Patrick Ganster - Academia.edu (original) (raw)

Papers by Patrick Ganster

arXiv (Cornell University), Jul 31, 2012

Oxidization of a dilute Si(Ge) alloy is modeled using an original protocol based on molecular dyn... more Oxidization of a dilute Si(Ge) alloy is modeled using an original protocol based on molecular dynamics simulation and rules for the oxygen insertions. These rules, deduced from ab-initio calculations, favor the formation of SiO 2 against GeO 2 oxide which leads to segregation of Ge atoms into the alloy during the oxidization front advance. Ge condensation is then observed close to the SiO 2 /Ge interface due to the strain induced by oxydization in this region. From the analysis of the simulation process, we propose a onedimensional description of Ge condensation wich perfectly reproduces the evolution of the Ge concentration during oxidization of the SiGe alloy.

Journal of Chemical Physics, Jun 1, 2004

We study a calcium aluminosilicate glass of composition (SiO 2) 0.67-(Al 2 O 3) 0.12-(CaO) 0.21 b... more We study a calcium aluminosilicate glass of composition (SiO 2) 0.67-(Al 2 O 3) 0.12-(CaO) 0.21 by means of molecular-dynamics (MD) simulations, using a potential made of two-body and threebody interactions. In order to prepare small samples that can subsequently be studied by firstprinciples, the finite size effects on the liquid dynamics and on the glass structural properties are investigated. We find that finite size effects affect the Si-O-Si and Si-O-Al angular distributions, the first peaks of the Si-O, Al-O and Ca-O pair correlation functions, the Ca coordination and the oxygen atoms environment in the smallest system (100 atoms). We give evidence that these finite size effects can be directly attributed to the use of three-body interactions.

Journal of the American Ceramic Society, Jan 19, 2023

Microwave heating of pure alumina is studied experimentally and numerically, in a 2.45 GHz single... more Microwave heating of pure alumina is studied experimentally and numerically, in a 2.45 GHz single‐mode cavity, for different density levels. Even considering a constant incident power, the results show a complex evolution of the alumina temperature: first a two‐step increase, then a maximum, and finally a cooling stage. In addition, a density dependence of the heating efficiency is observed: a more efficient heating occurs for lower densities. Using the effective medium approximation (EMA) to derive the physical data as functions of density, the numerical simulations are in contradiction with the experiments, proving that the EMA approach is not able to correctly predict the imaginary part of the permittivity. Furthermore, the simulations do not accurately describe the first moments of the heating, nor the long‐term evolution of the temperature (cooling). We then explain the origin of this discrepancy: the need to adjust the movable stub on the one hand, and to account for heat exchange between the cavity and its surroundings on the other.

MRS Advances, Feb 29, 2016

Using molecular statics calculations, sodium silicate glasses are expanded in an isotropic manner... more Using molecular statics calculations, sodium silicate glasses are expanded in an isotropic manner to analyze the composition dependence of the mechanical response. Increasing the amount of sodium makes the systems more ductile. The tensile strength is reduced and the final load bearing strain limit is increased. Hydrostatic strain hardening appears in the ductile samples. To explain this phenomena, the density is coarse-grained to identify microscopic defects. In samples containing a significant amount of sodium, a large amount of nano-voids appear before reaching the maximum load bearing capacity. In high sodium content silicates these cracks may cause the hardening observed in the pressure results. In samples with low sodium content, the failure is abrupt and only a large crack is observed. Increasing the amount of long term but weaker Na-O interactions, instead of the short range Si-O ones could explain the observed transition.

Physical Review B, Aug 2, 2012

Using the ART NOUVEAU method, we study the initial stages of silicon oxide formation. After valid... more Using the ART NOUVEAU method, we study the initial stages of silicon oxide formation. After validating the method's parameters with the characterization of point defects diffusion mechanisms in pure Stillinger-Weber silicon, which allows us to recover some known results and to detail vacancy and self-interstitial diffusion paths, the method is applied onto a system composed of an oxygen layer deposited on a silicon substrate. We observe the oxygen atoms as they move rapidly into the substrate. From these ART NOUVEAU simulations, we extract the energy barriers of elementary mechanisms involving oxygen atoms and leading to the formation of an amorphouslike silicon oxide. We show that the kinetics of formation can be understood in terms of the energy barriers between various coordination environments.

