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Optical properties of metals at high temperatures
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DumHed
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how does the crystal structure affect the optical properties though?

Other materials are crystalline, but transparent - and mercury is liquid and opaque.
What is it that really causes opacity?

From what I've been reading it's all to do with electrons. Metals are generally very opaque because the electrons are "free" which means they can resonate at almost all frequencies - and are therefore very efficient at absorbing and reflecting most electromagnetic radiation.

Other materials have electrons at energy levels that respond more to specific wavelengths, which can give them colour, or allow visible light through but not ultra violet light, etc.

If it's all about the electrons then I think there's a good chance that the metal's opacity could be affected quite a bit by temperature...
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Post Wed Nov 09, 2005 10:40 pm 
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Spockie-Tech
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Nothing like a good myth to create some interesting discussion..

Even If Transparent Turbo's do fall into the same category as Elvis sightings, I'm learning a lot about Metallurgy along the way, so its all good..

O.T. a Friend of mine (having seen the N2O injection system on my Charger ) asked me if he could fit one to his 173 Kingswood. I told him I didnt think the engine would handle it, to which he responded "Who's talking about the engine ? I want it injected into the cabin !" Laughing

Back On topic. I would also question whether the thermal conductivity of the turbo charger housing material was low enough that significant variations in its localised temperature could occur with sufficient "resolution" for you to make out the shape of the turbine blades inside.

I can maybe believe a vague donut-shaped glow where the radiative cooling was reflected by the shiny turbine giving you a warmer circle, but distinguishing the blades clearly enough to make someone on the outside go "cool !, look I can see the turbine !" ? I doubt it.

If you aim an oxy torch (probably a higher density heat source than turbine radiation) at an old turbo housing, see how sharply defined a glowing point you can get, and then ask if its sharp enough to make a turbine visible.
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Post Thu Nov 10, 2005 12:10 am 
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Big AL
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from what i read i got the imprestion that specific wave lengths of light *might* be able to squeese thought vibrating atoms to allow some sort of image of the object thought but to remain solid enought to keep the turbo from melting.

sort of like a person wearing a white shirt running amoungst a crowd of red shirts.
the person might be moving around but unless the crowd is moving at a certain rate you won't be able to see them thought the "solid wall"
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Post Thu Nov 10, 2005 12:27 am 
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DumHed
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this is where we need to verify the sightings of translucent turbos Smile

Some quite reputable people claim to have seen it, but there's still a good chance it's purely an optical illusion.
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Spockie-Tech
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Damn ! Introducing verifiable *facts* into a lively argument ??! What are you trying to do - Kill it ? Wink
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Post Thu Nov 10, 2005 12:43 am 
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DumHed
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I think it could go on forever otherwise!

As soon as I get a chance my old jet engine is going back together in simplified form for some molten turbo housing destructive testing Smile
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Post Thu Nov 10, 2005 1:03 am 
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Totaly_Recycled
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Lol i have been just siting on the side of this one ..as ive never seen it my self i have seen glowing muflers on ride on mowers and some times a hot spot (brighter than the rest apears) then seems to reapear in a slightly diferent location like its moveing around mabee some thing to do with air movements cooling certain bits slightly and the other small spot is hoter for a second or two ? mabe someing similar is hapening on the turbo's

Post Thu Nov 10, 2005 1:17 am 
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Totaly_Recycled
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Or mabee its an electro magnetic efect from the hot spinning blades inside the turbine that is creating a rotateing magnetic field on the houseing which alinghes the random heat waves comeing off the houseing on the out side of the turbine and making these heat waves rotate in the direction of the spinning turbine ...these heat waves could be slightly casting a rotating shadow on the houseing thus creating the effect of --seeing the turbine through the houseing Very Happy

Post Thu Nov 10, 2005 1:26 am 
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Spockie-Tech
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I know - I know ! Its the Energy Polariser !

Harmonicallly Aligning the sub-quantum cystalline molecular structure and resonating the electron energy rings at a multiple of the fundamental frquency in such a way as to cause coherently tuned synchronisation of the photonic wave peaks in a visually discernible pattern thus engaging the non-critical image recognition sections of our human cortexes to match the desired and pre-expected view with a high enough commonality factor to suggest a higher correlation than in actuality exists !

