Phase Transformation Rate Research Articles

Physical and biological implications of accelerated aging on stereolithographic additive-manufactured zirconia for dental implant abutment.

This study aimed to comparatively investigate the effects of accelerated aging on the physical and biological features of zirconia manufactured by digital light processing (DLP) and conventional subtractive manufacturing (SM) with similar composition. Both the DLP- and SM-fabricated zirconia samples (7 mm × 7.5 mm × 1.5 mm) were grouped according to aging (134 °C, 0.2 MPa, 100% humidity) times, including 0 h, 5 h, and 10 h. Phase assemblage and surface topography of zirconia manufactured by different technologies were evaluated before and after aging. The biological effects of zirconia on human gingival fibroblast (HGF) cell events, including cell viability, proliferation, morphology and adhesion, were also evaluated by live/dead viability assay, cck-8 assay, scanning electron microscopy and confocal laser scanning microscopy respectively. The DLP-fabricated zirconia showed a higher initial cubic phase content and rate of phase transformation than the SM-fabricated zirconia. Among the different aging time-based groups, the 5 h-aged group exhibited significantly lower sub-micron scale surface roughness compared with the other groups. Aging did not significantly alter cellular behavior in any zirconia type, except for minor changes in adhesive cell numbers recorded in an aging time/culturing time-dependent manner. In addition to small differences in cell alignment patterns and overall cell morphology, the two zirconia types presented comparable biological performance before and after aging. Although the microstructure and surface characteristics of DLP-fabricated zirconia can be affected by autoclave aging, this newly manufactured zirconia is likely to maintain desirable long-term biocompatibility as an implant abutment material.

An approximate approach to estimation of dissociation rate of gas hydrate in porous rock bed

Development of deep shelf or onshore gas hydrate fields involves drilling wells with subsequent thermal, decompression or chemical action on the bed. In this case, the radius of thermal or decompression action is limited. As the field develops, recovery efficiency decreases, and necessity arises for drilling a new well that influences the cost of the technology. To determine the rational wells location, it is necessary to predict the advance of the phase transformation rate front into the depth of the bed. In this work, to study the movement dynamics of the gas hydrates dissociation front in a porous layer of rock, the Stefan problem solution is used. The method adequacy is substantiated by comparing the calculated results with known experimental data. The temperature fields are modelled in a porous bed during the methane hydrate dissociation. The temperature field dynamics for 200 days in a porous bed during the methane hydrate dissociation caused by thermal action is shown. The influence of porosity and excess temperature on the dissociation front movement rate is revealed.

Amorphization of S, Cl‐Salts Induced by Martian Dust Activities

AbstractA high proportion of noncrystalline (X‐ray‐amorphous) components has been found in all samples analyzed by CheMin on theCuriosity roverat Gale crater on Mars, and such X‐ray‐amorphous components probably occur at all sites that have been investigated thus far by landers and rovers. The amorphous material at Gale crater is rich in volatiles (S, Cl, and H2O), as indicated by other science payload elements (APXS, SAM). We demonstrate here that amorphization of S and Cl salts can be induced by energetic electrons and free radicals generated in a medium‐strength electrostatic discharge (ESD) process during Martian dust activities such as dust storms, dust devils, and grain saltation. Furthermore, we found that the amorphization is commonly accompanied by dehydration of the salts and oxidation of Cl, S, and Fe species. On the basis of experimentally observed rates of the above phase transformations and the mission‐observed dust activities and wind speeds on Mars, we anticipate that similar phase transformations could occur on Mars within a time frame of years to hundreds of years. Considering the high frequency, long duration, and large areal coverage of Martian dust activities, our study suggests that the ESD induced by Martian dust activities may have contributed to some the S‐ and Cl‐rich portion of X‐ray amorphous materials observed in surface soils at Gale crater. Furthermore, dust activities in the Amazonian period may have generated and deposited a significant quantity of S‐ and Cl‐rich amorphous materials all over Mars.

Phase Transformation Mechanism and Microstructure Evolution of TC4 Alloy during Continuous Cooling

The effects of cooling rate on the microstructure and phase transformation mechanism of TC4 alloy during the continuous cooling of β phase region were studied by non-isothermal expansion method combined with microstructure observation. The phase transformation feature points at different cooling rates were obtained by the expansion curve and its first derivative curve. The characteristics of the phase transformation products in the corresponding phase transformation feature points were observed by optical microscopy (OM). The results show that with the increase of cooling rate (excluding water cooling), the nonlinearity of the expansion curve caused by phase transformation changes from one place to two, and the temperature corresponding to the peak value of the phase transformation rate curve also showed different changes. As the cooling rate increases, the microstructure sequentially underwent lamellar α, massive αm, and fine-needle α′ martensite. The phase transformation conditions of massive αm and α′ martensite are significantly different, and showed a competition trend between them. According to the phase transformation feature points and their corresponding microstructure, the continuous cooling diagram for TC4 β solution treatment was plotted.

