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Faza označava oblik tvari u kojem su ujednačena i fizikalna i kemijska svojstva. Spontani prijelaz između dvije faze naziva se fazni prijelaz i odvija se pri određenim uvjetima. Ti se uvjeti mogu vizualizirati pomoću faznih dijagrama. Klasifikacija faza se temelji na ponašanju Gibbsove energije u ovisnosti o drugim termodinamičkim varijablama. Koristeći Clausius-Clapeyronovu jednadžbu, cilj je odrediti entalpiju isparavanja hlapljive tekućine na način da se mjeri tlak pare te tekućine pri različitim temperaturama. Osim što povezuje tlak pare i temperaturu, Clausius-Clapeyronova jednadžba daje podatke o obliku i položaju fazne granice tekuće-plinovito te granice kruto-plinovito., A phase is a state with uniformity in both physical and chemical properties. A spontaneous process of transition between two phases is called a phase transition and it occurs at certain conditions. Those conditions can be visualized with phase diagrams. The classification of phases is based on the behaviour of the Gibbs energy that is dependent on other thermodynamic variables. Using the Clausius-Clapeyron equation, the aim is to determine the enthalpy of vaporization of a volatile liquid by measuring the vapour pressure at different temperatures. Other than connecting the vapour pressure and the temperature, the Clausius-Clapeyron equation gives information about the shape and placement of the liquid-gas boundary and the solid-liquid boundary.

The paper presents and discusses questions on structure formation during the sintering process of Cr2O3-based composites using the hot pressing method, when a chemical reaction between the components takes place. The task was difficult because Cr2O3 decomposes when sintered at temperatures above 1300 degrees C. The proposed novel method allowed for interaction between aluminum and chromia, thus avoiding the decomposition of the latter. Here, ultrafine aluminum powder played the role of the active agent forming a liquid phase and reacting with Cr2O3. The appearance of the solid solutions of (Cr,Al)(2)O-3 with different stoichiometry of Cr and Al depended on the aluminum content in the initial mixture. The solid solution significantly strengthened boundaries between composite phases, resulting in the composite material of high fracture toughness between 5 and 7 MPa m(1/2) and bending strength of ca. 500 MPa. The best mechanical properties exhibited the cermet with 22 wt.% of the restored chromium. Web of Science 15 17 art. no. 5960

Dissertation, RWTH Aachen University, 2022; Aachen : RWTH Aachen University 1 Online-Ressource : Illustrationen, Diagramme (2022). = Dissertation, RWTH Aachen University, 2022, In this thesis the ion transport across different phase boundaries in strontium titanate, SrTiO3, was investigated. The oxygen transport across the gas|SrTiO3 interface was investigated by isotope exchange experiments followed by depth profiling with Secondary Ion Mass Spectrometry. The influence of surface orientation [(100), (110) and (111)] and the gas phase (dry: O2 and wet: H2O) on the oxygen surface exchange coefficient k*_O and the surface space-charge potential Φ_0 were examined. The surface orientation has a surprisingly low influence on the surface exchange coefficient [in general: k*_O(111) ≈ k*_O(110) > k*_O(100)]. In dry exchange conditions, all three surface orientations showed a transition from a high-temperature regime, with a high activation enthalpy, ΔH_k*_O, to a low-temperature regime with a lower ΔH_k*_O. In this low temperature regime and dry exchange conditions, the values of k*_O and Φ_0 agree well with those found for the wet exchange conditions on (100) oriented SrTiO3. This suggests, that a similar incorporation mechanism takes place for the wet exchange experiments and the dry exchange experiments at low temperature; being a mechanism where charged OH species at the surface play a vital role.The interface between metallic SrRuO3 and semi-conducting SrTiO3 was investigated by isotope exchange experiments followed by depth profiling with Secondary Ion Mass Spectrometry. The interface is characterised by the interface potential ϕ_i, which describes the defect redistribution of electronic and ionic charge carriers between the interface and the adjacent space-charge layer. A thin-film of SrRuO3 was shown to modify the space-charge zone at the SrTiO3 surface. The strontium transport at Ruddlesden-Popper type antiphase boundaries was investigated with different simulation techniques employing empirical pair potentials. Molecular static simulations showed, that the strontium vacancies prefer residing in the rocksalt-type antiphase boundary and not in the perovskite type bulk phase. The strontium vacancies were shown, with nudged elastic band calculations and molecular dynamics simulations, to exhibit a smaller migration barrier in the rocksalt-type antiphase boundary compared to the bulk phase., Published by RWTH Aachen University, Aachen

