New Methods to Study the Kinetics of Phase Transformation in Shocked Cerium Metal
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36 MATERIALS SCIENCE↗
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Kinetics of hexacelsian to celsian phase transformation in SrAl2Si2O8
The kinetics of hexacelsian to celsian phase transformation in SrAl2Si2O8 have been investigated. Phase pure hexacelsian was prepared by heat treatment of glass flakes at 990 C for 10 h. Bulk hexacelsian was isothermally heat treated at 1026, 1050, 1100, 1152, and 1200 C for various times. The amounts of monoclinic celsian formed were determined using quantitative X-ray diffraction. Values of reaction rate constant, k, at various temperatures were evaluated from the Avrami equation. The Avrami parameter was determined to be 1.1, suggesting a diffusionless, one-dimensional transformation mechanism. From the temperature dependence of k, the activation energy for this reaction was evaluated to be 527 plus or minus 50 kJ/mole (126 plus or minus 12 kcal/mole). This value is consistent with a mechanism involving the transformation of the layered hexacelsian structure to a three-dimensional network celsian structure which necessitates breaking of the strongest bonds, the Si-O bonds.
Bansal, Narottam P.↗
Kinetics of hexacelsian-to-celsian phase transformation in SrAl2Si2O8
The kinetics of hexacelsian to celsian phase transformation in SrAl2Si2O8 have been investigated. Phase pure hexacelsian was prepared by heat treatment of glass flakes at 990 C for 10 h. Bulk hexacelsian was isothermally heat treated at 1026, 1050, 1100, 1152, and 1200 C for various times. The amounts of monoclinic celsian formed were determined using quantitative X-ray diffraction. Values of reaction rate constant, k, at various temperatures were evaluated from the Avrami equation. The Avrami parameter was determined to be 1.1, suggesting a diffusionless, one-dimensional transformation mechanism. From the temperature dependence of k, the activation energy for this reaction was evaluated to be 527 plus or minus 50 kJ/mole (126 plus or minus 12 kcal/mole). This value is consistent with a mechanism involving the transformation of the layered hexacelsian structure to a three-dimensional network celsian structure which necessitates breaking of the strongest bonds, the Si-O bonds.
Bansal, Narottam P.↗
Visible light photocatalytic degradation of amitriptyline using cobalt doped titanate nanowires: Kinetics and characterization of transformation products
Not Available
A. Osawa, Rodrigo (ORCID:0000000191628191)↗
Kinetics of the phase transformation in a Ti-15Mo-5Zr-3Al alloy as studied by X-ray diffraction
The purpose of the study is to make the T-T-T diagram available and to describe the X-ray diffraction techniques used to determine the fraction of transformed phase in the Ti-15Mo-5Zr-3Al metastable beta-alloy which decomposes into the hexagonal alpha-phase and the bcc beta-phase of a higher Mo concentration. The sheet material studied for this study is not ideal for an X-ray examination because of both a rolling and annealing texture as well as grain size problems. These difficulties are overcome using special X-ray techniques. Equations are given that indicate the approximations to be accepted if pole figure data are disregarded. Lattice parameter data from the beta phase enables one to obtain an approximate phase diagram.
Rao, V. B.↗
Kinetics and Mechanisms of ZnO to ZIF-8 Transformations in Supercritical CO2 Revealed by in situ X-ray Diffraction
ZIF-8 was synthesized in supercritical carbon dioxide (scCO2). In situ powder X-ray diffraction, ex situ microscopy and simulations, provides a encompassing view of the formation of ZIF-8 and intermediary ZnO@ZIF-8 composites in this nontraditional solvent. Time-resolved imaging exposed divergent physicochemical reaction pathways from previous studies of the growth of anisotropic ZIF-8 core@shell structures in traditional solvents. Synthetically relevant physio-chemical properties of scCO2 were integrated into classical nucleation theory, relating interfacial forces with 3D nu-cleation outcomes. The kinetics of crystallization were examined and displayed a characteristic signature of time- and temperature-dependent mechanisms over the extent of the reaction. Lastly, we show that subtle factors, such as the extent of reaction and the size/shape of sacrificial templates can tailor ZIF-8 composition and size, eliciting control over hierarchical porosity in a nonconventional green solvent.
