Séparation de phase amorphe et cristallisation dans le système BaO-TiO2-SiO2: une approche expérimentale et une étude thermodynamique.

Glass-ceramics are of growing interest due to their enhanced properties compared to the base glasses. More specifically, the control of microstructures is a major challenge as the properties of glass-ceramics are the direct consequences of microstructures. Microstructures can be modified by forming specific crystal phases or by using a prior amorphous phase separation before crystallization. The PhD thesis objectives are to demonstrate that the properties of silicate glasses can be enhanced by controlling their microstructure genesis with composition and thermal process parameters. More specifically, two systems were studied and compared: the BaO-TiO2-SiO2 system and the soda-lime silica Na2O-CaO-SiO2 used industrially. Both systems exhibit a large zone of immiscibility allowing the study of the influence of phase separation on crystallization.The first system BaO-TiO2-SiO2 has gathered interest from the interesting properties of fresnoite (Ba2TiSi2O8): piezo and pyroelectricity, second harmonic generation and blue/white photoluminescence. Many studies on the stoichiometric composition were conducted to understand and improve those promising properties. However, it was recently suggested that the photoluminescence can be improved with composition exhibiting phase separation. This indicates that the photoluminescence intensity can be improved through a microstructural control. The possible role of a prior amorphous phase separation on the subsequent crystallization has been however the topic of vigorous debates over the last decades and has not yet been clarified, especially regarding the role of the interfaces created by the phase separation. In this PhD, the effect of phase separation on fresnoite crystallization was studied. This had to pass through the calculation of the liquid-liquid immiscibility in the phase diagram in order to select suitable compositions to compare in a systematic study. The systematic study concludes to a surface crystallization mechanism for all non- stoichiometric compositions and shows no influence between amorphous droplets and matrix crystallization. This study was also completed with the investigation of the effect of composition (i.e. SiO2-excess), annealing temperature and prior heat treatment, i.e. heating rate, cooling rate or a prior isothermal step before annealing. It is shown that specific microstructures are obtained depending on the process parameters. Finally, selected compositions and heat treatment show how photoluminescence intensity can be improved by a microstructural control. The highest intensity is obtained with a high crystallization fraction and a maximization of the number of interfaces.The results obtained in the study of the BaO-TiO2-SiO2 system are extended to the soda-lime-silica system in order to study the effect of phase separation on crystallization. It is shown that cristobalite forma- tion from the surface cannot be avoided and that the involved composition shift inhibits phase separation. It is consequently difficult to observe an interplay. Those studies lead to a general discussion about the criteria allowing to observe an interplay between phase separation and crystallization in oxide glasses.Doctorat en Sciences de l'ingénieurinfo:eu-repo/semantics/nonPublishe

Influence of Amorphous Phase Separation on the crystallization mechanisms in the BaO-TiO2-SiO2 system

The control of microstructures is a major challenge to enhance the properties of base glasses. More specifically, the controlled crystallization of glasses through a Prior Amorphous Phase Separation (APS) may be an elegant way to ensure a bulk process. Glasses in the BaO-TiO2-SiO2 system undergo APS for specific composition ranges. The interfaces created can have a significant effect on the crystallization behavior since it allows bulk nucleation of fresnoite to be obtained, instead of surface crystallization. This phenomenon can enhance optical properties such as blue photoluminescence, particularly interesting for plasma screen applications. The aim of this work is to compare the crystallization behavior with and without prior APS. The microstructures were investigated using Scanning and Transmission Electron Microscopy (SEM & TEM). Differential Scanning Calorimetry (DSC) and X-Ray Diffraction (DRX) were also used to characterize the crystallization process. The prior APS is shown to have a major influence for the glass compositions investigated Consequently, a modeling effort is presently being carried out in order to determine the immiscibility region, in order to compare compositions closer to the immiscibility boundary.info:eu-repo/semantics/nonPublishe

A thermodynamic assessment of the liquid immiscibility in the BaO-TiO2-SiO2 system using the Ionic Two Sublattice Model

Présentation séminaire Thermo-Calc (Leuven)info:eu-repo/semantics/nonPublishe

Influence of phase separation on the crystallization behavior of glass-ceramics in the BaO-TiO2-SiO2 system