The effect of long-term natural aging on the iPB-1 structure and the II – I phase transformation rate

The long-term natural aging of isotactic polybutene-1 samples of different molecular weight has shown that the transformation rate from the initial phase II to the stable phase I significantly decreased after natural aging, ranging from 0 to 17 years. It was found that the total crystallinity decreased with aging time and a small amount of phase II remained untransformed for at least 17 years. The transformation rate of a lower molecular weight sample, DP 0400, was higher than the PB 0110 sample, even after repeated polymer melting of aged samples and their new melt crystallization. The major phenomenon of the iPB-1 aging is the change in a ratio of methyl/methylene functional groups; possibly because of a side chain splitting that reduces the geometric regularity of the molecular chain and consecutively slows down the proceeding phase transformation.

Effects of austenizing temperature, cooling rate and isothermal temperature on overall phase transformation characteristics in high carbon steel

Phase transformations in high-carbon steel has been investigated by dilatometry during continuous cooling and isothermal transformations, following austenizing at temperatures of 900 °C–1200 °C (1173–1473 K). Optical microscopy and high-resolution scanning electron microscopy techniques revealed the presence of martensite, complex bainite, pearlite and metastable retained austenite under a variety of heat treatments. Magnetic measurements proved to be a useful technique to determine the fraction of retained austenite. Quantitative image processing with ImageJ software and magnetic techniques were used to calculate phase fractions. The rate of phase transformations increased by an increase in austenizing temperature for transformations occurring during continuous cooling and isothermal transformations. A mere increase in cooling rate from 3 °C (276 K) per second to 5 °C (278 K) per second changed the relative phase fractions and hardness significantly. The hardness of isothermally cooling specimens was a strong function of temperature and microstructure. Although isothermal holding at 500–525 °C (773–798 K) resulted in a mixture of bainite and pearlite, the hardness decreased significantly by decreasing the isothermal transformation temperature from 525 °C (798 K) to 500 °C (773 K). These outcomes provide valuable guidelines for the development of novel microstructure in high carbon steel in industrial practice.

Insights into the stable and fast lithium storage performance of oxygen-deficient LiV3O8 nanosheets

Oxygen-deficient LiV3O8 is considered as one of the promising cathode materials for lithium ion batteries (LIBs) because of its high cycling stability and rate capability. However, it is very difficult to control and study the content and position of V4+ and oxygen vacancies in LiV3O8, and therefore the mechanism of improving electrochemical performance of LiV3O8 is still unclear. Herein, we developed four LiV3O8 nanosheets with different V4+ and oxygen vacancy contents and positions. The physicochemical and lithium storage properties indicate that the V4+ and oxygen vacancies in the surface layer increase the contribution of pseudocapacitive lithium storage on the nanosheet surface. The V4+ and oxygen vacancies in the lattice improve the electrical conductivity of LiV3O8, and enhance the phase transformation and lithium ion diffusion rates. By adjusting the content of V4+ and oxygen vacancies, we obtained an oxygen-deficient LiV3O8 nanosheet which maintained more than 93% of the initial reversible capacity after 300 cycles at 5,000 mA·g−1. The V4+ and oxygen vacancies play an important role in improving the stability and rapidity of lithium storage. This work is helpful to understand the stable and fast lithium storage mechanism of oxygen-deficient LiV3O8, and might lay a foundation for further studies of other oxygen-deficient metal oxide electrodes for long-life and high-power LIBs.

Novel silicothermic reduction method to obtain Si3N4 ceramics with enhanced thermal conductivity and fracture toughness

The development of bimodal microstructure in Si3N4 ceramics was crucial to the thermal conductivity and fracture toughness. Silicothermic reduction treatment (SRT) combined with gas-pressure sintering (GPS) were conducted to promote the development of bimodal microstructure. SRT leads to a reduced amount of liquid phase and an increased N/O ratio in the liquid phase, resulting in a faster phase transformation rate relative to densification and a promoted grain growth during GPS. Consequently, large β-Si3N4 grains were well developed in a porous fine β-Si3N4 matrix skeleton without grain impingement. Dense Si3N4 ceramics with exaggerated bimodal microstructure was obtained after sintered at 1900 °C for 4 h. Summarily, the addition of Si leads to the improvement of thermal conductivity and fracture toughness simultaneously.

