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Sotiris E Pratsinis - One of the best experts on this subject based on the ideXlab platform.
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direct Synthesis of maghemite magnetite and wustite nanoparticles by Flame spray pyrolysis
Advanced Powder Technology, 2009Co-Authors: Reto Strobel, Sotiris E PratsinisAbstract:Abstract Magnetic iron-oxide nanoparticles have been prepared by Flame spray pyrolysis (FSP) under controlled atmosphere. This way controlled and direct Flame Synthesis of Fe 2 O 3 (maghemite), Fe 3 O 4 (magnetite) and FeO (wustite) particles is possible by a scalable process. The Fe oxidation state was controlled by varying the fuel to air ratio during combustion as well as by varying the valence state of the applied Fe precursor. The as-prepared materials were characterized by electron microscopy, nitrogen adsorption, X-ray diffraction and Raman spectroscopy. Magnetic properties were investigated with SQUID, which unravelled superparamagnetic behaviour for all materials and typical features for the corresponding crystal structures and particle sizes. Maximum magnetisation was achieved for a mixture of maghemite and magnetite.
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Flame aerosol Synthesis of smart nanostructured materials
Journal of Materials Chemistry, 2007Co-Authors: Reto Strobel, Sotiris E PratsinisAbstract:Recent advances in aerosol and combustion science and engineering now allow scalable Flame Synthesis of mixed oxides, metal salts and even pure metals in the form of nanoparticles and films with closely controlled characteristics. In this way, high purity materials with novel metastable phases are made that are not accessible by conventional wet-phase and solid state processes. Here, Flame processes are classified into vapour-fed and liquid-fed ones depending on the employed state of the metal precursor. Liquid-fed Flame processes are distinguished for their flexibility in producing materials of various compositions and morphologies that result in unique product functionalities. Parameters controlling the characteristics of Flame-made particles and films are summarized and selected classes of materials are reviewed focusing on catalysts, sensors, biomaterials (orthopaedic, dental or nutritional), electroceramics (fuel cells, batteries) and phosphors exhibiting superior performance over conventionally made ones. Just a few years ago it seemed impossible to make these materials in the gas phase. Finally, health effects of such particles are discussed while future challenges and opportunities for Flame-made materials are highlighted.
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aerosol Flame Synthesis of catalysts
Advanced Powder Technology, 2006Co-Authors: Reto Strobel, Alfons Baiker, Sotiris E PratsinisAbstract:Abstract A review of Synthesis and performance of Flame-made catalytic materials is presented. Emphasis is placed on Flame technology for its dominance in aerosol manufacturing of materials of high purity with minimal liquid byproducts. Flame aerosol processes are characterized in terms of the precursor state supplied to the Flame. During the last decade, a better understanding of aerosol and combustion Synthesis of materials contributed to the development of one-step, dry Synthesis of catalysts that are prepared conventionally by multi-step wet-phase processes. This includes TiO 2 -based photocatalysts, mixed oxides (e.g. V 2 O 5 /TiO 2 , TiO 2 /SiO 2 , perovskites, etc.) as well as supported metals (e.g. Pt/TiO 2 , Pd/Al 2 O 3 , Pt/CeO 2 /ZrO 2 , Pt/Ba/Al 2 O 3 , Ag/ZnO, Cu/ZnO/Al 2 O 3 bimetallic Pd/Pt/Al 2 O 3 and Au/TiO 2 ) made by single- or multi-nozzle Flames. In general, highly crystalline and non-porous nanoparticles are formed during Flame Synthesis, resulting in materials with high thermal stability. Unique particle structures, only available through aerosol processes, lead to improved performance in various catalytic applications.
