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Spark disk toy




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From:  Robert W. Stephens [SMTP:rwstephens-at-headwaters-dot-com]
Sent:  Friday, February 06, 1998 8:40 PM
To:  Tesla List
Subject:  Re: Spark disk toy


> From:  gweaver [SMTP:gweaver-at-earthlink-dot-net]
> Sent:  Tuesday, February 03, 1998 11:18 PM
> To:  Tesla List
> Subject:  Re: Spark disk toy
> 
> I know the thing your talking about.  I saw 2 at a Halloween supply store
> just before Halloween and one made White sparks and the other one was BLUE.
> Spencers had one also that made White sparks.  I took some measurements so I
> could make one. I also did a post on it about a week before Halloween.  I
> got a sheet of plexaglass and was going to have the 23" diameter circles cut
> out with a laser cutter at a company down the street from where I work.  No
> problem they said, we can cut the disks, $40.00 for the computer program and
> $180.00 and hour labor.  Turns out the labor costs will be about $5.00
> because the laser can cut out the 3 disks in about 2 minutes.  The plastic
> is a bit expensive also.  If I have them cut out several disks at a time the
> total cost would be a lot less per part but what would I do with enough
> parts to make 10 of these things.  The cost for 10 units would be $5.00
> labor, $4.00 for the computer program plus the cost of the plexaglass.  If
> 10 people on the list all wanted one of these things I would go back and
> talk serious to the laser company about making 10 of them.  They look easy
> to make.  The power supply on the back was 2.5" square so it couldn't have a
> lot of power being so small.  The electrode in the middle was probably the
> head of a screw through one of the disks.  The disks are glues together and
> filled with some type of gas like argon.  The welder at work uses argon so I
> can get some free gas.  
> 
> Gary Weaver
<snip>

Gary,

Easy as pie right?.....Unfortunately not!  Forget employing plastic 
disks for any plasma display project like this you propose.  In fact, 
try not to use ANY plastics in the construction of an evacuated or low 
pressure inert gas electrical discharge vessel. The plastic will outgass bigtime
as the plasma etches it.  Your pumped down and freshly charged display will
quickly change colour and then go dead.  When small amounts of plastic are
bombarded by ions in an otherwise glass plasma globe or similar 
display, being accelerated to great velocities by the high field 
gradient electric field, the surface molecules of the plastic become vaporized and
deposit themselves quite efficiently over the entire interior of the glass portions
of the display.  This is just as aluminum is deposited in a vacuum 
chamber onto glass to make front surfaced mirrors.

If you wish to work with plasma displays successfully, I suggest you 
stick with glass panels.  The other problem in a homemade device is 
that you often cannot do a vacuum bake out on the completed vessel to 
make it clean enough to last for any appreciable time.

If your display is just filled with low pressure air and has a vacuum 
pump sucking on it continuously, then this is another matter entirely 
and almost anything will work.

Good luck,

Robert W. Stephens
Director
Lindsay Scientific Co.
RR1 Shelburne, ON Canada L0N-1S5
Tel: 1-519-925-1771   Fax: 
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