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1.
We present results from low-temperature heat capacity measurements of spinels along the solid solution between MgAl2O4 and MgCr2O4. The data also include new low-temperature heat capacity measurements for MgAl2O4 spinel. Heat capacities were measured between 1.5 and 300 K, and thermochemical functions were derived from the results.
No heat capacity anomaly was observed for MgAl2O4 spinel; however, we observe a low-temperature heat capacity anomaly for Cr-bearing spinels at temperatures below 15 K. From
our data we calculate standard entropies (298.15 K) for Mg(Cr,Al)2O4 spinels. We suggest a standard entropy for MgAl2O4 of 80.9 ± 0.6 J mol−1 K−1. For the solid solution between MgAl2O4 and MgCr2O4, we observe a linear increase of the standard entropies from 80.9 J mol−1 K−1 for MgAl2O4 to 118.3 J mol−1 K−1 for MgCr2O4. 相似文献
2.
Planewave pseudopotential calculations of supercell total energies were used as bases for first-principles calculations of
the CaCO3–MgCO3 and CdCO3–MgCO3 phase diagrams. Calculated phase diagrams are in qualitative to semiquantitative agreement with experiment. Two unobserved
phases, Cd3Mg (CO3)4 and CdMg3(CO3)4, are predicted. No new phases are predicted in the CaCO3–MgCO3 system, but a low-lying metastable Ca3Mg(CO3)4 state, analogous to the Cd3Mg(CO3)4 phase is predicted. All of the predicted lowest-lying metastable states, except for huntite CaMg3(CO3)4, have dolomite-related structures, i.e. they are layer structures in which A
m
B
n
cation layers lie perpendicular to the rhombohedral [111] vector.
Received: 6 May 2002 / Accepted: 23 October 2002
Acknowledgements This work was partially supported by NSF contract DMR-0080766 and NIST. 相似文献
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Shigeto Hirai Yohei Kojima Hiroaki Ohfuji Norimasa Nishiyama Tetsuo Irifune Stephan Klemme Geoffrey Bromiley J. Paul Attfield 《Physics and Chemistry of Minerals》2011,38(8):631-637
Raman spectroscopy and heat capacity measurements have been used to study the post-perovskite phase of CaIr0.5Pt0.5O3, recovered from synthesis at a pressure of 15 GPa. Laser heating CaIr0.5Pt0.5O3 to 1,900 K at 60 GPa produces a new perovskite phase which is not recoverable and reverts to the post-perovskite polymorph
between 20 and 9 GPa on decompression. This implies that Pt-rich CaIr1−xPtxO3 perovskites including the end member CaPtO3 cannot easily be recovered to ambient pressure from high P–T synthesis. We estimate an increase in the thermodynamic Grüneisen
parameter across the post-perovskite to perovskite transition of 34%, of similar magnitude to those for (Mg,Fe)SiO3 and MgGeO3, suggesting that CaIr0.5Pt0.5O3 is a promising analogue for experimental studies of the competition in energetics between perovskite and post-perovskite
phases of magnesium silicates in Earth’s lowermost mantle. Low-temperature heat capacity measurements show that CaIrO3 has a significant Sommerfeld coefficient of 11.7 mJ/mol K2 and an entropy change of only 1.1% of Rln2 at the 108 K Curie transition, consistent with the near-itinerant electron magnetism. Heat capacity results for post-perovskite
CaIr0.5Rh0.5O3 are also reported. 相似文献
6.
