Papers by Keyword: Non-Equilibrium

Abstract: Spark plasma sintering can be carried out at a low temperature with short heating, holding and cooling times, which allows for the fabrication of non-equilibrium materials. In this article, metal-matrix-composite fabrication with thermally unstable reinforcements by spark plasma sintering is described.

Abstract: The process of a eutectic alloy crystallization is considered when the eutectic alloy is instantly cooled from the liquid state to below the eutectic transformation temperature. The features of such crystallization are considered. The mathematical model of the process is constructed that takes into account the nucleation of new phases particles, their growth and the associated change the concentrations of the melt components. The nuclei of new phases are supposed be spherical. As they grow, they come into contact and become lamellar. The developed approach was applied to the amorphization process of the eutectic alloys. An amorphous state has been reached if the clusters of solid phases can’t grow above nanosize. The model allows researching the necessary amorphization conditions.

Abstract: The size distribution of carrying capacity as the forefront of current non-equilibrium transportation of non-uniform suspended sediment research was introduced. The nonequilibrium transportation of suspended sediment concept was further studied. The preliminary calculations and verification of the size distributions of carrying capacity and effective bed material under nonequilibrium transportation condition were given after derived by Qiwei Han. The formula is tested by experimental data and the theoretical results are consistent with the measured values.

Abstract: In this paper, a 2-D numerical simulation of the wind turbine S825 airfoil is conducted with Spalart-Allmaras (SA) turbulence model at different attack angles. By comparing with experimental data, a novel method of modifying SA model is proposed. The key parameter in SA turbulence model is set with different values in the non-separating region and separating region divided by separating point respectively. This method improves the predictive accuracy of SA turbulence model when the airfoil works at stall conditions.

Abstract: Cobalt ferrite CoFe₂O₄ tabular crystals were synthesized via two-step coprecipitation using non-equilibrium crystallization conditions by supplying a solution of CoCl₂6H₂O and FeCl₃6H₂O and a solution containing NaOH at a later crystallization stage. Mean particle size of ~16.5 nm CoFe₂O₄ primary particles synthesized by coprecipitation showed non-oriented structure. Effect of heat treatment temperature on the microstructures of the final CoFe₂O₄ crystal was examined, orderly arranged plate-like tabular CoFe₂O₄ crystals were formed under calcination at 800 °C. Magnetic hyspersis loops measured at 300 and 5 K indicated the anisotropy in the tabular crystals.

Abstract: At present the concept of instantaneous equilibrium is often adopted for simulating the wellbore pressure and temperature distribution in heavy oil wells. In this paper, the mathematical model was built and the diffusion of gas in the oil phase was researched. It proves that the non-equilibrium phenomenon is not obvious in convenient oil wells and it could be overlooked, while in heavy oil wells the non-equilibrium phenomenon is too prominent to be overlooked. Basing on the mass conservation principle, the momentum conservation principle and the energy conservation principle, the calculated model for wellbore pressure and temperature in heavy oil wells considering of the non-equilibrium effect was established. One example shows that the model can accurately reflect the flowing laws in heavy oil wells, which has a relative value for engineering.

Abstract: This work consists of the numerical simulation of high enthalpy flows. The numerical model is governed by Euler equations and supplemented by the equations of the chemical kinetics modeling the phenomena of the chemical air components in a non-equilibrium state. The finite differences method is used for numerical simulations, the phenomena of a hypersonic flow one-dimensional reactive, non-viscous, chemical non-equilibrium is developed taking into account the physicochemical phenomena like the vibration, the dissociation of the diatomic molecules, the ionization of molecules and the formed atoms of chemical species to higher temperatures which appear behind a strong shock detached and evolve according to time in a relaxation range until to reach the equilibrium state. We are interesting in particular on the temperature effect in ionization of the atoms and the molecules.

Abstract: Sulfur is the main element which caused Nickel-based alloy embrittlement. In this study, the sulfur in Hastelloy X superalloy was determinated with Auger Electron Spectroscopy (AES) for samples quenched from 1180 °C and aged at 500 °C for different time. Experiments results confirmed the non-equilibrium segregation characteristics of sulfur. The results showed that a segregation peak of sulfur is at about 20 min during ageing. This peak was satisfactorily elucidated by the theory of non-equilibrium grain-boundary segregation. By theoretical calculation, the critical time constant of impurities sulfur atom in the Hastelloy X δs= 357. At the same time, the result provides a theoretical basis for sulfur segregation mechanism.

Abstract: In this present work, non-equilibrium coatings (like glassy state but not amorphous texture) were prepared by electric arc spraying using Zn-Al-Mg-RE-Si powder core spun alloy, and the effect of Mg content on corrosion resistance of coatings and the electrochemical properties of alloy coatings in corrosion process were investigated by CASS test, weight-loss test, XRD, SEM, polarization curves and electrochemical impedance spectroscopy. The results indicate that: The corrosion process of non-equilibrium coatings in CASS test includes corrosion inhibition stage and substrate corrosion stage; There appears much micro-crystallite and exists grain refinement in corrosion process; Before CASS test, the corrosion potential of non-equilibrium coatings shuffles when Mg content increases; Before CASS test and after CASS test at 120h and 216h, the corrosion current density approaches the minimum value and the corrosion rate is slowest when Mg content is 2%. Before CASS test, there appears the feature of Warburg impedance, but there did not appear the feature of Warburg impedance after CASS test at 120h and 216h. When Mg content is 2%, the charge-transfer resistance of coating is obviously higher than the coatings with other Mg content. Finally, an optimization composition of non-equilibrium coating—Zn-Al-2Mg-RE-Si coating is obtained by synthesis comparing.

Abstract: We have developed non-equilibrium simulation model of GTA. In this paper, simulation results of plasma property of argon GTA at atmospheric pressure are presented and, furthermore, the reliability of the simulation model is evaluated. As a result, it was revealed that non-equilibrium characteristic appears in regions close to both electrodes and the fringe of the arc column where the temperatures decrease below approximately 10000K. It was also found that non-equilibrium region near the anode surface has thickness of 0.3mm. This result agrees with the simulation result predicted with one-dimensional electrical sheath model.