Glass ceramics are of growing interest due to their enhanced properties comparing to the base glasses. The control of microstructures is consequently a major challenge in those systems. Even if it has been the topic of vigorous debates over the last decades, the possible role of a prior amorphous phase separation (APS) on the subsequent crystallization has not yet been clarified. This study focuses on the interplay between amorphous phase separation and the crystallization of fresnoite in glasses pertaining to the BaO-TiO2-SiO2 system. These glasses are known to undergo subliquidus phase separation via binodal or spinodal mechanisms for specific composition ranges in the ternary phase diagram. This process eventually leads to a final microstructure consisting of silica-rich droplets within a glassy matrix. The prior amorphous phase separation may have a significant effect on the subsequent nucleation and growth of crystals and furthermore on their morphology. Indeed, glasses with compositions falling outside the immiscibility gap have been reported to crystallize as strongly oriented crystals whereas glasses undergoing a prior APS lead to finer and randomly oriented crystals. This could be considered as an elegant way to improve optical properties such as the blue photoluminescence of fresnoite, particularly interesting for plasma screen applications. The aim of this work is to compare the crystallization behavior of glasses (i) with and (ii) without prior amorphous phase separation and also (iii) with the stoichiometric composition of fresnoite. This particular glass composition is well-known to bulk crystallize and to show high photoluminescence. The prior amorphous phase separation is shown to have a major influence for the glass compositions investigated. The microstructures of bulk samples are investigated using Scanning and Transmission Electron Microscopy. Differential Scanning Calorimetry and X-Ray Diffraction are also used to characterize the crystallization process on powder samples. The possible influence of the various interfaces present within the microstructure is investigated. In particular, the role of free surfaces or of droplets/matrix interfaces is scrutinized. Their respective influence on the nucleation and growth of fresnoite crystals is discussed in detail.info:eu-repo/semantics/publishe

THERMODYNAMIC ASSESSMENTS OF THE LIQUID IMMISCIBILITIES IN THE BAO-SIO2 AND TIO2-SIO2 SYTEMS USING THE IONIC TWO SUBLATTICE MODEL

Glass-ceramics in the BaO-SiO2-TiO2 system exhibit strong photoluminescence properties due to the fresnoite phase formation. This effect can be enhanced by controlling a prior amorphous phase separation, which promotes the formation of finer crystals. The thermodynamic stability and metastability of the liquid phase in this system are critical information in order to design optimal compositions and processes of the glass exhibiting the maximum photoluminescence effect. However, the liquid phase in the BaO-SiO2-TiO2 system has never been assessed in the past and there is a lack of experimental data. Corresponding sub-binary systems were evaluated in literature but using different thermodynamic models: the BaO-SiO2 system was performed on the basis of the structural model for silicate melts and glasses [1] and the TiO2-SiO2 binary system using a Margule type excess polynomial model [2]. The BaO-TiO2 system was already assessed by using the Ionic Two Sublattice model [3]. To construct a ternary description of the BaO-SiO2-TiO2 system, the Ionic Two Sublattice model was used in this work to first describe liquid phases in both BaO-SiO2 and TiO2-SiO2 systems. Available experimental data from literature were evaluated to assess the thermodynamic parameters of these liquid phases by the CALPHAD method. The assessments were conducted using a PARROT module of the Thermo-Calc software. A set of optimized parameters was obtained and calculated phase diagrams related to the stable and metastable liquid miscibility gaps in the BaO-SiO2 and TiO2-SiO2 are consistent with experimental data as shown in Figure 1 and Figure 2. The validity of liquidus projection interpolations into the ternary system by Muggianu’s model is investigated. Discussion is further expanded to experiments and the parameter assessment required for the prediction of the resulting BaO-SiO2-TiO2 equilibrium diagrams.[1] A. Romero-Serrano et al. Thermodynamic modeling of the BaO-SiO2 binary melts. Glass Phys. and Chem. 2010, Vol.36 n°2, pp.171-178.[2] M. Kirschen, C. DeCapitani, Immiscible silicate liquids in the system SiO2-TiO2-Al2O3. Eur.J.Mineral, 1999, Vol.11, pp.427-440.[3] X. Lu, Z. Jin, Thermodynamic assessment of the BaO-TiO2 quasibinary system. Calphad. Pergamon, 2000, Vol.24, 3, pp.319-338.info:eu-repo/semantics/nonPublishe

Human mitochondria-derived N-formylated peptides are novel agonists equally active on FPR and FPRL1, while Listeria monocytogenes-derived peptides preferentially activate FPR.

