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A low-temperature heat-capacity study of synthetic anhydrous Mg-cordierite (Mg₂Al₄Si₅O₁₈)

¹ Institute of Inorganic Chemistry, Lavrentiev prosp. 3, Novosibirsk 630090, Russia
² Institut für Geowissenschaften, Universität Kiel, Olshausenstrasse 40, 24098 Kiel, Germany

Correspondence: ^* E-mail: paukov{at}che.nsk.su

The heat capacity of synthetic anhydrous Mg-cordierite (Mg₂Al₄Si₅O₁₈) was measured using adiabatic calorimetry between 6 and 300 K. Mg-cordierite was synthesized from a glass of stoichiometric cordierite composition at 1250 °C for one week. The refined cell dimensions using powder X-ray diffraction give a = 17.0553(2) Å, b = 9.7167(1) Å, and c = 9.3375(1) Å with V = 1547.428(1) ų and a distortion index of = 0.25 indicating complete Al-Si ordering. The absence of channel H₂O was confirmed by powder IR spectroscopy, which did not show the presence of any bands located around 3600 cm^–1. The C_P results values agree with those obtained previously by Weller and Kelley (1963) who measured the C_P of Mg-cordierite between 50 K and 298 K. The calculated entropy of Mg-cordierite at standard condition is S⁰_298.15 = 404.0 ± 1.6 J/(mol·K) using the C_P data from this study. This value is in agreement with the value presented by Weller and Kelley [407.2 ± 3.77 J/(mol·K)], but appears to be very slightly lower than estimates made from various modeling studies incorporating phase-equilibrium data on Mg-cordierite.

Key Words: Calorimetry • cordierite • low-temperature study • crystal synthesis

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