Study Of Phase Transformations Research Articles

Recovery of phosphorus rich krill shell biowaste for uranium immobilization: A study of sorption behavior, surface reaction, and phase transformation

Increased generation of shrimp shell from exploitation of krill results in emerging biowaste pollution, in addition, uranium pollution has drawn public concern due to the rapid development of nuclear power, uranium mining, and nuclear fuel processing. In this study, krill shells were recovered and used as a potential natural biosorbent for uranium immobilization, thereby enabling both uranium decontamination and krill shell reutilization. Interaction of uranium with krill shell surface and their transformation were investigated by using batch sorption experiments, scanning electron microscopy, and transmission electron microscopy. Krill shell had high uranium sorption ability. Uranium was transformed into a nano-scale precipitate. The mapping of phosphorus and uranium was related to the nano-scale precipitate, indicating that sorption of uranium was dependent on phosphorus. Surface chemisorption between phosphate in krill shell and uranium as well as the formation of the nano-scale precipitate were interpreted as the mechanism of uranium immobilization. Thus, natural krill shell waste has potential for extensive use as a promising and cost-effective sorbent for uranium immobilization and krill shell reutilization.

RHEGAL: Resistive heating gas enclosure loadframe for in situ neutron scattering.

In situ neutron scattering is a powerful tool to reveal materials atomic structural response such as phase transformation, lattice straining, and texture under external stimuli. The advent of a high flux neutron source such as the Spallation Neutron Source (SNS) allows fast measurement in even non-equilibrium conditions, i.e., phase transformation in steels. However, the commercial fast heating apparatus such as commercial physical simulation equipment is not designed for in situ neutron scattering, which limits its application to in situ materials research by using neutrons. Here we present a resistive heating gas enclosure loadframe (RHEGAL) for non-equilibrium phase transformation studies by using in situ neutron scattering, which takes the advantage of high flux neutron sources like SNS. RHEGAL enables fast resistive heating of metal samples to 1200 °C at a rate up to 60 °C/s in an inert atmosphere. It provides both horizontal and vertical positions for scattering optimization. The mechanical loading capability also allows in situ high temperature tension above the oxidation temperature limit. The optimized translucent neutron scattering window by silicon allows both reflection and transmission measurements, making this equipment applicable for neutron diffraction, small angle scattering, and imaging. To demonstrate the fast heating capability, the phase transformations of an example of advanced high strength steel heated at 3 °C/s and 30 °C/s were measured with the VULCAN engineering diffractometer, and the different phase transformation kinetics by neutron diffraction were presented.

Finite element procedure and simulations for a multiphase phase field approach to martensitic phase transformations at large strains and with interfacial stresses

A detailed finite element procedure for a new phase field approach (Basak and Levitas, 2018) to temperature- and stress induced multivariant martensitic transformations at large strains and with interfacial stresses is developed. A system with austenite and N martensitic variants is considered. N+1 order parameters related to the transformation strains are used, one of which describes the austenite↔martensite transformation; the other N order parameters describe N martensitic variants. Evolution of the order parameters is governed by coupled Ginzburg–Landau and mechanics equations. Assuming a non-monolithic strategy for solving the governing equations by using Newton’s iterative method, a weak formulation with emphasis on the derivation of the tangent modulus has been presented. Notably, the fourth order tangent modulus for the equilibrium equations has a contribution not only from the elastic stresses but also from the structural interfacial stresses, which appears here for the first time. A second order backward difference scheme is used to discretize the time derivative in the Ginzburg–Landau equations. An adaptive time stepping is considered. A finite element code has been developed within an open source package deal.II for a system with austenite and two martensitic variants and used to solve three problems: (i) simple shear deformation of a rectangular parallelepiped with evolution of austenite and single martensitic variant; (ii) twinning in martensite and the effect of sample size on the twinned microstructures; (iii) a rectangular block under nanoindentation. The results for the first two problems describe the well-known analytical solutions. Two kinematic models (KMs) for the transformation deformation gradient tensor are used and the corresponding results are compared: KM-I represents a linear transformation rule in the Bain tensors and KM-II is an exponential-logarithmic type of transformation rule in the Bain tensors. The algorithm can naturally be extended for the study of phase transformations in multiphase solids, solidification, diffusive phase transitions, interaction between phase transformations and plasticity and/or fracture, etc.

