Thermal barrier coatings (TBC) are used in the hot sections of gas turbine engine in order to insulate the substrate at high temperature. Molten salt infiltration retards the durability of TBCs. The current standard material, i.e. 8YSZ is susceptible to molten salt infiltration. Therefore, alternate TBC materials are desirable. In addition to material composition, the TBC microstructure plays an important role in mitigating molten salt infiltration. Therefore, in this work, three different TBC variations were investigated. The first variation was a columnar microstructured 48YSZ TBC processed by SPS (48YSZ-SPS). The second variation was a columnar microstructured 8YSZ TBC processed by SPS (8YSZ-SPS), and the third variation was a lamellar microstructured 8YSZ TBC deposited by APS (8YSZ-APS). The as-sprayed TBC specimens were characterized by SEM/EDS, porosity analysis and XRD measurements. Later, the TBC specimens were exposed to hot corrosion test and their interaction with the molten salts were investigated using SEM (EDS and XRD). It was shown that an increase in stabilizer content (yttria content) in zirconia (in the case of 48YSZ) leads to an improved hot corrosion resistance due to the adequate amount of yttria content, which restricts the molten salt infiltration by forming needle like YVO4 phase. In terms of microstructure comparison, the infiltration behavior was similar for columnar microstructured 8YSZ and lamellar microstructured 8YSZ-APS as the molten salts infiltrated the coatings completely compared to the 48YSZ TBC. Furthermore, it seems that the molten salt infiltrates the TBC through globular pores, delamination cracks and splat boundaries in the case of APS-TBCs whereas the column gaps favor easier infiltration of molten salts in the case of columnar microstructured SPS processed TBCs.

The increasing miniaturization of electric and mechanical components makes the synthesis and assembly of nanoscale structures an important step in modern technology. Functional materials, such as the ferroelectric perovskites, are vital to the integration and utility value of nanotechnology in the future. In the present work, chemical methods to synthesize one-dimensional (1D) nanostructures of ferroelectric perovskites have been studied. To successfully and controllably make 1D nanostructures by chemical methods it is very important to understand the growth mechanism of these nanostructures, in order to design the structures for use in various applications. For the integration of 1D nanostructures into devices it is also very important to be able to make arrays and large-area designed structures from the building blocks that single nanostructures constitute. As functional materials, it is of course also vital to study the properties of the nanostructures. The characterization of properties of single nanostructures is challenging, but essential to the use of such structures. The aim of this work has been to synthesize high quality single-crystalline 1D nanostructures of ferroelectric perovskites with emphasis on PbTiO3 , to make arrays or hierarchical nanostructures of 1D nanostructures on substrates, to understand the growth mechanisms of the 1D nanostructures, and to investigate the ferroelectric and piezoelectric properties of the 1D nanostructures. In Paper I, a molten salt synthesis route, previously reported to yield BaTiO3 , PbTiO3 and Na2Ti6O13 nanorods, was re-examined in order to elucidate the role of volatile chlorides. A precursor mixture containing barium (or lead) and titaniumwas annealed in the presence of NaCl at 760 °C or 820 °C. The main products were respectively isometric nanocrystalline BaTiO3 and PbTiO3. Nanorods were also detected, but electron diffraction revealed that the composition of the nanorods was respectively BaTi2O5/BaTi5O11 and Na2Ti6O13 for the two different systems, in contradiction to the previous studies. It was shown that NaCl reacted with BaO(PbO) resulting in loss of volatile BaCl2 (PbCl2 ) and formation and preferential growth of titanium oxide-rich nanorods instead of the target phase BaTiO3 (or PbTiO3 ). The molten salt synthesis route may therefore not necessarily yield nanorods of the target ternary oxide as reported previously. In addition, the importance of NaCl(g) for the growth of nanorods below the melting point of NaCl was demonstrated in a special experimental setup, where NaCl and the precursors were physically separated. In Paper II and III, a hydrothermal synthesis method to grow arrays and hierarchical nanostructures of PbTiO3 nanorods and platelets on substrates is presented. Hydrothermal treatment of an amorphous PbTiO3 precursor in the presence of a surfactant and PbTiO3 or SrTiO3 substrates resulted in the growth of PbTiO3 nanorods and platelets aligned in the crystallographic <100> orientations of the SrTiO3 substrates. PbTiO3 nanorods oriented perpendicular to the substrate surface could also be grown directly on the substrate by a modified synthesis method. The hydrothermal method described in Paper II and III was developed on the basis of the method described in Appendices I and II. In Paper IV, a template-assisted method to make PbTiO3 nanotubes is presented. An equimolar Pb-Ti sol was dropped onto porous alumina membranes and penetrated into the channels of the template. Single-phase PbTiO3 perovskite nanotubes were obtained by annealing at 700 °C for 6 h. The nanotubes haddiameters of 200 - 400 nm with a wall thickness of approximately 20 nm. Excess PbO or annealing in a Pb-containing atmosphere was not necessary in order to achieve single phase PbTiO3 nanotubes. The influence of the heating procedure and the sol concentration is discussed. In Paper V, a piezoresponse force microscopy study of single PbTiO3 nanorods is presented. The piezoelectric properties were studied in both vertical and lateral mode. Piezoelectric activity and polarization switching was observed in the vertical mode, demonstrating the ferroelectric nature of the nanorods. The nanorods decomposed after repeated cycling of the dc bias at one spot on the nanorod, which resulted in parts of the nanorod disappearing and/or accumulation of particles on the surface of the nanorod. In Paper VI, a method to contact single nanorods by electron beam induced deposition of platinum is presented. An organometallic compound, (trimethyl)-methylcyclopentadienylplatinum(IV), was used as precursor. A home-made apparatus was constructed for the purpose and was mounted onto a scanning electron microscope. Calculations based on apparatus geometry and molecular flow were used to estimate the deposition time and the height of the deposits. The location and height of the deposits were controlled so that single nanorods could be successfully contacted at the ends of the nanorods. Fabrication of a sample device for piezoresponse force microscopy studies of single nanorods using an axial dc bias setup is described in Appendix IV. A proposed experimental setup for such studies is also presented.