The Expanded Lever Rule on the Phase Transformation Rate Curve for Phase Volume Fraction Calculation in Thermal Simulations

The expanded lever rule is more efficient for calculating phase volume fraction when two phases are partly overlapped. It can make up the deficiency of metallography analysis when phases are similar in morphology. In this study, the expanded lever rule on the phase transformation rate curve is introduced, the approximate symmetry principle in applying the expanded lever rule is modified, and the resulting measurement uncertainty is discussed. Results show that (i) the calculated volume fraction of pearlite by the expanded lever rule in an overlapped two-phase process of a high strength low alloy (HSLA) weld metal is in accordance with the result by metallography analysis, and (ii) the expanded lever rule has an advantage over metallography analysis as it can calculate upper bainite, lower bainite, and lath-like martensite volume fractions in a three-phase process with two overlaps of a HSLA steel. The expanded lever rule is applicable to overlapped two-phase processes of any material theoretically since each phase process can be described by Johnson–Mehl–Avrami–Kolmogorov equation.

RETRACTED: Study of strain-driven martensitic phase transformation rate via data-driven approach

Abstract In the kinetic studies of martensitic phase transformation, the propagation velocity of the phase boundary is considered as the speed of transformation. But there is no interface at the beginning of phase transformation, we cannot track the development of the interface. Here we propose a new mathematical model that describes the rate of martensitic transformation by the data-driven method, which is based on the study of the change in area fraction in each phase. In this paper, the K-means clustering method is used to classify martensite and austenite through advanced quantitative differential interference contrast microscopy system. After classification, the clustering results are in good agreement with microscopic observations. The phase transformation rate for a set of tensile tests under various strain rates is determined. Our work provides a useful reference for modeling the strain-driven martensitic transformation rate.

The multiple stages towards crystal formation of L-glutamic acid

Governing polymorph selection is a crucial issue in the pharmaceutical, food, and fine chemical industry. However, the multiple stages during the formation of the polymorphic crystals from solution and the concurrent processes selecting the final polymorph are still unclear. In this study, we demonstrate the existence of hydrated amorphous intermediates in the early stages of separation of organic crystal L-glutamic acid where the nucleation of crystalline metastable α-form spontaneously occurred within these intermediates, leading to the formation of odd-shaped and intergrown crystal aggregates. Further, we found that these amorphous intermediates severed not only as a transient intermediate in a nucleation process, but they also co-determined the size distribution, mean particle size, and phase transformation rates of polymorphic L-glutamic acid.

Quantifying Nucleation Rates in Phase-Transforming Metal-Ion Intercalation Materials Based on Cyclic Voltammetry and Chronoamperometry Data

Phase-transforming cathode materials with a wide miscibility gap have been extensively studied for both Li-ion (LiFePO4, Li4Ti5O12) and Na-ion (Na3V2(PO4)3) batteries. In particular, LiFePO4 material has become a model system for the investigation of intercalation induced phase transformation mechanisms.1 Most of the state-of-the-art research on the phase-separating intercalation materials focuses on the elucidation of phase transformation mechanisms as well as on the theoretical assessment of the nucleation barrier heights based on the evidence from structural investigation and microscopic single particle-level experiments.2 In this work, we show that the new phase nucleation appears to be a characteristic rate-determining step for a wide range of intercalation materials (LiFePO4, V2O5, cation-rich Prussian blue analogues, Na3V2(PO4)3). We demonstrate that the nucleation rates (probabilities of critical nucleus formation) can be straightforwardly determined from the electrochemical experimental data. A simple experimental approach is proposed based on the classical nucleation theory toward interpreting electrochemical cyclic voltammetry and chronoamperometry data for phase-transforming electrodes.3 The new methodology provides for a facile assessment of the influence of various experimental factors (particle size, defect concentration, solvent nature, and surface coating) on the nucleation-controlled phase-transformation rates in intercalation materials.4 Experimental data analysis illustrates the validity of the applied approaches, which allows developing diagnostic criteria for distinguishing slow nucleation rate control from other possible rate-determining steps as well as obtaining quantitative estimates of the nucleation rate constants. R e f e r ence s 1. Malik, R.; Abdellahi, A.; Ceder, G. J. Electrochem. Soc. 2013, 160, A3179.2. Bai, P.; Bazant, M. Z. Nat. Commun. 2014, 5, 3585.3. Vassiliev, S.Yu.; Levin, E.E; Presnov, D.E; Nikitina, V.A. J. Electrochem. Soc. 2019, 166, A829.4. Iarchuk, A.R.; Nikitina, V.A.; Karpushkin, E.A.; Sergeyev, V.G.; Antipov, E.V.; Stevenson, K.J.; Abakumov, A.M. ChemElectroChem 2019, 6, 5090. Figure 1

