Clausius-Clapeyron Slope Research Articles

Occurrence and Gas-Particle Partitioning of Organic UV-Filters in Urban Air.

A retrospective analysis of a comprehensive series of high-volume air samples (n = 70) collected during 2010-2011 in Toronto (Canada) was performed. Seven UV compounds were analyzed by gas chromatography-tandem mass spectrometry (GC-MS/MS) with sum of concentrations (gas + particle phase) ranging from 80 to 2030 pg/m3. Homosalate (HMS) was the most prevalent organic UV-filter in air (47% of the total concentration), followed by 2-ethylhexyl salicylate (EHS, ∼29%), E- and Z-2-ethylhexyl 4-methoxycinnamate (EHMC, ∼17%). Ambient air (gas + particle phase) concentrations of organic UV-filters showed a strong seasonality, with peak levels during the summer. An analysis of Clausius-Clapeyron slopes indicated that much of the ambient burden of organic UV-filters are explained by volatilization from terrestrial and aquatic surfaces and supplemented with human activities and use of lotions and sunscreens, containing organic UV-filters, in addition to its use in plastics, textiles, paints, and pesticides. The results showed that organic UV-filters exist mainly in the gas phase with some exceptions, for instance, octocrylene (OCR), which was associated with both gas and particle phases, and avobenzone (AVB), which was predominantly in the particle phase. Lastly, this study revealed the need for basic physical chemical property data for organic UV-filters, including information on transformation rates and products, for better evaluating their environmental fate and effects.

Superelasticity of (TiZrHf)50Ni25Co10Cu15 high entropy shape memory alloy

The paper elucidates the superelastic characteristics of high entropy shape memory alloy (HESMA) (TiZrHf)50Ni25Co10Cu15 over a wide range of deformation temperatures. Axial compression experiments are presented for different heat treatments and local recoverable strains up to 5% are noted. Superelasticity is observed over a large temperature range up to 175°C. Depending on heat treatment, the critical stress exhibits a Clausius-Clapeyron (CC) slope between 1.4 and 6 MPa/°C up to 80 °C deformation temperature. Obvious deviations from linearity however and significantly higher transformation stresses reaching 1200 MPa are reported at higher temperatures. The temperature change during transformation is reported at 9 °C.

FeMnNiAl Iron-Based Shape Memory Alloy: Promises and Challenges

Among all shape memory alloys, the iron-based FeMnNiAl has emerged as one of the most promising compositions with a huge superelasticity temperature window (> 400 °C). In this article, we first point to the high local transformation strains (> 10%) and high transformation stress levels (500–700 MPa) that result in a large work output. When subjected to either tensile or compressive loading, the transformation stress exhibits very small temperature dependence (Clausius–Clapeyron slope less than 0.2 MPa/°C in compression and 0.5 MPa/°C in tension) and an extremely small adiabatic temperature rise (less than 1 °C) during transformation. The complexity in transformation behavior associated with the presence of grain boundaries (GBs) is discussed. In particular, the work provides insight in the localization occurring at GBs due to transformation front–GB interactions and the potential cracking that can degrade fatigue performance. Overall, this work provides a deeper insight into the deformation response, advantages, and drawbacks of FeMnNiAl SMA. The comprehensive handling of various aspects of this alloy system paves the way for the development of future iron-based shape memory alloys.

Orientation dependence of superelasticity in FeMnAlNi single crystals under compression

The orientation dependence of the martensitic transformation characteristics and superelasticity were investigated in the Fe43.5Mn34Al15Ni7.5 single crystalline shape memory alloy along the [100], [111] and [123] orientations under compression. Solution heat treated samples exhibited a strong orientation dependence of the slopes for the stress vs. temperature phase diagrams (i.e. Clausius-Clapeyron slopes), while peak-aged samples demonstrated reduced orientation dependence. Maximum superelastic strains determined in the experiments along various single crystal orientations match well with the theoretical predictions.

