Phase Transformation Process Research Articles

High efficient phosphate removal by lanthanum modified hydroxyapatite with a phase transformation process

High efficient phosphate removal by lanthanum modified hydroxyapatite with a phase transformation process

Specifics of Structure Formation of Cement Stone with Silica Raw Material - A Substrate of Photocatalytic Composite Material

The increasing urbanization of urban areas poses the challenge of the development of materials capable of self-cleaning from organic pollutants formed. Previous papers substantiated the possibility of the coating of titanium oxide as the main agent of the photocatalytic method of cleaning structural materials on silica raw materials in order to increase the degree of its distribution in the volume of cement matrix and, as a result, increase its efficiency.It is obvious that a silica substrate will affect the processes of structure formation during hardening of a cement matrix. During the research, the processes of phase transformations of cement stone modified with silica raw materials of natural and technogenic origin were studied. As a result, the influence of siliceous modifiers on the strength characteristics of the cement stone was determined, which allowed ranking them according to the degree of decrease in efficiency as follows: technogenic raw materials; natural raw materials of silicate composition; natural raw materials of aluminosilicate composition. Quantitative assessments of the degree of efficiency showed the irrationality of using aluminosilicate composition as a silica modifier of natural raw materials, which is explained by its low pozzolanic activity.

Thermomechanical modeling of nonlinear internal hysteresis due to incomplete phase transformation in pseudoelastic shape memory alloys

This paper presents a thermomechanical model for pseudoelastic shape memory alloys (SMAs) accounting for internal hysteresis effect due to incomplete phase transformation. The model is developed within the finite-strain framework, wherein the deformation gradient is multiplicatively decomposed into thermal dilation, rigid body rotation, elastic and transformation parts. Helmholtz free energy density comprises three components: the reversible thermodynamic process , the irreversible thermodynamic process and the physical constraints of both. In order to capture the multiple internal hysteresis loops in SMA, two internal variables representing the transition points of the forward and reverse phase transformation, $$\phi _s^f$$ and $$\phi _s^r$$ , are introduced to describe the incomplete phase transformation process. Evolution equations of the internal variables are derived and linked to the phase transformation. Numerical implementation of the model features an Euler discretization and a cutting-plane algorithm. After validation of the model against the experimental data, numerical examples are presented, involving a SMA-based vibration system and a crack SMA specimen subjected to partial loading–unloading case. Simulation results well demonstrate the internal hysteresis and free vibration behavior of SMA.

2D/3D heterostructure derived from phase transformation of 0D perovskite for random lasing applications with remarkably improved water resistance.

Phase transformation between metal halide perovskites serves as a promising route to create new optoelectronic functionalities. Nevertheless, the transformation reported thus far mainly involves the transition between two individual phases (e.g., 0D-3D and 3D-2D), while the transition from one phase to a heterostructure with distinct phases has been rarely disclosed. Here, we report a straightforward one-step procedure to directly convert 0D perovskite to 2D/3D heterostructures and demonstrate the application of the derivatives in random lasing beyond 0D perovskite. This phase transformation was triggered by exposing the 0D perovskite to a water environment and the resultant 2D/3D heterostructure showed much improved water resistance compared to that of its corresponding 3D counterpart as for chemical stability and photoluminescence performance. In addition, we demonstrated that the derived 2D/3D heterostructure readily exhibited random lasing characteristic of incoherent feedback upon optical pumping, while the parent 0D Cs4PbBr6 exhibited no sign of light amplification even pumped much harder. The pump threshold and the PL spectral profile were well maintained upon recycling treatment with water, implying the water resistance capability of the developed random lasing. The results suggest that the 2D/3D perovskite composites derived from the phase transformation of their 0D counterpart can serve as promising platforms for nanophotonic applications.

Optimizing the morphology of calcium d-pantothenate by controlling phase transformation processes

A process for preparing calcium d-pantothenate tetramethanol monohydrate (d-PC·4MeOH·H2O) with a block-like morphology was developed, the solvent-free D-PC with a block-like morphology was obtained by controlling the de-solvation of d-PC·4MeOH·H2O.