N-formyl peptides are cleavage products of bacterial and mitochondrial proteins, and can attract leukocytes to sites of infection or tissue damage. In this study, HL-60 cell lines expressing the human N-formyl peptide receptor FPR or its two homologues (FPRL1, FPRL2) were used to determine the receptor selectivity of N-formylated peptides derived from Listeria monocytogenes or from human mitochondrial proteins. Bacterial peptides were 100-fold more potent on FPR than on FPRL1, whereas none of them could trigger intracellular signaling through FPRL2. In contrast, N-formylated hexapeptides corresponding to the N terminus of mitochondrial NADH dehydrogenase subunits 4 (fMLKLIV) and 6 (fMMYALF), and cytochrome c oxidase subunit I (fMFADRW) were equally potent on FPR and FPRL1. They triggered cellular responses with the following order of potency: fMMYALF > fMLKLIV > fMFADRW, with an EC50, in a Fura-2 calcium mobilization assay, of 10 nM, 44 nM, and 160 nM on FPR-expressing cells, and 15 nM, 55 nM and 120 nM on FPRL1-expressing cells. fMMYALF was also a low-affinity agonist of FPRL2 (EC50 of 1 microM) and was chemotactic for both FPRL1- and FPRL2-expressing cells. We identified novel mitochondrial host-derived agonists for human N-formyl-peptide receptors that might play a role in inflammatory or degenerative processes linked to their stimulation

The N-formyl peptide receptors and the anaphylatoxin C5a receptors: an overview.

Leukocyte recruitment to sites of inflammation and infection is dependent on the presence of a gradient of locally produced chemotactic factors. This review is focused on current knowledge about the activation and regulation of chemoattractant receptors. Emphasis is placed on the members of the N-formyl peptide receptor family, namely FPR (N-formyl peptide receptor), FPRL1 (FPR like-1) and FPRL2 (FPR like-2), and the complement fragment C5a receptors (C5aR and C5L2). Upon chemoattractant binding, the receptors transduce an activation signal through a G protein-dependent pathway, leading to biochemical responses that contribute to physiological defense against bacterial infection and tissue damage. C5aR, and the members of the FPR family that were previously thought to be restricted to phagocytes proved to have a much broader spectrum of cell expression. In addition to N-formylated peptides, numerous unrelated ligands were recently found to interact with FPR and FPRL1. Novel agonists include both pathogen- and host-derived components, and synthetic peptides. Antagonistic molecules have been identified that exhibit limited receptor specificity. How distinct ligands can both induce different biological responses and produce different modes of receptor activation and unique sets of cellular responses are discussed. Cell responses to chemoattractants are tightly regulated at the level of the receptors. This review describes in detail the regulation of receptor signalling and the multi-step process of receptor inactivation. New concepts, such as receptor oligomerization and receptor clustering, are considered. Although FPR, FPRL1 and C5aR trigger similar biological functions and undergo a rapid chemoattractant-mediated phosphorylation, they appear to be differentially regulated and experience different intracellular fates

A Spline-Based Analytical Model for the Design of an Automotive Anti-Roll Bar

The new corner-based architecture of electrified road vehicles requires a redesign of vehicle suspension components. The design protocol must satisfy the target parameters derived from dynamics requirements. The roll stiffness of the anti-roll bar is a crucial parameter for the handling performance of a vehicle. During the development of a new suspension, the design of the anti-roll bar needs to be modified. To this aim, two-dimensional beam theory models can quickly provide a preliminary design of this component. However, the simplified models might be inaccurate due to the three-dimensional and complex shapes of the bars. The present study aims to overcome this limitation. An analytical beam model based on the spline description of the bar has been developed, which is accurate even for complex geometries of the bars. Assuming a hollow and closed circular cross-section, the model returns the average diameter and the radial thickness needed to achieve the stiffness performance. Three different approaches for the thickness have been analyzed by assuming: (I) a prescribed thickness, (II) a prescribed global mass, and (III) a prescribed maximum value of stress. The first two methods present a uniform thickness along the bar, whereas, in the third one, the thickness varies to obtain the lightest solution. This latter method can be modified to ensure a feasible minimum thickness. Finally, a full-factorial design of the experiments algorithm has been developed to reduce the stress by varying the position of the spline control points. The proposed methods can provide a good preliminary design of the bar and can drive a material replacement process from a lightweight viewpoin