Phase relations in the system Fe–Ni–Si to 200 GPa and 3900 K and implications for Earth's core

Phase relations in Fe–5 wt%Ni–4 wt%Si alloy was examined in an internally resistive heated diamond anvil cell under high pressure (P) and temperature (T) conditions to about 200 GPa and 3900 K by in-situ synchrotron X-ray diffraction. The hexagonal close-packed (hcp) structure was observed to the highest P–T condition, supporting the idea that the stable iron alloy structure in Earth's inner core is hcp. The P–T locations of the phase transition between the face-centred cubic (fcc) and hcp structures were also constrained to 106 GPa. The transition occurs at 15 GPa and 1000 K similar to for pure Fe. The Clausius–Clapeyron slope is however, 0.0480 GPa/K which is larger than reported slopes for Fe (0.0394 GPa/K), Fe–9.7 wt%Ni (0.0426 GPa/K), and Fe–4 wt%Si (0.0394 GPa/K), stabilising the fcc structure towards high pressure. Thus the simultaneous addition of Ni and Si to Fe increases the dP/dT slope of the fcc–hcp transition. This is associated with a small volume change upon transition in Fe–Ni–Si. The triple point, where the fcc, hcp, and liquid phases coexist in Fe–5 wt%Ni–4 wt%Si is placed at 145 GPa and 3750 K. The resulting melting temperature of the hcp phase at the inner core-outer core boundary lies at 550 K lower than in pure Fe.

Combined high-pressure and high-temperature vibrational studies of dolomite: phase diagram and evidence of a new distorted modification

A combined high-pressure mid-infrared absorption and Raman spectroscopy study on a natural CaMg0.98Fe0.02(CO3)2 dolomite sample was performed both at ambient and high temperatures. A pressure–temperature phase diagram was constructed for all the reported dolomite ambient- and high-pressure polymorphs. In addition, a local distortion of the ambient-pressure dolomite structure was identified close to 11 GPa, just before the transition toward the first known high-pressure phase. All the Clausius–Clapeyron slopes are found to be positive with similar magnitudes. Complementary first-principles calculations suggest a metastable nature of the high-pressure dolomite polymorphs. Finally, theoretical spectroscopy is used to interpret and discuss the observed changes in the measured vibrational spectra.

Helium substitution of natural gas hydrocarbons in the analysis of their hydrate

This communication successfully characterises the thermodynamic phase equilibrium conditions for a synthetic natural gas comprising of methane, ethane, propane, i-butane, n-butane, i-pentane, n-pentane and carbon dioxide. Experimental determination of the hydrate stabilization effects of the present hydrate formers was performed using a novel approach involving helium substitution of each hydrate guest species in an otherwise identical synthetic natural gas. Results in the ranges of 30–180 bar largely agreed with the van der Waals-Platteeuw (vdW-P) models in Aspen HYSYS and Calsep PVTsim with Peng-Robinson (PR) and Soave-Redlich-Kwong (SRK) equations of state. The substitution of propane and i-butane significantly shifted hydrate equilibrium conditions to lower temperatures at a given pressure and was confirmed with the Clausius-Clapeyron equation. A slope of −17372 K was calculated for the original gas mixture, a value 3000 and 2000 K steeper than an identical mixture with the substitution of propane and i-butane respectively. Dissociation enthalpies were also calculated; 100.7 (±0.4) kJ/mol for hydrates of the original gas and 87.8 (±0.4) and 94.9 (±0.8) kJ/mol for hydrates of the propane and i-butane substituted gas. Reliability and consistency of the presented results is complimented by a propagated relative uncertainty of ±1.28%.Computed data was used to calculate dissociation enthalpies and Clausius-Clapeyron slopes, both of which are consistent with experimental calculations when using PR and SRK equations. The helium substitution approach in the experimental determination of the extent of hydrate stabilization in a complex gas mixture provided by each possible hydrate former is a viable method. Results are particularly important to the general design of refinement processes, as they provide real implications on the changes in hydrate equilibrium conditions for a natural gas separation process.

