The thermal expansion of synthetic aluminosilicate-sodalites,M
8(Al6Si6O24)X
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Authors: | C M B Henderson D Taylor |
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Institution: | 1. Department of Geology, University of Manchester, M13 9PL, Manchester, England 2. 15 Leigh Road, CW12 2EG, Congleton, Cheshire, England
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Abstract: | Thermal expansion data, determined by powder X-ray diffraction methods are presented for 11 members of the (Li,Na,K,Rb)8(Al6Si6O24)Cl2 solid solution series, 3 members of the (Na,K)8(Al6Si6O24)Br2 solid solution series and Na8(Al6Si6O24)I2. Only the latter showed a discontinuity in its expansion curve at 810° C wigh a mean linear expansion coefficient of 22.0×10?6 °C?1 below and 7.7×10?6 °C?1 above the discontinuity. The mean expansion coefficients from 0° to 500° C decrease gradually over the range of room temperature cell edges from 8.4 to 8.89 Å, then increase up to a cell edge of 9.01 Å above which they decrease sharply and extrapolate to a zero coefficient at 9.4 Å. These variations may be related to the expansion characteristics of the bonds between the cavity cations and cavity anions in different sodalites. The aluminosilicate-sodalites which show a discontinuity in their thermal expansion curves are those with large cavity anions, I? or SO 4 2? ; the discontinuity is believed to occur at the point when the x-coordinate of the cavity cation becomes 0.25. |
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