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1.
Data from the revised Geneva-Copenhagen catalog are used to study the influence of radial migration of stars on the age dependences
of parameters of the velocity ellipsoids for nearby stars in the thin disk of the Galaxy, assuming that the mean radii of
the stellar orbits remain constant. It is demonstrated that precisely the radial migration of stars, together with the negative
metallicity gradient in the thin disk, are responsible for the observed negative correlation between the metallicities and
angular momenta of nearby stars, while the angular momenta of stars that were born at the same Galactocentric distances do
not depend on either age or metallicity. The velocity components of the Sun relative to the Local Standard of Rest derived
using data for stars born at the solar Galactocentric distance are (U
⊙, V
⊙, W
⊙)
LSR
= (5.1 ± 0.4, 7.9 ± 0.5, 7.7 ± 0.2) km/s. The two coordinates of the apex of the solar motion remain equal to 〈l
⊙〉 = 70° ± 7° and 〈b
⊙〉 = 41° ± 2°, within the errors. The indices for the power-law age dependences of them ajor, middle, and minor semi-axes become
0.26±0.04, 0.32±0.03, and 0.07±0.03, respectively. As a result, with age, the velocity ellipsoid for thin-disk stars born
at the solar Galactocentric distance increases only in the plane of the disk, remaining virtually constant in the perpendicular
direction. Its shape remains far from equilibrium, and the direction of the major axis does not change with age: the ellipsoid
vertex deviation remains constant and equal to zero within the errors (〈L〉 = 0.7° ± 0.6°, 〈B〉 = 1.9° ± 1.1°). Such a small increase in the velocity dispersion perpendicular to the Galactic plane with age can probably
be explained by “heating” of the stellar system purely by spiral density waves, without a contribution from giant molecular
clouds. 相似文献
2.
I. F. Malov 《Astronomy Reports》2010,54(10):925-931
The latest observational data are analyzed to investigate their consistency with two known models for anomalous X-ray pulsars
(AXPs) and soft gamma-ray repeaters (SGRs): the magnetar and drift models. The results of spectral measurements disagree with
the predictions of theories that assume the presence of super-strong magnetic fields on AXPs and SGRs and associated processes
for the generation of electron-positron plasma in the upper layers of the neutron-star magnetosphere. We present arguments
against the use of magnetic-dipole braking for these objects. The rotational periods P, period derivatives dP/dt, and magnetic fields B of known AXPs and SGRs are calculated for the drift model. The mean values of these parameters in the sample used are 〈P〉 = 108 ms and 〈log B
s
[G]〉 = 12.08. Overall, the measured profiles, polarizations, and spectra can be brought into agreement with the drift model. 相似文献
3.
I. S. Savanov I. I. Romanyuk E. A. Semenko E. S. Dmitrienko 《Astronomy Reports》2011,55(12):1115-1122
We have analyzed polarization observations of the subdwarf Bal 09, which is one of a group of hybrid sdB stars that display
simultaneously both short- and long-period pulsations. Certain properties previously unknown for subdwarfs have been established
for Bal 09, such as variations of the pulsation amplitude of the main oscillation mode, rotational splitting of multiplets,
and variations of this splitting. Information about the stellar magnetic field must be considered if we wish to explain these
properties. New observational data enabling estimation of the longitudinal magnetic field of Bal 09 have been obtained on
the main stellar spectrograph of the 6-m telescope of the Special Astrophysical Observatory. Studies of the longitudinal component
of the magnetic field 〈B
z
〉 were carried out using a regression analysis. This method simultaneously yields estimates of the uncertainty in 〈B
z
〉. Test measurements of 〈B
z
〉 were carried out using the same method. For the star HD 158974, which has zero total magnetic field, the estimated longitudinal
magnetic field is 〈B
z
〉 = −4 ± 5 G. The standard magnetic field for the Ap star α
2CVn was measured to be −363 ± 17 G, in very good agreement with measurements in the literature. The estimated longitudinal
magnetic field for Bal 09 is 34 ± 63G—appreciably lower than values established earlier for six subdwarfs, ≈1.5 kG. The results
of the regression analysis for both individual spectral subranges and for intervals containing characteristic spectral features
did not indicate reliable detections of a magnetic field exceeding the uncertainties in 〈B
z
〉. The uncertainty in 〈B
z
〉, which was 60–80 G for the entire spectral range and 140–200 G for selected spectral intervals, leads to an estimated upper
limit on the longitudinal magnetic field 〈B
z
〉 for Bal 09. This estimate for 〈B
z
〉 can place observational constraints on theoretical explanations for the amplitude variations of the pulsations, rotational
splitting of multiplets, and possible variations of the internal structure of the star. 相似文献
4.
