Premelting Effects Research Articles

Pre-critical and Giant Post-Freezing and Pre-Melting Effects for Dielectric Properties in a Binary Mixture of Limited Miscibility

This report presents the results of dielectric studies in a nitrobenzene–decane critical mixture in the homogeneous liquid, biphasic mesophase, and the solid crystal phase. It focuses on detecting critical effects in the broad surrounding of the critical consolute temperature and pre-melting and post-freezing effects in the solid crystal phase. The strong manifestation of the diameter critical anomaly in the biphasic domain and the Mossotti catastrophe type pre-melting and post-freezing effects in the solid phase are evidenced. Studies include the puzzling low-frequency (LF) domain related to translational processes. The real part of electric conductivity, in LF limit, is well portrayed by the super-Arrhenius-type equation in the homogenous liquid and solid phases. The obtained experimental evidence can be significant for the cognitive progress of the still puzzling melting/freezing canonic discontinuous transition.

A Raman Spectroscopic Study of Lightning‐Induced Glass Produced From Five Mineral Phases

AbstractLightning‐induced volcanic spherules (LIVS) are glasses produced by the rapid melting and solidification of molten volcanic ash grains. High temperatures generated by lightning will alter the physical and chemical properties of minerals exposed to the discharge. Laboratory experiments reveal that LIVS glass composition varies depending on the starting material, exhibiting heterogeneous compositional features common in other glasses created by cloud‐to‐ground lightning, nuclear explosions, and high velocity impact events. This study uses scanning electron microscopy, energy dispersive spectroscopy, and Raman spectroscopy to investigate the structure and Raman signatures of lightning‐induced glass spherules manufactured from five igneous minerals (<32 μm powders of albite, labradorite, augite, hornblende, and magnetite). LIVS were created through high‐current impulse experiments using peak currents of 25 and 40 kA. Analysis of the post‐experimental albite, labradorite, augite, and hornblende LIVS reveal primarily homogeneous silicate or aluminosilicate glasses with limited heterogeneity. Their amorphous Raman spectra are comparable to rhyolitic and mafic natural glasses along with Na2O‐K2O‐Al2O3‐SiO2, CaCO3‐Al2O3‐SiO2, and CaO‐MgO‐SiO2 synthetic glass networks. A few of the augite and hornblende LIVS spectra exhibit premelting effects, which occur below the melting point and represent the onset of cation disordering in phases that remain crystalline. Magnetite samples produced crystal‐rich, glass‐poor LIVS characterized by the growth of dendritic microcrystals and crystalline spectra that also contain a few bands alluding to the composition of their silicate–phosphate glass matrix. By understanding these chemical changes induced by lightning, we can extract information from other types of glasses produced during high temperature, short duration events.

Supercriticality, Glassy Dynamics, and the New Insight into Melting/Freezing Discontinuous Transition in Linseed Oil

The long-range supercritical changes of dielectric constant, resembling ones observed in the isotropic liquid phase of liquid crystalline compounds, are evidenced for linseed oil—although in the given case, the phenomenon is associated with the liquid–solid melting/freezing discontinuous phase transitions. This ‘supercriticality’ can be an additional factor supporting the unique pro-health properties of linseed oil. Broadband dielectric spectroscopy studies also revealed the ‘glassy’ changes of relaxation times, well portrayed by the ‘activated and critical’ equation recently introduced. In the solid phase, the premelting effect characteristic for the canonic melting/freezing discontinuous transition, i.e., without any pretransitional effect in the liquid phase, has been detected. It is interpreted within the grain model, and its parameterization is possible using the Lipovsky model and the ‘reversed’ Mossotti catastrophe concept. For the premelting effect in the solid state, the singular ‘critical’ temperature correlates with the bulk discontinuous melting and freezing temperatures. Consequently, the report shows that linseed oil, despite its ‘natural and complex’ origins, can be considered a unique model system for two fundamental problems: (i) pretransitional (supercritical) effects in the liquid state associated with a weakly discontinuous phase transition, and (ii) the premelting behavior in the solid side of the discontinuous melting/freezing discontinuous transition.