Dmytro M. Trots Alexander Kurnosov Leonid Vasylechko Marek Berkowski Tiziana Boffa Ballaran Daniel J. Frost 《Physics and Chemistry of Minerals》2011,38(7):561-567
A single crystal X-ray diffraction study on lithium tetraborate Li2B4O7 (diomignite, space group I41
cd) has been performed under pressure up to 8.3 GPa. No phase transitions were found in the pressure range investigated, and
hence the pressure evolution of the unit-cell volume of the I41
cd structure has been described using a third-order Birch–Murnaghan equation of state (BM-EoS) with the following parameters:
V
0
= 923.21(6) Å3, K
0
= 45.6(6) GPa, and K′ = 7.3(3). A linearized BM-EoS was fitted to the axial compressibilities resulting in the following parameters a
0
= 9.4747(3) Å, K
0a
= 73.3(9) GPa, K′
a
= 5.1(3) and c
0
= 10.2838(4) Å, K
0c
= 24.6(3) GPa, K′
c
= 7.5(2) for the a and c axes, respectively. The elastic anisotropy of Li2B4O7 is very large with the zero-pressure compressibility ratio β
0c
/β
0a
= 3.0(1). The large elastic anisotropy is consistent with the crystal structure: A three-dimensional arrangement of relatively
rigid tetraborate groups [B4O7]2− forms channels occupied by lithium along the polar c–axis, and hence compression along the c axis requires the shrinkage of the lithium channels, whereas compression in the a direction depends mainly on the contraction of the most rigid [B4O7]2− units. Finally, the isothermal bulk modulus obtained in this work is in general agreement with that derived from ultrasonic
(Adachi et al. in Proceedings-IEEE Ultrasonic Symposium, 228–232, 1985; Shorrocks et al. in Proceedings-IEEE Ultrasonic Symposium, 337–340, 1981) and Brillouin scattering measurements (Takagi et al. in Ferroelectrics, 137:337–342, 1992). 相似文献
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Philippe Léone Charlotte Doussier-Brochard Gilles André Yves Moëlo 《Physics and Chemistry of Minerals》2008,35(4):201-206
Mn2+Sb2S4, a monoclinic dimorph of clerite, and benavidesite (Mn2+Pb4Sb6S14) show well-individualized single chains of manganese atoms in octahedral coordination. Their magnetic structures are presented
and compared with those of iron derivatives, berthierite (Fe2+Sb2S4) and jamesonite (Fe2+Pb4Sb6S14). Within chains, interactions are antiferromagnetic. Like berthierite, MnSb2S4 shows a spiral magnetic structure with an incommensurate 1D propagation vector [0, 0.369, 0], unchanged with temperature.
In berthierite, the interactions between identical chains are antiferromagnetic, whereas in MnSb2S4 interactions between chains are ferromagnetic along c-axis. Below 6 K, jamesonite and benavidesite have commensurate magnetic structures with the same propagation vector [0.5, 0, 0]:
jamesonite is a canted ferromagnet and iron magnetic moments are mainly oriented along the a-axis, whereas for benavidesite, no angle of canting is detected, and manganese magnetic moments are oriented along b-axis. Below 30 K, for both compounds, one-dimensional magnetic ordering or correlations are visible in the neutron diagrams
and persist down to 1.4 K. 相似文献
9.
Akio Suzuki Eiji Ohtani Hidenori Terasaki Keisuke Nishida Hiromi Hayashi Tatsuya Sakamaki Yuki Shibazaki Takumi Kikegawa 《Physics and Chemistry of Minerals》2011,38(1):59-64
The viscosity of a silicate melt of composition NaAlSi2O6 was measured at pressures from 1.6 to 5.5 GPa and at temperatures from 1,350 to 1,880°C. We employed in situ falling sphere
viscometry using X-ray radiography. We found that the viscosity of the NaAlSi2O6 melt decreased with increasing pressure up to 2 GPa. The pressure dependence of viscosity is diminished above 2 GPa. By using
the relationship between the logarithm of viscosity and the reciprocal temperature, the activation energies for viscous flow
were calculated to be 3.7 ± 0.4 × 102 and 3.7 ± 0.5 × 102 kJ/mol at 2.2 and 2.9 GPa, respectively. 相似文献
10.
M. Zhang G. J. Redhammer E. K. H. Salje M. Mookherjee 《Physics and Chemistry of Minerals》2002,29(9):609-616
Synthetic aegirine LiFeSi2O6 and NaFeSi2O6 were characterized using infrared spectroscopy in the frequency range 50–2000 cm−1, and at temperatures between 20 and 300 K. For the C2/c phase of LiFeSi2O6, 25 of the 27 predicted infrared bands and 26 of 30 predicted Raman bands are recorded at room temperature. NaFeSi2O6 (with symmetry C2/c) shows 25 infrared and 26 Raman bands. On cooling, the C2/c–P21/c structural phase transition of LiFeSi2O6 is characterized by the appearance of 13 additional recorded peaks. This observation indicates the enlargement of the unit
cell at the transition point. The appearance of an extra band near 688 cm−1 in the monoclinic P21/c phase, which is due to the Si–O–Si vibration in the Si2O6 chains, indicates that there are two non-equivalent Si sites with different Si–O bond lengths. Most significant spectral
changes appear in the far-infrared region, where Li–O and Fe–O vibrations are mainly located. Infrared bands between 300 and
330 cm−1 show unusually dramatic changes at temperatures far below the transition. Compared with the infrared data of NaFeSi2O6 measured at low temperatures, the change in LiFeSi2O6 is interpreted as the consequence of mode crossing in the frequency region. A generalized Landau theory was used to analyze
the order parameter of the C2/c–P21/c phase transition, and the results suggest that the transition is close to tricritical.
