In-situ Observation and Mathematical Modelling of the Nucleation and Growth of Intermetallics and Micropores During the Solidification of Aluminium Alloys

The performance of aluminium alloy castings is limited by the level of two major defects: porosity and iron intermetallics, because both phases can lead to the initiation and propagation of cracks of casting components at high cyclic regime. To improve the fatigue life and thus increase usage of these energy-saving light metals, the mechanisms by which such microstructure features form and possible approaches to control them were investigated via a mathematical model which was validated by synchrotron x-ray radiography and tomography experiments. A multicomponent and multiphase model was developed to incorporate both nucleation and growth of Fe intermetallics using different techniques including Monte Carlo, phase field, and pseudo front-tracking. The classic heterogeneous nucleation was simulated by solving stochastic functions which were related to the local Gibbs free energy or total undercooling. The non-equilibrium growth of intermetallic phases was calculated by two separate methods: control volume and phase-field. Using realistic Gibbs free energy functions, the advancing S/L interface was simulated either by calculating kinetic velocity or by solving phase field equations. Anisotropy of S/L interfacial energy was implemented via a decentred needle/plate technique and phase field method. In addition, the probability of atomic attachment entered the propagation of cells by Monte Carlo method. Coupling this model with a pseudo front-tracking model, the evolution of microstructure features, including primary Al, gas and shrinkage porosity, and Fe-rich intermetallics, was simulated. To predict the formation of these microstructures in casting components, e.g. an engine block, this micromodel was directly implemented as a subroutine into a macroscale heat transfer and fluid flow model. Numerical investigations were compared between control volume technique and phase field method, showing better efficiency and reasonable accuracy using the former. To correct the empirical parameters in the model, the kinetic data was successfully obtained from in-situ observations of micropores and Fe-rich intermetallics during solidification using the state-of-the-art x-ray imaging and quantification techniques. Three dimensional predictions of micropores from the multiscale model were then validated by x-ray tomography experiments on Al-Cu, Al- Si, and Al-Si-Cu alloys in different casting conditions. Synchrotron x-ray tomography experiments were used to validate the distribution of size and morphology of Fe-rich intermetallics in multicomponent Al-7.5wt.%Si-3.5wt.%Cu alloys with varying levels of Fe content. Good agreement between predictions and experiments was successfully obtained qualitatively and quantitatively. Applying this multiscale model to industrial castings, both microporosity and Fe-rich intermetallics were predicted in various casting conditions. Decreasing initial concentration of Fe and/or increasing cooling rates, smaller intermetallic phases formed during solidification, matching the experimental observation well. Complex interactions between pores and Fe intermetallic phases were simulated by preferentially segregating hydrogen and reducing G/S interfacial energy. Satisfactory results were obtained to reflect the influence of Fe-rich intermetallics on the nucleation and growth of pores. Therefore, practical measures to control microstructures and thus increase fatigue life of casting components can be summarized from the model predictions, which may significantly improve the efficiency of alloy design and process optimization

Novel Silica-Based Hybrid Adsorbents: Lead(II) Adsorption Isotherms

Water pollution caused by the lead(II) from the spent liquor has caught much attention. The research from the theoretical model to application fundaments is of vital importance. In this study, lead(II) adsorption isotherms are investigated using a series of hybrid membranes containing mercapto groups (–SH groups) as the hybrid adsorbents. To determine the best fitting equation, the experimental data were analyzed using six two-parameter isotherm equations (i.e., Langmuir, Freundlich, Dubinin-Radushkevich (D-R), Temkin, Harkins-Jura, and Halsey isotherm models). It was found that the lead(II) adsorption on these samples followed the Freundlich, Dubinin-Radushkevich (D-R), and Halsey isotherm models. Moreover, the mean free energy of adsorption was calculated using Dubinin-Radushkevich (D-R) isotherm model and it was confirmed that the adsorption process was physical in nature. These findings are very meaningful in the removal of lead(II) ions from water using the hybrid membranes as adsorbents

Medical Health Resources Allocation in Liaoning Province Based on System Dynamics

On the perspective of social security and the complex system theory, we discuss the choice of the path to the sustainable development of medical health resources in Liaoning province, and then provide theory support for perfecting medical and health resources in Liaoning province by building a system dynamics model on simulation software AnyLogic6.4.1 platform

