Aimen E. Gheribi

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• phd
• Senior Researcher at 5N Plus inc.

In recent years, there has been a renewed interest in accurately quantifying the ion’s transference number within molten salts. Surprisingly, despite efforts to address the severe lack of experimental data, there is still no reliable theoretical framework that establishes a clear link between the transference number and simulated phase trajectories...

This work introduces \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\textsf{solar }$$\end{document}, a collection of ten optimization problem instances for benchmarkin...

Contrary to the solid state, the understanding of thermal transport within molten salts remains limited. This study aims at establishing a robust theoretical framework for describing and predicting thermal transport in complex and dissociated multicomponent molten salt mixtures, considering both the composition and temperature variables. The propos...

This work introduces solar, a collection of ten optimization problem instances for benchmarking blackbox optimization solvers. The instances present different design aspects of a concentrated solar power plant simulated by blackbox numerical models. The type of variables (discrete or continuous), dimensionality, and number and types of constraints...

This work introduces solar, a collection of ten optimization problem instances for benchmarking blackbox optimization solvers.The instances present different design aspects of a concentrated solar power plant simulated by blackbox numerical models.The type of variables (discrete or continuous), dimensionality, and number and types of constraints (i...

Synthesis and characterization of (Al,Si) 3 (Zr,Ti)-D0 22 /D0 23 intermetallics: Understanding the stability of silicon substitution Please cite this article as: J.-R. Castillo-Sánchez, G. Salloum-Abou-Jaoude, A.E. Gheribi et al., Synthesis and characterization of (Al,Si) 3 (Zr,Ti)-D0 22 /D0 23 intermetallics: Understanding the stability of silicon...

We present in this work a new formalism for the rapid and accurate evaluation of the thermodynamic properties of compounds and solid solution end-members which are required in the high-throughput computational thermochemistry discovery of new materials. The method is based on the Debye approximation and is fully thermodynamically self-consistent. I...

This study presents a theoretical model, based on kinetic theory, for accurately predicting thermal conductivity in molten salt mixtures, a vital factor in designing advanced energy systems such as concentrating solar power, thermal energy storage, and advanced nuclear reactors. Applicable to non-complex, non-reciprocal systems, the model represent...

Aluminum alloys commonly contain Si as an impurity or alloying element. The energetic behavior of Si within multiple compounds and solutions is incorporated inside thermochemical packages, such as FactSage. This tool allows determining the Si partitioning within complex multiphasic systems. Recent experimental research suggests that Si can be found...

In Hall–Héroult cells the uninvolved alumina precipitates on the top of the cathode to form resistive deposits which could significantly impact the energy consumption. A dynamic energy conservation (DEC) approach has been developed to quantify the flux of undissolved alumina piercing the interface between the electrolyte and the liquid metal in Hal...

A theoretical model for predicting the temperature-dependent thermal conductivity of pure molten salts, both simple and complex, is presented. The model is based on kinetic theory and incorporates Einstein’s concept of minimum thermal conductivity. The proposed formulation can consider the magnitude of thermal conductivity for separate salts, inclu...

Classical molecular dynamics simulations of metallic systems have been extensively applied in recent years for the exploration of the energetic behavior of mesoscale structures and for the generation of thermodynamic...

Thermal diffusivity Microstructural parameter Multiscale model Intraparticle porosity Interparticle porosity Grain size Measurement Transient hot plate Thermal quadrupole method Inverse problems X-Ray tomography Scanning electron microscopy Theoretical model Percolation theory a b s t r a c t This study deals with the effective thermal conductivity...

In Hall-Héroult cells the uninvolved alumina precipitates on the top of the cathode tp form resistive deposit which could significantly impact the energy consumption. A dynamic energy conservation (DEC) approach has been developed to quantify the flux of undissolved alumina piercing the interface between the electrolyte and the liquid metal in Hall...

An accurate knowledge of the interfacial tension between liquid aluminium and cryolitic melts is critical to better understand the process parameters influencing the current efficiency in electrolysis cells. In principle, the interfacial tension can be predicted from the surface tension of liquid aluminium, cryolitic melts and their adhesion energy...

