20 results on '"Itani, Lama"'
Search Results
2. Internal and near nozzle measurements of Engine Combustion Network “Spray G” gasoline direct injectors
- Author
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Duke, Daniel J., Kastengren, Alan L., Matusik, Katarzyna E., Swantek, Andrew B., Powell, Christopher F., Payri, Raul, Vaquerizo, Daniel, Itani, Lama, Bruneaux, Gilles, Grover, Ronald O., Jr., Parrish, Scott, Markle, Lee, Schmidt, David, Manin, Julien, Skeen, Scott A., and Pickett, Lyle M.
- Published
- 2017
- Full Text
- View/download PDF
3. Influence of alkalinity of the starting system on size and morphology of the zeolite A crystals
- Author
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Bronić, Josip, Palčić, Ana, Subotić, Boris, Itani, Lama, and Valtchev, Valentin
- Published
- 2012
- Full Text
- View/download PDF
4. Centimeter-sized zeolite bodies of intergrown crystals: Preparation, characterization and study of binder evolution
- Author
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Itani, Lama, Valtchev, Valentin, Patarin, Joël, Rigolet, Séverinne, Gao, Feifei, and Baudin, Gérard
- Published
- 2011
- Full Text
- View/download PDF
5. Silicalite-1 films with preferred orientation
- Author
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Wee, Lik H., Wang, Zheng, Tosheva, Lubomira, Itani, Lama, Valtchev, Valentin, and Doyle, Aidan M.
- Published
- 2008
- Full Text
- View/download PDF
6. Entwicklung und Anwendung optischer Diagnostiktechniken zur Untersuchung des Effektes der preferentialen Verdampfung von multikomponenten Kraftstoffen unter motorisch-relevanten Bedingungen
- Author
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Itani, Lama, Schulz, Christof (Akademische Betreuung), STAR, ABES, Schulz, Christof, Laboratoire d'Énergétique Moléculaire et Macroscopique, Combustion (EM2C), Université Paris Saclay (COmUE)-Centre National de la Recherche Scientifique (CNRS)-CentraleSupélec, Université Paris-Saclay, Universität Duisburg-Essen, Gilles Bruneaux, and Christof Schulz
- Subjects
Laser-induced fluorescence (LIF) ,gasoline ,Éaporation ,LIF ,multi-component ,[SPI.NRJ]Engineering Sciences [physics]/Electric power ,Fakultät für Ingenieurwissenschaften » Institut für Verbrennung und Gasdynamik ,Evaporation ,Essence ,Benzin ,Verdampfung ,Multi-Component ,Strahl ,evaporation ,Maschinenbau ,Jet ,jet ,Multikomponenten ,ddc:620 ,Multi-Composant ,Gasoline ,[SPI.NRJ] Engineering Sciences [physics]/Electric power - Abstract
Eine berührungsfreies quantitatives Verfahren auf Basis von laserinduzierter Fluoreszenz (LIF) wurde entwickelt, um simultan präferenzielle Verdampfung, Temperaturverteilung und Kraftstoffkonzentration im verdampften Bereich eines Mehrkomponenten-Kraftstoffsprays unter motorrelevanten Bedingungen zu messen. Verfahren beruht auf Zwei-tracer-LIF mit Anregungmit einem Laser.Es wurde ein Tracer-Paar mit geeigneten Verdampfungs- und spektralen Eigenschaften auf Basis von Dampf-Flüssigkeits-Gleichgewichtsrechnungen für Otto-Kraftstoffe ausgewählt. Verdampfungsmessungen haben gezeigt, dass ein Tracer (p-Difluorbenzol) gleichzeitig mit dem mittel- und höherflüchtigen Siedeklassen verdampft, während der andere (1-Methylnaphthalin) den schwerflüchtigen Komponentenfolgt. Für quantitative Messungen wurden die photophysikalischen Eigenschaften beider Tracer (einzeln und als Kombination) in einem weiten Bereich von Druck, Temperatur und Gaszusammensetzung bestimmt. 1-Methylnaphthalin-LIF zeigt eine starke Rotverschiebung mit der Temperatur, die Messungen der Temperaturverteilung ermöglicht. Es wurde ein Tracer-Paar mit geeigneten Verdampfungs- und spektralen Eigenschaften auf Basis von Dampf-Flüssigkeits-Gleichgewichtsrechnungen für Otto-Kraftstoffe ausgewählt. Verdampfungsmessungen haben gezeigt, dass ein Tracer (p-Difluorbenzol) gleichzeitig mit dem mittel- und höherflüchtigen Siedeklassen verdampft, während der andere (1-Methylnaphthalin) den schwerflüchtigen Komponentenfolgt. Für quantitative Messungen wurden die photophysikalischen Eigenschaften beider Tracer (einzeln und als Kombination) in einem weiten Bereich von Druck, Temperatur und Gaszusammensetzung bestimmt. 