From: charles.e.wood@medtronic.com (Chucker)
Newsgroups: sci.physics.plasma
Subject: Bizarre Plasma Cleaning of Platinum Parts
Date: 16 Apr 2004 07:12:19 -0700
Organization: http://groups.google.com


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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