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Letter: Experimental observation of an interface-controlled pseudomorphic replacement reaction in a natural crystalline pyrochlore
-
Thorsten Geisler
,
Philipp Pöml
Veröffentlicht/Copyright:
28. März 2015
Abstract
Pyrochlore-type (A2B2O6O’) ceramics are considered for the immobilization of highly radioactive waste. Understanding the alteration process of such potential nuclear waste form materials in aqueous media is critical for the prediction of their long-term stability in a nuclear repository. Current models on pyrochlore alteration are based on a diffusion-controlled hydration and ion exchange process. However, we present results of a hydrothermal experiment at 200 °C with a natural, polycrystalline pyrochlore and 18O-enriched aqueous solution, which are not compatible with a process based on solid-state diffusion. TOF-SIMS and confocal μ-Raman mapping of the run product revealed the occurrence of 18O-enriched alteration zones with sharp chemical gradients to relict unreacted areas when compared to the extent of the alteration zones. The data are consistent with a pseudomorphic reaction that involves the dissolution of the pyrochlore parent accompanied by the simultaneous reprecipitation of a defect pyrochlore at a moving dissolution-reprecipitation front.
Received: 2005-4-21
Accepted: 2005-5-12
Published Online: 2015-3-28
Published in Print: 2005-10-1
© 2015 by Walter de Gruyter Berlin/Boston
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Artikel in diesem Heft
- Presidential Address To The Mineralogical Society Of Amrica, Boston, November 6, 2001: Some Precambrian Banded Iron-Formations (BiIFs) From Around The World: Their Age, Geologic Setting, Mineralogy, Metamorphism, Geochemistry, And Origin
- Effects of high pressure and high temperature on cation ordering in magnesioferrite, MgFe2O4, using in situ synchrotron X-ray powder diffraction up to 1430 K and 6 GPa
- Raman spectroscopy and vibrational analyses of albite: From 25 °C through the melting temperature
- A new occurrence of xitieshanite [Fe3+(SO4)Cl⋅6H2O] crystals in acid-mine seepways, Green Valley, Vigo County, Indiana, U.S.A.
- Effect of A-site cation radius on ordering of BX6 octahedra in (K,Na)MgF3 perovskite
- Crystal chemistry of NaMgF3 perovskite at high pressure and temperature
- Hyperfine electric field gradient tensors at Fe2+ sites in octahedral layers: Toward understanding oriented single-crystal Mössbauer spectroscopy measurements of micas
- Does the bazhenovite structure really contain a thiosulfate group? A structural and spectroscopic study of a sample from the type locality
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- Coupled dichotomies of apatite and fluid composition during contact metamorphism of siliceous carbonate rocks
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