1-Methylnaphthalin-LIF zeigt eine starke Rotverschiebungmit der Temperatur, die Messungen der Temperaturverteilung ermöglicht., A non-intrusive quantitative laser-induced fluorescence (LIF) technique capable of simultaneously measuring preferential evaporation, temperature distribution, and fuel-mass concentration across a multi-component vaporized spray has been developed and investigated under engine-relevant conditions. The measurement technique is based on two-tracer LIF with single wavelength excitation.To assess preferential evaporation, a tracer pair with suitable co-evaporation and spectral properties was selected based on vapor-liquid equilibrium calculations repre-sentative for gasoline fuels. Evaporation studies have shown that one tracer (p-difluoro-benzene) co-evaporates with the high-to-medium-volatility end of the multi-component fuel while the other (1-methylnaphthalene) co-evaporates with the low-volatility end. For quantitative measurements the photophysical properties of both tracers (each tracer separately and the combined tracers) were determined under a wide range of pressure, temperature, and bath-gas composition conditions. 1-methylnaphthalene LIF shows a strong red-shift with temperature which enables measurements of the temperature distribution across the spray.Spray evaporation and vapor mixing experiments were performed in a high-pressure high-temperature vessel capable of simulating in-cylinder conditions. An ECN Spray-G and a piezo-electric outward opening injector were used in this study. Initial measure-ments were carried out with each tracer added separately to the fuel to assess signal cross-talk and to determine the best tracer concentrations. Once the proportions were determined, accuracy and precision of the method were determined from the LIF-signal ratio of spray images within identical spectral bands. Temperature fields, obtained by two-color 1-methylnaphthalene LIF and derived from fuel concentration maps based on the assumption of adiabatic evaporation, were examined for inhomogeneities in the area of interest since fluctuations potentially influence the two-color method. It was shown that the temperature is homogeneous in the measurement volume.To localize preferential evaporation, two-color two-tracer LIF images were evaluated. Taking into account the measurement accuracy and precision, variations in the spatial distribution of the fuel volatility classes were observed for 550–600 K. At higher tem-peratures, the effect is less pronounced, which is consistent with the fact that evapora-tion is faster. The localization of preferential evaporation varied with each injector used indicating the impact of injector nozzle geometry and jet structure on mixture formation., Dans le cadre de cette thèse, une technique de diagnostic optique a été développée pour mesurer simultanément l’évaporation différentielle, la distribution de température, et la concentration massique de fuel dans un jet multi-composant. Cette technique a été examinée dans les conditions d’un moteurs essence. La technique de mesure est basée sur l’utilisation des deux traceurs excités par une seule longueur d’onde.Pour pouvoir examiner l’évaporation différentielle d’un carburant multi-composant, deux traceurs ont été sélectionnés : le p-difluorobenzène et le 1-methylnaphtalène. Ces traceurs reproduisent deux types de volatilité : faible et moyenne à élevée. Les traceurs choisis fluorescent dans deux régions spectrales distinctes ce qui rend l’application de cette technique possible. Une étude photophysique a été menée pour caractériser les deux traceurs, indépendamment puis en mélange, pour différentes conditions de pression, température, et composition du bain gazeux. L’étude photophysique est essentielle pour pouvoir mesurer quantitativement l’évaporation différentielle. Les résultats photophysiques montrent que le spectre du 1-methylnaphthalène est sensible à la température. Cette caractéristique permet de mesurer la distribution en température dans le jet.Les essais ont été réalisés dans une cellule haute pression / haute température, ca-pable de simuler les conditions d’un moteur thermique. Des sprays générés par un injecteur ECN Spray G et un piézo-électrique d’une ouverture annulaire ont été étudiés. Des mesures initiales ont été menées avec chaque traceur pour pouvoir fixer la proportion de mélange des traceurs. La précision de la méthode de mesure a été calculée suivant une configuration de filtres identiques. Ensuite, les champs de tempé-rature calculés par la LIF et ceux déterminés depuis les champs de concentration massique, ont été comparés. Les résultats