The Experts below are selected from a list of 315 Experts worldwide ranked by ideXlab platform
Mark A. Stadtherr - One of the best experts on this subject based on the ideXlab platform.
-
Reliable Phase Stability analysis for asymmetric models
Fluid Phase Equilibria, 2005Co-Authors: William D. Haynes, Mark A. StadtherrAbstract:A deterministic technique for reliable Phase Stability analysis is described for the case in which asymmetric modeling (different models for vapor and liquid Phases) is used. In comparison to the symmetric modeling case, the use of multiple thermodynamic models in the asymmetric case adds an additional layer of complexity to the Phase Stability problem. To deal with this additional complexity we formulate the Phase Stability problem in terms of a new type of tangent plane distance function, which uses a binary variable to account for the presence of different liquid and vapor Phase models. To then solve the problem deterministically, we use an approach based on interval analysis, which provides a mathematical and computational guarantee that the Phase Stability problem is correctly solved, and that thus the global minimum in the total Gibbs energy is found in the Phase equilibrium problem. The new methodology is tested using several examples, involving as many as eight components, with NRTL as the liquid Phase model and a cubic equation of state as the vapor Phase model. In two cases, published Phase equilibrium computations were found to be incorrect (not stable).
-
Reliable Phase Stability Analysis for Excess Gibbs Energy Models
Chemical Engineering Science, 2000Co-Authors: Stephen R Tessier, Joan F. Brennecke, Mark A. StadtherrAbstract:Because models used to represent the Gibbs energy of mixing are typically highly nonlinear, the reliable prediction of Phase Stability from such models is a challenging computational problem. The Phase Stability problem can be formulated either as a minimization problem or as an equivalent nonlinear equation solving problem. However, conventional solution methods are initialization dependent, and may fail by converging to trivial or nonphysical solutions or to a point that is a local but not global minimum. Since the correct prediction of Phase Stability is critical in the design and analysis of separation processes, there has been considerable recent interest in developing more reliable techniques for Stability analysis. Recently we have demonstrated a technique that can solve the Phase Stability problem with complete reliability. The technique, which is based on interval analysis, is initialization independent, and if properly implemented provides a mathematical guarantee that the correct solution to the Phase Stability problem has been found. In this paper, we demonstrate the use of this technique in connection with excess Gibbs energy models. The NRTL and UNIQUAC models are used in examples, and larger problems than previously considered are solved. We also consider two means of enhancing the efficiency of the method, both based on sharpening the range of interval function evaluations. Results indicate that by using the enhanced method, computation times can be substantially reduced, especially for the larger problems.
-
ROBUST Phase Stability ANALYSIS USING INTERVAL METHODS
1998Co-Authors: Mark A. Stadtherr, Carol A. SchnepperAbstract:Conventional equation solving and optimization techniques for solving the Phase Stability problem may fail to converge or may converge to an incorrect result. A technique for solving the problem with mathematical certainty is needed. One approach to providing such assurance can be found in the use of interval methods. An interval Newton/generalized bisection technique is applied here to solve the Phase Stability problem. Results for two models of liquid-Phase systems, using several different feed compositions, indicate that the technique used is reliable and very efficient.
-
Enhanced Interval Analysis for Phase Stability: Cubic Equation of State Models
Industrial & Engineering Chemistry Research, 1998Co-Authors: James Z. Hua, Joan F. Brennecke, Mark A. StadtherrAbstract:The reliable prediction of Phase Stability is a challenging computational problem in chemical process simulation, optimization, and design. The Phase Stability problem can be formulated either as a minimization problem or as an equivalent nonlinear equation-solving problem. Conventional solution methods are initialization dependent and may fail by converging to trivial or nonphysical solutions or to a point that is a local but not a global minimum. Thus, there has been considerable recent interest in developing more reliable techniques for Stability analysis. Recently, the authors have demonstrated, using cubic equation of state models, a technique that can solve the Phase Stability problem with complete reliability. The technique, which is based on interval analysis, is initialization independent and, if properly implemented, provides a mathematical guarantee that the correct solution to the Phase Stability problem has been found. However, there is much room for improvement in the computational efficiency of the technique. In this paper, the authors consider two means of enhancing the efficiency of the method, both based on sharpening the range of interval function evaluations. Results indicate that, by using the enhanced method, computation times can be reduced by nearly an order of magnitude in some cases.
