Top PDF Phase Transformations and Entropy of Non-Equilibrium Materials

Phase Transformations and Entropy of Non-Equilibrium Materials

Phase Transformations and Entropy of Non-Equilibrium Materials

Recent measurements on VULCAN, an engineering materials diffractometer at the Spallation Neutron Source, have demonstrated the ability to obtain information about the chemical and struc- tural changes in a commercial pouch cell for a spatially-defined region of the cell [124, 125, 126]. Thus, there is considerable opportunity to obtain real-time information about the structural changes that occur during cycling for conditions that replicate a real system. Pair distribution function anal- ysis is often performed for in situ x-ray studies of batteries, but here, the poor sensitivity of x-rays to lithium is especially problematic [127]. As the pouch cell system is further optimized for diffraction measurements, the ability to obtain PDF information will offer insight on the local structural changes that may be occurring locally in regions of the electrode material. Reflectometry measurements will present unique challenges to obtain atomically thin films with small enough surface roughness to extract meaningful depth profiles. However, more reports are emerging of successful iin situ mea- surements of Li half-cells [128], and the information that can be revealed about surface effects on the preferential extraction and insertion of lithium is uniquely accessible with this technique.
Show more

196 Read more

High temperature and ion implantation-induced phase transformations in novel reduced activation Si-Fe-V-Cr (-Mo) high entropy alloys

High temperature and ion implantation-induced phase transformations in novel reduced activation Si-Fe-V-Cr (-Mo) high entropy alloys

From these room temperature data, it was unclear whether the BCC or sigma type phases were most thermodynamically stable, or whether one was a high temperature phase that had been quenched in on cooling. Metastability is observed in HEAs, especially in the small scale samples used for research purposes, such as the discovery of precipitation in CoCrFeNiMn when treated at moderate temperatures for extended times (Pickering et al., 2016). The variation in phase assemblages observed in the as-cast alloys here could be due to differential rates of cooling during alloy production. The SiFeVCrMo alloy was produced as a 5 g ingot, while the SiFeVCr alloy was produced as a 2.5 g ingot. Therefore, the smaller SiFeVCr alloy may have cooled more quickly during casting, effectively enabling the quenching in of a high temperature BCC phase.
Show more

15 Read more

Effects of High Magnetic Fields on Phase Transformations in Amorphous Nd2Fe14B

Effects of High Magnetic Fields on Phase Transformations in Amorphous Nd2Fe14B

To further explore the phase evolution, ribbons were annealed at shorter times, 3 min and water quenched, to interrupt the microstructural evolution prior to achieving a state of equilibrium. It should be noted here that, due to the experimental setup described in the Materials and Methods, there was certainly a temperature lag between the thermocouple that lay outside of the sealed quartz ampule and the Ta foil-wrapped specimen such that the temperature reported was not the exact temperature of the specimen during this short heating time. Figure 3a,b display bright field TEM micrographs and selected area diffraction (SAD) patterns for zero-field and 90 kOe annealing, respectively. At 630 ◦ C, the zero-field case resulted in significant precipitation of Nd 2 Fe 14 B particles,
Show more

12 Read more

Numerical investigations of heat transfer in phase change materials using non equilibrium model

Numerical investigations of heat transfer in phase change materials using non equilibrium model

Phase change materials (PCMs) are drawing increasing attention of researchers nowadays, and they play a pivotal role in thermal energy storage (TES) used in renewable energy resources applications, since these renewable energy, such as solar energy, wind energy and tidal energy, are intermittent and not available at any time. However, most of PCMs suffer from low thermal conductivities prolonging the charging and discharging processes.

