Thermal Expansion Coefficient Alpha Research Articles

Upper mantle density modelling for large-scale Moho gravity inversion: case study on the Atlantic Ocean

Moho geometry is an important parameter in geodynamic understanding. Seismic methods can provide accurate burial depths, but the coverage is low; the widely used CRUST1.0 model under oceans is greatly restricted by a low coverage of seismic data. Gravity inversion can provide high coverage of Moho undulations, but the accuracy is relatively low. Observed gravity anomalies integrate gravity effects induced by 3-D density perturbations in the Earth. For studies of the geometry of a specific density interface based on gravity, all gravity effects caused by other interfaces should be removed from the total anomaly map based on 3-D density distributions. We use temperature-based and velocity-based methods to model the lithospheric/upper mantle density; two temperature-calculation parameter models (PSM and GDH1), three thermal expansion coefficients (alpha) and three scaling ratio models are tested for each method. PSM and GDH1 result in a similar mantle gravity anomaly (MGA) pattern but different MGA average values when the alpha model is the same. Different alpha and scaling ratio models result in different Moho inversion results, and the optimal result from the temperature-based method has an RMS of 3.2 km with the CRUST1.0 model. A comparison between this inversion result and the CRUST1.0 model shows that the temperature-based method performs well in reproducing Moho geometry in the main part of the Atlantic Ocean, especially in the central basin. The optimal result from the velocity-based method has an RMS of 4.3 km with the CRUST1.0 model. Compared with the temperature-based method, the velocity-based method performs worse in the central basin but better in regions with low-velocity and low-density mantle away from the mid-ocean ridge.

Ab initiobased thermal property predictions at a low cost: An error analysis

Ab initio calculations often do not straightforwardly yield the thermal properties of a material yet. It requires considerable computational efforts, for example, to predict the volumetric thermal expansion coefficient alpha(V) or the melting temperature T-m from first principles. An alternative is to use semiempirical approaches. They relate the experimental values to first-principles predictors via fits or approximative models. Before applying such methods, however, it is of paramount importance to be aware of the expected errors. We therefore quantify these errors at the density-functional theory level using the Perdew-Burke-Ernzerhof functional for several semiempirical approximations of alpha(V) and T-m, and compare them to the errors from fully ab initio methods, which are computationally more intensive. We base our conclusions on a benchmark set of 71 ground-state elemental crystals. For the thermal expansion coefficient, it appears that simple quasiharmonic theory, in combination with different approximations to the Gruneisen parameter, provides a similar overall accuracy as exhaustive first-principles phonon calculations. For the melting temperature, expensive ab initio molecular-dynamics simulations still outperform semiempirical methods.

Crystallographic, electronic, thermal, and magnetic properties of single-crystal SrCo2As2

In tetragonal SrCo2As2 single crystals, inelastic neutron scattering measurements demonstrated that strong stripe-type antiferromagnetic (AFM) correlations occur at a temperature T = 5 K [W. Jayasekara et al., arXiv:1306.5174] that are the same as in the isostructural AFe2As2 (A = Ca, Sr, Ba) parent compounds of high-Tc superconductors. This surprising discovery suggests that SrCo2As2 may also be a good parent compound for high-Tc superconductivity. Here, structural and thermal expansion, electrical resistivity rho, angle-resolved photoemission spectroscopy (ARPES), heat capacity Cp, magnetic susceptibility chi, 75As NMR and neutron diffraction measurements of SrCo2As2 crystals are reported together with LDA band structure calculations that shed further light on this fascinating material. The c-axis thermal expansion coefficient alpha_c is negative from 7 to 300 K, whereas alpha_a is positive over this T range. The rho(T) shows metallic character. The ARPES measurements and band theory confirm the metallic character and in addition show the presence of a flat band near the Fermi energy E_F. The band calculations exhibit an extremely sharp peak in the density of states D(E_F) arising from a flat d_{x^2 - y^2} band. A comparison of the Sommerfeld coefficient of the electronic specific heat with chi(T = 0) suggests the presence of strong ferromagnetic itinerant spin correlations which on the basis of the Stoner criterion predicts that SrCo2As2 should be an itinerant ferromagnet, in conflict with the magnetization data. The chi(T) does have a large magnitude, but also exhibits a broad maximum at 115 K suggestive of dynamic short-range AFM spin correlations, in agreement with the neutron scattering data. The measurements show no evidence for any type of phase transition between 1.3 and 300 K and we propose that metallic SrCo2As2 has a gapless quantum spin-liquid ground state.

