Die Vakuum-Mikrowellentrocknung in Multimodekammern stellt eine Möglichkeit zur schnellen und fehlerfreien Trocknung von porösen Körpern dar. In der vorliegenden Arbeit wurden der Einfluss von spezifischer absorbierter Leistung, Kammerdruck, Probenlänge, Probendicke und Anfangsfeuchte auf die Trocknung von Schnittholz untersucht. In Abhängigkeit von Holzart und Anordnung konnten Trocknungsgeschwindigkeiten von bis zu 7 %/min erzielt werden. Die daraus resultierenden Trocknungszeiten ermöglichen die Nutzung einer kontinuierlichen Prozessführung, die die Beobachtung von einzelnen Brettern erlaubt. Die Ergebnisse der Arbeit erlauben eine Bewertung der Entwicklung von Feuchte- und Temperaturverteilung im Material bei Variation der genannten Parameter. Es werden Ansätze zur Steuerung eines kontinuierlichen Mikrowellentrocknungsprozesses und zur Gestaltung geeigneter Applikatoren vorgestellt. / One possibility to dry porous materials at high rates and without structural damage is vacuum microwave drying, a combination of low pressure and microwave application. The influence of specific absorbed power, pressure level, length and thickness of the sample and initial moisture content on drying was investigated by the example of wood. Drying rates of up to 7 %/min were reached depending on the wood species and the configuration. The resulting drying times are suitable to design a continuous process, which allows single board processing. The results of this work give the possibility to evaluate the development of moisture and temperature fields within the material during variation of the mentioned parameters. Basic approaches are discussed for the control of a continuous microwave drying process and for the qualified design of applicators.

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Metal-organic frameworks (MOFs) are crystalline materials with metal ions covalently bonded to organic ligands. The ligands act as spacers often creating a porous structure with very high pore volume and surface area. MOFs are known for their robust structures, high porosity, and different chemical functionalities and are considered for applications in adsorptions, separations, catalysis and gas storage. This work focuses on the synthesis of new MOFs using copper compounds. Different types of carboxylate ligands were used for the synthesis. Two new copper-organic frameworks, [Cu3(pyz)(btc)] (1), and [(Cu3(btc))•xH2O] (2) (btc= benzene-1,3,5-tricarboxylate, pyz= pyrazine) have been synthesized using hydro/solvothermal methods and have been characterized using X-ray diffraction, IR, TGA, fluorescence and CHN analysis.

In this study SBA-15 mesoporous silica template was synthesized and used as a sacrificial template in the preparation of ordered mesoporous carbon material. A chemical vapour deposition (CVD) technique using LPG or alternatively sucrose, pyrolyzed upon a mesoporous Si matrix were used to produce nanostructured ordered mesoporous carbon (OMC) with graphitic character after removing the Si template. The sucrose method was found to be a suitable route for preparing OMC. The OMC was used as a conductive three dimensional porous support for depositing catalytic nanophase Pt metal. Deposition of Pt nanoparticles on OMC was accomplished using a CVD method with Pt(acac)2 as a precursor. The synthesized nano-composite materials were characterized by several techniques such as, HRTEM, HRSEM, EDS, XRD, BET, TGA, FT-IR and CV.

In the current context of rapidly depleting petroleum resources and growing environmental concerns, it is important to develop materials to harvest and store energy from renewable and sustainable sources. Hydrogen has the potential to be an alternative energy source, since it has higher energy content than petroleum. However, since hydrogen has very low volumetric energy density, hence it is important to design nano porous materials which can efficiently store large volumes of hydrogen gas by adsorption. In this regard carbon nanotube and Metal Organic Framework (MOFs) based materials are worth studying. Ionic liquids (IL) are potential electrolytes that can improve energy storage capacity and safety in Li ion batteries. Therefore it is important to understand IL's thermodynamic and transport properties, especially when it is in contact with electrode surface and mixed with Li salt, as happens in the battery application. This dissertation presents computation and simulation based studies on: 1. Hydrogen storage in carbon nanotube scaffold. 2. Mechanical property and stability of various nanoporous Metal Organic Frameworks. 3. Thermodynamic and transport properties of [BMIM][BF4] ionic liquid in bulk, in Li Salt mixture, on graphite surface and under nanoconfinement. In the first study, we report the effects of carbon nanotube diameter, tube chirality, tube spacer distance, tube functionalization and presence of Li on hydrogen sorption capacity and thermodynamics at different temperature and pressure. In the second one, we observe high pressure induced structural transformation of 6 isoreticular MOFs: IRMOF-1. IRMOF-3, IRMOF-6, IRMOF-8, IRMOF-10 and IRMOF-14, explore the deformation mechanism and effect of Hydrogen inside crystal lattice. In the third study, we observe the equilibrium thermodynamic and transport properties of [BMIM][BF4] ionic liquid. The temperature dependence of ion diffusion, conductivity, dielectric constant, dipole relaxation time and viscosity have been observed and found similar behavior to those of supercooled liquid. The ion diffusion on graphite surfaces and under nanoconfinement was found to be higher compared to those in bulk.