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Flame made pd la2o3 al2o3 nanoparticles thermal stability and catalytic behavior in methane combustion
Journal of Materials Chemistry, 2005Co-Authors: Reto Strobel, Sotiris E Pratsinis, Alfons BaikerAbstract:Palladium nanoparticles supported on lanthanum-stabilized alumina were prepared by Flame spray pyrolysis. The as-prepared materials were characterized by high-resolution transmission electron microscopy, CO chemisorption, nitrogen adsorption, X-ray diffraction and temperature programmed reduction. These materials were tested for the catalytic combustion of methane with a focus on the thermal stability of the support and the palladium particles. Flame spray pyrolysis afforded small palladium particles (<5 nm) attached to the surface of the supporting La2O3/Al2O3 ceramic nanoparticles with specific surface areas in the range of 50–180 m2 g−1. Compared to commercial reference materials the Flame-made catalysts showed excellent thermal stability in terms of specific surface area up to 1200 °C and retarded γ- to α-alumina transformation. Catalysts were tested as-prepared (small Pd particles, <5 nm) and after sintering at 1000 °C (large Pd particles, 50–150 nm). By cycling the temperature several times from 200 to 1000 °C during catalytic combustion, it could be shown that all catalytic materials, regardless of specific surface area, lanthanum content, and preparation method (Flame-Synthesis or impregnated), exhibited similar catalytic performance after an initial conditioning cycle.
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fluoro apatite and calcium phosphate nanoparticles by Flame Synthesis
Chemistry of Materials, 2005Co-Authors: Stefan Loher, Wendelin J. Stark, Frank Krumeich, Sotiris E Pratsinis, Alfons Baiker, M Maciejewski, Dennis Reichardt, Fabrice Maspero, Detlef GuntherAbstract:Calcium phosphate nanoparticles with calcium/phosphorus molar ratios ranging from 1.43 to 1.67 have been synthesized by simultaneous combustion of calcium carboxylate and tributyl-phosphate based precursors in a Flame spray reactor. Fluoro-apatite and zinc or magnesium doped calcium phosphates were obtained by adding trifluoroacetic acid or corresponding carboxylates into the fuel. Nanoparticle morphology and the structure of sintered ceramics were studied using transmission and scanning electron microscopy. Thermal evolution of calcium phosphate phases was investigated by powder X-ray diffraction, Fourier transform infrared spectroscopy, and thermal analysis. A molar ratio of Ca/P < 1.5 in the precursor promoted the formation of dicalcium pyrophosphate (Ca2P2O7). Phase pure β-tricalcium phosphate was obtained with a precursor Ca/P ratio of 1.52 after subsequent calcination at 900 °C. The regular, open structure with interconnecting micropores and the facile substitution of both anions and cations suggest...
Wendelin J. Stark - One of the best experts on this subject based on the ideXlab platform.
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energy efficient noble metal recovery by the use of acid stable nanomagnets
Industrial & Engineering Chemistry Research, 2010Co-Authors: Michael Rossier, Robert N Grass, Evagelos K Athanassiou, Detlef Gunther, Fabian M Koehler, Markus Waelle, Karin Birbaum, Wendelin J. StarkAbstract:The present work investigates the potential use of metal-based carbon-coated magnetic nanoparticles for the efficient extraction of gold and platinum at high dilution (milligram to gram per ton ≡ ppb to ppm) at a mini-pilot level (0.1 m3). Acid-stable nanomagnets were first prepared by reducing Flame Synthesis and consisted of graphene-like carbon-coated cobalt metal nanoparticles (20−40 nm diameter) with an onion-like core/shell structure. The use of a metal core affords high saturation magnetization, while carbon shells are highly resistant to most chemical conditions. The nanomagnet surface was further coated with a standard noble metal extraction resin-like polymer (thiourea groups on a poly(ethylene imine)). Extraction runs were tested both at laboratory scale (0.1−10 L; Au and Pt removal > 95%; down to the milligram per ton level) and in a tank model (vertical tank section, 4 m height, 0.1 m3 volume, Pt removal > 80% at 50 mg/ton of acid water). Delivery of freshly dispersed nanomagnet dispersions o...
