Phase Transition Region Research Articles

Атомистическое моделирование характеристик золота в области фазового перехода плавление–кристаллизация

Атомистическое моделирование характеристик золота в области фазового перехода плавление–кристаллизация

Магнитострикционные аномалии редкоземельных фаз Лавеса c морфотропным фазовым переходом

Оver recent years in the process of searching for compounds with high or almost zero magnetostriction values, a number of pseudo-binary Laves RT2 phases with morphotropic phase transitions are attracted particular attention. That is, systems of compounds with a morphotropic phase boundary in the phase diagram. In this paper, the magnetic and magnetostrictive properties of multicomponent systems of compounds Tb0.2Dy0.8-хGdxCo2 and Tb0.2Dy0.8-хGdxCo1.9Al0.1 in which a morphotropic phase transition is observed when replacing dysprosium with gadolinium have been studied. A relationship between the temperature behavior, the sign and magnitude of magnetostrictive deformations, and the type of distortion of the cubic lattice of the studied Laves phases is revealed. In the region of magnetic phase transitions, the magnetocaloric effect was investigated.

FEATURES OF POROUS MEDIUM HEATING WHILE GAS HYDRATES FORMATION

Background Many technological processes in the oil and gas industry are accompanied by the formation and deposition of gas hydrates both in the reservoir and in the systems of underground and surface equipment of oil and gas fields. In this case, the processes of hydrate formation lead to the release of latent heat of hydrate formation, which can lead to a significant increase in temperature in a porous medium. The mathematical model of the formation and decomposition of gas hydrates in a porous medium of infinite length was considered earlier. It was found that, depending on the initial and boundary conditions, the formation and decomposition of gas hydrate can occur both on the frontal surface and in an extended region. Aims and Objectives Consider a mathematical model of the formation of gas hydrate in a porous medium of finite length with the formation of an extended region of phase transitions. Methods Math modelling. Results The influence of the initial parameters, as well as the parameters at the boundary of the medium, on the evolution of the temperature fields in the reservoir is investigated. It is shown that the injection of cold gas leads to the heating of the formation, and it is the stronger, the higher the pressure of the injected gas.

Thermal behaviors of exotic $$Z_{c}$$ (3900) state in tetraquark approach

The discovery of the charged $$Z_{c}$$(3900) exotic resonance with the quantum numbers $$J^{P}$$= $$1^{+}$$ has crucial consequences for comprehending the nature of multi-quark hadrons. In this work, the meson-current coupling constant and mass of $$Z_{c}$$ state are calculated using the Thermal QCD Sum Rules method. We suppose that the positively charged state $$Z_{c}$$ has a quark content $${\bar{c}}cu{\bar{d}}$$ and use tetraquark current with the corresponding quantum numbers. We evaluate the two-point correlation function taking into account the non-perturbative condensates up to six-dimension. We found the hot medium contributions to hadronic parameters of the $$Z_{c}$$ state and exhibit that its meson-current coupling constant and mass are unsusceptible to the change of temperature in low temperature region, but these parameters significantly change in the vicinity of phase transition region. At critical temperature, the meson current-coupling constant reaches approximately to 10% of its vacuum value, while the mass decreases about 28%.

Development and Characterization of Nano-emulsions Based on Oil Extracted from Black Soldier Fly Larvae.

Insect-based biorefinery is seen as a potential alternative approach to manufacturing foods, feeds, and fuel because of the increasing demand for renewable and sustainable products. Insect oil and protein are the two major components that can be quantitatively obtained from insect farming. However, very few attempts have been conducted to utilize insect oil for the production of value-added products. In this study, the oil extracted from the black soldier fly (Hermetia illucens) larvae (BSFL) was used as a novel feedstock for preparing nano-emulsions. The nano-emulsions were prepared with BSFL oil, hydrogenated lecithin (HL), and d-α-tocopheryl polyethylene glycol 1000 succinate (TPGS) in water using pre-homogenization followed by ultrasonication. The morphology and the particle size of nano-emulsions were affected by ratios of HL to TPGS. Moreover, the nano-emulsions showed a nearly Newtonian liquid behavior and the presence of TPGS was able to improve the storage stability of HL nano-emulsions. The addition of TPGS could eliminate the phase transition region of HL nano-emulsions but did not provide a significant change for the molecular mobility in the HL nano-emulsions. In summary, the BSFL oil could be used as a renewable feedstock for formulating nano-emulsions from the aspect of high value-added applications and physicochemical characteristics of the nano-emulsions could be adjusted by the mixed surfactant ratio, surfactant to oil ratio, and oil content. Graphical Abstract The physicochemical characteristics and optimization of nano-emulsions based on black soldier fly larvae oil were investigated.