Phase transformations in the W–Cr system at the nanoscale

In order to enhance the thermal stability of nanomaterials, it is important to understand phase transformations at the nanoscale in high detail. In this study, the phase transformations occurring in the nanocrystalline W–Cr system were investigated using nanometallic multilayers to shift the kinetics of nucleation and to increase the diffusivities of W and Cr. The initial metastable state of the multilayers was tailored to favor the formation of solutions rich in W. In addition, the higher diffusivities in the system made it possible to observe the nucleation of the W3Cr intermetallic at 1000 °C, a temperature lower than that reported in previous studies. In this manuscript, the use of nanometallic multilayers is proposed as an approach to modify the thermal evolution of a nanocrystalline systems and study phase transformations at the nanoscale.

Propagation topography of redox phase transformations in heterogeneous layered oxide cathode materials

Redox phase transformations are relevant to a number of metrics pertaining to the electrochemical performance of batteries. These phase transformations deviate from and are more complicated than the conventional theory of phase nucleation and propagation, owing to simultaneous changes of cationic and anionic valence states as well as the polycrystalline nature of battery materials. Herein, we propose an integrative approach of mapping valence states and constructing chemical topographies to investigate the redox phase transformation in polycrystalline layered oxide cathode materials under thermal abuse conditions. We discover that, in addition to the three-dimensional heterogeneous phase transformation, there is a mesoscale evolution of local valence curvatures in valence state topographies. The relative probability of negative and positive local valence curvatures alternates during the layered-to-spinel/rocksalt phase transformation. The implementation of our method can potentially provide a universal approach to study phase transformation behaviors in battery materials and beyond.

A Study of Phase Transformations in High-Chromium Ferritic-Martensitic Steels by Magnetometry

Phase transformations in high-chromium ferritic-martensitic steels are studied using magnetometric analysis of the magnetic field. A designed, certified and experimentally tested facility for measuring the magnetic permeability of small (pea-size) specimens is described. The facility makes it possible to determine the temperatures of magnetic transformations and, in some cases, the thermal effects of phase transformations. Examples of application of the developed method for determining the characteristics mentioned are given and used to plot diagrams of isothermal transformation of supercooled austenite. An analysis of pairs “mechanical properties – parameters of diagrams of isothermal transformation” is performed, and the dependences obtained are analyzed. The formulated features of the parameters of the diagrams of isothermal decomposition may be used for developing high-chromium ferritic-martensitic steels with high refractoriness. The limits of the applicability of the developed methods and of the used facility are presented.

Cubic martensite in high carbon steel

A distinguished structural characteristic of martensite in Fe-C steels is its tetragonality originating from carbon atoms occupying only one set of the three available octahedral interstitial sites in the body-centered-cubic (bcc) Fe lattice. Such a body-centered-tetragonal (bct) structure is believed to be thermodynamically stable because of elastic interactions between the interstitial carbon atoms. For such phase stability, however, there has been a lack of direct experimental evidence despite extensive studies of phase transformations in steels over one century. In this Rapid Communication, we report that the martensite formed in a high carbon Fe-8Ni-1.26C (wt%) steel at room temperature induced by applied stress/strain has actually a bcc rather than a bct crystal structure. This finding not only challenges the existing theories on the stability of bcc vs bct martensite in high carbon steels, but also provides insights into the mechanism for martensitic transformation in ferrous alloys.

Upgrading of Waste Gypsum for Building Materials

In this research, waste gypsum (CaSO4·2H2O), a by-product material from industrial factory, was upgraded and then used as raw material for building materials. The by-product gypsum possessed a high acidic value of 3-point pH scale and moisture content of 40 %. The two properties had an impact on setting reaction and hardening of gypsum. Therefore, the studies of gypsum phase transformation to calcium sulfate hemihydrate (CaSO4·0.5H2O) were focused on washing process and amount of calcium carbonate (CaCO3) added at 0, 1, 3 and 5 % wt. After washing, waste gypsum and washed water were reduced from high acidic value to neutralization (pH = 7) as a result of CaCO3. Next, the neutralized gypsum was heated to the optimal temperature at 160 °C for 2 hours and transformed to hemihydrate gypsum phase observed by XRD. Finally, the relationship of amount of CaCO3-mechanical property such as bending strength will be investigated.

