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Subject:
From:
Pecho Juraj <[log in to unmask]>
Reply To:
Stable Isotope Geochemistry <[log in to unmask]>
Date:
Wed, 25 Feb 2004 09:37:46 +0100
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Hi John

Thanks a lot for your answer.
We want to prepare a material with ca. 10 - 20 % of "18"O. The particles
sizes ca. 200 micrometers (few grams).
We do not need a homogeneously 18O-rich olivine, therefore we want to do it
with quarz tube.
Do you think, wouldn't it be enough do it in this way, when we heated by
1000 C for ca. 40 hours?


Nice day

Juraj

Juraj Pecho
High Tepmeratur Solar Chemistry
Paul Scherrer Institut
Switzerland
T: ++41-(0)56 310 2074
F: ++41-(0)56 310 2688
mail: [log in to unmask]


-----Original Message-----
From: John Eiler [mailto:[log in to unmask]]
Sent: Dienstag, 24. Februar 2004 17:42
To: [log in to unmask]
Subject: Re: [ISOGEOCHEM] 18O dopt olivin


You are going to have trouble achieving high degrees of exchange between
low-pressure vapor and crystalline olivine.  If the rate limiting step is
volume diffusion within olivine, the 18O will not penetrate more than a
couple of microns on laboratory timescales.  You will have much more success
if you drive exchange by dissolution/reprecipitation in a silicate melt or
supercritical aqueous fluid.  If I had to do this, and assuming my goal was
to create a homogeneously 18O-rich olivine, I would exchange silicate melt
with 18O-rich gas in a Deltech furnace, slowly cool the melt to precipitate
olivine, quench the melt-olivine mix, and then separate the minerals from
glass by density separation.  This is alot of work, but I think is likely to
produce a better quality material than you would make by exchange with
super-critical water (which I suspect would lead to zonation within
partially re-crystallized grains).  Good luck,

John

>Hi all
>
>I have one small question on you.
>We need to introduce Oxygen "18"O into natural and synthetic olivine.
>
>Our idea is, to do it in a quarz tube, in which olivin and H218O are
>closed under vakuum and then heated in furnace to achieve the
>equilibrium. Just we do not know the temperature and reaction time.
>
>Does has somebody some experience or reference for this method or some
>other way of "18"O dopt olivin?
>
>Thanks a lot
>
> Juraj
>
>
>
>Juraj Pecho
>High Tepmeratur Solar Chemistry
>Paul Scherrer Institut
>Switzerland
>T: ++41-(0)56 310 2074
>F: ++41-(0)56 310 2688
>mail: [log in to unmask]

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