On the effect of titanium on quenching sensitivity and pseudoelastic response in Fe-Mn-Al-Ni-base shape memory alloy

In the present study, the effect of Ti addition on the microstructure evolution and pseudoelastic properties of a Fe-Mn-Al-Ni shape memory alloy were investigated. By replacing 1.5at.% Al by Ti in Fe-Mn-Al-Ni, it was possible to strongly hamper the formation of the ductile, non-transforming γ-phase, which is detrimental to the pseudoelastic performance. Single crystalline samples were fabricated via abnormal grain growth. Following aging treatment at 250°C compression testing at various testing temperatures was conducted up to 10.5% strain using a near 〈102〉 oriented single crystal. A low Clausius-Clapeyron slope and good pseudoelastic properties were found.

Rates and styles of planetary cooling on Earth, Moon, Mars, and Vesta, using new models for oxygen fugacity, ferric-ferrous ratios, olivine-liquid Fe-Mg exchange, and mantle potential temperature

Mantle potential temperatures ( T p ) provide insights into mantle circulation and tests of whether Earth is the only planet to exhibit thermally bi-modal volcanism—a distinctive signature of modern plate tectonics. Planets that have a stagnant lid, for example, should exhibit volcanism that is uni-modal with T p , since mantle plumes would have a monopoly on the genesis of volcanism. But new studies of magmatic ferric-ferrous ratios ( X liq Fe2O3 / X liq FeO ) (Cottrell and Kelley 2011) and the olivine-liquid Fe-Mg exchange coefficient, K D (Fe-Mg) Ol-liq (or K D ) (Matzen et al. 2011) indicate that re-evaluations of T p are needed. New tests and calibrations are thus presented for oxygen fugacity ( f O 2 ), X liq Fe 2 O 3 / X liq FeO , potential temperature ( T p ), melt fraction ( F ), K D , and peridotite enthalpies of fusion (Δ H fus ) and heat capacities ( C P ). The new models for X liq Fe 2 O 3 / X liq FeO and f O 2 reduce error by 25–30%, and residual error for all models appears random; this last observation supports the common, but mostly untested, assumption that equilibrium is the most probable of states obtained by experiment, and perhaps in nature as well. Aggregate 1σ error on T p is as high as ~±77 oC, and estimates of F , and mantle olivine composition, are the greatest sources of error. Pressure and Δ H fus account for smaller, but systematic uncertainties (a constant Δ H fus can under-predict T excess = T p plume – T p ambient ; assumptions of 1 atm can under-predict T p ). However, assumptions about whether parental magmas are incremental, accumulated, or isobaric batch melts induces no additional systematic error. The new models show that maximum T p estimates on the oldest samples from Earth, Mars, Moon, and Vesta, decrease as planet size decreases. This may be expected since T p should scale with accretion energy and reflect the Clausius-Clapeyron slope for the melting of silicates and Fe-Ni alloys. This outcome, however, occurs only if shergottites (from Mars) are 4.3 Ga (e.g., Bouvier et al. 2009; Werner et al. 2014), and the highest MgO komatiites from Earth’s Archean era (27–30% MgO; Green et al. 1975) are used to estimate T p . With these assumptions, Earth and Mars exhibit monotonic cooling, and support for Stevenson’s (2003) idea that smaller planets cool at similar rates (~90–135 oC/Ga), but at lower absolute temperatures. T p estimates for Mars and Earth are also important in two other ways: Mars exhibits non-linear cooling, with rates as high as 275–550 oC/Ga in its first 0.5 Ga, and Archean volcanism on Earth was thermally bi-modal. Several hundred Archean volcanic compositions are in equilibrium with Fo92–94 olivine, and yield T p modes at 1940 and 1720 oC, possibly representing plume and ambient mantle, respectively. These estimates compare to modern T p values of 1560–1670 oC at Mauna Loa (plume) and 1330–1450 oC at MORB (ambient). We conclude that plate tectonics was active in some manner in the Archean, and that assertions of an Archean “thermal catastrophe” are exaggerated. Our new models also show that the modern Hawaiian source, when compared at the same T , has a lower f O 2 compared to MORB, which would discount a Hawaiian source rich in recycled pyroxenite.

