Papers by Keyword: Thermodynamic Modeling

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Authors: Mohammad Mezbahul-Islam, Elhachmi Essadiqi, Mamoun Medraj
Abstract: The Mg-Cu-Y system has been experimentally investigated using differential scanning calorimetry (DSC). Vertical sections and phase assemblage diagrams are calculated using thermodynamic modeling. Solidification behavior of the key alloys was discussed in light of the thermodynamic calculation. Melting temperatures of two of the ternary compounds; Mg18CuY and Mg4CuY, are predicted using the modified thermodynamic database of this system. Key words: Mg alloys, Bulk metallic glass, Differential scanning calorimetry, Thermodynamic modeling.
Authors: P. Szakàlos
Abstract: This paper gives an overview of the different processes of metal dusting (MD) that operate on low and high alloyed iron and nickel base alloys exposed in CO+H2–containing environments with or without water vapour. MD of pure metals like iron and nickel occur with a solely carbon-induced corrosion mechanism. However, in high alloyed materials with strong oxide formers such as Cr and Al, a more complex MD-process takes place which involves both carbon and oxygen in close collaboration. The “alloyed” carbides, i.e normally Cr-containing carbides, formed in such materials are thermodynamically stable with respect to the carbon activity. However, in the reaction front of a MD-pit with non-protective spinel oxide, they destabilise and dissolve due to the influence of the low oxygen activity determined by CO-dissociation. Based on recent results in the field of MD a chart with tentative MD mechanisms is presented as a function of alloy composition and temperature.
Authors: Armin Paar, Leonel Elizondo, Michael Brandner, Thomas Trickl, Bernhard Sonderegger, Coline Beal, Christof Sommitsch
Abstract: The thermodynamic modeling of alloy systems consisting of stable and metastable phases e.g. high-alloyed mottled cast iron can be problematic. Thermodynamic databases are rather well-developed for low, medium and high alloyed steels (e.g. HSS) but the application of those databases is not yet very common for high-alloyed (mottled) cast irons. The Thermo-Calc software together with the TCFE7 database is used to calculate isopleth and property diagrams, using the CALPHAD method. Additionally Scheil-Gulliver calculations are performed to simulate the effects of microsegregation during solidification. The results from the thermodynamic calculations are compared with measurements on own samples and with literature values. Those measurements include quantitative light-optical analysis, SEM with BSE detector, EDX measurements for the distribution of the alloying elements as well as XRD and DSC measurements. The investigations show the possibilities which are offered by thermodynamic calculations for high-alloyed mottled cast iron as well as the limitations and the compromises which have to be taken into account when calculating stable and metastable phases existing next to each other.
Authors: Hong Yu Zhang, Jin Sen Tian, Li Hong Liang, Hua Wei, Qi Zheng, Tao Jin, Xiao Feng Sun
Abstract: A model for diffusion is applied to the nickel-chromium-aluminum (Ni-Cr-Al) system to optimize the mobility parameters for the B2 phase by fitting the experimentally obtained inter-diffusivities. In the model, the activation energy for diffusion is expressed as a function of the degree of ordering which is evaluated from thermodynamic data. These data are used to evaluate the thermodynamic factors of the B2 phase in the Ni-Cr-Al ternary system. The interdiffusivities from the model are used to simulate diffusion experiments. The results are generally agreed with the experimental data.
Authors: Humbul Suleman, Abdulhalim Shah Maulud, Zakaria Man
Abstract: With the advent of Equation of State/ Excess Gibbs Energy (EOS/GE) models, the linear co-volume based mixing rules have gained vast importance for predicting multi-component VLE for polar mixtures. Owing to their inherent ease of calculation and good prediction abilities, these mixing rules have been applied in extension, to a variety of systems especially for CO2-H2O-alkanolamine systems. However, no comparative study is available to select appropriate mixing rule for prediction of thermodynamic properties. In this study, pressure prediction of various linear co-volume mixing rules has been compared for CO2 – MEA and CO2 – MDEA systems, while effects of activity coefficients and process parameters have been kept constant. The infinite pressure mixing rules have heavily under – predicted and approximate zero reference pressure mixing rules have over – predicted, but latter are valid for low and medium pressure ranges. The linear combination of Vidal and Michelsen (LCVM) mixing rule have good predictions at high pressures.
Authors: Oleg Y. Sheshukov, Valentina P. Ermakova, Larisa A. Marshuk, Valentina G. Smirnova, Vladimir V. Kataev
Abstract: Laboratory researches of cooling rate influence on matrix structure, composition and quantity of nonmetallic inclusions in iron-aluminum alloys, containing 25-33%Al, are conducted. Thermodynamic modeling of composition and quantity of phases, which were formed in alloy system, containing Fe-Al-Si-C-O, for equilibrium conditions by means of the program complex ASTRA-4 (TERRA) is carried out. It is established, that irrespective of cooling rate the matrix has structure of intermetallic Fe-Al, and nonmetallic inclusions have platelet shape and composite of iron and aluminum oxy-carbides. It is confirmed, that ferroalloy with the optimal structure, necessary for receiving the high heat-resistance cast iron, should be cooled after smelting with the highest speed in these condition.
Authors: Humbul Suleman, Muhammad Zubair Shahid, Abdulhalim Shah Maulud, Zakaria Man, Mohammad Azmi Bustam Khalil
Abstract: Alkanolamines based carbon dioxide absorption from flue gases remains the most industrially implemented technique. The effective design of absorbers and associated equipment requires robust thermodynamic and kinetic models thus, instigating research efforts in chemical speciation and characterization of CO2 loaded alkanolamine solutions. In this study, the potential of Raman spectroscopy has been investigated to determine the in situ chemical speciation in MDEA – CO2 – Water system. The Raman spectra have been fitted to thermodynamic values using principal component regression. Results are in good agreement for carbonate, bicarbonate, MDEA and protonated MDEA chemical species.
Authors: M.S. Toprak, Do-Kyung Kim, Maria Mikhaylova, Yun Suk Jo, Mamoun Muhammed
Abstract: Templating methods provide an alternative approach for fabricating macroporous solids with three-dimensionally ordered arrays of pores with diameters from tens to hundreds of nanometers. The main goal of this work is the fabrication of thermoelectric-opal composite and inverse opals made of thermoelectric material in order to obtain enhanced performance by reducing the thermal conduction. Chemical bath deposition (CBD) has been employed and thermodynamic modelling was used to obtain optimum conditions for the desired phase of particle formation within the channels of the opal-like structures. The wetting behaviours of opals were considered in the choiceof the appropriate solvents. When loading is finished, the precursor is decomposed and reduced when appropriate. The opal template is then removed by pyrolysis to obtain the macroporous structures. The structural properties of materials produced were investigated.
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