Physical review, Apr 14, 2017

The elastoplastic behavior of sodium silicate glasses is studied at different scales as a functio... more The elastoplastic behavior of sodium silicate glasses is studied at different scales as a function of composition and pressure, with the help of quasistatic atomistic simulations. The samples are first compressed and then sheared at constant pressure to calculate yield strength and permanent plastic deformations. Changes occurring in the global response are then compared to the analysis of local plastic rearrangements and strain heterogeneities. It is shown that the plastic response results from the succession of well-identified localized irreversible deformations occurring in a nanometer-size area. The size and the number of these local rearrangements, as well as the amount of internal deviatoric and volumetric plastic deformation, are sensitive to the composition and to the pressure. In the early stages of the deformation, plastic rearrangements are driven by sodium mobility. Consequently, the elastic yield strength decreases when the sodium content increases, and the same when pressure increases. Finally, good correlation was found between global and local stress-strain relationships, reinforcing again the role of sodium ions as local initiators of the plastic behavior observed at larger scales.

Acta Materialia, Jun 1, 2016

Silicate glasses are macroscopically brittle but ductile at the micron scale. This plastic respon... more Silicate glasses are macroscopically brittle but ductile at the micron scale. This plastic response is complex: in open structure materials, such as amorphous silica, plastic yield results in significant densification. While, more compact structures (e.g. soda-silicate glasses) are known to suppress densification and promote shear flow. We have carried out atomic scale simulations to analyze the plastic response of a series of silicates with increasing sodium content. Quasi-static, multi-axial deformation tests were performed on large samples (≈ 10 3 nm 3). Their yield behavior was quantified at different stress states, by measuring permanent volume changes. Qualitative agreement was found between the response of modeled systems and experimental results. Strong coupling between plastic yield and densification was observed. Our results also suggest that sodium silicates may densify not only under hydrostatic compression but also upon shear at large strains. Based on these numerical results, we propose a general yield criterion for soda-silicate glasses in which density is an internal variable. As density increases, the elliptic yield surface (characterizing amorphous silicates with open structures) gradually

Physical Review B, Jan 20, 2010

In this paper, we present a theoretical study of the elastic deformations arising in the vicinity... more In this paper, we present a theoretical study of the elastic deformations arising in the vicinity of the Si/ SiO 2 interface upon oxidation of a silicon substrate. The oxidation is modelized using an algorithm which alternates the inclusion of oxygen atoms and Molecular Dynamics simulations at high temperature. We find that the SiO 2 film undergoes an overall compressive state while a more complex strain field is found in the first few Si layers under the interface where tensile and compressive microstructures coexist, the former being definitely larger than the latter. The analysis of the formation energies of the main defects responsible for Si diffusion reveals that, in spite of the complexity of the deformation field at the Si/ SiO 2 interface, their dependence with respect to the local deformation obeys the same laws as those derived from the application of a simple biaxial stress.

arXiv (Cornell University), Mar 20, 2019

We propose a new statistical physics model to study equilibrium solute segregation at grain bound... more We propose a new statistical physics model to study equilibrium solute segregation at grain boundaries and the resulting embrittlement effect. This low-temperature expansion model is general and efficient, and its parameters can be obtained from atomistic calculations. It is possible to take into account multiple species, multiple segregation sites with different segregation free energies, account for configurational entropy, grain radius and site competition between solutes. As an example, the model is then applied to the study of phosphorus and hydrogen co-segregation at Σ3 109.5° 011 {111} twin boundaries in α-Fe, using energetic parameters from density-functional theory calculations. We show that P-H interactions may lead to increased P segregation at grain boundaries and cause additional embrittlement compared to the case where P and H are considered separately.

