Preparation and characterization of ceramics laser alloyed with WO3 and CuO nanopowders

A well defined surface layer of a ceramic substrate can be modified by introducing a selected second phase into a melt pool generated locally by a laser beam. CuO, WO3 powders with nano-sized particles were used to alloy alumina and a glass ceramic LTCC (Low Temperature Co-fired Ceramic). Depending on the process parameters the nano-particles were melted during the laser process and solidified during cooling in the ceramic matrix. As a result a composite with complex multiphase microstructure was developed with particle agglomerates, small crystals as well as grains covered with reaction phase, in parts with typical length scales down to the submicron range. Also the geometry of the modified area could be controlled by the process parameters. A significant change of properties could be established for the laser alloyed tracks. Especially the thermal and electrical properties were changed in comparison to that of the ceramic substrate. The developed composites showed a measurable electrical conductivity with a negative temperature coefficient for the resistivity. Therefore, the resistivity decreases with increasing temperature, which is typical for a thermally activated conduction mechanism as in semiconductors. The thermal conductivity could be increased to about 20% for CuO- and up to 70% for WO3-powder compared to the unmodified LTCC-substrate

VII International Conference on Mechanochemistry and Mechanical Alloying INCOME 2011: Programme and the Book of Abstracts

The INCOME series of conferences initiated by International Mechanochemistry Association [an associate member of International Union of Pure and Applied Chemists (IUPAC)] has served as a common platform to bring together all stakeholders from academia, Research and Development organisations, and industry to foster the growth of the discipline. The first international conference on ‘Mechanochemistry and Mechanical Alloying’ (INCOME 1993) was held in Košice (Slovakia) in 1993. This was followed by INCOME 1997 in Novosibirsk (Russia), INCOME 2000 in Prague (Czech Republic); INCOME 2003, in Braunschweig (Germany), INCOME 2006 again in Novosibirsk, INCOME 2008 in Jamshedpur (India), and INCOME 2011 (Montenegro)

Combustion of nanocomposite thermite powders

This work investigates combustion of nanocomposite thermite powders prepared by arrested reactive milling (ARM). The focus is on how ARM as a top-down approach to nano-thermite building generating fully-dense nanocomposite particles with dimensions of 1-100 µm affects the rates and mechanism of their combustion. A variety of thermites are milled using both aluminum and zirconium as fuels combined with several oxidizers (WoO3, MoO3, CuO, Fe2O3, and Bi2O3). The powders are ignited using both an electrostatic discharge (ESD) and a CO2 laser beam. A range of parameters vary in the first set of experiments in order to broadly understand the underlying combustion mechanisms of nanocomposite thermite powders. Only the aluminum thermites are considered in these experiments and had their particle sizes, preparation method (milled, mixed, or electrosprayed), and milling times adjusted in order to see their effects on combustion. Additionally the ESD ignition experiments vary the environment between air, argon, and vacuum, as well as varying the ignition voltages from 5 up to 20 kV at a constant capacitance of 2000 pF. The ignited particles are monitored using a photomultiplier tube (PMT) equipped with an interference filter. It is observed that the reaction rates of the ESD-initiated powders are unaffected by their particle size but are affected by their scale of mixing between their fuel and oxidizer within the particles themselves. The different preparation methods play a significant role in determining the powders performance. Mixed nano-powders agglomerated quite easily, which hinder their combustion performance. The electrosprayed powders perform well in all environments, and the milled powders perform best in oxidizer-free environments (when no reoxidation of the oxidizer could occur). A set of experiments employing ESD ignition focus on the effects of powder load on its combustion properties. The experiments utilize a similar PMT setup with an additional 32-channel PMT coupled with a spectrometer to record optical emission in the range of 373-641 nm. It is discovered that when a monolayer of the powder was ignited, only single particles are ejected from the substrate and burned very rapidly. A thicker layer of powder (0.5 mm) struck by ESD produce an aerosol cloud, which ignite with a delay and burn substantially longer. It is theorized that the difference was due to different heating rates between the two experiments. In monolayer experiments, all ignited particles are ignited directly by ESD. Only a small fraction of particles in the thicker layered powder is heated directly by ESD; most particles are heated slower due to heat transfer from the initially ignited powder. More in depth experiments on the heating rate are conducted utilizing the fast heating of the thermites powders by ESD at ca. 109 K/s along with an experiment, in which the same thermite particles are heated and ignited by laser with the heating rate of ca. 106 K/s. It is discovered that laser-ignited particles combusted slower due to a loss of their nanostructure, while ESD-ignited particles maintained their nanostructure and burned much more quickly. Utilizing the results from all the experiments, and combining them with combustion information previously obtained for Al and its ignition, with reaction controlled by polymorphic phase transformations in alumina (amorphous, gamma, and alpha), a model is developed enabling one to describe quantitatively the very high burn rates observed for the nanothermite particles rapidly heated by ESD. The model considers nanostructure accounting for the inclusion size distribution obtained from SEM images of actual milled particles, along with other considerations including heat loses, phase transformations, density changes, and particle size. The model is able to match combustion times and temperatures with those recorded from the earlier ESD combustion experiments

