Then why do the connector manufacturers (like Pomona and others) promote them as such. And companies such as IETlabs, Agilent, Fluke that should know these things also claim it?:
http://www.ietlabs.com/bp-1500-bindingposts.html
http://www.home.agilent.com/en/pd-1000000309%3Aepsg%3Apro-pn-11058A/low-thermal-emf-banana-to-banana-jumper-set?&cc=AU&lc=eng
http://assets.fluke.com/manuals/54407002iseng0200.pdf
http://www.lowthermal.com/cables-and-connectors.php
The use of tellurium copper instead of beryllium copper or brass, as well as gold plating with no nickel under plating ensure these posts exhibit the lowest contribution of thermal EMF.
Gear from the masters like Keithley also use "low EMF" tellurium copper input jacks I believe.
It's not a tellurium on it's own, it's something to do with the interaction with the other platings. Perhaps tellurium allows direct gold plating whilst the others don't?
Its low EMF because its Copper instead of Brass not because its Tellurium Copper instead of pure Copper. If you scan the info from many suppliers below you will see the larger uses of Telurium copper are very mundane parts that could care less about thermal EMFs. BUT they all have one thing in common, they are machined items not stamped.
@ rolycat
If the minimally better oxidation resistance was why it is superior why do many gold plate the Tellurium Copper?
From Metal suppiers online
Applications Welding and cutting torch tips, products requiring high conductivity and high machinability.
From ANCHOR BRONZE AND METALS
Applications
Forgings, screw machine products and parts requiring high conductivity, extensive machining, corrosion resistance, copper color, or a combination of these; electrical connectors, motor and switch parts, plumbing fittings, soldering coppers, welding torch tips, transistor bases and furnace brazed articles.
From FARMERS COPPER
Farmer’s Copper Ltd. inventories C14500 Tellurium copper round rod. C145 Tellurium is adapted for use in high-speed automatic screw machines. The copper telluride precipitations become finely dispersed throughout the matrix and assist in chip breakage into short pieces, thus enabling a much higher machining speed than with pure copper. Copper 145 Tellurium has a machinability rating scale of 85%, compared to pure copper of 20%, thus insuring longer tool life. The high conductivity of tellurium copper makes it a suitable material for electrical applications, and is an outstanding alloy for the production of hot forged products.
Tellurium C145
Typical applications
Electrical Switches on power semiconductors
Welding Torch tips
Transformer & Circuit-breaker terminals
Fasteners
From LUVATA WOLVERHAMPTON
Pure copper is a very ductile metal. For many applications this is an advantage, but not when copper is to be machined. However, the cutting properties of copper can be significantly improved by alloying copper with half per cent of tellurium. The electrical and thermal conductivity and ductility of this free machining copper are only slightly altered.
The effect of tellurium is based on copper telluride precipitations in the microstructure. These precipitates have the effect of cutting the chips into short pieces thus enabling a much higher machining speed than is possible with pure copper. On a machinability rating scale with 100 for free cutting brass and 20 for copper, tellurium copper is rated at 90. The tools last longer too.
Tellurium copper is resistant to hydrogen embrittlement. Electrical conductivity is high, approx. 52 m/W mm2 (90% IACS).
From ESPI METALS
Tellurium copper’s resistance to hydrogen embrittlement and high conductivity make it a good choice for electrical applications, especially those which require extensive machining. The addition of tellurium to copper results in short, clean chips and allows cutting speeds of five times those used with pure copper, with much less wear on tool life. Also, the electrical conductivity, thermal conductivity and ductility are only slightly altered from pure copper. Typical applications include welding tips, switch gears, bolts and studs, and relay parts.
From Key to Metals website
Conducting springs, contacts and similar highly stressed members that also may have to be formed may use either chromium copper or beryllium copper. Parts are shaped soft and then strengthened by heat treatment. Parts that must be highly machined and highly conductive are made from the free-machining coppers. Widely used is tellurium copper, which has 90% minimum conductivity and a machinability rating of 80 to 90 (free-cutting brass = 100). Leaded copper (1% Pb) or sulfurized copper is also used because of the 80% machinability rating, with most other properties similar to copper. If tensile strengths of 440 to 525 MPa are required at 80% machinability, heat-treated and hard drawn forms of tellurium-nickel copper may be chosen, provided electrical conductivity of 50% is permissible.
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