2016-Sustainable Industrial Processing Summit, Jun 1, 2016

Even the slightest content of species segregating at the grain boundaries (GBs) of a polycrystall... more Even the slightest content of species segregating at the grain boundaries (GBs) of a polycrystalline material can dramatically change its physical (mechanical, thermal, electrical, optical) features and its lifetime. While some nonmetallic species may improve its mechanical properties, sulfur segregating in nickel GBs yields its embrittlement, when the S-content reaches a critical concentration specific of a ductile-brittle transition [1]. Recent observations of different GBs using the NanoSIMS device revealed that one has to account for the atomic-scale structure of the GB to understand its S content, as different GBs with different orientations display different enrichments [2]. But the expected small thickness of the segregated layers prevent a straightforward observation and requires complementary atomic-scale models. Literature abounds with first-principles computations on the Ni-S, but only very few and specific GBs can be handled for tractability reasons. While many very efficient interatomic potentials can deal with pure metals and metallic alloys, up-to-date only the ReaxFF approach allows to account for Ni-S at the atomic scale [3]. We discuss its use to reach an atomic-scale description of a given GB (chemistry-structure coupling) and the challenges to solve both from computational and experimental developments to describe the interface of Ni-S GBs. [1] J. K. Heuer, P. R. Okamoto, N. Q. Lam and J. F. Stubbins, Applied Physics Letters 76 (23), 3403-3405 (2000) [2] F. Christien, C. Downing, K.L. Moore, C.R.M. Grovenor, Surface and Interface Analysis 44, 377-387 (2012) [3] H.-P. Chen, R. K. Kalia, E. Kaxiras, G. Lu, A. Nakano, K. Nomura, A. C. T. van Duin, P. Vashishta, and Z. Yuan, Phys. Rev. Lett. 104, 155502 (2010)

Journal of the American Ceramic Society

Microwave heating of pure alumina is studied experimentally and numerically, in a 2.45 GHz single... more Microwave heating of pure alumina is studied experimentally and numerically, in a 2.45 GHz single‐mode cavity, for different density levels. Even considering a constant incident power, the results show a complex evolution of the alumina temperature: first a two‐step increase, then a maximum, and finally a cooling stage. In addition, a density dependence of the heating efficiency is observed: a more efficient heating occurs for lower densities. Using the effective medium approximation (EMA) to derive the physical data as functions of density, the numerical simulations are in contradiction with the experiments, proving that the EMA approach is not able to correctly predict the imaginary part of the permittivity. Furthermore, the simulations do not accurately describe the first moments of the heating, nor the long‐term evolution of the temperature (cooling). We then explain the origin of this discrepancy: the need to adjust the movable stub on the one hand, and to account for heat exch...

arXiv (Cornell University), Jul 31, 2012

Oxidization of a dilute Si(Ge) alloy is modeled using an original protocol based on molecular dyn... more Oxidization of a dilute Si(Ge) alloy is modeled using an original protocol based on molecular dynamics simulation and rules for the oxygen insertions. These rules, deduced from ab-initio calculations, favor the formation of SiO 2 against GeO 2 oxide which leads to segregation of Ge atoms into the alloy during the oxidization front advance. Ge condensation is then observed close to the SiO 2 /Ge interface due to the strain induced by oxydization in this region. From the analysis of the simulation process, we propose a onedimensional description of Ge condensation wich perfectly reproduces the evolution of the Ge concentration during oxidization of the SiGe alloy.

Even the slightest content of species segregating at the grain boundaries (GBs) of a polycrystall... more Even the slightest content of species segregating at the grain boundaries (GBs) of a polycrystalline material can dramatically change its physical (mechanical, thermal, electrical, optical) features and its lifetime. While some nonmetallic species may improve its mechanical properties, sulfur segregating in nickel GBs yields its embrittlement, when the S-content reaches a critical concentration specific of a ductile-brittle transition [1]. Recent observations of different GBs using the NanoSIMS device revealed that one has to account for the atomic-scale structure of the GB to understand its S content, as different GBs with different orientations display different enrichments [2]. But the expected small thickness of the segregated layers prevent a straightforward observation and requires complementary atomic-scale models. Literature abounds with first-principles computations on the Ni-S, but only very few and specific GBs can be handled for tractability reasons. While many very effi...

We propose a new method using coarse-graining and molecular dynamics to calculate structural and ... more We propose a new method using coarse-graining and molecular dynamics to calculate structural and mechanical properties for sodium silicate glasses at different scales. Using this method we were able to describe the mechanical behavior of the material, this way a new constitutive model was developed which could be used in continuum calculations.