Volumetric properties of human islet amyloid polypeptide in liquid water

The volumetric properties of human islet amyloid polypeptide (hIAPP) in water were studied in a wide temperature range by computer simulations. The intrinsic density rho(p) and the intrinsic thermal expansion coefficient alpha(p) of hIAPP were evaluated by taking into account the difference between the volumetric properties of hydration and bulk water. The density of hydration water rho(h) was found to decrease almost linearly with temperature upon heating and its thermal expansion coefficient was found to be notably higher than that of bulk water. The peptide surface exposed to water is more hydrophobic and its rho(h) is smaller in conformation with a larger number of intrapeptide hydrogen bonds. The two hIAPP peptides studied (with and without disulfide bridge) show negative alpha(p), which is close to zero at 250 K and decreases to approximately -1.5 x 10(-3) K(-1) upon heating to 450 K. The analysis of various structural properties of peptides shows a correlation between the intrinsic peptide volumes and the number of intrapeptide hydrogen bonds. The obtained negative values of alpha(p) can be attributed to the shrinkage of the inner voids of the peptides upon heating.

The Study on Thermal Expansion of Sintered Sm$_{2}$Co$_{17}$ Magnets

Sintered Sm2Co17 magnets are widely used in aviation, spaceflight and precision instruments, etc. Thermal expansion coefficients alpha are necessary engineering data for the precision applications of the magnets (alphamacr presents the average thermal expansion coefficient). Here, we report an investigation on thermal expansion of sintered Sm2Co17 magnets. The effects of the substitutions of Gd, Dy, Er, and Pr for Sm on thermal expansion characteristics were discussed, respectively. The thermal expansion characteristics were measured using a NETZSCH DIL 402C thermal dilatometer. alpha// is the thermal expansion coefficient in the c axis and alphaperp is the coefficient in the base plane. All the specimens for each material were cut from the same block. A scanning electronic microscope (SEM) equipped with an energy dispersive X-ray analysis system is employed to observe the microstructure. It shows that the thermal expansion coefficient of Sm2Co17 magnets obviously exhibit anisotropy. The alphaperp is higher than the alpha//. The thermal expansion coefficient (both alpha// and alphaperp) increases and the thermal expansion anisotropy (alphaperp-alpha//) decreases with increasing temperature. The substitutions of heavy-rare earth elements, such as Gd+Dy, and Er decrease alphamacr//, the substitution of Pr for Sm moderately increases alphamacr// . The phenomenon is especially obvious in low-temperature range.

Thermal expansion ofLaFeAsO1−xFx: Evidence for high-temperature fluctuations

We present measurements of the thermal expansion coefficient alpha of polycrystalline LaFeAsO1-xFx (x <= 0.1). The magnetic and structural transitions of the samples with x <= 0.04 give rise to large anomalies in alpha(T), while the onset of superconductivity in the crystals with x >= 0.05 is not resolved. Above the structural transition, the thermal expansion coefficient of LaFeAsO is significantly enhanced. This is attributed to fluctuations, which also affect the electrical transport properties of the compound. The complete absence of these fluctuations in the superconducting samples even for x = 0.05 is taken as evidence for an abrupt first-order type of suppression of the structural and magnetic transitions upon F doping.

The Emergence of Nonbulk Properties in Supported Metal Clusters: Negative Thermal Expansion and Atomic Disorder in Pt Nanoclusters Supported on γ-Al2O3

