Phase Zone Research Articles

Numerical and analytical investigation of the possibilities to enhance the thermal conductivity of core-shell particle packed beds

We report on a numerical study of the thermal conductivity of core-shell particle packed bed columns. Covering a variety of packing structures and a broad range of mobile phase and porous zone conductivities, it was in all cases found that switching to particles with a highly conducting core (e.g., with a gold or copper core instead of a silica core) would produce a much smaller increase of the effective heat conductivity of the bed (keff) than previously expected in literature. We found maximal increases on the order of some 20–70%, which is much lower than the potential increases up to 2000% assumed in literature. The overestimation in literature could be attributed to the fact that this literature was based on an incorrect extrapolation of the Zarichnyak-model which was the heat conductivity model predominantly used up till now. On the other hand, the computed relationships between keff and the core conductivity obtained in the present study are in good agreement with an analytical solution derived from the effective medium theory, a theory which is physically much more relevant for the case at hand than the Zarichnyak-model. The results also show that the observed increase in effective bed conductivity between fully porous and core-shell particle beds frequently observed in literature is not only due to the presence of the core, but that differences in the shell layer conductivity can play an equally important role. In addition, it could also be demonstrated that, if ways could be found to increase the conductivity of the shell layer, this would produce a much stronger increase of the overall bed conductivity than will ever be possible by increasing the conductivity of the cores.

Influence of post-weld heat treatment on microstructure and adhesion of Ti/Cu composite

ABSTRACTIt is well known that brittle interfacial intermetallics are typically present in laminated composites and degrade their mechanical performance. To investigate the relationship between intermetallics and mechanical properties, Ti/Cu-laminated composite plates prepared by explosive welding were studied with different heat treatments. A transition layer containing four zones of intermetallic phases, Cu4Ti, Cu4Ti3, CuTi, and CuTi2, was found at the interface between Ti and Cu after explosive welding. The intermetallics became thicker as the temperature of the heat treatment increased, especially for the CuTi phase. The sample treated at 473 K exhibited the highest bonding strength of 199.7 MPa, which was attributed to the elimination of residual stress during the welding and the diffusion of copper to improve interfacial bonding.

Effects of Nb on the Microstructure and Properties of Ti-Added Hypereutectic High-Cr Cast Iron

Effects of Nb on the microstructure and properties of Ti-added hypereutectic high-Cr cast iron were studied. With the addition of Nb, a new phase (Nb,Ti)C was formed. The microstructure analysis revealed that the amount of primary carbides was decreased from 18.6 to 8.8% and the primary and eutectic carbides were greatly refined. The decrease in the amount of primary carbides was attributed with the shrinking of primary M7C3 phase zone in the phase diagram, while the refinement of primary carbides was attributed to the heterogeneous nucleus of (Nb,Ti)C phase for the primary M7C3 carbides. The macrohardness of the alloy increased from 60.8 to 63.5HRC, and the impact toughness increased from 3.8 to 5.2 J cm−2. Furthermore, the wear resistance was enhanced with the addition of Nb due to the formation of hard (Nb,Ti)C carbides.

An Alternative Way To Enhance Piezoelectricity and Temperature Stability in Lead-Free Sodium Niobate Piezoceramics.

To further balance the relationship between piezoelectricity and temperature stability, the (0.975 - y)NaNbO3- yBaTiO3-0.025BaZrO3 ( y = 0-0.20) ceramics are developed by constructing a wide tetragonal phase region. Effects of BaTiO3 on the relationships among phase structure, electrical properties, and temperature dependence are investigated. With increasing BaTiO3 contents, the ceramics endure the structural evolutions from orthorhombic phase to tetragonal phase, and then to relaxor cubic phase. A wide tetragonal phase zone of 24-180 °C can be realized in the ceramics with y = 0.08, together with an enhanced piezoelectric coefficient d33 = 215 pC/N. Intriguingly, excellent temperature stability of unipolar strain ( Suni) and piezoelectric coefficient ( d33) are observed in the ceramics with y = 0.08 within 20-180 °C. This work provides an alternative way to enhance piezoelectricity and temperature stability in lead-free piezoceramics.