Journal of the American Ceramic Society, 2020

A comparison between experiment and numerical simulation of microwave heating of a parallelepiped... more A comparison between experiment and numerical simulation of microwave heating of a parallelepipedic silicon carbide (SiC) sample is presented. Using a‐2.45 GHz single‐mode cavity, the evolution of the surface temperature is first experimentally studied for different orientations of the sample. A finite element analysis of this electromagnetic‐thermal coupled problem is then conducted with the COMSOL Multiphysics® software. Despite the different approximations of our model, a good agreement between experimental and numerical results is found, confirming that the heating of SiC depends only on the electric field. The effect of sample orientations and the cavity length on heating is also highlighted and analyzed.

Journal of Alloys and Compounds, 2021

Self-polarized ferrimagnetic nanowires of CoFe2O4 are electrochemically grown by the electrodepos... more Self-polarized ferrimagnetic nanowires of CoFe2O4 are electrochemically grown by the electrodeposition technique in AAO membranes. XRD, EDS and SQUID analysis confirm the formation of highly stoichiometric CoFe2O4 nanowires with high magnetic response into 20 nm-AAO membrane. SEM and AFM images revealed a total filling of the AAO membrane with Co and Fe at an applied potential of-1.2 V. In addition, the electrodeposition and cooling in the presence of an applied magnetic field improve the magnetic response of CoFe2O4 nanowires. The SQUID measurements confirmed the elaboration of CoFe2O4 nanowires with an internal magnetic field of 1.52 T. As a result, this ferrimagnetic nanowired substrate will be suitable for future miniaturized self-biased microwave devices.

Applied Surface Science, 2019

We propose a new statistical physics model to study equilibrium solute segregation at grain bound... more We propose a new statistical physics model to study equilibrium solute segregation at grain boundaries and the resulting embrittlement effect. This low-temperature expansion model is general and efficient, and its parameters can be obtained from atomistic calculations. It is possible to take into account multiple species, multiple segregation sites with different segregation free energies, account for configurational entropy, grain radius and site competition between solutes. As an example, the model is then applied to the study of phosphorus and hydrogen co-segregation at Σ3 109.5° 011 {111} twin boundaries in α-Fe, using energetic parameters from density-functional theory calculations. We show that P-H interactions may lead to increased P segregation at grain boundaries and cause additional embrittlement compared to the case where P and H are considered separately.

Physical Review E, 2017

The elastoplastic behavior of sodium silicate glasses is studied at different scales as a functio... more The elastoplastic behavior of sodium silicate glasses is studied at different scales as a function of composition and pressure, with the help of quasistatic atomistic simulations. The samples are first compressed and then sheared at constant pressure to calculate yield strength and permanent plastic deformations. Changes occurring in the global response are then compared to the analysis of local plastic rearrangements and strain heterogeneities. It is shown that the plastic response results from the succession of well-identified localized irreversible deformations occurring in a nanometer-size area. The size and the number of these local rearrangements, as well as the amount of internal deviatoric and volumetric plastic deformation, are sensitive to the composition and to the pressure. In the early stages of the deformation, plastic rearrangements are driven by sodium mobility. Consequently, the elastic yield strength decreases when the sodium content increases, and the same when pressure increases. Finally, good correlation was found between global and local stress-strain relationships, reinforcing again the role of sodium ions as local initiators of the plastic behavior observed at larger scales.

Surface and Interface Analysis, 2017

An adequate model of quantification when there are many segregating elements is required for indu... more An adequate model of quantification when there are many segregating elements is required for industry and research. Hence, for the first time, surface segregation kinetics on industrial 16MND5 steel was studied by XPS spectroscopy at temperatures ranging from 500 to 600 o C. From measurements that highlight the competitive segregation of P, S, Sn, Sb, As, and Cu impurities at the surface, a quantification model was developed and successfully used to deduce the surface concentrations during segregation kinetics as well as derive the corresponding diffusion coefficients. We observed that phosphorus and sulfur are the first elements covering the surface, then they are supplanted by others' impurities. This result may reflect impurities segregation behavior at the grain boundaries that impacts mechanical behavior of the material. Indeed, to further the research, 16MND5 samples were aged in the same range of temperatures. Then, Auger spectroscopy measurements at grain boundaries were conducted on broken samples exhibiting intergranular cracking. Results show that phosphorus is the only segregating element present at grain boundaries after 2 months of aging. Importantly, it appears that phosphorus grain boundary segregation kinetics is significantly lower than at surface.

