Nanoenergetic Materials for MEMS: A Review

New energetic materials (EMs) are the key to great advances in microscale energy-demanding systems as actuation part, igniter, propulsion unit, and power. Nanoscale EMs (nEMs)particularly offer the promise of much higher energy densities, faster rate of energy release, greater stability, and more security sensitivity to unwanted initiation). nEMs could therefore give response to microenergetics challenges. This paper provides a comprehensive review of current research activities in nEMs for microenergetics application. While thermodynamic calculations of flame temperature and reaction enthalpies are tools to choose desirable EMs, they are not sufficient for the choice of good material for microscale application where thermal losses are very penalizing. A strategy to select nEM is therefore proposed based on an analysis of the material diffusivity and heat of reaction. Finally, after a description of the different nEMs synthesis approaches, some guidelines for future investigations are provided

Influence of nanoscaled surface modification on the reaction of Al/Ni multilayers

Sputtered reactive multilayers applied as a heat source in electronic joining processes are an emerging technology. Their use promises low-stress assembly of components while improving thermal contact and reducing thermal resistance. Nanostructured surface modifications can significantly enhance adhesion and reliability of joints between different materials. This work examines reactive multilayer of nickel and aluminum, directly sputtered on nanostructured black silicon surfaces and compares their phase transformation with reference samples deposited on pristine silicon surface. The investigation of the quenched self-propagating reaction reveals a clear influence of the nanostructured surface on the prolongation of the phase transition. Rapid thermal annealing tests result in the formation of Al1.1Ni0.9 phase. The nanostructured interface seems to hinder the full transformation of the parent material. The surface modification improves the adhesion of the formed alloy on silicon surfaces and can possibly increase the reliability of joints based on reactive aluminum/nickel multilayer. The use of black silicon, a nanostructured surface modification, is thus a promising approach to realize reliable multi-material joints in complex systems

Effect of process control agents used in mechanochemical synthesis on properties of the prepared composite reactive materials

The study explores synthesis and reactivity of new reactive materials prepared by ball milling. High-energy ball milling became a ubiquitous mechano-chemical tool to manufacture diverse powders, from pharmaceuticals or foods to alloys to new solid rocket propellants. It enabled a dramatic expansion of the range of chemical compositions obtainable; however, it did not so far, allowed one to fine-tune morphology or interfaces in the generated powders. It is shown in this work how different process control agents (PCAs) can serve to tune the powder morphology and reactivity. Commonly used as lubricants and cooling agents during milling, liquid PCAs can be used as an effective tool in modifying both chemistry and morphology of mechanochemically prepared reactive materials. For example, a polar, non-oxidizing fluid, e.g., acetonitrile, can reduce the size of aluminum particles, but more interestingly, it can modify their surface to enable new redox reaction pathways leading to accelerated ignition and combustion. Using such modified aluminum in a composite prepared by milling makes it possible to design unusual reactive materials. Materials with the same chemical compositions, and thus the same overall energy densities can be made with controllable reaction dynamics and tunable heat release. Thus, it becomes possible to separate the effects of chemical composition and interface structure on the reaction mechanisms and rates. An even more unusual capability of manipulating shapes and sizes of the synthesized powders is discovered in this study when liquid PCA comprises two immiscible fluids. A complex system including an emulsion combined with suspended particles is generated inside the milling vial. When such a system is milled, solid particles can be refined, mixed, and eventually accumulated inside the droplet phase. Thus, spherical solid aggregates are formed with narrow size distributions. Milling conditions can be found to tune size, density, and porosity of such spheres. Produced narrowly-sized spherical powders are attractive because of their dramatically improved flowability. The existing methods for synthesizing spherical powders (e.g., spray-drying, extrusion-spheronization, droplet-melting) are more expensive, time-consuming, and energy-intensive. Unlike milling, they cannot be employed to a diverse range of materials and the challenges associated with wide particle size distributions often are unsurmountable. Our approach has been validated experimentally for elemental (e.g., Al, B), alloyed (B-Ti, Al-Ti), ceramic (Fe2O3), organic (melamine), and composite (Al-CuO) spheres from materials with a broad range of initial particle sizes and mechanical properties. The average size of the particles could be selectable from 5 to 200 µm. Experiments also confirmed superior rheological properties of the prepared reactive powders and their enhanced reactivity. For future, this study can be expanded beyond reactive materials to discover a new generation of value-added materials for catalysts, adsorbents, and feedstock powders for additive manufacturing

