The effect of carbonate solid solution on the elasticity of natural fluorapatites Apatite is an important mineral and knowledge of its stability at the Earth's interior is essential to understand its role as potential repository of phosphorous at the mantle depth. In biomedical field its mechanical properties are also important as apatite is a dental enamel constituent. Changes in the chemical and physical properties of apatite are observed when carbonate is incorporated into the apatite structure. Incorporation of carbonate can occur by substitution for both the channel anion and the phosphate ion with different effects on unit-cell parameters. Substitution of hydroxyl (OH) by type A carbonate results in progressive increase in a and decrease in c, whereas substitution of phosphate by type B carbonate results in progressive decrease in a and increase in c. So far several compression experiments have been carried out to investigate the compressibility of synthetic samples of fluorapatite, hydroxylapatite, and chlorapatite. A study of natural fluorapatite was performed by [1], who found a lower value of KT than previous work (using a BM2, KT = 91.6(1.0) GPa by [1] versus 97.9(1.9) GPa [2] and 97.8(1.0) GPa by [3]). Recently [4] have studied the effect of carbonate substitution on the compressibility of hydroxylapatite: the substitution of carbonate (both type A and B) lowers the value of KT. However, it is difficult to assess if the softening is due to type-A or type-B or both types of substitution. Among the available data, only [3] have performed a single crystal diffraction study. In order to clarify such discrepancies, we have performed a single crystal diffraction study of two natural fluorapatite and type-B carbonate fluorapatite ('francolite') samples coming from Muséum National d'Histoire Naturelle, Paris. Two crystals were mounted together in a DAC using quartz as pressure calibrant and a 16:3:1 mixture of methanol:ethanol:water as pressure-transmitting medium. We used SINGLE program [5] to collect data on a Siemens P4 four-circle diffractometer and EosFit7c [6] to fit the data. Our data (16 pressure points up to 5.8 GPa), fit to a 3rd order Birch-Murnaghan Equation of State (BM3-EoS) show that type-B carbonate substitution effectively decreases the bulk modulus from KT = 88.41(1.9) GPa [with KT' = 5.8(0.8)] to KT = 85.3(1.4) GPa [with a KT' of 5.6(0.6)]. However, careful inspection of the F-f plot shows that two different elastic regimes (low-P <3.25GPa and high-P 3.25GPa) should be actually taken into account for fluorapatite. Moreover, collecting more data during decompression will allow to better constrain both pressure ranges. So far we have used a BM2 EoS for both the low-P and the high-P regimes obtaining KT of 91.94(99) and 98.9(1.6) GPa for the low-P and the high-P regimes respectively. This preliminary result agrees well with previous findings for fluorapatite as the value obtained by [2] were probably biased by high pressure regime (although high pressure data > 9 GPa was probably not hydrostatic) while the value obtained by [1] did not have enough observations at high pressure. In both cases the authors fitted the whole observed pressure range as a unique pressure regime. References: [1] Matsukage KN , Ono S, Kawamoto T, Kikegawa T (2004) Phys Chem Minerals 31: 580-584 [2] Brunet F, Allan DR, Redfern SAT, Angel RJ, Miletich R, Reichmann HJ, Sergent J, Hanfland M (1999) Eur J Mineral 11: 1023-1035 [3] Comodi P, Liu Y, Zanazzi PF, Montagnoli M (2001) Phys Chem Minerals 28: 219-224 [4] Liu X, Shieh SR, Fleet ME, Zhang L, He Q (2011) Am Mineral 96:74-80 [5] Angel RJ, Finger LW (2011) J Appl Crystallogr 44: 247-251 [6] Angel RJ, Gonzalez-Platas J, Alvaro M (2014) Zeit Kristallogr, in press (DOI: 10.1515/zkri-2013-1711).

