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Thermal expansion of nepheline-kalsilite crystalline solutions

Published online by Cambridge University Press:  05 July 2018

G. L. Hovis
Affiliation:
Department of Geology & Environmental Geosciences, Lafayette College, Easton, PA 18042, USA
J. Crelling
Affiliation:
Applied Research Laboratory, Pennsylvania State University, University Park, PA 16802, USA
D. Wattles
Affiliation:
GZA GeoEnvironmental, Incorporated, One Edgewater Drive, Norwood, MA 02062, USA
B. Dreibelbis
Affiliation:
McLane Environmental, LLC, 707 Alexander Road, Princeton, NJ 08540, USA
A. Dennison
Affiliation:
ENSCO Incorporated, 5400 Port Royal Road, Springfield, VA22151, USA
M. Keohane
Affiliation:
ENSCO Incorporated, 5400 Port Royal Road, Springfield, VA22151, USA
S. Brennan
Affiliation:
ENSCO Incorporated, 5400 Port Royal Road, Springfield, VA22151, USA

Abstract

Eleven nepheline-kalsilite crystalline solutions with various proportions of K:Na have been studied from room temperature to 1050/11500C by X-ray powder diffraction. Nepheline expansion is relatively high and little affected by composition, whereas kalsilite expansion is lower but affected to a significant degree by K:Na ratio. The generally higher rate of expansion in nepheline is apparently related to the collapse of the tetrahedral framework around the smaller of its two alkali sites. Occupancy of these sites by the relatively small Na ion fürther extends the potential for thermal vibration before the structure is stretched to the critical degree required for phase transformation. Once the structure changes to that of kalsilite, with its single alkali site, an increase in content of the larger K ion limits the degree to which kalsilite can expand. Crucial to the overall expansion behaviour of these minerals are the specific tetrahedral configurations of nepheline vs. kalsilite, the number and geometry of their alkali sites, the occupancies of those sites, and the flexibility inherent in each structure that allows for adjustment with increasing temperature.

Information

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2003

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