The α − β transition of quartz was successfully observed with using a single sample by means of the rectangular parallelepiped
resonance (RPR) method. An oriented rectangular parallelepiped of α-quartz single crystal was prepared and the resonant frequencies
of 30–11 vibrational modes were measured from room temperature to 700°C. The softening of quartz crystal was observed as the
significant reduction of resonant frequencies near the α–β transition. The present study is the first application of the RPR
method to the study of phase transition. The complete set of elastic constants of α- and β-quartz were determined as a function
of temperature by the least-squares inversion of the measured frequency data obtained by a single run. This is a merit yielded
by the RPR method. It is shown near the α − β transition in both α- and β-quartz that the elastic parameters decrease proportionally
to |T−T
0|−n
, where T is temperature and T
0 is the transition temperature, 573.0°C for α-quartz and 574.3°C for β-quartz. It was also seen that linear incompressibilities
K
1 = (C
11
+C
12
+C
13)/3 and K
3 = (C
33
+2C
13)/3 decrease rapidly toward the transition, whereas, shear moduli C
44, C
S1 = (C
11
+C
33
-2C
13)/4 and C
S3 = (C
11
-C
12)/2 = C
66 decrease only slightly. The shear modulus C
S3 = C
66 increased slightly in α-quartz. The elastic properties of isotropic aggregate of quartz were calculated, and it is shown
that the longitudinal wave velocity significantly decreases at the α − β transition, whereas, the shear wave velocity decreases
only slightly. 相似文献
5.
G. Diego Gatta Marco Merlini Hanns-Peter Liermann André Rothkirch Mauro Gemmi Alessandro Pavese 《Physics and Chemistry of Minerals》2012,39(5):385-397
The thermoelastic behavior of a natural clintonite-1M [with composition: Ca1.01(Mg2.29Al0.59Fe0.12)Σ3.00(Si1.20Al2.80)Σ4.00O10(OH)2] has been investigated up to 10 GPa (at room temperature) and up to 960°C (at room pressure) by means of in situ synchrotron
single-crystal and powder diffraction, respectively. No evidence of phase transition has been observed within the pressure
and temperature range investigated. P–V data fitted with an isothermal third-order Birch–Murnaghan equation of state (BM-EoS) give V
0 = 457.1(2) ?3, K
T0 = 76(3)GPa, and K′ = 10.6(15). The evolution of the “Eulerian finite strain” versus “normalized stress” shows a linear positive trend. The
linear regression yields Fe(0) = 76(3) GPa as intercept value, and the slope of the regression line leads to a K′ value of 10.6(8). The evolution of the lattice parameters with pressure is significantly anisotropic [β(a) = 1/3K
T0(a) = 0.0023(1) GPa−1; β(b) = 1/3K
T0(b) = 0.0018(1) GPa−1; β(c) = 1/K
T0(c) = 0.0072(3) GPa−1]. The β-angle increases in response to the applied P, with: βP = β0 + 0.033(4)P (P in GPa). The structure refinements of clintonite up to 10.1 GPa show that, under hydrostatic pressure, the structure rearranges
by compressing mainly isotropically the inter-layer Ca-polyhedron. The bulk modulus of the Ca-polyhedron, described using
a second-order BM-EoS, is K
T0(Ca-polyhedron) = 41(2) GPa. The compression of the bond distances between calcium and the basal oxygens of the tetrahedral
sheet leads, in turn, to an increase in the ditrigonal distortion of the tetrahedral ring, with ∂α/∂P ≈ 0.1°/GPa within the P-range investigated. The Mg-rich octahedra appear to compress in response to the applied pressure, whereas the tetrahedron
appears to behave as a rigid unit. The evolution of axial and volume thermal expansion coefficient α with temperature was
described by the polynomial α(T) = α0 + α1
T
−1/2. The refined parameters for clintonite are as follows: α0 = 2.78(4) 10−5°C−1 and α1 = −4.4(6) 10−5°C1/2 for the unit-cell volume; α0(a) = 1.01(2) 10−5°C−1 and α1(a) = −1.8(3) 10−5°C1/2 for the a-axis; α0(b) = 1.07(1) 10−5°C−1 and α1(b) = −2.3(2) 10−5°C1/2 for the b-axis; and α0(c) = 0.64(2) 10−5°C−1 and α1(c) = −7.3(30) 10−6°C1/2for the c-axis. The β-angle appears to be almost constant within the given T-range. No structure collapsing in response to the T-induced dehydroxylation was found up to 960°C. The HP- and HT-data of this study show that in clintonite, the most and the less expandable directions do not correspond to the most and
the less compressible directions, respectively. A comparison between the thermoelastic parameters of clintonite and those
of true micas was carried out. 相似文献
6.