In-situ Measurement of Phase Transformation Processes in Carbon Steel Combined with Conical Nozzle Levitation and Energy Window Type 2D CdTe Detector

In-situ Measurement of Phase Transformation Processes in Carbon Steel Combined with Conical Nozzle Levitation and Energy Window Type 2D CdTe Detector

Investigation on solidification and phase transformation of heterogenous interface structure in dissimilar metal weld between high Cr heat-resistant steel and nickel-based alloy 617

The present study characterized heterogenous interface structure in dissimilar metal weld between a high Cr martensitic heat-resistant steel and nickel-based alloy weld metal (WM), and revealed its solidification and phase transformation processes during welding. The heterogenous interface structure consists of a martensitic peninsula structure and a partially mixed zone (PMZ) of austenitic stainless steel. The K–S relationship between peninsula structure and its surroundings indicates: 1. phase transformation of (δ-Fe) to (γ-Fe) of peninsula occurs only after previous austenitic PMZ has solidified; 2. the subsequent WM solidifies epitaxially on (γ-Fe) of peninsula. Due to that the liquidus temperature of PMZ is lower than that of base metal (BM), the peninsula structure can form in the early stage of solidification by quick freezing of liquid BM.

Directional fracturing excavation technology based on liquid CO2 phase transition in freezing shaft sinking

ABSTRACT In the tunneling of frozen soil section of shaft sinking by freezing method, the traditional air pick excavation has large consumption of pick and drill rod, low excavation efficiency, and high labor intensity. The drilling explosive blasting method has a poor working environment and potential safety hazards. The safe and efficient excavation of frozen soil section is a difficult problem faced by freezing method shaft sinking. In this paper, a directional fracturing method by liquid CO2 phase change for freezing shaft sinking is proposed. Based on the traditional CO2 phase change fracturing device, a liquid CO2 phase change fracturing device with directional function is designed. It can not only fully crush and weaken the frozen soil in the shaft, but also can not disturb the shaft wall structure. The liquid CO2 phase change directional fracturing technology is firstly applied to the assisted tunneling in freezing shaft sinking. The field test results indicate that the directional liquid CO2 phase change generator has a good directional fracturing function. There are many obvious cracks formed around the directional fracture drilling hole, and the cracks are all extending toward the center of the protection circle. The angle between the two outermost cracks is close to the phase angle of directional discharge hole of liquid CO2 phase change generator. According to the statistics of field construction, the average daily excavation speed of frozen soil section is increased from 1.67 m/d to 2.45 m/d after directional fracturing by phase change of liquid CO2. Compared with explosive blasting weakening, liquid CO2 phase change fracturing has the advantages of no spark in the phase transformation process, easy control of pressure, convenient storage and transportation, simple operation, and relatively safe construction process. Liquid CO2 phase change fracturing shows a good application prospect in some fields which have high safety requirements. It is expected to be popularized and applied in slope excavation, tunnel chamber excavation, and other fields in the future.

A facile way to regenerate FePO4∙2H2O precursor from spent lithium iron phosphate cathode powder: Spontaneous precipitation and phase transformation in an acidic medium

Recycling the end-of-life lithium-ion batteries including the lithium iron phosphate (LiFePO4) battery has been one of the most important technology areas since electric vehicles are gradually dominating the way of transportation. For the recycling of LiFePO4 batteries, the regeneration of pure iron phosphate dihydrate (FePO4∙2H2O) from spent cathode material is essential but difficult. The challenge is how to effectively synthesize battery-grade iron phosphate from the impurity-bearing acid solution by precipitation since the spent cathode powder usually holds various impurities. To avoid the introduction of impurities into the iron phosphate, a one-step spontaneous precipitation and phase transformation mode without acidity adjustment was preferred and studied in this work. The focus of this research included the process of phase transformation from amorphous to crystalline, and its effects on precipitation and the properties of the precipitate. It was interestingly found that there was an induction period for phase transformation from amorphous FePO4∙xH2O to monoclinic FePO4∙2H2O during the precipitation, which was distinctly shortened with the elevated temperature. Phase transformation led to fast increased precipitation efficiency, morphology evolution, and composition change, which benefited the consistency of iron phosphate. Phase transformation could be kinetically described by the JMA equation, with a rate-limiting step of materials diffusion towards the nucleation point and an activation energy of 20.4 kJ/mol. The critical crystal size for transformation was increasing along with the temperature’s raising, which was ascribed to the changes in the volume energy and the surface energy. The results in this study have built the feasibility of chemically regenerating FePO4∙2H2O precursors from the spent cathode powder by precipitation purification in an acidic medium.

