Papers by Keyword: Phase Equilibrium

Abstract: The article analyzes the state of the global problem of the fuel and energy crisis and environmental pollution by the combustion products of hydrocarbon fuels of industrial and transport power plants. To ensure the energy security of the state, the Cabinet of Ministers of Ukraine developed and adopted the «Energy Strategy of Energy Saving of Ukraine for the period until 2030», which was updated in 2008, to protect the country from energy risks. In addition, the Cabinet of Ministers of Ukraine approved the «Concept of a targeted scientific and technical program for the development of the production and use of biological fuels». To increase the efficiency of using alternative motor fuels, as one of the aspects of solving the problem, an original method and results of calculating the thermophysical properties of a wide class of such motor fuels (hydrogen, natural gas, biogas, mine gas, coke, blast furnace and synthesis gas, etc.) are proposed. A description of the developed mathematical model for determining parameters of phase equilibria and thermophysical properties of dense molecular systems (dense gases and liquids) is given. Calculation procedures are based on the thermodynamic theory of disturbances without the involvement of empirical parameters. Features of the proposed method are: limitation of initial information, high accuracy, the possibility of application in any practically important ranges of states. Calculation errors are at the level of traditional experimental errors.

Abstract: Regularities of change of electrophysical properties of glasses S87-2, S78-4, S78-5, applied in electronic optics had been studied. The correlation between structural changes and electrical conductivity is established. A comparative analysis of the electric current influence on the new phase formation and the time to achieve phase equilibrium in the glasses is carried out.

Abstract: The electron microscopic and diffraction analysis presented in the article showed that the structure of the surface layer of the titanium alloy OT4 after implantation at an accelerating voltage of 30 kV from the cathode Cu-Pb-Bi has a different hierarchical character. As a result of investigations of each of the levels, it was determined experimentally that the deformation mechanism under the action of internal stresses, as well as diffusion-relaxation reactions, are the main reasons for their formation, leading to the appearance of structural features in the surface layer of the OT4 alloy. In this case, penetration of alloying components to a depth of 10-25 nm is observed.

Abstract: Heusler NiMnGa alloys are often categorized as ferromagnetic shape memory alloys or magnetocaloric materials, which are important for both practical applications and fundamental research. The NiMnGa alloys undergo a series of diffusion and diffusionless transformation from high temperature to low temperature. Among these transformation, martensitic transformation from austenitic phase to martensitic phase is critical in determining the properties of the alloys. Although martensitic transformation is considered diffusionless, diffusion also has important applications in the research of NiMnGa alloysDiffusion couples along with equilibrium alloys have been used to determine the ternary phase diagrams in NiMnGa alloys. Phase diagrams are important in selecting NiMnGa alloys, in particular two-phase NiMnGa alloys for practical applications. Furthermore, the diffusion couples effectively assist in the determination of compositions that exhibit martensitic transformation temperature near room temperature. Diffusion coefficients have been assessed for NiMnGa alloys. Tracer diffusivity of Ni, Mn and Ga was reported in a wide temperature range and followed Arrhenius behavior. Two different activation energies were obtained, corresponding to B2 and L2₁ crystal structure, respectively. Interdiffusion coefficients for NiMnGa alloys with B2 crystal structure are measured, which showed that Ni diffuses the fastest, followed by Mn then Ga. The diffusion coefficients provide useful information for fabricating NiMnGa alloys through diffusional process.A combinatorial approach involving diffusion couples and advance characterization has been developed to investigate the mechanical properties, microstructure and crystallography of NiMnGa alloys rapidly and systematically over a large compositional range. The composition-dependent modulus and hardness for NiMnGa alloys was extracted from the diffusion couples with the help of nanoindentation. Martensitic phases with non-modulated and various modulated crystal structures, and austenitic phase were identified in the interdiffusion zones by transmission electron microscopy. The results demonstrate the capability of using diffusion couples to speed up the discovery of new NiMnGa alloys or other similar alloys showing martensitic transformation.