Günther J. Redhammer Fernando Cámara Matteo Alvaro Fabrizio Nestola Gerold Tippelt Sebastian Prinz Jan Simons Georg Roth Georg Amthauer 《Physics and Chemistry of Minerals》2010,37(10):685-704
A synthetic clinopyroxene with composition LiFe3+Ge2O6, monoclinic s.g. P21/c, a = 9.8792(7), b = 8.8095(5), c = 5.3754(3) Å, β = 108.844(6)°, V = 442.75(16) Å3, has been studied by in situ low- and high-temperature single-crystal X-ray diffraction. The variation of lattice parameters and the intensity of the b-type reflections (h + k = 2n + 1, only present in the P-symmetry) with increasing temperature showed a displacive phase transition from space group P21/c to C2/c at a transition temperature T tr = 789 K, first order in character, with a sudden volume increase of 1.6% and a decrease of β by 1° at the transition. This spontaneous dilatation is reversible, shows a limited hysteresis of ±10°C, and corresponds to the vanishing of the b-type reflections, thus indicating a symmetry increase to space group C2/c. Below T tr an expansion is observed for all the cell parameters, while the β angle remained almost constant; at T > T tr the thermal volume expansion is due to dilatation of the structure in the $(\bar{1}\,0\,1) A synthetic clinopyroxene with composition LiFe3+Ge2O6, monoclinic s.g. P21/c, a = 9.8792(7), b = 8.8095(5), c = 5.3754(3) ?, β = 108.844(6)°, V = 442.75(16) ?3, has been studied by in situ low- and high-temperature single-crystal X-ray diffraction. The variation of lattice parameters
and the intensity of the b-type reflections (h + k = 2n + 1, only present in the P-symmetry) with increasing temperature showed a displacive phase transition from space group P21/c to C2/c at a transition temperature T
tr = 789 K, first order in character, with a sudden volume increase of 1.6% and a decrease of β by 1° at the transition. This spontaneous dilatation is reversible, shows a limited hysteresis of ±10°C, and corresponds
to the vanishing of the b-type reflections, thus indicating a symmetry increase to space group C2/c. Below T
tr an expansion is observed for all the cell parameters, while the β angle remained almost constant; at T > T
tr the thermal volume expansion is due to dilatation of the structure in the ([`1] 0 1)(\bar{1}\,0\,1) plane, mostly along [0 1 0], and pure shear in the (0 1 0) plane due to the decrease of β. From comparison with silicate analogues, the germanate clinopyroxenes are more expansible, while the P21/c expands more than the C2/c phase. The evolution of Q
2 (calculated as the normalized intensity of b-type reflections) with T in the framework of the Landau theory has been done using a standard expression for a first order phase transition. We observe
a jump of Q
02 = 0.538(2) at T
tr, with T
c of 481(7) K, b/a = −2,290 K, and c/a = 3,192 K, and thus far from being tri-critical point. A closely related composition (LiFe3+Si2O6) shows an equivalent phase transition at 228 K, which is very close to the tri-critical point and 561 K cooler. This result
indicates that a change in the composition of tetrahedral sites can have dramatic effects on the P21/c ↔ C2/c displacive phase transition in clinopyroxenes. The major changes observed in the evolution of the crystal structure with
T are observed in the M2 polyhedron, with a volume decrease by ca. 13.3%, compared to ca. 1.3% observed in the M1 polyhedron.