The recovery boiler in a pulp and paper mill plays a dual role of recovering pulping chemicals and generating steam for either chemical processes or producing electricity. The efficiency of producing steam in the recovery boiler is limited by the first melting temperature of ash deposits that accumulate on the superheater tubes. Above the first melting temperature, the molten salt reacts with the protective oxide film that develops and dissolves it. The most protective oxide is determined by evaluating how little it dissolves and how its solubility changes in the molten salt. Solubility tests were done on several protective oxides in a known salt composition from a recovery boiler that burns hardwood derived fuel. ICP-OES was used to measure concentration of dissolved metal in the exposure tests while EDS and XRD were used to verify chemical compositions in exposure tests. NiO was found to be the least soluble oxide while Cr₂O₃ and Al₂O₃ had similar solubility with Fe₂O₃ being less soluble than Cr₂O₃ but more soluble than NiO. Exposure tests with pure metals and selected alloys indicated that even though Fe₂O₃ has little solubility, it is not a protective oxide and causes severe corrosion in stainless steels. The change in performance of iron based alloys was due to the development of a negative solubility gradient for Fe₂O₃ where Fe₂O₃ precipitated out of solution and created a continuous leaching of oxide. Manganese was found to be beneficial in stainless steels but its role is still unknown. Nickel based alloys were found to be least corroded due to nickel's low solubility and because it did not form a negative solubility gradient.

The Liquid-Salt-Cooled Very High-Temperature Reactor (LS-VHTR) was modeled using the neutronics analysis code SCALE6.0 and the thermal-hydraulics and kinetics modeling code RELAP5-3D with objective to devise, analyze, and evaluate the feasibility and stability of a start-up procedure for this reactor using natural circulation of the coolant and under the Loss Of Offsite Power (LOOP) conditions. This Generation IV reactor design has been studied by research facilities worldwide for almost a decade. While neutronics and thermal-hydraulics analyses have been previously performed to show the performance of the reactor during normal operation and for shutdown scenarios, no study has heretofore been published to examine the active or passive start-up of the reactor. The fuel temperature (Doppler) and coolant density coefficient of reactivity of the LS-VHTR were examined using the CSAS6 module of the SCALE6.0 code. Negative Doppler and coolant density feedback coefficients were calculated. Two initial RELAP5 simulations were run to obtain the steady-state conditions of the model and to predict the changes of the thermal-hydraulic parameters during the shutdown of the reactor. Next, a series of step reactivity additions to the core were simulated to determine how much reactivity can be inserted without jeopardizing safety and the stability of the core. Finally, a start-up procedure was developed, and the restart of the reactor with natural convection of the coolant was simulated. The results of the simulations demonstrated the potential of a passive start-up of the LS-VHTR.