Sinnwell, Michael A.↗
In situ neutron diffraction measurements of FeCrNi0.06 model alloy and DSS2507 heated to 700 and 850 °C to study sigma phase formation kinetics
This dataset contains neutron diffraction data of a ferritic single phase model alloy (FeCrNi) and a commercial grade duplex stainless steel (DSS2507) collected during in situ heating and holding at 700 and 850 °C at BL1B-NOMAD at the Spallation Neutron Source.
36 MATERIALS SCIENCE↗
Oxyanion Surface Complexes Control the Kinetics and Pathway of Ferrihydrite Transformation to Goethite and Hematite
The rate and pathway of ferrihydrite (Fh) transformation at oxic conditions to more stable products is controlled largely by temperature, pH, and the presence of other ions in the system such as nitrate (NO 3 - ), sulfate (SO 4 2- ), and arsenate (AsO 4 3- ). Although the mechanism of Fh transformation and oxyanion complexation have been separately studied, the effect of surface complex type and strength on the rate and pathway remains only partly understood. We have developed a kinetic model that describes the effects of surface complex type and strength on Fh transformation to goethite (Gt) and hematite (Hm). Two sets of oxyanion-adsorbed Fh samples were prepared, nonbuffered and buffered, aged at 70 ± 1.5 °C, and then characterized using synchrotron X-ray scattering methods and wet chemical analysis. Kinetic modeling showed a significant decrease in the rate of Fh transformation for oxyanion surface complexes dominated by strong inner-sphere (SO 4 2- and AsO 4 3- ) versus weak outer-sphere (NO 3 - ) bonding and the control. The results also showed that the Fh transformation pathway is influenced by the type of surface complex such that with increasing strength of bonding, a smaller fraction of Gt forms compared with Hm. In conclusion, these findings are important for understanding and predicting the role of Fh in controlling the transport and fate of metal and metalloid oxyanions in natural and applied systems.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Influence of External Conditions on the Black-to-Yellow Phase Transition of CsPbI 3 Based on First-Principles Calculations: Pressure and Moisture
All-inorganic CsPbI 3 perovskite has emerged as a promising candidate for next-generation solar cells. However, owing to the poor structural stability of black phase CsPbI 3 perovskite at room temperature, it spontaneously transforms to the yellow, photoinactive, nonperovskite phase at room temperature, limiting further development of CsPbI 3 perovskite solar cells. Here, to better understand the mechanism driving such undesirable phase transformation, we examine the thermodynamics and kinetics associated with γ-to-δ phase transformation using density functional theory calculation. A solid-state nudged elastic band method was employed to find minimum energy pathways assuming a concerted solid-state phase transformation between these two phases. The gas molecules representing atmospheric (H 2 O, O 2 , and N 2 ) and inert (Ar) ambient environments, as well as applied external pressure, were considered to examine the influence of external conditions on the black-to-yellow phase transition. Our calculation reveals that, with increasing pressure, the thermodynamic driving force for converting the γ-phase to the δ-phase increases, whereas a larger activation energy must be overcome for the phase transition to occur. We also investigate the moisture-induced phase transformation with an H 2 O molecule and its dissociated species (H + /OH – ) and demonstrate that the reaction energy barriers can be significantly lowered in the presence of H 2 O or OH – . On the other hand, other nonpolar species (O 2 , N 2 , and Ar) have a negligible effect on the phase transformation kinetics, while they might reduce the thermodynamic driving force for the phase transformation and suppress the undesirable phase transformation. Our theoretical prediction could support recent observations that the γ-to-δ phase transformation occurs rapidly and catalytically in the presence of moisture, whereas in dry argon and dry oxygen atmospheres, the γ-CsPbI 3 remains stable.
14 SOLAR ENERGY↗
Kinetic energy budgets in areas of intense convection
A kinetic energy budget analysis of the AVE-SESAME 1 period which coincided with the deadly Red River Valley tornado outbreak is presented. Horizontal flux convergence was found to be the major kinetic energy source to the region, while cross contour destruction was the major sink. Kinetic energy transformations were dominated by processes related to strong jet intrusion into the severe storm area. A kinetic energy budget of the AVE 6 period also is presented. The effects of inherent rawinsonde data errors on widely used basic kinematic parameters, including velocity divergence, vorticity advection, and kinematic vertical motion are described. In addition, an error analysis was performed in terms of the kinetic energy budget equation. Results obtained from downward integration of the continuity equation to obtain kinematic values of vertical motion are described. This alternate procedure shows promising results in severe storm situations.
