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I was wondering what kind of properties i should be looking for when selecting ideal materials for electrodes in a conductivity sensor measuring the conductivity of liquids (1,1,1,2-Tetrafluorethane). The liquid is really resistive (about 10^14 ohm-cm) and is non-corrosive. I found mentions of stainless steel and titanium electrodes in commercial conductivity sensors but maybe there are others more suited to high resistivity fluids, i'm not sure. Thanks in advance.

J. Doe
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  • Platinum is a popular material for electrodes in electrochemistry, but all you really need is something that won't react with your fluid. I don't think R-134a reacts readily with metals, but you should check that it won't dissolve any wires' insulation. – Hearth Mar 24 '19 at 17:33
  • @Hearth yh it doesn't react with metals or dissolve any insulation. Was wondering if you know why platinum and these other metals (as well as graphite apparently) in particular are used as electrodes? Why not brass for example or other metals? Thanks. – J. Doe Mar 24 '19 at 19:04
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    Platinum is used because it's the closest thing you can get to a chemically inert metal. Graphite is used because it's cheap and resists chemical attack. Stainless steel is also chemically resistant and cheaper by far than platinum. You might see a pattern here! Non-consumable electrodes used for electrochemical processes tend to be as chemically resistant as possible. – Hearth Mar 24 '19 at 19:22
  • @Hearth thanks for the help. Yh that makes sense. – J. Doe Mar 24 '19 at 20:16
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    I think mention should also be given to gold coating on copper electrodes. Gold is quite inert and can perform this function with incredibly thin platings. Its malleability may also help with the task of ensuring the plate is smooth. – K H Mar 24 '19 at 21:47
  • Is there something dissolved in the R-134a? By itself, up to a temperature of several hundred K, conductivity should be far lower than the value you give. It should be as good an insulator as polyethylene. Unless this is being used with ionizing radiation?? – DrMoishe Pippik Mar 24 '19 at 23:09
  • @DrMoishePippik Do you mind me asking why you say it should be lower? Because there is nothing online about its conductivity. I gave the value from what i was told by the company i'm working with which says they performed an experiment somehow to determine this but have lost all records of it, except that conductivity value which they seem sure about (at room temperature, nothing dissolved, high purity). – J. Doe Mar 24 '19 at 23:16
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    Aromatic and substituted aromatic compounds are usually excellent insulators, because it would take a lot of energy to ionize them. Sorry, I don't have specific information about R-134a, but I'd guess it would be difficult to measure conduction of the unionized substance (i.e. below breakdown: see https://en.wikipedia.org/wiki/Dielectric_gas ) – DrMoishe Pippik Mar 24 '19 at 23:26
  • @DrMoishePippik thanks a lot for the info, will look into it. – J. Doe Mar 24 '19 at 23:30

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