On the theory of bulk crystallization in the moving phase transition layer

Abstract The paper deals with the process of directional steady-state crystallization in the presence of a metastable phase transition region, where nucleation and crystal growth occur. A new analytical solution describing such a nonlinear heat and mass transfer phase transformation process is constructed on the basis of the saddle-point method for a Laplace-type integral. The crystal-size distribution function, supercooling and solid fraction in a moving metastable two-phase region are found analytically.

Investigation of phase transitions in vegetable oils through temperature-dependent optical measurements: supercooling effect

Measurements of the phase transitions in vegetable oils such as coconut, palm (fruit), palm kernel (from the seeds), macauba (Acrocomia aculeata) and its biodiesel have been taken through temperature-dependent optical transmittance. Room-temperature optical transmittance spectroscopy experiments in the UV–Vis–NIR region showed that oils begin to transmit at different wavelengths and present different wavelength rates of light transmission. A peak level of absorption at 930 nm is present for all samples and attributed to the third harmonic of vibrational mode of chemical groups with covalent C–H bonds. Viscosity and density measurements of the vegetable oils and biodiesel were also carried out in order to aid in the interpretation of their thermal behavior. The phase transition regions were determined, and the supercooling effect was detected in the oils due to their high viscosity. The effect was not observed in the macauba biodiesel due to its low viscosity.

Raman opalescence near the phase transition point in lead germanate crystals

It was established that the nature of opalescence near the phase transition point in a lead germanate crystal is dynamic and is caused by a sharp increase in the spectral intensity of Raman scattering on a soft mode responsible for the instability of the crystal lattice near the phase transition temperature. Experimental studies of combination opalescence in a soft mode were performed using the method of constructing isofrequency temperature dependences of the spectral intensity for fixed values of the frequency shift Ω of the scattered radiation relative to the frequency ω0 of the exciting radiation. It is shown that the experimentally observed anomalies of the spectral intensity agree with the dynamic theory of phase transitions in crystals, based on the concept of softening of the crystal lattice in the phase transition region.

Features of the Temperature Dependences of the Photoconductivity of Organometallic CH3NH3PbI3 Perovskite Films

The effect of temperature on the photoconductivity and its spectral dependence for thin films of organometallic CH3NH3PbI3 perovskite is studied. The measurements performed at temperatures below room temperature reveal the features of the change in the photoconductivity with temperature in the region of the phase transition from the tetragonal to orthorhombic structure (140–170 K). On the basis of analysis of the effect of temperature on the nature of the change in the spectral dependences of the photoconductivity in the phase-transition region, mechanisms are proposed, which clarify the observed change in the photoconductivity.

Предпереходные явления в области структурного фазового перехода в карбонате калия

Предпереходные явления в области структурного фазового перехода в карбонате калия

Study on Surface Longitudinal Crack Formation of Typical Hypoeutectoid Steel Produced on a Caster with Billet and Slab

This paper investigates the formation mechanism of typical hypoeutectoid steel with longitudinal cracks produced on a caster with billet and slab. It was found that the microstructure of the proeutectoid ferrite is the most critical factor affecting the longitudinal crack. The formation conditions of the proeutectoid ferrite and the reasonable control direction were determined through experiments and calculations. High-temperature tensile experiments revealed that enhanced cooling did not cause additional cracks. Therefore, the final plan was to reduce the formation of proeutectoid ferrite by strengthening the cooling process. As a result, the optimized surface temperature quickly passed the phase transition region of the proeutectoid ferrite and no cracks were found in the optimized billet.