Received: 21 January 2002 / Accepted: 22 July 2002 相似文献
11.
The crystal structure of the unstable mineral alumoklyuchevskite K3Cu3AlO2(SO4)4 [monoclinic, I2, a = 18.772(7), b = 4.967(2), c = 18.468(7) Å, β = 101.66(1)°, V = 1686(1) Å] was refined to R 1 = 0.131 for 2450 unique reflections with F ≥ 4σF hkl. The structure is based on oxocentered tetrahedrons (OAlCu 3 7+ ) linked into chains via edges. Each chain is surrounded by SO4 tetrahedrons forming a structural complex. Each complex is elongated along the b axis. This type of crystal structure was also found in other fumarole minerals of the Great Tolbachik Fissure Eruption (GTFE, Kamchatka Peninsula, Russia, 1975–1976), klyuchevskite, K3Cu3Fe3+O2(SO4)4; and piypite, K2Cu2O(SO4)2. 相似文献
12.
Stabilities of hexagonal new aluminous (NAL) phase and Ca-ferrite-type (CF) phase were investigated on the join NaAlSiO4-MgAl2O4 in a pressure range from 23 to 58 GPa at approximately constant temperature of 1,850 K, on the basis of in situ synchrotron
X-ray diffraction measurements in a laser-heated diamond-anvil cell. The results show that NAL is formed as a single phase
up to 34 GPa, NAL + CF between 34 and 43 GPa, and only CF at higher pressures in 40%NaAlSiO4-60%MgAl2O4 bulk composition. On the other hand, both NAL and CF coexist below 38 and 36 GPa, and only CF was obtained at higher pressures
in 60%NaAlSiO4-40%MgAl2O4 and 20%NaAlSiO4-80%MgAl2O4 composition, respectively. These results indicate that NAL appears only up to 46 GPa at 1,850 K, and CF forms continuous
solid solution at higher pressures on the join NaAlSiO4-MgAl2O4. NAL has limited stability in subducted mid-oceanic ridge basalt crust in the Earth’s lower mantle and undergoes a phase
transition to CF in deeper levels. 相似文献
13.
V. Nourozi Rad M. Anbia M. Hossaini Sadr 《International Journal of Environmental Science and Technology》2018,15(3):631-636
The Claus process has been used for the conversion of H2S and SO2 to elemental sulfur. These two sulfur compounds need special attention because they are very poisonous with negative impact on both the environment and human health. Here, highly active Fe–Ni/TiO2 catalyst has been prepared and shaped by three different binders (bentonite, polyethylene glycol and carboxymethyl cellulose) into extrudes. Comparing the mechanical strength and surface area of prepared extrudes, the optimal shaped catalyst was selected with 20% of bentonite, 2% of PEG and 2% of CMC. The optimal catalyst was characterized by X-ray powder diffraction, temperature-programmed reduction, Brunauer–Emmett–Teller specific surface area, Barrett–Joyner–Halenda, scanning electron microscopy and energy-dispersive X-ray techniques and used for sulfur recovery process. The performance of this product for sulfur recovery via Claus process was excellent with the conversion of hydrogen sulfide of 76.77% and sulfur dioxide of 97.83%. The catalyst also provides high hydrolysis activity of CS2 (83.06%). Therefore, a highly active TiO2-supported shaped catalyst with 85.62% of conversion efficiency has been prepared successfully to convert the small amounts of H2S, SO2 and CS2 to elemental sulfur. 相似文献
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15.