Thermodynamic, structural and magnetic studies of phase transformations in MnAl nanocomposite alloys

We have undertaken a temperature-dependent, investigation of the thermodynamics, structure, morphology and magnetism of two MnAl nanocomposite alloys (Mn60Al40 and Mn55Al45). Differential scanning calorimetry (DSC) studies allowed the determination of the exo-effects occurring in the structural phase transformation of MnAl, while by using temperature-dependent X-ray diffraction of synchrotron radiation we were able to monitor the phase transformation effects and the evolution with temperature of various structural phases occurring in the samples. We have shown that slight changes in stoichiometry (5 at.%) give rise to different phase structure in the as-cast state. While in Mn60Al40 only hcp ε phase can be found, in Mn55Al45 as-cast alloy, there is a quite complex phase structure with a mixture of γ2 (Al8Mn5) and ε as well as ferromagnetic MnAl τ-phase. Activation energies of about 165 kJ/mol and 290 kJ/mol have been calculated from the Ozawa-Flynn-Wall analysis of DSC experimental data. These findings are in good agreement with the results obtained from XRD. For the Mn55Al45 as-cast alloy, we have confirmed by temperature-dependent synchrotron XRD that the hcp ε phase decomposes through the migration of interphase interfaces with the transformation rate controlled by boundary diffusion processes. High-resolution transmission electron microscopy have confirmed the phase structure obtained by XRD, while magnetic properties, obtained for the as-cast alloys are consistent with the multiphase character of the samples and in good agreement with previously reported results. The magnetization does not saturate for the maximum applied field of about 4 × 106 A/m and a marked coercivity of about 160 kA/m is obtained for the Mn55Al45 as-cast alloy.

Efficient first-principles prediction of solid stability: Towards chemical accuracy

The question of material stability is of fundamental importance to any analysis of system properties in condensed matter physics and materials science. The ability to evaluate chemical stability, i.e., whether a stoichiometry will persist in some chemical environment, and structure selection, i.e. what crystal structure a stoichiometry will adopt, is critical to the prediction of materials synthesis, reactivity and properties. Here, we demonstrate that density functional theory, with the recently developed strongly constrained and appropriately normed (SCAN) functional, has advanced to a point where both facets of the stability problem can be reliably and efficiently predicted for main group compounds, while transition metal compounds are improved but remain a challenge. SCAN therefore offers a robust model for a significant portion of the periodic table, presenting an opportunity for the development of novel materials and the study of fine phase transformations even in largely unexplored systems with little to no experimental data.

Novel polymorph of ambrisentan: Characterization and stability

The present work highlights a novel polymorph (form II) of ambrisentan (AMT), a selective endothelin type A (ETA) receptor antagonist used in the treatment of pulmonary arterial hypertension (PAH). Form II was isolated by solution crystallization and characterised by differential scanning calorimetry, powder X-ray diffraction, solution calorimetry and aqueous solubility. The single crystal X-ray diffraction shows that it crystallizes in monoclinic system with space group P21/c different from the form I (commercial form). Form II was found to be enantiotropically related to form I. Apparent solubility of form II was performed in 0.1 N HCl (pH 1.2) was found to be higher (1.5 fold) than of form I. Solution mediated and stress-induced phase transformation studies revealed conversion of form II to form I. Accelerated stability studies (40 °C & 75% RH) also reveal that form II converted to form I after one month. However, this does not belittle the improved solubility of a new solid form.

Kinetic study of hydrogen-induced direct phase transformation in Y2Fe17 magnetic alloy on the basis of Kolmogorov’s model

The kinetics of the hydrogen induced direct phase transformation in Y2Fe17 magnetic alloy has been analysed within the framework of Kolmogorov’s kinetic model. It is established that the transformation can be classified as a diffusion-controlled transformation, which occurs by a mechanism of nucleation and growth with a decreasing nucleation rate of new phases, namely α-Fe and YH2. A kinetic equation has been obtained that well describes the isothermal kinetic curves of the phase transformation in Y2Fe17 as a function of the transformation temperature.