Because of its easy implementation and flexibility, the quasiharmonic approximation (QHA) method is widely used to describe the Gibbs energy of stoichiometric compounds. Attempts to modify or extend the QHA formalism have recently been proposed in order to overcome its several limitations. The aim of this work is to propose an alternative and origi...

An original theoretical model that can predict the temperature-dependent thermal conductivity for pure molten salts that are both simple and complex is proposed. The model is derived from kinetic theory and implements the Einstein's concept of minimum thermal conductivity. The proposed formulation can separately consider the magnitude of thermal di...

Multi-component and multiphasic materials are continually being developed for electronics, aircraft, automotive, and general applications. Integrated Computational Materials Engineering (ICME) is a multiple-length scale approach that greatly benefits from atomistic scale simulations to explore new alloys. Molecular Dynamics (MD) allows to perform l...

La conductivité thermique effective de lits de poudres dépend d'un nombre important de paramètres. Dans cet article est présentée l'influence apparente de la taille des grains et de leurs géométries sur ce paramètre du milieu, en s'appuyant sur un modèle de conductivité thermique de milieux poreux non-connectés dans l'air à pression atmosphérique,...

Molten salts are being proposed for numerous advanced energy applications, including advanced nuclear reactors, concentrating solar power plants, thermal energy storage, and fusion reactors. Accurate knowledge of the thermophysical properties of molten salts directly impact the performance of these energy systems and are essential for design and sa...

Among all the properties required for the design of the next generation of phase change materials (PCMs) (density, heat capacity, thermal expansion, latent energy, volume change upon melting, corrosion rate, etc.) the thermal transport properties are by far the least known, especially for molten salt mixtures and solid solutions. We present in this...

The next generations of Concentrated Solar Thermal Power (CSTP) systems use anhydrous salts as the heat transfer fluid and thermal storage medium. Unfortunately, a severe lack of experimental data is observed for the thermal transport properties of molten salt mixtures, generating constraints in exploring new potential materials for CSTP systems. T...

Among all the properties required for the design of the next generation of PCM (density, heat capacity, thermal expansion, latent energy, volume change upon melting, corrosion rate, etc.) the thermal transport properties are by far the least known, especially for molten salt mixtures and solid solutions. We present in this paper a theoretical frame...

This article reviews blackbox optimization applications of direct search optimization methods over the past twenty years. Emphasis is placed on the Mesh Adaptive Direct Search (Mads) derivative-free optimization algorithm. The main focus is on applications in three specific fields: energy, materials science, and computational engineering design. Ne...

The structural, thermochemical, and thermophysical properties of the NaF–ThF4 fuel system were studied with experimental methods and molecular dynamics (MD) simulations. Equilibrium MD (EMD) simulations using the polarizable ion model were performed to calculate the density, molar volume, thermal expansion, mixing enthalpy, heat capacity, and distr...

The short-range structures of LiF-ThF4, NaF-AnF4, KF-AnF4, and Cs-AnF4 (An = Th, U), were probed using in situ high temperature Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. Signally, the EXAFS spectra of pure molten ThF4 and UF4 were measured for the first time. The data were interpreted with the aid of Molecular Dynamics (MD) and...

LiF-UF4 is a key binary system for molten fluoride reactor technology, which has not been scrutinized as thoroughly as the closely related LiF-ThF4 system. The phase diagram equilibria in the system LiF-UF4 are explored in this work with X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The short-range ordering in the molten salt...

Contrary to the ionic conductivity, the electronic conductivity of cryolitic melts, which can be up to 30 pct of the total conductivity in industrial electrolysis cells, remains largely unknown as very few experimental data are reported in the literature. The aim of this work is to fill this gap by providing reliable estimations of the electronic c...

The discovery of new metallic materials is of prime importance for the development of new technologies in many fields such as electronics, aerial and ground transportation as well as construction. These materials require metals which are obtained from various pyrometallurgical processes. Moreover, these materials need to be synthesized under extrem...

Phosphorus is known to be a strongly segregating element in steel; even small amounts influence the solidification phenomena and product quality during casting processes. In order to provide an accurate prediction tool for process control in steelmaking, a CALPHAD-type thermodynamic optimization of the Fe–C–P system was performed including modeling...