Crystallization behavior of glass-ceramics in the BaO-TiO2-SiO2 system

Glass ceramics are of growing interest due to their enhanced properties compared to the base glasses. The control of microstructures is consequently a major challenge in those systems. A glass with the stoichiometric composition of fresnoite (Ba2TiSi2O8) has been reported by Cabral et al. to show a very large nucleation rate leading to the formation of nanometric crystals. Komatsu et al. reported that transparent nanocrystallized glasses exhibit blue/white photoluminescence by UV excitation, demonstrating that fresnoite has a significant potential as luminescent material. Furthermore, it was recently reported by Hijiya et al. that non stoichiometric compositions included inside the miscibility gap in the phase diagram allow enhancing the photoluminescence properties; the heterogeneous crystallization is finer, providing an enhancement of the fluorescence effect. The possible role of a prior Amorphous Phase Separation (APS) on the subsequent crystallization has been the topic of vigorous debates over the last decades and has not yet been clarified. This study proposes to focus on the interplay between APS and the crystallization of fresnoite by comparing the crystallization behavior of the stoichiometric composition with two non-stoichiometric ones, one outside the miscibility gap and one inside. The crystallization mechanism is studied using Differential Scanning Calorimetry. It reveals that interfaces created by the APS have no effect on the crystallization mechanism since both non-stoichiometric compositions exhibit surface crystallization. The evolution of the microstructure is investigated by conventional Scanning Electron Microscopy (SEM). It confirms the surface crystallisation mechanism and the very limited role of APS. However, the final microstructures depend on the compositions investigated. The size of the crystals become finer when the silica content is increased and the composition falls inside the miscibility gap. Two possible scenarios are proposed to explain the formation of oriented but finer microstructures: the presence of amorphous silica-rich droplets or a higher viscosity, both disturbing the dendritic growth of fresnoite observed for the non-stoichiometric composition. In order to explore those hypotheses, the microstructures of bulk samples with prior APS are investigated more deeply by coupling SEM to local crystallographic orientation mapping using Electron BackScatterred Diffraction techniques to scrutinize the local orientation around the droplets at the early and final stages of crystallization. High Resolution Transmission Electron Microscope coupled with Electron Energy Loss Spectroscopy is also used in order to characterize the nanoscale composition gradients at the interface between the matrix and the droplets both in the amorphous state and after the crystallization of fresnoite. In order to minimize the effect of composition and the associated viscosity change, two specific glass compositions are further investigated. They are chosen such that they are very close but fall respectively inside and outside the miscibility gap. Their final microstructures are compared.info:eu-repo/semantics/nonPublishe

The role of beta-arrestins in the formyl peptide receptor-like 1 internalization and signaling.

The N-formyl peptide receptor-like 1 (FPRL1) is a G protein-coupled receptor (GPCR) that transmits intracellular signals in response to a variety of agonists, many of them being clearly implicated in human pathology. beta-arrestins are adaptor proteins that uncouple GPCRs from G protein and regulate receptor internalization. They can also function as signal transducers through the scaffolding of signaling molecules, such as components of the extracellular signal-regulated kinase (ERK) cascade. We investigated the role of beta-arrestins in ligand-induced FPRL1 internalization and signaling. In HEK293 cells expressing FPRL1, fluorescence microscopy revealed that agonist-stimulated FPRL1 remained co-localized with beta-arrestins during endocytosis. Internalization of FPRL1, expressed in a mouse embryonic fibroblast (MEF) cell line lacking endogenous beta-arrestins, was highly compromised. This distinguishes FPRL1 from the prototypical formyl peptide receptor FPR that is efficiently internalized in the absence of beta-arrestins. In both HEK293 and MEF cells, FPRL1-mediated ERK1/2 activation was a rapid and transient event. The kinetics and extent of ERK1/2 activation were not significantly modified by beta-arrestin overexpression. The pattern of FPRL1-mediated ERK1/2 activation was similar whether cells express or not beta-arrestins. Furthermore, treatment of the FPRL1 expressing cells with pertussis toxin inhibited ERK1/2 activation in MEF and in HEK293 cells. These results led us to conclude that activation of ERK1/2 mediated by FPRL1 occurs primarily through G protein signaling. Since beta-arrestin-mediated signaling has been observed essentially for receptors coupled to G proteins other than G(i), this may be a characteristic of G(i) protein-coupled chemoattractant receptors