VII International Conference on Mechanochemistry and Mechanical Alloying INCOME 2011: Programme and the Book of Abstracts

The INCOME series of conferences initiated by International Mechanochemistry Association [an associate member of International Union of Pure and Applied Chemists (IUPAC)] has served as a common platform to bring together all stakeholders from academia, Research and Development organisations, and industry to foster the growth of the discipline. The first international conference on ‘Mechanochemistry and Mechanical Alloying’ (INCOME 1993) was held in Košice (Slovakia) in 1993. This was followed by INCOME 1997 in Novosibirsk (Russia), INCOME 2000 in Prague (Czech Republic); INCOME 2003, in Braunschweig (Germany), INCOME 2006 again in Novosibirsk, INCOME 2008 in Jamshedpur (India), and INCOME 2011 (Montenegro)

Décharge électrique à l'interface de deux liquides : application à la synthèse de nanoparticules

Les procédés plasma-liquide sont considérablement étudiés en raison de leur potentiel élevé dans la production de divers nanomatériaux, parmi d’autres applications technologiques. En plus d'un rendement relativement élevé (mg/min) et d'une infrastructure simplifiée, les mécanismes de synthèse sont directs. Le fait que les produits restent confinés dans la solution, la manipulation de nanomatériaux ne présente un danger ni aux vivants ni à l’environnement. Dans ce mémoire de maitrise, les méthodes les plus courantes pour la synthèse de nanomatériaux, en particulier les systèmes plasma-liquide, sont discutées. La formation de différents régimes de plasma dans des liquides, dont chacun a des caractéristiques et des applications différentes, est présentée. Ensuite, le système multi-liquide et ses caractéristiques, telles que les caractéristiques électriques et la dynamique de l’émission des décharges dans différentes conditions, sont exposés. Pour la synthèse de nanoparticules, on traite les décharges Sparks (étincelles) avec une attention particulière. Au lieu de les produire entre deux électrodes immergées dans un liquide diélectrique, les décharges sont produites dans un hydrocarbure liquide entre une électrode et une solution conductrice. Cette dernière est produite via l’ajout de nitrate d’argent dans l’eau. Le plasma, via ses espèces réactives, réduit les ions Ag+ en Ag0 qui forment ensuite les nanoparticules. La décomposition de l’hydrocarbure produit aussi des espèces carbonées qui se recombinent sous forme d’une matrice hydrocarbonée. En se basant sur différentes méthodes de caractérisations (FTIR, MEB, MET, UV-vis, etc.), nous identifions deux zones de réactions : dans le plasma dans l’heptane et à l’interface plasma-solution. Les produits dans la première zone sont majoritairement des nanoparticules (< 10 nm) d’Ag enrobées dans une matrice de carbone hydrogénée. Cependant, les produits dans la solution sont des nanoparticules d’Ag (sans matrice) ayant une distribution de taille de quelques dizaines de nanomètres.Plasma-liquid systems are significantly investigated due to their high potential in the production of various nanomaterials, among other technological applications. In addition to relatively high efficiency in production (mg/min) and simplified infrastructure, the mechanisms of synthesis are rather direct. Also, because the products are confined in solution, the handling of the nanomaterials do not present risks to the living or to the environment. In this master thesis, the most common methods for nanomaterial synthesis, in particular plasma-liquid systems, are discussed. Formation of different plasma regimes in liquids, which each of them has different features and application, are explained. Then, the multiple liquid system and their feature such as electrical characteristics and emission dynamic of the discharges at different conditions, are investigated. To produce nanoparticles, we present the Spark discharges with special attention. Instead of their production between two electrodes immersed in a liquid dielectric, the discharges are produced in a liquid hydrocarbon between one electrode and a conductive solution. This latter is prepared by adding silver nitrate to water. The plasma, through its reactive species, reduces the ions Ag+ to Ag0 that produces nanoparticles. The decomposition of the hydrocarbon produces carbonaceous species that recombine as hydrocarbon matrix. Based on the different characterisation techniques (FTIR, SEM. TEM. UV-vis, etc.), we identified two zones of reactions: in plasma in heptane and at the interface plasma-solution. The products in the former zone are majority 10 nm-particles of Ag embedded in a hydrocarbon matrix, while the products in solution are Ag nanoparticles (without matrix) with size of several tens of nanometers