The tetrahedra behave as rigid units with neither a significant change of volume at T > T
tr (<1‰), nor a change of tilting of the basal plane. No change in coordination is observed at T > T
tr in the M2 polyhedron, which remains sixfold coordinated although a strong deformation of this polyhedron is observed. This
deformation is related to a strong change by 51.4° at T
tr of the kinking angle (O3–O3–O3 angle) of the B-chain of tetrahedra, which switches from O-rotated to S-rotated [from 143.3(5)°
to 194.7(6)°]. The A-chain is S-rotated at T < T
tr [206.8(5)° at 703 K] and extends by 12° at the transition. 相似文献
7.
M. Akaogi H. Takayama H. Kojitani H. Kawaji T. Atake 《Physics and Chemistry of Minerals》2007,34(3):169-183
The low-temperature isobaric heat capacities (C
p) of β- and γ-Mg2SiO4 were measured at the range of 1.8–304.7 K with a thermal relaxation method using the Physical Property Measurement System.
The obtained standard entropies (S°298) of β- and γ-Mg2SiO4 are 86.4 ± 0.4 and 82.7 ± 0.5 J/mol K, respectively. Enthalpies of transitions among α-, β- and γ-Mg2SiO4 were measured by high-temperature drop-solution calorimetry with gas-bubbling technique. The enthalpies of the α−β and β−γ
transitions at 298 K (ΔH°298) in Mg2SiO4 are 27.2 ± 3.6 and 12.9 ± 3.3 kJ/mol, respectively. Calculated α−β and β−γ transition boundaries were generally consistent
with those determined by high-pressure experiments within the errors. Combining the measured ΔH°298 and ΔS°298 with selected data of in situ X-ray diffraction experiments at high pressure, the ΔH°298 and ΔS°298 of the α−β and β−γ transitions were optimized. Calculation using the optimized data tightly constrained the α−β and β−γ transition
boundaries in the P, T space. The slope of α−β transition boundary is 3.1 MPa/K at 13.4 GPa and 1,400 K, and that of β−γ boundary 5.2 MPa/K at 18.7 GPa
and 1,600 K. The post-spinel transition boundary of γ-Mg2SiO4 to MgSiO3 perovskite plus MgO was also calculated, using the optimized data on γ-Mg2SiO4 and available enthalpy and entropy data on MgSiO3 perovskite and MgO. The calculated post-spinel boundary with a Clapeyron slope of −2.6 ± 0.2 MPa/K is located at pressure
consistent with the 660 km discontinuity, considering the error of the thermodynamic data. 相似文献
8.
H. Graetsch 《Physics and Chemistry of Minerals》2001,28(5):313-321
The crystal structure of intermediate incommensurate tridymite was refined at 150 °C from powder data. Upon cooling from
above 220 °C, the basic structure with space group symmetry C2221 is gradually distorted from orthorhombic to monoclinic symmetry. With decreasing temperature, the monoclinic angle γ smoothly
opens up to 90.3°, while a displacive modulation with temperature-dependent wavelength develops. The 3 + 1 dimensional superspace
group of the incommensurate phase is C1121(αβ0). The modulation mainly consists of two sinusoidal transverse displacement waves for the silicon atoms coupled to rotations
of the rigid SiO4/2 tetrahedra. The wave vector is r=0.1192(1)a* − 0.0043(1)b* at 150 °C. Below 150 °C tridymite discontinuously transforms to another orthorhombic phase and the modulation partially
locks in at the wave vector r
1=1/3a*. Simultaneously, an additional incommensurate modulation with r
2= 0.0395(1)b* − 0.3882(1)c* is formed. The two-dimensional modulation does not vary significantly with the temperature.
Received: 13 September 2000 / Accepted: 29 January 2001 相似文献
9.
10.