Operating technical characteristics on asymmetrical arrangement of six cyclones in a 600 MW supercritical CFB boiler

In order to obtain the operating characteristics of the first 600 MW supercritical circulating fluidized bed (CFB) boiler with six cyclones in an asymmetrical arrangement, the gas-solid flow information and temperature distribution of six circulating loops were measured and analyzed. The experimental results indicate that bed temperature in the furnace presents an S-type distribution pattern along the furnace height direction, for three cyclones of the same side, the temperature in the middle cyclone is high and the temperature on both side cyclones is low. At high boiler loads (450–600 MW), the temperature distribution of six cyclones and the gas-solid flow uniformity along the furnace height direction is more uniform, the temperature distribution uniformity in dense phase zone of furnace and three circulating loops on the right side wall are superior to those of the left side wall. The calculation results indicate that the particle flow distribution of six cyclone inlets is relatively uniform, the calculated results are consistent with the test results. The gas-solid flow asymmetry phenomenon of six circulating loops on both sides of the furnace is found, and the relative standard deviation of six cyclones inlet temperature does not exceed 4.30%, the back pass structure needs further optimization.

Fibonacci terahertz imaging by silicon diffractive optics.

Fibonacci or bifocal terahertz (THz) imaging is demonstrated experimentally employing a silicon diffractive zone plate in continuous wave mode. Images simultaneously recorded in two different planes are exhibited at 0.6THz frequency with the spatial resolution of wavelength. Multifocus imaging operation of the Fibonacci lens is compared with a performance of the conventional silicon phase zone plate. Spatial profiles and focal depth features are discussed varying the frequency from 0.3 to 0.6THz. Good agreement between experimental results and simulation data is revealed.

Flame Structure of Ammonium-Dinitramide-Based Liquid Propellant in a Small Thruster

In this paper, the flame structure of a liquid propellant ammonium dinitramide–methanol aqueous solution in a small model thruster is investigated. The thruster is composed of an injector and a combustion chamber (including a catalyst bed) with optical windows, through which the combustion process in the atmosphere is inspected, and the temperature distribution along the flame is measured by the tunable diode laser absorption spectroscopy method. Obvious fluctuations in temperature and flickering yellowish flame downstream of the combustion chamber are observed, indicating that the combustion is not stable. The mean temperature distribution has a significant peak where a yellowish flame appears. To explain the experimental observations, a detailed gas-phase ammonium dinitramide–methanol reaction model is used to establish the flame structure of an ideal liquid propellant, which can be divided into several different regions, including the liquid phase, aerosol zone, and two flame zones. The decomposition of ammonium dinitramide and the evaporation of methanol take place in the liquid phase and aerosol zone, whereas the gas phase reactions of methanol and the decomposition products of ammonium dinitramide take place in the two flame zones. Based on the proposed theory of flame structure, it is seen that, in our experiment, the physical and chemical processes in the liquid phase and aerosol zone are completed upstream of the catalyst bed, and the unstable yellowish flame appearing in the combustion chamber is caused by competitive influence between the two flame zones.

Laser heterodyne interference signal processing method based on phase shift of reference signal.

A novel signal processing method based on phase shift of reference signal is proposed for heterodyne interferometer. The integer fringe counting method based on overflow judgment and compensation can realize longtime and correct integer number measurement. In order to eliminate the influence of jitter in measurement signals on combination of integer and fraction fringe counting, the reference signal with phase shift of 180° is used to obtain integer compensating number to compensate the unstable integer number in unstable phase zone, which guarantees the correct combination of integer and fraction fringe counting. The principle of the proposed signal processing was described in detail. The static and dynamic resolution of the proposed method were discussed. A signal processing board based on FPGA was developed, and three tests were performed to verify the feasibility of the proposed method. A displacement measurement experimental setup was constructed, and two experiments verified the effectiveness of proposed method in application of an interferometer to realize precision displacement and testing of a stage.