démontrent que la température est homo-gène ce qui signifie que les mesures d’évaporation différentielle n’ont pas influencé par la distribution de température dans le jet.Les images obtenues en détectant les signaux depuis le mélange de traceurs ont permis de localiser l’évaporation différentielle. Une variation en distribution spatiale des composants est observée 550–600 K. Cet effet disparaît en augmentant la température, ce qui explique que l’évaporation est plus rapide à haute température. La localisation de l’évaporation différentielle varie avec le type d’injecteur. La géométrie du nez ainsi que la structure du jet a donc un impact sur la formation du mélange.
- Published
- 2018
7. Quantitative measurements of preferential evaporation effects of multicomponent gasoline fuel sprays at ECN Spray G conditions
- Author
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Cordier, Matthieu, primary, Itani, Lama, additional, and Bruneaux, Gilles, additional
- Published
- 2019
- Full Text
- View/download PDF
8. Quantitative measurements of preferential evaporation effects of multicomponent gasoline fuel sprays at ECN Spray G conditions.
- Author
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Cordier, Matthieu, Itani, Lama, and Bruneaux, Gilles
- Abstract
A two-tracer laser-induced fluorescence technique is used to quantify the effects of preferential evaporation of multicomponent fuels on the fuel component distribution. The technique is based on the simultaneous detection of the fluorescence of two aromatic tracers with complementary evaporation characteristics matched to different components of a multicomponent fuel. Relative variations in the spatial distribution of tracer distribution as a consequence of preferential evaporation are determined from the ratio of laser-induced fluorescence signals measured within two distinct spectral bands. A thermodynamic model is then used to relate the ratio map with the fuel component map. The accuracy and precision of the method are characterized from determining the laser-induced fluorescence signal ratio within two identical spectral bands. Measurements are performed in a high-pressure high-temperature vessel equipped with an eight-hole injector. The Engine Combustion Network Spray G target conditions are chosen as reference conditions at injection. The only difference with these target conditions is the use of a multicomponent surrogate fuel. Parametric variations around these target conditions are also performed in order to investigate their effect on the preferential evaporation effect. The ambient temperature is varied between 525 and 625 K and the injection pressure is reduced from 200 to 100 bar. The impact of ethanol addition is also studied with two different fuel mixtures in addition to the reference surrogate fuel: E20 and E85 which feature 20% and 85% of pure ethanol within surrogate, respectively. A significant preferential evaporation effect is observed in this condition representative of engine applications and results in a spatial segregation between low- and high-volatility fuel components, respectively, at the tail and tip of the plumes. This effect is enhanced by the addition of ethanol and the decrease in ambient temperature and injection pressure. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
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9. Internal and near nozzle measurements of Engine Combustion Network 'Spray G' gasoline direct injectors
- Author
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Universitat Politècnica de València. Departamento de Máquinas y Motores Térmicos - Departament de Màquines i Motors Tèrmics, U.S. Department of Energy, Duke, Daniel J., Kastengren, Alan L., Matusik, Katarzyna E., Swantek, Andrew B., Powell, Christopher F., Payri, Raul, Vaquerizo, Daniel, Itani, Lama, Bruneaux, Gilles, Grover Jr., Ronald O., Parrish, Scott, Markle, Lee, Schmidt, D., Manin, Julien, Skeen, Scott A., Pickett, L.M., Universitat Politècnica de València. Departamento de Máquinas y Motores Térmicos - Departament de Màquines i Motors Tèrmics, U.S. Department of Energy, Duke, Daniel J., Kastengren, Alan L., Matusik, Katarzyna E., Swantek, Andrew B., Powell, Christopher F., Payri, Raul, Vaquerizo, Daniel, Itani, Lama, Bruneaux, Gilles, Grover Jr., Ronald O., Parrish, Scott, Markle, Lee, Schmidt, D., Manin, Julien, Skeen, Scott A., and Pickett, L.M.
