Re: Corrected di-el strength of gas

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "john cooper" <tesla-at-tesla-coil-dot-com> 


Here's a bit more information:

That table was merely a sample of what was listed, I just pulled out a few 
of the common and interesting ones.  The di-el strength is measured using 
U.S. standard ASTM D149 which uses symmetrical electrodes.  In the U.K. 
standard BS2918, one electrode is a plane and the other is a rod with the 
axis normal to the plane.

Because the di el strength (breakdown voltage) of gases strongly depends on 
the electrode geometry and surface condition and the gas pressure, it's 
generally accepted to present the data for a particular gas as a fraction 
of the di el strength of either nitrogen or sulfur hexafluoride measured at 
the same conditions.  The table I posted presents a comparison with the di 
el strength of nitrogen, which is considered = 1.00

The CRC Handbook doesn't specify which electrode pair is used but here's 
the possibilities:

TF-2-50 Type 1 electrodes - per ASTM D149 - 2" diameter electrode with 
edges rounded to 0.25" radius - for use with the 750-2-D149 or lower 
voltage units
TF-1-50 Type 2 electrodes - per ASTM D149 - 1" diameter electrode with 
edges rounded to 0.125" radius - for use with the 750-2-D149 or lower 
voltage units
TF-.25-50 Type 3 electrodes - per ASTM D149 - 1Ú4" diameter electrode with 
edges rounded to 0.0313" radius - for use with the 750-2-D149 or lower 
voltage units
TF-2-75 Type 1 electrodes - per ASTM D149 - 2" diameter electrode with 
edges rounded to 0.25" radius, 75kV rated - for use with the 775-5-D149 
units and 7100-5-D149 units
TF-1-75 Type 2 electrodes - per ASTM D149 - 1" diameter electrode with 
edges rounded to 0.125" radius, 75kV rated - for use with the 775-5-D149 
units and 7100-5-D149 units
TF-.25-75 Type 3 electrodes - per ASTM D149 - 1Ú4" diameter electrode with 
edges rounded to 0.0313" radius, 75kV rated - for use with the 775-5-D149 
units and 7100-5-D149 units

Just like zooming in on the moon with a tele-photo lens, the closer you 
look, the more detail is revealed.

John

 > > Air, 0.97
 > > Argon, 0.18
 > > Carbon Dioxide, 0.82 - 0.88
 > > Carbon Monoxide, 1.02 - 1.05
 > > Chlorine, 1.55
 > > Helium, 0.15
 > > *Hexafluoroethane, 1.82 - 2.55
 > > Hydrogen, 0.50
 > > Methane, 1.00 - 1.13
 > > Nitrogen, 1.00
 > > Neon, 0.16 - 0.25
 > > Nitrous Oxide, 1.24
 > > *Octafluoropropane, 2.19 - 2.47
 > > *Sulfur Hexafluoride, 2.50 - 2.63
 > > Tetrachloromethane, 6.21 - 6.33
 > >
 > > *used in industry and research as di-electrics
 >
 >
 >