transparent for infrared (IR-- wavelengths above about 1.2 and 1.8 microns. You can see through a slab of silicon with night-vision goggles.
Don’t they make some crystal out of lead?
% of lead crystal is lead. Good crystal is usually 24-36%. Lower grade is 14-24%
Why are the alkali metals transparent to UV, given the electromagnetic effects Popup brought up? (Assuming, of course, the question can be answered in a post, rather than 45 pages of partial diffys.)
Transparent Alumina (Aluminum Oxide) has been created, though I suppose that doesn’t really count as a metal. Still, pretty nifty looking!
The specific limitation is definitional. A metal is in part defined as being opaque and lustrous. So if you made a material that was a transparent conductor of electricity and heat, even if it were malleable and ductile, it would not be a metal. Even if it were an allotrope of an element that is usually metallic, such as aluminium, it would not be a metal if it were transparent. The distinction may not be important, but that’s what the word ‘metal’ means.
As for transparent alumina, it is neither the same thing as aluminium, nor a metal, nor anything new. It is alumium oxide in the form of large crystals, that is, the mineral corundum. Commercial forms of transparent alumina have long been known as the gemstones ruby (coloured red), sapphire (coloured by iron oxide and titanium oxide), Oriental emerald (coloured green), Oriental aquamarine (coloured light blue), and corundum (pink, violet, yellow, and colourless).
Regards,
Agback