Ohmic contact formation mechanisms of TiN film on 4H–SiC

The atomic structure, interfacial charge distribution, bonding nature, and interfacial electronic states of a 4H–SiC/TiN interface are systematically investigated to understand the Ohmic contact formation mechanisms of TiN to 4H–SiC. The experiment results clearly demonstrate that the well-arranged TiN (111)-oriented lattice planes are parallel to the (0001) SiC-oriented substrate, which is in line with the XRD results. In addition, the interface is coherent without any secondary phase layers, amorphous layers, or transition regions, which confirms the direct contact of TiN to SiC at the atomic scale, exhibiting a linear current–voltage relationship. Quantitatively, first-principle calculations reveal that the Schottky barrier height (SBH) is as low as 0.03 eV and that the band gap nearly vanishes at the interface, indicating an excellent Ohmic contact of TiN to 4H–SiC. Furthermore, the SBH is significantly reduced through the interfacial charge polarization effect and strong coupling of interfacial electronic states, enhancing the quantum electron transport. The present results provide insight into the complicated electronic effects of the Ohmic contact interface and indicate that TiN is a promising SiC Ohmic contact material for advanced next-generation power device applications.

Isochoric heat capacity and PVT properties of n-heptane – water binary azeotropic system

The isochoric heat capacity and the pressure of n-heptane – water binary layering system were measured using the high-temperature adiabatic calorimeter-piezometer method. Characteristic properties of a change in the temperature dependences of the heat capacity and the pressure along the isochores were revealed in a region of phase transitions. These features allow for fixing the azeotropy state in the system and for estimation of the influence a polar component (water) on a change in the azeptrope state temperature.

Resolving the topological classification of bismuth with topological defects.

The growing diversity of topological classes leads to ambiguity between classes that share similar boundary phenomenology. This is the status of bulk bismuth. Recent studies have classified it as either a strong or a higher-order topological insulator, both of which host helical modes on their boundaries. We resolve the topological classification of bismuth by spectroscopically mapping the response of its boundary modes to a screw-dislocation. We find that the one-dimensional mode, on step-edges, extends over a wide energy range and does not open a gap near the screw-dislocations. This signifies that this mode binds to the screw-dislocation, as expected for a material with nonzero weak indices. We argue that the small energy gap, at the time reversal invariant momentum L, positions bismuth within the critical region of a topological phase transition between a higher-order topological insulator and a strong topological insulator with nonzero weak indices.

The linear thermal expansion coefficient of iron in the temperature range of 130–1180 K

The results of a dilatometric study of the thermal coefficient of linear expansion of polycrystalline iron in the temperature range of 130–1180°K are presented. The measurements were made with an error of 3%. Temperature dependences were obtained and reference tables of the recommended values of volume properties were calculated. The region of the magnetic phase transition was studied in detail, and the critical indices of thermal expansion at the Curie point were determined.

On the issue of the solutions existence of the problem of gas hydrate dissociation in a porous medium with the formation of an extended region of phase transitions

Mathematical model of the gas hydrate dissociation in a porous medium with the formation of an extended region of phase transitions is proposed. In a rectilinear-parallel approximation self-similar solutions are constructed that describe the distribution of pressure, temperature, and hydrate saturation in a reservoir. Based on the obtained solutions analysis it was proved that for the problem of injecting warm gas into a hydrate saturated reservoir with piezoconductivity coefficient exceeds the thermal diffusivity coefficient, there are no solutions with an extended region of phase transitions. The existence of such solutions is possible during gas production from a gas hydrate reservoir due to a decrease in pressure at the extraction point.