The diffusion path in NiCu-Ti ternary diffusion couples

The formation and growth of intermetallic compounds by reactive diffusion between model alloy Ni30-Cu70 (composition given in at.%) and high purity Ti was investigated at a temperature of 850 °C using bulk diffusion couples for 100 h. Only three stable intermediate compounds of the Ni30Cu70-Ti system were formed in the diffusion reaction zone in the sequence Ti2Cu, TiNi and τ1 (Ti(Ni1−xCux)2. Moreover, on the microstructure the two phase zone consisting of TiNi2Cu + Ni30Cu70 can be observed. Next to the experimental description, a model determining the diffusion path in a multiphase system was proposed. The proposed model is based on mass conservation law and geometrical lemmas, that allow for the determination of the unique diffusion path in complicated systems.

Phase transformations in functional coatings of tungsten carbon steels

AnnotationStructural and phase transformations in tungsten-containing functional coatings of carbon steels, obtained in high-energy processes of implanting tungsten carbide micropowders by the method of complex pulse electromechanical processing, were studied. It is shown that during thermoforce action in the deformation zone, an intensive austenization of steel occurs with the dissolution of a powder of tungsten carbide with the subsequent formation of composite gradient structures as a result of the decomposition of supercooled austenite supersaturated with tungsten both by the diffusion mechanism and by the spinodal decomposition mechanism. It is shown that individual zones of the tungsten-containing phases of the alloy are in the liquid-phase state and undergo spinodal decomposition with the formation of highly disperse carbide phases of globular morphology.

Two-stage approach based on zone and dose findings for two-agent combination Phase I/II trials

ABSTRACTIn Phase I/II trials for a combination therapy of two agents, we ideally want to explore as many dose combinations as possible with limited sample size in Phase I and to reduce the number of untried dose combinations before moving to Phase II. Efficient collection of toxicity data in Phase I would eventually improve the accuracy of optimal dose combination identification in Phase II. In this paper, we develop a novel dose-finding method based on efficacy and toxicity outcomes for two-agent combination Phase I/II trials. We propose a “zone-finding stage” that determines the most admissible toxicity zone on the dose combination matrix and subsequently select the dose combination allocated to the next patient from that zone in Phase I. Upon completion of this zone-finding stage, we allocate the next patient to the dose combination determined by adaptive randomization of the admissible toxicity and efficacy dose combinations in Phase II. Simulation studies demonstrated the utility of the proposed zone-finding stage and proved that the operating characteristic of the proposed method was no worse than the existing method. The sensitivity of the proposed method, as well as the operating characteristic of this method when the efficacy outcome is delayed, was also examined.

Influence of coke content on sintering process of chromium-containing vanadium-titanium magnetite

The sintering of chromium-containing vanadium-titanium magnetite using different coke contents was studied through the sintering pot tests, X-ray diffraction analysis and mineralogical phase analysis. Results showed that, as the coke content increased from 3.2% to 4.4%, the liquid phase and combustion zone thickness increased while the vertical sintering rate and ratio of sintered product decreased. In addition, the combustion ratio of exhaust gas also increased with increasing the coke content, indicating that combustion zone temperature also increased, and the excessive the coke content in the sintering process of vanadiumtitanium magnetite is harmful. As the coke content increased, the magnetite, silicates, and perovskite contents of the sintered ore increased while the contents of hematite and calcium ferrite of sintered ore decreased; drum strength decreased, and reduction degradation properties increased while reduction ability decreased. We found that the appropriate coke content for the sintering process is 3.6 wt%.

Softening of sound velocity and Hugoniot parameter measurement for shocked bismuth in the solid-liquid mixing pressure zone