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preparation of homogeneous bulk nanocrystalline ni mo alloys with tripled vickers hardness using Flame made metal nanoparticles
Chemistry of Materials, 2007Co-Authors: Evagelos K Athanassiou, Robert N Grass, Neil Osterwalder, Wendelin J. StarkAbstract:Metals and metal−alloys have been traditionally prepared by large-scale reduction and ore refining. The present work demonstrates how this reduction and alloying step can be executed within Flame aerosol reactors on a sub-second time scale and gives access to metal−alloy nanoparticles of 10−50 nm size at high production rate. We demonstrate the preparation of Ni/Mo and Hastelloy like metal nanoparticles as examples for this process and showed that the product particles exhibited an exceptionally high air stability and narrow particle size distribution in comparison to presently accessible materials. Sintering and compaction gave access to centimeter-sized bulk nanocrystalline alloys with strongly enhanced Vickers hardness. The versatility of already broadly used aerosol processing of oxides suggests that the extension of Flame Synthesis to metals and alloys may offer an alternative for the preparation of multicomponent nanocrystalline metals.
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Preparation of nano-gypsum from anhydrite nanoparticles: Strongly increased Vickers hardness and formation of calcium sulfate nano-needles
Journal of Nanoparticle Research, 2007Co-Authors: Neil Osterwalder, Robert N Grass, Tobias J Brunner, Stefan Loher, Ludwig K. Limbach, Samuel C. Halim, Wendelin J. StarkAbstract:The preparation of calcium sulfate by Flame Synthesis resulted in the continuous production of anhydrite nanoparticles of 20–50 nm size. After compaction and hardening by the addition of water, the anhydrite nanoparticles reacted to nano-gypsum which was confirmed by X-ray diffraction, diffuse reflectance IR spectroscopy and thermal analysis. Mechanical properties were investigated in terms of Vickers hardness and revealed an up to three times higher hardness of nano-gypsum if compared to conventional micron-sized construction material. The improved mechanical properties of nano-gypsum could in part be due to the presence of calcium sulfate nano-needles in the nano-gypsum as showed by electron microscopy.
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gas phase Synthesis of fcc cobalt nanoparticles
Journal of Materials Chemistry, 2006Co-Authors: Robert N Grass, Wendelin J. StarkAbstract:Air stable cobalt nanoparticles have been prepared continuously at a production rate of 30 g h−1 by a modified Flame Synthesis method under highly reducing conditions. Nanoparticles of 20–60 nm in diameter consisted of metallic face-centered-cubic cobalt. The metal particles were protected against oxidation by a surface layer of less than 1 nm of cobalt oxide. The material was highly magnetic exhibiting a high saturation magnetisation (>124 emu g−1) together with a low (<100 Oe) coercivity. Experiments under varying fuel to oxygen ratio were combined with thermodynamic calculations to illustrate the necessity for highly reducing conditions and enhanced gas mixing to enable the formation of metallic cobalt nanoparticles in Flames.
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glass and bioglass nanopowders by Flame Synthesis
Chemical Communications, 2006Co-Authors: Tobias J Brunner, Robert N Grass, Wendelin J. StarkAbstract:The preparation of amorphous nanopowders by Flame Synthesis opens access to common soda-lime, metal-doped glasses or bioglasses in the range of 20-80 nm and offers an alternative to conventional wet-phase preparation, solid state reactions or melting.
Dušan Galusek - One of the best experts on this subject based on the ideXlab platform.