Thermodynamic models of solid solutions used in computational thermochemistry have not been modernized in recent years. With the advent of fast and cheap computers, it is nowadays possible to add, at a minimal computational cost, physical ingredients such as coordination numbers, inter-atomic distances and classical interatomic potentials to the fu...

An accurate knowledge of the electrical properties of molten salts and slags is important for the design, optimization and control of several electrochemical processes. The electrical conductivity of molten salts and slags is in principle of ionic nature, however when metals are dissolved in electrolyte electrons may also contribute to the electric...

The charge and electron transport properties of molten ionic systems are among the most relevant properties to consider in the control of several electrochemical processes. First-principles\revadd{-based} equilibrium molecular dynamics (EMD) can provide reliable predictions of both the total and partial charge transport properties. \revadd{In this...

Thermal Energy Storage (TES) systems coupled to thermodynamic power cycles capable of generating electrical work are becoming strategic technologies of the future. The efficiency of TES fluids is a function of several thermodynamic and physical properties such as their heat capacity, latent enthalpy of melting and thermal conductivity. The stored t...

Due to the important similarities between olivine-LiFePO4 and olivine-LiMnPO4, manganese doping has drawn a lot of attention since it can improve the electronic and ionic conductivity of LiFePO4, hence enhance the electrochemical properties. The thermodynamic behavior of Mn-doped-LiFePO4 cathodes has been examined through the thermodynamic investig...

In aluminium reduction cells, an electrochemical reaction occurs between the molten electrolyte film below the aluminium pad and the carbon cathode blocks, leading to the formation of an Al4C3 layer on the cathode blocks. The properties and role of this Al4C3 layer are therefore important for the aluminium production industry, as they could help in...

The (Li,Be)Fx fluoride salt is an ionic liquid with complex non-ideal thermodynamic behaviour due to the formation of short-range order. In this work, we explore the relationship between local structure, thermo-physical and thermodynamic properties in this system using a multidisciplinary approach that couples molecular dynamics simulations using t...

Experimental surface tension data for many binary, ternary and higher order metallic systems is unfortunately currently unavailable in the literature. This could be detrimental in several practical and industrial applications. Consequently, having a theoretical model with a good predictive capability is highly desirable. In general, the surface ten...

Knowing the charge-transport properties of molten oxides is essential for industrial applications, particularly when attempting to control the energy required to separate a metal from its ore concentrate. Nowadays, in the context of a drastic increase of computational resources, research in industrial process simulation and their optimization is ga...

An accurate knowledge of the surface tension of liquid metals is critical for many theoretical and practical applications, especially in the current context of emerging growth of nanotechnology. The surface tension and its temperature dependence are drastically influenced by the level of impurities in the metal such as oxygen, sulphur or carbon. Fo...

In many metallurgical applications, an accurate knowledge of miscibility gaps and spinodal decompositions is highly desirable. Some binary systems where the main constituents of the same crystal structures have similar lattice parameters (less than 15 % difference) reveal a composition, temperature shift of the miscibility gap due to lattice cohere...

Not all carbons graphitize in equal measure. Some will develop a structure which approaches the one of perfect graphite (graphitizable carbons)upon heat treatment, while others will not (non-graphitizable carbons). The present work develops a phenomenological model for the conceptual understanding of graphitizability (capacity to graphitize). To su...

The surface tension of liquid metals depends strongly on atmosphere conditions, in particular on the partial pressure of oxygen, on top of temperature. Predicting the surface tension of metals in different atmosphere conditions is highly desirable for many fundamental and practical applications. Currently, none of the theoretical and semi-empirical...

The development at the Delft University of Technology (TU Delft, The Netherlands) of an experimental set-up dedicated to high-temperature in situ EXAFS measurements of radioactive, air-sensitive and corrosive fluoride salts is reported. A detailed description of the sample containment cell, of the furnace design, and of the measurement geometry all...

A thermodynamic model for the FePO4‐LiFePO4 olivine join has been developed in order to provide support for the understanding of the charge transport behaviour within the cathode material during the battery operation. The Gibbs energy model for the olivine solution is based on the compound energy formalism with long‐range‐order and has been calibra...

