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GM7HUD > TECH 28.05.06 16:47l 60 Lines 3026 Bytes #999 (0) @ WW
BID : 8F3785GM7HUD
Read: DL1LCA GUEST
Subj: Re: Resistivity of Chromium
Path: DB0FHN<DB0RGB<DB0MRW<OK0PPL<DB0RES<DK0WUE<7M3TJZ<F6CDD<ON4HU<GB7YFS<
GB7LGS<GB7ESX
Sent: 060528/1221z 17201@GB7ESX.#31.GBR.EU $:8F3785GM7HUD [Witham, Esx]NNA V3.1
VK2ZRG wrote:-
> The resistance of chromium in chromium plating is what I would like to know.
> Interesting what you said about the thin films. I have a Russian book on metals
> that says the properties of chromium, including conductivity, change
> drastically at 37 Celsius.
Once upon a time we all relied on published reference standards such as
those you have referred too in previous bulls. Nowadays, more and more
people will simply look up stuff on the web and take the 1st value given as
gospel. Sadly referrence works on the web often lack the quality control
that paper published versions have.
In addition there is a huge amount of plagiarism and straight theft on the
web. That makes trying to check out anything harder. You never know whether
another site has simply stolen the data from the 1st site you checked. In
addition to that, there are simple "Adsense" spam sites. These exist to
milk money out of Google advertisers, they regurgitate existing web content
but plaster it with ads and links to other sites.
The end result makes a simple search for some data harder than it should be
nowadays. If I still worked for a proper engineering company then I'd have
wandered over and looked up the answer in the "Rubber" book (The CRC
Handbook of Chemistry and Physics). But I don't, so I can't. However, most
websites are giving figures around 12.4 to 13.2 for Chromium. Where a
temperature is specified then it's 20C.
One site gave the resistivity as 18 and the temp coeff for resistivity as
5900 ppm/C. It was the only site to mention the Neel effect in Chromium
which occurs at 311K (38C).
The Neel effect is named after the 1970 Nobel prize winner who pioneered
work on magnetochemistry. In Chromium at 311K the metal (and it's the only
pure metal to do so) enters a spin density wave state. IANAP (I am not a
physicist) so don't ask me to explain other than free electrons that were
used to conduct current get paired up and can no longer be used in current
conduction. The result is at this temperature there is a step change in
resistivity.
So I can't help with a definitive value for resistivity but at least you
can go and look up Neel effects if you are interested. I suppose the
important thing is that you know it occurs above 38C.
If you can't find an definitive answer you could try measuring similar
chromium and copper rods. A simple schoolab physics experiment involving a
variable power supply and a couple of DVMs should at least confirm the
values being quoted. You could also warm the chromuium bar up with a small
blowtorch and observe the Neel effect cut in.
Or you could cut and run with 12.5 as it's probably good enough in reality.
If you want a CRC handbook cheap, (they're big and packed full of stuff)
then probably the best place to look is on Abebooks. Abebooks is like
Amazon but for secondhand books. There's an Abebooks service for Australia
and NZ now at http://dogbert.abebooks.com/docs/ANZ/
UK readers should try http://www.abebooks.co.uk
73 de Andy GM7HUD
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