arXiv (Cornell University), Jul 31, 2012

Oxidization of a dilute Si(Ge) alloy is modeled using an original protocol based on molecular dyn... more Oxidization of a dilute Si(Ge) alloy is modeled using an original protocol based on molecular dynamics simulation and rules for the oxygen insertions. These rules, deduced from ab-initio calculations, favor the formation of SiO 2 against GeO 2 oxide which leads to segregation of Ge atoms into the alloy during the oxidization front advance. Ge condensation is then observed close to the SiO 2 /Ge interface due to the strain induced by oxydization in this region. From the analysis of the simulation process, we propose a onedimensional description of Ge condensation wich perfectly reproduces the evolution of the Ge concentration during oxidization of the SiGe alloy.

Journal of Chemical Physics, Jun 1, 2004

We study a calcium aluminosilicate glass of composition (SiO 2) 0.67-(Al 2 O 3) 0.12-(CaO) 0.21 b... more We study a calcium aluminosilicate glass of composition (SiO 2) 0.67-(Al 2 O 3) 0.12-(CaO) 0.21 by means of molecular-dynamics (MD) simulations, using a potential made of two-body and threebody interactions. In order to prepare small samples that can subsequently be studied by firstprinciples, the finite size effects on the liquid dynamics and on the glass structural properties are investigated. We find that finite size effects affect the Si-O-Si and Si-O-Al angular distributions, the first peaks of the Si-O, Al-O and Ca-O pair correlation functions, the Ca coordination and the oxygen atoms environment in the smallest system (100 atoms). We give evidence that these finite size effects can be directly attributed to the use of three-body interactions.

Journal of the American Ceramic Society, Jan 19, 2023

Microwave heating of pure alumina is studied experimentally and numerically, in a 2.45 GHz single... more Microwave heating of pure alumina is studied experimentally and numerically, in a 2.45 GHz single‐mode cavity, for different density levels. Even considering a constant incident power, the results show a complex evolution of the alumina temperature: first a two‐step increase, then a maximum, and finally a cooling stage. In addition, a density dependence of the heating efficiency is observed: a more efficient heating occurs for lower densities. Using the effective medium approximation (EMA) to derive the physical data as functions of density, the numerical simulations are in contradiction with the experiments, proving that the EMA approach is not able to correctly predict the imaginary part of the permittivity. Furthermore, the simulations do not accurately describe the first moments of the heating, nor the long‐term evolution of the temperature (cooling). We then explain the origin of this discrepancy: the need to adjust the movable stub on the one hand, and to account for heat exchange between the cavity and its surroundings on the other.

MRS Advances, Feb 29, 2016

Using molecular statics calculations, sodium silicate glasses are expanded in an isotropic manner... more Using molecular statics calculations, sodium silicate glasses are expanded in an isotropic manner to analyze the composition dependence of the mechanical response. Increasing the amount of sodium makes the systems more ductile. The tensile strength is reduced and the final load bearing strain limit is increased. Hydrostatic strain hardening appears in the ductile samples. To explain this phenomena, the density is coarse-grained to identify microscopic defects. In samples containing a significant amount of sodium, a large amount of nano-voids appear before reaching the maximum load bearing capacity. In high sodium content silicates these cracks may cause the hardening observed in the pressure results. In samples with low sodium content, the failure is abrupt and only a large crack is observed. Increasing the amount of long term but weaker Na-O interactions, instead of the short range Si-O ones could explain the observed transition.

Physical Review B, Aug 2, 2012

Using the ART NOUVEAU method, we study the initial stages of silicon oxide formation. After valid... more Using the ART NOUVEAU method, we study the initial stages of silicon oxide formation. After validating the method's parameters with the characterization of point defects diffusion mechanisms in pure Stillinger-Weber silicon, which allows us to recover some known results and to detail vacancy and self-interstitial diffusion paths, the method is applied onto a system composed of an oxygen layer deposited on a silicon substrate. We observe the oxygen atoms as they move rapidly into the substrate. From these ART NOUVEAU simulations, we extract the energy barriers of elementary mechanisms involving oxygen atoms and leading to the formation of an amorphouslike silicon oxide. We show that the kinetics of formation can be understood in terms of the energy barriers between various coordination environments.