Effects of aging on the shape memory behavior of Ni-rich Ni50.3Ti29.7Hf20 single crystals

The shape memory properties of solutionized and aged Ni-rich Ni50.3Ti29.7Hf20 single crystals were investigated along the [001], [011] and [111] orientations in compression. The effects of crystal orientation and aging temperature on the transformation strain, thermal hysteresis and Clausius–Clapeyron (CC) relation were determined. Aging at 550°C for 3h introduced coherent 10–20nm precipitates in the matrix, which substantially improved the shape memory and mechanical properties of the Ni50.3Ti29.7Hf20 crystals. [001]-oriented single crystals showed high dimensional stability under stress levels as high as 1500MPa in both the solutionized and aged conditions, but with transformation strains of <2%. Thermal treatments can be used to tailor the transformation temperatures over a wide range with the martensite start temperature varying from −25°C in the solutionized case to 123°C by aging at 650°C for 3h. Compared to the solutionized condition, thermal hysteresis was reduced after aging at 550°C/3h, but increased with aging at 650°C. Perfect superelasticity with recoverable strain of >4% was observed for solutionized and 550°C/3h aged single crystals along the [011] and [111] orientations, and general superelastic behavior was observed over a wide temperature range. In contrast, aged [001]-oriented single crystals have a very high CC slope, in the range of 30–40MPa°C−1, which results in a lack of superelasticity. Theoretical transformation strains were calculated by using the energy minimization method and lattice deformation theory. The calculated transformation strains were higher than the experimentally observed strains since the calculated strains could not capture the formation of martensite plates with (001) compound twins.

Microstructure and transformation related behaviors of a Ni45.3Ti29.7Hf20Cu5 high temperature shape memory alloy

Effects of heat treatment temperature and time on the microstructure and shape memory behaviors (e.g. transformation temperatures, load-biased shape memory effect, superelasticity, two-way shape memory effect, and related properties) were investigated in a Ni45.3Ti29.7Hf20Cu5 (at%) high temperature polycrystalline shape memory alloy. Heat treatments could be used to control the TTs and to a lesser extent recoverable and irrecoverable strains. The Ni45.3Ti29.7Hf20Cu5 alloy was capable of recovering shape memory strains of up to 2% at temperatures above 100°C under high compressive stresses (700MPa) and up to 0.8% TWSME strain was possible after a non-intense stress-cycling training process. However, due to high Clausius–Clapeyron slopes, large temperature hysteresis, and a strong dependence of transformation stress on temperature, fully recoverable superelastic behavior was not observed because plastic deformation occurred concurrently with the stress-induced martensitic transformation.

High pressure and temperature structure of liquid and solid Cd: implications for the melting curve of Cd

The structure of cadmium was characterized in both the solid and liquid forms at pressures to 10 GPa using in situ x-ray diffraction measurements in a resistively heated diamond anvil cell. The distorted hexagonal structure of solid cadmium persists at high pressures and temperatures, with anomalously large c/a ratio of Cd becoming larger as the melting curve is approached. The measured structure factor S(Q) for the melt reveals that the cadmium atoms are spaced about 0.6 Angstroms apart. The melt structure remains notably constant with increasing pressure, with the first peak in the structure factor remaining mildly asymmetric, in accord with the persistence of an anisotropic bonding environment within the liquid. Evolution of powder diffraction patterns up to the temperature of melting revealed the stability of the ambient-pressure hcp structure up to a pressure of 10 GPa. The melting curve has a positive Clausius–Clapeyron slope, and its slope is in good agreement with data from other techniques. We find deviations in the melting curve from Lindemann law type behavior for pressures above 1 GPa.