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Y3Al5O12-α-Al2O3 composites with fine-grained microstructure by hot pressing of Al2O3-Y2O3 glass microspheres
Journal of the European Ceramic Society, 2020Co-Authors: Anna Prnova, Milan Parchovianský, Robert Klement, Els Bruneel, Peter Švančárek, Jana Valúchová, Wolfgang Wisniewski, Ľubomír Hric, Dušan GalusekAbstract:Abstract Yttrium aluminate glass microspheres with the eutectic composition 76.8 mol. % Al2O3 and 23.2 mol. % Y2O3 were prepared by combining the sol-gel Pechini method with Flame Synthesis. The sol-gel method was applied to achieve the desired composition homogeneity of the prepared glass and hence, improve the microstructure homogeneity and mechanical properties of bulk polycrystalline materials. The latter were prepared by hot pressing, more specifically pressure assisted sintering, at 1050 °C, 1300 °C and 1600 °C using pressures of 30 MPa and 80 MPa and holding times between 0 and 30 min. This also led to the crystallization of the glass. A composite with the Vickers hardness 18.0 ± 0.7 GPa and an indentation fracture toughness 4.9 ± 0.3 MPa.m1/2 was obtained by sintering at 1600 °C, at the pressure of 80 MPa and with 30 min isothermal heating at the maximum temperature. Improved mechanical properties were observed when increasing the temperature of sintering and the holding time. This can be attributed to the formation of a unique microstructure consisting of α-Al2O3 grains in the μm-scale embedded in a YAG (yttrium-aluminium garnet) matrix in the hot-pressed samples.
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crystallization and visible near infrared luminescence of bi doped gehlenite glass
Royal Society Open Science, 2018Co-Authors: Melinda Majerová, Anna Prnova, Robert Klement, Els Bruneel, Jozef Kraxner, Dušan GalusekAbstract:Gehlenite glass microspheres, doped with a different concentration of Bi3+ ions (0.5, 1, 3 mol%), were prepared by a combination of solid-state reaction followed by Flame Synthesis. The prepared gl...
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gehlenite eu3 phosphors from a silicone resin and nano sized fillers
Optical Materials, 2014Co-Authors: Enrico Bernardo, Anna Prnova, Laura Fiocco, Robert Klement, Dušan GalusekAbstract:Abstract Gehlenite (Ca 2 Al 2 SiO 7 ) ceramics have been successfully prepared by a novel approach, consisting of the heat treatment of a silicone resin embedding CaO and Al 2 O 3 precursors, in the form of nano-sized particles that act as reactive fillers. Luminescence was due to the use of nano-sized Eu 2 O 3 as secondary additive, particularly adopting a charge compensation formulation, i.e. Ca 2−2 x Eu 2 x Al(Al 1+2 x Si 1−2 x O 7 ), with x = 0.07. The phase development and the emission characteristics could be adjusted by simply changing the thermal treatment applied to powders of silicone/fillers mixtures. While conventional firing at 1300 °C (for 1 h) led to practically phase-pure crystalline Eu-doped gehlenite, exhibiting a strong red luminescence, Flame Synthesis yielded amorphous powders, exhibiting an emission in a much broader range. When excited at 394 nm both gehlenite glass and polycrystalline gehlenite emitted light, which CIE chromaticity coordinates were found to be ( x = 0.65, y = 0.35), indicating that both systems are good candidates for red light emitting phosphors.
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the preparation of bulk aluminate glasses by hot pressing of glass microspheres
Advanced Ceramic Materials, 2014Co-Authors: Anna Prnova, Robert Klement, Els Bruneel, Dušan Galusek, Katarina Bodisova, Natalia Skvarkova, Isabel Van DriesscheAbstract:In this work the yttrium-aluminate glasses with different composition A60Y40M (76.8 mol.% Al2O3), A63Y37M (81.8 mol.% Al2O3), and YAG (62.6 mol.% Al2O3) were prepared by Flame Synthesis in the form of glass microspheres and characterized by OM, SEM, XRD, HT XRD and DSC analysis. On the basis of the results of HT XRD and DSC analysis, the individual crystallisation experiments were performed. The morphology of crystallized microspheres was studied by SEM and the content of individual crystalline phases was evaluated. The microspheres with the eutectic composition A60Y40M were hot-pressed in vacuum under various conditions (temperatures 900-1600°C, pressure 80 MPa, isothermal dwell time 0-30 min). The highest hardness 17.7 GPa and fine grained microstructure was observed for the samples hot pressed at 1300°C with isothermall dwell time of 30 min.