- Abstract
[EN] Gasoline direct injection (GDI) sprays are complex multiphase flows. When compared to multi-hole diesel sprays, the plumes are closely spaced, and the sprays are more likely to interact. The effects of multi-jet interaction on entrainment and spray targeting can be influenced by small variations in the mass fluxes from the holes, which in turn depend on transients in the needle movement and small-scale details of the internal geometry. In this paper, we present a comprehensive overview of a multi-institutional effort to experimentally characterize the internal geometry and near-nozzle flow of the Engine Combustion Network (ECN) Spray G gasoline injector. In order to develop a complete pictitre of the near-nozzle flow, a standardized setup was shared between facilities. A wide range of techniques were employed, including both X-ray and visible-light diagnostics. The novel aspects of this work include both new experimental measurements, and a comparison of the results across different techniques and facilities. The breadth and depth of the data reveal phenomena which were not apparent from analysis of the individual data sets. We show that plume-to-plume variations in the mass fluxes from the holes can cause large-scale asymmetries in the entrainment field and spray structure. Both internal flow transients and small-scale geometric features can have an effect on the external flow. The sharp turning angle of the flow into the holes also causes an inward vectoring of the plumes relative to the hole drill angle, which increases with time due to entrainment of gas into a low-pressure region between the plumes. These factors increase the likelihood of spray collapse with longer injection durations.
- Published
- 2017
10. Investigation of the physicochemical changes preceding zeolite nucleation in a sodium-rich aluminosilicate gel
- Author
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Itani, Lama, Yong Liu, Weiping Zhang, Bozhilov, Krassimir N., Delmotte, Luc, and Valtchev, Valentin
- Subjects
Aluminum silicates -- Chemical properties ,Sodium hydroxide -- Chemical properties ,Xenon -- Chemical properties ,Zeolites -- Structure ,Zeolites -- Chemical properties ,Chemistry - Abstract
The changes in composition and structure of sodium hydroxide rich aluminosilicate gel yielding zeolite A are studied. The studies have shown the unrivaled sensitivity of hyperpolarized (HP) [super 129]Xe NMR that is capable of identifying presence of small amounts of crystalline zeolite material in amorphous medium with detection limit extending below 1 wt%.