-
Reliable computation of Phase Stability using interval analysis : Cubic equation of state models
Computers & Chemical Engineering, 1998Co-Authors: James Z. Hua, Joan F. Brennecke, Mark A. StadtherrAbstract:The reliable prediction of Phase Stability is a challenging computational problem in chemical process simulation, optimization and design. The Phase Stability problem can be formulated either as a minimization problem or as an equivalent nonlinear equation solving problem. Conventional solution methods are initialization dependent, and may fail by converging to trivial or non-physical solutions or to a point that is a local but not global minimum. Thus there has been considerable recent interest in developing more reliable techniques for Stability analysis. In this paper we demonstrate, using cubic equation of state models, a technique that can solve the Phase Stability problem with complete reliability. The technique, which is based on interval analysis, is initialization independent, and if properly implemented provides a mathematical guarantee that the correct solution to the Phase Stability problem has been found.
Hamish L. Fraser - One of the best experts on this subject based on the ideXlab platform.
-
Tuning Phase Stability in nanocomposite multilayers
Applied Physics Letters, 2003Co-Authors: Gregory B. Thompson, R. Banerjee, Hamish L. FraserAbstract:As thin-film layers in a multilayered stack are reduced in thickness, changes in Phase Stability can result within the individual layers. These changes in Phase are expected to have a significant influence upon the functional properties of the nanostructured composite. The ability to engineer, or tune, Phase Stability at this nanometer length scale is of significant importance in order to maximize the functional properties of these materials. We report the prediction and experimental conformation of tuning the hcp to bcc Phase Stability in Ti for Ti/Nb multilayered nanocomposites. The prediction was based upon selective alloying of Ti with a bcc β stabilizing element using a new form of a thermodynamic Phase diagram for predicting Phase Stability in thin-film multilayers.
-
A Thermodynamic Approach in Tuning Phase Stability in Nanocomposite Multilayers
MRS Proceedings, 2003Co-Authors: Gregory B. Thompson, R. Banerjee, Hamish L. FraserAbstract:ABSTRACTChanges in the crystallographic Phase Stability of individual layers in a multilayered thin film stack are expected to have a significant influence upon the functional properties of the structure. The ability to predict and tune these Phase Stability states is of relevant importance in order to maximize the functional properties of the multilayer. A classical thermodynamic methodology, based upon competitive volumetric and interfacial free energies, has been used in the prediction and subsequent confirmation of the hcp to bcc Phase Stability in a Ti/Nb multilayer. An outcome of this model is a new type of Phase Stability diagram that can be used to predict the hcp Ti and bcc Ti Phase Stability as a function of length scale and volume fraction. The Ti layers were subsequently alloyed with a bcc-stabilizing element. The alloyed sputtered deposited Ti layers were able to stabilize the bcc Ti Phase to a larger layer thickness as compared to the unalloyed Ti/Nb multilayers. The percentage of alloying element added to the Ti layer in controlling the critical transition thickness between the two Phase states had good agreement with the predictions proposed by the thermodynamic model.
Quanlin Liu - One of the best experts on this subject based on the ideXlab platform.
-
Tolerance Factor and Phase Stability of the Normal Spinel Structure
Crystal Growth & Design, 2020Co-Authors: Zhen Song, Quanlin LiuAbstract:Tolerance factor for the normal-spinel structure is introduced as a structural descriptor to predict the Phase Stability. It is derived following similar principles as those of perovskite and garne...
-
Tolerance factor and Phase Stability of the garnet structure.