Direct Imaging of Surface Melting on a Single Sn Nanoparticle.

Despite previous studies, understanding the fundamental mechanism of melting metal nanoparticles remains one of the major scientific challenges of nanoscience. Herein, the kinetics of melting of a single Sn nanoparticle was investigated using in situ transmission electron microscopy heating techniques with a temperature step of up to 0.5 °C. We revealed the surface premelting effect and assessed the density of the surface overlayer on a tin particle of 47 nm size using a synergetic combination of high-resolution scanning transmission electron microscopy imaging and low electron energy loss spectral imaging. Few-monolayer-thick disordered phase nucleated at the surface of the Sn particle at a temperature ∼25 °C below the melting point and grew (up to a thickness of ∼4.5 nm) into the solid core with increasing temperature until the whole particle became liquid. We revealed that the disordered overlayer was not liquid but quasi-liquid with a density intermediate between that of solid and liquid Sn.

Critical-like behavior of low-frequency dielectric properties in compressed liquid crystalline octyloxycyanobiphenyl (8OCB) and its nanocolloid with paraelectric BaTiO3

The report presents pressure-related broadband dielectric spectroscopy (BDS) studies in liquid crystalline octyloxycyanobiphenyl (8OCB) and its nanocolloid with BaTiO3 paraelectric nanoparticles. It is focused on the low-frequency (LF) domain, and the impact of pretransitional fluctuations. Studies were carried out in isotropic liquid, nematic, Smectic A, and solid crystal phases. In each case, the critical-type behavior for the LF contribution to the real part of dielectric permittivity and DC electric conductivity is evidenced. Studies of dielectric constant, related to the static frequency domain, revealed in SmA mesophase the shift from the XY-type to the mean-field type criticality when adding nanoparticles. The ‘giant’ premelting effect, with the critical-like portrayal, in the solid crystal phase, is also evidenced. Studies are supplemented by the polarizing microscopy insight into all tested phases appearing on compressing in 8OCB, and the nanocolloid. Photos show prenematic fluctuations in the isotropic liquid phase, phase transitions, changes within nematic and smectic mesophases on compressing, and the impact of nanoparticles.

Giant Premelting Effects for Solid–Liquid Discontinuous Transition in Nitrobenzene under Compression

This report presents ‘giant’ and long-range premelting effects appearing in dielectric properties for the temperature and pressure paths of studies, with an explicit critical-like portrayal. The result was obtained for the ‘classic’ low molecular weight compound: nitrobenzene, tested in the solid and liquid phases. Dielectric studies enable the ‘extraction’ of the response from liquid layers between crystalline grains. Compressing increased the premelting effects, probably due to the ‘crushing’ of crystalline grains by isotropic squeezing and increasing the liquid layers between grains. This report indicates the significance of considering the melting/freezing phenomenon from the point of view of the ‘solid crystalline grains and critical-type liquid layers in synergic interactions’ concept.

MEAM potential-based MD simulations of melting transition on Ni surfaces.

Based on the modified embedded atom method (MEAM) potential suggested by Jin et al. (Appl. Phys. A120: 189, 2015), the molecular dynamics (MD) simulations were adopted to investigate the melting transition of the FCC transition metal Ni, and in the MD simulations, the forces acting on atoms were calculated by using the newly derived formulas. We first studied the melting points of Ni samples with low-index surfaces including Ni(100), Ni(110), and Ni(111). Then, we investigated the structural properties on the surface layers with increasing temperature up to the melting points. The simulation results exhibit that with the temperature increasing, the (110) surface firstly disorders, followed by the (100) surface, while the stability of the (111) surface is maintained until near the melting point. The disorder of surface layer atoms diffuses from the surface to the inside of the crystal lattice. With the density of atoms decreasing on the surface, the premelting effect also increases, being most pronounced on Ni(110) which corresponds to the lowest surface density. This conclusion is linked with the behavior found for the BCC transition metal Fe in our previous simulation study.