The structural dynamics-cluster size and adsorbate-dependent thermal behaviors of the metal-metal (M-M) bond distances and interatomic order-of Pt nanoclusters supported on a gamma-Al(2)O(3) are described. Data from scanning transmission electron microscopy (STEM) and X-ray absorption spectroscopy (XAS) studies reveal that these materials possess a dramatically nonbulklike nature. Under an inert atmosphere small, subnanometer Pt/gamma-Al(2)O(3) clusters exhibit marked relaxations of the M-M bond distances, negative thermal expansion (NTE) with an average linear thermal expansion coefficient alpha = (-2.4 +/- 0.4) x 10(-5) K(-1), large static disorder and dynamical bond (interatomic) disorder that is poorly modeled within the constraints of classical theory. The data further demonstrate a significant temperature-dependence to the electronic structure of the Pt clusters, thereby suggesting the necessity of an active model to describe the cluster/support interactions mediating the cluster's dynamical structure. The quantitative dependences of these nonbulklike behaviors on cluster size (0.9 to 2.9 nm), ambient atmosphere (He, 4% H(2) in He or 20% O(2) in He) and support identity (gamma-Al(2)O(3) or carbon black) are systematically investigated. We show that the nonbulk structural, electronic and dynamical perturbations are most dramatically evidenced for the smallest clusters. The adsorption of hydrogen on the clusters leads to an increase of the Pt-Pt bondlengths (due to a lifting of the surface relaxation) and significant attenuation of the disorder present in the system. Oxidation of these same clusters has the opposite effect, leading to an increase in Pt-Pt bond strain and subsequent enhancement in nonbulklike thermal properties. The structural and electronic properties of Pt nanoclusters supported on carbon black contrast markedly with those of the Pt/gamma-Al(2)O(3) samples in that neither NTE nor comparable levels of atomic disorder are observed. The Pt/C nanoclusters do exhibit, however, both size- and adsorbate-induced trends in bond strain that are similar to those of their Pt/gamma-Al(2)O(3) analogues. Taken together, the data highlight the significant role that electronic effects--specifically charge exchange due to both metal-support and metal-adsorbate interactions--play in mediating the structural dynamics of supported nanoscale metal clusters that are broadly used as heterogeneous catalysts.

Temperature Dependence of Single-Crystal Elastic Constants of Flux-Grown α-GaPO4

The lattice parameter change with respect to temperature (T) has been measured using high-temperature powder X-ray diffraction techniques for high-temperature flux-grown GaPO(4) single crystals with the alpha-quartz structure. The lattice and the volume linear thermal expansion coefficients in the temperature range 303-1173 K were computed from the X-ray data. The percentage linear thermal expansions along the a and c axes at 1173 K are 1.5 and 0.51, respectively. The temperature dependence of the mass density rho of flux-grown GaPO(4) single crystals was evaluated using the volume thermal expansion coefficient alpha(V)(T) = 3.291 x 10(-5) - 2.786 x 10(-8) [T] + 4.598 x 10(-11)[T](2). Single-crystal high-resolution Brillouin spectroscopy measurements have been carried out at ambient pressure from 303 to 1123 K to determine the elastic constants C(IJ) of high-temperature flux-grown GaPO(4) material. The single-crystal elastic moduli were calculated using the sound velocities via the measured Brillouin frequency shifts Deltanu(B). These are, to our knowledge, the highest temperatures at which single-crystal elastic constants of alpha-GaPO(4) have been measured. Most of the room-temperature elastic constant values measured on flux-grown GaPO(4) material are higher than the ones found for hydrothermally grown GaPO(4) single crystals. The fourth-order temperature coefficients of both the Brillouin frequency shifts T(nuB)((n)) and the single-crystal elastic moduli T(C(IJ))((n)) were obtained. The first-order temperature coefficients of the C(IJ) are in excellent agreement with previous reports on low-temperature hydrothermally grown alpha-GaPO(4) single crystals, while small discrepancies in the higher-order temperature coefficients are observed. This is explained in terms of the OH content in the GaPO(4) network, which is an important parameter in the crystal thermal behavior.

