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Source of Copper oxide - pics included

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  • 08-05-2017 10:44pm
    #1
    Dubh Geannain
    Registered Users Posts: 3,397 ✭✭✭


    Hi, I'm not a chemistry expert and am looking for possible theories of what caused the build-up of copper oxide seen in the pic below.

    34410984891_de92069689.jpg

    Any theories appreciated. I'm looking at a Double Action push button with the common pin being the centre stud. In the picture you can see a green material deposited between all metal elements along the black plastic separator.

    Evidence that a high level of moisture was possibly in around the contacts at some point can be see on the top of the switch. Note the shine on the black plastic
    34410985691_6cc7170ce4.jpg

    An SEM analysis highlights the material to be Copper Oxide. I'm assuming the source is the contacts themselves, which were gold plated.
    34410983911_5d733f9cb9.jpg

    My theory is a high level of moisture, coupled with a potential difference that existed initially (24 Vdc) causes electrolysis to happen. But I've no idea how it came to be deposited on the plastic separator if that is the case.

    Another colleague suggested micro fretting with the copper oxide being attracted to the plastic by static.

    Like I said, I'd be interested to hear any theories.

    Cheers


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    #2
    SOL
    Registered Users Posts: 1,155 ✭✭✭SOL


    I guess it's actually basic copper carbonate with it having that green colour. Presumebably its coming from the brass components which will corrode if you leave them with water on them.

    If there is moisture and a constant potential difference you can get black wire rot which forms copper oxide which turns into copper carbonate after some time in the air (like the way copper buildings go green). Black wire rot is a fairly common problem in marine environments or for people who left model airplanes in the garage all winter with the batteries left in...


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    #3
    bduffy
    Registered Users Posts: 405 ✭✭bduffy


    Hi,
    I'd be interested to see where the salts came from! The EDX of the green spots seems clean, but the absence of Zn would indicate that the brass may not be a source (although it may have been omitted from the quant table). It looks like a 7-10keV scan which wouldn't pick up the strong Zn signal above 8keV.
    Saying that, signals with a % less than 0.5 are only qualitative anyways.
    Dealloying is also possible but you'd need a galvanic couple......maybe the moisture was sufficient to enable this?
    Do you have a high resolution image of the switch to see if there is fretting or microcracking ?
    Another question is how well adhered were the Cu deposits?


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