Polymorphic phase transformation and melting under shock wave loading are important for studying the material dynamic mechanical behavior and equation of state in condensed matter physics. In this paper, the accurate Hugoniot parameter and sound velocity of shocked pure bismuth (Bi) in a pressure range of 17.3-28.3 GPa are obtained by using flyer impact method and rarefaction overtaking technique, respectively, and the sound velocity softening trend in shock-induced melting zone and the melting kinetics of Bi are then analyzed. In each experiment, six Bi samples with different thickness values are affected by oxygen-free-high-conducticity copper flyer fired through power gun. Shock wave velocity and particle velocity in Bi are experimentally determined through measuring the impact velocity and shock wave time in the thickest sample by photon Doppler velocimetry (PDV) technique. The velocity profiles on each interface between Bi and lithium fluoride (LiF) window are measured by displacement interferometer system of any reflector (DISAR), and then the sound velocity of shocked Bi is determined using the rarefaction overtaking method. The analyses of our results show that the softening of sound velocity of Bi approximatively satisfies the linear relation of Cs=3.682-0.015 p in the solid-liquid coexistence zone, and the pressure zone of the solid-liquid coexistence phase is further affirmed to be in a range of 18-27.4 GPa. Additionally, the obtained Hugoniot data for Bi in this paper supply a gap in the pressure zone of solid-liquid mixing phase. The quadratic equation with the expression of Ds=0.401+ 3.879 up-0.876 up2 can better demonstrate the relation between shock wave velocity and particle velocity than a linear one when the particle velocity lies in a range of 0.5-1.0 km/s, and this non-linear property maybe has a relationship with the shock-induced melting of Bi. Finally, our wave profile measurement of the Bi/LiF interface shows peculiar ramp characteristics in the expected velocity plateau zone in the pressure zone of solid-liquid coexistence phase, which may be associated with both the nonhomogeneous melting kinetics and the long time scale of melting for bismuth.

Modeling of the optical vortex generation using a silver spiral zone plate

Using a FDTD-method implemented in the FullWAVE (RSoft) software, a process of generating optical vortices during the propagation of a left- or right-hand circularly polarized Gaussian pulse through a phase and amplitude spiral zone plate with topological charge 2, a diameter of 8 μm, and a focal length of 532 nm is numerically modeled. An investigation of the amplitude and phase distributions in the focal plane shows the presence of optical vortices with topological charge 2. Analysis of the longitudinal component of the Umov-Poynting vector shows the presence of an inverse energy flow in the focal plane. In the case of using an amplitude spiral zone plate, the magnitude of the reverse flow decreases sharply until it disappears completely for the left circularly polarized incident beams.

Structural characterization of aluminized steel heat treated in different environments

Thermal and plasma based heat treatments of Aluminized P91 steel under different environments such as 100%O2, 100%Ar and 50%O2+50% Ar are attempted to investigate microstructural defects. Heat treatment of Al coated P91 steel involving normalizing treatment at 980°C and tempering at 750°C for 0.5h and 1.5h respectively in above mentioned environments under thermal and plasma processing conditions at 5mbar pressure was conducted. Detailed study of microstructural evaluation of the resultant diffusion coating under different environment is reported with SEM-EDS and EBSD characterization in current study. Further the vacancy concentration, CV was evaluated based on the precise combination of the changes in the bulk length and the X-ray lattice parameter from XRD data. The effect of vacancy concentration, grain size and strain on resultant coating has been presented. Presence of stable α-Al2O3 and metastable θ-Al2O3 along with FeAl was confirmed by XRD analysis in both thermal and plasma processed samples under 100%O2 and 50%O2+50%Ar environment while in Ar environment minor presence of θ-Al2O3 was observed during plasma treatment. Plasma heat treatment under 50%O2+50%Ar environment results in coating with stable α-Al2O3 followed by diffusion zone of FeAl with lowest vacancies, residual strain and area fraction of kirkendall porosity with maximum length of diffusion zone of FeAl phase for aluminized P91 steels than plasma treatment under 100% Ar environment and 100% O2.

Micro-structural evolution during diffusion bonding of C-SiC/C-SiC composite using Ti interlayer

Diffusion bonding of C-SiC composite was achieved with Ti interlayer at 1500°C for 3h with the applied pressure of 20MPa. The joined C-SiC composite showed the apparent shear strength of 19MPa and the sample fractured away from the joint. The microstructure of joint consists of Ti3SiC2 MAX phase, TiSi2 and TiC in which Ti3SiC2 was the major phase. The distribution of phases in the microstructure of joint was categorized into three different zones based on electron backscattered diffraction (EBSD) results. The first zone consists of a thin continuous TiSi2 phase, which was followed by a thick zone of Ti3SiC2 MAX phase. In the middle of the sample, a mix phase zone was found. The reaction mechanism was established for the evolution above microstructure of joined C-SiC composite.