Robert N Grass - One of the best experts on this subject based on the ideXlab platform.
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energy efficient noble metal recovery by the use of acid stable nanomagnets
Industrial & Engineering Chemistry Research, 2010Co-Authors: Michael Rossier, Robert N Grass, Evagelos K Athanassiou, Detlef Gunther, Fabian M Koehler, Markus Waelle, Karin Birbaum, Wendelin J. StarkAbstract:The present work investigates the potential use of metal-based carbon-coated magnetic nanoparticles for the efficient extraction of gold and platinum at high dilution (milligram to gram per ton ≡ ppb to ppm) at a mini-pilot level (0.1 m3). Acid-stable nanomagnets were first prepared by reducing Flame Synthesis and consisted of graphene-like carbon-coated cobalt metal nanoparticles (20−40 nm diameter) with an onion-like core/shell structure. The use of a metal core affords high saturation magnetization, while carbon shells are highly resistant to most chemical conditions. The nanomagnet surface was further coated with a standard noble metal extraction resin-like polymer (thiourea groups on a poly(ethylene imine)). Extraction runs were tested both at laboratory scale (0.1−10 L; Au and Pt removal > 95%; down to the milligram per ton level) and in a tank model (vertical tank section, 4 m height, 0.1 m3 volume, Pt removal > 80% at 50 mg/ton of acid water). Delivery of freshly dispersed nanomagnet dispersions o...
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preparation of homogeneous bulk nanocrystalline ni mo alloys with tripled vickers hardness using Flame made metal nanoparticles
Chemistry of Materials, 2007Co-Authors: Evagelos K Athanassiou, Robert N Grass, Neil Osterwalder, Wendelin J. StarkAbstract:Metals and metal−alloys have been traditionally prepared by large-scale reduction and ore refining. The present work demonstrates how this reduction and alloying step can be executed within Flame aerosol reactors on a sub-second time scale and gives access to metal−alloy nanoparticles of 10−50 nm size at high production rate. We demonstrate the preparation of Ni/Mo and Hastelloy like metal nanoparticles as examples for this process and showed that the product particles exhibited an exceptionally high air stability and narrow particle size distribution in comparison to presently accessible materials. Sintering and compaction gave access to centimeter-sized bulk nanocrystalline alloys with strongly enhanced Vickers hardness. The versatility of already broadly used aerosol processing of oxides suggests that the extension of Flame Synthesis to metals and alloys may offer an alternative for the preparation of multicomponent nanocrystalline metals.
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Preparation of nano-gypsum from anhydrite nanoparticles: Strongly increased Vickers hardness and formation of calcium sulfate nano-needles
Journal of Nanoparticle Research, 2007Co-Authors: Neil Osterwalder, Robert N Grass, Tobias J Brunner, Stefan Loher, Ludwig K. Limbach, Samuel C. Halim, Wendelin J. StarkAbstract:The preparation of calcium sulfate by Flame Synthesis resulted in the continuous production of anhydrite nanoparticles of 20–50 nm size. After compaction and hardening by the addition of water, the anhydrite nanoparticles reacted to nano-gypsum which was confirmed by X-ray diffraction, diffuse reflectance IR spectroscopy and thermal analysis. Mechanical properties were investigated in terms of Vickers hardness and revealed an up to three times higher hardness of nano-gypsum if compared to conventional micron-sized construction material. The improved mechanical properties of nano-gypsum could in part be due to the presence of calcium sulfate nano-needles in the nano-gypsum as showed by electron microscopy.
