Sciencemadness Discussion Board

Very high boiling point determination: how is it done ?

metalresearcher - 11-9-2012 at 08:46

Some elements have extreme high boiling points: Ta: 5400ºC, W: 5800ºC, Re: 5700ºC all hotter than the solar surface.
But my question is: how it it determined and often even to 1ºC (1K) accurate ?
See this site. http://en.wikipedia.org/wiki/List_of_elements_by_boiling_poi...

As there is no substance which can be solid at these temperatures, no thermcouple or resistance thermometer or even a crucible to hold the boiling metal exists.

I can only imagine enclosing a small sample of the metal in a kind of diamond cell which is vacuum and in a strong magnetic field keeping it levitated while induction / electron beam heating the sample.
And then measuring the inside pressure which is the saturation pressure at the current temperature. But, again, no pressure gauge can withstand this. Other option is observing the blackbody spectrum, but that is difficult again due to lack of 'spectral classes'.
I think measuring temperature of the in some cases much hotter surface of a distant star is easier as the spectrum (and chemical composition) of a star tells about the temperature.

Your ideas ?

watson.fawkes - 11-9-2012 at 09:28

Quote: Originally posted by metalresearcher  
But, again, no pressure gauge can withstand this. Other option is observing the blackbody spectrum, but that is difficult again due to lack of 'spectral classes'.
I think measuring temperature of the in some cases much hotter surface of a distant star is easier as the spectrum (and chemical composition) of a star tells about the temperature.
Atomic and molecular spectral lines are overlaid on top of the black-body spectrum. When measuring high temperatures by spectroscopy, you first remove these spectral lines and then fit the remaining data to the theoretical equation for black-body radiation.