Transformation pathways of structural transitions between BaMg(CO3)2polymorphs

In-situ investigations on BaMg(CO3)2 (= α-phase, space group R-3c) by means of single-crystal diffraction and Raman spectroscopy yield the existence of novel structural polymorphs at high-pressure (γ-phase, C2/c) and high-temperature (β-phase, R-3m) conditions. Isothermal hydrostatic compression at room temperature yield a high-pressure phase transition at Pc ≍ 2.3210.04 GPa, which is weakly first order in character and reveals significant elastic softening of the high-pressure form (α: K0 = 66.212.3 GPa, dK/dP = 2.011.8; γ: K0 = 41.910.4 GPa, dK/dP = 6.110.3). X-ray structure determination confirms a distorted but topologically similar crystal structure of the γ-phase, with Ba in twelve-fold and Mg in octahedral coordination together with characteristic CO3 units. Based on the experimental series of in-situ HPHT data points, the phase boundary of the α-to-γ-transition was determined with a Clausius-Clapeyron slope of 9.8(7) × 10-3 GPa K-1. In-situ measurements of the X-ray intensities carried out to identify the nature of the structural variation correspond to the previously reported transformation from α- to β-BaMg(CO3)2 at 343 K and 1 bar. The investigations revealed, in contrast to all X-ray diffraction data recorded at 298 K, the disappearance of the superstructure reflections and the observed reflection conditions confirm the anticipated R-3m space-group symmetry. The pathway of structural transformation follows a typically displacive fashion, involving exclusively positional shifts of the oxygen atoms for the α-β-transformation. In contrast, in the atomic displacement of the Ba atoms in addition to the three crystallographically independent oxygen sites is responsible for a comparably higher flexibility of the C2/c structure, which explains the origin of the remarkable elastic softening.

Puzzling calcite-III dimorphism: crystallography, high-pressure behavior, and pathway of single-crystal transitions

High-pressure phase transformations between the polymorphic forms I, II, III, and IIIb of CaCO3 were investigated by analytical in situ high-pressure high-temperature experiments on oriented single-crystal samples. All experiments at non-ambient conditions were carried out by means of Raman scattering, X-ray, and synchrotron diffraction techniques using diamond-anvil cells in the pressure range up to 6.5 GPa. The composite-gasket resistive heating technique was applied for all high-pressure investigations at temperatures up to 550 K. High-pressure Raman spectra reveal distinguishable characteristic spectral differences located in the wave number range of external modes with the occurrence of band splitting and shoulders due to subtle symmetry changes. Constraints from in situ observations suggest a stability field of CaCO3-IIIb at relatively low temperatures adjacent to the calcite-II field. Isothermal compression of calcite provides the sequence from I to II, IIIb, and finally, III, with all transformations showing volume discontinuities. Re-transformation at decreasing pressure from III oversteps the stability field of IIIb and demonstrates the pathway of pressure changes to determine the transition sequence. Clausius–Clapeyron slopes of the phase boundary lines were determined as: ΔP/ΔT = −2.79 ± 0.28 × 10−3 GPa K−1 (I–II); +1.87 ± 0.31 × 10−3 GPa K−1 (II/III); +4.01 ± 0.5 × 10−3 GPa K−1 (II/IIIb); −33.9 ± 0.4 × 10−3 GPa K−1 (IIIb/III). The triple point between phases II, IIIb, and III was determined by intersection and is located at 2.01(7) GPa/338(5) K. The pathway of transition from I over II to IIIb can be interpreted by displacement with small shear involved (by 2.9° on I/II and by 8.2° on II/IIIb). The former triad of calcite-I corresponds to the [20-1] direction in the P21/c unit cell of phase II and to [101] in the pseudomonoclinic C $${\bar{1}}$$ setting of phase IIIb. Crystal structure investigations of triclinic CaCO3-III at non-ambient pressure–temperature conditions confirm the reported structure, and the small changes associated with the variation in P and T explain the broad stability of this structure with respect to variations in P and T. PVT equation of state parameters was determined from experimental data points in the range of 2.20–6.50 GPa at 298–405 K providing $$K_{{{\text{T}}_{0} }}$$ = 87.5(5.1) GPa, (δK T/δT) P = −0.21(0.23) GPa K−1, α 0 = 0.8(21.4) × 10−5 K−1, and α 1 = 1.0(3.7) × 10−7 K−1 using a second-order Birch–Murnaghan equation of state formalism.

