Thermophysical properties of ilvaite CaFe
2
2+
Fe3+Si2O7O (OH); heat capacity from 7 to 920 K and thermal expansion between 298 and 856 K |
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Authors: | Richard A Robie Howard T Evans Jr Bruce S Hemingway |
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Institution: | 1. U.S. Geological Survey, MS 959, 22092, Reston, VA, USA
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Abstract: | The heat capacity of ilvaite from Seriphos, Greece was measured by adiabatic shield calorimetry (6.4 to 380.7 K) and by differential
scanning calorimetry (340 to 950 K). The thermal expansion of ilvaite was also investigated, by X-ray methods, between 308
and 853 K.
At 298.15 K the standard molar heat capacity and entropy for ilvaite are 298.9±0.6 and 292.3±0.6 J/(mol. K) respectively.
Between 333 and 343 K ilvaite changes from monoclinic to orthorhombic. The antiferromagnetic transition is shown by a hump
in C
p
0
with a Néel temperature of 121.9±0.5 K. A rounded hump in C
p
0
between 330 and 400 K may possibily arise from the thermally activated electron delocalization (hopping) known to take place
in this temperature region. |
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Keywords: | |
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