Numerical Simulation and Analysis of Arc Anode Erosion Process with Electrode Rotation

A three-dimensional geometric model of anode contact of vacuum circuit breaker is established. Considering the influence of electrode rotation on vacuum arc and anode thermal process, a physical model of phase transformation process is established for the melting and evaporation of anode surface. The solid-liquid mixing area is treated by the description method of porous media, and the numerical simulation of anode thermal process is carried out. The conclusion is that with the increase of time, the anode surface temperature increases, molten pool development, molten pool depth deepening, in addition, with the increase of electrode speed, the highest temperature on the surface of the contact and the size of the molten pool were reduced, the temperature distribution more uniform. It provides theoretical basis for evaluating the breaking capacity of vacuum circuit breaker.

Effect of magnetic field on stability in mushy layer during binary alloy solidification

During directional solidification of binary alloy mixtures, instability in the solid/liquid interface appears due to constitutional undercooling. As a result of this instability, a reactive porous medium, namely mushy layer, is formed, and it separates the liquid phase from the solid phase completely. The intrinsic structure of the mushy layer is of fine-scale dendritic crystal that shelters solute in the interstitial fluid. In a gravitational field, the rejection of lighter solute components from an advancing solidification front brings about unstable density gradient. Ensuing convective motions in the mush are driven by a density difference. The convection can change the solid matrix of the mushy layer. Hence, the dynamic response of the mushy layer is driven by interaction among heat transfer, solute transport and convection. As a contactless control tool, external magnetic field can change the heat and solute transport, which has a significant effect on the phase change process. Therefore, when magnetic field, thermal diffusion, solute transport and buoyancy convection are considered simultaneously in the phase transformation process, the mechanism of mushy region will become more complex and interesting. In this paper, the effect of external magnetic field on the stability of mushy layer during binary alloy solidification is studied. The coupling effects of magnetic field, temperature field, concentration field and convection are considered in the model. Including the direct mode and the oscillation mode, the resulting dispersion relation reveals the influence of magnetic field on the stability of mushy layer through linear stability analysis. It is found that the Lorentz force can reduce the instability effect which is caused by buoyancy convection. In the oscillation mode, an external magnetic field brings about a stabilizing effect on the mushy layer, but in the direct mode, the effect of external magnetic field on stability of the mushy layer is uncertain. In conclusion, the finding in this paper provides an important theoretical reference for improving products quality by applying an external magnetic field in the metals processing industry.

Phase transformation and microstructure evolution of a beta-solidified gamma-TiAl alloy

In this study, TiAl alloy with nominal composition of Ti-43.5Al-6V-1Cr was fabricated by inductive skull melting technology. Microstructure evolution and microstructure formation mechanism were invested by quenching experiments. The results show that Ti-43.5Al-6V-1Cr alloy consists of lamellar colony (α2/γ), isolated γ phase and B2 phase. Phase transition equations and reaction temperatures during heating from RT to 1350 ℃ were identified: α2→γ, 835 ℃; α2→B2 + γ, 990 ℃; α2 + B2 + γ→B2 + γ, 1132 ℃; B2 + γ→α + γ, 1144 ℃; γ→α, 1183 ℃; α + γ→α + β + γ, 1278 ℃; α + β + γ→α + β, 1290 ℃; α + β→β, 1313 ℃. It’s found that adding of β-stabilizing elements makes β phase field of Ti43.5Al6V1Cr alloy expand to Al rich side, decreases temperature of β→α transition by 127 ℃ and causes β + α + γ phase field appearing in the phase diagram. Orientation relation (111)B2//(110)γ was found between B2 and isolated γ phase, besides (110)B2//(111)γ(K-S relation), the match of the two phases declares that β phase is parent phase of isolated γ phase. Above all, the phase transformation process during heating and cooling was deduced. During heating it’s: α2/γ + B2 + γ→B2 + γ→α + γ→β + α + γ→α + β→β, while during cooling it’s L→L + β→β→α + β→α + β + γ →α + B2 + γ→α2/γ + B2 + γ. Besides, the microstructure evolution mechanism was explained and depicted in schematic.