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

Studies on the Impact Initiation and Kinetics of Condensed Phase Reactives with Application to the Shock Induced Reaction Synthesis of Cubic Boron Nitride

Shock induced reaction synthesis is a complex, scientifically rich field with the potentially to produce novel materials with unique properties. This work seeks to understand the processes governing shock induced reaction synthesis. Particular emphasis is placed on the reaction kinetics of condensed phase reactives under various mechanical and thermal heating rates. This understanding was then applied to the synthesis of cubic boron nitride through shock induced reaction synthesis. Mechanical initiation of reactions in powder systems involve complex interactions that can yield unexpected results. Two materials that exhibit similar thermal responses can behave very differently under the same loading conditions due to differences in their mechanical properties. Reactive composite powders with small characteristic dimensions can exhibit short ignition delays and reduced thermal ignition thresholds; however, a full understanding of the response of these powders to rapid mechanical loading is still unclear. This work seeks to clarify the role of mechanical properties in impact induced ignition by considering the response of nanolaminate (NL) powders and high energy ball milled (HEBM) Ni-Al powders subjected to impact loading. The powders were placed into a windowed enclosure and mechanically loaded using a light gas gun, which allowed the resulting reactions to be observed using high-speed imaging. Even though the thermal ignition temperatures for the two powders are within 30 °C of each other, it was observed that the NL powders reacted on the microsecond timescale, immediately following the compaction wave for a short distance before decoupling from the compaction front. In contrast, the HEBM powders reacted after a several millisecond delay and clearly propagated as a deflagration front. Microindentation showed that the HEBM powders are much more ductile than those of NL. This suggests that the primary difference between the behavior of these materials on impact results from the ability and degree of the material to fracture, illustrating that the mechanical properties of a reactive material can have a dramatic effect on ignition during impact loading. By using the jump equations to understand compaction events, it is easy to think about the compaction wave as a discontinuity, with no structure. In practice this is not the case. Both shock waves and compaction events have been observed to have a structure with a finite thickness. Studies of the propagation of shocks through monolithic solids have shown that the strain rate, which is directly related to the shock width, scales with the pressure rise to the fourth power. Studies of dynamic compaction of porous materials have shown that this relationship is closer to linear. This work seeks to study the effect that increasing the crush strength of the compact has on the width of the compaction wave. Ball milling is used to produce strain hardened powders that are then pressed to form a porous compact. Plate impact experiments are performed to evaluate the equation of state and measure the shock width of both milled and unmilled powders. The results show that a Mie-Gruneisen equation of state accurately predicts the response of all materials tested; however, the compaction width is found to change with milling condition. For all materials tested, the compaction width is found to decrease with increase pressure rise; however, the unmilled material is found to have a longer rise time compared to the ball milled material. This results in a reduction in apparent viscosity with increased crush strength. It is suggested that stress waves percolating ahead of the compaction front (since the velocity of the compaction wave is below the acoustic velocity of the parent material) and their interaction defines the compaction width. In a weaker material, a weaker stress is required to begin compaction, resulting in a broader front compared to a stronger material and an increased viscosity. Despite their widespread use, the reaction pathways of thermite (reduction-oxidation) reactions are relatively unknown. Multilayer thin films produced through magnetron sputtering provide a highly controlled geometry and direct contact between reactives, making them an ideal platform to study atomic-scale processes underlying thermite reactions. This work utilizes the multilayer thin film geometry to study the combustion and reaction pathway of equimolar Al-NiO. The low heating rate kinetics and product phase growth are studied through hot-stage X-ray diffraction and differential scanning calorimetry. The results indicate significant product formation beginning as low as 180°C, and results in the formation of nickel aluminum intermetallic phases. Hot-plate ignition experiments show that ignition occurs in the solid state for fine bilayer thicknesses, with a transition to melt dependent reaction for multilayers with larger bilayer thicknesses. Laser ignition and self-propagating reactions are observed to exhibit a similar length scale dependence in reaction behavior. The activation energy determined from the hot-plate ignition experiments was found to be less than that for the laser ignition experiments, indicating a heating rate dependent response. This work culminates with the direct synthesis of cubic boron nitride through shock loading of 3B+TiN composite particles. It was found that reduction of the diffusion distance through high energy ball milling before loading was critical for success, with unmilled powders showing no evidence of reaction after recovery. The results show the possibility of rapid reaction occurring in a condensed phase system at microsecond timescales. As a results, optimization of this process may provide a route for the fabrication and discovery of other advanced compounds

