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Stable Isotope Geochemistry

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Subject:
From:
John Eiler <[log in to unmask]>
Reply To:
Stable Isotope Geochemistry <[log in to unmask]>
Date:
Tue, 24 Feb 2004 08:42:21 -0800
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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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