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gas phase Synthesis of fcc cobalt nanoparticles
Journal of Materials Chemistry, 2006Co-Authors: Robert N Grass, Wendelin J. StarkAbstract:Air stable cobalt nanoparticles have been prepared continuously at a production rate of 30 g h−1 by a modified Flame Synthesis method under highly reducing conditions. Nanoparticles of 20–60 nm in diameter consisted of metallic face-centered-cubic cobalt. The metal particles were protected against oxidation by a surface layer of less than 1 nm of cobalt oxide. The material was highly magnetic exhibiting a high saturation magnetisation (>124 emu g−1) together with a low (<100 Oe) coercivity. Experiments under varying fuel to oxygen ratio were combined with thermodynamic calculations to illustrate the necessity for highly reducing conditions and enhanced gas mixing to enable the formation of metallic cobalt nanoparticles in Flames.
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glass and bioglass nanopowders by Flame Synthesis
Chemical Communications, 2006Co-Authors: Tobias J Brunner, Robert N Grass, Wendelin J. StarkAbstract:The preparation of amorphous nanopowders by Flame Synthesis opens access to common soda-lime, metal-doped glasses or bioglasses in the range of 20-80 nm and offers an alternative to conventional wet-phase preparation, solid state reactions or melting.
Markus Kraft - One of the best experts on this subject based on the ideXlab platform.
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understanding the anatase rutile stability in Flame made tio2
Combustion and Flame, 2021Co-Authors: My Manuputty, Markus Kraft, Casper S Lindberg, Jochen A H Dreyer, Jethro Akroyd, Jack R EdwardsAbstract:Abstract The relative stability of anatase and rutile in stagnation Flame Synthesis with stoichiometric mixtures is investigated experimentally. The measurements reveal a high sensitivity of anatase-rutile composition to the Flame dilution. It is demonstrated that anatase formation is favoured in more dilute (colder) Flames while rutile is favoured in less dilute (hotter) Flames. A particle model with a detailed description of aggregate morphology and crystal phase composition is applied to investigate the anatase-rutile stability. A phase transformation model is implemented in which rutile is formed for particles larger than a “crossover” size while anatase is formed for those smaller. Two formation mechanisms/pathways are discussed and evaluated. In the first pathway, the nascent particles are assumed to be stoichiometric and the crossover size is determined solely by the surface free energy. This hypothesis captures the general trend in the measured anatase-rutile composition but fails to explain the sensitivity. In the second pathway, non-stoichiometric TiO 2 − x oxide intermediates are assumed and the crossover size is hypothesised to be composition-dependent. This shows an excellent agreement with the experimental data. However, this hypothesis is found to be strongly influenced by assumptions about the initial particle growth stages. This study demonstrates the importance of a better description of the high-temperature chemistry and initial clustering mechanism in order to understand the crystal phase formation.
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modelling the Flame Synthesis of silica nanoparticles from tetraethoxysilane
Chemical Engineering Science, 2012Co-Authors: Shraddha Shekar, Markus Sander, Rebecca C Riehl, Alastair J Smith, Andreas Braumann, Markus KraftAbstract:This work proposes a kinetic model and an inception pathway for the Flame Synthesis of silica nanoparticles from tetraethoxysilane (TEOS). The kinetic model for the decomposition of TEOS is developed by generating reactions involving species that were reported in high concentrations at equilibrium. Flux and sensitivity analyses are then performed to identify the main reaction pathways. The parameters for these reactions are systematically fitted to experimental data using low discrepancy (LD) sequences and response surfaces. The main product of TEOS decomposition is deduced to be silicic acid (Si(OH)4). To increase computational efficiency, the kinetic model has been reduced by determining the level of importance (LOI) of each species and retaining only the important ones. This reduced kinetic model is then coupled to a detailed population balance model using an operator splitting technique. New particle inception and surface growth steps have been incorporated into the particle model in which particles form and grow by the interaction of Si(OH)4 monomers. Coagulation and sintering of particles are also included in the model and the material dependent sintering parameters have been determined by fitting the model to experimental values of collision and primary particle diameters using LD sequences. The particle size distributions and computer-generated TEM-style images have been generated and good agreement with experiments is observed. The gas-phase reactor composition and the temporal evolution of particle size at different temperatures are also presented.