Ru/Al Multilayers Integrate Maximum Energy Density and Ductility for Reactive Materials

Established and already commercialized energetic materials, such as those based on Ni/Al for joining, lack the adequate combination of high energy density and ductile reaction products. To join components, this combination is required for mechanically reliable bonds. In addition to the improvement of existing technologies, expansion into new fields of application can also be anticipated which triggers the search for improved materials. Here, we present a comprehensive characterization of the key parameters that enables us to classify the Ru/Al system as new reactive material among other energetic systems. We finally found that Ru/Al exhibits the unusual integration of high energy density and ductility. For example, we measured reaction front velocities up to 10.9 (+/- 0.33) ms(-1) and peak reaction temperatures of about 2000 degrees C indicating the elevated energy density. To our knowledge, such high temperatures have never been reported in experiments for metallic multilayers. In situ experiments show the synthesis of a single-phase B2-RuAl microstructure ensuring improved ductility. Molecular dynamics simulations corroborate the transformation behavior to RuAl. This study fundamentally characterizes a Ru/Al system and demonstrates its enhanced properties fulfilling the identification requirements of a novel nanoscaled energetic material.Peer reviewe

Development of PVD-coated and nanostructured reactive multilayer films

This dissertation addresses nanoscale reactive multilayer films (RMFs) for the purpose of storing chemical energy as heat and supplying localized heat for joining and other industrial applications. Here, self-propagating reactions were analyzed for magnetron sputtered deposited binary Ti-Al, Zr-Al and ternary Ti-Al-Si RMF systems as a function of different Al-molar ratios, bilayer thicknesses and layer sequences. Reaction properties, namely reaction front velocity, temperature, and heat vary quantitatively over a wide range. The maximum reaction temperature of ~ 1800 °C has been achieved in ternary RMFs. This work also highlights the effects of oxidation and the unsteady propagation on the reaction properties. The scalability concept of RMFs was improved and ternary Ti/Si/Ti/Al RMFs were applied in the reactive joining. This dissertation provides new insights into multilayer modulation and opens more freedom to design ternary RMFs by controlling both, diffusion interfaces and distances. It is further shown that the development processes, simulation and experimental analysis are beneficial to design and to synthesize application tailored new RMFs.Als eine neue Klasse von energetischen Materialien speichern die reaktiven Multilagensysteme die chemische Energie. Sie setzen eine große Menge der Energie durch eine schnelle Reaktionspropagation nach einer Aktivierung in der Form von Wärme frei. Im Zusammenhang mit dem zunehmenden Potenzial in den hochmodernen Fügetechnologien und den anderen Industrieanwendungen finden solche Typen von reaktiven Mehrschichtensystemen große Aufmerksamkeit. Das hohe Interesse konzentriert sich auf die Anwendung der sehr schnellen und lokalisierten Energie Freisetzung. Die Kenntnisse über die Materialkombinationen und Morphologie spielt eine wichtige Rolle, um reaktive Mehrschichtensysteme mit entsprechenden Reaktionseigenschaften und Wärmemenge herzustellen. Im Mittelpunkt dieser Arbeit stehen daher die Entwicklung der Schichtweise abgeschiedenen reaktiven Multilagenschichten und die Charakterisierung der Reaktionseigenschaften. Die eingestellten Bereiche können wie folgt zusammengefasst werden; • Die reaktiven Multilagenschichten von binären Ti-Al, Zr-Al und ternären Ti-Al-Si Kombinationen wurden mittels