Hostname: page-component-848d4c4894-ttngx Total loading time: 0 Render date: 2024-05-14T06:18:11.654Z Has data issue: false hasContentIssue false
  • English
  • Français

Zirconolite transformation under reducing conditions

Published online by Cambridge University Press:  31 January 2011

B. D. Begg ,
E. R. Vance ,
B. A. Hunter  and
J. V. Hanna
B. D. Begg
Affiliation:
ANSTO, PMB 1, Menai, New South Wales, 2234, Australia
E. R. Vance
Affiliation:
ANSTO, PMB 1, Menai, New South Wales, 2234, Australia
B. A. Hunter
Affiliation:
ANSTO, PMB 1, Menai, New South Wales, 2234, Australia
J. V. Hanna
Affiliation:
CSIRO North Ryde NMR Facility, P.O. Box 52, North Ryde, New South Wales, 2234, Australia
Get access

Abstract

The structural behavior of zirconolite (CaZrTi2O7) under reducing conditions at high temperature has been studied, mainly by scanning electron microscopy (SEM) and x-ray diffraction (XRD), but also with x-ray absorption spectroscopy, thermogravimetry, and electron paramagnetic resonance. The partial reduction of Ti4+ to Ti3+, associated with a reducing atmosphere heat treatment, led to the initial formation of perovskite (CaTiO3) as a second phase. As the concentration of Ti3+ in the zirconolite increased, so did the amount of perovskite until the zirconolite was totally transformed into a fluorite structured phase. Analysis of the reduced zirconolites showed them to be consistently deficient in Ca and enriched in Zr, in proportion to the concentration of Ti3+. To determine how electroneutrality was preserved in these reduced zirconolites, a series of zirconolites were prepared in air using In3+ and Ga3+ as models for Ti3+. These samples were then investigated by neutron and x-ray diffraction, SEM, solid state nuclear magnetic resonance (NMR), and nuclear quadrupole resonance (NQR). 71Ga MAS NMR studies of the Ga substituted zirconolite exhibited a narrow resonance at ˜13 ppm which was attributed to six-coordinate Ga incorporated in a trace perovskite phase. Broadline 71Ga NMR and 69/71Ga NQR were required to characterize the Ga incorporated in the zirconolite. The resultant quadrupolar parameters of CQ = 30.0 ± 0.05 MHz and η = 1.0 ± 0.03 indicate that the Ga site is in a highly distorted environment which would suggest that it is located on the five-coordinate Ti site within the zirconolite lattice. These results were complemented by Rietveld refinement of the neutron diffraction data from the In-doped zirconolite sample, which was optimal when all the In was located on the five-coordinate Ti site with the excess Zr located on the Ca site. It would therefore appear that charge compensation for the presence of Ti3+ in zirconolite is effected via the substitution of an appropriate amount of Zr on the Ca site. The Ti3+-stabilized fluorite structure was readily oxidized back to a single phase zirconolite upon heating in air.

Type
Articles
Information
Journal of Materials Research , Volume 13 , Issue 11 , November 1998 , pp. 3181 - 3190
Copyright
Copyright © Materials Research Society 1998

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

REFERENCES

1.Ringwood, A. E., Kesson, S. E., Ware, N. G., Hibberson, W., and Major, A., Nature (London) 278, 219 (1979).Google Scholar
2.Gatehouse, B. M., Grey, I. E., Hull, R. J., and Rossell, H. J., Acta Crystallog. B37, 306–312 (1981).CrossRefGoogle Scholar
3.Ringwood, A. E., Kesson, S. E., Reeve, K. D., Levins, D. M., and Ramm, E. J., in Radioactive Waste Forms for the Future, edited by Lutze, W. and Ewing, R. C. (Elsevier, New York, and London, 1988).Google Scholar
4.Samoson, A. and Lippmaa, E., Phys. Rev. B 28, 6567 (1983).CrossRefGoogle Scholar
5.Lippmaa, E., Samoson, A., and Magi, M., J. Am. Chem. Soc. 108, 1730 (1986).CrossRefGoogle Scholar
6.Bastow, T. J., Smith, M. E., and Stuart, S. N., Chem. Phys. Lett. 191, 125 (1992).CrossRefGoogle Scholar
7.Bastow, T. J and Smith, M. E., Solid State Nucl. Magn. Reson. 1, 165 (1992).CrossRefGoogle Scholar
8.Kunwar, A. C., Turner, G. L., and Oldfield, E., J. Magn. Reson. 69, 124 (1986).Google Scholar
9.Votinov, M. P and Demidenko, N. I., Fiz. Tverd. Tela 4, 3277 (1962).Google Scholar
10.Antuf'ev, V. V., Vasil'ev, Ya.V., Votinov, M. P., Kharitonova, O. K., and Kharitonov, E. V., Fiz. Tverd. Tela 4, 1496 (1962).Google Scholar
11.Bancroft, G. M and Platt, R. H., Adv. Inorg. Chem. Radiochem. 15, 59 (1972).CrossRefGoogle Scholar
12.Smith, J. A., J. Chem. Ed. 48, 39 (1971).CrossRefGoogle Scholar
13.Lucken, E. A., Z. Naturforsch. 49a, 155 (1994).CrossRefGoogle Scholar