The compressional behaviour of (triclinic) pyrophyllite-1Tc was investigated by means of in situ synchrotron single-crystal diffraction up to 6.2 GPa (at room temperature) using a diamond anvil cell. Its thermal behaviour was investigated by in situ synchrotron powder diffraction up to 923 K (at room pressure) with a furnace. No evidence of phase transition has been observed within the pressure range investigated. The alpha angle decreases whereas the beta and gamma angles increase with P, with the following linear trends: alpha(P) = alpha (0) - 0.203(9)center dot Delta P, beta(P) = beta (0) + 0.126(8)center dot Delta P, and gamma(P) = gamma (0) + 0.109(5)center dot Delta P (angles in A degrees and P in GPa). P-V data fits with isothermal Murnaghan and third-order Birch-Murnaghan Equations of State yield: K (T0) = 47(3) GPa and K' = 6.6(14) for the M-EoS fit, K (T0) = 47(4) GPa and K' = 7.3(19) for a III-BM-EoS fit, with the following anisotropic compressional scheme: beta (a) :beta (b) :beta (c) = 1.06:1:4.00. The evolution of the "Eulerian finite strain" versus "normalized stress" leads to: Fe(0) = 47(3) GPa as intercept value and regression line slope with K' = 7.1(18). A drastic and irreversible change of the thermal behaviour of pyrophyllite-1Tc was observed at 700 < T < 850 K, likely ascribable to the first stage of the T-induced de-hydroxylation. Between 298 and 700 K, the alpha angle shows a slight decrease whereas the beta and gamma angles tend to be unaffected in response to the applied temperature; all the unit-cell edges show a monotonic increase. The axial and volume thermal expansion coefficients of pyrophyllite were modelled between 298 and 773 K following the equation alpha (V)(T) = alpha (0)(1 - 10T (-1/2)), with alpha (V298 K) = 2.2(2) x 10(-5) K-1 [with V (0) = 424.2(1) (3) and alpha (0) = 5.5(3) x 10(-5) K-1] and thermal anisotropic scheme alpha (a) :alpha (b) :alpha (c) = 1.20:1:2.72. By linear regression, we obtained: V(T)/V (0) = 1 + alpha (0V)center dot T = 1 + 3.1(2) x 10(-5) (T - T (0)). The thermal behaviour of talc-1Tc was investigated by in situ synchrotron powder diffraction up to 1,173 K (at room-P) with a furnace. At 423 K, the diffraction pattern was indexable with a monoclinic unit-cell but with a doubling of the c-axis (as expected for the 2M-polytype). At T > 1,123 K, an irreversible transformation occurs, likely ascribable to the first stage of the T-induced de-hydroxylation. Between 423 and 1,123 K, the beta angle decreases in response to the applied temperature; all the unit-cell edges show a monotonic increase. The volume expansion coefficient of talc was modelled between 423 and 1,123 K by the linear regression, yielding: V(T)/V (0) = 1 + alpha (0V)center dot T = 1 + 2.15(3) x 10(-5) (T - T (0)). The comparative elastic analysis of pyrophyllite and talc, using the data obtained in this and in previous studies, shows that pyrophyllite is more compressible and more expandable than talc.
Elastic behaviour and phase stability of pyrophyllite and talc at high pressure and temperature / G.D. Gatta, P. Lotti, M. Merlini, H.P. Liermann, A. Lausi, G. Valdrè, A. Pavese. - In: PHYSICS AND CHEMISTRY OF MINERALS. - ISSN 0342-1791. - 42:4(2015), pp. 309-318.
|Titolo:||Elastic behaviour and phase stability of pyrophyllite and talc at high pressure and temperature|
GATTA, GIACOMO DIEGO (Primo) (Corresponding)
LOTTI, PAOLO (Secondo)
PAVESE, ALESSANDRO (Ultimo)
|Parole Chiave:||Pyrophyllite; Talc; Synchrotron diffraction; High pressure; High temperature; Compressibility; Expansivity|
|Settore Scientifico Disciplinare:||Settore GEO/09 - Georisorse Miner.Appl.Mineral.-Petrogr.per l'amb.e i Beni Cul|
Settore GEO/06 - Mineralogia
|Data di pubblicazione:||2015|
|Digital Object Identifier (DOI):||http://dx.doi.org/10.1007/s00269-014-0721-x|
|Appare nelle tipologie:||01 - Articolo su periodico|
File in questo prodotto:
|Pyrophyllite_PCM.pdf||Publisher's version/PDF||Administrator Richiedi una copia|
|Gatta_Pyrophyllite_R1.pdf||Versione accettata dall'editore per la stampa||Post-print, accepted manuscript ecc. (versione accettata dall'editore)||Open Access Visualizza/Apri|