10 Read more

PHASE TRANSFORMATIONS IN CALCIUM SUBSTITUTED LANTHANUM FERRITE

PHASE TRANSFORMATIONS IN CALCIUM SUBSTITUTED LANTHANUM FERRITE

Lanthanum Calcium Ferrites (LCF) belongs to a class of materials known as mixed ionic and electronic conductors. Dense, non-porous, membranes synthesized out of LCF materials will spontaneously transport oxygen through the material with high flux and chemical selectivity when a chemical potential gradient is applied at temperatures in excess of 700°C. 1, 2 High temperature oxygen conducting membranes have a wide range of potential applications in commercial devices such as fuel cell cathodes, oxygen separation, and syngas production. Lanthanum calcium ferrite membranes have been specifically identified as a promising material for oxygen conducting membranes in syngas reactors, due to the combination of high oxygen flux rates and necessary chemical and mechanically stability in reducing atmospheres as discussed in the patent held by Air Products Inc (US 6,942,290). 2 The ability to reliably produce syngas in a cost effective manor benefits both the environment and economy. Much of the natural gas at remote oil extraction facilities around the world is combusted rather than collected due to the
Show more

147 Read more

V2O3(0001) surface termination : phase equilibrium

V2O3(0001) surface termination : phase equilibrium

atomic layers at which the bulk structure might be terminated. One fundamental question that is particularly relevant to these materials is whether, in practice, a surface can be created that is truly in equilibrium with its surroundings under preparation conditions. Starting from a bulk crystal of the oxide one might anticipate that it may be difficult to overcome the kinetic barriers to achieve this equilibrium under conditions of temperature and oxygen partial pressure accessible to surface science experiments. Alternatively, epitaxial growth of the oxide on a suitable substrate, by deposition of metal vapour in the presence of a partial pressure of oxygen, may offer a better means of achieving this gas-solid equilibrium. Growth is intrinsically a non-equilibrium process, yet by using low metal deposition rates in an excess of oxygen gas, the kinetic barriers to achieving equilibrium may be much lower than those needed to modify an existing non-equilibrium surface. In fact, previous structural studies of the surface of bulk crystals of α-Al 2 O 3 and Cr 2 O 3 , and of Cr 2 O 3 produced by
Show more

15 Read more

Structure and Non Equilibrium Phase Diagram of the Co Sputtered and Post Annealed Fe ZnO System

Structure and Non Equilibrium Phase Diagram of the Co Sputtered and Post Annealed Fe ZnO System

If thin films are used to determine the phase diagram of oxide materials, the equilibrium state using the thin film reaction can be obtained easily in comparison with use of bulk material due to the small volume and large surface resulting from the shape of the thin film. Thus, this method was adopted in the present study to obtain the phase diagram of the Fe-ZnO system when the films were as-sputtered in a reduced atmosphere and post-annealed in air. The aim of the present study was to determine the temperature dependence of the solubility limit and the structure of the co-sputtered and, subsequently, the annealed films of the Fe-ZnO system. Single crystalline films epitaxially grown on a ð011 12Þ sapphire single crystalline substrate using the co-sputtering method were adopted to exclude the effect of structural inhomogeneity due to the existence of grains and grain boundaries. X-ray diffraction, electron diffraction, high resolution imaging and EDS analysis by transmission electron microscopy were used to determine the phase diagram and the nanostructure.
Show more

6 Read more

A Generalized Statement of Highest Entropy Principle for Stable Equilibrium and Non Equilibrium in Many Particle Systems

A Generalized Statement of Highest Entropy Principle for Stable Equilibrium and Non Equilibrium in Many Particle Systems

Chemical entropy definition can be proved by means of PMM2. One could imagine a machine with a two- phase fluid operating at constant temperature between two different and constant pressures. The impossibility of PMM2 does not allow to withdrawn work interaction without net changes in the environment here constituted by the reservoir interacting with the system by mass transport. The proof, already provided by Gyftopoulos and Beretta to define the thermodynamic entropy, is general and no specific mention is made to its physical meaning, or to specific assumptions relating to the characteristics of the system, the number and type of particles, the type of potential as well as to the thermodynamic state. This is the rationale behind the generality of the theorems and proofs which, therefore, may be considered still valid also for chemical entropy here defined. This results from the fact that chemical entropy is an inherent property of any system, in any state. Therefore, the chemical entro- py can be adopted to state the Highest-Chemical-Entropy Principle which can be assumed as complementary to the Lowest-Chemical-Energy Principle.
Show more