Control of the surface electron-beam alloying process by vibration monitoring

The experimental results prove the ability to realize technology of chemical heat treatment of some materials by surface alloying using a wide-aperture low-energy high-current electron beam. Doped hardened layers were produced due to initiating exothermic chemical reactions between the base and the thin film covered on it. Nevertheless, it is quite difficult to control the process of surface electron-beam alloying due to the significant variation in the parameters of the microsecond electron beam pulse and the instability of its interaction with the processed material. It leads to significant random changes that occur spontaneously, regardless of the control system. In this situation, it is proposed to use the method based on monitoring of oscillations and acoustic emission, which has long proved to be an effective tool in the study of phase transformations and plastic deformation. The appearance of a process with high vibroacoustic activity under irradiation of plates made of pre-nitrated steel 08Cr17Ti with a deposited film Nb70Hf22Ti8in the range of 11–22 kHz 10 ms after the electronic pulse was experimentally shown on this background. The source of this vibroacoustic signal is a change in the microstructure of the alloy, including the appearance of a martensitic component in the near-surface layer of the sample caused by the formation of nitride based on niobium. Tracking changes in the effective value of the vibroacoustic signal allow choosing the rational modes of irradiation with electron-beam surface alloying, involving the supply of maximum power, limited by the possibility of evaporation of the film with alloying components.

Исследование фазового перехода жидкость—кристалл в растворе KNO3 с использованием рамановской спектроскопии

Исследование фазового перехода жидкость—кристалл в растворе KNO3 с использованием рамановской спектроскопии

Studies on Se75Te25–xInx chalcogenide glasses; a material for phase change memory

This research paper describes the non-isothermal crystallization during phase transformation in Se75Te25–xInx glasses synthesized by melt quenching method. For crystallization studies in these glasses, non-isothermal differential scanning calorimetry (DSC) measurements was done at constant heating rates of 5, 10, 15, 20 and 25 K min−1 in air atmosphere. The glass transition temperature (Tg), on-set crystallization temperature (Tc), peak crystallization temperature (Tp) and melting temperatures (Tm) were derived by DSC thermograms. Using various thermal parameters the activation energy of glass transition and crystallization were determined by using Kissinger, Moynihan and Ozawa approaches and found to be in good agreement. The value of the activation energy of glass transition (ΔEt) was found to be minimum for Se75Te19In6 alloys confirming its maximum probability of transition in a metastable state. Thermal stability parameters of Se75Te25–xInx were determined and found to be increased with indium content. High resolution x-ray diffraction and field emission scanning electron microscopy studies were employed for the study of phase transformation in Se75Te25–xInx glasses. The outcome of these studies shows that the investigated materials may be suitable for phase change memory devices.

A Mechanistic Study of Phase Transformation in Perovskite Nanocrystals Driven by Ligand Passivation

Active control over the shape, composition, and crystalline habit of nanocrystals has long been a goal. Various methods have been shown to enable postsynthesis modification of nanoparticles, including the use of the Kirkendall effect, galvanic replacement, and cation or anion exchange, all taking advantage of enhanced solid-state diffusion on the nanoscale. In all these processes, however, alteration of the nanoparticles requires introduction of new precursor materials. Here we show that for cesium lead halide perovskite nanoparticles, a reversible structural and compositional change can be induced at room temperature solely by modification of the ligand shell composition in solution. The reversible transformation of cubic CsPbX3 nanocrystals to rhombohedral Cs4PbX6 nanocrystals is achieved by controlling the ratio of oleylamine to oleic acid capping molecules. High-resolution transmission electron microscopy investigation of Cs4PbX6 reveals the growth habit of the rhombohedral crystal structure is compos...