Multifunctional reactive nanocomposite materials

Many multifunctional nanocomposite materials have been developed for use in propellants, explosives, pyrotechnics, and reactive structures. These materials exhibit high reaction rates due to their developed reaction interfacial area. Two applications addressed in this work include nanocomposite powders prepared by arrested reactive milling (ARM) for burn rate modifiers and reactive structures. In burn rate modifiers, addition of reactive nanocomposite powders to aluminized propellants increases the burn rate of aluminum and thus the overall reaction rate of an energetic formulation. Replacing only a small fraction of aluminum by 8Al•MoO3 and 2B•Ti nanocomposite powders enhances the reaction rate with little change to the thermodynamic performance of the formulation; both the rate of pressure rise and maximum pressure measured in the constant volume explosion test increase. For reactive structures, nanocomposite powders with bulk compositions of 8Al•MoO3, 12Al•MoO3, and 8Al•3CuO were prepared by ARM and consolidated using a uniaxial die. Consolidated samples had densities greater than 90% of theoretical maximum density while maintaining their high reactivity. Pellets prepared using 8Al•MoO3 powders were ignited by a CO2 laser. Ignition delays increased at lower laser powers and greater pellet densities. A simplified numerical model describing heating and thermal initiation of the reactive pellets predicted adequately the observed effects of both laser power and pellet density on the measured ignition delays. To investigate the reaction mechanisms in nanocomposite thermites, two types of nanocomposite reactive materials with the same bulk compositions 8Al•MoO3 were prepared by different methods. One of the materials was manufactured by ARM and the other, so called metastable interstitial composite (MIC), by mixing of nano-scaled individual powders. Clear differences in the low-temperature redox reactions, well- detectable by differential scanning calorimetry (DSC), were established between MIC and ARM-prepared materials. However, the materials behaved similarly to each other in the ignition experiments. It is proposed that the ignition of both MIC and ARM-prepared materials at the same temperature can be explained by a thermodynamically driven transformation of a protective amorphous alumina into a crystalline polymorph. Low temperature redox reactions in ARM-prepared Al-CuO nanocomposites were characterized using DSC and isothermal microcalorimetry. The results were interpreted using a Cabrera-Mott reaction model. Simultaneous processing of both experimental data sets identified the parameters for the respective Cabrera-Mott kinetics. The low temperature kinetic model was coupled with a multi-step oxidation model describing diffusion-controlled growth of amorphous and γ-Al2O3 polymorphs. The kinetic parameters for the multistep oxidation model from previous research were adjusted based on DSC measurements. The combined heterogeneous reactions model was used to interpret results of ignition experiments. It is proposed that the heterogeneous reactions considered serve as ignition triggers and ensuing gas release processes contributes to additional heat release and temperature runaway

Microwave-assisted processing of solid materials for sustainable energy related electronic and optoelectronic applications

Materials processing using microwave radiation is emerging as a novel and innovative technology that has proven useful in a number of applications. It has various advantages over conventional processing, such as; time and energy saving, very rapid heating rates, considerably reduced processing time and temperature, fine microstructures and improved mechanical properties, better product performance, etc. Microwave irradiation has shown great potential for the processing of different semiconductor materials and inorganic solids for various advanced electronic and optoelectronic devices such as solar cells, batteries, supercapacitors, fuel cells etc. This work intends to investigate the effect of microwave radiation on various semiconductor materials and inorganic solids, in particular the changes in their chemical, physical and photoelectrochemical properties after microwave treatment. Microwaves have been used as an alternative method to conventional thermal annealing for post annealing of widely used semiconductors (TiO2, ZnO nanorods), battery materials (lithium aluminium titanium phosphates), and synthesis of materials (ZnO, Ti0.97Pd0.03O1.97). It is found that, in contrast to conventional thermal annealing, microwave treatment of such materials improves the crystallinity without any structural changes by preserving their nanostructure due to the difference in the heating mechanism (volumetric heating). The results demonstrate that microwave processing is a promising alternative method to the traditional conventional sintering for materials processing for advanced electronic and optoelectronic devices. Also the microwave annealing method offers energy savings of up to ~75%, which would make it highly desirable for industrial scale up

パルス放電による軽元素微粒子の作製、粒径制御と応用

国立大学法人長岡技術科学大

Continuous Hydrothermal Synthesis of Inorganic Nanoparticles: Applications and Future Directions

Nanomaterials are at the leading edge of the emerging field of nanotechnology. Their unique and tunable size-dependent properties (in the range 1-100 nm) make these materials indispensable in many modern technological applications. In this Review, we summarize the state-of-art in the manufacture and applications of inorganic nanoparticles made using continuous hydrothermal flow synthesis (CHFS) processes. First, we introduce ideal requirements of any flow process for nanoceramics production, outline different approaches to CHFS, and introduce the pertinent properties of supercritical water and issues around mixing in flow, to generate nanoparticles. This Review then gives comprehensive coverage of the current application space for CHFS-made nanomaterials including optical, healthcare, electronics (including sensors, information, and communication technologies), catalysis, devices (including energy harvesting/conversion/fuels), and energy storage applications. Thereafter, topics of precursor chemistry and products, as well as materials or structures, are discussed (surface-functionalized hybrids, nanocomposites, nanograined coatings and monoliths, and metal-organic frameworks). Later, this Review focuses on some of the key apparatus innovations in the field, such as in situ flow/rapid heating systems (to investigate kinetics and mechanisms), approaches to high throughput flow syntheses (for nanomaterials discovery), as well as recent developments in scale-up of hydrothermal flow processes. Finally, this Review covers environmental considerations, future directions and capabilities, along with the conclusions and outlook