Fuelberg, H. E.↗
Friction and wear of tin and tin alloys from minus 100 C to 150 C
Sliding friction experiments were conducted with an iron (110) single-crystal pin sliding on single and polycrystalline tin and tin alloys. Specimens were examined at various ambient temperatures from -100 to 150 C. Applied loads varied from 1 to 50 grams, and sliding velocity was constant at 0.7 mm/min. Results indicate that the crystal transformation of tin influences the friction coefficient. Friction was higher for the diamond structure (gray tin) than it was for the body-centered tetragonal structure (white tin). Bismuth arrested the crystal transformation, which resulted in constant friction over the temperature range -100 to 150 C. Both copper and aluminum enhanced the kinetics of transformation, with aluminum producing a nearly twofold change in friction with the crystal transformation.
Buckley, D. H.↗
Large thermal hysteresis in a single-phase NiTiNb shape memory alloy
Large thermal hysteresis ($T$ hys ) is favorable in shape memory alloys (SMAs) because it renders wide service and storage temperature range of the SMA-made parts. In this letter, we show that large intrinsic $T$ hys up to 100 K is achieved in a low Nb content (2 at.%), β-Nb-free and single-phase NiTiNb SMA fabricated by casting, forging, wire-drawing and annealing. Such a large $T$ hys is comparable to that of the widely used dual-phase NiTiNb SMAs in which high Nb content and β-Nb are required. By exploiting the grain-size-dependence of $T$ hys in our single-phase NiTiNb SMA and that in an equiatomic NiTi SMA, we attribute the large $T$ hys to the enhanced kinetic resistance of transformation by the small grains. In conclusion, the connection between the $T$ hys and the kinetic resistance is demonstrated by a modified dislocation-based kinetic model.
36 MATERIALS SCIENCE↗
Magnetic ordering suppressed phase transformation of a TRIP-HEA during thermal cycling
Transformation-induced plasticity (TRIP) high-entropy alloys (HEAs) have drawn great attention as they present excellent mechanical properties, and their phase stability is critical for the underlying deformation mechanisms and the application temperature range. In this study, the kinetic phase transformation behavior of a dual-phase TRIP-HEA Fe 50 Mn 30 Co 10 Cr 10 (at. %) was probed by in situ neutron diffraction during thermal cycling between 293 and 425 K. Continuous austenitic and martensitic transformation were visualized through the evolution of hexagonal close-packed phase fraction during thermal cycling. Specifically, thanks to the magnetic sensitivity of neutron diffraction, it was found that the martensitic transformation under cooling became suppressed when the antiferromagnetic ordering started at ~326 K. This temperature was further confirmed as the Néel temperature by magnetization measurements. In this work, thermodynamic calculations revealed that the suppression effect on martensitic transformation is attributed to the consumption of the chemical driving force by the magnetic ordering. The magnetic ordering at such relatively high temperature is associated with the high Mn content. These findings shed light on a potential strategy to achieve better mechanical properties of Mn-containing alloys by manipulating the magnetic property through tuning the Mn content.