Pretransitional of behavior of electrooptic Kerr effect in liquid thymol

Melting/freezing are canonical examples of discontinuous phase transitions, for which no pretransitional effects in the liquid phase are expected. For the solid phase, weak premelting effects are evidenced. This report shows long-range, critical-like, pretransitional effects in liquid thymol detected in electrooptic Kerr effect (EKE) studies. Notably is the negative sign of EKE pretransitional anomaly. Studies are supplemented by the high-resolution dielectric constant temperature-related scan, which revealed a weak premelting effect in the solid phase. Both EKE and dielectric constant show a ‘crossover’ change in the liquid phase, ca, 10 K above the freezing temperature. It can be recognized as the hallmark of the challenging liquid–liquid transition phenomenon.Graphical abstract

Effect of Impurities on Polycrystal Anelasticity

AbstractRock anelasticity causes seismic low velocity and high attenuation if, and only if, attenuation spectrum has a large “high‐frequency peak” superposed on the monotonic background. As a result, it is critical to define the conditions for peak existence. It is known that a large and broad high‐frequency peak exists at near solidus temperatures because grain boundary sliding is enhanced by the significant increase in grain boundary disorder called pre‐melting. The current study experimentally investigated the high‐frequency peak caused by impurities using organic polycrystals as an analog to mantle rock. A method for removing impurities was developed and anelasticity, viscosity, and grain growth rate of polycrystalline borneol with and without impurities were measured. The results showed that impurities can also significantly disorder the grain boundaries and cause a large and broad high‐frequency peak. This impurity‐induced peak disappeared, when the impurities were removed. On the basis of these results, this study draws a conclusion that the existence or non‐existence of the high‐frequency peak is strongly coupled with the grain boundary structure. This study also shows that the underlying mechanism of the peak is diffusionally accommodated grain boundary sliding, which is different from the prediction of existing models, and that further refinement of the models is needed. I further confirmed that the effects of impurities were minor in the published data which demonstrated the mechanical effects of premelting.

Inside out Approach to Rotator State in Hydrogen-Bonded System-Experimental and Theoretical Cross-Examination in n-Octanol.

The experimental and theoretical description of premelting behavior is one of the most challenging tasks in contemporary material science. In this paper, n-octanol was studied using a multi-method approach to investigate it at macroscopic and molecular levels. The experimental infrared (IR) spectra were collected in the solid state and liquid phase at temperature range from C to −15 C to detect temperature-related indicators of pretransitional phenomena. Next, the nonlinear dielectric effect (NDE) was measured at various temperatures (from −30 C to −15 C) to provide insight into macroscopic effects of premelting. As a result, a two-step mechanism of premelting in n-octanol was established based on experimental data. It was postulated that it consists of a rotator state formation followed by the surface premelting. In order to shed light onto molecular-level processes, classical molecular dynamics (MD) was performed to investigate the time evolution of the changes in metric parameters as a function of simulation temperature. The applied protocol enabled simulations in the solid state as well as in the liquid (the collapse of the ordered crystal structure). The exact molecular motions contributing to the rotator state formation were obtained, revealing an enabling of the rotational freedom of the terminal parts of the chains. The Car–Parrinello molecular dynamics (CPMD) was applied to support and interpret experimental spectroscopic findings. The vibrational properties of the stretching of OH within the intermolecular hydrogen bond were studied using Fourier transformation of the autocorrelation function of both dipole moments and atomic velocity. Finally, path integral molecular dynamics (PIMD) was carried out to analyze the quantum effect’s influence on the bridged proton position in the hydrogen bridge. On the basis of the combined experimental and theoretical conclusions, a novel mechanism of the bridged protons dynamics has been postulated—the interlamellar hydrogen bonding pattern, resulting in an additional OH stretching band, visible in the solid-state experimental IR spectra.

