Phase Transformation Rate Research Articles

Unveiling the interaction mechanism between facet-dependent pyrite nanoparticles and Cr(VI) under anaerobic environment: adsorption, redox, and phase transformation

The environmental migration and bioavailability of Hexavalent chromium (Cr(VI)) could be affected by facet-dependent pyrite (FeS2) existing in soils and sediments. Conversely, the occurrence state of facet-dependent FeS2 might also be influenced by Cr(VI). However, the complex interactive mechanism at the solid–liquid interface between facet-dependent FeS2 and Cr(VI) still remained ambiguous. Herein, FeS2 nanobelts, FeS2 nanosheets, and FeS2 nanocubes with corresponding dominant facets of (−110), (001), (100)/(210) were prepared. The adsorption and reduction experimental results reflected that Cr(VI) species were predominantly adsorbed and a portion of them was reduced to Cr(III) at the FeS2 interfaces. In particular, the adsorption efficiency of Cr(VI) on (001) facet was 1.39 and 4.69 times than those on (−110) and (100)+(210) facets, respectively. The results of in situ Attenuated Total Reflectance Fourier Transform Infrared spectroscopy (ATR-FTIR) measurements and Density Functional Theory (DFT) calculations suggested that bidentate binuclear (BB) coordinated chromates were generated on the (001) facet while monodentate mononuclear (MM) coordinated chromates were formed on (−110), (100), and (210) facets. Due to the stronger adsorption energy and more stable coordination mode of BB for Cr(VI) species on (001) facet, FeS2 NS exhibited higher efficiency of Cr(VI) removal and reduction compared with FeS2 NB and FeS2 NC. In addition, partial FeS2 particles were proved to be transformed to goethite under the effect of Cr(VI). Owing to the stronger adsorption of Cr(VI) species on (001) facet, FeS2 NS also had a faster phase transformation rate than FeS2 NB and FeS2 NC. Above results all reflected the good structure–reactivity relationships between the FeS2 facets and the Cr(VI) removal efficiency as well as the phase transformation of FeS2 particles.

A phase-field model for interactive evolution of phase transformation and cracking in superelastic shape memory ceramics

This work presents a modified phase-field model for accurate coupling of phase transformation and cracking in shape memory ceramics. The existing phase-field models underestimate the elastic response at the beginning of the mechanical response. We modified the chemical free energy to control the rate of phase transformation and consequently obtain a physical elastic response before initiation of phase transformation. First, the forward and reverse martensitic phase transformation in a superelastic single crystal 3 mol% yttria-stabilized tetragonal zirconia is studied. Then, the interaction between phase transformation and fracture under displacement-controlled loading condition is investigated. The model predicts a realistic mechanical response and the experimentally observed microstructure and crack deflection due to the phase transformation. In addition, the model captures the reverse phase transformation and the stress drop due to the crack propagation.

Transformation kinetics for low temperature post-deposition crystallization of TiO2 thin films prepared via atomic layer deposition from TDMAT and water

Background: We report on the fundamental crystallization kinetics of atomic layer deposited (ALD) TiO2 thin films undergoing a post-deposition anneal (PDA) at low temperatures to probe differences in the as-deposited film microstructure. Methods: The system of study is ALD TiO2 thin films prepared from tetrakis(dimethylamino)titanium(IV) (TDMAT) and water at 120 °C, 140 °C and 160 °C followed by ex situ low temperature annealing at temperatures ranging from 140 °C to 220 °C. All as-deposited TiO2 thin films are amorphous by X-ray diffraction (XRD). Post-deposition annealing (PDA) produces large grain anatase crystals, confirmed by XRD and top-view scanning electron microscopy (SEM). A detailed SEM study is performed to quantify the nucleation and growth kinetics by fitting microstructural data to the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation. Finally, a time-temperature-transformation (TTT) diagram is constructed to summarize the differences in crystallization behavior at different ALD deposition temperatures. Results and Conclusions: Fitting microstructural data to the JMAK equation reveals an Avrami exponent close to 3 with continuous nucleation, suggesting two-dimensional, plate-like crystal growth. Applying an Arrhenius relationship to the phase transformation data, the combined activation energy for nucleation and growth is found to be 1.40–1.58 eV atom-1. Nucleation rates are determined, and an Arrhenius relationship is used to calculate the critical Gibbs free energy for nucleation (~1.3-1.4 eV atom-1). As such, nucleation is the rate-limiting step for the amorphous to anatase phase transformation. ALD growth temperature is found to dictate film microstructure with lower deposition temperatures reducing the nucleation rate and leading to larger grain sizes irrespective of PDA conditions. The nucleation rate pre-exponential frequency factor increases with increasing deposition temperature, thereby increasing the likelihood for nucleation. Interestingly, it is this difference in the vibrational modes of the amorphous structure, as indicated by the variation in the nucleation rate pre-exponential frequency factor, that alters the phase transformation rates and not a change in the activation energies for the transformation.

