Question for anyone in to materials?

[bsodmike]

I've googled quite a bit, but unfortunately typing in 'platinum' causes one to be bombarded in links to jewellery stores.

I would like to know what causes Platinum (at least PT950 that is) to "feel" warmer than other metals like 18/22k white gold or even simple Sterling Silver.

I'm sure someone who has taken courses involving the study of materials/material sciences would know more...

Thanks!

[Mblaster]

Usually what makes one material feel warmer than another is how well it conducts heat, since the feeling of warmth/cold is actually heat energy transfering to/from your body. It's like how metal feels cold where wood doesn't, even if they are both at the same temperature (assuming that temperature is below the temperature of the part of you that's touching it! Otherwise the metal will feel hot where the wood doesn't).

Not sure if there are any other specific things relating to platinum, but I can't think of any.

[bsodmike]

Well, Pt has a higher density than most metals...which is why it is also much more heavier (for a comparable metal of the same volume).

I've not looked into the specific heat capacity of Pt (yet)..but maybe that has something to do with this as well.

I've found that putting on a WG ring feels far colder, than putting on a Pt ring. This also holds true for WG watches (such as the WG Daytona) and the Pt. Day Date.

Steel feels 'colder' than 18k WG/YG...

[chrestomanci]

It will be becuase of the differneces in the thermal conductivity. Basicaly, the higher the thermal conductivity of a matteral, the faster it removes heat from you when you touch it, so the colder it feels.

There is an article about in Wikipeda:

The numbers for each element are listed on the page for that element:
Platinum : 71.6  W·m−1·K−1
Silver: 429  W·m−1·K−1
Gold : 318  W·m−1·K−1

From those numbers we can see that platinum has a much lower conductivity than Gold or silver so it is not supprising it does not feel as cold to the touch.

Another factor would be the heat capacity, but they are all very similar, so in this case it will have no effect.

[MadduckUK]

i knew this just from reading the spiel in heatsink reviews. thats pretty sad

[finlay666]

Maybe your body reacts well to precious metals

[bsodmike]

Thank you chrestomanci, although I have a couple questions.

I found this data (for the thermal conductivity) for the following metals:

904L stainless steel (as used in modern Rolex wrist watches): 13.0 W/m.K
316L stainless steel: 21.4 W/m-K
Iron: 80.4 W·m−1·K−1

Platinum still feels far warmer than these metals...how come?

[chrestomanci]

Thank you chrestomanci, although I have a couple questions.

I found this data (for the thermal conductivity) for the following metals:

904L stainless steel (as used in modern Rolex wrist watches): 13.0 W/m.K
316L stainless steel: 21.4 W/m-K
Iron: 80.4 W·m−1·K−1

Platinum still feels far warmer than these metals...how come?

It could be the heat capacity of of the object you are holding. The lump of Pt you are holding is probably only a few grammes, as otherwise it would cost a fortune, but the steel (Fe) would typically be much larger. Even something small like a knife blade would weigh 10 times as much as a Pt wedding ring.

Even if the two objects your are comparing weight the same, the heat capacity per gram is different. Both elements have a specific heat capacity of around 25 J·mol−1·K−1, but Pt has a much higher atomic weight than Fe, (195 vs 56), so per gram Pt has a quarter of the heat capacity of Fe.

All this means that if you hold a Pt wedding ring in the palm of your hand, it will heat up to body temperature and not feel cold any more much more quickly than if you where holding an Iron object.

[Ferral]

It could well have something to do with conduction. Human body carries electricity and electricity moving through metals makes it warm. Higher the density of the metal the slower the current travels and thereefore doesn't get as warm.

Hence why copper is used a lot in electric components, current flies through that extremely fast.

[Steve B]

It could well have something to do with conduction. Human body carries electricity and electricity moving through metals makes it warm. Higher the density of the metal the slower the current travels and thereefore doesn't get as warm.

Electricity will only flow when there is a potential difference. Since the ring on the finger sits at the same potential as the human body, there would be no current flow. That is if the human body was capable of sourcing sufficient current, which it isn't afaik.

Hence why copper is used a lot in electric components, current flies through that extremely fast.

Conductive metals have similar electrical properties. Copper is used alot because there's lots of it and it's cheap. It's also quite easy to work with. Aluminium could be used instead, although it's more expensive.

[Ferral]

Just a theory!

Remeber doing conduction stuff in Physics at school nearly 20 yrs ago!

[bsodmike]

It could be the heat capacity of of the object you are holding. The lump of Pt you are holding is probably only a few grammes, as otherwise it would cost a fortune, but the steel (Fe) would typically be much larger. Even something small like a knife blade would weigh 10 times as much as a Pt wedding ring.

Even if the two objects your are comparing weight the same, the heat capacity per gram is different. Both elements have a specific heat capacity of around 25 J·mol−1·K−1, but Pt has a much higher atomic weight than Fe, (195 vs 56), so per gram Pt has a quarter of the heat capacity of Fe.

All this means that if you hold a Pt wedding ring in the palm of your hand, it will heat up to body temperature and not feel cold any more much more quickly than if you where holding an Iron object.

Thanks for the clarification So in essence, the smaller heat capacity and lower (sluggish) thermal conductivity are the reason for this.

[bsodmike]

Conductive metals have similar electrical properties. Copper is used alot because there's lots of it and it's cheap. It's also quite easy to work with. Aluminium could be used instead, although it's more expensive.

As for copper the reason it is used a lot is due to many free electrons in it's structure. When a voltage is applied, these free electrons (and holes) move through the lattice, and the nett effect is the flow of current.

The only electrical activity in the human body I can think of is at the neuron/synapse level and static electricity developed between hair follicles.

Steve's explanation of a potential difference is correct.

[MadduckUK]

Conductive metals have similar electrical properties. Copper is used alot because there's lots of it and it's cheap. It's also quite easy to work with. Aluminium could be used instead, although it's more expensive.

thought copper was more expensive than aluminium..

[Steve B]

As for copper the reason it is used a lot is due to many free electrons in it's structure. When a voltage is applied, these free electrons (and holes) move through the lattice, and the nett effect is the flow of current.

The same can be said for any conductor though.

Copper used to be cheap, but its getting more expensive as supplies begin to wane.
Its got good resistivity properties; I think the only metal which can conduct better is silver, but I might be wrong.

You are correct though Mike.

PS Sorry if i seemed a bit rude there Ferral, I didn't mean to be!

[Ferral]

Na its ok man!

Like I said just a theory, I am getting old and it has been a long time since I did physics at school!