Virgin Mary Toast anyone ? :Wink:
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Post Thu Nov 10, 2005 6:38 am 
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DumHed
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I'd settle for a toaster that works!
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Post Thu Nov 10, 2005 8:48 am 
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Spockie-Tech
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How about a Talkie-Toaster (Patent Applied for) ? Wink

Why dont you give your local rice-burner dyno tuning shop a call and ask the dyno operator if they have seen, or even better can show you a transparent turbo on the rolling-road ?

That would be much more likely than some "Nismo-Racing-Team" sticker wearing winged plastic fantastic driver telling you about the time they had their turbo glowing so hot is was see through.. I'd be more likely to believe palm-inspired friction heating as the cause from one of those guys.. Wink
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Post Thu Nov 10, 2005 9:08 am 
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DumHed
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that's what I'd expect too, but when there are people like ex garrett turbine engineers now working for aftermarket performance development companies claiming to see it I take a bit more notice.

I've seen hundreds of cars running on a dyno, but generally they don't get quite that hot.
It's only on lengthy tuning runs that they really heat the turbo up as much as a decent run down a mountain road or constant very high speed run.
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Post Thu Nov 10, 2005 9:36 am 
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kkeerroo
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Since there are apparently some well known people who have seen this effect I thought I would try searching for it on google but was unable to find anything.

So I searched for some info on why certain materials are trnaparent and others arn't. Here's a good website http://science.howstuffworks.com/question404.htm:
For those who only want to read the good bits here's a cut and paste job:

"Another factor happens at the sub-atomic level. The atoms that bind together to make the molecules of any particular substance have electrons, usually lots of them. When photons come in contact with these electrons, the following can occur:

* An electron absorbs the energy of the photon and transforms it (usually into heat)
* An electron absorbs the energy of the photon and stores it (this can result in luminescence, which is called fluorescence if the electron stores the energy for a short time and phosphorescence if it stores it for long time)
* An electron absorbs the energy of the photon and sends it back out the way it came in (reflection)
* An electron cannot absorb the energy of the photon, in which case the photon continues on its path (transmitted)

Most of the time, it is a combination of the above that happens to the light that hits an object. The electrons in different materials vary in the range of energy that they can absorb. A lot of glass, for example, blocks out ultraviolet (UV) light. What happens is the electrons in the glass absorb the energy of the photons in the UV range while ignoring the weaker energy of photons in the visible light spectrum. If the electrons absorb the energy of any portion of the visible spectrum, the light that transmits through will appeared colored according to the portion of the spectrum absorbed. In fact, the color of any object is a direct result of what levels of energy the electrons in the substance will absorb! "

So for metal to become transparent when it is heated a change would need to take place within the atomic structure of the metal to stop the electrons from absorbing the incoming photons. Since to do this you would need to remove all of the free electrons from the metal it doesn't sound possible to me. The removal of the free electrons would also stop the metal from glowing but isn't that part of the story?
Strange, didn't I read that someone was arguing that it was the free electrons causing the metal to become transparent?

I also deceided that since the concept seems so apealing then someone somewhere would be getting paid to research it. Here is what I found in the way of "clear" metals:
The U.S. Air Force has spent billions of dollars researching transparent armour for their aircraft. The latest stuff they are playing with is aluminum oxynitride (ALONtm). It is a clear aluminium based ceramic that can stop a .50cal armour piercing round but since it is a ceramic it doesn't count.
http://www.scienceblog.com/cms/air_force_testing_new_transparent_armor_9113
A German university has also been looking into clear Aluminium oxide panels but again this a cermic not a metal.
A very common clear "metal" is that used in ESD safe bags (the silver bags electronic componants come in). But looking at Descos Material Safety DataSheet for their ESD bags you can see that it is actualy a metallized polyester and therfor a plastic.
http://desco.com/pdf/tb-7024.pdf
The best transparent metal I could find is a aluminium foam. The theory is if you can create enough "bubbles" in the metal then you should be able to see through it. To me this sounds like trying to look through a foam mattress.
But Star Trek fans are convinced that clear aluminium is possible because they saw it on TV.
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Post Thu Nov 10, 2005 7:25 pm 
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DumHed
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I did some testing tonight, which I'd re post here, but it might be easier to look at it directly:

http://www.nissansilvia.com/forums/index.php?showtopic=120630&st=180&p=1758319&

Anywho, I'm off racing for the next three days, so have fun finding info Smile
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Post Fri Nov 11, 2005 12:42 am 
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Knightrous
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That's pretty cool Andrew! It that a Mini EV on the electric turbine Razz

Anyway, enjoy your race weekend!
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Post Fri Nov 11, 2005 9:51 am 
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