Magnetronsputtern-Deposition produziert, die zu der niedrigen - Medium oder hohen Energieklasse gehören. • Die selbstverbreitenden Reaktionseigenschaften wurden in Bezug auf Wärme, Temperatur, Reaktionsgeschwindigkeit und Propagationsweisen charakterisiert. • Herstellung der großflächigen freistehenden reaktiven Folien wurde aufgezeigt. Für die Bestimmung der Reaktionswärme wurde die Standardbildungsenthalpie zu Beginn der Arbeit durch thermodynamische Simulationen mit Thermo-Calc 3.1 berechnet. Die Menge der Reaktionswärme hängt von der chemischen Zusammensetzung des Ti-Al-, Zr-Al- und Ti-Si Systems ab. Dann wurden Ti/Al, Zr/Al und Ti/Si/Ti/nAl Multilagenschichten für unterschiedliche Periodendicken, Molverhältnisse und Multischichtaufbau abgeschieden. Die Ti/nAl (n = 1-3) reaktiven Multilagenschichten wurden mit verschiedenen Al-Molverhältnissen hergestellt. Die Reaktionsgeschwindigkeit änderte sich zwischen (0.68±0.4) m/s und (2.57±0.6) m/s. Die Reaktionstemperatur änderte sich im Bereich 1215-1298 °C. Die 1Ti/3Al Schicht zeigt auch eine instationäre Reaktionspropagation mit der Kräuselungsbandbildung. Außerdem wurden der Temperaturfluss und die chemische Vermischung in nanoskalige Schichten von 1Ti/1Al Zusammensetzung (für 20 nm Periodendicke) erstmals mittels Strömung Simulation berechnet. Die Ergebnisse zeigten, dass der Temperaturfluss viel schneller als das chemische Mischen während der fortschreitenden Reaktion ist. Die 1Zr/1Al Schichten wurden mit der verschiedenen Periodendicken von 20 nm bis 55 nm untersucht. Die Reaktionsgeschwindigkeit und Reaktionstemperatur änderten sich im Bereich 0.23-1.22 m/s und 1581-1707 °C. Hier wurde auch die Oxidationsreaktion während der fortschreitenden Reaktion aufgezeigt. Zum ersten Mal wurden ternäre Multilagenschichten von Ti, Si und Al-Reaktanten für verschiedene Schichtenanordnung (Si/Ti/Al/Si und Ti/Si/Ti/nAl, n = 1- 3) abgeschieden. Hier, Reaktionseigenschaften hängten von Schichtenanordnung und Al-Molverhältnissen ab. Für den Ti/Si/Ti/Al Schicht konnte eine maximale Reaktionspropagation von (9.2±2) m/s und eine Reaktionstemperatur von (1807±30) °C bestimmt werden. Danach wurden die vorgenannten ternären Folien erstmals in einem reaktiven Fügeprozess eingesetzt. Für die Herstellung großflächiger freistehenden RMS, würde der Einfluss der Substratwerkstoffe in Hinblick auf der Ablöseverhalten nach der Beschichtung untersucht. Die Verwendung des Kupfersubstrats zeigt eine einfache und schnelle Weise, freistehende Folie zu produzieren. Diese Methode ermöglicht die Produktion von freistehenden 1Zr/1Al und 1Ti/1Si/1Ti/Al Folien mit der großen Fläche von 11 cm × 2 cm × 45 µm und 8 cm × 4 cm × 52 µm. Außerdem zeigt diese Arbeit einen verbesserten Herstellungsprozess mit der Skalierbarkeit und homogenen Mikrostrukturen von Multilagenschichten. Die Untersuchungen in dieser Arbeit zeigen, dass die Zusammensetzung und Morphologie die Reaktionseigenschaften unmittelbar beeinflussen und bieten potenzielle Möglichkeiten als eine kontrollierbare Wärmequelle auf der Basis Ti/Al-, Zr/Al- und Ti/Si/Al RMS zur Verfügung stellen. Andererseits schließt die Reaktion die Effekte der Oxidation und instationären Reaktionspropagation ein, die dabei hilfreich wären, die Reaktionskinetik zu verstehen. Die Ergebnisse in dieser Arbeit können als ein Beitrag zu einem Modell um ideale RMS in Bezug auf Reaktionseigenschaften zu entwickeln.As a new class of energetic materials, reactive multilayer systems store chemical energy. They release a large amount of energy in the form of heat by fast reaction propagation after activation. In connection with increasing potentiality in advanced joining technology and other industrial applications, such type of reactive multilayer systems pay attention. The high interests focus on the