Re: Color Fades in discharges

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Mddeming@xxxxxxx 

In a message dated 12/6/04 1:46:51 PM Eastern Standard Time, 
tesla@xxxxxxxxxx writes:
Original poster: dave pierson <davep@xxxxxxxx>

This, or a very similar, issue was addressed in the early days of
  'neon' lamp (as in advertising) development.  If i recall (I've a
  text around somewhere...)
Issues include:
  fill gas purity
  fill gas (as such: Oxygen is 'bad')
  LARGELY (if i recall) its an electrode issue:  the fields and
  temperatures peak at/near the electrode surface and, over time,
  accelerated (as noted) by current density) the electrode and
  fill gas can react.  Its tricky to get these to be stable over
  time.  electrode materials vary in their stability...

There are advantages to controlled operation to bake out or otherwise
remove contaminants/strays on glass and electrode surfaces....

''air' fill' as such, is likely never to be stable, as the discharge
  drives changes in the gases.

best
dwp



Hi Dave, All,
    Air as a fill gas, even at low pressure is going to contain many 
unintended compounds over time. The oxygen will react over time with any 
metals, carbon compounds, such as organic vapors from 
manufacturing/sealing. During the bad old days of atmospheric testing of 
nuclear weapons, burning the air ( 2O2+N2-->2NO2 etc.) was a common 
phenomenon in test areas. ( By the 1980s there were three times enough 
weapons in the Us & USSR  to combine all the atmospheric oxygen into CO2 & 
NOx, but that's another story)
    Over time, the container becomes contaminated with H2O, CO2, CO, NOx, 
WO3, ThO2, Cu2O, CuO, etc. Esoteric compounds such as XeO3 are highly 
unlikely. It would take some careful, old-fashioned spectroscopy to 
determine which compounds were causing the visible light changes. Tedious - 
Yes, Impossible - No,

Hope this helps,

Matt D.