Phase transformation and its effect on the piezopotential in a bent zinc oxide nanowire

Most piezotronic nanodevices rely on the piezopotential generated by the bending of their component piezoelectric nanowires (NWs). The mechanical behaviours and piezopotential properties of zinc oxide (ZnO) NWs under lateral bending are investigated in this paper by using a multiscale modelling technique combining first-principles calculations, molecular dynamics simulations and finite-element calculations. Two phase transformation processes are successively found in ZnO NWs by increasing the bending force. As a result, the inner and outer surfaces of bent ZnO NWs transform from the parent wurtzite (WZ) structure to a hexagonal (HX) structure and a body-centred-tetragonal (BCT-4) structure, respectively. Different material properties are found among the WZ, BCT-4, and HX structures, which result in a significant change in the piezopotential distribution in bent ZnO NWs after the phase transformation. Meanwhile, the piezopotential generated in bent ZnO NWs can be enhanced by an order of magnitude due to the phase transformation. Moreover, a significant increase in the electronic band gap is found in the transformed HX structure, which implies that the phase transformation may also affect the piezopotential in bent ZnO NWs by modifying their semiconducting properties especially when the doping level of NWs is large.

The study of high-temperature stability of the thermoprotective coating made of zirconium dioxide

Laser heating method is proposed for the evaluation of high-temperature stability of thermal protective coatings of zirconium dioxide. Structural-phase state of plasma thermal protective coating of zirconium dioxide has been investigated after laser pulse altering with a different energy. Processes of phase transformation, melting and recrystallization are registered. It has been found that the degradation of the coating affects the surface layers with a thickness of several layers. By changing the parameters of laser radiation it is possible to carry out rapid diagnostics and comparative tests of heat resistance of ceramic protective coatings obtained by different methods from different initial materials.

Study on Failure Mechanism and Phase Transformation of 304 Stainless Steel during Erosion Wear

In this paper, the failure mechanism and phase transformation process of 304 stainless steel during the erosion wear process were studied with a rotary erosion wear test device. The surface morphologies of the worn 304 stainless steel were investigated by scanning electron microscopy (SEM). The metallographic structures of the nonworn and worn 304 stainless steel were analyzed by optical microscope (OM) and transmission electron microscopy (TEM). In addition, the surface hardness on different areas of the sample was also measured. The results demonstrated that the failure mechanism of 304 stainless steel during the process of erosion wear was cutting and spalling caused by plastic deformation. The high-density dislocations move along the slip planes between slip lines, which resulted in the formation of martensite phase between the slip lines. Meanwhile, the martensitic transformation on the worn surface caused by severe plastic deformation was the coordination of dislocation martensite and twin martensite.

Mathematical Model and Simulation of Austenite Reverse Phase Transformation Process in Cold Rolled Low Carbon Steel

Mathematical Model and Simulation of Austenite Reverse Phase Transformation Process in Cold Rolled Low Carbon Steel

Numerical Study of Stress Analysis for the Different Widths of Padding Welds

In the presented study, the cases of regeneration of the element made of C45 steel, using the MAG (Metal Active Gas) method are analysed. The base material is applied to the regeneration process. The analysis of the influence of the padding weld width (0.006 m, 0.01 m, 0.014 m) and the preheating temperature on the phase transformations and effective stresses of the regenerated layer are performed. A non-standard approach to preheating (before each padding weld after the cooling to ambient temperature) is considered. Due to the possibility of simplifying the model from 3D to 2D (symmetry of calculations for long padding welds), calculations were performed using the finite element method in the transverse to the padding direction. Each new padding weld was included as an additional area in the finite element mesh. The developed numerical model includes a temperature model, phase transformations in the liquid and solid states, and the stress model in the elastic-plastic range. The aim of the regeneration is not only to obtain the original geometry of the element, but it is also important that the filler material used (in the considered case identical to the base material) has appropriate properties. These properties largely depend on the phase composition. The used filler material affects not only the hardness, brittleness, and ductility of the material. Its kinetics and changes in the geometry can cause significant stresses and even cracks. Based on the obtained results, it can be concluded that increasing the width of the padding welds causes a decrease in the level of residual effective stress; however, it is technologically difficult to accomplish. The most unfavourable stresses occur in the initial area of the pad welding zone. For lower preheating temperatures and smaller welds, areas with possible cracks are identified. In these cases, lower preheating and tempering should be carried out, which leads to similar energy costs as at higher preheating temperatures. Due to the complex phase transformation process for medium carbon steels and the need for the process parameters control, proper regeneration is possible only in automated workstations. Keywords: computational mechanics, numerical simulation, padding weld, preheating, strain analysis, stress

Charge-separated metal-couple-site in NiZn alloy catalysts towards furfural hydrodeoxygenation reaction