Heat transfer coefficients of praseodymium in condensed state

The thermal diffusivity and the thermal conductivity coefficients of praseodymium have been investigated by the laser flash technique with an error of 3–6% in the temperature range from 295 to 1625 K of the solid and liquid states, including the regions of phase transitions. Comparison of measurement results with the available literature data was carried out. The fitting equations and the table of reference data on the heat transfer coefficients of praseodymium for scientific and practical use have been developed.

Probing diffusive phase transition in Ba(Ti0.80 Zr0.20)O3-0.5(Ba0.70 Ca0.30)TiO3 nanofibers by temperature-dependent piezoelectric force microscopy

Ba(Ti0.80 Zr0.20)O3-0.5(Ba0.70 Ca0.30)TiO3 (BTZ-0.5BCT) nanofibers (NFs) demonstrated diffusive phase transition, resulting in an enhanced Curie temperature TC. As a result, it is scientific significant to probe the variation of ferro/piezoelectricity during such diffusive phase transition region. In this letter, the ferro/piezoelectricity of BTZ-0.5BCT NF was probed by piezoelectric force microscopy (PFM) under a series of temperatures revealing the piezoresponse of BTZ-0.5BCT NF increased with temperatures as the temperature is less than 180°C. The result shows that the first harmonic piezoresponse initially increased with temperatures, yet two singularities appeared at 120 and 180°C, and subsequently rapidly decreased to less than room temperature, demonstrating the corresponding ferroelectric transition process was a diffusive phase transition. Such a diffusive phase transition is caused by the discontinuous internal nanostructure of the NF and the size effect of ferro/piezoelectricity originated from the nano-ceramics. More importantly, the principal ferroelectric phase transition of nano-ceramics during such diffusive phase transition region was further quantified by principal component analysis (PCA) study. This indicates that the principal TC of BTZ-0.5BCT nano-ceramics is around 180°C, representing the TC of the whole BTZ-0.5BCT NF. Such a vivid description of the variated ferro/piezoelectricity with temperatures allows to provide a scientific method to quantify diffusive phase transition by PCA study.

New models for generating hard random boolean formulas and disjunctive logic programs

We propose two models of random quantified boolean formulas and their natural random disjunctive logic program counterparts. The models extend the standard models of random k-CNF formulas and the Chen-Interian model of random 2QBFs. The first model controls the generation of programs and QSAT formulas by imposing a specific structure on rules and clauses, respectively. The second model is based on a family of QSAT formulas in a non-clausal form. We provide theoretical bounds for the phase transition region in our models, and show experimentally the presence of the easy-hard-easy pattern and its alignment with the location of the phase transition. We show that boolean formulas and logic programs from our models are significantly harder than those obtained from the standard k-CNF and Chen-Interian models, and that their combination yields formulas and programs that are “super-hard” to evaluate. We also provide evidence suggesting that formulas from one of our models are well suited for assessing solvers tuned to real-world instances. Finally, it is noteworthy that, to the best of our knowledge, our models and results on random disjunctive logic programs are the first of their kind.

Thermally-induced phase transformations in KNNS-BNKZ lead-free piezoceramics

Promising piezoelectric properties have been reported in potassium sodium niobate-based ceramics by introducing Bi0.5(Na0.82K0.18)0.5ZrO3 (BNKZ) into K0.48Na0.52Nb0.95Sb0.05O3 (KNNS) solid solutions in order to control the polymorphic phase transformation temperatures. In the present study, synchrotron x-ray powder diffraction (SXPD) was employed in combination with dielectric and ferroelectric measurements in order to clarify the influence of BNKZ on the phase transition temperatures of (1-x)KNNS-(x)BNKZ ceramics (with x = 0 to 0.05). The results, presented in terms of temperature-dependent SXPD patterns, dielectric permittivity and thermal depolarisation characteristics, confirmed that polymorphic phase transformation temperatures all shifted in a systematic manner with increasing BNKZ content. Broadening of the phase transition regions was also observed with increasing BNKZ content, leading to improvements in thermal stability of the ferroelectric properties. Microstructural examination of the KNNS-BNKZ ceramics revealed the presence of core-shell microstructures; this was correlated with the presence of weak shoulders on the diffraction peaks.