The use of Gold as a Thermal insulator

[Scotracer]

Ta - thanks for confirming it.

[WhiteBlue]

The use in satellites is probably the highest profile use but it is also used in thermal blankets for emergency kits in mountaineering.

[Richard]

I've learnt something new. I'd always thought of "insulation" as exclusive to conduction and now I know better.

[PlatinumZealot]

Well It's a good radiation reflector. But if it was a situation of conduction or convection where the heat source is actually touching the object, the gold is going to let the heat through since it's a good conductor.

[avatar]

It is immune to rust when heated, something that's not true of silver or aluminium, so it keeps its reflectivity.

more than that, gold is chemically inert; completely unreactive.

p.s. I think by "rust" you mean oxidise or maybe corrode. Technically, rust describes only iron oxides, but the rest of the post was really clear. Thanks!

p.p.s.
I was redirected here from RB8 thread as I was wondering why NASA used gold on the lunar landers if (as was posted on the other thread) "aluminium beats gold all day long" - seems in this context, it doesn't.

[marcush.]

so we are getting there -
The gold foil has NOTHING in terms of conducting any heat -basically the gold is a layer of gold atoms there is no substance mass to conduct any significant heat.It´s completely relying on it´s radiated heat reflective abilities.

You may look up what the Mylar film on which it is deposited can conduct ...I will not.

The aluminium foil is actually quite a bit of Aluminium and it will maybe not be as efficient in reflecting the radiated heat -but it will be very efficient in spreading out the heat over its area and this will help the matter .But on two layers of aluminium and you get an even better effect and make it three and you can forget Gold all day long...

Has anyone ever measured temps in front and at the rear of their insulations ?
I have,just recently.

also something to take into:you may be able to reflect radiated heat with the gold stuff -but what is happening with the reflected heat? it will go straight in where it is not reflected ,methinks...Of course some will go into the airstream but what with the car standing still and no air worth speaking of going through the sidepods ?

In space ,where you have ONLY radiated heat ,it does make sense to use the best in terms of reflecting but a race car is experiencing everything radiated heat from the exhausts take your choice when exhaust gas may be 1200°C what temperature the pipes may reach and 130+ C° from the rads and 150°C from the engine oil you sure have more to look at than radiated heat ..you need to slow the heat going throu your insulatiuon and try to spread it out.


Brings me to the concept of using CArbon as a heat spreader .Carbon is a very good heat conductor and could be used to transport heat very efficiently ,it is already in use with high efficiency electronics heat sinks and as a replacement for heat conducting paste in mounting of electronic cicuits

[Just_a_fan]

The exhaust pipes get visibly red hot at full chat so they are radiating huge amounts of energy. If you can reflect that with a few grams of gold leaf rather than placing large slabs of aluminium heat spreaders everywhere then which would you choose?

Gold is used because it is the best material for the job for which it has been picked - in this case it's to reflect readiated heat energy. And it's way better than aluminium for that.

[marcush.]

The exhaust pipes get visibly red hot at full chat so they are radiating huge amounts of energy. If you can reflect that with a few grams of gold leaf rather than placing large slabs of aluminium heat spreaders everywhere then which would you choose?

Gold is used because it is the best material for the job for which it has been picked - in this case it's to reflect readiated heat energy. And it's way better than aluminium for that.

That Gold foil stuff is not much lighter than a triple layer of alumnium with 0.3mm thickness each . I will come up with a weight comparison for the stuff and will crosscheck if I can find something puslished in the web to confirm my claims -unfortunatelly my work is proprietary and I cannot share.
a reallife test gold foil compared to other stuff did not go out too well for the gold stuff even though all involved favoured it just by the looks...

and to put a bit fire in the gold dust:
http://en.wikipedia.org/wiki/Multi-layer_insulation

the idea behind multilayer foils is the interesting bit .You don´t need the gold.save your money for something useful.