The effect of coherent strains which is involved during the fast charge/discharge processes and the influence of particle size reduction which improves the electrochemical performance of the cathode material are modelled in this study. An extension of the linear isotropic approximation for elastic energy stored in the coherent boundaries of an orth...

In an attempt to identify new low-cost metallic materials with interesting thermo-physical properties from the Fe-Cr-Mn-Ni-V-Ti-Al- (Co-Mo) system, we present here an original tool for the design of first-generation High Entropy Alloys (HEAs). The composition of potential HEAs is calculated under a set of non-smooth and non-linear constraints and m...

Molten cryolite mixed with some additives is used as solvent of alumina by aluminium producers. Cryolite represents the dominating compounds in the wall protecting side-ledge and at the bottom part of the frozen crust on the top of the cells. As the heat, generated in the cell, is lost mainly through the top and the lateral sides of the pot, the th...

The aim of this work is a formulation of a thermodynamic model for the development of new aluminum machining alloys. The three additives Bi, Pb and Sn have proven to help machining. Hence, a review of the literature showed that the liquid phase equilibria and thermodynamic data for the three binary systems Al-Bi, Al-Pb and Al-Sn is very thorough bu...

The present work describes the application of a recently developed Calculation of Phase Diagrams (CALPHAD) method to perform condensed-phase thermochemical equilibrium calculations of Chapman–Jouguet (CJ) detonation properties for a number of new mixtures speculated to support gasless detonation. Mixtures in question are titanium–silicon (Ti–Si), t...

Individual transport numbers provide a measure of the charge ratio which is carried by each ionic species of an electrolyte. However, unlike the electrical conductivity or diffusion coefficients, this quantity lacks a clear definition from the statistical mechanics point of view. In practice, it is measured via complex experimental setups, and most...

The present paper develops a thermodynamic model for the calculation of the Gibbs energy of graphitizable carbons near the graphitization temperature threshold of 2550K. The graphitization threshold is the minimal heat treatment temperature for the establishment of true graphitic ordering in a graphitizable carbon. The present model represents the...

An electrothermodynamic model is proposed for the carbon anode consumption of the aluminium electrolysis process. Anode consumption produces a primary anode gas composed of CO and CO2. Experimentally, higher electrolysis potentials at the bath/anode interface promotes the formation of CO2 over CO, reducing the carbon consumption at the cost of grea...

This paper presents a database for the temperature-dependent thermal conductivity of compounds potentially present in the side ledge formed in aluminium electrolysis cells, between the molten electrolyte used to dissolve the alumina and the side wall. The database is given in the form of an analytical model with sets of parameters for each compound...

In aluminum electrolysis cells, a ledge of frozen electrolyte is formed on the sides. Controlling the side ledge thickness (a few centimeters) is essential to maintain a reasonable life span of the electrolysis cell, as the ledge acts as a protective layer against chemical attacks from the electrolyte bath used to dissolve alumina. The numerical mo...

During aluminiumelectrolysis, a ledge of frozen electrolytes is generally formed, attached to the sides of the cells. This ledge acts as a protective layer, preventing erosion and chemical attacks of both the electrolyte melt and the liquid aluminium on the side wall materials. The control of the sideledge thickness is thus essential in ensuring a...

It has been already shown that the density functional theory (DFT) combined with the quasi-harmonic approximation (QHA) overestimates the specific heat capacity (and in general the thermal properties) of fcc metals. DFT + QHA seemingly shows a large anharmonic contribution to the heat capacity. However, in this article we show that this anharmonici...

Numerical modeling of heat transport in the side ledge of a cryolite bath as a function of its thickness requires an accurate knowledge of the thermal transport properties of the cryolite bath as well as the solid phases constituting the side ledge. Unfortunately, due to experimental limitations, there is a lack of experimental data on this subject...

In aluminium electrolysis cells, a ledge of frozen electrolyte is formed, attached to the sides of the cell. The control of the side ledge thickness is essential in ensuring a reasonable lifetime for the cells. Numerical modelling of the side ledge thickness requires an accurate knowledge of the thermal transport properties as a function of tempera...