Abstract: Effect of B addition on the microstructure and mechanical properties of AZ84 Mg alloy was investigated in this study. Through calculation of phase equilibria of AZ84 Mg alloy, carried out by using FactSage® and FTLite database, solution treatment temperature was decided as temperature of 330^oC, where supersaturated solid solution can be obtained. Solid solution treatment of AZ84 Mg alloy was successfully conducted at 330^oC and supersaturated microstructure with all almost all phases resolved into matrix was obtained. After solution treatment, hot rolling was successfully conducted by reduction of 60%. Compression and tension tests were carried out at room temperature on the samples in as-cast, solution treated, hot-rolled and subsequently recrystallized states. After solid solution treatment, each alloy was soaked at temperatures of 180 and 200^oC for time intervals from 1 min to 48 hrs and hardness of each condition was measured by micro-Vickers method. Peak aging conditions were deduced as at the temperature of 200 ^oC for 10 hrs for ZA84 Mg alloy. By addition of boron, aging kinetics was expedited and strength was enhanced.

Abstract: The equilibrium alloys closed to Mg-Nd side in the Mg-rich corner of the Mg-Zn-Nd system at 400°C have been investigated by scanning electron microscopy, electron probe microanalysis and X-ray diffraction. The binary solid solutions Mg₁₂Nd and Mg₃Nd with the solubility of Zn have been identified. The maximum solubility of Zn in Mg₁₂Nd is 4.8at%, and Mg₁₂Nd phase can be in equilibrium with Mg solid solution. However, only when the solubility range of Zn in 26at%~32.2at%, Mg₃Nd can be in two-phase equilibrium with Mg solid solution. As the results, two two-phase regions as Mg+Mg₁₂Nd and Mg+Mg₃Nd and a three-phase region as Mg+Mg₁₂Nd+Mg₃Nd in Mg-Nd-Zn ternary isothermal section at 400°C have been identified.

Abstract: Due to their high melting temperatures, low densities and excellent high-temperature strengths, Nb-Si-Ti-based ultra high temperature alloys shows great potential for vane materials on the next generation of high thrust-weight ratio aero-engines. In the present paper, the Nb-Si-Ti ternary system was studied, the phase diagram of Nb-Si-Ti and the phase fraction calculated, and the curve of solidification process established. The calculated results provide primary guidance for developing Nb-Si-Ti-X ultrahigh temperature alloys. Moreover, it is very useful as a guide for alloy design and processing development.

Abstract: Dry gas seal is often used as the seal devices in centrifugal compressor and other high-speed rotating equipment, which requires seal gas clean and dry. If there is some liquid in the seal gas, the dry gas seal will rapidly fail. When the seal gas flows through the filters, valves, orifices, seal faces and so on, the gas temperature will decrease resulted from the Joule- Thomson effect. If the gas temperature is lower than the corresponding dew point, there will be liquid condensation in dry gas seal system. Wet air is taken as an example to show how to calculate the pressure and temperature relationship when it is adiabatic expansion. Dew point lines at different conditions are calculated by considering the vapor-liquid equilibrium. Liquid condensation conditions are acquired by comparing expansion lines and dew point lines, and the factors of influencing liquid condensation were analyzed. The results shows that decreasing gas humidity, increasing the gas temperature can effectively reduce the liquid condensation.

Abstract: Gas hydrates are a major concern in oil and gas industry, Gas hydrates form in small amounts of water, gas, and the appropriate pressure and temperature conditions. Gas hydrate storage and transportation technology starts a new way for energy storage and transportation industry. The most critically technical problem is how to improve the hydrate formation rate, storage capacity and form continuously. The influences of surfactants on induction time in three types of solution with equal concentration were studied by means of visual hydrate experimental equipment, and generalized induction time was measured by direct observation method. Specific effects of different surfactants on hydrate formation were summarized, as well as the hydrate formation mechanism of surfactants . The lack of research and the research direction of the future were concluded . The further study of surfactant mechanism and build kinetics model containing surfactant have important theoretical value . The result shows that the gas molecules saturated due to the solubilization of surfactant, which promotes the progress of mass transfer in the hydrates. And driving force is provided for the complexation of host molecules and guest molecules during the formation progress of gas hydrates.

Abstract: Aspen Plus is a simulation system of large-scale generalized flowsheet. It is to describe the chemical process by using a digital model, and to obtain the desired results on the computer by changing various effective conditions. The main component with higher value in citronella oil is high purity citronellal. Due to its boiling point, temperature-sensitive and other issues, the difficulty of distillation process increases. This paper conducts process design and simulation on citronella oil high vacuum distillation process by using Aspen Plus software, obtains the process parameters of citronellal extraction tower, explores the relationship between reflux ratio and the number of theoretical plates, and provides data support for the continuous production of citronellal in citronella oil system.