D. L. Kohlstedt H. Keppler D. C. Rubie 《Contributions to Mineralogy and Petrology》1996,123(4):345-357
The solubility of hydroxyl in the α, β and γ phases of (Mg,Fe)2SiO4 was investigated by hydrothermally annealing single crystals of San Carlos olivine. Experiments were performed at a temperature
of 1000° or 1100 °C under a confining pressure of 2.5 to 19.5 GPa in a multianvil apparatus with the oxygen fugacity buffered
by the Ni:NiO solid-state reaction. Hydroxyl solubilities were determined from infrared spectra obtained of polished thin
sections in crack-free regions ≤100 μm in diameter. In the α-stability field, hydroxyl solubility increases systematically
with increasing confining pressure, reaching a value of ∼20,000 H/106Si (1200 wt ppm H2O) at the α-β phase boundary near 13 GPa and 1100 °C. In the β field, the hydroxyl content is ∼400,000 H/106Si (24,000 wt ppm H2O) at 14–15 GPa and 1100 °C. In the γ field, the solubility is ∼450,000 H/106Si (27,000 wt ppm H2O) at 19.5 GPa and 1100 °C. The observed dependence of hydroxyl solubility with increasing confining pressure in the α phase
reflects an increase in water fugacity with increasing pressure moderated by a molar volume term associated with the incorporation
of hydroxyl ions into the olivine structure. Combined with published results on the dependence of hydroxyl solubility on water
fugacity, the present results for the α phase can be summarized by the relation C
OH
= A(T)f nH2Oexp(−PΔV/RT), where A(T) = 1.1 H/106Si/MPa at 1100 °C, n = 1, and ΔV = 10.6×10–6 m3/mol. These data demonstrate that the entire present-day water content of the upper mantle could be incorporated in the mineral
olivine alone; therefore, a free hydrous fluid phase cannot be stable in those regions of the upper mantle with a normal concentration
of hydrogen. Free hydrous fluids are restricted to special tectonic environments, such as the mantle wedge above a subduction
zone.
Received: 10 February 1995 / Accepted: 23 October 1995 相似文献
11.
Qiong Liu Travis J. Tenner Rebecca A. Lange 《Contributions to Mineralogy and Petrology》2007,153(1):55-66
Brackets on the melting temperature of K2CO3 were experimentally determined at 1.86 ± 0.02 GPa (1,163–1,167°C), 2.79 ± 0.03 GPa (1,187–1,195°C), and 3.16 ± 0.04 GPa (1,183–1,189°C) in a piston-cylinder apparatus. These new data, in combination with published experiments at low pressure (<0.5 GPa), establish the K2CO3 fusion curve to 3.2 GPa. On the basis of these experiments and published thermodynamic data for crystalline and liquid K2CO3, the high-pressure density and compressibility of K2CO3 liquid were derived from the fusion curve. The pressure dependence of the liquid compressibility (K′0 = dK
0/dP, where K
0 = 1/β0) is between 16.2 and 11.6, with a best estimate of 13.7, in a third-order Birch–Murnaghan equation of state (EOS). This liquid K′0 leads to a density of 2,175 ± 36 kg/m3 at 4 GPa and 1,500°C, which is ∼30% lower than that reported in the literature on the basis of the falling-sphere method at the same conditions. The uncertainty in the liquid K′0 leads to an error in melt density of ± 2% at 4 GPa; the error decreases with decreasing pressure. With a K′0 of 13.7, the compressibility of K2CO3 at 1,500°C and 1 bar (K
0 = 3.8 GPa) drops rapidly with increasing pressure (
), which prevents a density crossover with silicate melts, such as CaAlSi2O8 and CaMgSi2O6, at upper mantle depths. 相似文献
12.
Transmission electron microscopy (TEM) has been used to investigate deformation microstructures of synthetic stishovite specimens deformed at 14 GPa, 1,300°C. Geometrical characteristics of numerous dislocations have been characterized by dislocation contrast and stereographic analyses in order to identify the easy slip systems of stishovite. TEM data allowed us to characterize the following slip systems: 〈100〉{001}, 〈100〉{010}, 〈100〉{021}, [001]{100}, [001]{110}, [001]{210} and
Observation of sub-grain boundaries and scalloped edge dislocations suggest that climb has been activated in the specimens. 相似文献
13.