A new thermodynamically self-consistent (TSC) method, based on the quasi-harmonic approximation (QHA), is used to obtain the Debye temperatures of LiFePO4 (LFP) and FePO4 (FP) from available experimental specific heat capacities for a wide temperature range. The calculated Debye temperatures show an interesting critical and peculiar behavior so tha...

The FactSage computer package consists of a series of information, calculation and manipulation modules that enable one to access and manipulate compound and solution databases. With the various modules running under Microsoft Windows® one can perform a wide variety of thermochemical calculations and generate tables, graphs and figures of interest...

How graphitic structures evolve from non-graphitic carbons, during heat treatment, is conceptually understood through the graphitization mechanisms of the turbostratic model. However, inadequacies exist, most notably concerning the temperature behaviour of the intercrystalline carbon material located between turbostratic crystallites. Previous ther...

The FactSage computer package consists of a series of information, calculation and manipulation modules that enable one to access and manipulate compound and solution databases. With the various modules running under Microsoft Windows® one can perform a wide variety of thermochemical calculations and generate tables, graphs and figures of interest...

The thermal diffusivity of Cu-W sintered alloys microstructures is measured at room temperature at different compositions, using rear face flash experiments. The samples are synthesized with the Spark Plasma Sintering technique. The resulting microstructures are slightly porous and consist of angular nanoscale grains of tungsten with medium spheric...

Introduction LiFePO 4 (LFP) was proposed by Padhi et al. ¹ in 1997 as a promising cathode material for Li-ion batteries and very soon became the center of attention for researchers and industries in energy fields. Nowadays, it is commercialized and available in mass production through different methods. A lot of improvements in terms of material an...

This work describes the application of a direct search method to the optimization of problems of real industrial interest, namely three new material science applications designed with the FactSage software. The search method is BiMADS, the biobjective version of the mesh adaptive direct search (MADS) algorithm, designed for blackbox optimization. W...

In this study, density functional theory (DFT) with a thermodynamically self-consistent (TSC) method are used to predict the thermophysical properties of metallic compounds. The TSC method used in this work is, in summary, an extension of the classical quasi-harmonic approximation satisfying the Maxwell relations and thus ensuring thermodynamic con...

A theoretical model for the description of thermal conductivity of molten salt mixtures as a function of composition and temperature is presented. The model is derived by considering the classical kinetic theory and requires, for its parametrization, only information on thermal conductivity of pure compounds. In this sense, the model is predictive....

A structural molar volume model based on the silicate tetrahedral Q-species has been developed to accurately predict the molar volume of molten oxides. In this study, the molar volumes of ternary and multicomponent melts in the Li2O-Na2O-K2O-MgO-CaO-MnO-PbO-Al2O3-SiO2 system are reviewed and compared with the predicted molar volumes from the newly...

As part III of this series, the model is extended to iron oxide-containing melts. All available experimental data in the FeO-Fe2O3-Na2O-K2O-MgO-CaO-MnO-Al2O3-SiO2 system were critically evaluated based on the experimental condition. The variations of FeO and Fe2O3 in the melts were taken into account by using FactSage to calculate the Fe2+/Fe3+ dis...

A structural molar volume model was developed to accurately reproduce the molar volume of molten oxides. As the non-linearity of molar volume is related to the change in structure of molten oxides, the silicate tetrahedral Q-species, calculated from the modified quasichemical model with an optimized thermodynamic database, were used as basic struct...

The quasi-harmonic approximation (QHA) model is often used nowadays for prediction of the thermodynamic properties of materials subjected to high pressures and temperatures. However, QHA is not accurate enough in many cases and, as shown in this work, it is not thermodynamically consistent because it leads to violations of the Maxwell relations. Th...

A method for the prediction of the thermal transport properties of macroscopic and isotropic oxides systems, above the standard temperature of T = 298.15 K , is presented. This method combines: (i) the kinetic theory, (ii) a thermodynamically self consistent method for the density of the lattice vibration energy, and (iii) the three-phonon umkl...

Rear face flash experiments were performed in order to determine the thermal conductivity of sintered tungsten at room temperature. Ten different samples were synthesized with the spark plasma sintering technique. The microstructure obtained from the sintering is porous and consists of angular grains with medium sphericity. The average grain size (...

