Physics and Chemistry of Minerals最新文献

Marialite (Na₃Al₃Si₉O₂₄·NaCl) represents a key end-member of the scapolite mineral group because it has the potential for revealing the chloride content of the paleofluid from which it formed. Here we provide measurements of the basic thermophysical properties of synthetic marialite which do not currently exist and which complement similar data for calcium-carbonate-bearing scapolites. Synthetic marialite was made from reagent oxides and NaCl treated at 1050 °C and 1.7 GPa for 48–120 h. Average unit-cell dimensions for synthetic marialite at 298 K and 1 atm are a_o = 12.038 ± 0.002 Å, c_o = 7.539 ± 0.004 Å, and V_o = 1092.6 ± 0.8 ų, with a molar volume of 328.99 ± 0.24 cm³/mole. Thermal expansion measurements were made at 1 atm from 298–1105 K and showed that a increases while c decreases with an overall increase in volume upon heating. Compressibility measurements were made at room temperature in a diamond-anvil cell using 4:1 methanol: ethanol pressure medium in transmission mode at the Cornell High Energy Synchrotron Source facility with pressures ranging from 1 atm to 9.6 GPa. The a dimension is more compressible than c up to ~ 5 GPa, beyond which there is noticeable softening along the c axis. Equation of state modeling was done on the combined pressure–temperature-volume data using a Tait equation of state yielding bulk modulus and thermal expansion values for K_o, K’, and α of 51.0 ± 2.0 GPa, 6.68 ± 0.83, and 2.75 ± 0.17 × 10^–5/K, respectively. Compared with other scapolite data in the literature, the marialite (Na₃Al₃Si₉O₂₄·NaCl)-meionite (Ca₃Al₆Si₆O₂₄·CaCO₃) join behaves similarly to the albite-anorthite plagioclase join, with end-member marialite having the highest thermal expansion and lowest bulk modulus along the compositional join.

The phase diagram of the ZnO-SnO₂ system at 800–1600 °C was experimentally investigated using the classical equilibration/quenching method and differential thermal analysis (DTA) followed by X-ray diffraction (XRD) phase analysis and electron probe micro-analysis (EPMA). Sealed platinum capsules were employed to prevent the evaporation of ZnO and SnO₂ in the experiments. Based on new experimental phase diagram data and all available data in literatures, the binary ZnO-SnO₂, SnO₂-TiO₂, and ZrO₂-TiO₂ and the ternary ZnO-SnO₂-TiO₂ system was thermodynamically optimized using the CALculation of PHAse Diagram (CALPHAD) method to prepare a set of Gibbs energies of all phases within the binary systems which can be utilized to predict unknown phase equilibria and thermodynamic properties in the system.

The common wisdom that volume decreases with pressure and increases with temperature is analyzed in terms of Hillert nonequilibrium thermodynamics in the present work. It is shown that the derivative of volume to pressure in a stable system is always negative, i.e., volume decreases with the increase of pressure, when all other natural variables of the system are kept constant. This originates from the stability requirement that the conjugate variables, such as volume and negative pressure, must change in the same direction in a stable system. Consequently, since volume and temperature are not conjugate variables, they do not have to change in the same direction and thus do change in opposite directions in both natural and man-made systems. It is shown that the decrease of volume with the increase of temperature, commonly referred as negative thermal expansion (NTE) in the literature, originates from the statistical competitions of configurations in the system when the volumes of metastable configurations are smaller than that of the ground-state configuration. It is demonstrated that the zentropy theory can concisely explain and accurately predict NTE based on the density functional theory without fitting parameters.

In this study, the thermodynamic parameters of the Mn–Si–O system were re-evaluated using the CALPHAD approach. Available experimental data on phase equilibria were taken into account and thermodynamic properties such as heat capacity, standard entropy and standard enthalpy were reproduced within uncertainties. Three ternary compounds are found to be stable in the Mn–Si–O system: rhodonite (MnSiO(_3)), braunite (Mn(_7)SiO(_{12})) and tephroite (Mn(_2)SiO(_4)). Braunite was modeled by CEF, while tephroite and rhodonite were modeled as stoichiometric compounds. Two-sublattice partially ionic liquid model was used to describe the liquid phase. The braunite phase exhibits a homogeneity range and can dissolve Mn(_2)O(_3) in some extension. Phase diagrams for the MnO–SiO(_2) system in the presence of metallic Mn and the MnO(_x)–SiO(_2) system in air were calculated and showed good agreement with existing literature data. The thermodynamic parameters were evaluated to describe the experimental data over the entire compositional range of the system.

Perovskite-type oxides BaZr_1–xY_xO_3−x/2 (x = 0.1, 0.2) were synthesized and their enthalpy increments were measured by means of high-temperature drop calorimetry in the temperature range of (373–1273) K in air. The data obtained were used for estimating the high-temperature thermodynamic functions (constant pressure heat capacity and entropy increments) of the zirconates BaZr_1–xY_xO_3−x/2 (x = 0.1, 0.2). They were found to be only weakly dependent on the concentration of Y-dopant. Thermal expansion coefficient of zirconates BaZr_1–xY_xO_3−x/2 (x = 0.1, 0.2) was successfully estimated by Grüneisen equation. Also, Neumann-Kopp rule was shown to be inapplicable for accurate estimation of heat capacities of the studied oxides. Thermodynamic analysis showed that BaZr_1–xY_xO_3−x/2 (x = 0.1, 0.2) oxides are prone to chemical interaction with CO₂ at typical working temperatures of proton-conducting solid oxide fuel cells. Some possibilities to overcome this issue have been discussed.