36 MATERIALS SCIENCE↗
Size Transformation of the Au 22 (SG) 18 Nanocluster and Its Surface-Sensitive Kinetics
For many applications of well-defined gold nanoclusters, it is desirable to understand their structural evolution behavior under working conditions with molecular precision. Here we report the first systematic investigation of the size transformation products of the Au 22 (SG) 18 nanocluster under representative working conditions and highlight the surface effect on the transformation kinetics. Under thermal and aerobic conditions, the consecutive and pH-dependent transformation from Au 22 to both well-defined clusters and small Au(I)SR species was identified by ESI-MS and UV-vis spectroscopy. By introducing a perturbation onto the Au 22 surface, significant changes in the activation parameters were determined from the kinetic study of the Au 22 transformation. This indicates the sensitivity of the nanocluster transformation pathway to the cluster surface. Finally, the systematic study of cluster transformation and the sensitivity of cluster transformation to the surface revealed herein has significant implications for future attempts to design gold nanoparticles with adaptation to the working environment and the regeneration of active nanoparticles.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Quasilinear theory of general electromagnetic fluctuations including discrete particle effects for magnetized plasmas: General analysis
The general quasilinear Fokker–Planck kinetic equation for the gyrophase-averaged plasma particle distribution functions in magnetized plasmas is derived, making no restrictions on the energy of the particles and on the frequency of the electromagnetic fluctuations and avoiding the often made Coulomb approximation of the electromagnetic interactions. Here, the inclusion of discrete particle effects breaks the dichotomy of nonlinear kinetic plasma theory divided into the test particle and the test fluctuation approximation because it provides expression of both the non-collective and collective electromagnetic fluctuation spectra in terms of the plasma particle distribution functions. Within the validity of the quasilinear approach, the resulting full quasilinear transport equation can be regarded as a determining nonlinear equation for the time evolution of the plasma particle distribution functions.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Elucidating the temperature dependence of TRIP in Q&P steels using synchrotron X-Ray diffraction, constituent phase properties, and strain-based kinetics models
Understanding the deformation-induced martensitic transformation (DIMT) is critical for interpreting the structure-property relationships that govern the performance of transformation-induced plasticity (TRIP) assisted steels. However, modern TRIP-assisted steels often exhibit DIMT kinetics that are not easily captured by existing empirical models based on bulk tensile strain. We address this challenge by combined bulk uniaxial tensile tests and in-situ high energy synchrotron X-ray diffraction, which resolved the phase volume fractions, stress-strain response, and microstructure evolution of each constituent phase. A modification of the Olson-Cohen model is implemented, which describes the martensitic transformation kinetics as a function of the estimated partitioned strain in austenite, rather than the bulk tensile strain. This DIMT kinetic model is used as a framework to clarify the root cause of an insufficiently understood toughness trough reported for TRIP-assisted steels during deformation at elevated temperatures. Here, the importance of the temperature-dependent toughness is discussed, based on the opportunity to modify deformation processes to tailor the DIMT kinetics and mechanical properties during forming and in service.
36 MATERIALS SCIENCE↗
Design Principles of Single Atoms on Carbons for Lithium–Sulfur Batteries
The study of lithium-sulfur (Li-S) batteries has generated various rationally designed cathodes and modified separators. However, the shuttle of soluble lithium polysulfides (LiPSs) and the sluggish kinetics of transformation of LiPSs to Li2S2/Li2S still hinder the achievement of long-life cycling and high-rate of Li-S batteries. Even though several kinds of nanocatalysts have been studied, the catalytic effects for Li-S batteries are not ideal. Single atoms (SAs) with high surface free energy are found to serve as both anchoring and electrocatalytic centers for LiPSs. Furthermore, atomically dispersed metal catalyst on carbon provide conductive and flexible host for dielectric sulfur. Moreover, SAs as the uniform lithiophilic sites can reduce the nucleation overpotential and ensure uniformly plating of Li. In this review, the latest strategies for preparation of SAs supported on carbons are provided on the application of Li-S batteries, including cathode, modified separator and Li metal anode. In addition, it also discusses how SAs with high catalytic activity can help build better Li-S batteries and the design principles for SAs. Finally, the future directions of SAs in energy storage applications is proposed.
25 ENERGY STORAGE↗
A rapid heating and high magnetic field thermal analysis technique
Abstract A new thermal analysis technique is described that allows measurements to be performed on bulk samples at extreme heating and cooling rates and in high magnetic fields. High heating rates, up to 1000 °C min −1 , are achieved through electromagnetic induction heating of a custom-built apparatus fitted with commercial thermal analysis heads and sensor. Rapid cooling rates, up to 100 °C min −1 , are enabled by gas quenching and the small thermal mass of the induction furnace. The custom apparatus is designed to fit inside a superconducting magnet capable of fields up to 9 Tesla. This study demonstrates that the instrument is capable of collecting accurate thermal analysis data in high magnetic fields and rapidly acquiring data for dynamic processes. While the full potential of the technique is still unrealized, currently, it can provide insight into phenomena at time scales relevant to heat treatment in many industrial processes and into little understood effects of high magnetic field processing.
47 OTHER INSTRUMENTATION↗