The cubic-plus-association equation of state was applied to model the phase behaviour of bitumen/n-alkane systems including saturation pressures, liquid-liquid boundaries, yields, and phase compositions. Yield is defined here as the mass of bitumen in the heavy phase divided by the mass of bitumen in the feed. To implement the model, the bitumen was divided into a set of pseudo-components based on a distillation assay and either the n-pentane insoluble content of the oil (CPA-C5 approach) or the propane insoluble content (CPA-C3 approach). The pseudo-components in the solvent insoluble part of the oil were defined as self-associating components, all other pseudo-components were non-associating. The critical properties and acentric factor for each pseudo-component were determined from established correlations. A set of CPA parameters was then developed to fit the available phase behavior data. The self-associating pseudo-components were assigned a distribution of self-association energies in order to capture the sequential partitioning of asphaltenes to the heavy phase upon solvent addition or in different solvents. Both approaches matched the phase behavior data for mixtures of bitumen with n-pentane and higher carbon number n-alkanes almost to within the experimental error. The CPA-C3 approach also matched the phase behavior data for mixtures of propane and bitumen. The CPA-C5 approach could not match the yield data for propane diluted bitumen but was more straightforward to implement and was less computationally intensive because it employed fewer self-associating components. To apply either approach to another oil, only the self-association energy of the self-associating pseudo-components need be adjusted. The cross-association energy between the solvent and the self-associating pseudo-components must be tuned for any new solvent.

A phase diagram, which is understood as a graphical representation of the physical states of materials under varied temperature and pressure conditions, is one of the basic concepts employed in high-pressure research. Its general definition refers to the equilibrium state and stability limits of particular phases, which set the stage for its terms of use. In the literature, however, a phase diagram often appears as an umbrella category for any pressure–temperature chart that presents not only equilibrium phases, but also metastable states. The current situation is confusing and may lead to severe misunderstandings. This opinion paper reviews the use of the “phase diagram” term in many aspects of scientific research and suggests some further clarifications. Moreover, this article can serve as a starting point for a discussion on the refined definition of the phase diagram, which is required in view of the paradigm shift driven by recent results obtained using emerging experimental techniques.

In this work, we address the occurrence of infinite pinning in a random medium. We suppose that an initially flat interface starts to move through the medium due to some constant driving force. The medium is assumed to contain random obstacles. We model their positions by a Poisson point process and their strengths are not bounded. We determine a necessary condition on its distribution so that regardless of the driving force the interface gets pinned., 12 pages, 4 figures

We consider a discrete and a continuum model for the propagation of a curvature sensitive interface in a time independent random medium. In both cases we suppose that the medium contains obstacles that act on the propagation of the interface with an inhibitory or an acceleratory force. We show that the interface remains bounded for all times even when a small constant external driving force is applied. This phenomenon has already been known when only inhibitory obstacles are present. In this work we extend this result to the case of, for example, a random medium of random zero mean forcing., Comment: 18 pages, 10 figures

The stress field due to a half-plane inhomogeneity with plane eigenstrain is obtained by a limiting procedure from the one of a circular Eshelby inhomogeneity/inclusion. This field, which requires tractions to be applied at infinity to be sustained, has minimum strain energy versus any other superposed homogeneous one, and is the Eshelby solution inside plus the Hill jump conditions. By superposition, the stresses due to an infinite strip (Eshelby property domain) inhomogeneity with eigenstrain are obtained, and, by superposition periodic strips or laminates can be obtained. By cancelling the stresses on a free-surface, strips of inclusions meeting a free surface are solved. They exhibit tensile stresses under the free surface, and logarithmic singularities in the tensile stress at the vertex, which may initiate cracking. The Eshelby self-forces on the boundary of circular and half-plane inhomogeneities are computed.

