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Does a flame-heated red-hot metal emit electrons?

  1. Jun 30, 2014 #1
    Hello this is my first post in this forum.
    I would like to ask something relatively simple and I need a simple answer please, since I am not a physics expert.
    Does a metal that has been red-hot heated using a flame, emit electrons? (like the electrically heated cathode of a vacuum tube does)
    Last edited: Jun 30, 2014
  2. jcsd
  3. Jun 30, 2014 #2


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    hi there
    welcome to PF :smile:

    have a look at this wiki link on thermionic emission

    if that doesn't help, try typing thermionic emission into google as I did, there are many, many links of interest

  4. Jun 30, 2014 #3
    So a heated metal does emit electrons. Thanks a lot Dave!
  5. Jun 30, 2014 #4


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    However, it isn't quite so simple.
    As the Thermionic electrons in a vacuum tube leave the cathode, it becomes positively charged. this limits the total number that will be lost before there are as many being re-attracted to the cathode as are leaving it (so called space charge around the cathode). If the rod is in air and not a vacuum, those electrons will be rapidly slowed down (collisions with air molecules) and will soon recombine with the rod again. The space charge will be restricted to a region very close to the hot rod.
    If a vacuum tube is driven correctly, the thermionic electrons will be attracted to an Anode (+) electrode and a current will flow rather than a space charge being formed.
  6. Jun 30, 2014 #5
    Thank you, this makes sense.
    However, if a flame is allowed to burn the cathode electrode and at the same time placed between the hot cathode and an anode, then the flame conductivity should allow electrons to pass through it to the anode, eventhough no vacuum is used. Effectively, it should be possible to build an open-air vlame diode this way.

    Reading at your reply, I was wondering, what if one could place the anode very close to the cathode, so that the space charge electrons can flow to the anode without the use of vacuum?

    Another thought is that, what if one could use higher potential between the cathode and the anode, so that no cathode heating is needed at all? If this works, it could be called an "electrostatic air tube" or something like that.
  7. Jun 30, 2014 #6


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    I think that's what most of us would call a "spark". Lol
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