- Published
- 2009
11. Factors Controlling Zeolite L Crystal Size
- Author
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Itani, Lama, Bozhilov, Krassimir N., Clet, Guillaume, Delmotte, Luc, Valtchev, Valentin, Institut de Science des Matériaux de Mulhouse (IS2M), Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Centre National de la Recherche Scientifique (CNRS), Laboratoire catalyse et spectrochimie (LCS), Centre National de la Recherche Scientifique (CNRS)-École Nationale Supérieure d'Ingénieurs de Caen (ENSICAEN), Normandie Université (NU)-Normandie Université (NU)-Institut de Chimie du CNRS (INC)-Université de Caen Normandie (UNICAEN), Normandie Université (NU), Laboratoire de Matériaux à Porosité Contrôlée (LMPC), and Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Ecole Nationale Supérieure de Chimie de Mulhouse-Centre National de la Recherche Scientifique (CNRS)
- Subjects
[CHIM]Chemical Sciences - Abstract
Accessed by 02/2011; International audience
- Published
- 2011
12. Investigation of the Mixing Process and the Fuel Mass Concentration Fields for a Gasoline Direct-Injection Spray at ECN Spray G Conditions and Variants
- Author
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Itani, Lama M., primary, Bruneaux, Gilles, additional, Hermant, Laurent, additional, and Schulz, Christof, additional
- Published
- 2015
- Full Text
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13. Micro- to Macroscopic Observations of MnAlPO-5 Nanocrystal Growth in Ionic-Liquid Media
- Author
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Ng, Eng-Poh, Itani, Lama, Sekhon, Satpal Singh, Mintova, Svetlana, Laboratoire de Matériaux à Porosité Contrôlée (LMPC), Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Ecole Nationale Supérieure de Chimie de Mulhouse-Centre National de la Recherche Scientifique (CNRS), Institut de Science des Matériaux de Mulhouse (IS2M), Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Centre National de la Recherche Scientifique (CNRS), Laboratoire catalyse et spectrochimie (LCS), Centre National de la Recherche Scientifique (CNRS)-École Nationale Supérieure d'Ingénieurs de Caen (ENSICAEN), Normandie Université (NU)-Normandie Université (NU)-Institut de Chimie du CNRS (INC)-Université de Caen Normandie (UNICAEN), Normandie Université (NU), and Roland, Pascal
- Subjects
ionic liquids ,[CHIM] Chemical Sciences ,Zeolites ,ionothermal synthesis ,[CHIM]Chemical Sciences ,nanoparticles ,Crystal growth - Abstract
International audience; Micro-and macroscopic studies of nucleation and growth processes of MnAlPO-5 nanosized crystals under ionothermal synthesis conditions are reported herein. The samples treated at 150 degrees C were extracted from the reaction mixture at various stages of crystallization, and characterized by XRD; SEM; thermogravimetric analysis (TGA); (31)P and (27)Al solid-state magic angle spinning (MAS) NMR, Raman, UV/Vis, and X-ray fluorescence spectroscopy (XRF). The starting raw materials (alumina, manganese, and phosphorous) were dissolved completely in the ionic liquid and transformed into an amorphous solid after 5 h of ionothermal treatment. This amorphous solid then undergoes structural changes over the following 525 h, which result in an intermediate phase that consists of octahedral Al species linked to the manganese and phosphate species. The first MnAlPO-5 nuclei on the surface of the intermediate can be observed after 50 h ionoheating. These nuclei further grow, as the surface of the intermediate is in full contact with the ionic liquid, to give crystalline MnAlPO-5 nanoparticles with a mean diameter of 80 nm. The crystals become fully detached from the intermediate and are then liberated as discrete particles after 90 h heating. The transformation process from amorphous to intermediate and then to the crystalline MnAlPO-5 nanoparticles shows that nucleation starts at the solid-liquid interface and continues through surface-to-core reversed-growth until the entire amorphous solid is transformed into discrete nanocrystals.
