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Thermodynamic investigation on β- and γ-Ca3(PO4)2 and the phase equilibria by Shuangmeng Zhai; Masaki Akaogi; Hiroshi Kojitani; Weihong Xue; Eiji Ito is a Earth and Planetary Sciences article available to read on EtoBox.

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c-Ca 3 (PO 4 ) 2 , naturally known as tuite, is regarded as an important potential reservoir for rare earth elements and large ion lithophile elements. It is a high-pressure polymorph of b-Ca 3 (PO 4 ) 2 whitlockite and a decomposed product of apatite under high-pressure and temperature. Drop-solution enthalpies of b-and c-Ca 3 (PO 4 ) 2 were obtained as 298.59 ± 3.02 and 278.74 ± 2.98 kJ/mol, respectively, by the drop-solution calorimetry with 2PbOÁB 2 O 3 solvent at 978 K. Thus the enthalpy of transition from b-to c-Ca 3 (PO 4 ) 2 at 298 K (DH o tr;298 ) was 19.85 ± 4.24 kJ/mol. The isobaric heat capacities of b-and c-Ca 3 (PO 4 ) 2 were measured at temperature range of 300-770 K by differential scanning calorimetry, and compared with the results calculated from the Kieffer model. The equilibrium phase boundary between b-and c-Ca 3 (PO 4 ) 2 was calculated using present measured data combined with other available thermochemical and thermoelastic data. The calculated boundary gave a phase transition boundary with a dP/dT slope of 4.7 ± 0.2 MPa/K in the temperature range of 900-2000 K. Based on the phase relationship, the occurrences of tuite and whitlockite in meteorites are discu

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Author

Shuangmeng Zhai; Masaki Akaogi; Hiroshi Kojitani; Weihong Xue; Eiji Ito

Publisher

Elsevier BV

Published

2014

Language

EN

Field

Earth and Planetary Sciences (Physical Sciences)