The binary manganese-antimony (Mn-Sb) phase diagram was reinvestigated in the whole composition range using powder-XRD, DTA and SEM-EDX. The phase boundaries and melting temperatures of the ferromagnetic phases MnSb and Mn2Sb were modified by taking into account the new experimental data. Most of the reaction temperatures could be verified within a range of ±10 °C. Nevertheless, a few temperatures had to be revised, such as the eutectic reaction L → β-Mn + Mn 2 Sb at 893 °C and the eutectoid reaction β-Mn → α-Mn + Mn 2 Sb at 718 °C. The previously reported peritectic melting behavior of MnSb could be confirmed. The variation of the lattice parameters of the NiAs-(B8 1 ) type MnSb phase with composition was determined. A revised version of the of the Mn-Sb phase diagram is presented.

This technical note is a complement to an earlier paper [Benzoni-Gavage & Rosini, Comput. Math. Appl. 2009], which aims at a deeper understanding of a basic model for propagating phase boundaries that was proved to admit surface waves [Benzoni-Gavage, Nonlinear Anal. 1998]. The amplitude equation governing the evolution of weakly nonlinear surface waves for that model is computed explicitly, and is eventually found to have enough symmetry properties for the associated Cauchy problem to be locally well-posed.

Among hyperbolic Initial Boundary Value Problems (IBVP), those coming from a variational principle ‘generically’ admit linear surface waves, as was shown by Serre (J Funct Anal 236(2):409–446, 2006). At the weakly nonlinear level, the behavior of surface waves is expected to be governed by an amplitude equation that can be derived by means of a formal asymptotic expansion. Amplitude equations for weakly nonlinear surface waves were introduced by Lardner (Int J Eng Sci 21(11):1331–1342, 1983), Parker and co-workers (J Elast 15(4):389–426, 1985) in the framework of elasticity, and by Hunter (Nonlinear surface waves. In: Current progress in hyberbolic systems: Riemann problems and computations (Brunswick, 1988). Contemporary mathematics, vol 100. American Mathematical Society, pp 185–202, 1989) for abstract hyperbolic problems. They consist of nonlocal evolution equations involving a complicated, bilinear Fourier multiplier in the direction of propagation along the boundary. It was shown by the authors in an earlier work (Benzoni-Gavage and Coulombel Arch Ration Mech Anal 205(3):871–925, 2012) that this multiplier, or kernel, inherits some algebraic properties from the original IBVP. These properties are crucial for the (local) well-posedness of the amplitude equation, as shown together with Tzvetkov (Adv Math, 2011). Properties of amplitude equations are revisited here in a somehow simpler way, for surface waves in a variational setting. Applications include various physical models, from elasticity of course to the director-field system for liquid crystals introduced by Saxton (Dynamic instability of the liquid crystal director. In: Current progress in hyperbolic systems: Riemann problems and computations (Brunswick, 1988). Contemporary mathematics, vol 100. American Mathematical Society, Providence, pp 325–330, 1989) and studied by Austria and Hunter (Commun Inf Syst 13(1):3–43, 2013). Similar properties are eventually shown for the amplitude equation associated with surface waves at reversible phase boundaries in compressible fluids, thus completing a work initiated by Benzoni-Gavage and Rosini (Comput Math Appl 57(3–4):1463–1484, 2009).