The temperature dependence of the infrared absorption spectra of two Verneuil-grown corundum samples is investigated in the OH stretching range. The spectra display three main bands at 3184, 3232 and 3309 cm^− 1, belonging to the so-called “3309 cm^− 1 series”, as well as two additional bands at 3163 and 3278 cm^− 1 previously reported in some synthetic corundum samples. The anharmonic behavior of the observed bands is analyzed using the pure dephasing model of Persson and Ryberg and depends on the local geometry of the OH defects, which are all associated with Al vacancies. The unexpected increase with temperature in the absorbance of a weak band at 3209 cm^− 1 supports a revised interpretation of both the 3209 and 3232 cm^− 1 bands. These two bands are interpreted as resulting from the low-temperature equilibrium between two Ti-associated OH defects, enabled by the possibility of hydrogen hopping within the Al vacancy. The temperature-dependent properties of the 3278 cm^− 1 band are similar to those of the other Al-vacancy related defects and a comparison with the theoretical properties of selected OH defects suggests that this band corresponds to the association of the H atom with a non-dissociated Al Frenkel pair. Finally, the properties of the band at 3163 cm^− 1 are consistent with its previously proposed association with Si for Al substitution in corundum.

Studies conducted in NaF-containing hydrothermal fluids have shown that the oxide compounds Sb⁵⁺ are unstable at 800 °C, Р_total = 200 MPa and fO₂ (fH₂) specified by Co–CoO and Ni–NiO buffers interact with the Pt material of the ampoule, forming antimony intermetallics with platinum on the inner surface of the ampoule. The formation of the following intermetallics was established through the analysis of data obtained from studies conducted on an electronic microscope: Pt_90.3±0.8Sb_9.7 (~ Pt₁₀Sb), Pt_82.8±1.3Sb_17.2 (~ Pt₅Sb) and Pt_69.2±4.4Sb_30.8. Pt₁₀Sb compound which was obtained on the inner surface of the Pt ampoule is the limiting solid solution of antimony in platinum at 800 °C. It exhibits a cubic crystal system (Fmoverline{3}m) with a lattice constant of a = 3.943(3) Å and forms an underdeveloped surface < 111>. Pt₅Sb compound, presumably hexagonal P6/mmm crystal system with unit cell parameters a = b = 4.56(4), c = 4.229(2) Å, α = β = 90°, γ = 120°, forms a thin film (≤ 10 μm) on the Pt surface and appears to be a metastable phase. The intermetallic compound of Pt₆₉Sb₃₁ is a rapidly cooled melt of appropriate composition.

A mechanism for deep penetration of Sb into the walls of the Pt ampoule is proposed.

The rhenium carbide Re₃C was predicted to be stable under high pressure and expected to have high hardness and low compressibility. In this study, we realise the synthesis of Re₃C at megabar pressures of 105(3) and 140(5) GPa in laser-heated diamond anvil cells and characterise its structure using synchrotron single-crystal X-ray diffraction. The structure of Re₃C has the monoclinic space group C2/m and is built of CRe₇ capped octahedra. Our combined ab initio calculations and quantitative topological analysis support experimental structural data and further deepen the understanding of the chemical bonding in the newly synthesized compound.

Single-crystal Brillouin scattering measurements are important for interpreting seismic velocities within the Earth and other planetary interiors. These measurements are rare, however, at temperatures above 1000 K, due to the fact that the transparent samples cannot be heated by common laser heating systems operating at a wavelength on the order of 1 μm. Here we present Brillouin scattering data on pyrope collected at pressures up to 23.8 GPa and temperatures between 850 and 1900 K using a novel CO₂ laser heating system confined in either a flexible hollow silica waveguide or an articulated arm with mirrors mounted in each junction to direct the laser to the exit point. Pyrope has been chosen because it has been extensively studied at high pressures and moderate temperatures and therefore it is an excellent sample for bench-marking the CO₂ laser heating system. The new high-temperature velocity data collected in this study allow the room pressure thermal parameters of pyrope to be constrained more tightly, resulting in values that reproduce the temperature dependence of the unit-cell volume of pyrope measured in recent studies at ambient pressure. Aggregate wave velocities of pyrope calculated along an adiabat using the thermoelastic parameters determined in this study are larger than those obtained using published values, implying that velocities for many mantle components may be underestimated at mantle temperatures because high temperature experimental data are lacking.

Scandium (Sc) is a rare element that finds uses in modern technologies. Thermodynamic properties of Sc phases could help in the development of innovative technologies to extract Sc from mining waste. In this work, we investigated the FeOOH–ScOOH solid solution with the goethite structure. The end members and five intermediate compositions were synthesized and characterized. The lattice parameters show that the solid solution is non-ideal, with complex behavior induced by the Fe–Sc substitution. The excess unit-cell volume deviates negatively for the Sc-rich region, and positively for the Fe-rich region from the ideal behavior (Vegard’s law). Enthalpies of dissolution were determined by acid-solution calorimetry in 5 mol(cdot hbox {dm}^{-3}) HCl at T = 343.15 K. Enthalpies of mixing ((Delta _{mix}H)), calculated from the experimental data, are small and positive. The available data allow for fitting the data as (Delta _{mix}H = W x (1-x)), with the mixing parameter (W = 15.2pm)1.0 kJ(cdot hbox {mol}^{-1}). Using (Delta _fG^o) of ScOOH from earlier literature, we calculated a Lippmann diagram that shows that Sc should strongly partition into the aqueous phase upon goethite precipitation. The field observations from lateritic profiles show that Sc is primarily harbored by goethite via adsorption. It seems that under weathering conditions, thermodynamically driven partitioning of (hbox {Sc}^{3+}) into the aqueous phases and its subsequent adsorption onto goethite surfaces controls the mobility of Sc in the weathering profiles.