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Re: Conductivity of Copper



At 10:30 AM 3/7/01 -0600, Steven T. Ratliff asked a simple question:
(1) Is deoxidized copper the same as OFHC (oxygen-free high conductivity)
copper?

Simple answer: No.

Longer answer: I quote from
http://www.alascop.com/HTML/pdf_files/indiv_sections/Copper_pages.pdf

****ELECTROLYTIC TOUGH PITCH COPPER
ETP has long been the standard type of commercial wrought copper used for
the production of wire, rod, plate, sheet and strip. The presence of very
small amounts of oxygen affects some of the mechanical properties to a
measurable extent, but this grade of copper is entirely satisfactory for
most of the usual processes. It is easy to deep draw, spin, or stamp. It is
the logical choice for bus connections, switch and panel boards, circuit
breakers, and power feed systems in general, because of high electrical
conductivity, ease of soft or silver soldering and ability to receive a
silver plate. Expansion joints, kettles, vats, pressure vessels, distillery
and other process equipment are readily formed from the metal. Its
resistance to corrosion assures a long life. For welding and high
temperature applications see Deoxidized Copper and Oxygen Free Copper.

****Phosphor Deoxidized, Residual Phosphorus (UNS C12200)
DEOXIDIZED COPPER is produced by introducing phosphorus or another element
as a deoxidizing agent to assure the removal of all oxygen. This type
differs from ETP Copper in that it has lower electrical and thermal
conductivity, but it forms and bends more readily in difficult
applications. It is particularly suitable for applications requiring hot
working, annealing, soldering, brazing or welding, operations in which the
residual phosphorus prevents the absorption of oxygen by the copper. If
copper sheets or plates are to be welded, this type of copper is preferred
because of its resistance to embrittlement by reducing gases, such as
hydrogen, at high temperatures. Deoxidized Copper is widely used for pipe
and tube for plumbing, gas and oil lines, refrigeration, condensers, pulp
and paper lines, brewery and distilling tubes, brew kettles, vats and
indus-trial tanks. Our stock of Copper Tubing is Normally
PHOSPHOR-DEOXIDIZED COPPER, (DHP) Composition: Copper (Min.) 99.90%
Phosphorus .02%

****High Conductivity, Carbon Deoxidized, OFHC ® (UNS C10200)
OXYGEN-FREE HIGH CONDUCTIVITY COPPER is produced by melting and pouring
Copper in the presence of carbon or carbonaceous gases, so that no oxygen
can be absorbed. No deoxidizing agent is required. It combines most of the
advan-tages of ETP and Deoxidized Copper. It is excellent for deep drawing,
has a high electrical and thermal conductivity, and resists the embrittling
effect of reducing gases (hydrogen) on equipment operated at elevated
temperatures, although it is not as suitable for welding as Deoxidized
Copper. This type of copper is specially good for severe deep drawing,
spinning, and close radius bending, and is used in electronic tubes or
similar applications because it makes a perfect seal to glass. For
electrical uses requiring conductivity higher that Deoxidized Copper
affords, Oxygen-Free Copper is usually specified.


(2) What is electrolytic copper?

Crude copper is used as the anode in an electrolytic cell. Very pure
copper is electroplated onto the cathode.



(3) What is the resistivity of non-OFHC copper? I was wondering how much
difference the OFHC makes.

*) At room temperature, there's not a heck of a lot of difference in
electrical properties between OFHC and good non-OFHC. That's because at
some point, the resistivity is dominated by thermal scattering, and the
impurity scattering is irrelevant.

*) OTOH, by going to cryogenic temperatures you can get rid of the thermal
scattering, and then you really, really care about impurities in general
and oxygen impurities in particular. There is a thing called the Residual
Resistivity Ratio that tells you how much you can improve the resistivity
by cooling the thing off before the remaining impurities limit you. RRR
values of 100 or 200 are not uncommon, and you can do better, e.g.
http://wwwsoc.nacsis.ac.jp/jim/jour/tran/t97de/t97de_ab9.html

And by the way..... Once upon a time, somebody wanted to see how far he
could go in obtaining a really big RRR. He used mercury because he knew
how to make really pure mercury.... and the rest is history:
http://www.nobel.se/physics/laureates/1913/onnes-bio.html