Pretransitional and premelting effects in menthol

To canonic features of melting/freezing discontinuous phase transitions, one can encounter the lack of pretransitional effects in the liquids state and weak premelting effects with non-defined temperature evolutions in the crystalline state. This report shows the evidence for long-range and critical-like pretransitional effects in liquid menthol for electrooptic Kerr effect (EKE) and nonlinear dielectric effect (NDE). These methods are inherently associated with a strong electric field.The premelting effect, with well-defined temperature evolution, was evidenced in the crystalline state. Model explanations of these phenomena are proposed. For the premelting effect, the ‘reversed’ Mossotti-Catastrophe behavior is suggested.

Precise determination of the effect of temperature on the density of solid and liquid iron, nickel, and tin

Abstract Density and thermal expansion coefficient of metals are fundamental characteristics to describe the equation of state. Especially for liquid metals, the reported data for density and thermal expansion coefficient vary in the literature, even at ambient pressure. To determine the density of solid and liquid metals precisely at high temperatures and ambient pressure, we have developed a high-temperature furnace. The densities of solid Sn, Ni, and Fe were determined from the sample image with an uncertainty of 0.11–0.7% in the temperature range of 285–1803 K with increments of 1–10 K. The density of solid Sn decreased linearly with increasing temperature up to 493 K, and then the decrease became drastic until the melting temperature (Tm) was reached. By contrast, for solid Ni and Fe, the densities decreased linearly with increasing temperature up to the Tm (1728 and 1813 K) without any drastic density drop near Tm. This suggests that Ni and Fe do not exhibit the “premelting effect.” The density of liquid Fe was determined with an uncertainty of 0.4–0.7% in the range of 1818–1998 K with temperature increments of 5 K. The obtained thermal expansion coefficient (α) of liquid Fe was well approximated as either a constant value of α = 2.42(1) × 10–4 K–1 or a linear function of temperature (T); α = 1.37(10) × 10–3 – [6.0(6) × 10–7]T [K–1] up to at least 2000 K.

Desalination and enrichment of phosphorus-containing wastewater via cyclopentane hydrate

With the rapid development of agriculture, controlling phosphorus emissions is a pressing challenge for preventing water eutrophication. A graphite-promoted cyclopentane (CP) hydrate-based desalination was proposed to remove K3PO4 from effluents. It was found via the in situ optical microscopy that the reaction temperature and the concentration of feeding K3PO4 solution significantly affect the morphologies and amount of the as-produced CP hydrate crystals. The lower reaction temperature produces more crystals with irregular shapes, while fewer crystals formed in K3PO4 solution with higher concentration. The reaction temperature, time and feeding concentration-dependent desalination and salt enrichment performances were studied. It was found that desalination efficiency linearly increases with the elevated reaction temperature ranging from − 2 °C to 3 °C; however, water recovery declines with temperature. The temperature-dependent water recovery is due to the strong driving force for hydrate formation at low temperatures. The time-dependent water recovery shows a three-stage feature, including exponential growth, linear increase, and stable stages, owing to the interaction between the driving force of supercooling and the increasing K3PO4 concentration during the reaction processes. The desalination efficiency shows an inverted volcanic shape with the increased concentration of feeding K3PO4 solution. The pre-melting effect plays a critical role in improving desalination efficiency at high K3PO4 concentrations. A maximum desalination efficiency of 85.0% was reached for treating an artificial solution with salinity as high as 42452 mg/L. Both desalted water and concentrated phosphorus-containing solution can be recovered by this method, which is attractive for producing freshwater with potential for recovery of resources.