Summary
Low-temperature phase transitions of leonite-type compounds, K2Me2+(SO4)2 · 4H2O (Me = Mg, Mn, Fe), are investigated by temperature dependent measurements of single-crystal X-ray reflection intensities
and lattice parameters. The transition temperatures and the progress of the transitions are determined by birefringence data
and differential scanning calorimetry. The cause for the phase transitions of leonite-type compounds is a dynamic disorder
of sulphate groups at room temperature (C2/m), that freezes in to an ordered structure (I2/a) at −4(1) °C in leonite, K2Mg(SO4)2 · 4H2O. At −153(1) °C the crystal structure switches to another ordered phase (P21/a). The Mn analogue shows the same succession with transition temperatures at −68(1) °C and −104(1) °C. The disordered room
temperature structure of the isotypic mineral mereiterite, K2Fe(SO4)2 · 4H2O, transforms directly to the ordered P21/a structure at 3(2) °C.
Analysis of X-ray intensities and of excess birefringence reveals that the displacive I2/a ⇔ P21/a phase transition of leonite and Mn-leonite is first order. According to Landau theory the C2/m ⇔ I2/a (leonite, Mn-leonite) and C2/m ⇔ P21/a (mereiterite) order-disorder transitions are almost tricritical.
Received March 7, 2001; revised version accepted June 27, 2001 相似文献
14.
Matteo Alvaro Fernando Cámara M. Chiara Domeneghetti Fabrizio Nestola Vittorio Tazzoli 《Contributions to Mineralogy and Petrology》2011,162(3):599-613
A natural Ca-poor pigeonite (Wo6En76Fs18) from the ureilite meteorite sample PCA82506-3, free of exsolved augite, was studied by in situ high-temperature single-crystal
X-ray diffraction. The sample, monoclinic P21/c, was annealed up to 1,093°C to induce a phase transition from P21/c to C2/c symmetry. The variation with increasing temperature of the lattice parameters and of the intensity of the b-type reflections (h + k = 2n + 1, present only in the P21/c phase) showed a displacive phase transition P21/c to C2/c at a transition temperature T
Tr = 944°C, first order in character. The Fe–Mg exchange kinetics was studied by ex situ single-crystal X-ray diffraction in
a range of temperatures between the closure temperature of the Fe–Mg exchange reaction and the transition temperature. Isothermal
disordering annealing experiments, using the IW buffer, were performed on three crystals at 790, 840 and 865°C. Linear regression
of ln k
D versus 1/T yielded the following equation:
ln k\textD = - 3717( ±416)/T(K) + 1.290( ±0.378); (R2 = 0.988) \ln \,k_{\text{D}} = - 3717( \pm 416)/T(K) + 1.290( \pm 0.378);\quad (R^{2} = 0.988) . The closure temperature (T
c) calculated using this equation was ∼740(±30)°C. Analysis of the kinetic data carried out taking into account the e.s.d.'s
of the atomic fractions used to define the Fe–Mg degree of order, performed according to Mueller’s model, allowed us to retrieve
the disordering rate constants C
0
K
dis+ for all three temperatures yielding the following Arrhenius relation:
ln( C0 K\textdis + ) = ln K0 - Q/(RT) = 20.99( ±3.74) - 26406( ±4165)/T(K); (R2 = 0.988) \ln \left( {C_{0} K_{\text{dis}}^{ + } } \right) = \ln \,K_{0} - Q/(RT) = 20.99( \pm 3.74) - 26406( \pm 4165)/T(K);\quad (R^{2} = 0.988) . An activation energy of 52.5(±4) kcal/mol for the Fe–Mg exchange process was obtained. The above relation was used to calculate
the following Arrhenius relation modified as a function of X
Fe (in the range of X
Fe = 0.20–0.50):
ln( C0 K\textdis + ) = (21.185 - 1.47X\textFe ) - \frac(27267 - 4170X\textFe )T(K) \ln \left( {C_{0} K_{\text{dis}}^{ + } } \right) = (21.185 - 1.47X_{\text{Fe}} ) - {\frac{{(27267 - 4170X_{\text{Fe}} )}}{T(K)}} . The cooling time constant, η = 6 × 10−1 K−1 year−1 calculated on the PCA82506-3 sample, provided a cooling rate of the order of 1°C/min consistent with the extremely fast late
cooling history of the ureilite parent body after impact excavation. 相似文献
15.