Physical review, Apr 14, 2017

The elastoplastic behavior of sodium silicate glasses is studied at different scales as a functio... more The elastoplastic behavior of sodium silicate glasses is studied at different scales as a function of composition and pressure, with the help of quasistatic atomistic simulations. The samples are first compressed and then sheared at constant pressure to calculate yield strength and permanent plastic deformations. Changes occurring in the global response are then compared to the analysis of local plastic rearrangements and strain heterogeneities. It is shown that the plastic response results from the succession of well-identified localized irreversible deformations occurring in a nanometer-size area. The size and the number of these local rearrangements, as well as the amount of internal deviatoric and volumetric plastic deformation, are sensitive to the composition and to the pressure. In the early stages of the deformation, plastic rearrangements are driven by sodium mobility. Consequently, the elastic yield strength decreases when the sodium content increases, and the same when pressure increases. Finally, good correlation was found between global and local stress-strain relationships, reinforcing again the role of sodium ions as local initiators of the plastic behavior observed at larger scales.

Acta Materialia, Jun 1, 2016

Silicate glasses are macroscopically brittle but ductile at the micron scale. This plastic respon... more Silicate glasses are macroscopically brittle but ductile at the micron scale. This plastic response is complex: in open structure materials, such as amorphous silica, plastic yield results in significant densification. While, more compact structures (e.g. soda-silicate glasses) are known to suppress densification and promote shear flow. We have carried out atomic scale simulations to analyze the plastic response of a series of silicates with increasing sodium content. Quasi-static, multi-axial deformation tests were performed on large samples (≈ 10 3 nm 3). Their yield behavior was quantified at different stress states, by measuring permanent volume changes. Qualitative agreement was found between the response of modeled systems and experimental results. Strong coupling between plastic yield and densification was observed. Our results also suggest that sodium silicates may densify not only under hydrostatic compression but also upon shear at large strains. Based on these numerical results, we propose a general yield criterion for soda-silicate glasses in which density is an internal variable. As density increases, the elliptic yield surface (characterizing amorphous silicates with open structures) gradually

Physical Review B, Jan 20, 2010

In this paper, we present a theoretical study of the elastic deformations arising in the vicinity... more In this paper, we present a theoretical study of the elastic deformations arising in the vicinity of the Si/ SiO 2 interface upon oxidation of a silicon substrate. The oxidation is modelized using an algorithm which alternates the inclusion of oxygen atoms and Molecular Dynamics simulations at high temperature. We find that the SiO 2 film undergoes an overall compressive state while a more complex strain field is found in the first few Si layers under the interface where tensile and compressive microstructures coexist, the former being definitely larger than the latter. The analysis of the formation energies of the main defects responsible for Si diffusion reveals that, in spite of the complexity of the deformation field at the Si/ SiO 2 interface, their dependence with respect to the local deformation obeys the same laws as those derived from the application of a simple biaxial stress.

arXiv (Cornell University), Mar 20, 2019

We propose a new statistical physics model to study equilibrium solute segregation at grain bound... more We propose a new statistical physics model to study equilibrium solute segregation at grain boundaries and the resulting embrittlement effect. This low-temperature expansion model is general and efficient, and its parameters can be obtained from atomistic calculations. It is possible to take into account multiple species, multiple segregation sites with different segregation free energies, account for configurational entropy, grain radius and site competition between solutes. As an example, the model is then applied to the study of phosphorus and hydrogen co-segregation at Σ3 109.5° 011 {111} twin boundaries in α-Fe, using energetic parameters from density-functional theory calculations. We show that P-H interactions may lead to increased P segregation at grain boundaries and cause additional embrittlement compared to the case where P and H are considered separately.

