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Licensed Unlicensed Requires Authentication Published by De Gruyter (O) September 25, 2009

The transformation mechanism of the sodalite- to the melilite-topology: Thermal expansion and decomposition of bicchulite-type to melilite-type compounds

  • Lars Peters , Karsten Knorr , Hannelore Katzke , Michael Knapp and Wulf Depmeier

Abstract

The mineral bicchulite, |Ca8(OH)8|[Al8Si4O24]-SOD, has the sodalite-(SOD-)type structure. At elevated temperatures it decomposes into gehlenite, Ca2Al2SiO7 (melilite-type structure), and water (vapour). We report on the thermal expansion of two bicchulite-type compounds, the mineral bicchulite up to T = 740 K and |Ca6Eu2(OH)8|[Al10Si2O24]-SOD up to T = 1025 K. The expansion mechanism is described. Insitu X-ray powder diffraction experiments were performed to evaluate the thermal decomposition of |Ca6Eu2(OH)8|[Al10Si2O24]-SOD into 4 (Ca1.5Eu0.5)T1[T22O7] and 4 H2O, with Ti = Al or Si in a ratio of 5 : 1. A structural mechanism for the transformation from the sodalite to the melilite topology is proposed, based on geometrical considerations.

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Published Online: 2009-9-25
Published in Print: 2006-3-1

© by Oldenbourg Wissenschaftsverlag, München

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