Modern microwave methods in solid state inorganic materials chemistry: from fundamentals to manufacturing

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3D printing of a palladium-alumina cermet monolithic catalyst: catalytic evaluation in microwave-assisted cross-coupling reactions

A straightforward manufacture strategy is proposed to obtain an efficient and robust palladium-alumina (Pd0/Al2O3) cermet monolithic catalyst, specifically designed to perform safe microwave assisted organic synthesis (MAOS). In this approach, a cermet catalyst with high surface area, controlled composition and adapted shape and dimensions to a microwave reactor vessel is generated via 3D printing technology and sintering. The resulting catalyst has been explored in heterogeneous Suzuki, Sonogashira, Stille and Heck cross-coupling reactions, in MAOS. The Pd0 catalyst is permanently active, stable, without leaching and can be recycled and reused at least 200 reaction cycles. The generation of hot spots, sparking or hazardous discharges is controlled by the effective immobilization of the palladium in the monolithic structure during the reaction. The palladium content is forming part of both the internal and external structure, providing greater mechanical resistance and catalytic activity with respect to the basic ceramic material (alumina)This work was financially supported by the Consellería de Cultura, Educación e Ordenación Universitaria of the Galician Government: EM2014/022 to A.C., ED431B2016/028 to F.G. The Strategic Grouping AEMAT grant No. ED431E2018/08 and the Spanish Ministry of Science, Innovation and Universities with grant No: MAT2017-90100-C2-1-P "MA thanks Xunta de Galicia and the ERDF (ED431C 2021/21)"S

Spark-Plasma Sintering and Related Field-Assisted Powder Consolidation Technologies

Electromagnetic field-assisted sintering techniques have increasingly attracted attention of scientists and technologists. Spark-plasma sintering (SPS) and other field-assisted powder consolidation approaches provide remarkable capabilities to the processing of materials into configurations previously unattainable. Of particular significance is the possibility of using very fast heating rates, which, coupled with the field-assisted mass transport, stand behind the purported ability to achieve high densities during consolidation and to maintain the nanostructure of consolidated materials via these techniques. Potentially, SPS and related technologies have many significant advantages over the conventional powder processing methods, including the lower process temperature, the shorter holding time, dramatically improved properties of sintered products, low manufacturing costs, and environmental friendliness

Nonlinear mechanisms in passive microwave devices

Premi extraordinari doctorat curs 2010-2011, àmbit d’Enginyeria de les TICThe telecommunications industry follows a tendency towards smaller devices, higher power and higher frequency, which imply an increase on the complexity of the electronics involved. Moreover, there is a need for extended capabilities like frequency tunable devices, ultra-low losses or high power handling, which make use of advanced materials for these purposes. In addition, increasingly demanding communication standards and regulations push the limits of the acceptable performance degrading indicators. This is the case of nonlinearities, whose effects, like increased Adjacent Channel Power Ratio (ACPR), harmonics, or intermodulation distortion among others, are being included in the performance requirements, as maximum tolerable levels. In this context, proper modeling of the devices at the design stage is of crucial importance in predicting not only the device performance but also the global system indicators and to make sure that the requirements are fulfilled. In accordance with that, this work proposes the necessary steps for circuit models implementation of different passive microwave devices, from the linear and nonlinear measurements to the simulations to validate them. Bulk acoustic wave resonators and transmission lines made of high temperature superconductors, ferroelectrics or regular metals and dielectrics are the subject of this work. Both phenomenological and physical approaches are considered and circuit models are proposed and compared with measurements. The nonlinear observables, being harmonics, intermodulation distortion, and saturation or detuning, are properly related to the material properties that originate them. The obtained models can be used in circuit simulators to predict the performance of these microwave devices under complex modulated signals, or even be used to predict their performance when integrated into more complex systems. A key step to achieve this goal is an accurate characterization of materials and devices, which is faced by making use of advanced measurement techniques. Therefore, considerations on special measurement setups are being made along this thesis.Award-winningPostprint (published version

National Educators' Workshop: Update 1991. Standard Experiments in Engineering Materials Science and Technology

Given here is a collection of experiments presented and demonstrated at the National Educators' Workshop: Update 91, held at the Oak Ridge National Laboratory on November 12-14, 1991. The experiments related to the nature and properties of engineering materials and provided information to assist in teaching about materials in the education community