Catalytic conversion of biomass furfural (FAL) to high value-added products (e.g., 2-methylfuran, MF) has attracted considerable attention, in which control over catalytic selectivity plays a crucial issue. Herein, a series of heterogonous NiZn alloy supported on the mixed metal oxides (MMO) were synthesized derived from layered double hydroxides (LDHs) with various Ni/Zn ratio (3/1, 1/1 or 1/3). XRD, HRTEM and XAFS measurements confirm that with the increase of Zn content, the corresponding NiZn alloy transforms from α-NiZn (Ni3Zn1-MMO and Ni1Zn1-MMO) to β-NiZn (Ni1Zn3-MMO). Dramatically, the selectivity of MF displays an improvement from 12% to 95% along with this phase transformation process; and the MF yield reaches to 95% over Ni1Zn3-MMO sample. A combination study including XPS, CO-DRIFTS, in situ FT-IR and DFT calculation verifies that metallic Ni serves as active site, resulting in an effective suppression of side reactions (furan ring hydrogenation). Moreover, a charge-separated metal-couple-site (Niδ--Znδ+) is on the surface of Ni1Zn3-MMO originating from electron transfer between Ni and Zn. This active structure stabilizes a η2(C, O) adsorption configuration of intermediate, in which C atom is bonded to the Niδ− site and O atom is attached to the Znδ+ site. Then, this adsorption configuration facilitates the CO cleavage, giving rise to the production of MF. This work provides an efficient and cost-effective catalyst that can simultaneously inhibit CC hydrogenation and promote CO cleavage, which would be potentially used in catalytic conversion of biomass-derived platform molecules.

Effects of Heat Treatment on Indomethacin-Cimetidine Mixture; Investigation of Drug-Drug Interaction Using Singular Value Decomposition in FTIR Spectroscopy.

This study investigated the effect of phase transformation on indomethacin (IMC), cimetidine (CIM), and their 1:1 eutectic mixture, using FTIR spectra and multivariate analysis. The IMC form γ, CIM form A, and IMC-CIM 1:1 mixture molar ratio samples were heated on a hot plate at 303-453K for 5min and cooled till room temperature. The prepared samples were investigated by powder X-ray diffraction analysis and infrared spectroscopy with KBr powder. The PXRD patterns suggested the bulk IMC form γ, bulk CIM form A, and 1:1 physical mixture samples phase transformed into low-crystallinity IMC form γ, amorphous CIM, and eutectic mixture, respectively. FTIR spectra combined with singular value decomposition (SVD) suggested by absorbance peak shifts of several vibration modes that the polymorphic transformations of the samples affect their molecular interactions. The estimated melting points of heated samples were evaluated by sigmoid fitting based on the SVD results. The principal components of SVD show that the process of phase transformation of IMC-CIM 1:1 mixture samples affect the IR vibration of the CO stretch of IMC and the C-C stretch and C-H bending of CIM. These results suggest that molecular interaction is an important factor in the eutectic condition of IMC-CIM 1:1 mixture. This observation enables to evaluate for in co-amorphous formulations or stability of drug combinations in a poly pill.

Manipulation of upconversion property and enhancement of sensitivity by tailoring the local structure

AbstractTailoring the local crystal environment around the activators is one of an important way to enhance the upconversion (UC) luminescence intensity. Herein, we substitute the Y3+ lattice with La3+ ion gradually in Y2Ti2O7:Yb3+, Er3+ phosphor and investigate the effect of La3+ concentration on the UC luminescent properties as well as the temperature sensing behaviors. During the phase transformation process from cubic Y2Ti2O7 to monoclinic La2Ti2O7, the La3+ ions also play an important role on the adjustment of size and morphology of particles. Furthermore, the cooperation of La3+ ion is in favor of the crystal growth toward the easy growth directions. The UC luminescence intensities can be enhanced efficiently with the increasing of La3+ concentration. The sensitivity for temperature sensing can be improved by the increasing of La3+ concentration in the Y2Ti2O7 and La2Ti2O7 two‐phase coexistence system and the maximum SA is 45.3 × 10−4 K−1 at 410K when the La3+ concentration is 80%. The maximum SA and corresponding temperature can be adjusted by controlling the La3+ concentration, which means that (Y0.94‐xLax)2Ti2O7: Er3+/Yb3+ phosphors may be applicable to different working environment.