14 Read more

Fluorite Phase Transformations under Vacuum

Fluorite Phase Transformations under Vacuum

Complex crystal aggregates from fluorspar vapor phase were grown at specific low-pressure/high- temperature conditions. The quasi-equilibrium of initiated crystal-chemical reactions at the pro- ceeding vapour-crystal phase transformation was strongly dependent on the mass-transport in- side an originally designed multicameral crucible, loaded by several portions of natural fluorite. By changing the temperature pressure over the already molten fluorspar portions as well as the gas-permeability of the channels connecting different sections in crucible interior to vacuum am- bient, one may control the rate of gaseous-vapour diffusion and the degree of supper-saturation inside the peripheral crucible compartment wherein nucleation and crystal growing occurred. In this way, grown aggregates revealed a complicated habit formed during three-stage growing process provided by relevant thermodynamic and phase. Residual stresses were not observed in the aggregates whereas those in simultaneously grown boules from the non-vaporized melts in crucible cameras were clearly distinguished. The optical transmittance spectra of the boules were obtained considerably better, especially in the UV, comparing to those for crystal aggregates, both showing several peaks of specific light-absorption due to enhanced presence of rare-earth (RE) impurities. The aggregates manifest nearly full reflectivity from Vis to near IR region. The vapor phase growth mechanisms, when natural fluorite with some RE contents has been used, were ex- plained on thermodynamic grounds that shown the manner of reliable control on the phenome- non. The results were anticipated to help for developing new perspective techniques for growth from vapor of several fluoride compounds with complex structure and composition and wide ap- plication. It was speculated that similar growth mechanisms of CaF 2 crystals were possible on the
Show more

13 Read more

A Combined Entropy/Phase-Field Approach to Gravity

A Combined Entropy/Phase-Field Approach to Gravity

Similar to entropy also the Lagrange formalism takes a significant role in many areas of physics. Besides the derivation of the Boltzmann factor being depicted above, the Lagrange formalism is a major basis for quantum mechanics and has especially been used to derive relations between symmetries and conservation laws. The Noether theorems being derived using the Lagrange formalism showed that invariance of physics laws under a translation implies the conservation of momentum or invariance under translation in time implies the conservation of energy. A further striking observation is that major physics laws all contain a Laplacian operator (resp. a Poisson type equation) somehow suggesting a common ground of all these models, which comprise all different length scales like gravitation, electrostatics, thermal conductivity, diffusion, flow, phase-field, Schrödinger equations, density functional equations and many others. Some operators being present in the Lagrange scheme have the property of generating Laplacian operators.
Show more

13 Read more

Entropy driven formation of the gyroid cubic phase

Entropy driven formation of the gyroid cubic phase

In this letter, we extend the range of phases accessible to purely repulsive objects by showing that tapered or pear-shaped particles can freely self-assemble to form the 3d periodic gyroid cubic phase. Due to their complexity and the supramolecular length-scales of their periodicities, very few particle-based simulations of cubic phases have been performed. The most convincing of these is Marrink and Tieleman’s molecular dynamics (MD) study of glyc- erolmonoolein molecules organised in a diamond cubic structure [7]. Here, however, the cubic arrangement had to be preconstructed and weak constraints imposed to maintain the structure; without these, this system slowly converted into an inverted hexagonal arrangement [8]. Simulation has also been used to probe the rheological properties of the gyroid phase [9]. Here, though, so as to make hydrodynamic behaviour accessible, it was necessary to employ a phenomenological Lattice-Boltzmann description which offered no link to the nature of the underlying particles.
Show more

14 Read more

The high pressure phase transformations of silicon and germanium at the nanoscale

The high pressure phase transformations of silicon and germanium at the nanoscale