Katja Etzel Artur Benisek Edgar Dachs Lado Cemič 《Physics and Chemistry of Minerals》2007,34(10):733-746
The unite cell parameters and heat capacities of a series of synthetic clinopyroxenes on the join Ca-Tschermak (CaTs)−diopside
(Di) were measured using X-ray powder diffraction and calorimetric methods, respectively. The volume of mixing at 298 K shows
a negative asymmetric deviation from ideality. A two-parameter Margules fit to the data yields W
CaTs−Di
V
= −0.29 ± 0.11 cm3 mol−1 and W
Di−CaTs
V
= −1.14 ± 0.14 cm3 mol−1. Heat capacities were determined between 5 and 923 K by heat-pulse at 5−302 K and differential-scanning calorimetry at 143−923 K.
The precision of the low and high temperature C
p
data is better than ±1%. Polynomials of the form C
p
= a + bT
−1/2 + cT
−2 + dT
−3 were fitted to the C
p
data in the temperature range between 250 and 925 K. Thermal entropy values [S
298 − S
0] and [S
900 −S
0] as well as enthalpies [H
298 − H
0] and [H
900 − H
0] were calculated for all members of the solid solution series. No significant deviation from ideal mixing behavior was observed. 相似文献
16.
L. A. Koroleva N. D. Shikina P. G. Kolodina A. V. Zotov B. R. Tagirov Yu. V. Shvarov V. A. Volchenkova Yu. K. Shazzo 《Geochemistry International》2012,50(10):853-859
The hydrolysis of the Pd2+ ion in HClO4 solutions was examined at 25–70°C, and the thermodynamic constants of equilibrium K (1)0 and K (2)0were determined for the reactions Pd2+ + H2O = PdOH+ + H+ and Pd2+ + 2H2O = Pd(OH)20 + 2H+, respectively. The values of log K (1)0 = −1.66 ± 0.5 (25°C) and −0.65 ± 0.25 (50°C) and log K (2)0 = −4.34 ± 0.3 (25°C) and −3.80 ± 0.3 (50°C) were derived using the solubility technique at 0.95 confidence level. The values of log K (1)0 = −1.9 ± 0.6 (25°C), −1.0 ± 0.4 (50°C), and −0.5 ± 0.3 (70°C) were obtained by spectrophotometric techniques. The palladium ion is significantly hydrolyzed at elevated temperatures (50–70°C) even in strongly acidic solutions (pH 1–1.5), and its hydrolysis is enhanced with increasing temperature. 相似文献
17.
Sytle M. Antao Ian Jackson Baosheng Li Jennifer Kung Jiuhua Chen Ishmael Hassan Robert C. Liebermann John B. Parise 《Physics and Chemistry of Minerals》2007,34(5):345-350
The elastic moduli of magnesioferrite spinel, MgFe2O4, and their temperature dependence have been determined for the first time by ultrasonic measurements on a polycrystalline
specimen. The measurements were carried out at 300 MPa and to 700°C in a gas-medium high-pressure apparatus. On heating, both
the elastic bulk (K
S) and shear (G) moduli decrease linearly to 350°C. By combining with extant thermal-expansion data, the values for the room-temperature
K
S and G, and their temperature derivatives are as follows: K
0 = 176.3(7) GPa, G
0 = 80.1(2) GPa, (∂K
S/∂T)
P
= −0.032(3) GPa K−1 and (∂G/∂T)
P
= −0.012(1) GPa K−1. Between 350 and 400°C, there are abrupt increases of 1.4% in both of the elastic moduli; these closely coincide with the
magnetic Curie transition that was observed by thermal analyses at about 360°C. 相似文献
18.