Application of a Premelting Model to the Lithosphere‐Asthenosphere Boundary

AbstractA seismic discontinuity known as the G‐discontinuity, which has been prevailingly detected in the oceanic mantle, is considered to provide evidence of a sharp lithosphere‐asthenosphere boundary (LAB). We investigate whether this sharp LAB is explained by grain boundary premelting, which causes a solid‐state weakening of rock from just below the solidus temperature. We use an experimentally derived mechanical model describing the effect of premelting and calculate vertical profiles of and for various sets of oceanic geotherm and solidus values. Based on the realistic volatile distribution and solidus profile obtained from a model of fractional decompression melting, we show that even when the oceanic upper mantle is melt free, geotherm sufficiently approaches the solidus at various plate ages, resulting in a steep reduction in due to the anelastic effect of premelting. A small amount of volatile adsorbed to grain boundary plays an important role in this result. The predicted seismic discontinuity sharpness (mostly 15 km) is consistent with seismological observations (≤15 km), predicted discontinuity depth (along 1300°C isotherm) is deeper than observations (along 1100°C isotherm), and predicted velocity reduction amplitude (1%–2%) is considerably smaller than observations (≥5%). Because the predicted velocity reduction amplitude is subject to uncertainty resulted from the limited experimental data, further study is needed for the mechanical effect of premelting. We further discuss a discrepancy of seismological results from receiver function and SS precursor studies and from surface wave studies, making it difficult to explain both data consistently.

Structure and dynamics of the Lennard-Jones fcc-solid focusing on melting precursors

The Lennard-Jones potential is taken as a basis to study the structure and dynamics of the face centered cubic (fcc) solid along an isochore from low temperatures up to the solid/fluid transition. The Z method is applied to estimate the melting point. Molecular dynamics simulations are used to calculate the pair distribution function, numbers of nearest neighbors, and the translational order parameter, analyzing the weakening of the fcc-symmetry due to emerging premelting effects. A range of dynamic properties, such as the mean-squared displacement, non-Gaussian parameter, Debye-Waller factor, and vibrational density of states, is considered for the analysis of the solid state. All of these parameters clearly show that bulk mobility is activated at about 2/3 of the melting temperature, known as the Tammann temperature. This indicates that vibrational motion of atoms is not maintained exclusively in the entire stable solid state and that collective atomic motion constitutes a precursor of the melting process.

Using a composite flow law to model deformation in the NEEM deep ice core, Greenland – Part 2: The role of grain size and premelting on ice deformation at high homologous temperature

Abstract. The ice microstructure in the lower part of the North Greenland Eemian Ice Drilling (NEEM) ice core consists of relatively fine-grained ice with a single maximum crystallographic preferred orientation (CPO) alternated by much coarser-grained ice with a partial (great circle) girdle or multi-maxima CPO. In this study, the grain-size-sensitive (GSS) composite flow law of Goldsby and Kohlstedt (2001) was used to study the effects of grain size and premelting (liquid-like layer along the grain boundaries) on strain rate in the lower part of the NEEM ice core. The results show that the strain rates predicted in the fine-grained layers are about an order of magnitude higher than in the much coarser-grained layers. The dominant deformation mechanisms, based on the flow relation of Goldsby and Kohlstedt (2001), between the layers is also different, with basal slip rate limited by grain boundary sliding (GBS-limited creep) being the dominant deformation mechanism in the finer-grained layers, while GBS-limited creep and dislocation creep (basal slip rate limited by non-basal slip) contribute both roughly equally to bulk strain in the coarse-grained layers. Due to the large difference in microstructure between finer-grained ice and the coarse-grained ice at premelting temperatures (T>262 K), it is expected that the fine-grained layers deform at high strain rates, while the coarse-grained layers are relatively stagnant. The difference in microstructure, and consequently in viscosity, between impurity-rich and low-impurity ice can have important consequences for ice dynamics close to the bedrock.

