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Potential in Pourbaix Diagrams

  • 1.  Potential in Pourbaix Diagrams

    Posted 06-11-2021 13:49

    Dear All,

     

    I'd appreciate your help with the following question.

     

    A semiconductor device is being powered up and working. The device has a metal plate that is subjected to a voltage of 3V (relative to the ground potential). The metal plate is covered by a thin layer of water. I am trying to assess the corrosion of the metal plate with its Pourbaix diagram.

     

    The electrode potential in a Pourbaix diagram is expressed relative to the standard hydrogen electrode (SHE). In the Pourbaix diagram of the metal, what is the electrode potential corresponding to this 3V of voltage?

     

    In general, how to translate the electric voltage (relative to the ground potential) to the electrode potential (relative to SHE) in a Pourbaix diagram?

     

    Meanwhile, I am reading some papers on the subject.

     

    Thanks,

    Wentao

     

     



    ------------------------------
    Wentao Qin
    Engineer
    On Semiconductor
    Phoenix AZ
    ------------------------------


  • 2.  RE: Potential in Pourbaix Diagrams

    Posted 06-12-2021 01:07
    Wentao,
    First, let me understand the question. The metal in question is subjected to 3V with respect to the ground.  On that, water droplets or a thin layer of water exist. Is that correct?
    If I understood this correctly, the next thing to know will be, does this water layer also in contact with any other metal or material that enables current flow between the metal and the other material ( metal).  If that happens this potential ( 3V) could seriously affect the corrosion.  If not, the corrosion will be entirely due to the water layer.  Thin water layers can cause severe corrosion, as atmospheric oxygen can reach the metal surface very easily-Raja

    ------------------------------
    V S Raja
    Professor
    Indian Institute of Technology Bombay
    Mumbai
    ------------------------------



  • 3.  RE: Potential in Pourbaix Diagrams

    Posted 06-14-2021 18:43

    Raja,

     

    The configuration is as follows.

     

    There is an Al line connected to the Cu plate. Both of them are biased at 3V relative to the ground potential, and a thin layer of water covers both of them.

     

    My questions are

     

    1.     what is the electrode potential (in the Pourbaix diagram) that corresponds to this 3V of voltage?

     

    2.     In general, how to translate the electric voltage (relative to the ground potential) to the electrode potential (relative to SHE) in a Pourbaix diagram?

     

    Thanks,

    Wentao






  • 4.  RE: Potential in Pourbaix Diagrams

    Posted 06-15-2021 07:31
    Wentao

    Let me try to respond to your following queries

    1.     what is the electrode potential (in the Pourbaix diagram) that corresponds to this 3V of voltage?

    Firstly, what is shown in the Pourbaix diagram is potential across an element of interest ( in this case Al) and the electrolyte measured with respect to a reference electrode, generally standard hydrogen electrode.  What you refer here is the potential of Al with respect to the ground.  Both do not correspond.

    Secondly, when the current flows across the metal it is not expected to cause any additional corrosion. Only, if the current leaves the metal into the electrolyte, would the metal gets affected.  Let me explain further.  If one considers, the corrosion of an aluminum wire of 10 cm and at its center over a distance of 1 cm length water layer exists. If one examines the corrosion of this location  with and without an application of voltage across the two ends of the wire, no significant corrosion variation can be noticed.

    However, the problem that you seem to have is that Al is in electrical contact with Cu.  If water layer exists at the junction, galvanic corrosion is expected to occur and in which case Al shall corrode preferentially. Here again, the current passing through Al-Cu junction, as long as it remains electronic and not become electrolytic, I do not see the influence of grounding on the galvanic corrosion
     

     

    2.     In general, how to translate the electric voltage (relative to the ground potential) to the electrode potential (relative to SHE) in a Pourbaix diagram?
    In my opinion, there is no correlation between the two.
    Hope it clarifies.



    ------------------------------
    V S Raja
    Professor
    Indian Institute of Technology Bombay
    Mumbai
    ------------------------------



  • 5.  RE: Potential in Pourbaix Diagrams

    Posted 06-15-2021 21:30

    Thank you Raja for your help.

    Do you have any materials on the subject to recommend for a reading?

    Thanks,

    Wentao



    ------------------------------
    Wentao Qin
    Engineer
    On Semiconductor
    Phoenix AZ
    ------------------------------



  • 6.  RE: Potential in Pourbaix Diagrams

    Posted 06-16-2021 00:53
    Wentao,
    Unfortunately, I am not aware of any literature specific to it. Wish you success in addressing this problem-Raja

    ------------------------------
    V S Raja
    Professor
    Indian Institute of Technology Bombay
    Mumbai
    ------------------------------