The density and percolation of Triple phase boundary sites are important quantities in analyzing microstructures of solid oxide fuel cell electrodes from tomography data. However, these measures do not provide descriptions of the quality of the TPB sites in terms of the length and radius of the pathways through which they can be reached. New methods for performing TPB specific pathway analysis on 3D image data are introduced, analyzing the pathway properties of each TPB site in the electrode structure. The methods seek to provide additional information beyond whether the TPB sites are percolating or not by also analyzing the pathway length to the TPB sites and the bottleneck radius of the pathway. We show how these methods can be utilized in quantifying and relating the TPB specific results to cell test data of an electrode reduction protocol study for Ni/Scandia-and-Yttria-doped-Zirconia (Ni/ScYSZ) anodes. A study of the TPB density and particle size distribution alone did not provide an explanation for the differences observed in electrode performance. However, the analysis of pathway lengths to the TPBs and the bottleneck radii to reach these TPB sites provided valuable microstructural insight that supported the findings from the electrochemical characterization of the Ni/ScYSZ anodes.

We prove that the Cauchy problem for an n×n system of strictly hyperbolic conservation laws in one space dimension admits a weak global solution also in presence of sonic phase boundaries. Applications to Chapman–Jouguet detonations, liquid–vapor transitions and elastodynamics are considered.

Unsteady-state sorption of a vapor or liquid by a polymer is modeled to include the influence of the moving phase boundary associated with the polymer swelling and diffusion-induced convection. A formulation presented clearly elucidates the influence of these two effects on the overall sorption process. Numerical solutions of the model equations indicate the errors that can be induced when swelling or convection are neglected. For most polymer-solvent systems, the influence of the diffusion-induced convection associated with volume changes in mixing can be neglected in the analysis of sorption processes. In contrast, the correction for the moving boundary or swelling of the polymer phase can be quite significant, particularly when a large step change in solvent concentration is considered.

International audience; The electrocaloric (EC) effect in lead-free (1-x)(K0.48Na0.52)(Nb0.95Sb0.05)O3-xBi0.5(Na0.82K0.18)0.5ZrO3 ceramics was investigated using an indirect thermodynamic method. Large EC temperature changes were obtained in the vicinity of a polymorphic phase boundary at 40 kV/cm, e.g., 0.32 K at 359 K for x = 0.03, 0.51 K at 350 K for x = 0.04, and 0.48 K at 300 K for x = 0.05, respectively. These values are larger than the previous results at inter-ferroelectric phase transition and, more interestingly, are found to be comparable to those usually explored at the Curie temperature. The operational temperature window is broad near the polymorphic phase boundary due to the diffuseness of the phase transition. The enhanced electrocaloric effect is attributed to the formation of nanodomains near the polymorphic phase boundary, which reduces domain wall energy and facilitates the polarization rotation. The construction of a polymorphic phase boundary and the arrangement of coexisting phases at the nanoscale may open a promising route to explore EC materials. © 2017 Author(s).

The (0.90-x)Pb(In1/2Nb1/2)O3-xPbTiO 3-0.10PbZrO3 (PINTZ10) ceramics are prepared by solid state reaction and their structural, dielectric and piezoelectric properties near morphotrophic phase boundary (MPB) has been examined systematically. The structure undergoes a gradual change from rhombohedral to tetragonal when the PbTiO3 content (x) is increased. From the frequency and temperature dependent dielectric measurement it is found that the dielectric relaxation (?T) decreases with Ti4+ substitution. Even though the MPB of this ternary system is formed with lower PT content (0.62PIN-0.28PT-0.10PZ), the substitution of Zr4+ in the B site maintains the transition temperature (Tm) at 300 C resembling its binary, 0.67PIN-0.37PT. The higher saturation polarization obtained for x = 0.27 and the high piezoelectric co-efficient obtained for x = 0.29 substantiate the existence of MPB between these two compositions. � 2013 Springer Science+Business Media New York.