Microstructural Analysis During the Step-Cooling Annealing of Iron-Rich Sm(Co0.65Fe0.26Cu0.07Zr0.02)7.8 Anisotropic Sintered Magnets

Microstructural analysis during the step-cooling procedure of iron-rich Sm(Co0.65Fe0.26Cu0.07Zr0.02)7.8 anisotropic sintered magnets was investigated systematically. The sintered magnet exhibits the maximum energy product of about 32 MGOe together with a remanence of about 11.5 kGs. It is found that the cellular structure has formed at the stage of isothermal annealing (heat treating at 1103 K for 20 h). Moreover, the average cell size of the 2:17 cell phase in magnets decreases from ~150 to ~105 nm, and the density of the lamella phase increases from ~0.03 to ~0.05 1/nm during the step-cooling procedure. It is also found that the Cu concentration is homogeneous in the specimen quenched at a temperature of 1103 K and then becomes nonuniform, especially enriched in the cell boundaries during the step cooling to 873 K. Interestingly, the typical twining structure along the [010] zone of the main phase exists in the specimen quenched at 873 K. Furthermore, it is inferred that the magnetization mechanism of the specimens transforms from the nucleation-dominated type to the coexisting type of pinning and nucleation effect during the step-cooling procedure.

An experimental investigation of creaming phenomenon using a novel optical method: A case study of mineral oil-in-water emulsion

ABSTRACTThe present study elucidates the creaming phenomenon of mineral oil-in-water macroemulsion using a new noninvasive method based on turbidimetry. Additionally, microscopic observation of the phenomenon is carried out to derive an in-depth understanding of the mechanisms. Accumulation of the particles in the emulsions under the formed cream is monitored during a relatively prolonged period of time. Backflow of continuous and dispersed phases in temporary channels is observed at the proximity of the cream. In addition to the backflow, a high traffic density of the dispersed particles and deflocculation of the cream are the main reasons for the accumulation of the dispersed phase particles and a temporary stability against creaming. The deflocculation hinders cream growth and increases the stratification of the cream. A low concentration zone of the dispersed phase with the width of ∼100 µm is observed under the cream.

Effect of long term aging on the fatigue crack propagation in the β titanium alloy Ti 17

This work aims to evaluate the impact of a prolonged thermal aging on the fatigue crack growth properties of a commercial Ti 17 (Ti-5Al-2Sn-2Zr-4Mo-4Cr) titanium alloy. Aging was operated at 450°C for extended times, of 1000h and 10,000h respectively. In terms of room-temperature tensile properties, aging is mainly responsible for a strain hardening of the material and a decrease in ductility, the total elongation dropping from 5.1% in the as-received state to 1.5% after 10,000h. A significant increase in crack propagation rates at room temperature for R = 0.1 is observed, emphasizing an embrittling effect of aging. This last effect is however only noticed beyond a critical value of ΔK (ΔKcr), which decreases with increasing aging times. It is observed that the effect of long-term aging on the mechanical properties is more pronounced during the early stage of the aging process, and tends to saturate for longer times. Tests with different load ratio of R = 0.4 and 0.7 were performed to gain a better understanding of the occurrence of these ΔKcr values. The results indicate that the increase in propagation rates is actually governed by the static Kmax component of the fatigue loading. Fractographical analysis of the failed specimens reveal that aging affects the material's resistance at a very fine scale, namely the α lamellae/β matrix interfaces. The detrimental role played by both grain boundary α phase and precipitate-free zones on the fatigue crack growth resistance of the material were finally discussed.

Spinodal decomposition of tungsten-containing phases in functional coatings obtained via high-energy implantation processes

We have studied structural and phase transformations in tungsten-containing functional coatings of carbon steels obtained during the high-energy processes of implanting tungsten carbide micropowders by the method of complex pulse electromechanical processing and micropowders of tungsten by technology of directed energy of explosion based on the effect of superdeep penetration of solid particles (Usherenko effect). It has been shown that, during thermomechanical action, intensive steel austenization occurs in the deformation zone with the dissolution of tungsten carbide powder, the carbidization of tungsten powder, and the subsequent formation of composite gradient structures as a result of the decay of supercooled austenite supersaturated by tungsten according to the diffusion mechanism and the mechanism of spinodal decomposition. Separate zones of tungsten-containing phases of the alloy are in the liquid-phase state, as well as undergo spinodal decomposition with the formation of highly disperse carbide phases of globular morphology.