2016-Sustainable Industrial Processing Summit, Jun 1, 2016

Even the slightest content of species segregating at the grain boundaries (GBs) of a polycrystall... more Even the slightest content of species segregating at the grain boundaries (GBs) of a polycrystalline material can dramatically change its physical (mechanical, thermal, electrical, optical) features and its lifetime. While some nonmetallic species may improve its mechanical properties, sulfur segregating in nickel GBs yields its embrittlement, when the S-content reaches a critical concentration specific of a ductile-brittle transition [1]. Recent observations of different GBs using the NanoSIMS device revealed that one has to account for the atomic-scale structure of the GB to understand its S content, as different GBs with different orientations display different enrichments [2]. But the expected small thickness of the segregated layers prevent a straightforward observation and requires complementary atomic-scale models. Literature abounds with first-principles computations on the Ni-S, but only very few and specific GBs can be handled for tractability reasons. While many very efficient interatomic potentials can deal with pure metals and metallic alloys, up-to-date only the ReaxFF approach allows to account for Ni-S at the atomic scale [3]. We discuss its use to reach an atomic-scale description of a given GB (chemistry-structure coupling) and the challenges to solve both from computational and experimental developments to describe the interface of Ni-S GBs. [1] J. K. Heuer, P. R. Okamoto, N. Q. Lam and J. F. Stubbins, Applied Physics Letters 76 (23), 3403-3405 (2000) [2] F. Christien, C. Downing, K.L. Moore, C.R.M. Grovenor, Surface and Interface Analysis 44, 377-387 (2012) [3] H.-P. Chen, R. K. Kalia, E. Kaxiras, G. Lu, A. Nakano, K. Nomura, A. C. T. van Duin, P. Vashishta, and Z. Yuan, Phys. Rev. Lett. 104, 155502 (2010)

Journal of the American Ceramic Society

Microwave heating of pure alumina is studied experimentally and numerically, in a 2.45 GHz single... more Microwave heating of pure alumina is studied experimentally and numerically, in a 2.45 GHz single‐mode cavity, for different density levels. Even considering a constant incident power, the results show a complex evolution of the alumina temperature: first a two‐step increase, then a maximum, and finally a cooling stage. In addition, a density dependence of the heating efficiency is observed: a more efficient heating occurs for lower densities. Using the effective medium approximation (EMA) to derive the physical data as functions of density, the numerical simulations are in contradiction with the experiments, proving that the EMA approach is not able to correctly predict the imaginary part of the permittivity. Furthermore, the simulations do not accurately describe the first moments of the heating, nor the long‐term evolution of the temperature (cooling). We then explain the origin of this discrepancy: the need to adjust the movable stub on the one hand, and to account for heat exch...

arXiv (Cornell University), Jul 31, 2012

Oxidization of a dilute Si(Ge) alloy is modeled using an original protocol based on molecular dyn... more Oxidization of a dilute Si(Ge) alloy is modeled using an original protocol based on molecular dynamics simulation and rules for the oxygen insertions. These rules, deduced from ab-initio calculations, favor the formation of SiO 2 against GeO 2 oxide which leads to segregation of Ge atoms into the alloy during the oxidization front advance. Ge condensation is then observed close to the SiO 2 /Ge interface due to the strain induced by oxydization in this region. From the analysis of the simulation process, we propose a onedimensional description of Ge condensation wich perfectly reproduces the evolution of the Ge concentration during oxidization of the SiGe alloy.

Even the slightest content of species segregating at the grain boundaries (GBs) of a polycrystall... more Even the slightest content of species segregating at the grain boundaries (GBs) of a polycrystalline material can dramatically change its physical (mechanical, thermal, electrical, optical) features and its lifetime. While some nonmetallic species may improve its mechanical properties, sulfur segregating in nickel GBs yields its embrittlement, when the S-content reaches a critical concentration specific of a ductile-brittle transition [1]. Recent observations of different GBs using the NanoSIMS device revealed that one has to account for the atomic-scale structure of the GB to understand its S content, as different GBs with different orientations display different enrichments [2]. But the expected small thickness of the segregated layers prevent a straightforward observation and requires complementary atomic-scale models. Literature abounds with first-principles computations on the Ni-S, but only very few and specific GBs can be handled for tractability reasons. While many very effi...

We propose a new method using coarse-graining and molecular dynamics to calculate structural and ... more We propose a new method using coarse-graining and molecular dynamics to calculate structural and mechanical properties for sodium silicate glasses at different scales. Using this method we were able to describe the mechanical behavior of the material, this way a new constitutive model was developed which could be used in continuum calculations.