Some five membered heterocyclic compounds were synthesized by the reaction of 2,4-thiazolidinedione or 5,5-diphenylhydantoin potassium salts with 2-chloro-N-alkylacetamides and alkyl-2-chloroacetates. The structure confirmations of the synthesized compounds were performed by FT-IR, 1 H NMR, 13 C NMR spectra. The inhibitory effectiveness of the compounds were evaluated against the corrosion of steel strip immersed in water containing paraffin based mineral oil medium in accordance to standard test method. Surface characterization studies of the metal coupons used were performed by SEM analysis and also by the contact angle measurements using the Sessile–Drop method. In addition the 3D image of the metal surface was obtained using optical profilometer. The test results and surface characterization studies showed that all synthesized compounds are excellent corrosion inhibitors in such a water in oil emulsion system.

The hydrogen absorption kinetics in the system Zr1−xHoxCo2 (x = 0.4, 0.6 and 0.8) were studied in the temperature range 50–200 °C. A change in slope is observed at the phase boundary as indicated in the first-order fit, which implies that different rate controlling steps are involved during different stages of the reaction. It is believed that the surface process, the interface process and the diffusion of hydrogen in the product β layer are the possible rate controlling steps in the α, α+β and β phases respectively. The diffusion coefficients obtained from the diffusion rate constants are found to be of the order of 10−10 cm2 s−1 at 300 K. The average activation energy (Ea) in the α+β phase and the β phase are found to be 20 and 16 kJ mol−1 respectively.

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich., This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively., For a model for the propagation of a curvature sensitive interface in a time independent random medium, as well as for a linearized version which is commonly referred to as Quenched Edwards– Wilkinson equation, we prove existence of a stationary positive supersolution at non-vanishing applied load. This leads to the emergence of a hysteresis that does not vanish for slow loading, even though the local evolution law is viscous (in particular, the velocity of the interface in the model is linear in the driving force).

The potential hydrogen storage compound NH(3)BH(3) has three known structural phases in the temperature and pressure ranges 110-300 K and 0-1.5 GPa, respectively. We report here the boundaries between, and the ranges of stability of, these phases. The phase boundaries were located by in situ measurements of the thermal conductivity, while the actual structures in selected areas were identified by in situ Raman spectroscopy and x-ray diffraction. Below 0.6 GPa, reversible transitions involving only small hysteresis effects occur between the room-temperature tetragonal plastic crystal I4mm phase and the low-temperature orthorhombic Pmn2(1) phase. Transformations of the I4mm phase into the high-pressure orthorhombic Cmc2(1) phase, occurring above 0.8 GPa, are associated with very large hysteresis effects, such that the reverse transition may occur at up to 0.5 GPa lower pressures. Below 230 K, a fraction of the Cmc2(1) phase is metastable to atmospheric pressure, suggesting the possibility that dense structural phases of NH(3)BH(3), stable at room temperature, could possibly be created and stabilized by alloying or by other methods. Mixed orthorhombic Pmn2(1)/Cmc2(1) phases were observed in an intermediate pressure-temperature range, but a fourth structural phase predicted by Filinchuk et al. [Phys. Rev. B 79, 214111 (2009)] was not observed in the pressure-temperature ranges of this experiment. The thermal conductivity of the plastic crystal I4mm phase is about 0.6Wm(-1) K(-1) and only weakly dependent on temperature, while the ordered orthorhombic phases have higher thermal conductivities limited by phonon-phonon scattering.

Traveling waves are constructed that represent the internal structure of phase boundaries in compressible binary fluid mixtures.