Influence of chemical segregation on bainitic microstructures in a carburized bearing steel

Bainite to austenite reversal is one of the grain refinement techniques employed in carburized steels. However, chemical segregation influences the homogeneity of the bainitic structure, which is seminal to exploit the advantages associated with austenite reversal. It is therefore important to understand the influence of chemical segregation on bainite formation, which is investigated in this work. Characterizations were performed on the microstructures obtained from the case and core regions of a carburized steel after 30 h of bainite treatment at 320 °C for two carbon compositions: 0.85 wt% C (zcase) and 0.16 wt% C (zcore). The microstructure of zcase is shown to contain bands with bainite in alloy-lean regions and martensite/austenite in alloy-rich regions. For zcore, although the chemical bands are not composed of different phases, the alloy-rich regions have a fraction of martensite-austenite (MA) islands that is twice the fraction in alloy-lean regions. Despite this difference, the austenite phase fractions in the chemical bands of zcore are low and almost similar, indicating that the MA islands are mostly martensite. From experimental results and thermodynamic and kinetic simulations, it is elucidated that a different rate of phase transformation in the chemical bands is the cause for the observed microstructural inhomogeneities.

Temperature and vibration-assisted effects in nanoimprint gold: An atomistic study

This study surveys the effects of taper angle, temperature, vibration, and grain size on the groove formation of the NIL process of a gold substrate. The results indicate that the taper angle has a great impact on the residual stress and groove depth. Imprinting with a taper with angles of 10°, 15°, and 45° could obtain a deep and symmetrical groove. In addition, imprinting at 300 K–500 K could generate a good groove shape. In the range of 300 K–600 K, the temperature does not strongly affect the structure change rate. Besides, imprinting at a vibration amplitude of 2.5 Å-5 Å, a deep and good groove shape can be generated. At the same time, increasing the vibration frequency gives rise to the groove depth. The grain size strongly affects the deformation and phase transformation rate. Increasing the grain size from 3 nm to 7 nm leads to a decrease in the phase transformation rate and an improvement in the groove depth. The grain size is the strongest factor that affects the shape and the phase transformation of the gold substrate compared to other factors. The taper angle, temperature, and vibration factors also have a strong effect on the groove shape. However, they have a lower rate of effect on the phase transformation than the grain size.

Modeling of a Double Gas Hydrate Particle Ignition

This paper presents the numerical research findings for the conditions and characteristics of methane-propane hydrate particle ignition. The curves of the ignition delay times of a hydrate particle versus its size and ambient temperature were obtained. The effect of the rates of phase transformations (evaporation and dissociation) on the hydrate particle ignition behavior was analyzed. Following the mathematical modeling of the processes under study using different heating schemes of gas hydrates, the patterns of processes developing in a particle during the induction period were identified. It was established that the ignition behavior of methane, propane, and other gases was significantly different from that of other gases produced from hydrate decomposition. The established differences form the basis for predicting the characteristics of gas hydrate ignition at different power plants.

A new approach to estimating kinetic rate factors of phase transformations

An original approach is proposed to estimate of the main kinetic factors that determine the rate of phase transformations in condensed matter. These factors define the frequency of atom transitions from different phases during phase transformation induced by undercooling, high pressures or mechanical impact. On the example of crystallization of a model amorphous system, it is shown that this approach gives a correct estimation of the crystal growth and crystal decay rates both at the initial stage of the phase transition and at the stage of coalescence of crystalline structures.

