From:
"PJ" <atmospheric_plasma@hotmail.dotcom>
Newsgroups:
sci.physics.plasma
References:
<c5pj8n$47fi$1@saturn.cs.uml.edu>
Subject: Re: Bizarre Plasma
Cleaning of Platinum Parts
Organization: none
Date: Sat, 08 May 2004
20:08:38 GMT
ZZ
You are seeing something called the hollow
cathode effect... Basically at
certain
pressure regimes you get electron trapping inside the cylindrical
parts... This greatly enhances ionization within the
cylindrical part.
Your parts are probably getting red hot... The platinum is most likely
forming an
oxide that is being sputtered and evaporated onto your titanium
fixture. This effect is common at this pressure. You might try operating
at a different
pressure to reduce this. If you hit the
"perfect" pressure
you might get them all to light up!
PJ
"Chucker"
<charles.e.wood@medtronic.com> wrote in message
news:c5pj8n$47fi$1@saturn.cs.uml.edu...
>
>
Hi, I have a thought experiment regarding something I'm seeing when I
>
plasma clean platinum parts. I'm
currently using a
> desktop plasma cleaner at the following settings to
prepare platinum
> parts for platinization:
>
>
Time: 15 minutes
> Gas: Oxygen
> Flow: 25ml/min
> Microwave Power: 250 Watts
> Pressure: 40 Pa (0.30 Torr)
> Fixture
material: Titanium
> Part
material: 90/10 Platinum/Iridium
> Part shape: Hollow cylindrical part about 0.1"
diameter and 0.5" long
>
> 100 parts are held against
individual V-grooves with a neoprene
> O-ring. There are 2 rings, an inner ring holding 40
parts and
> an outer ring holding 60 parts.
> The weird thing
I'm seeing is that a couple of parts will glow orange
> on the outside
ring, burning through the O-ring and
> discoloring the titanium fixture
a bluish-gold at the particular
> v-groove. My initial reaction is the
glow is due to heat.
>
> What could be causing this? I'm a mechanical engineer by training
so
> I'm way out of my element.
Could it be the platinum is
> acting as a catalyst? Does it have something to do with the
microwave
> energy? How about a
secondary plasma? Is a current be
developed
> between the fixture and part, generating heat?
>
>
Any thoughts would be appreciated.
>
>
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