The effect of carbonate solid solution on the elasticity of natural fluorapatites

CAMARA ARTIGAS, Fernando;CURETTI, Nadia;BENNA, Piera;
2014

Abstract

The effect of carbonate solid solution on the elasticity of natural fluorapatites Apatite is an important mineral and knowledge of its stability at the Earth's interior is essential to understand its role as potential repository of phosphorous at the mantle depth. In biomedical field its mechanical properties are also important as apatite is a dental enamel constituent. Changes in the chemical and physical properties of apatite are observed when carbonate is incorporated into the apatite structure. Incorporation of carbonate can occur by substitution for both the channel anion and the phosphate ion with different effects on unit-cell parameters. Substitution of hydroxyl (OH) by type A carbonate results in progressive increase in a and decrease in c, whereas substitution of phosphate by type B carbonate results in progressive decrease in a and increase in c. So far several compression experiments have been carried out to investigate the compressibility of synthetic samples of fluorapatite, hydroxylapatite, and chlorapatite. A study of natural fluorapatite was performed by [1], who found a lower value of KT than previous work (using a BM2, KT = 91.6(1.0) GPa by [1] versus 97.9(1.9) GPa [2] and 97.8(1.0) GPa by [3]). Recently [4] have studied the effect of carbonate substitution on the compressibility of hydroxylapatite: the substitution of carbonate (both type A and B) lowers the value of KT. However, it is difficult to assess if the softening is due to type-A or type-B or both types of substitution. Among the available data, only [3] have performed a single crystal diffraction study. In order to clarify such discrepancies, we have performed a single crystal diffraction study of two natural fluorapatite and type-B carbonate fluorapatite ('francolite') samples coming from Muséum National d'Histoire Naturelle, Paris. Two crystals were mounted together in a DAC using quartz as pressure calibrant and a 16:3:1 mixture of methanol:ethanol:water as pressure-transmitting medium. We used SINGLE program [5] to collect data on a Siemens P4 four-circle diffractometer and EosFit7c [6] to fit the data. Our data (16 pressure points up to 5.8 GPa), fit to a 3rd order Birch-Murnaghan Equation of State (BM3-EoS) show that type-B carbonate substitution effectively decreases the bulk modulus from KT = 88.41(1.9) GPa [with KT' = 5.8(0.8)] to KT = 85.3(1.4) GPa [with a KT' of 5.6(0.6)]. However, careful inspection of the F-f plot shows that two different elastic regimes (low-P <3.25GPa and high-P 3.25GPa) should be actually taken into account for fluorapatite. Moreover, collecting more data during decompression will allow to better constrain both pressure ranges. So far we have used a BM2 EoS for both the low-P and the high-P regimes obtaining KT of 91.94(99) and 98.9(1.6) GPa for the low-P and the high-P regimes respectively. This preliminary result agrees well with previous findings for fluorapatite as the value obtained by [2] were probably biased by high pressure regime (although high pressure data > 9 GPa was probably not hydrostatic) while the value obtained by [1] did not have enough observations at high pressure. In both cases the authors fitted the whole observed pressure range as a unique pressure regime. References: [1] Matsukage KN , Ono S, Kawamoto T, Kikegawa T (2004) Phys Chem Minerals 31: 580-584 [2] Brunet F, Allan DR, Redfern SAT, Angel RJ, Miletich R, Reichmann HJ, Sergent J, Hanfland M (1999) Eur J Mineral 11: 1023-1035 [3] Comodi P, Liu Y, Zanazzi PF, Montagnoli M (2001) Phys Chem Minerals 28: 219-224 [4] Liu X, Shieh SR, Fleet ME, Zhang L, He Q (2011) Am Mineral 96:74-80 [5] Angel RJ, Finger LW (2011) J Appl Crystallogr 44: 247-251 [6] Angel RJ, Gonzalez-Platas J, Alvaro M (2014) Zeit Kristallogr, in press (DOI: 10.1515/zkri-2013-1711).
21st General Meeting of the International Mineralogical Association IMA.
Gauten, South Africa
1-5 September 2014
IMA 2014 Abstract Volume
Geological Society & Mineralogical Society S.A.
37
37
9780620600828
http://www.ima2014.co.za
apatite; high pressure
Cámara F.; Curetti N.; Benna P.; Ferraris C.
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