Acta Crystallographica Section C Structural Chemistry, 2019Co-Authors: Zhen Song, Dandan Zhou, Quanlin LiuAbstract:We introduce a structural descriptor, the tolerance factor, for the prediction and systematic description of the Phase Stability with the garnet structure. Like the tolerance factor widely adopted for the perovskite structure, it is a compositional parameter derived from the geometrical relationship between multi-type polyhedra in the garnet structure, and the calculation only needs the information of the ionic radius. A survey of the tolerance factor over 130 garnet-type compounds reveals that the data points are scattered in a narrow range. The tolerance factor is helpful in understanding the crystal chemistry of some garnet-type compounds and could serve as a guide for predicting the Stability of the garnet Phase. The correlation between the tolerance factor and the garnet-Phase Stability could be utilized by machine learning or high-throughput screening methods in material design and discovery.
James Z. Hua - One of the best experts on this subject based on the ideXlab platform.
-
Reliable computation of Phase Stability using interval analysis : Cubic equation of state models
Computers & Chemical Engineering, 1998Co-Authors: James Z. Hua, Joan F. Brennecke, Mark A. StadtherrAbstract:The reliable prediction of Phase Stability is a challenging computational problem in chemical process simulation, optimization and design. The Phase Stability problem can be formulated either as a minimization problem or as an equivalent nonlinear equation solving problem. Conventional solution methods are initialization dependent, and may fail by converging to trivial or non-physical solutions or to a point that is a local but not global minimum. Thus there has been considerable recent interest in developing more reliable techniques for Stability analysis. In this paper we demonstrate, using cubic equation of state models, a technique that can solve the Phase Stability problem with complete reliability. The technique, which is based on interval analysis, is initialization independent, and if properly implemented provides a mathematical guarantee that the correct solution to the Phase Stability problem has been found.
-
Enhanced Interval Analysis for Phase Stability: Cubic Equation of State Models
Industrial & Engineering Chemistry Research, 1998Co-Authors: James Z. Hua, Joan F. Brennecke, Mark A. StadtherrAbstract:The reliable prediction of Phase Stability is a challenging computational problem in chemical process simulation, optimization, and design. The Phase Stability problem can be formulated either as a minimization problem or as an equivalent nonlinear equation-solving problem. Conventional solution methods are initialization dependent and may fail by converging to trivial or nonphysical solutions or to a point that is a local but not a global minimum. Thus, there has been considerable recent interest in developing more reliable techniques for Stability analysis. Recently, the authors have demonstrated, using cubic equation of state models, a technique that can solve the Phase Stability problem with complete reliability. The technique, which is based on interval analysis, is initialization independent and, if properly implemented, provides a mathematical guarantee that the correct solution to the Phase Stability problem has been found. However, there is much room for improvement in the computational efficiency of the technique. In this paper, the authors consider two means of enhancing the efficiency of the method, both based on sharpening the range of interval function evaluations. Results indicate that, by using the enhanced method, computation times can be reduced by nearly an order of magnitude in some cases.
-
Reliable prediction of Phase Stability using an interval Newton method
Fluid Phase Equilibria, 1996Co-Authors: James Z. Hua, Joan F. Brennecke, Mark A. StadtherrAbstract:Abstract A key step in Phase equilibrium calculations is determining if, in fact, multiple Phases are present. Reliably solving the Phase Stability and, ultimately the Phase equilibrium problem, is a significant challenge for high pressure vapor/liquid, liquid/liquid and vapor/liquid/liquid equilibrium. We present the first general-purpose computational method, applicable to any arbitrary equation of state or activity coefficient model, that can mathematically guarantee a correct solution to the Phase Stability problem. In this paper, we demonstrate the use of this new method, which uses techniques from interval mathematics, for the van der Waals equation of state to determine liquid/liquid and liquid/vapor Phase Stability for a variety of representative systems. Specifically, we describe and test interval methods for Phase Stability computations for binary mixtures that exhibit Type I and Type II behavior, as well as for a relatively simple ternary mixture. This shows that interval techniques can find with absolute certainy all stationary points, and thus solve the Phase Stability problem with complete reliability.
Gregory B. Thompson - One of the best experts on this subject based on the ideXlab platform.