The thermal efficiency of concentrated solar power (CSP) system depends on the maximum operating temperature of the system which is determined by the operating temperature of the TES device. Organic materials (such as synthetic oil, fatty acid, or paraffin wax) are typically used for TES. This limits the operating temperature of CSP units to below 400 degrees C. Increasing the operating temperature to 560 degrees C (i.e., the creeping temperature of stainless steel), can enhance the theoretical thermal efficiency from 54 percent to 63 percent. However, very few thermal storage materials are compatible for these high temperatures. Molten salts are thermally stable up to 600 degrees C and beyond. Using the molten salts as the TES materials confers several benefits, which include: (1) Higher operating temperature can significantly increase the overall cycle efficiency and resulting costs of power production. (2) Low cost of the molten salt materials can drastically reduce the cost. (3) The molten salts, which are environmentally safe, can also reduce the potential environmental impact. However, these materials suffer from poor thermo-physical properties. Impregnating these materials with nanoparticles can enhance these properties. Solvents doped with nanoparticles are termed as nanofluids. Nanofluids have been reported in the literature for the anomalous enhancement of their thermo-physical properties. In this study, the poor thermal properties of the molten salts were enhanced dramatically on mixing with nanoparticles. For example the specific heat capacity of these molten salt eutectics was found to be enhanced by as much as ~ 26 percent on mixing with nanoparticles at a mass fraction of ~ 1 percent. The resultant properties of these nanomaterials were found to be highly sensitive to small variations in the synthesis protocols. Computational models were also developed in this study to explore the fundamental transport mechanisms on the molecular scale for elucidating the anomalous enhancements in the thermo-physical properties that were measured in these experiments. This study is applicable for thermal energy storage systems utilized for other energy conversion technologies – such as geothermal energy, nuclear energy and a combination of energy generation technologies.

O presente trabalho tem como objetivo principal um estudo sistemático de líquidos iônicos imidazólicos, ou seja, sais líquidos a temperaturas relativamente baixas derivados do anel imidazol, tendo como técnica principal a espectroscopia Raman. Foram estudados os cátions 1-alquil-3- metilimidazólio e 1-alquil-2,3-dimetilimidazólio, sendo o grupo alquil composto por 2, 4, 6, 8 ou 10 átomos de carbono, com os ânions brometo, hexafluorofosfato ou bis(trifluorometanosulfonil)imida (TFSI-), totalizando 30 sistemas distintos. O estudo foi dividido em três partes. Na primeira, foram estudados compostos derivados de imidazol, neutros e catiônicos, para entender as diferenças entre os cátions formadores (o ânion foi desconsiderado) de ILs e seus precursores. A espectroscopia Raman forneceu informações sobre as alterações nos modos vibracionais com as substituições, sendo possível constatar que os modos do anel se tornaram menos intensos com as substituições e a contribuição de grupos -CH se tornou mais importante. Cálculos de cargas de Mulliken foram realizados para estas espécies e os resultados obtidos reforçam as interpretações dos espectros vibracionais. A segunda etapa consistiu no estudo de ILs puros, analisando tanto cátion quanto ânion. A cadeia carbônica tem grande influência no espectro Raman, sendo observadas bandas atribuídas a confôrmeros diferentes, que aparecem em maior número e menor intensidade à medida que a cadeia se torna menor. Os ânions foram estudados nos ILs e em sais inorgânicos, sendo observados espectros muito semelhantes destes nos diversos ILs, porém diferentes nos sais inorgânicos. Os mesmos resultados foram encontrados nas medidas de XANES (espectroscopia de raio-X próxima à borda de absorção), que permitiu sondar a estrutura eletrônica ao redor de diversos átomos, utilizada como técnica auxiliar. Após analisado cátions e ânions, foi possível caracterizar o par iônico formado por estes íons, enfocando as bandas Raman das cadeias carbônicas, já que, como a interação de Coulomb é baixa, estes se ligam principalmente via ligação de hidrogênio. Para os ILs com -H no carbono 2, o ânion Br- forma um par iônico mais forte com os diversos cátions, enquanto PF6- e TFSI-</sup formam pares iônicos fracos, já que são menos coordenantes. A adição do metil no carbono 2 altera essa dinâmica, e mesmo o brometo não consegue formar um par iônico forte. Por fim, a terceira etapa visou o estudo destes sistemas em solução com um solvente molecular, a dimetilformamida (DMFA), usada como sonda, pois foi analisado o deslocamento da banda correspondente ao grupo C=O. Em um primeiro momento foram estudadas soluções equimolares de ILs e DMFA, em que foi possível observar a estruturação dos ILs na mistura, diferenciando efeito do cátion e do ânion. Posteriormente, selecionou-se alguns sistemas para um estudo em diversas frações molares de IL e DMFA. Em baixas concentrações de IL, o comportamento foi semelhante ao observado para solventes moleculares. Conforme se aumentou a concentração destes sais, observou-se um comportamento anômalo no deslocamento da banda C=O, que pode ser atribuída ao caráter iônico destes sistemas. / The present work aims to be a systematic study, by Raman spectroscopy, of imidazolic ionic liquids, which means low temperature molten salts derived from imidazole ring. The study involved the cations 1-alkil-3-methylimidazolium and 1-alkyl-2,3-dimethylimidazolim, being alkyl chain composed of 2, 4, 6, 8 or 10 carbon atoms and with the anions bromide, hexafluorophosphate and bis(trifluoromethanesulfonyl)imide (TFSI-), in a grand total of 30 species with distinct properties. The study has been separated in three steps. The first one aimed to study both neutral and cationic molecules derived from imidazolic ring to understand the difference between cations that can form ILs and their precursors. Raman spectroscopy gave information about the changes in the vibrational modes with the substitutions. The results show that the intensity of modes from the ring decreases with the substitutions, while the contribution of -CH modes increases. In accordance with this are the results obtained from theoretical calculation of Mulliken charge, used as an auxiliary technique. The second step consisted in the study of pure ILs, analyzing both cation and anion effects. The carbonic chain plays a major role in Raman spectra, exhibiting bands attributed to different conformers. These bands become more abundant and less intense when the chain length increases. The anions have been studied in both ILs and inorganic salts, being observed very similar spectra for all the ILs but different ones for the inorganic salts. These results have been confirmed by XANES (X-ray absorption near edge structure) spectroscopy, which makes possible to probe the electronic structure of different atoms. After the analysis of both cation and anion, it was possible to better understand the ion pair formation in ILs, focusing in hydrogen bonds in the carbonic chain, since the Coulombic interaction is too weak. For ILs with hydrogen in carbon 2, it could be observed that bromide anion forms a stronger ion pair when compared to PF6- and TFSI-, less coordinating anions. The addition of methyl group in carbon 2 modifies this behavior, and even bromide does not form the strong ion pair. At last, the third step focused in the better understanding of binary systems containing ILs and a molecular solvent, dimethylformamide (DMFA), used also as probe since the shift of the band attributed to C=O group was used in this study. In a first stage it has been studied equimolar solutions of ILs and DMFA, in which it has been observed the organization of ILs in the mixture, and the contribution of both cation and anion. The second stage was dedicated to the understanding of these mixtures with different molar fraction of ILs and DMFA, for which some ILs have been selected. For low concentration of ILs, their behavior was similar to molecular solvents, but when the concentration of IL was increased, an anomalous behavior in the shift of C=O band has been observed, which can be attributed to the ionic character of these systems.