Journal of the American Ceramic Society, 2020

A comparison between experiment and numerical simulation of microwave heating of a parallelepiped... more A comparison between experiment and numerical simulation of microwave heating of a parallelepipedic silicon carbide (SiC) sample is presented. Using a‐2.45 GHz single‐mode cavity, the evolution of the surface temperature is first experimentally studied for different orientations of the sample. A finite element analysis of this electromagnetic‐thermal coupled problem is then conducted with the COMSOL Multiphysics® software. Despite the different approximations of our model, a good agreement between experimental and numerical results is found, confirming that the heating of SiC depends only on the electric field. The effect of sample orientations and the cavity length on heating is also highlighted and analyzed.

Journal of Alloys and Compounds, 2021

Self-polarized ferrimagnetic nanowires of CoFe2O4 are electrochemically grown by the electrodepos... more Self-polarized ferrimagnetic nanowires of CoFe2O4 are electrochemically grown by the electrodeposition technique in AAO membranes. XRD, EDS and SQUID analysis confirm the formation of highly stoichiometric CoFe2O4 nanowires with high magnetic response into 20 nm-AAO membrane. SEM and AFM images revealed a total filling of the AAO membrane with Co and Fe at an applied potential of-1.2 V. In addition, the electrodeposition and cooling in the presence of an applied magnetic field improve the magnetic response of CoFe2O4 nanowires. The SQUID measurements confirmed the elaboration of CoFe2O4 nanowires with an internal magnetic field of 1.52 T. As a result, this ferrimagnetic nanowired substrate will be suitable for future miniaturized self-biased microwave devices.

Applied Surface Science, 2019

We propose a new statistical physics model to study equilibrium solute segregation at grain bound... more We propose a new statistical physics model to study equilibrium solute segregation at grain boundaries and the resulting embrittlement effect. This low-temperature expansion model is general and efficient, and its parameters can be obtained from atomistic calculations. It is possible to take into account multiple species, multiple segregation sites with different segregation free energies, account for configurational entropy, grain radius and site competition between solutes. As an example, the model is then applied to the study of phosphorus and hydrogen co-segregation at Σ3 109.5° 011 {111} twin boundaries in α-Fe, using energetic parameters from density-functional theory calculations. We show that P-H interactions may lead to increased P segregation at grain boundaries and cause additional embrittlement compared to the case where P and H are considered separately.

Physical Review E, 2017

The elastoplastic behavior of sodium silicate glasses is studied at different scales as a functio... more The elastoplastic behavior of sodium silicate glasses is studied at different scales as a function of composition and pressure, with the help of quasistatic atomistic simulations. The samples are first compressed and then sheared at constant pressure to calculate yield strength and permanent plastic deformations. Changes occurring in the global response are then compared to the analysis of local plastic rearrangements and strain heterogeneities. It is shown that the plastic response results from the succession of well-identified localized irreversible deformations occurring in a nanometer-size area. The size and the number of these local rearrangements, as well as the amount of internal deviatoric and volumetric plastic deformation, are sensitive to the composition and to the pressure. In the early stages of the deformation, plastic rearrangements are driven by sodium mobility. Consequently, the elastic yield strength decreases when the sodium content increases, and the same when pressure increases. Finally, good correlation was found between global and local stress-strain relationships, reinforcing again the role of sodium ions as local initiators of the plastic behavior observed at larger scales.

Surface and Interface Analysis, 2017

An adequate model of quantification when there are many segregating elements is required for indu... more An adequate model of quantification when there are many segregating elements is required for industry and research. Hence, for the first time, surface segregation kinetics on industrial 16MND5 steel was studied by XPS spectroscopy at temperatures ranging from 500 to 600 o C. From measurements that highlight the competitive segregation of P, S, Sn, Sb, As, and Cu impurities at the surface, a quantification model was developed and successfully used to deduce the surface concentrations during segregation kinetics as well as derive the corresponding diffusion coefficients. We observed that phosphorus and sulfur are the first elements covering the surface, then they are supplanted by others' impurities. This result may reflect impurities segregation behavior at the grain boundaries that impacts mechanical behavior of the material. Indeed, to further the research, 16MND5 samples were aged in the same range of temperatures. Then, Auger spectroscopy measurements at grain boundaries were conducted on broken samples exhibiting intergranular cracking. Results show that phosphorus is the only segregating element present at grain boundaries after 2 months of aging. Importantly, it appears that phosphorus grain boundary segregation kinetics is significantly lower than at surface.