utilization of very fast and localized heat. The knowledge about material combination, morphology plays an important role to design reactive multilayer systems with an appropriate reaction propagation and heat release. Therefore, this research attributes the development of layer-by-layer-deposited planar reactive multilayer film and characterizing corresponding self-propagating reaction properties. The focused areas are summarized as follows; • Reactive multilayer films of binary Ti-Al, Zr-Al and ternary Ti-Al-Si combinations were produced by Magnetron Sputter Ion Platting process, which belong to different energy classed reactive systems. • The self-propagating exothermic reaction properties were characterized in terms of heat flow, temperature, reaction propagation velocity and propagation modes. • The fabrication concept of freestanding foils with large surface was demonstrated. In connection with the reaction heat, standard heat of formation was initially calculated by using Thermo-Calc 3.1 simulation. The amount of heat released has been influenced by the chemical compositions. Then Ti/Al, Zr/Al und Ti/Si/Ti/nAl reactive films were deposited for different bilayers, molar ratios and multilayer design. The Ti/nAl (n = 1-3) reactive films with different Al-molar ratios were investigated. The reaction speed varies between (0.68±0.4) m/s and (2.57±0.6) m/s. The maximum reaction temperature varies in the range of 1215-1298 °C. The 1Ti/3Al film exhibits unsteady propagation with ripple band formation. Moreover, temperature flow and atomic mixing were characterized by using computational fluid dynamics simulation in 1Ti/1Al reactive foil for 20 nm bilayer thickness for the first time. The results show that the temperature flow is much faster than the chemical mixing during an exothermic reaction. Zr/Al reactive films with different bilayer thicknesses of 20-55 nm were deposited. Here, reaction speed and maximum temperature were found in the range of 0.23-1.22 m/s and 1581-1707 °C, respectively. Oxidation characteristic during a self-propagating reaction was also shown. For the first time the ternary reactive films were investigated for two different multilayer design and Al- molar ratios (Si/Ti/Al/Si und Ti/Si/Ti/nAl, n = 1- 3). Reaction properties depend on chemical compositions. For Ti/Si/Ti/Al reactive film, a maximum reaction propagation of (9.2±2) m/s and temperature (1807±30) °C was estimated. Then reactive joining was attempt first time by using this ternary film. For the production of large-area freestanding RMS, the influence of the substrates with regard to the peel behavior was investigated. In that case, selection of a proper and cost effective substrate and developing synthesis methods are of great interest for large size films. The use of copper substrate shows a simple and efficient way to produce freestanding films. This work assures the production of 1Zr/1Al und 1Ti/1Si/1Ti/Al freestanding films with the size of ~ 11 cm × 2 cm × 45 µm und ~ 8 cm × 4 cm × 52 µm. Furthermore, this work shows an improved fabrication process of reactive films with scalability and uniform microstructure throughout the cross-section. Then reactive joining of steels was performed by using developed ternary reactive films. The experimental results in this work predict composition and morphology dependent reaction properties and offer the potential use of Ti/Al-, Zr/Al- and Ti/Si/Ti/Al reactive films as controllable heat source due to their wide range of reaction properties. On the other hand, the reaction propagation includes the effects of oxidation and unsteady reaction, which will help to understand the reaction kinetics. The achieved results can be used as a contribution to model an ideal reactive multilayer film in terms of reaction properties

