Stable Isotope Geochemistry


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Irene Ellis <[log in to unmask]>
Reply To:
Stable Isotope Geochemistry <[log in to unmask]>
Mon, 11 Jul 2005 14:15:44 -0400
text/plain (112 lines)
Hello Dr. Giesemann,

I am very sorry to hear of this mess.

Your crucible is a true ceramic but your insulators may not be.  You did
not indicate the instrument or the exact source of the insulators.

A "ceramic" is a subset of the general class of insulating materials--
alumina (Al2O3), zirconia (ZrO2), hafnia (HfO2), are examples.  So is the
porcelain body of crucibles--a silica-alumina compound that is compatible
with high temperatures. Ceramics are usually powders fired to fusion at
high temperatures and are expensive.

An "insulator" is a material that does not conduct electricity.  Glass and
MACOR (mica filled glass) are insulators that are in use in some ion
sources, but they are absolutely NOT for high temperatures.  They are cheap
and easy to machine which is why they are used. They are much less strong
than ceramic insulators and some of us would like to ban them from any use
where they might get heated by mistake. The glaze in some crucibles is also
a glass and not compatible with 1200C.

I don't know what materials you have.  The "quartz" should not turn to dust-
-it manages to survive extended life in the 1000-1200C combustion area of
elemental analyzers. Fused silica may shatter on a single heating if it was
weakened in machining or by alkaline chemical residues.

I hope that you can take the opportunity to overhaul the insulating parts
of your ion source with true ceramics, you will find their superior
properties to be more than just ease in cleaning.

Irene Ellis
IsoTrace Lab, U of T

On Thu, 7 Jul 2005 09:27:07 +0100, Dr. Anette Giesemann
<[log in to unmask]> wrote:

>Dear Irene and others,
>we have been cleaning our source for years using the "scrape things off"
>method for ceramics, which is time consuming. So I was very happy to
>read that just baking out the ceramics is fine.
>Yesterday, we followed the procedure mentioned and the result was a
>mess !!!!
>Several parts of the ceramics stuck to the crucible and couldn't be
>removed, some had ceramics on them when we finally happened to get
>them off, the quartz rings were broken into several parts, some of them
>were like being atomized  to dust...
>Is anybody out there having a good idea what happened to the
>The crucibles were new, clean ones and had been baked out several
>times prior to using them, the temperature of the oven was adjusted to
>1200C, it showed being 1175C. We did not open the oven until the
>temperature was down.
>I have no idea what we didn't do right if we did something wrong (which
>to a certain extent I expect, as Irene, you give this method as your
>routine one)
>Hope somebody could help.
>Datum:          Wed, 29 Jun 2005 18:52:14 -0400
>Antwort an:             Stable Isotope Geochemistry
<[log in to unmask]>
>Von:                    Irene Ellis <[log in to unmask]>
>Betreff:                Re: [ISOGEOCHEM] Ion Source Cleaning
>An:                     [log in to unmask]
>Cleaning an ion source with solvents will leave a thin film of the
>azeotrope unless precautions are taken.
>This is the sequence that I used for the metal parts:
>--non-ionic soap and water after polishing off all carbon and sonicate 15
>--deionized water 3X and sonicate each time
>--methanol to cover, sonicate, decant and drain as much as possible by
>capillary action to kimwipes (metal parts stay in beaker, drain at lip)
>--chloroform to cover, sonicate, and decant.  Bake dry at 80C (about an
>hour).  The beakers can then be sealed with new Al foil.  Store in
>dessicator if waiting longer than overnight.
>This leaves all parts clean and the source will not need to bake out longer
>than the time to pump down.
>To clean ceramics, put into clean crucible and bake overnight at 1200C.  No
>need to scrape or sandblast--the carbon just evaporates perfectly. NB you
>will destroy MACOR insulators this way if any such nasties are lurking in
>the same lab (personal pet peeve).
>Irene Ellis
>IsoTrace Lab, U of T-------------------------------------------------------
>Dr. Anette Giesemann
>Institute of Agroecology, Federal Agricultural Research Centre
>Bundesallee 50, D-38116 Braunschweig
>Tel.:++49 531/596-2538; FAX: ++49 531/596-2599
>E-mail: [log in to unmask]