Transport of Water in Small Pores

Experimental measurements of the thermal expansion coefficient (alpha), permeability (k), and diffusivity (D) of water and 1 M solutions of NaCl and CaCl(2) are interpreted with the aid of molecular dynamics (MD) simulations of water in a 3 nm gap between glass plates. MD shows that there is a layer approximately 6 A thick near the glass surface that has alpha approximately 2.3 times higher and D about an order of magnitude lower than bulk water. The measured D is approximately 5 times lower than that for bulk water. However, when the MD results are averaged over the thickness of the 3 nm gap, D is only reduced by approximately 30% relative to the bulk, so the measured reduction is attributed primarily to tortuosity of the pore space, not to the reduced mobility near the pore wall. The measured alpha can be quantitatively explained by a volume-weighted average of the properties of the high-expansion layer and the "normal" water in the middle of the pore. The permeability of the porous glass can be quantitatively predicted by the Carman-Kozeny equation, if 6 A of water near the pore wall is assumed to be immobile, which is consistent with the MD results. The properties and thickness of the surface-affected layer are not affected significantly by the presence of the dissolved salts.

A monatomic system with a liquid-liquid critical point and two distinct glassy states

We study the glass transition (GT) in a model system that exhibits the presence of more than one liquid or glassy state ("polyamorphism") using molecular dynamics simulations. We study the Jagla model [E. A. Jagla, J. Chem. Phys. 111, 8980 (1999)], a two-scale spherically symmetric ramp potential with both attractive and repulsive interactions. The Jagla model is particularly interesting since, depending on its parametrization, it predicts two phases ("polyamorphism") not only in the glassy state but also in equilibrium as a liquid-liquid phase transition (LLPT). The Jagla model may also be useful in understanding a recent observation of polyamorphism in metallic glasses containing cerium. We use a parametrization for which crystallization can be avoided and the GT and LLPT are clearly separated, providing a unique opportunity to study the effects of the LLPT on the GT. We follow the experimental protocol employed in the classical differential scanning calorimetry experiments used to characterize the GT, cooling and heating the system through the GT and calculating the constant-pressure specific heat C(P) and the thermal expansion coefficient alpha(P). At pressures below and well above the LLPT, the same basic GT phenomenology of metallic glasses is observed, i.e., a single peak in C(P) (typical of ergodicity restoration) occurs upon heating across the GT. At pressures above the LLPT, a second peak in C(P) develops at higher temperature above the GT. This second peak in C(P) arises from the presence of a Widom line T(W) defined as the locus of maximum correlation length in the one-phase region above the liquid-liquid critical point (LLCP). The behavior of alpha(P) is different across the GT and Widom line. Near the GT temperature T(g), alpha(P) displays a small peak upon heating, which makes a negligible contribution to the C(P) peak. On the other hand, near T(W), alpha(P) displays a much larger peak, which makes a substantial contribution to the C(P) peak at higher temperature. We find that T(g) is almost independent of pressure for each of the two coexisting liquids, but shows an apparent discontinuity upon crossing the LLPT line, to a lower value for the higher-entropy phase. We compare the entropies of both phases, and the corresponding temperature dependencies, with those of the crystal phase. We also study the dependence of the GT on heating rate and find that for pressures below the LLCP, slow heating results in crystallization, as occurs in laboratory experiments. Regarding the thermal expansion properties of the Jagla model, we study the interplay of the density minimum recently observed in confined water and the GT.

Thermal expansivity of amyloid β16–22 peptides and their aggregates in water

Temperature dependence of the volumetric and structural properties of Abeta(16-22) peptides (wild type and pathogenic forms) and their aggregates in water was studied by simulations. The intrinsic thermal expansion coefficient alpha(p) of peptides was evaluated by taking into account the difference between the volumetric properties of hydration and bulk water. Single peptides show mainly positive values of alpha(p) that correlates with the increasing number of intrapeptide hydrogen bonds upon heating. Negative values of alpha(p) found for large peptide aggregates may be attributed to the shrinking of voids inside aggregates with increasing temperature or to their rubber-like elasticity. The peptide surface exposed to water becomes more hydrophobic with increasing aggregate size that appears in decreasing density of hydration water and evidences a hydrophilic character of aggregation.

First-principles calculations of structural and thermodynamic properties of BeB 2 compound

The lattice parameter, bulk modulus and pressure derivative of BeB2 are calculated by using the Cambridge Serial Total Energy Package (CASTEP) program in the frame of density function theory. The calculated results agree well with the average experimental data and other theoretical results. Through the quasi-harmonic Debye model, the dependences of the normalized lattice parameters a/a(0),c/c(0) and the normalized primitive cell volume V/V-0 on pressure P, the variation of the thermal expansion coefficient alpha with pressure P and temperature T, as well as the dependences of the heat capacity C-V on pressure P and temperature T are obtained systematically.