Crystallization kinetics and phase transformation studies on glassy Se85In15-xSbx system

Our aim in the present research work is to investigate the crystallization kinetics and phase transformation studies in Se85In15-xSbx semiconductor. DSC measurements were done at constant heating rates of 5, 10, 15, 20 and 25 K/min for Se85In15-xSbx alloys. The glass transition (Tg), on-set crystallization (Tc) and peak crystallization (Tp) temperature were found to be increases with heating rate for all samples. The activation energy for glass transition (ΔEg) and crystallization (ΔEc) were calculated by different approaches and found to be nearly identical. Thin films of Se85In15-xSbx alloys were prepared by the thermal evaporation technique and the effect of thermal annealing on optical properties were discussed by means of optical absorption measurements. The optical band gaps were found to decrease with annealing temperature. This decrease in optical band gap can be associated with phase change in Se85In15-xSbx alloys from amorphous to crystalline phase.

Study of structural phase transformation and hysteresis behavior of inverse-spinel α-ferrite nanoparticles synthesized by co-precipitation method

Abstract Substitution of cobalt (Co2+) ions in cobalt ferrite (CoFe2O4) with copper (Cu2+) and aluminum (Al3+) ions allows variations in their electric and magnetic properties which can be optimized for specific applications. In this article, synthesis of inverse-spinel Co1−xCuxFe2−xAlxO4 (0.0 ≤ x ≤ 0.8) nanoparticles by substituting Cu2+ and Al3+ ions in CoFe2O4 via co-precipitation method is reported. By controlling copper and aluminum (Cu-Al) substituent ratio, the magnetic moment and coercivity of synthesized cobalt ferrite nanoparticles is optimized. The role of substituents on the structure, particle size, morphology, and magnetic properties of nano-crystalline ferrite is investigated. The Co1−xCuxFe2−xAlxO4 (0.0 ≤ x≤ 0.8) nanoparticles with crystallite size in the range of 23.1–26.5 nm are observed, 26.5 nm for x = 0.0–23.1 nm for x = 0.8. The inverse-spinel structure of synthesized Co1−xCuxFe2−xAlxO4 (0.0 ≤ x ≤ 0.8) nano-particles is confirmed by characteristic vibrational bands at tetrahedral and octahedral sites using Fourier transform infrared spectroscopy. A decreases in coercive field and magnetic moment is observed as Cu-Al contents are increased (x = 0.0–0.8). The positive anisotropy of synthesized particles Co1−xCuxFe2−xAlxO4 (0.0 ≤ x ≤ 0.8) is obtained in the range 1.96 × 105 J/m3 for x = 0.0 to 0.29 × 105 J/m3 for x = 0.8.

The sintering behavior of plasma-sprayed YSZ coating over the delamination crack in low temperature environment

The sintering behavior of plasma-sprayed yttria-stabilized zirconia (YSZ) coating over the delamination crack and its influence on YSZ cracking were investigated via gradient thermal cycling test and finite element model (FEM). The gradient thermal cycling test was performed at a peak surface temperature of 1150°C with a duration of 240s for each cycle. A three-dimensional model including delamination cracks with different lengths was employed to elaborate the temperature evolution characteristics in YSZ coating over the delamination cracks. The temperature over the delamination crack increases linearly with the crack propagation, which continuously promotes the sintering of YSZ coating in the region. As a result, the YSZ coating over the delamination crack sinters dramatically despite of the low temperature exposure. Meanwhile, the temperature distribution difference in YSZ coating induces an nonuniform sintering along both free surface and thickness of YSZ coating. Correspondingly, the maximum vertical crack driving force locates at the YSZ free surface over the delamination crack center, which makes the vertical cracks generate in this region and propagate to the interface of YSZ /bond coat with YSZ further sintering. The vertical crack promotes the delamination crack propagation via accelerating the oxidation velocity of the bond coat. The influence of temperature rise on delamination crack propagation can be divided into two stages: the little contribution stage and the promotion stage. For the actual engine exposure to low temperature, the study of phase transformation of YSZ over the delamination crack is indeed needed because of an extended remarkable temperature rise period.

Study of hematite-iron phase transformation during iron-carbon core-shell nanoparticles synthesis and investigation of their magnetic and microwave properties

Study of hematite-iron phase transformation during iron-carbon core-shell nanoparticles synthesis and investigation of their magnetic and microwave properties