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May 2009

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Subject:
From:
"Craig S. Schwandt" <[log in to unmask]>
Reply To:
JEOL-Focused Probe Users List <[log in to unmask]>
Date:
Tue, 5 May 2009 07:27:55 -0500
Content-Type:
text/plain
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*

Ritchie,

Melting rocks, especially small volumes under vacuum can be tricky,
because it isn't simply a matter of contamination of the metal or the
carbon. In fact you have to be concerned about the vessel in terms of
solid-solid fO2 buffers.  The oxidation state of iron in particular is
very sensitive, so depending on the temperature achieved in your carbon
coater, which is extremely difficult to control and worse yet to try and
measure, your rock compositions are likely to vary a lot.  I suspect
this is why you can't find much about the proposed method.  You really
need a one atm gas-mixing furnace if you want to melt rock powders
without a flux reproducibly.  Alternatively, if you wanted to experiment
you could use a sintered pellet that is at least cohesive.  You can
press your powder with a small pellet press, suspend/support the pellet
with a loop of platinum wire and use a propane torch to provide a fusion
crust that holds the pellet together enough for gentle handling.  You
might then be able to use the laser to ablate the material and check
with depth the homogeneity of the powder, or perhaps embed it for EPMA,
but it will not likely polish well and be heterogeneous.  Unfortunately,
melting rocks isn't the simplest task.

Craig
 
Craig S. Schwandt, Ph.D.
Senior Research Scientist
 
McCrone Associates, Inc. 
850 Pasquinelli Drive
Westmont, IL  60559-5539
 
Reception: 630-887-7100
Office: 630-734-2422
FAX: 630-887-7417
[log in to unmask]       www.mccrone.com 


-----Original Message-----
From: JEOL-Focused Probe Users List [mailto:[log in to unmask]] On
Behalf Of Ritchie Sims
Sent: Monday, May 04, 2009 8:03 PM
To: [log in to unmask]
Subject: [PROBE-USERS] rock bead fusion method?

JEOL Probe Users Listserver

Moderator: Ellery Frahm, [log in to unmask], Electron Microprobe Lab,
University of Minnesota

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*

Hi

Is anyone out there using a metal strip or graphite method to fuse small
(maybe 100mg or
so) amounts of rock powder without flux into a glassy bead which can
then be mounted, cut, and polished for EPMA or LA-ICP-MS analysis?

I'm hoping to convert my (t)rusty old Edwards 306 vacuum coater into
such a device but I'm trying to avoid reinventing too many wheels.

I remember seeing such a method setup at UC Davis about ten years ago
but I haven't had any luck following that one up.

We actually want to use LA-ICP-MS so it seems to us that a graphite boat
setup would be better from a contamination viewpoint than a metal strip.

Any references, tips, experiences etc would be most welcome.

cheers
Ritchie Sims
Geology
Auckland University
NZ

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