The high-pressure-induced phase transformation behaviour of Si and Ge is affected by many factors such as shear, impurity level, strain rate, temperature, and volume of ma- terial. A summary of the factors that are known to influence the phase transformation behaviour, is found in Table 7.1. In this table, the known results from literature are shown in black whilst the new insights from this thesis are shown in blue. Before this study, the effect on pressure induced phase transformations of material volume had only been studied for very small size and near-bulk to bulk behaviour. This work focused on NWs and also small volume nanoindentation, and has provided the first comprehensive study of size effects during pressure induced phase transformation. In particular, it was found that the dc to β-Sn phase transformation threshold is increasingly suppressed as material volume is decreased. For some of the smallest (80-150 nm) SiNWs, the β-Sn phase was not observed, instead transforming directly to sh-Si. During decompression, a similar suppression of phase transformation was observed where β-Sn-Si was observed to remain until much lower pressures than for bulk materials. At ambient temperature, β-Sn-SiNWs phase transformed to predominately a-Si, in contrast to bulk-Si where bc8-Si formed. However, bc8-Si was observed to occasionally form in the larger SiNWs and also under very slow decompression. This suppression of phase transformation is believed the be caused by the small volumes of the NWs causing difficulties in the nucleation of new crystalline phases. It was additionally observed that SiNWs behave progressively more like bulk-Si as the size is increased. Increasing the temperature at which the SiNWs were compressed and decompressed resulted in the formation of bc8-Si and dc-Si end phases at intermediate temperatures (70-135 ◦ C), and predominately dc-Si at the highest temper- ature (165 ◦ C). When these phases formed, they were found to be polycrystalline. This differed from the behaviour observed in bulk-Si where bc8-Si formed at intermediate
Show more

142 Read more

TRANSFORMATIONS IN THE NOTION OF CONTRACTUAL EQUILIBRIUM BETWEEN PARTIES WITH EQUAL BARGAINING POSITION

TRANSFORMATIONS IN THE NOTION OF CONTRACTUAL EQUILIBRIUM BETWEEN PARTIES WITH EQUAL BARGAINING POSITION

Findings – the author concludes that the limits of intervention into the contractual relationship of parties with equal bargaining position (especially, business to business contracts) has to be reasoned taking into consideration the concept of contractual equilibrium applied in the period of the classical contract law. What is more, it has been concluded that the court judging on the basis of unequal bargaining power must take into consideration not only the experience and position of the party, but also it must determine, whether a party has used its advantageous position, therefore, the weaker party could not conclude the contract on better terms. In these cases it is important to determine which party has the burden of proof – the party invoking it’s weaker bargaining position must not only prove the real advantageous bargaining position of counterparty, but also - unsuccessful attempts to conclude the contract with more beneficial provisions.
Show more

10 Read more

4. Manning Roughness Coefficient Study on Materials Non Cohesive with Using Entropy to Open Channel Fl

4. Manning Roughness Coefficient Study on Materials Non Cohesive with Using Entropy to Open Channel Fl

[21]. Moramarco, T., and Singh, V.P., 2010. “ Formulation of the Entropy Parameter Based on Hydraulic and Geometric Characteristics of River Cross Sections “. Journal of Hydrologic Engineering 15(10), 852-858. [22]. Motovilov, Y.G., Gottschalk, L., Engeland, K. &Rodhe, A. 1999. Validation of a Distributed Hydrological Model Against Spatial Observations. Elsevier Agricultural and Forest Meteorology. 98, pp. 257-277

10 Read more

Phase Field Modeling of Phase Transformations in Platinum Based Alloy Nanoparticles

Phase Field Modeling of Phase Transformations in Platinum Based Alloy Nanoparticles

internal energy including the effects of phase transformations. In Sec. 3, the results of practical applications are explained. First, to verify the accuracy of this simulation, we compare this model with experimental and other simulation results for the phase transformations in FePt nanoparticles. Next, the effects of the alloying elements on the equilibrium microstructures of FePt, CoPt, NiPt, CuPt and IrPt binary alloy nanoparticles with diameters of less than 10 nm are investigated. Unfortunately, since the radial distribution of alloy components has not yet been fully investigated experimentally, it is difficult to evaluate the accuracy of our model in this regard. On the other hand, theoretical prediction of the microstructure formation of the nanoparticle has been made by using Monte Carlo simulations. Therefore, the validity of our simulation results is discussed mainly through comparisons with previously reported atomistic simulation results. The conclusions are given in Sec. 4.
Show more