The segregation of ten isovalent impurities (Al3+ Cr3+, Eu3+, Gd3+, Ho3+, La3+, Lu3+, Nd3+, Tb3+, Y3+) to the and the (0001) surfaces of haematite (-Fe2O3) have been studied using atomistic simulation where the forces between the atoms are modelled using the Born model of solids. Segregation is found to be energetically favoured in virtually every case. The results for the surface show that the most favourable impurity surface concentration is 33.33%. The (0001) surface has two possible terminations, one terminated by iron atoms and the other by oxygen. No minimum is calculated for the Fe termination of the (0001) surface at low temperatures, but when the effect of raising the temperature is considered, an energy minimum is found, also at 33.33% impurity coverage. In contrast, the O terminated (0001) surface has a minimum in the segregation energy for between 16.67 and 33.33% depending on the cation being considered. 相似文献
16.
Hanen Azaza Lassaad Mechi Amira Doggaz Virgil Optasanu Mohamed Tlili Mohamed Ben Amor 《Arabian Journal of Geosciences》2017,10(10):220
During the production of hydrocarbons from subterranean reservoirs, scaling with calcium carbonate and barium sulfate causes flux decline and dangerous problems in production facilities. This work is intended to study the effect of calcium ions on the precipitation of barium sulfate (barite); then, the effect of the formed barite on calcium carbonate crystallization. The conductometric and pH methods were used to follow the progress of the precipitation reaction in aqueous medium. The obtained precipitates were characterized by FTIR, RAMAN, SEM, and XRD. It was shown that Ca2+ in the reaction media does not affect the microstructure of barite even for higher calcium–barium molar ratio. It influences the precipitation kinetics and the solubility of barite by the formation of CaSO4° ion pairing as a predominant role of complex formation (CaSO4) and the increase of the ionic strength. In Ca(HCO3)2-BaSO4-NaCl aqueous system, experiments have showed that added or formed barite in the reaction media accelerates calcite precipitation. No effect on the microstructure of heterogeneous formed calcite which remain calcite shape. However the presence of carbonate ions affects slightly the microstructure of barite. 相似文献
17.
The structure of CaGe2O5 between room temperature and 923 K has been determined by X-ray powder diffraction. A continuous phase transition from triclinic C1¯ to monoclinic C2/c symmetry at Tc=714±3 K is observed. The transition is accompanied by a weak heat capacity anomaly. This anomaly and the strain analysis based on the measured lattice parameters indicate a classical second-order phase transition. The order parameter, as measured by the strain component e23, is associated with the displacement of the Ca cation. Electronic structure optimization by density functional methods is used to verify the centric space group of the low-temperature structure of CaGe2O5. 相似文献
18.
Using density functional simulations within the generalized gradient approximation and projector-augmented wave method together
with thermodynamic modelling, the reciprocal solubilities of MgSiO3 and CaSiO3 perovskites were calculated for pressures and temperatures of the Earth’s lower mantle from 25 to 100 GPa and 0 to 6,000 K,
respectively. The solubility of Ca in MgSiO3 at conditions along a mantle adiabat is found to be less than 0.02 atoms per formula unit. The solubility of Mg in CaSiO3 is even lower, and most important, the extent of solid solution decreases with pressure. To dissolve CaSiO3 perovskite completely in MgSiO3 perovskite, a solubility of 7.8 or 2.3 mol% would be necessary for a fertile pyrolytic or depleted harzburgitic mantle, respectively.
Thus, for any reasonable geotherm, two separate perovskites will be present in fertile mantle, suggesting that Ca-perovskite
will be residual to low degree melting throughout the entire mantle. At the solidus, CaSiO3 perovskite might completely dissolve in MgSiO3 perovskite only in a depleted mantle with <1.25 wt% CaO. These implications may be modified if Ca solubility in MgSiO3 is increased by other major mantle constituents such as Fe and Al. 相似文献
19.