Metal‐Ion Coupled Electron Transfer Kinetics in Intercalation‐Based Transition Metal Oxides

AbstractElectrochemical metal‐ion intercalation systems are acknowledged to be a critical energy storage technology. The kinetics of the intercalation processes in transition‐metal based oxides determine the practical characteristics of metal‐ion batteries, such as the energy density, power, and cyclability. With the emergence of post lithium‐ion batteries, such as sodium‐ion and potassium‐ion batteries, which function predominately in nonaqueous electrolytes of special formulation and exhibit quite varied material stability with regard to their surface chemistries and reactivity with electrolytes, the practical routes for the optimization of metal‐ion battery performance become essential. Electrochemical methods offer a variety of means to quantitatively study the diffusional, charge transfer, and phase transformation rates in complex systems, which are, however, rather rarely fully adopted by the metal‐ion battery community, which slows down the progress in rationalizing the rate‐controlling factors in complex intercalation systems. Herein, several practical approaches for diagnosing the origin of the rate limitations in intercalation materials based on phenomenological models are summarized, focusing on the specifics of charge transfer, diffusion, and nucleation phenomena in redox‐active solid electrodes. It is demonstrated that information regarding rate‐determining factors can be deduced from relatively simple analysis of experimental methods including cyclic voltammetry, chronoamperometry, and impedance spectroscopy.

Toughening FeMn-based high-entropy alloys via retarding phase transformation

Various high entropy alloys (HEAs) with improved mechanical properties were developed by reducing the phase stability and then promote the phase transformation. The promotion of deformation-induced martensitic transformation from face-centered cubic (fcc) to hexagonal close-packed (hcp) mostly focuses on overcoming the trade-off of strength-ductility of HEAs at room temperature. However, the hcp phase is brittle at cryogenic-temperature, and thus the enhancement of cryogenic ductility of these HEAs still remains a challenge. Here, we present a concept to toughening Fe50Mn30Co10Cr10 HEAs at cryogenic-temperature via retarding phase transformation. The retarded but more persistent phase transformation at high strain level was realized via tailoring the grain size. To further verify the effect of phase transformation rate on ductility of HEAs, the mechanical properties of Fe40Mn40Co10Cr10 HEAs with higher stacking fault energy were tested at room and cryogenic temperature, respectively. The present study sheds light on developing high performance HEAs, especially for alloys with brittle phase transformation products.

In Situ Neutron Diffraction Study of Phase Transformation of High Mn Steel with Different Carbon Content

In situ neutron diffraction was employed to examine the phase transformation behavior of high-Mn steels with different carbon contents (0.1, 0.3, and 0.5 wt.%C). With increasing carbon contents from 0.1 C to 0.5 C, the austenite phase fraction among the constituent phases increased from ~66% to ~98%, and stacking fault energy (SFE) increased from ~0.65 to ~16.5 mJ/m2. The 0.1 C and 0.3 C steels underwent phase transformation from γ-austenite to ε-martensite or α’-martensite during tensile deformation. On the other hand, the 0.5 C steel underwent phase transformation only from γ-austenite to ε-martensite. The 0.3 C steel exhibited a low yield strength, a high strain hardening rate, and the smallest elongation. The high strain hardening of the 0.3 C alloy was due to a rapid phase transformation rate from γ-austenite to ε-martensite. The austenite of 0.5 C steel was strengthened by mechanical twinning during loading process, and the twinning-induced plasticity (TWIP) effect resulted in a large ductility. The 0.5 wt.% carbon addition stabilized the austenite phase by delaying the onset of the ε-martensite phase transformation.

Crystallization and Dielectric Properties of MWCNT /Poly(1-Butene) Composite Films by a Solution Casting Method.

In this work, poly(1-butene) (PB-1) composite films with multi-walled carbon nanotubes (MWCNT) were prepared by a solution casting method. The relationship between the dielectric properties and the crystal transformation process of the films was investigated. It was indicated that there were two crystal forms of I and II of PB-1 during the solution crystallization process. With the prolongation of the phase transition time, form II was converted into form I. The addition of the conductive filler (MWCNT) accelerated the rate of phase transformation and changed the nucleation mode of PB-1. The presence of crystal form I in the system increased the breakdown strength and the dielectric constant of the films and reduced the dielectric loss, with better stability. In addition, the dielectric constant and the dielectric loss of the MWCNT/PB-1 composite films increased with the addition of MWCNT, due to the interfacial polarization between MWCNT and PB-1 matrix. When the mass fraction of the MWCNT was 1.0%, the composite film had a dielectric constant of 43.9 at 25 °C and 103 Hz, which was 20 times that of the original film.

