I have long pondered this question. Why exactly is gold chosen over other materials to insulate components? It is used in F1 especially around the exhaust components. But the density and thermal conductivity are higher than many other materials (and even some metals) and above all it's very expensive en masse.

Is it because Gold comes regularly in leaf form? Or the higher melting point compared to Aluminium (a better thermal insulator)? I fear I may have answered my own question.

Aluminum CONDUCTS heat, doesn't insulate it...

They are still using gold as they still think it is the most expensive ounce for ounce.

If they ever find out that aerogel is a better insulator, and more expensive per ounce, they'l find a use for it.

/sarcasm

Jersey Tom wrote:Aluminum CONDUCTS heat, doesn't insulate it...

That's what I'd been led to believe but the Thermal Conductivity of Al is lower than Au according to this

Another point.. how do you know that it's being used an insulator for conductive heat transfer? What about radiative heat transfer? What's the emissivity?

Jersey Tom wrote:Another point.. how do you know that it's being used an insulator for conductive heat transfer? What about radiative heat transfer?

I suppose that's a possibility. We'd really need to know the working temperatures in the areas it's used to know if radiative heat transfer is dominant or at least important.

Comparing Al and Au again with emissivity this time we get:

Al 0.039-0.057 (Highly Polished) to 0.77 (Anodised)
Au 0.018-0.035 (Highly Polished)

So that suggests that Gold will reflect more heat...but not by a huge margin. This would insulate if it's wrapped in the stuff - particularly around something very hot like an exhaust manifold. Gold seems to be one of the most reflective metals.

Maybe we've solved it.

My question is very fundamental. How do you know they are using gold?

Your question requires us to agree with your premise. Please explain your conclusion.

I would use ceramics.

Professor wrote:My question is very fundamental. How do you know they are using gold?

Your question requires us to agree with your premise. Please explain your conclusion.

I would use ceramics.

Ceramics make a good choice, and indeed they are used widespread but weight may be an issue.

I have found a few things to back up the original post:

http://en.wikipedia.org/wiki/McLaren_F1#Specifications wrote:The carbon fibre body panels and monocoque required significant heat insulation in the engine compartment, so Murray's solution was to line the engine bay with a highly efficient heat-reflector: gold foil. Approximately 25 g (0.8 ounce) of gold was used in each car.[7]

And here's a paper on the topic:

http://www.goldbulletin.org/assets/file ... ey_2_8.pdf

Tom was correct - it is the radiative heat transfer properties of gold that makes its use viable.

Related link

Maybe I am misunderstanding the term insulator. Your examples seem to be referring to reflectors not insulators. Reflectors deflect the heat away from a colder object while insulators contain the heat at the source. This may be just semantics. The difference is which object is covered. The source, or the material to be protected.

Again, this is just definition and not a disagreement. To protect the adjacent cold material one uses a reflector. To contain the heat at the source one uses an insulator. I would suppose the gold is being used as a reflector and is applied to the "cold" part as protection.

Or, have I gotten this all wrong?

On further reflection (humour) I do understand what you guys mean. It is on the cold parts but does prevent the cold parts from external heat, and herefore insulates.

As I said, semantics. Sorry to be a bother.

Professor wrote:On further reflection (humour) I do understand what you guys mean. It is on the cold parts but does prevent the cold parts from external heat, and herefore insulates.

As I said, semantics. Sorry to be a bother.

Yes, that's what I mean, at least.

Professor wrote:On further reflection (humour) I do understand what you guys mean. It is on the cold parts but does prevent the cold parts from external heat, and herefore insulates.

As I said, semantics. Sorry to be a bother.

It does not insulate.

Its not emissivity, conduction or insulation .... it is reflectivity

Gold, like any metal is a very good conductor compared to non metals, and a very poor insulator. Conductor is opposite of insulator. They are measures of how much heat is transmitted through a material.

As an example, hold a wooden spoon in one hand, and a metal spoon in the other. Place the ends of both in hot water. The wood is a good insulator, the metal is a very bad insulator.

Emissivity is how much heat is radiated out from a material. You'd notice this if you heated gold and aluminium to the same temperature. The glow from aluminium would feel warmer on your face than gold.

What the engine cover lining is doing is reflecting the heat. Generally metals are better at this than non metals. It also depends on the wavelength of the heat radiated from the engine. For some wavelengths, silver is better than gold. You can see the graph on the wiki page http://en.wikipedia.org/wiki/Reflectivity

Interestingly, this brings us onto selective surfaces which absorb heat quicker than they emit heat, which is good for heating solar panels. http://en.wikipedia.org/wiki/Selective_surface

Sorry to be picky, but it is a technical forum!

Sure gold is a thermal insulator. It's not semantics, it's technical terminology what it's at stake.

Heat transfer occurs by convection, radiation or conduction (duh!). Gold is a poor conduction insulator and a very good radiation insulator for infrared wavelengths (the range of almost-100% reflection starts at the infrared while it blocks about half of the visible light, that's why it's used in astronaut helmets: you can see but you're not fried).

It is also very cheap: a space helmet uses only 0.1 grams of gold to block almost all infrared, that's worth about 8 dollars.

If you want to appear to be rich but spend very little money, coat your heat sensitive areas with gold foil (available at many paper vending sites):



It's very efficient on a per weight base, because very thin layers work well, and few materials can produce layers so thin: that's why it is used at the back of F1 seats and on top of some engines.

Even McLaren F1 sports car has it on the engine cover:


It is immune to rust when heated, something that's not true of silver or aluminium, so it keeps its reflectivity. Thermal blankets doesn't last long around exhausts, much less stay pretty, as I can attest by personal experience.

Gold barriers are so light that they are used in many space probes. It seems like gold foil, but it's not. The method is called multilayered thermal insulation, probably the most efficient method of thermal insulation by weight. The fundamental idea is that radiation and reflection are balanced: the insulator receives as much thermal energy as it radiates and reflects.

Multi layer thermal insulation at the Large Area Telescope - Goddard: ten layers of very thin Mylar plastic, covered in gold, insulate the probe from almost all the heat. I wonder when we will see it in F1 (or notice it, if it's already used)

And for those of you lost souls who don't take Ciro's word for it;

http://en.wikipedia.org/wiki/Thermal_insulation