Extraction of essential oil from the aerial parts of Artemisia frigida Willd by way of hydrodistillation

This study aims to determine the optimum conditions for extraction of essential oil compounds in the aerial parts of Artemisia frigida Willd. Method: the considered extraction method is hydro-distillation, using a Clevenger apparatus. The effect of particle size of raw material, soaking time, liquid to plant material ratio and extraction time on essential oil yield were investigated through both single factor and multi-factor experiments. Results: In the single factor experiment, the influences of the following factors on essential oil extraction were studied; particle size 0.825 mm, soaking time 2 h, and liquid to plant material ratio 12:1. Under the multi-factor experiment, the influences of multiple factors of extraction conditions on essential oil were considered, particularly, extraction time (C)>soaking time (A)>liquid to plant material ratio. Conclusion: For extraction of essential oil from the aerial parts of Artemisia frigida Willd, the following optimum extraction parameters were identified: 2h of soaking time, 10:1 liquid to solid ratio, and 8h of extraction time

Tailoring the Spectra of White Organic Light-Emitting Devices by Trap Effect of a Concentration-Insensitive Dopant

Highly efficient phosphorescent organic light-emitting devices (PhOLEDs) had been fabricated by using a novel iridium complex, bis[2-(3′,5′-di-tert-butylbiphenyl-4-yl)benzothiazolato-N,C2′]iridium(III) (acetylacetonate) [(tbpbt)2Ir(acac)], as the emitter. With a wide doping ratio ranging from 15 wt% to 25 wt%, the PhOLEDs maintained a comparable high performance, indicating concentration-insensitive property of the (tbpbt)2Ir(acac). On the basis of the unique characteristic of concentration insensitivity, the application of this phosphor was explored by fabricating white organic light-emitting devices (WOLEDs) with altered doping ratio, indicating that trap effect of (tbpbt)2Ir(acac) could effectively tailor WOLEDs spectra. Typically, a high-power efficiency, current efficiency, and external quantum efficiency of 30.0 lm/W, 38.8 cd/A, 18.1%, were achieved by 20 wt% doped WOLEDs

High photoresponse inverted ultraviolet photodectectors consisting of iridium phosphor doped into poly(N-vinylcarbazole) polymeric matrix

Highly sensitive inverted polymer ultraviolet (UV) photodectectors were fabricated by doping a phosphorescent material of bis[2-(4-tertbutylphenyl)benzothiazolato-N,C2′] iridium(acetylacetonate) [(t-bt)2Ir(acac)] into poly(N-vinylcarbazole) (PVK) polymeric matrix. Under the UV-260 nm illumination with an intensity of 0.7 mW/cm2, the device achieved a photocurrent of 11.37 mA/cm2 at −3 V, corresponding to a photoresponse of 15.97 A/W, which is 381% higher than the undoped device. Detailed analysis of photoluminescence, charge carrier transportation and film morphologies of PVK polymer active layers were carried out, and the enhanced UV absorption, formation of the triplet excitons and better charge carrier transport are ascribed to the improved photodectector performance

Structural state detection using quaternion-based three-channel joint transmissibility

This paper presented the use of quaternion-based three-channel joint transmissibility (QTJT) in structural state detection. During the detection process, the time-domain pure quaternion sequences were obtained based on the three dimensional spatial vibration signals from two different testing points. Then QTJTs of the object structure under different states were calculated by discrete quaternion Fourier transform (DQFT). Subsequently, modular vectors of the QTJTs were utilized to construct the state matrix of the object structure and the Karhunen-Loeve Transform (K-LT) was employed to calculate the state feature index vectors. Finally, Euclidean distance between state feature index vectors was obtained, which was considered as the state indicator. An actual experiment was performed on the test platform of ballastless track and the result with 100 percent correct identification was achieved. Combined with the experimental results, the advantages of QTJT comparing to transmissibility based on scalar signals were discussed. The QTJT can be used when the vibration composes from multiple dimensional synchronous vibrations. And more importantly, the QTJT is consistent with its theoretical value in spite of the installation orientation of the sensors