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The primary goal of this research concerns the synthesis and characterization of metal-organic frameworks (MOFs) grafted with pendant alkyl substituents to enhance stability and gas sorption properties for use in clean-energy related technologies. Initially, the focus of this work was on the synthesis and comparison of two isostructural MOFs built upon octahedral secondary building blocks; one with no alkyl substituents, and its dimethyl-substituted counterpart. The dimethyl-substituents are observed to enhance the stability of the framework, resulting in high Langmuir surface area (4859 m2 g-1) and hydrogen uptake capacity at 77 K and 1 bar (2.6 wt%). In the second section, the length of pendant alkoxy substituents in semi-flexible MOFs was evaluated through the synthesis and characterization of two isostructural MOFs, one with dimethoxy (PCN-38) and one with diethoxy pendant groups (PCN-39). While PCN-38 exhibited moderate surface area and hydrogen uptake capacities, PCN-39 underwent structural change upon activation leading to a redistribution of pore sizes and selective adsorption of hydrogen over larger gases. This structural transformation is believed to originate from optimal space filling of the pendant groups. In the third section, a series of NbO-type MOFs were synthesized with dimethoxy, diethoxy, dipropoxy, and dihexyloxy substituents and the relationship between chain length and framework stability identified. Increasing chain length was observed to increase moisture stability of the MOFs, resulting in a superhydrophobic material in the case of the dihexyloxy derivative. Thermal stability, however, decreased with increasing chain length, as evidenced from in situ synchrotron powder X-ray diffraction measurements (PXRD). This is in contrast to data obtained from thermogravimetric analysis and shows that the standard use of thermogravimetric analysis, which measures combustion temperatures, may not always provide an accurate description of the thermal stability of MOFs. The role of pendant groups in gas adsorption processes was evaluated through identification of side chains and guest species in the pores of MOFs through in situ synchrotron PXRD measurements. In summary, three separate isostructural series of MOFs with various pendant groups have been discussed in this dissertation, with the roles of those pendant groups toward crystal structure, stability, and gas sorption properties analyzed.

In this investigation, the flow friction associated with laminar pulsating flows through porous media was numerically studied. The problem is of interest for understanding the regenerators of Stirling and pulse tube cryocoolers. Two-dimensional flow in a system composed of a number of unit cells of generic porous structures was simulated using a CFD tool, with sinusoidal variations of flow with time. Detailed numerical data representing the oscillating velocity and pressure variations for five different generic porous structure geometries in the porosity range of 0.64 to 0.84, with flow pulsation frequency of 40 Hz were obtained, and special attention was paid to the phase shift characteristics between the velocity and pressure waves. Based on these detailed numerical data, the standard unsteady volume-averaged momentum conservation equation for porous media was then applied in order to obtain the instantaneous as well as cycle-averaged permeability and Forchheimer coefficients. It was found that the cycle-averaged permeability coefficients were nearly the same as those for steady flow, but the cycle-averaged Forchheimer coefficients were about two times larger than those for steady flow. Significant phase lags were observed with respect to the volume-averaged velocity and pressure waves. The parametric trends representing the dependence of these phase lags on porosity and flow Reynolds number were discussed. The phase difference between pressure and velocity waves, which is important for pulse tube cryocooling, depended strongly on porosity and flow Reynolds number.

Low-density cellular materials, metallic bodies with gaseous voids, are a unique class of materials that are characterized by their high strength, low mass, good energy absorption characteristics, and good thermal and acoustic insulation properties. In an effort to take advantage of this entire suite of positive mechanical traits, designers are tailoring the cellular mesostructure for multiple design objectives. Unfortunately, existing cellular material manufacturing technologies limit the design space as they are limited to certain part mesostructure, material type, and macrostructure. The opportunity that exists to improve the design of existing products, and the ability to reap the benefits of cellular materials in new applications is the driving force behind this research. As such, the primary research goal of this work is to design, embody, and analyze a manufacturing process that provides a designer the ability to specify the material type, material composition, void morphology, and mesostructure topology for any conceivable part geometry. The accomplishment of this goal is achieved in three phases of research: Design Following a systematic design process and a rigorous selection exercise, a layer-based additive manufacturing process is designed that is capable of meeting the unique requirements of fabricating cellular material geometry. Specifically, metal parts of designed mesostructure are fabricated via three-dimensional printing of metal oxide ceramic powder followed by post-processing in a reducing atmosphere. Embodiment The primary research hypothesis is verified through the use of the designed manufacturing process chain to successfully realize metal parts of designed mesostructure. Modeling & Evaluation The designed manufacturing process is modeled in this final research phase so as to increase understanding of experimental results and to establish a foundation for future analytical modeling research. In addition to an analysis of the physics of primitive creation and an investigation of failure modes during the layered fabrication of thin trusses, build time and cost models are presented in order to verify claims of the process s economic benefits. The main contribution of this research is the embodiment of a novel manner for realizing metal parts of designed mesostructure.