-
Tuning Phase Stability in nanocomposite multilayers
Applied Physics Letters, 2003Co-Authors: Gregory B. Thompson, R. Banerjee, Hamish L. FraserAbstract:As thin-film layers in a multilayered stack are reduced in thickness, changes in Phase Stability can result within the individual layers. These changes in Phase are expected to have a significant influence upon the functional properties of the nanostructured composite. The ability to engineer, or tune, Phase Stability at this nanometer length scale is of significant importance in order to maximize the functional properties of these materials. We report the prediction and experimental conformation of tuning the hcp to bcc Phase Stability in Ti for Ti/Nb multilayered nanocomposites. The prediction was based upon selective alloying of Ti with a bcc β stabilizing element using a new form of a thermodynamic Phase diagram for predicting Phase Stability in thin-film multilayers.
-
Predicting Polymorphic Phase Stability in Multilayered Thin Films
2003Co-Authors: Gregory B. ThompsonAbstract:As individual thin film layers in a multilayered stack are reduced in thickness, polymorphic Phase transitions can result in which a Phase not observed in the standard state is stabilized. These pseudomorphic Phases are often serendipitously discovered in the laboratory. A classical thermodynamic model will be presented that can be used in the prediction of polymorphic Phase Stability in multilayered thin films. An outcome of the model is a new type of Phase Stability diagram, referred to as the biPhase diagram, which can predict pseudomorphic Phase Stability as a function of length scale and volume fraction. The model has been successfully applied in the prediction and confirmation of hexagonal closed packed (hcp) to body centered cubic (bcc) Phase Stability changes in Zr and Ti for Zr/Nb and Ti/Nb multilayered thin films, respectively. Modeling of the hcp to bcc interfacial energy reduction upon transformation has been coupled to the classical thermodynamic predictions. Additionally, the classical thermodynamic model predicted a novel bcc to hcp Nb Phase transformation for each multilayer system. Unlike Zr and Ti that undergo an allotropic Phase transformation from hcp to bcc at elevated temperatures, no such equilibrium Phase transition is reported for bcc to hcp Nb. X-ray and electron diffraction techniques have been used to identify these changes in Phase Stability. The compositional structure of the hcp to bcc Phase Stability in Ti for Ti/Nb will further be addressed in terms of Atom Probe Tomography results. Dr. Gregory Thompson is currently an assistant professor in the Department of Metallurgical and Materials Engineering at the University of Alabama. Prior to joining the department in August of 2003, Dr. Thompson was a Post-Doctoral Fellow for the Center for the Accelerated Maturation of Materials (CAMM) at The Ohio State University in Columbus, OH. Dr. Thompson’s research emphasis is in the processing, Phase Stability, and functional properties of nanoscaled materials. He received his Ph.D. and M.S. degrees from the Department of Materials Science and Engineering at The Ohio State University in 2003 and 1998 respectively. Previous to his doctoral degree, Dr. Thompson worked as a process engineer for the Southeast Regional Coating Center of Ion Bond, Inc. in Greenville, S.C. He holds a B.S. degree in physics with a minor in mathematics from Brigham Young University in Provo, UT.
-
A Thermodynamic Approach in Tuning Phase Stability in Nanocomposite Multilayers
MRS Proceedings, 2003Co-Authors: Gregory B. Thompson, R. Banerjee, Hamish L. FraserAbstract:ABSTRACTChanges in the crystallographic Phase Stability of individual layers in a multilayered thin film stack are expected to have a significant influence upon the functional properties of the structure. The ability to predict and tune these Phase Stability states is of relevant importance in order to maximize the functional properties of the multilayer. A classical thermodynamic methodology, based upon competitive volumetric and interfacial free energies, has been used in the prediction and subsequent confirmation of the hcp to bcc Phase Stability in a Ti/Nb multilayer. An outcome of this model is a new type of Phase Stability diagram that can be used to predict the hcp Ti and bcc Ti Phase Stability as a function of length scale and volume fraction. The Ti layers were subsequently alloyed with a bcc-stabilizing element. The alloyed sputtered deposited Ti layers were able to stabilize the bcc Ti Phase to a larger layer thickness as compared to the unalloyed Ti/Nb multilayers. The percentage of alloying element added to the Ti layer in controlling the critical transition thickness between the two Phase states had good agreement with the predictions proposed by the thermodynamic model.