8 Read more

Phase stability and distortion in high-entropy oxides

Phase stability and distortion in high-entropy oxides

batteries [1] and Thermoelectrics [2]. By increasing our number of components we massively increase the configurational space for exploration of new materials. Early attention in this field has on metallic systems, also known as “High-Entropy Alloys” [3–5]. These systems tend to exhibit single-phase solid solutions with simple crystal structures, mostly as face-centred cubic or body-centred cubic crystal structures. Inspired by the above-stated strategy, multiple component oxides of Mg, Co, Cu, Ni and Zn, exhibiting a rocksalt-type simple crystal structures with uniform distributions of ions in the crystal have been synthesised [6,7]. This was particularly surprising given that none of the constituent binary oxides show solid solubility within each other. Hence, the high configurational entropy of mixing has been attributed to explain the formation of the single phase solid solution. This has subsequently been further supported by the formation of a multicomponent rare-earth based oxide (Ce,La,Pr,Sm,Y)O [8] and more recently, class of high-entropy perovskite oxides have been reported [9]. This raises the clear question of how the entropy within these systems is able to overcome the presumed enthalpic penalty associated with mixing these oxides. Manipulating and controlling this entropy factor may facilitate the production of a whole new class of materials.
Show more

15 Read more

Non Linearity of Dynamics of the Non Equilibrium Systems

Non Linearity of Dynamics of the Non Equilibrium Systems

Another type of nonlinearity, which we have called “evolutionary nonlineari- ties”, is only possible for systems with nonholonomic constraints. A distinctive feature of “evolutionary nonlinearity” is that the corresponding nonlinear terms depend on variables of different symmetry groups, which is connected with the different hierarchical levels of the body. In the classical mechanics, the “evolutio- nary nonlinearities” have a place when the system of MP is moving in a nonho- mogeneous field of force. The presence of the gradient of field of force leads to engagement of the micro- and macro-variables defining the system dynamics and the dynamics of its internal structure. This leads to the transformation of the sys- tem motion energy into the internal energy. Thus, the “evolutionary nonlinearity” is inherent for the dissipative processes. They lead to the formation and develop- ment of structures accompanied by production of D-entropy in all hierarchical le- vels of the system. They determine the irreversibility of the system dynamics and violation of time symmetry.
Show more

14 Read more

Problems of Modeling the Phase Transformations in Nonlinear and Relaxed Optics

Problems of Modeling the Phase Transformations in Nonlinear and Relaxed Optics

Possibility of the condensation of soft mode in some point of Brillouin zone is determined of peculiarities of phonon spectrum the concrete system, more precision, the place of minimum in disperse curve of soft mode. The existence of this minimum in some symmetrical point of Brillouin zone isn’t a consequence symmetrical conditions, it depend from the peculiarities of the interatomic interaction of concrete crystal. Therefore may be happen situation, when minimum of soft mode will not correspond to symmetrical point of Brillouin zone. The condensation of this phonon is caused to the creation a structure with period, which is aliquant (incommensurate) to a period of initial crystal structure. For the phase transitions, which is corresponded to stars of Lifshitz type, module of wave vector can change continuously without a change of structure. Therefore, period of this structure is arbitrary (divisible to irrational number) relatively to a period of a lattice initial symmetric phase. Crystal phases, which are characterized of Lifshitz type vectors, are called incommensurate phases [8 – 11]. These phases may be created in the result structural, magnetic, mesomorphic and other types of phase transition.
Show more

14 Read more

Investigation of phase transformations of iron nanoparticles during thermal annealing

Investigation of phase transformations of iron nanoparticles during thermal annealing

While the magnitude of the hyperfine magnetic field for the sextet increases, this indicates the ordering of the structure and annealing of the defects that have arisen during the synthesis. The second phase of phase transformations is typical for temperatures of 200- 400 °C, which is characterized by a slight increase in the average size of nanoparticles and an increase in the degree of crystallinity. An increase in the annealing temperature above 200 °C leads to a rearrangement of the structure from Fe 3 O 4 into the Fe 2.12 O 3.19 structure

5 Read more

Phase Transformations in High Alloy Cold Work Tool Steel

Phase Transformations in High Alloy Cold Work Tool Steel

The differential thermal analysis technique/ thermomagnetometry is often used to determine the phase transitions including melting and solidification, liquation and formation of eutectics, recrystallization, dissolution and precipitation of new phases, solid-state transformation, and ferromagnetic to paramagnetic transition in a wide range of materials. Thermal analyses together with appropriate thermodynamic calculations can be used for analysis of such different materials as lead-free solders [24] and [25], carbon steels [26] and tool steels [27].

7 Read more

Show all 10000 documents...