Ignition mechanism in nanocomposites thermites

Nanocomposite thermites (n-thermites) have been actively investigated for a wide range of potential applications including propellants, explosives, and pyrotechnics. There have been several recent efforts aimed at understanding ignition mechanisms of nanocomposite reactive materials. Although significant progress has been made, ignition mechanisms remain elusive. At the same time, a robust ignition model is required to incorporate these materials in practical energetic formulations. A challenge of this effort is to describe the mechanisms of ignition of n-thermites prepared by Arrested Reactive Milling (ARM) with different stimuli, including heat, spark and impact and also develop a multi-step kinetic model describing different processes affecting ignition. The role of thermally initiated heterogeneous exothermic reactions is evaluated and the effect of decomposition of oxidizer and respective oxygen gas release on ignition is described. N-thermite powders are prepared by ARM and evaluated using thermal analysis, electron microscopy and other analytical techniques. Experimental studies of ignition of n-thermites stimulated by heating, electric spark and impact are conducted with the goal of developing a reaction model capable of describing different experimental data sets. State of the art thermo-analytical equipment and advanced isoconversion methods are used to describe stability and redox reaction mechanisms in the prepared samples. Multiple reaction steps are identified and described quantitatively. Thin layers of the prepared powders coated onto an electrically heated Ni-Cr filament are ignited at heating rates between 200-17000 K/s in a miniature vacuum chamber. Ignition is monitored based on both photodiode and pressure transducer signals recorded simultaneously. For spark-induced ignition, powder layers of different thickness are placed in a grounded brass holder. A needle-like electrode is placed above the powder and sparks with different energies are produced. Real time measurements of current and optical signatures produced by the ignited sample at different wavelengths are taken. The results are processed to determine the spark energy, minimum ignition energy, ignition delay, and other parameters. Shock ignition of nanocomposite 8Al-MoO3 thermite particles are independently carried out at the University of Illinois Urbana Champaign. An individual particle is targeted by a miniature, laser-driven flyer plate accelerated to a speed in the range of 0.5-2 km/s. Ignition delays observed in both shock and spark ignition experiments for the same material are close to each other and vary in the range of 120 - 200 ns. A reaction mechanism including multiple oxidation steps starting with the Cabrera-Mott (CM) reaction followed by direct oxidative growth of and phase changes in different alumina polymorphs is validated for a stoichiometric 2Al-3CuO nanocomposite powder prepared by ARM. The reaction kinetics describing these reaction steps are shown to remain credible for the ARM-prepared reactive composites with different scales of mixing, interface morphologies, and component ratios, as long as the components remained Al and CuO. This work presents a further validation and development of this multistep model to describe reaction in another ARM-prepared thermite system, 8Al-MoO3

Soldering interconnects through self-propagating reaction process

This thesis presents a research into the solder interconnects made through the reactive bonding process based on the self-propagating reaction. A numerical study of soldering conditions in the heat affected zone (HAZ) during bonding was initially carried out in order to understand the self-propagating reactive bonding and the related influencing factors. This was subsequently followed by an extensive experimental work to evaluate the feasibility and reliability of the reactive bonding process to enable the optimisation of processing parameters, which had provided a detailed understanding in terms of interfacial characteristics and bonding strengths. In addition, by focusing on the microstructure of the bonds resulted from the self-propagating reactions, the interfacial reactions and microstructural evolution of the bonded structures and effects of high-temperature aging were studied in details and discussed accordingly. To study the soldering conditions, a 3D time-dependent model is established to describe the temperature and stress field induced during self-propagating reactions. The transient temperature and stress distribution at the critical locations are identified. This thus allows the prediction of the melting status of solder alloys and the stress concentration points (weak points) in the bond under certain soldering conditions, e.g. ambient temperature, pressure, dimension and type of solder materials. Experimentally, the characterisation of interconnects bonded using various materials under different technical conditions is carried out. This ultimately assists the understanding of the feasibility, reliability and failure modes of reactive bonding technique, as well as the criteria and optimisation to form robust joints. The formation of phases such as intermetallic compounds (IMCs) and mechanism of interfacial reactions during reactive bonding and subsequent aging are elaborated. The composition, dimension, distribution of phases have been examined through cross-sectional observations. The underlying temperature and stress profile determining the diffusion, crystallization and growth of phases are defined by numerical predictions. XXI Through the comparative analysis of the experimental and numerical results, the unique phases developed in the self-propagating joints are attributed to the solid-liquid-convective diffusion, directional solidification and non-equilibrium crystallization. The recrystallization and growth of phases during aging are revealed to be resulted from the solid-state diffusion and equilibration induced by the high-temperature heating. In conclusion, the interfacial reactions and microstructural evolution of interconnect developed through self-propagating reactive bonding are studied and correlated with the related influencing factors that has been obtained from these predictions and experiments. The results and findings enable the extensive uses of self-propagating reactive bonding technology for new design and assembly capable of various applications in electronic packaging. It also greatly contributes to the fundamentals of the crystallization and soldering mechanism of materials under the non-equilibrium conditions

