The high-pressure-high-temperature behavior of bassanite

Journal Article · Thu Feb 11 04:00:00 EST 2010 · American Mineralogist

DOI:https://doi.org/10.2138/am.2009.3245· OSTI ID:1006084

Comodi, Paola; Nazzareni, Sabrina; Dubrovinsky, Leonid; Merlini, Marco

The pressure evolution of bassanite (CaSO{sub 4} {center_dot} 1/2 H{sub 2}O) was investigated by synchrotron X-ray powder diffraction along three isotherms: at room temperature up to 33 GPa, at 109 C up to 22 GPa, and at 200 C up to 12 GPa. The room-temperature cell-volume data, from 0.001 to 33 GPa, were fitted to a third-order Birch-Murnaghan equation-of-state, and a bulk modulus K{sub 0} = 86(7) GPa with K' = 2.5(3) was obtained. The axial compressibility values are {beta}{sub a} = 3.7(2), {beta}{sub b} = 3.6(1), and {beta}{sub c} = 2.8(1) GPa{sup -1} (x10{sup -3}) showing a slightly anisotropic behavior, with the least compressible direction along c axis. The strain tensor analysis shows that the main deformation occurs in the (010) plane in a direction 18{sup o} from the a axis. The bulk moduli for isotherms 109 and 200 C, were obtained by fitting cell-volume data with a second-order Birch-Murnaghan equation-of-state, with K' fixed at 4, and were found to be K{sub 109} = 79(4) GPa and K{sub 200} = 63(7) GPa, respectively. The axial compressibility values for isotherm 109 C are {beta}{sub a} = 2.4(1), {beta}{sub b} = 3.0(1), {beta}{sub c} = 2.5(1) (x10{sup -3}) GPa{sup -1}, and for isotherm 200 C they are {beta}{sub a} = 3.5(3), {beta}{sub b} = 3.4(3), {beta}{sub c} = 2.6(4) (x10{sup -3}) GPa{sup -1}. These two bulk moduli and the 20 C bulk modulus, K{sub 0,20} = 69(8) recalculated to a second-order Birch-Murnaghan EoS to be consistent, as well as the axial compressibilities, are similar for the three isotherms indicating that the thermal effect on the bulk moduli is not significant up to 200 C. The size variation of the pseudo-hexagonal channel with pressure and temperature indicates that the sulfate 'host' lattice and the H{sub 2}O 'guest' molecule in bassanite do not undergo strong change up to 33 GPa and 200 C.

• Research Organization: Argonne National Laboratory (ANL)
• Sponsoring Organization: USDOE
• OSTI ID: 1006084
• Journal Information: American Mineralogist, Journal Name: American Mineralogist Journal Issue: (11-12) ; 12, 2009 Vol. 94; ISSN AMMIAY; ISSN 0003-004X
• Country of Publication: United States
• Language: ENGLISH

Related Subjects

58 GEOSCIENCES
CALCIUM SULFATES
COMPRESSIBILITY
DEFORMATION
EQUATIONS OF STATE
HYDRATES
ISOTHERMS
MINERALOGY
PRESSURE RANGE GIGA PA
TEMPERATURE DEPENDENCE
X-RAY DIFFRACTION