- Published
- 2010
14. Mécanismes de formation et mise en forme de cristaux zéolithiques
- Author
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Itani, Lama and STAR, ABES
- Subjects
Contrôle de la porosité interparticulaire ,Binder ,Crystallization mechanisms ,Mécanismes de cristallisation ,Zeolitic objects ,Nucleation mechanisms ,Zéolithes ,Interparticle porosity control ,Liant ,Hydrogel ,Objets zéolithiques ,[CHIM.OTHE] Chemical Sciences/Other ,Mécanismes de nucléation ,Zeolites - Abstract
The present study includes two parts: i) fundamental study of zeolite nucleation-crystal growth mechanism; and ii) preparation of zeolite bodies with controlled interparticle porosity.Thus the first part of the present work deals with the study of the effect of physico-chemical characteristics of initial hydrogel on the nucleation and crystal growth kinetics of zeolite crystals. The obtained data revealed that the concentration of alkali metal hydroxide in the initial system controls the rate of polymerization of the aluminosilicate species, the size of initial gel particles, and the textural properties of the gel. Consequently, the following reaction was to great extent predetermined by the events taking place during mixing the initial reactants.The second part of this work was targeted at the preparation of centimeter-sized zeolite bodies of *BEA- and MFI-type with reduced to minimum inter-particle porosity. A preparation method consisting in assembling of zeolite nanocrystals (with or without a binder) was developed and further optimized. The preformed bodies were subjected to a hydrothermal treatrnent in a fresh zeolite synthesis solution in order to till up the inter-particle porosity. Depending onthe zeolite type, different methods of secondary growth treatrnents were employed. A particular attention has been paid on the study of the binder evolution during the calcination and secondary growth processes., Ce travail de thèse inclut deux parties : i) l'étude fondamentale de la formation de cristaux zéolithiques ; et ii) la préparation de massifs zéolithiques de taille centimétriques à porosité interparticulaire contrôlée. La première partie de ce travail est donc consacrée à l'étude de l'effet de la microstructure (propriétés physiques et texturales) et de la composition chimique du gel sur la vitesse de nucléation et la taille des cristaux formés. Les résultats de cette étude se résument par le rôle important que joue la composition du gel (plus particulièrement sa concentration en hydroxyde de cation alcalin) sur le degré de polymérisation des particules du gel, la détermination de sa microstructure et par conséquent sur la vitesse de nucléation des zéolithes et la taille des cristaux. Les connaissances acquises dans la première partie ont été utilisées dans le développement du deuxième objective. Notamment, la préparation de massifs zéolithiques de taille centimétrique de types structuraux *BEA et MFI. Le contrôle post-synthèse de la porosité interparticulaire de ces massifs était essentiel pour leur utilisation dans des applications bien précises. A cette fin, une méthode en deux étapes, comportant un assemblage de nanocristaux de zéolithes préformés (en présence ou en absence d'un liant) puis un traitement de croissance secondaire pour l'élimination de la porosité interparticulaire, a été mise en œuvre. Plusieurs traitements de croissance secondaire furent évalués selon le type de zéolithe étudié. Une attention particulière fut accordée à l'étude de l'évolution du liant au cours des processus de préparation et de calcination des massifs zéolithiques.
- Published
- 2010
15. Morphology of zeolite a crystals synthesized at different alcalinity
- Author
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Bronić, Josip, Palčić, Ana, Subotić, Boris, Itani, Lama, Valtchev, Valentin, Antonić Jelić, Tatjana, and Zabukovec Logar, Nataša
- Subjects
zeolite A ,morphology ,hydrothermal synthesis ,crystal size distribution - Abstract
The possibility to control particulate properties (particularly morphology) of the synthesized crystals can be implemented through several physico-chemical parameters. In this paper, we have studied the influence of the alkalinity of the system on the size and morphology of zeolite A crystals. Prepared hydrogels were heated at 80°C in reactors made of HDPE, under static conditions. Starting compositions were: 3.2/12.0 Na2O × 2 SiO2 × 1.1 Al2O3 × 300.0 H2O. The characterization of the samples was performed using several analytical methods such as: X-ray diffraction (XRD), laser light scattering (LLS), optical microscopy (OM) and scanning electron microscopy (SEM). The analysis of the results show that the increase of alkalinity of explored system had two major effects: increase of the number of nuclei (crystals) in system and formation of crystals with more irregular shape.