Perovskite Oxide Nanocrystals — Synthesis, Characterization, Functionalization, and Novel Applications

Perovskite oxide nanocrystals exhibit a wide spectrum of attractive properties such as ferroelectricity, piezoelectricity, dielectricity, ferromagnetism, magnetoresistance, and multiferroics. These properties are indispensable for applications in ferroelectric random access memories, multilayer ceramic capacitors, transducers, sensors and actuators, magnetic random access memories, and the potential new types of multiple-state memories and spintronic devices controlled by electric and magnetic fields. In the past two decades, much effort has been made to synthesize and characterize the perovskite oxide nanocrystals. Various physical and chemical deposition techniques and growth mechanisms are explored and developed to control the morphology, identical shape, uniform size, perfect crystalline structure, defects, and homogenous stoichiometry of the perovskite oxide nanocrystals. This chapter provides a comprehensive review of the state-of-the-art research activities that focus on the rational synthesis, structural characterization, functionalization, and unique applications of perovskite oxide nanocrystals in nanoelectronics. It begins with the rational synthesis of perovskite oxide nanocrystals, and then summarizes their structural characterizations. Fundamental physical properties of perovskite oxide nanocrystals are also highlighted, and a range of novel applications in nanoelectronics, information storages, and spintronics are discussed. Finally, we conclude this review with some perspectives/outlook and future researches in these fields

Tooling materials compatible with carbon fibre composites in a microwave environment

Although metals are the most commonly used tooling materials to cure composites, they do not provide optimal results in a microwave environment. Following a selection process based on the properties of the materials, an alternative tooling material in carbon fibre reinforced plastic (CFRP) was successfully utilised to cure CFRP panels in laboratory and industrial microwaves. The conductive carbon fibres in the tool facilitated the fast heat transfer across the part. Other tooling materials including a glass fibre cyanate ester prepreg and tooling board were trialled, although the latter exhibited damage during cure. These advantages demonstrate that the CFRP tool is a compatible material that can be used when microwave curing composites

Synthesis of Carbon Nanotube Materials from a Microwave Plasma

Carbon nanotubes (CNTs) possess numerous exceptional structural, thermal, and electrical properties that have the potential to be highly disruptive and impactful in many areas of technology. Unfortunately, synthesis methods of CNT-containing materials are often complex, expensive, and require prefabricated precursors. For CNT-based materials to experience widespread adoption, they must be produced by simple, inexpensive, and scalable means. The outcome of this work presents straightforward, fast, and industrially-relevant processes using microwave plasma for synthesis of CNT materials starting from widely-available, inexpensive precursor materials. The plasma system has been developed to accommodate multiple gases including mixtures with hydrogen fractions of at least 50%. Stabilization has been accomplished with custom ceramic "axial" and "swirl" torches which result in low background particle generation and the ability to operate nearly indefinitely with little to no component wear. The excitation temperature and electron density of the plasma were characterized using the Boltzmann plot method with a rubidium aerosol as a tracer species. The first application of the plasma system was to produce a metal oxide-CNT hybrid material for lithium-ion battery anodes. The process is both fully continuous and fast (~5 seconds from raw precursors to final product). The metal oxide particles are formed from readily-available coarse powders using a bespoke powder feeder and the final product was well-characterized using aerosol methods that agreed well with microscopy results. This anode material eliminated the need for a conductive additive in the electrode, and showed both good capacity recovery from high-rate cycling and promising long-term stability. Finally, work towards a high mass throughput CNT production process is also presented. High-quality CNTs were synthesized using the axial torch. Using the swirl torch, higher hydrogen fractions could be achieved and the carbon precursor could be introduced through the front of the reactor. This led to abundant growth of long CNTs (tens of µm) with diameters of ~50 nm. Given additional parameter optimization, it is likely that mass throughput could be increased further and aerogel formation may be possible. Fast, scalable processes such as those presented here may contribute to the widespread integration of CNTs in the next generation of high performance materials.Equipment funded by EPSRC grant EP/ M015211/1 (Advanced Nanotube Application and Manufacturing Initiative) Personal funding from Cambridge Trust, Churchill Society of Edmonton, and National Sciences and Engineering Research Council of Canad