Determining vibrational heat capacity and thermal expansivity and their change at glass-liquid transition

The vibrational parts of a liquid's heat capacity Cp and thermal expansion coefficient alpha may be determined from dynamic measurements. The Cp data for Pd40Ni40P20 and 0.4 Ca(NO3)(2).0.6 KNO3 have been analyzed accordingly, and it is found that change in the vibrational part at liquid-glass transformation is negligible. Analysis for alpha of poly(styrene) leads to the same conclusion. There is no discontinuity in the vibrational parts of Cp and alpha on structural unfreezing in the Tg range, and hence the change in Cp and alpha at Tg is almost entirely due to change in the configurational part. Crystallization decreases the vibrational part not because the molecular mobility is lost but because the density increases.

Study on the Properties of Amino Acid Ionic Liquid EMIGly

In terms of standard addition method, the density and surface tension of an amino acid ionic liquid EMIGly(1-ethyl-3-methylimidazolium aminoacetate) were measured under dry argon atmosphere in the temperature range of 288.15-343.15 K. The properties of volume and surface for pure EMIGly were discussed in terms of the interstice model and Glasser's theory. The thermal expansion coefficient alpha = 5.03 x 10(-4) K(-1) calculated using interstice model is in good agreement with alpha (experimental) = 5.20 x 10(-4) K(-1).

Advanced Thermal Characterization of Fractionated Natural Organic Matter

This work focuses on an experimental investigation of the thermodynamic properties of natural organic matter (NOM), and whether fractions of NOM possess the same thermodynamic characteristics as the whole NOM from which they are derived. Advanced thermal characterization techniques were employed to quantify thermal expansion coefficients (alpha), constant-pressure specific heat capacities (C(p)), and thermal transition temperatures (T(t)) of several aquatic- and terrestrial-derived NOM. For the first time, glass transition behavior is reported for a series of NOM fractions derived from the same whole aquatic or terrestrial source, including humic acid-, fulvic acid-, and carbohydrate-based NOM, and a terrestrial humin. Thermal mechanical analysis (TMA), standard differential scanning calorimetry (DSC), and temperature-modulated differential scanning calorimetry (TMDSC) measurements revealed T(t) ranging from -87 degrees C for a terrestrial carbohydrate fraction to 62 degrees C for the humin fraction. The NOM generally followed a trend of increasing T(t) from carbohydrate to fulvic acid to humic acid to humin, and greater T(t) associated with terrestrial fractions relative to aquatic fractions, similar to that expected for macromolecules possessing greater rigidity and larger molecular weight. Many of the NOM samples also possessed evidence of multiple transitions, similar to beta and alpha transitions of synthetic macromolecules. The presence of multiple transitions in fractionated NOM, however, is not necessarily reflected in whole NOM, suggesting other potential influences in the thermal behavior of the whole NOM relative to fractionated NOM. Temperature-scanning X-ray diffraction studies of each NOM fraction confirmed the amorphous character of each sample through T(t).

Critical linear thermal expansion in the smectic-Aphase near the nematic-smectic phase transition

Recent high-resolution x-ray investigations of the smectic- A (SmA) phase near the nematic-to-SmA transition provide information about the critical behavior of the linear thermal expansion coefficient alpha// parallel to the director. Combining such data with available volume thermal expansion alpha(V) data yields the in-plane linear expansion coefficient alpha(perpendicular) . The critical behaviors of alpha// and alpha(perpendicular) are the same as those for alpha(V) and the heat capacity Cp. However, for any given liquid crystal, alpha//(crit) and alpha(perpendicular)(crit) differ in sign. Furthermore, the quantity alpha// (crit) is positive for SmAd partial bilayer smectics, while it is negative for nonpolar SmAm monomeric smectics. This feature is discussed in terms of the molecular structural aspects of these smectic phases.