Phase evolution within multiphase stainless steels during simulated hot isostatic pressing cycles

Stainless steel hardfacing alloys are being developed for wear and corrosion resistant applications in pressurised water reactor environments. Two examples of this, the austenitic Tristelle 5183 and triplex RR2450 were produced by gas-atomisation before undergoing consolidation using hot isostatic pressing. The phase evolution of these alloys during simulated hot isostatic pressing cycles was observed in-situ, using synchrotron X-ray diffraction. During these cycles, the metastability of the gas-atomised powders is revealed, which influences the rate of high-temperature γ→δ transformation within the RR2450 alloy. Additionally, a high-strength silicide phase, named π-ferrosilicide, forms within these alloys. It decomposes by a eutectoid π→δ+M7C3 transformation, demonstrating a high carbon solubility within this phase. The observations of this study demonstrate the need to carefully consider the process parameters during hot isostatic pressing for such complex alloys, since alloy phase transformation rates are heavily influenced by the starting condition of the gas-atomised powder.

Reduction of thermally grown single-phase CuO and Cu2O thin films by in-situ time-resolved XRD

Copper oxide is used as a catalyst or catalyst precursor in chemical reactions that involve hydrogen as a reactant or a product. Controlled reduction and therefore known reduction kinetics of well-defined Cu-oxides in hydrogen is a key issue for the activation of oxide catalysts as well as for other technological fields such as gas sensing. The kinetics and mechanisms of reduction of single-phase CuO and Cu2O films in 5 vol% H2/Ar were investigated by in-situ real time synchrotron-based X-ray diffraction measurements. To this end, the incubation time, the CuO → Cu2O and Cu2O → Cu phase transformation rates, as well as the microstructure and strain state of the evolving Cu, CuO and Cu2O phases were studied during the reduction. Highly porous Cu and Cu-oxides scaffolds were obtained by alternating oxidation and reduction steps, which can be envisaged for a wealth of applications in the fields of catalysis, batteries, water treatment and biomedical applications.

Effect of Taylor vortex wavelength on polymorphic crystallization of L-histidine

Axial wavelength is a key characteristic parameter of Taylor vortex flows. Thus, in the current study, the effect of Taylor vortex wavelength on the polymorphic nucleation and phase transformation of L-histidine was examined. The vortex wavelength was altered by altering the gap width between the outer and inner cylinders. Further, the vortex velocity was changed by controlling the inner cylinder rotation speed. Owing to the promotion of stable nucleation by the periodic fluid motion, the primary polymorphic fraction of the stable Form A of L-histidine in Taylor vortex flow [Couette–Taylor (CT) crystallizer] was much greater than that in a turbulent eddy flow [mixing tank (MT) crystallizer]. As the vortex wavelength decreased, stable nucleation was promoted, thus increasing the initial polymorphic fraction of the stable Form A. Moreover, the initial polymorphic fraction of the stable Form A increased as the vortex velocity increased. These experimental results are described based on molecular alignment effect of Taylor vortex on stable nucleation. The phase transformation of L-histidine was also strongly influenced by the vortex wavelength and vortex velocity. Hence, the rate of phase transformation in CT crystallizer was approximately ten-fold better than MT crystallizer.

Effect of Cooling Rate on Phase Transformation Behavior during Isothermal Annealing of SCr420 Steel

Herein, the effect of cooling rate on microstructure formation and phase transformation behaviors during isothermal annealing of the SCr420 steel is investigated. During isothermal annealing, tempering is performed after normalizing, and the effect of cooling conditions from normalizing to tempering is analyzed. As the cooling rate increases, the nonuniform microstructure with the band structure formed after hot forging tends to be homogenized. When the temperature reached during cooling is lowered, the phase transformation is rapidly completed during the cooling process, and the microstructure becomes more homogeneous. Phase transformation behavior during cooling from the normalizing temperature is analyzed through differential scanning calorimetry. Two exothermic reaction peaks are detected, and those peaks are related with the γ → γ + α → α + θ phase transformation. The higher the cooling rate, the lower the phase transformation starting temperature and the higher the phase transformation rate. In addition, from the thermal analysis data, the phase transformation kinetics and activation energy during cooling are analyzed by the Friedman method and the additivity rule. Through this analysis, the Avrami exponent and the activation energy for the phase transformation are derived.