High-pressure polymorphism and structural transitions of norsethite, BaMg(CO3)2

In situ high-pressure investigations on norsethite, BaMg(CO3)2, have been performed in sequence of diamond-anvil cell experiments by means of single-crystal X-ray and synchrotron diffraction and Raman spectroscopy. Isothermal hydrostatic compression at room temperature yields a high-pressure phase transition at P c ≈ 2.32 ± 0.04 GPa, which is weakly first order in character and reveals significant elastic softening of the high-pressure form of norsethite. X-ray structure determination reveals C2/c symmetry (Z = 4; a = 8.6522(14) A, b = 4.9774(13) A, c = 11.1542(9) A, β = 104.928(8)°, V = 464.20(12) A3 at 3.00 GPa), and the structure refinement (R 1 = 0.0763) confirms a distorted, but topologically similar crystal structure of the so-called γ-norsethite, with Ba in 12-fold and Mg in octahedral coordination. The CO3 groups were found to get tilted off the ab-plane direction by ~16.5°. Positional shifts, in particular of the Ba atoms and the three crystallographically independent oxygen sites, give a higher flexibility for atomic displacements, from which both the relatively higher compressibility and the remarkable softening originate. The corresponding bulk moduli are K 0 = 66.2 ± 2.3 GPa and dK/dP = 2.0 ± 1.8 for α-norsethite and K 0 = 41.9 ± 0.4 GPa and dK/dP = 6.1 ± 0.3 for γ-norsethite, displaying a pronounced directional anisotropy (α: β −1 = 444(53) GPa, β −1 = 76(2) GPa; γ: β −1 = 5.1(1.3) × 103 GPa, β −1 = 193(6) GPa β −1 = 53.4(0.4) GPa). High-pressure Raman spectra show a significant splitting of several modes, which were used to identify the transformation in high-pressure high-temperature experiments in the range up to 4 GPa and 542 K. Based on the experimental series of data points determined by XRD and Raman measurements, the phase boundary of the α-to-γ-transition was determined with a Clausius–Clapeyron slope of 9.8(7) × 10−3 GPa K−1. An in situ measurement of the X-ray intensities was taken at 1.5 GPa and 411 K in order to identify the nature of the structural variation on increased temperatures corresponding to the previously reported transformation from α- to β-norsethite at 343 K and 1 bar. The investigations revealed, in contrast to all X-ray diffraction data recorded at 298 K, the disappearance of the superstructure reflections and the observed reflection conditions confirm the anticipated $$R\bar{3}m$$ space-group symmetry. The same superstructure reflections, which disappear as temperature increases, were found to gain in intensity due to the positional shift of the Ba atoms in the γ-phase.