Effect of Temperature Exposure on Elemental Iron Content in Alumosilicate Ceramic

The effect of temperature exposure on the elemental iron and other metal contents in specimens based on natural montmorillonite-containing clay of Orenburg oblast has been investigated. The content of iron, copper, and cobalt in the specimens after drying and sintering through stepwise annealing from 300 to 1000°C has been determined using X-ray fluorescence analysis. The maximum content of Fe, Cu, and Co metals in the system has been indicated after removal of physically bound water. With an increase in the temperature of annealing to 300–500°C, the content of all three metals decreases, because organic components are burned. At the temperature of 700°C, the copper content decreases by a factor of 1.3, while the cobalt and iron contents decrease by a factor of 1.5 and 1.7, respectively, owing to active redox chemical reactions. A decrease in the incorporation of iron in the crystal lattices of the phases of ceramic materials provides a decrease in the rates of phase transformations and an increase in the degree of structural homogeneity.

Characteristics of the reduction behavior of zinc ferrite and ammonia leaching after roasting

A novel method for recovering zinc from zinc ferrite by reduction roasting-ammonia leaching was studied in this paper. The reduction thermodynamic of zinc ferrite by CO was analyzed. The effects of roasting parameters on the phase transformation and conversion rate of zinc ferrite, and the leaching behavior of zinc from the reductive roasted samples by ammonia leaching, were experimentally investigated. The mineralogical phase compositions and chemical compositions of the samples were characterized by X-ray diffraction and chemical titration methods, respectively. The results showed that most of the zinc ferrite was transformed to zinc oxide and magnetite after weak reduction roasting. 86.43% of the zinc ferrite was transformed to zinc oxide under the optimum conditions: CO partial pressure of 25%, roasting temperature of 750°C, and roasting duration of 45 min. Finally, under the optimal leaching conditions, 78.12% of zinc was leached into the solution from the roasted zinc ferrite while all iron-bearing materials were kept in the leaching residue. The leaching conditions are listed as follows: leaching duration of 90 min, ammonia solution with 6 mol/L concentration, leaching temperature of 50°C, solid-to-liquid ratio of 40 g/L, and stirring speed of 200 r/min.

Quench Sensitivity and Phase Transformation Kinetics of AlSi7MnMg High Pressure Vacuum Die Casting

The quench sensitivity of an AlSi7MnMg alloy in high-pressure vacuum die (HPVD) casting was investigated by time-temperature-transformation and time-temperature-property diagrams with an interrupted quench technique. The quench sensitive temperature range of the alloy is from 260 to 430 °C and its nose temperature is 350 °C. The mechanical strength versus cooling rates of the HPVD casting was predicted using quench factor analysis method and verified by experimental results. The critical cooling rate is 6 °C/s to remain 95% of the maximal mechanical strength. The coefficientsk2-k5, related to the nucleation and precipitation kinetics of TTP curves, and phase transformation diagrams were determined. The precipitation of Mg2Si phase in the castings was observed during isothermal treatment using transmission electron microscope. Moreover, the quench sensitivity and kinetics of the phase transformation of AlSi7MnMg alloy and AlSi10MnMg alloys were compared. It reveals that the quench sensitivity and phase transformation rate of the former are lower than that of the latter.

A mechanism of defect-enhanced phase transformation kinetics in lithium iron phosphate olivine

Antisite defects are a type of point defect ubiquitously present in intercalation compounds for energy storage applications. While they are often considered a deleterious feature, here we elucidate a mechanism of antisite defects enhancing lithium intercalation kinetics in LiFePO4 by accelerating the FePO4 → LiFePO4 phase transformation. Although FeLi antisites block Li movement along the [010] migration channels in LiFePO4, phase-field modeling reveals that their ability to enhance Li diffusion in other directions significantly increases the active surface area for Li intercalation in the surface-reaction-limited kinetic regime, which results in order-of-magnitude improvement in the phase transformation rate compared to defect-free particles. Antisite defects also promote a more uniform reaction flux on (010) surface and prevent the formation of current hotspots under galvanostatic (dis)charging conditions. We analyze the scaling relation between the phase boundary speed, Li diffusivity and particle dimensions and derive the criteria for the co-optimization of defect content and particle geometry. A surprising prediction is that (100)-oriented LiFePO4 plates could potentially deliver better performance than (010)-oriented plates when the Li intercalation process is surface-reaction-limited. Our work suggests tailoring antisite defects as a general strategy to improve the rate performance of phase-changing battery compounds with strong diffusion anisotropy.