Günther Josef Redhammer Anatoliy Senyshyn Gerold Tippelt Clemens Pietzonka Georg Roth Georg Amthauer 《Physics and Chemistry of Minerals》2010,37(5):311-332
CoGeO3 was synthesized at 1,273 and 1,448 K using ceramic sintering techniques in the monoclinic and orthorhombic modification,
respectively. The two compounds were analysed by magnetic susceptibility measurements and neutron diffraction in order to
study magnetic ordering and spin structures at low temperature. The monoclinic form of CoGeO3 has C2/c symmetry and orders magnetically below 36 K with a small negative paramagnetic Curie temperature θ
P = −4.6 (2) K. The magnetic structure can be described with k = (1, 0, 0) in the magnetic space group C2′/c′ having a ferromagnetic spin arrangement within the chains of M1 sites, but a dominating antiferromagnetic coupling between
the chains. At the M1 sites the magnetic spins are aligned within the a–c plane forming an angle of 120° with the +a-axis and they are not parallel to the spins at M2. Here spins are also ferromagnetically coupled within, but antiferromagnetically
coupled between the M1/M2 site bands. The orthorhombic phase of CoGeO3 displays Pbca symmetry and transforms to an antiferromagnetically ordered state [θ
P = −18.6(2) K] below 33 K. The magnetic spin structure can be described with k = (0, 0, 0) in space group Pbca′ and it is similar to the one of the C2/c phase except that it is non-collinear in nature, i.e. there are components of the magnetic moment along all three crystallographic
axes. Small magneto-elastic coupling is observed in the orthorhombic phase. 相似文献
19.
The lattice constants of paragonite-2M1, NaAl2(AlSi3)O10(OH)2, were determined to 800 °C by the single-crystal diffraction method. Mean thermal expansion coefficients, in the range 25–600 °C,
were: αa = 1.51(8) × 10−5, αb = 1.94(6) × 10−5, αc = 2.15(7) × 10−5 °C−1, and αV = 5.9(2) × 10−5 °C−1. At T higher than 600 °C, cell parameters showed a change in expansion rate due to a dehydroxylation process. The structural refinements
of natural paragonite, carried out at 25, 210, 450 and 600 °C, before dehydroxylation, showed that the larger thermal expansion
along the c parameter was mainly due to interlayer thickness dilatation. In the 25–600 °C range, Si,Al tetrahedra remained quite unchanged,
whereas the other polyhedra expanded linearly with expansion rate proportional to their volume. The polyhedron around the
interlayer cation Na became more regular with temperature. Tetrahedral rotation angle α changed from 16.2 to 12.9°. The structure
of the new phase, nominally NaAl2 (AlSi3)O11, obtained as a consequence of dehydroxylation, had a cell volume 4.2% larger than that of paragonite. It was refined at room
temperature and its expansion coefficients determined in the range 25–800 °C. The most significant structural difference from
paragonite was the presence of Al in fivefold coordination, according to a distorted trigonal bipyramid. Results confirm the
structural effects of the dehydration mechanism of micas and dioctahedral 2:1 layer silicates. By combining thermal expansion
and compressibility data, the following approximate equation of state in the PTV space was obtained for paragonite: V/V
0 = 1 + 5.9(2) × 10−5
T(°C) − 0.00153(4) P(kbar).
Received: 12 July 1999 / Revised, accepted: 7 December 1999 相似文献
20.
Gianluca Iezzi Mario Tribaudino Giancarlo Della Ventura Fabrizio Nestola Fabio Bellatreccia 《Physics and Chemistry of Minerals》2005,32(7):515-523
The synthetic amphibole Na0.95(Li0.95Mg1.05)Mg5Si8O22(OH)2 was studied in situ at high-T, using IR OH-stretching spectroscopy and synchrotron X-ray powder diffraction. At room-T the sample has P21
/m symmetry, as shown by the FTIR spectrum. It shows in the OH region two well-defined and intense absorptions at 3,748 and
3,712 cm−1, respectively, and two minor bands at 3,667 and 3,687 cm−1. The main bands are assigned to the two independent O–H groups in the primitive structure. The two minor bands evidencing
the presence of small amount of vacant A-site (A□0.05). With increasing T, these bands shift continuously and merge into a unique absorption at high temperature. A change as a function of increasing
T is revealed by the evolution of the refined unit-cell parameters, whose trend shows a transition to C2/m at about 320–330°C. The spontaneous scalar strain, fitted with a tricritical 2–6 Landau potential, gives a T
c of 325(10)°C (β parameter = 0.27). Comparison with the second-order P21
/m ⇔ C2/m phase transition at 255°C for synthetic amphibole ANa0.8B(Na0.8Mg1.2)CMg5Si8O22(OH)2 indicates that the substitution of Na with Li at the B-sites strongly affects the thermodynamic character and the T
c of the phase transition. The comparison of LNMSH amphiboles with cummingtonitic ones shows that the high-T thermodynamic behaviour is affected by A-site occupancy. 相似文献