- Published
- 2010
16. Steam - assisted synthesis of zeolite films from spin – coated zeolite precursor costings
- Author
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H. Wee, Lik, Tosheva, Lubomira, Itani, Lama, Valtchev, Valentin, M. Doyl, Aidan, Laboratoire de Matériaux à Porosité Contrôlée (LMPC), Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Ecole Nationale Supérieure de Chimie de Mulhouse-Centre National de la Recherche Scientifique (CNRS), and Peche, Josiane
- Subjects
[CHIM.MATE] Chemical Sciences/Material chemistry ,[CHIM.MATE]Chemical Sciences/Material chemistry ,ComputingMilieux_MISCELLANEOUS - Abstract
International audience
- Published
- 2008
17. Factors That Control Zeolite L Crystal Size
- Author
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Itani, Lama, primary, Bozhilov, Krassimir N., additional, Clet, Guillaume, additional, Delmotte, Luc, additional, and Valtchev, Valentin, additional
- Published
- 2011
- Full Text
- View/download PDF
18. Steam-assisted synthesis of zeolite films from spin-coated zeolite precursor coatings
- Author
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Wee, Lik H., primary, Tosheva, Lubomira, additional, Itani, Lama, additional, Valtchev, Valentin, additional, and Doyle, Aidan M., additional
- Published
- 2008
- Full Text
- View/download PDF
19. Factors that control zeolite L crystal size.
- Author
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Itani L, Bozhilov KN, Clet G, Delmotte L, and Valtchev V
- Abstract
Time-series hydrothermal syntheses from two organic-cation-free gels with different compositions were employed to study the factors that control the final size of zeolite L crystals. The first gel had a starting K/Al ratio of 10, whereas in the second one it was three times lower. The relatively simple chemical composition of the starting gels and the combination of complementary characterization methods allowed us to track down the different stages of transformation of the initial amorphous gels into zeolite crystals and the factors that control the nucleation and growth processes. The role of the starting mixture components in the formation of the primary amorphous particles was explored. It was found that the profoundly different reaction kinetics in the two systems are caused by the difference in diffusion rates, which in turn are controlled by the extent of the polymerization reactions at room temperature during mixing of the starting components prior to hydrothermal treatment. As a consequence, nucleation is fast and ubiquitous in the first system with higher water content and K/Al ratio, whereas it is slow and sporadic in the second system with lower water content and K/Al ratio. Ultimately, these differences in the kinetics lead to the formation of two distinctly different patterns of crystal-size distribution, with a large number of small nanocrystals in the first sample and fewer large crystals in the second sample. The new findings put zeolite crystal growth on a rational basis that would enable the control of zeolite crystal size in similar organic-template-free systems., (Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)
- Published
- 2011
- Full Text
- View/download PDF
20. Micro- to macroscopic observations of MnAlPO-5 nanocrystal growth in ionic-liquid media.
- Author
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Ng EP, Itani L, Sekhon SS, and Mintova S
- Abstract
Micro- and macroscopic studies of nucleation and growth processes of MnAlPO-5 nanosized crystals under ionothermal synthesis conditions are reported herein. The samples treated at 150 °C were extracted from the reaction mixture at various stages of crystallization, and characterized by XRD; SEM; thermogravimetric analysis (TGA); (31)P and (27)Al solid-state magic angle spinning (MAS) NMR, Raman, UV/Vis, and X-ray fluorescence spectroscopy (XRF). The starting raw materials (alumina, manganese, and phosphorous) were dissolved completely in the ionic liquid and transformed into an amorphous solid after 5 h of ionothermal treatment. This amorphous solid then undergoes structural changes over the following 5-25 h, which result in an intermediate phase that consists of octahedral Al species linked to the manganese and phosphate species. The first MnAlPO-5 nuclei on the surface of the intermediate can be observed after 50 h ionoheating. These nuclei further grow, as the surface of the intermediate is in full contact with the ionic liquid, to give crystalline MnAlPO-5 nanoparticles with a mean diameter of 80 nm. The crystals become fully detached from the intermediate and are then liberated as discrete particles after 90 h heating. The transformation process from amorphous to intermediate and then to the crystalline MnAlPO-5 nanoparticles shows that nucleation starts at the solid-liquid interface and continues through surface-to-core reversed-growth until the entire amorphous solid is transformed into discrete nanocrystals.
- Published
- 2010
- Full Text
- View/download PDF
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