Thermal expansion coefficient of titanium casting

A reliable measurement of the thermal expansion coefficient (alpha) value is required to achieve a positive thermal mismatch between metal and porcelain for porcelain-fused to metal crowns. Heating rate and specimen conditions may significantly influence the alpha value and the effects of these factors were studied. Commercially pure cast titanium rods, 'as cast' and sandblasted, were heated at various conditions. According to this study, the discrepancy of alpha values between heating and cooling conditions was insignificant when the heating (cooling) rate was reduced to 1 degrees C min(-1). It was revealed that alpha values obtained from 1 degrees C min(-1) cooling rates should be utilized. Dental porcelain with an alpha value lower than 8.5 x 10(-6) degrees C will be suitable for titanium-ceramic applications.

Pressure dependence of structural relaxation time in terms of the Adam-Gibbs model.

A new equation describing the behavior of the structural relaxation time, tau(T,P), as a function of both pressure and temperature, is discussed. This equation has been derived from the Adam-Gibbs theory by writing the configurational entropy, S(c), in terms of the excess thermal heat capacity and of the molar thermal expansion. Consequently, the parameters introduced in the expression are directly related to specific physical properties of the material, such as the thermal expansion coefficient alpha and the isothermal bulk modulus K0. At a fixed pressure, for low pressures, the found equation reduces to a Vogel-Fulcher-Tammann equation of tau versus temperature with the fragility parameter independent from pressure. The equation for tau(T,P) was successfully tested directly by fitting the dielectric relaxation time data for two isothermal and one isobaric measurements on diglycidyl ether of bisphenol-A, carried out in previous experiments. The parameters estimated by the best fit were in reasonable agreement with the values determined from the known physical properties of the material. Finally, the expression for the change versus pressure of the temperatures at which the same value of tau(max) is obtained (e.g., the change versus pressure of the glass transition temperature) agrees with several expressions previously proposed in the literature to provide a phenomenological description of the observed phenomena.

Thermodynamically consistent equilibrium properties of normal-liquid3He

The high-precision data for the specific heat C_{V}(T,V) of normal-liquid Helium-3 obtained by Greywall, taken together with the molar volume V(T_0,P) at one temperature T_0, are shown to contain the complete thermodynamic information about this phase in zero magnetic field. This enables us to calculate the T and P dependence of all equilibrium properties of normal-liquid Helium-3 in a thermodynamically consistent way for a wide range of parameters. The results for the entropy S(T,P), specific heat at constant pressure C_P(T,P), molar volume V(T,P), compressibility kappa(T,P), and thermal expansion coefficient alpha(T,P) are collected in the form of figures and tables. This provides the first complete set of thermodynamically consistent values of the equilibrium quantities of normal-liquid Helium-3. We find, for example, that alpha(T,P) has a surprisingly intricate pressure dependence at low temperatures, and that the curves alpha(T,P) vs T do not cross at one single temperature for all pressures, in contrast to the curves presented in the comprehensive survey of helium by Wilks. Corrected in cond-mat/9906222v3: The sign of the coefficient d_0 was misprinted in Table I of cond-mat/9906222v1 and v2. It now correctly reads d_0=-7.1613436. All results in the paper were obtained with the correct value of d_0. (We would like to thank for E. Collin, H. Godfrin, and Y. Bunkov for finding this misprint.)

Thermal expansion of icosahedral Al-Pd-Mn and decagonal Al-Cu-Co quasicrystals

Thermal expansion measurements have been performed by X-ray diffractometry on icosahedral Al-Pd-Mn (i-(Al-Pd-Mn)) in the temperature range between 10 and 700K and on decagonal Al-Cu-Co (d-(Al-Cu-Co)) in the range between 100 and 750K. The linear thermal expansion coefficient alpha(T) of i-(Al-Pd-Mn) is about half of that for the pure aluminium phase at room temperature and does not show a negative thermal expansion at low temperatures. The degree of anisotropy in the thermal expansion of d-(Al-Cu-Co) is small; the ratio of the average alpha between the tenfold periodic direction and a quasiperiodic direction perpendicular to it is 0:93 +/- 0:05. The Gruneisen parameter gamma(T) has been evaluated from the measured alpha(T). gamma for d-(Al-CuCo) is almost isotropic, similar to alpha. The gamma values for the two phases lie in the range between 1.5 and 1.8, which are comparable with those for conventional metallic crystals. They are almost constant over the temperature range studied.