Effects of initial α‐phase content on properties of pressureless solid‐state sintered SiC ceramics

Abstractα‐ and β‐SiC starting powders of similar particle sizes were used to investigate the effect of initial α‐phase content on the electrical, thermal, and mechanical properties of pressureless solid‐state sintered (PSS) SiC ceramics with B4C and C additives. For β‐SiC starting powders, a coarse‐grained microstructure with elongated platelet grains was formed by the transformation of 3C to 6H and finally to 4H‐SiC phase. In contrast, materials prepared from α‐SiC powders exhibited a fine‐grained microstructure with platelet grains. This study revealed the beneficial effect of α‐SiC starting powders in achieving low electrical resistivity and high thermal conductivity in PSS SiC ceramics, which was attributable to their higher sinterability, lower impurity content, and lower 6H to 4H‐SiC phase transformation rate compared with β‐SiC powders. The electrical resistivity decreased by an order of magnitude and the thermal conductivity increased by 32% with an increase in initial α‐phase content from 0 to 100%. The flexural strength increased by approximately 16% with increasing initial α‐phase content due to a decreased flaw size with decreasing grain size. However, the fracture toughness and hardness were insensitive to the change in initial α‐phase content.

Tailoring crystallization and physical properties of palm mid-fraction with sorbitan tristearate and sucrose stearate

This paper addresses sorbitan and sucrose ester in physical transformations of palm mid-fraction (PMF). Both emulsifiers influenced the crystallization properties of PMF, mainly due to emulsifier solubility, which affects its ability to interfere with the kinetics of solution-mediated phase transformations. DSC results corroborate the polymorphism analysis, indicating that the mechanism and rate of phase transformation depend on the chemical structure and amount of each emulsifier. The addition of sorbitan tristearate (STS) and sucrose stearate (S-370) increased the crystallization speed of the PMF and caused changes in the crystallization behavior. STS favored the β'→β transition, while S-370 stabilized the β'-form. We can conclude that the presence of emulsifiers dissimilar to the composition of PMF modified its physical structure, either by increasing the liquid fraction or by reducing molecular motion, facilitating or preventing polymorphic transformations.

BaTiF6:Mn4+ Red Phosphor: Synthesis of Single Crystals at Room Temperature and the High Hydrolysis-Resistant Property.

Due to the low solubility of BaF2, the BaTiF6:Mn4+ phosphor for whitelight-emitting diodes application has been generally synthesized by the hydrothermal route, during which process the valence of the manganese dopant is difficult to be controlled as tetravalent. In this paper, a new synthesis method that proceeded at room temperature was reported. This method uses BaTiOF4 as the precursor and allows for the control of the phase transformation rate from BaTiOF4 to BaTiF6 in the K2MnF6/HF acid solution. Benefitting from that, we successfully prepared red-emitting BaTiF6:Mn4+ elongated crystals with a single-crystal nature up to a record-breaking length of 200-300 μm. The effects of the crystallinity of the BaTiOF4 precursor on its phase transformation rate into BaTiF6 and on the optimal Mn4+ doping concentration were studied. The BaTiF6:Mn4+ single-crystal phosphor exhibits relatively excellent hydrolysis-resistant behavior after being immersed in water for 3 h, at which condition the commercial K2SiF6:Mn4+ has become brown. This study may inspire the room-temperature preparation of other hydrolysis-resistant alkali earth fluorotitanate or fluorosilicate phosphors with stable tetravalent manganese doping.

Effect of aluminum-containing raw materials on the melting of borosilicate glass for fiber

Aluminum-containing raw materials for the synthesis of aluminum-borosilicate glasses for E-glass fiber should be rationally chosen to comprehensively assess their effect on the glass melting processes. The characteristic properties of the chemical, phase, and granulometric composition of the raw materials such as metallurgical alumina, non-metallurgical alumina, disthene, and kaolin were under study. It was revealed that the type of aluminum-containing raw materials significantly influenced the rate of glass formation processes and heat consumption required for these processes. The efficiency of aluminum-containing raw materials is influenced by the following factors: the phase composition, which determines the sequence and rate of phase transformations, as well as the heat-absorbing ability of the furnace batch and glass melt. The most energy-efficient material is non-metallurgical alumina of the White Alumina brand. Using it facilitates saving energy resources for glass formation processes from 2.64% to 16.30% as compared with other types of aluminum-containing raw materials. The use of kaolin proves to be the least efficient due to the additional energy consumption for the process of destruction of the crystal structure of kaolinite, the reduced thermal conductivity of the batch, and the thermal transparency of the borosilicate glass melt.

