Lambda-Eyde
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Anyone up for some platinum?
http://cgi.ebay.com/Platinum-Wire-Type-S-thermocouple-scrap-...
That piece of wire has a market value of about 1500$! Right now the bid is 102,50$.
If you're an investor or a precious metals chemist with deep pockets, this might be a very good chance.
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Contrabasso
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It sounds too good to be true! it may be..........
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stygian
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looks like a very fine specimen to me...
very fine solder 
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densest
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It looks like it could be platinum - the sheen is not like solder!
I expect some dozens of bids in the last 30 seconds. It'll probably go for more than it's worth. Platinum/rhodium wire is pretty expensive, though,
and if you need some...
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Contrabasso
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If it's a good trade then it's fine, but yes the final price will depend on several people trying to put bids on in the last few seconds, not on the
market value.
HOWEVER there IS a platinum scam recalled in another thread, and at anywhere near the metal price for this lot that would be a lot of money for a
fellow scientist to lose.
Caveat Emptor
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hissingnoise
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The seller's 100% positive rating looks good until you realise he's being rated as a buyer rather than as a seller.
The photo too, looks a bit iffy - the wire somehow looks overly flexible for platinum. . . ?
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woelen
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The wire looks quite realistic. I have 100% platinum wire and this is very flexible. It can be bent and when it is left on its own, then it does not
act like a spring which goes back to its original shape. I also have an alloy 95/5 Pt/Ir and this behaves like a spring and cannot be bent like the
shown wire. So, the presence of some other metals highly influences the mechanical properties.
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hissingnoise
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I have Pt and Pt/Ir wire too, woelen, so suspicion aroused by the seller's ratings may just have coloured my perceptions. . .
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jock88
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http://www.ebay.co.uk/itm/AST-Electronik-S-Type-Thermocouple...
Is this item worth the money?
If it is greatly underpriced I (of course) wish to be informed of this fact (don't go buying it )
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hyfalcon
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I would go for something more like this:
http://www.ebay.com/itm/Vintage-platinum-iridium-ring-wear-o...
Bit more substantial piece of platinum then that thermocouple.
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jock88
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I actually want a thermocouple, not cheap precious metals.
How would you know that the Pt/Ir ring is pure or close to pure before purchasing?
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DraconicAcid
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Quote: Originally posted by jock88  |
I actually want a thermocouple, not cheap precious metals.
How would you know that the Pt/Ir ring is pure or close to pure before purchasing? |
"Specifications: Inside diam. = 11/16"; outside diam. = 13/16"; thickness = 1/16"; weight = 2.76 grams (0.088 oz. troy)."
Those measurements may not be correct, because that gives me a volume of 0.0368 cubic inches, which is 0.603 cm^3. The density would then be 4.6
g/cm^3, which is closer to tin than to platinum.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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jock88
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I was going to purchase some Pt/Rhodium wire + some platinum wire to make a thermocouple.
How would I join/weld the wires together at the end or would just twisting together ge good enough?
I have oxy acetylene. Can I just meld the wires together?
What wire would make a good extension. I don't want to purchase a meter of precious metals.
EDIT
I see omega have some type C thermocouples. This one at 175 stg (not lovely).
XMO-W5R26-U-125-30-H-HX-6 3 Weeks GBP 175.00 Type C Thermocouple. 1/8" dia 6" long molybdenum sheath with Hafnia insulation and standard size
ceramic connectors
Thanks,
Mr 88
[Edited on 8-5-2015 by jock88]
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Sulaiman
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Thermocouples produce a voltage in the wires where there is a temperature gradient,
not at the junction (which is what I assumed for a long time)
it is named the Seebeck effect http://en.wikipedia.org/wiki/Thermoelectric_effect
So the junction must have good electrical conductivity,
just twisting the wires together will work
but the junction will become unreliable as the wires oxidise/corrode etc.
Ideally thermocouple extension wires should be of the same materials as the thermocouple, but
provided that there are no temperature gradients at the end of the thermocouple wires, then both can be extended by copper wire.
only if all four wires in the vicinity of the extension joint are at the same temperature as your measuring instrument!
[Edited on 9-5-2015 by Sulaiman]
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jock88
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THanks for that. I had always assumed it was at the actual interface between the metals.
I presume I can melt the Pt /Rh wires together using a reducing oxy gas flame.
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