[Just_a_fan]

But gold reflects infrared better than aluminium and has the added benefit of being able to be hammered out to a foil that is microns thick. So it weighs almost nothing in the car and takes up almost no room. Multi layer insulations are thicker and heavier. In the tight confines of an F1 car that is a big issue.

We are talking about a sport where a benefit of 5% is huge. Gold leaf is 10% better than aluminium at reflecting infrared. That's a big difference and the cost is almost nothing in the context of an F1 car's total cost.

The gold is only there to reflect infrared from the exhausts. Airflow deals with the rest of the heat energy.

[olefud]

The point has been made that gold is a noble metal, i.e. no oxidation and degraded reflection of radiant energy. Aluminum is highly reactive and forms an oxide almost immediately when exposed to air. Gold is thus the better choice since it stays shiny and reflective.

[marcush.]

you are assuming there is just radiated heat involved ,which is definitively not the case.the case of gold foil is only good for this special case...and even for this in space they use MLI (Multilayerinsulation see wiki link above) ,I don´t say gold is bad or useless but i say the thin layer of gold atoms on a mylar foil is not really the ideal candidate close to a redhot glowing exhaust pipe inside a sidepod.

[Just_a_fan]

And yet that is what they use and it works perfectly well for their needs...

[olefud]

you are assuming there is just radiated heat involved ,which is definitively not the case.the case of gold foil is only good for this special case...and even for this in space they use MLI (Multilayerinsulation see wiki link above) ,I don´t say gold is bad or useless but i say the thin layer of gold atoms on a mylar foil is not really the ideal candidate close to a red-hot glowing exhaust pipe inside a sidepod.

But the only purpose of the reflecting foil is to protect against radiant heating that is the major heat transfer mechanism for brakes, exhaust etc operating at high temperature. A small air gap with cooling convection flow protects the foil from sensible heat. With high temps, the substrate is probably a polyimide rather than Mylar (PET).

A single layer would be better than multi layer foil since it would radiate/absorb to ambient rather than with a heated second layer. I suspect that both aluminum and gold foils are produced in a vacuum by vapor deposition. Aluminum would need to then be overcoated with a second protective layer to protect against oxidation. The gold can go naked and is thus less likely to absorb IR.

[marcush.]

you are assuming there is just radiated heat involved ,which is definitively not the case.the case of gold foil is only good for this special case...and even for this in space they use MLI (Multilayerinsulation see wiki link above) ,I don´t say gold is bad or useless but i say the thin layer of gold atoms on a mylar foil is not really the ideal candidate close to a red-hot glowing exhaust pipe inside a sidepod.

But the only purpose of the reflecting foil is to protect against radiant heating that is the major heat transfer mechanism for brakes, exhaust etc operating at high temperature. A small air gap with cooling convection flow protects the foil from sensible heat. With high temps, the substrate is probably a polyimide rather than Mylar (PET).

A single layer would be better than multi layer foil since it would radiate/absorb to ambient rather than with a heated second layer. I suspect that both aluminum and gold foils are produced in a vacuum by vapor deposition. Aluminum would need to then be overcoated with a second protective layer to protect against oxidation. The gold can go naked and is thus less likely to absorb IR.

The gold foil needs to actually "see" the radiated heat to be able to work at all. To think the air in the area around the headers will not get -very-hot is a wish not coming true ,especially right at the start when the car is not moving for long long seconds.
To think multilayer is inferior .go back and investigate it works very ,very well -ask Boltzmann -sorry i think he has passed away long time ago...
in a real world test the gold foil was under same conditions surpassed by aluminium multilayer insulation by a factor of 2 when it came to reaching the target critical temp behind the insulation.
I have not actually tested against simple aluminium tape like the one you take to seal welding area when working with purging gas ,but my feeling is the effect is fairly similar..

you are right the gold is deposited on a polymide film which is on a thin layer of glass fabric which is sticked to the panel by means of a silicone glue.