Effect of Batchelor Flow on Polymorphic Crystallization in a Rotating Disk Crystallizer

In this work, the influence of Batchelor flow on the polymorphic crystallization in a rotating disk (RD) crystallizer was investigated. By regulating crystallization parameters, i.e., the rotation speed, cooling rate, and ethanol fraction, we found that a higher fraction of L-histidine stable Form-A at the induction time and a faster rate of phase transformation could be obtained in the RD crystallizer as compared to previous results in a mixing tank crystallizer. Based on these results, we concluded that the polymorphic crystallization in the RD crystallizer was more effective due to Batchelor flow fluid motion.

Production Rate of SiO Gas from Industrial Quartz and Silicon

The production rate of SiO gas from industrial quartz and silicon has been investigated by isothermal heat treatment experiments. Mixtures of silicon and different quartz samples have been heated to temperatures ranging from 1650 °C to 1950 °C and held for 30 to 120 minutes before cooling. The weight loss of each sample has been correlated to degree of reaction and a model for the reaction rate of Si + SiO2 has been developed based on these values. Five different types of industrial quartz were used in the experiments. No significant difference was found in their reaction rate, even though there are large variations in impurity content, melting rate, decrepitation, and phase transformation rate of each sample. Further on, it is shown that the reaction rate of silicon mixed with various types of quartz can be described by an Arrhenius equation: {{rm {d}}alpha /{rm {d}}t = k_0 , A , {rm {exp}} (- Q / RT)}. A reaction constant (k0) equal to {6.25 , 10^8 {rm {g}}, {rm {s}}^{-1}, {rm{m^{-2}}}} and an activation energy (Q) equal to {557, {rm {kJ , mol^{-1}}}} were obtained by linear regression. The degree of reaction ({alpha }) is shown to be increasing with available reaction area, temperature, and time.

Shear-Modulated Rates of Phase Transitions in Sphere-Forming Diblock Oligomer Lyotropic Liquid Crystals.

Hydration of the amphiphilic diblock oligomer C16H33(CH2CH2O)20OH (C16E20) leads to concentration-dependent formation of micellar body-centered cubic (BCC) and Frank-Kasper A15 lyotropic liquid crystals (LLCs). Quiescent thermal annealing of aqueous LLCs comprising 56-59 wt % C16E20 at 25 °C after quenching from high temperatures established their ability to form short-lived BCC phases, which transform into long-lived, transient Frank-Kasper σ phases en route to equilibrium A15 morphologies on a time scale of months. Here, the frequency and magnitude of applied oscillatory shear show the potential to either dynamically stabilize the metastable BCC phase at low frequencies or increase the rate of formation of the A15 to minutes at high frequencies. Time-resolved synchrotron small-angle X-ray scattering (TR-SAXS) provides in situ characterization of the structures during shear and thermal processing. This work shows that the LLC morphology and order-order phase transformation rates can be controlled by tuning the shear strain amplitude and frequency.

Cavitation failure analysis of 90-degree elbow of mixing point in ethylene glycol recovery and concentration system

For the failure case of the 90-degree elbow of mixing point in the ethylene glycol recovery and concentration system of a refining and chemical company in China, the surface morphology of different cavitation degree was observed by scanning electron microscope(SEM). The composition and content of chemical material and working condition was calculated and analyzed by Aspen technical process simulation software to draw the conclusion that the failure form of elbow is cavitation of liquid water. The failure location of elbow was investigated by CFD numerical simulation used the VOF multiphase flow model and Schnerr and Sauer cavitation model. The distribution and variation of gas phase fraction is used to describe the cavitation dynamic development process at different times. The cavitation corrosion angle of elbow in the axial and circumferential direction was determined by the value of phase transformation rate, actual cavitation failure angle in the circumferential direction is basically consistent with that of numerical simulation, which verifies the reliability of the characterization method to a certain extent. The cause of the angle deviation between actual and simulation in the axial direction is explained. This paper can provide some reference for using phase transformation rate to predict cavitation location and characterize cavitation intensity.

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.