NEON- Sintering and burning

To: neon-l@lists.io.com
Subject: NEON- Sintering and burning
From: neonthom@earthlink.net (Tom U.)
Date: Sun, 1 Sep 1996 18:52:41 -0700 (PDT)
Reply-To: neon-l@lists.io.com
Sender: owner-neon-l@io.com
Ed (eduzuzio, that is) wrote:
>I am going to lean in Dirk's direction and guess the coating or binder is
>>helping the staining. Could be that the binder was not sintered at the
>factory >or the units were bombarded to the extent of burning the coating.
>I suppose the >rest of the box of glass would provide a few clues. While
>bombing post coated
>glass you can tell during the pocess if the tubes were baked properly.
>Tubes >that have been coated with suspension and not properly baked yield
>similar >results. At the very least the light from the tubes is sort of
>gray...
>Peace

I know this post was a while ago, but I had it on my list to respond to.
I'm interested in hearing more.  While visiting the Dutchies and Neon Lewa
and watching them pump, I noticed a difference between the dry powder units
being pumped and the liquid suspension ones.  You could almost watch the
difference in pressure increase with the dry powder units since they'd not
been baked out.

That is what the sintering process is, right; the tube is heated just below
the melting point to fuse the phosphor particles to the glass?  If so, is
that what I saw with the dry powder units; more than usual gasses being
released as the phosphor particles become fused by the heat and pressure?
Is it the binder outgassing or a pressure build up from all that activity
(or is that one and the same)?

At any rate, Ed's post made me wonder about seeing that in precoated
tubing.  He seemed to imply that it does happen if the tubes aren't baked
out sufficiently.  I've never really noticed anything in precoated tubes
that I can compare to watching this happen at the Dutch shop.  At Neon
Lewa; it was such a contrast between the oven baked tubes and the dry
powdered, it was subtle, but I could tell.

Ed also mentioned burning the coating during bombing.  I know that I've
done this on occassion and am curious if anyone could speak to this.  At
what temp. does this happen.  I know that when I've made the error and done
this, it's a result of bringing the glass temp. up too fast and then having
to heat the electrodes after the glass has reached temp.  So, the glass
ends up getting hotter than it should.  What's the upper temp. limit for
damaging the phosphor in precoated tubes, does it vary by manufacturer,
phosphor, etc.  I'd say from my experience I've seen it happen around a
tight window within 250-275C, yes/no/higher/lower?

Thanks,

Tom U.