Scaling Potential Evapotranspiration with Greenhouse Warming

Abstract Potential evapotranspiration (PET) is a supply-independent measure of the evaporative demand of a terrestrial climate—of basic importance in climatology, hydrology, and agriculture. Future increases in PET from greenhouse warming are often cited as key drivers of global trends toward drought and aridity. The present work computes recent and “business as usual” future Penman–Monteith PET fields at 3-hourly resolution in 13 modern global climate models. The percentage change in local annual-mean PET over the upcoming century is almost always positive, modally low double-digit in magnitude, usually increasing with latitude, yet quite divergent between models. These patterns are understood as follows. In every model, the global field of PET percentage change is found to be dominated by the direct, positive effects of constant-relative-humidity warming (via increasing vapor deficit and increasing Clausius–Clapeyron slope). This direct-warming term accurately scales as the PET-weighted (warm-season daytime) local warming, times 5%–6% °C−1 (related to the Clausius–Clapeyron equation), times an analytic factor ranging from about 0.25 in warm climates to 0.75 in cold climates, plus a small correction. With warming of several degrees, this product is of low double-digit magnitude, and the strong temperature dependence gives the latitude dependence. Similarly, the intermodel spread in the amount of warming gives most of the spread in this term. Additional spread in the total change comes from strong disagreement on radiation, relative humidity, and wind speed changes, which make smaller yet substantial contributions to the full PET percentage change fields.

Phase-Transition Induced Elastic Softening and Band Gap Transition in Semiconducting PbS at High Pressure

We have investigated the crystal structure and phase stability, elastic incompressibility, and electronic properties of PbS based on high-pressure neutron diffraction, in-situ electrical resistance measurements, and first-principles calculations. The refinements show that the orthorhombic phase is structurally isotypic with indium iodide (InI) adopting a Cmcm structure (B33). The cubic-to-orthorhombic transition occurs at ∼2.1(1) GPa with a 3.8% volume collapse and a positive Clausius-Clapeyron slope. Phase-transition induced elastic softening is also observed, which is presumably attributed to the enhanced metallic bonding in the B33 phase. On the basis of band structure simulations, the cubic and orthorhombic phases are typical of direct and indirect semiconductors with band gaps of 0.47(1) and 1.04(1) eV, respectively, which supports electrical resistivity measurements of an abrupt jump at the structural transition. On the basis of the resolved structure for B33, the phase transition paths for B1→B33→B2 involve translation of a trigonal prism in B1 and motion of the next-nearest neighbor Pb atom into {SPb7} coordination and subsequent lattice distortion in the B33 phase.

Plume’s buoyancy and heat fluxes from the deep mantle estimated by an instantaneous mantle flow simulation based on the S40RTS global seismic tomography model

It is still an open question as to how much heat is transported from the deep mantle to the upper mantle by mantle upwelling plumes, which would impose a strong constraint on models of the thermal evolution of the earth. Here I perform numerical computations of instantaneous mantle flow based on a recent highly resolved global seismic tomography model (S40RTS), apply new simple fluid dynamics theories to the plume’s radius and velocity, considering a Poiseuille flow assumption and a power-law relationship between the boundary layer thickness and Rayleigh number, and estimate the plume’s buoyancy and heat fluxes from the deep lower mantle under varying plume viscosity. The results show that for some major mantle upwelling plumes with localized strong ascent velocity under the South Pacific and Africa, the buoyancy fluxes of each plume beneath the ringwoodite to perovskite+magnesiowüstite (“660-km”) phase decomposition boundary are comparable to those inferred from observed hotspot swell volumes on the earth, i.e., on the order of 1Mgs−1, when the plume viscosity is 1019–1020Pas. This result, together with previous numerical simulations of mantle convection and the gentle Clausius–Clapeyron slope for the 660-km phase decomposition derived from recent high-pressure measurements under dehydrated/hydrated conditions in the mantle transition zone, implies that mantle upwelling plumes in the lower mantle penetrate the 660-km phase decomposition boundary without significant loss in thermal buoyancy because of the weak thermal barrier at the 660-km boundary. The total plume heat flux under the South Pacific is estimated to be about 1TW beneath the 660-km boundary, which is significantly smaller than the core–mantle boundary heat flux. Previously published scaling laws for the plume’s radius and velocity based on a plume spacing theory, which explains well plume dynamics in three-dimensional time-dependent mantle convection, suggest that these plume fluxes depend critically on plume viscosity. This result implies that the predicted plume viscosity may not be as low as expected, i.e., on the order of 1020Pas, considering the weak thermal barrier for upwelling plumes at the 660-km boundary, and the plume heat fluxes in the deep lower mantle under the South Pacific may be comparable to the lower limit for estimated core-mantle boundary heat flux inferred from a number of independent geodynamic studies.

