Hi, Does anyone have any idea where I should go to find out the answers to those questions? (1) What are the best liquid conductors in term of low resistance, and what are the resistance? (2) How stable are those materials? (3) Are they corrosive? (4) Does the conductivities change if temperature change?
Thanks
Nick.
I believe mercury is pretty good, as far as liquid conductors go.
0.000000961 ohm-m is its resistivity.If you can guarantee room temperature or warmer environments, there are other metals and metal alloys that are liquids. If you don't mind
100-200C, you can use sodium and other alkaline metals.
Most liquid metals can cause trouble for other metals through liquid metal embrittlement, but can be avoided with the right alloys. The alkaline metals have a reputation for causing corrosion in metal piping.
Always. The question is, how sensitive is your application to changes in conductivity? The difference in mercury's conductivity between 20C and 200C isn't much.
Typically (always?) the conductivity of a metal goes down as the temperature goes up. So, a metal that is liquid at room temperature (e.g. mercury) should show a decrease in conductivity as temperature goes up. You should be able to find a tilt switch with a little sealed container of mercury contacted by two electrodes in the "on" position--perfect for experimentation!
Grant
Try Google
"temperature conductivity metal" - 230,000 hits
Mercury would work nicely. "Stability" and "corrosive" are relative terms.
Conductivity is proportional to temperature. QED.
Thanks to both Mike, Uncle Al, Grant and everybody who responded. My required range of temperatures is -40C -- 70C. The low the better on ohm-m readings. Be able to stay in a copper or aluminum container under heavy load of electricity for 20 years.
Nick.
Why not just use alkali metal ammonia solutions?
Why do you need a liquid? Is noise an issue? Wouldn't you want a positive engaging contactor, even a vacuum switch under high loads?
Can SCR's work for your app?
We used to pass hundreds of amps (DC) through a rotary contactor constructed from an iron donut shaped pot (think of a donut cut in half, filled with mercury). This had a rotating shaft passing through the center, with Nickel/Phosphorus coated copper fingers attached for current transfer (kind of like a "commutator" of sorts). We coatd the mercury with a heavy machine oil to supress the vapor pressure.
Worked like a champ (as long as no one tipped the assembly ~300# strongback), and most of us, at least are still alive some 30 years later.
As always, YMMV, of course... no guarentees
John
I am sure that your health & safety & environmental officers would have had conniptions if they heard about that! ;-) Just tell 'em "it's good for the gonads brother". And the switch probably lasted 30 years or did someone forget to train the new guy on oiling the contactors... Ah, the good old days...
Thanks for the tip and the link. There are tones of article on the web about these solutions. I tried but have not yet find answer: (1) Do you know at what temperature those solution stay liquid? (2) How are they compared with mercury in term of conductivity? (3) Are they very corrosive?
Nick
This doesn't sound very realistic. I think conductive liquids would certainly be corrosive these metals over that time frame. In addition to the inherent corrosivity of the liquid to the metal, you must consider the charge transfer reactions (how the charge moves from the metal to the liquid and back). These will involve dissolution of metal and/or consumption of the conducting liquid (except when using liquid metals) (e.g. water conducts by breaking down into hydrogen and oxygen). Often the resulting concentration gradients cause the current carrying ability to become diffusion limited (the bulk conductivity of the liquid will no longer be relevant). Good luck,
Chris
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