Instead of performing expensive experiments, it is common in industry to make predictions of important material properties based on some existing experimental results. Databases consisting of experimental observations are widely used in the field of Material Science Engineering. However, these databases are expected to be noisy since they rely on h...

The development is presented of a model of the thermodynamic functions of enthalpy, entropy and Gibbs energy for the elements carbon and hydrogen in coke crystallites. It is applicable to varying degrees of graphitization, described by the crystallite length La and the crystallite height Lc. The model parameters are derived from known properties su...

We propose a new approach to parameterizing the Gibbs energy of a multicomponent solution as a function of temperature, pressure and composition. It uses the quasichemical model in the second nearest neighbour approximation and considers both a polynomial representation (for low pressure) and an exponential decay representation (for moderate-to-hig...

The composition dependence of thermal transport properties of the (Na,K)Cl rocksalt solid solution is investigated through equilibrium molecular dynamics (EMD) simulations in the entire range of composition and the results are compared with experiments published in recent work [Gheribi et al., J. Chem. phys. 141, 104508 (2014)]. The thermal diffusi...

Changes in the quality of green cokes available for the production of pre-baked carbon anodes used in the production of aluminum are stimulating the development of a better understanding of the thermodynamic behavior of cokes. Impurity content and crystallite sizes (over a wide range of temperature) are of particular concern. No thermodynamic model...

The present paper describes a theoretical method of examining thermodynamic equilibrium detonation states for reactions producing little or no gaseous products. Calculation of Phase Diagram (CALPHAD) techniques are used to calculate the thermodynamic states of the condensed-phase reaction at ambient conditions, and an analytical shock physics appro...

Changes in the quality of green cokes available for the production of pre-baked carbon anodes used in the production of aluminum are stimulating the development of a better understanding of the thermodynamic behavior of cokes. Impurity content and crystallite sizes (over a wide range of temperature) are of particular concern. No thermodynamic model...

We present two theoretical models to predict the lattice thermal conductivity degradation of insulating materials at high temperature (above one-third of the Debye temperature). This degradation is due to the presence of grains, with known sizes and shapes, inducing thermal resistance at their boundaries. The first model is derived directly from th...

The composition dependence of the lattice thermal conductivity in NaCl-KCl solid solutions has been measured as a function of composition and temperature. Samples with systematically varied compositions were prepared and the laser flash technique was used to determine the thermal diffusivity from 373 K to 823 K. A theoretical model, based on the De...

Gaussian process regression (GPR) is a non-parametric approach that can be used to make predictions based on a set of known points. It has been widely employed in recent years on a variety of problems. However the Gaussian process regression algorithm performs matrices inversions and the computational time can be extensive when accessing large trai...

A model for the prediction of the thermal conductivity of molten alkali and alkaline earth salts is proposed. The model is a function of simple thermophysical properties of salts. The parameters required in the calculations are density, heat capacity, velocity of sound and melting temperature. Predictions are in good agreement with reliable experim...

In this paper, using both experimental data and theoretical modelling, we investigate the degradation of the thermal conductivity of sintered metals due simultaneously to the grain boundary thermal resistance and the porosity. We show that the porosity dependence of the thermal conductivity of sintered material from spherical particle powder, exhib...

Molten fluorides are known to show favorable thermophysical properties which make them good candidate coolants for nuclear fission reactors. Here we investigate the special case of mixtures of lithium fluoride and thorium fluoride, which act both as coolant and fuel in the molten salt fast reactor concept. By using ab initio parameterized polarizab...

The FactSage® package consists of a series of information, database and calculation modules that enable one to access pure substances and solution databases and perform thermochemical equilibrium calculations. FactSage was originally founded by process pyrometallurgists and has since expanded its applications to include hydrometallurgy, electrometa...

The complete Mn–Nd phase diagram was established experimentally by means of key samples and diffusion couple techniques. The phase transformation temperatures, crystal structures and phase equilibria were studied using differential scanning calorimetry (DSC), X-ray diffraction (XRD), electron probe microanalysis (EPMA), and scanning electron micros...