Thermodynamics of stress-induced ferroelastic transitions: Influence of anisotropy and disorder

Stress-induced stress-strain constitutive behavior has been studied in detail in ferroelastic martensites. It has been found that the weights of the long-range anisotropic interactions and of the disorder are important to determine the fine structure of the stress-strain curves. As experiments show, a wide variety of behaviors has been observed. A decrease of anisotropy and/or increase in the disorder results in changes in the temperature range where pseudoplastic and superelastic regimes are observed. Also, a smoothing of the stress-induced ferroelastic transition, accompanied with a decrease in the transition stress and the hysteresis area, is found. However, Clausius-Clapeyron slope has been observed not to depend on the specific values of anisotropy and disorder. This is in general agreement with experimental results in different alloy families, although some particular features differ from those in experiments. Elastocaloric effect has been studied as well. Varying the anisotropy slightly modifies the shape of the entropy change-temperature curve but the magnitude of the entropy change remains essentially constant.

Is low-spin Fe2+ present in Earth's mantle?

Abstract Recently, X-ray spectroscopy indicated that the low-spin (LS) electronic configuration of Fe 2+ and Fe 3+ ions substituting in silicate perovskite of various compositions, and also in magnesiowustite is stable at room temperature above pressures of ∼49 to 120 GPa [J. Badro, G. Fiquet, F. Guyot, J.-P. Rueff, V.V. Struzhkin, G. Vanko, G. Monaco, Iron partitioning in Earth's mantle: toward a deep lower mantle discontinuity, Science 300 (2003), 789–791.; J. Badro, J.-P. Rueff, G. Vanko, G. Monaco, G. Figuet, F. Guyot, Electronic transition in perovskite: possible non-convecting layers in the lower mantle, Science 305 (2004) 383–386.; J. Li, V.V. Struzhkin, H.K. Mao, J. Shu, R.J. Hemley, Y. Fei, B. Mysen, P. Dera, V. Prakapenka, G. Shen, Electronic spin state of iron in lower mantle perovskite, Proc. Natl. Acad. Sci. 101 (2004) 14027–14030.; J.M. Jackson, W. Sturhahn, G. Shen, J. Zhao, M.Y. Hu, D. Errandonea, J.D. Bass, Y. Fei, A synchrotron Mossbauer study of (Mg,Fe)SiO 3 perovskite up to 120 GPa, Am. Mineral. 90 (2005) 199–205.; J.F. Lin, V.V. Struzhkin, S.D. Jacobsen, M.Y. Hu, P. Chow, J. Kung, H. Liu, H.K. Mao, R.J. Hemley, Spin transition of iron in magnesiowustite in the Earth's lower mantle, Nature 436 (2005) 377–380.]. Simple thermodynamic relationships combined with crystal field theory provide a minimum Clausius–Clapeyron slope of ∼0.23 to 0.4 GPa/K for the high-spin (HS) to low-spin transition of Fe ions in perovskite, consistent with lower mantle temperatures stabilizing the disordered HS state. This computation of ∂ P / ∂ T utilizes experimentally determined parameters only ( P and T at the transition), and is supported by microstructural analysis of the change in volume and entropy considerations. Similarly, (∂ P / ∂ T ) min ∼0.18 to 0.31 GPa/K for magnesiowustite. High spin Fe 2+ should be stable in silicates throughout Earth's mantle for compositions of Fe / (Mg + Fe) ∼0.1, consistent with disorder prevailing at high temperature, although partial conversion of octahedral Fe 3+ to LS may occur. Similarly, partial conversion of octahedral Fe 2+ in magnesiowustite to the LS is possible for Fe-rich compositions, which transform at relatively low pressures.