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The Structure and Properties of Two New Silicotitanate Zeolites

Published online by Cambridge University Press:  03 September 2012

M. L. Balmer ,
Y. Su ,
I. E. Grey ,
A. Santoro ,
R. S. Roth ,
Q. Huang ,
N. Hess  and
B. C. Bunker
M. L. Balmer
Affiliation:
Materials and Chemical Sciences Department, Pacific Northwest National Laboratory, Richland, WA 99352
Y. Su
Affiliation:
Materials and Chemical Sciences Department, Pacific Northwest National Laboratory, Richland, WA 99352
I. E. Grey
Affiliation:
CSIRO Division of Minerals, Melbourne, Australia
A. Santoro
Affiliation:
Reactor Division, National Institute of Standards and Technology, Gaithersburg, MD 20899
R. S. Roth
Affiliation:
Reactor Division, National Institute of Standards and Technology, Gaithersburg, MD 20899
Q. Huang
Affiliation:
University of Maryland, College Park, MD 20742
N. Hess
Affiliation:
Materials and Chemical Sciences Department, Pacific Northwest National Laboratory, Richland, WA 99352
B. C. Bunker
Affiliation:
Materials and Chemical Sciences Department, Pacific Northwest National Laboratory, Richland, WA 99352
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Abstract

Two new zeolitic crystalline phases with stoichiometry, CSTiSi2O6.5 and CS2TiSi6O15, have been discovered. CSTiSi2O6.5 has a crystal structure isomorphous to the mineral pollucite, CsAlSi2O6, with Ti+4 replacing Al+3. This replacement requires a mechanism for charge compensation. A combination of techniques including neutron diffraction, single crystal x-ray diffraction and x-ray absorption spectroscopy have revealed that eight extra oxygens are present per unit cell Cs2TiSi2O6.5 as compared to pollucite. As a result of the extra oxygen, the titanium coordination geometry is five-fold. Pentacoordinate titanium and tetrahedral silicon form a network structure with Cs residing in cages formed by the network. The crystal structure of Cs2TiSi6O15 is unique, with titanium octahedra and silicon tetrahedra forming an open framework structure with the Cs residing in large cavities. The largest covalently bonded ring opening to the Cs cavities in both compounds are smaller than a Cs ion, revealing that the Cs ion has minimal mobility in the structure. Cesium leach rates for both compounds are lower than or comparable to borosilicate glass.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 465: Symposium II – Scienfific Basis for Nuclear Waste Management XX , 1996 , 449
Copyright
Copyright © Materials Research Society 1997

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References

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