It is shown that the temperature dependence of the magnetoresistance (MR) in manganites can be appreciably broadened by enhancing phase competition. By substituting Mn4+ with small amounts of Ti4+, the ferromagnetic metallic La0.815Sr0.185MnO3 is pushed closer to the ferromagnetic metallic (FMM)/ferromagnetic insulating (FMI) phase boundary. Ti4+ substitution significantly reduces the ferromagnetic and insulator-metal transition temperatures and broadens their evolution. This results in weak temperature dependence of the MR across the M-I transition with a variation of only about 0.5%. Thus, the route adopted is well suited for overcoming one of the major limitations of using colossal magnetoresistive manganites as magnetosensitive devices. � 2006 Elsevier B.V. All rights reserved.

This thesis deals with two aspects of the mechanics of symmetry-breaking defects such as phase boundaries, inclusions and free surfaces, and their role in the macroscopic response of active materials. We first examine the problem of kinetics using a nonlocal theory, and then study the role of geometry in active materials with fields that are not confined to the material. Classical PDE continuum models of active materials are not closed, and require nucleation and kinetic information or regularization as additional constitutive input. We examine this problem in the peridynamic formulation, a nonlocal continuum model that uses integral equations to account for long-range forces that are important at small scales, and allows resolution of the structure of interfaces. Our analysis shows that kinetics is inherent to the theory. Viewing nucleation as a dynamic instability at small times, we obtain interesting scaling results and insight into nucleation in regularized theories. We also exploit the computational ease of this theory to study an unusual mechanism that allows a phase boundary to bypass an inclusion. Shifting focus to problems of an applied nature, we consider issues in the design of ferroelectric optical/electronic circuit elements. Free surfaces and electrodes on these devices generate electrical fields that must be resolved over all space, and not just within the body. These fields greatly enhance the importance of geometry in understanding the electromechanical response of these materials, and give rise to strong size and shape dependence. We describe a computational method that transforms this problem into a local setting in an accurate and efficient manner. We apply it to three examples: closure domains, a ferroelectric slab with segmented electrodes and a notch subjected to electro-mechanical loading.

We consider the Bose-Hubbard model in a two dimensional rotating optical lattice and investigate the consequences of the effective magnetic field created by rotation. Using a Gutzwiller type variational wavefunction, we find an analytical expression for the Mott insulator(MI)-Superfluid(SF) transition boundary in terms of the maximum eigenvalue of the Hofstadter butterfly. The dependence of phase boundary on the effective magnetic field is complex, reflecting the self-similar properties of the single particle energy spectrum. Finally, we argue that fractional quantum Hall phases exist close to the MI-SF transition boundaries, including MI states with particle densities greater than one., 5 pages,3 figures. High resolution figures available upon request

We propose a discrete model providing a unified description of lattice induced drag for a class of defects which includes martensitic phase boundaries, dislocations and cracks. Although the model is Hamiltonian, it generates a non-trivial macroscopic friction law which we present as a closed form functional relation between the velocity of the defect and the conjugate configurational force. The possibility to obtain an exact analytic solution of the dynamic problem allows us to expose both the similarities and the differences in the kinetics of various types of defects. In particular, we trace the origin of the symmetry related resonances, specific for dislocations, and show how the flattening of one of the energy wells, indicating transition to fracture, generates a morphological instability of the displacement profile at a critical velocity.

Des essais de cisaillements cycliques, à des températures variant de 360 °C à 460 °C, ont été réalisés sur l'eutectique lamellaire Al-Al2Cu(θ) obtenu par solidification dirigée. La cission appliquée est parallèle aux joints Al/θ et à la direction de croissance. L'expérience indique que la contrainte d'écoulement du matériau correspondant à chaque cycle ne dépend pratiquement que de la température et de la vitesse de charge actuelles du matériau. Le glissement macroscopique g résulte de glissements interfaciaux très localisés, délimitant le plus souvent des paquets de lamelles en nombre pair. Ces glissements interfaciaux sont tous proportionnels à g. L'utilisation d'une loi constitutive analogue à celle de Mukherjee, Bird et Dorn (1969) conduit à un exposant m égal à 0,26 pour la vitesse de glissement g et une énergie d'activation apparente voisine de 128 kJ.mole-1.