L. Z. Reznitsky E. V. Sklyarov T. Armbruster Z. F. Ushchapovskaya E. V. Galuskin Yu. S. Polekhovsky I. G. Barash 《Geology of Ore Deposits》2010,52(7):574-583
Oxyvanite has been identified as an accessory mineral in Cr-V-bearing quartz-diopside meta- morphic rocks of the Slyudyanka Complex in the southern Baikal region, Russia. The new mineral was named after constituents of its ideal formula (oxygen and vanadium). Quartz, Cr-V-bearing tremolite and micas, calcite, clinopyroxenes of the diopside-kosmochlor-natalyite series, Cr-bearing goldmanite, eskolaite-karelianite dravite-vanadiumdravite, V-bearing titanite, ilmenite, and rutile, berdesinskiite, schreyerite, plagioclase, scapolite, barite, zircon, and unnamed U-Ti-V-Cr phases are associated minerals. Oxyvanite occurs as anhedral grains up to 0.1–0.15 mm in size, without visible cleavage and parting. The new mineral is brittle, with conchoidal fracture. Observed by the naked eye, the mineral is black, with black streak and resinous luster. The microhardness (VHN) is 1064–1266 kg/mm2 (load 30 g), and the mean value is 1180 kg/mm2. The Mohs hardness is about 7.0–7.5. The calculated density is 4.66(2) g/cm3. The color of oxyvanite is pale cream in reflected light, without internal reflections. The measured reflectance in air is as follows (λ, nm-R, %): 440-17.8; 460-18; 480-18.2; 520-18.6; 520-18.6; 540-18.8; 560-18.9; 580-19; 600-19.1; 620-19.2; 640-19.3; 660-19.4; 680-19.5; 700-19.7. Oxyvanite is monoclinic, space group C2/c; the unit-cell dimensions are a = 10.03(2), b = 5.050(1), c = 7.000(1) Å, β = 111.14(1)°, V = 330.76(5)Å3, Z = 4. The strongest reflections in the X-ray powder pattern [d, Å, (I in 5-number scale)(hkl)] are 3.28 (5) (20\(\bar 2\)); 2.88 (5) (11\(\bar 2\)); 2.65, (5) (310); 2.44 (5) (112); 1.717 (5) (42\(\bar 2\)); 1.633 (5) (31\(\bar 4\)); 1.446 (4) (33\(\bar 2\)); 1.379 (5) (422). The chemical composition (electron microprobe, average of six point analyses, wt %): 14.04 TiO2, 73.13 V2O3 (53.97 V2O3calc, 21.25 VO2calc), 10.76 Cr2O3, 0.04 Fe2O3, 0.01 Al2O3, 0.02 MgO, total is 100.03. The empirical formula is (V 1.70 3+ Cr0.30)2.0(V 0.59 4+ Ti0.41)1.0O5. Oxyvanite is the end member of the oxyvanite-berdesinskiite series with homovalent isomorphic substitution of V4+ for Ti. The type material has been deposited at the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow. 相似文献
20.
V. L. Vinograd O. G. Safonov D. J. Wilson L. L. Perchuk L. Bindi J. D. Gale B. Winkler 《Petrology》2010,18(4):447-459
Atomistic model was proposed to describe the thermodynamics of mixing in the diopside-K-jadeite solid solution (CaMgSi2O6-KAlSi2O6). The simulations were based on minimization of the lattice energies of 800 structures within a 2 × 2 × 4 supercell of C2/c diopside with the compositions between CaMgSi2O6 and KAlSi2O6 and with variable degrees of order/disorder in the arrangement of Ca/K cations in M2 site and Mg/Al in Ml site. The energy
minimization was performed with the help of a force-field model. The results of the calculations were used to define a generalized
Ising model, which included 37 pair interaction parameters. Isotherms of the enthalpy of mixing within the range of 273–2023
K were calculated with a Monte Carlo algorithm, while the Gibbs free energies of mixing were obtained by thermodynamic integration
of the enthalpies of mixing. The calculated T-X diagram for the system CaMgSi2O6-KAlSi2O6 at temperatures below 1000 K shows several miscibility gaps, which are separated by intervals of stability of intermediate
ordered compounds. At temperatures above 1000 K a homogeneous solid solution is formed. The standard thermodynamic properties
of K-jadeite (KAlSi2O6) evaluated from quantum mechanical calculations were used to determine location of several mineral reactions with the participation
of the diopside-K-jadeite solid solution. The results of the simulations suggest that the low content of KalSi2O6 in natural clinopyroxenes is not related to crystal chemical factors preventing isomorphism, but is determined by relatively
high standard enthalpy of this end member. 相似文献