Relationship between grain boundary segregation and grain boundary diffusion in Cu-Ag alloys

While it is known that alloy components can segregate to grain boundaries (GBs), and that the atomic mobility in GBs greatly exceeds the atomic mobility in the lattice, little is known about the effect of GB segregation on GB diffusion. Atomistic computer simulations offer a means of gaining insights into the segregation-diffusion relationship by computing the GB diffusion coefficients of the alloy components as a function of their segregated amounts. In such simulations, thermodynamically equilibrium GB segregation is prepared by a semi-grand canonical Monte Carlo method, followed by calculation of the diffusion coefficients of all alloy components by molecular dynamics. As a demonstration, the proposed methodology is applied to a GB is the Cu-Ag system. The GB diffusivities obtained exhibit non-trivial composition dependencies that can be explained by site blocking, site competition, and the onset of GB disordering due to the premelting effect.

Point defect populations of forsterite revealed by two-stage metastable hydroxylation experiments

Hydroxylation is a method that allows “decoration” of the pre-existing point defect structure of nominally anhydrous minerals, such as olivine. We tested this method on synthetic forsterite (Fo: $${\text{Mg}}_{2} {\text{SiO}}_{4}$$ ) crystals. To control starting point defect structures, Fo crystals were pre-annealed at different temperatures ( $$1100{-}1500\,{^\circ }{\text{C}}$$ ), silica activity conditions (forsterite–enstatite Fo–En and forsterite–periclase Fo–Per) and oxygen fugacity (0.21 and $$10^{-6}$$ bars). Then low-temperature hydroxylation (900 °C, 1.5 GPa) of the crystals successfully allowed the decoration with protons of pre-existing point defect structures, as subsequently revealed by infrared spectroscopy. Protons are arranged in three different point defect stoichiometries in Fo, related to Mg and Si vacancies ([Mg] and [Si], respectively) as well as to a trivalent cation-associated substitution mechanism ([triv]). Over the timescale and equilibrium conditions studied, hydroxylation does not reset the point defect structure inherited from pre-anneal. The data further show that the concentrations of [Mg]-, [Si]- and [triv]-hydrated defects are function of pre-anneal silica activity and temperature. Laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis of the crystals revealed diffusion of Al and Fe into the crystals during the pre-annealing, a phenomenon clearly promoted at high $${\text{a}}_{{{\text{SiO}}_{2} }}$$ . The data confirm a very fast mechanism of Al diffusion in Fo during pre-annealing, and suggest a strong coupling between $${\text{H}}^{+}$$ and $${\text{Al}}^{3+}$$ during hydroxylation. Overall, they show the strong importance of $${\text{a}}_{{{\text{SiO}}_{2} }}$$ and temperature in the incorporation of trace cations in forsterite, and the subsequent effects of incorporation of trace cations on Mg- and Si-related point defects in Fo. The dry point defect population of Fo is determined by interactions between the trace trivalent cations and dry Si and Mg vacancies. Without trace elements, T only has a limited effect on Mg- and Si-related point defect populations. Finally, approaching or potentially slightly exceeding the Fo–En solidus leads to strong changes in the trace element concentration and point defect population in Fo, which may be related to either partial melting or pre-melting effects.

Sound velocity of Fe3C at high pressure and high temperature determined by inelastic X-ray scattering

The sound velocity of Fe3C was measured at pressures from 33 to 86GPa and at ambient and high temperatures up to 2300K using inelastic X-ray scattering (IXS) from laser-heated samples in diamond anvil cells (DACs). The compressional velocity (VP) and density of Fe3C at room temperature were observed to follow a linear relationship (Birch's law). The temperature dependency of Birch's law was not clearly observed and can be ignored. Birch's law for Fe3C is expressed by: VP=1.09±0.14×ρ−1.79±1.26. The result indicates that VP and VS (shear velocity) of the preliminary reference Earth model (PREM) inner core at the Inner Core Boundary (ICB) were by 12% and 48% smaller than those of Fe3C, which could be accounted for by the premelting effect by analogy from pure Fe or by partial melting of the Fe–Fe3C mixture in the inner core.

Diffusion process in BaSi2film formation by thermal evaporation and its relation to electrical properties

Abstract