Etude théorique du vieillissement des nanolaminés Al/CuO

Les thermites permettent, une fois initiées, de générer une grande quantité d'énergie chimique, stockée dans des structures métastables dans lesquelles coexistent des un oxydant (typiquement un oxyde métallique) et un réducteur (typiquement l'aluminium). Les thermites nanolaminés, empilements successifs de couches d'oxydant et de réducteur, offrent une architecture hautement contrôlable et ont été incorporées à une variété de dispositifs micro-pyrotechniques couramment utilisés dans les systèmes micro-electromécaniques (micro-electromechanical systems - MEMS) afin de produire des pyroMEMS. Au cours des deux dernières décennies, les nanolaminés Al/CuO ont particulièrement attiré l'attention en raison de leur réactivité élevée et de leur capacité à générer du gaz. Cependant, malgré les nombreux travaux dédiés aux nanothermites durant cette période, la littérature spécifiquement consacrée aux problèmes de vieillissement est rare et concerne exclusivement les nanothermites sous forme de poudres. Dans ce contexte, le LAAS-CNRS et le CEA ont étudiés le vieillissement des nanolaminés Al/CuO, et ce en réalisant des images in silico des modifications structurelles responsables des altérations de performances observées lorsque les nanolaminés sont sujets à un stockage sur le long terme à température ambiante et après recuit. Concrètement, dans cette thèse, différentes types structures nanolaminés Al/CuO sont considérées, et leur vieillissement analysé, particulièrement en termes d'évolution de l'épaisseur des interfaces et de consommation du réservoir énergétique. Cet effet du vieillissement (vieillissement thermique) sur le délai d'initiation et les performances de combustion de diverses structures est étudié. En complément des simulations, des nanolaminés Al/CuO ont été produits, et certains ont été recuits tels que prescrit par le modèle de vieillissement proposé afin de valider les prédictions théoriques. Ce travail a permis pour la première fois, d'éclaircir la cinétique de l'évolution des couches de réactifs et produits (incluant Al, CuO, Cu2O, Al2O3) de nanolaminés Al/CuO recuits à relativement basses températures (ambiante à 500 °C). Il s'agit d'un progrès important pour la communauté des thermites, non seulement grâce aux données collectées sur le vieillissement des nanolaminés Al/CuO, mais également car il propose une méthodologie pouvant être appliquée à d'autres types de thermites.Thermite materials allow, once ignited, to release a great amount of chemical energy, stored in metastable structures where coexist an oxidizing material (typically a metal oxide) and a reducing material (typically aluminum). Thermite nanolaminates, alternative layer of oxidizer and fuel, offer a highly controllable architecture and have been incorporated into a variety of micro-pyrotechnic devices commonly used in micro-electromechanical systems (MEMS) to produce pyroMEMS. Over the two last decades, Al/CuO nanolaminates have drawn particular attention due to their high reactivity and gas generation ability. But, despite the active research dedicated to nanothermites over the two last decades, the literature specifically dedicated to aging issues is rare and exclusively concerns nanothermites in the form of mixed powders. In this context, the LAAS-CNRS and the CEA investigate Al/CuO nanolaminates aging in an original manner, allowing for effcient in silico screening of structures modification and ensuing performances alteration when the Al/CuO thermite nanolaminates are subject to long-term storage at the ambient temperature and upon annealing. Concretely, within this phD thesis, representative types of Al/CuO nanolaminates structures are considered, and their aging analyzed, notably in terms of interfacial layer thickness evolution and energetic reservoir consumption. This aging effect (temperature out of any other chemistry associated with the storage environment) on both initiation time and combustion performances (ignition and combustion) of various structures is investigated. In complement to simulations, Al/CuO nanolaminates structures were fabricated, and some of them were annealed as prescribed by the proposed aging model to support the theoretical predictions. This work permits for the first time to unravel the kinetics of the reactant and product layer thicknesses (including Al, CuO, Cu2O, Al2O3) of reacting sputter-deposited Al/CuO nanolaminates upon annealing at low temperature (ambient to 500 °C). It represents an important progress for the community of thermites, not only thanks to the data collected on the aging of Al/CuO nanolaminates, but also as it presents an original methodology that can be applied to other thermite materials