This is a report of a verification study of the multiphysics simulation framework MOOSE which was preformed at the company Seaborg Technologies. In the process of designing molten salt reactors there is a special need of making credible multiphysics simulations since the fuel is in motion. In this study the incompressible version of Navier-Stokes equations of finite volumes available in the Navier-Stokes module of the MOOSE framework is verified by modelling and simulations of fluid flow and heat transfer in two different systems with available benchmarks. The first system, a thin buoyancy driven molten sodium hydroxide test loop which is verified by a similar model made with the high fidelity CFD software STAR-CCM+ as benchmark. The second system, forced convection of air through a straight pipe with heated walls which is verified by comparisons with an analytical solution. The resulting velocity profiles from simulations of the first system corresponds well with the benchmark but certain conclusions can not be drawn from it since the the transient simulations stops to converge before reaching equilibrium. The results from simulations of the second system corresponds well with the analytical solution and no convergence issues arise. The conclusion from the results is that the incompressible version of Navier-Stokes equations of finite volumes available in the Navier-Stokes module of the MOOSE framework has potential to be used in multiphysics simulations of molten salt reactors but seemingly not in cases of buoyancy driven flows in thin geometries. Two proposals for further work is recommended. The first is that this implementation is applied in a context with forced fluid flow or a context with thicker fluid domain. The second proposal is that the other available abilities of MOOSE such as finite element method and/or the compressible version of the Navier-Stokes equations should be tested.

Thermal energy storage (TES) in a concentrating solar power (CSP) plant allows for continuous operation even during times when solar radiation is not available, thus providing a reliable output to the grid. Energy can be stored either as sensible heat or latent heat, of which latent heat storage is advantageous due to its high volumetric energy density and the high Rankine cycle efficiency owing to the isothermal operation of latent thermal energy storage (LTES) system. Storing heat in the form of latent heat of fusion of a phase change material (PCM), in addition to sensible heat, significantly increases the energy density, thus potentially reducing the storage size and cost. However, a major technical barrier to the use of latent thermal energy of PCM is the high thermal resistance to energy transfer due to the intrinsically low thermal conductivity of PCMs, which is a particularly acute constraint during the energy discharge. Secondly, for integration of TES in CSP plants, it is imperative that the cyclic exergetic efficiency be high, among other requirements, to ensure that the energy extracted from the system is at the maximum possible temperature to achieve higher cycle conversion efficiency in the power block. The first objective is addressed through computational modeling and simulation to quantify the effectiveness of two different approaches to reduce the thermal resistance of PCM in a LTES, viz. (a) developing innovative, inexpensive and passive heat transfer devices that efficiently transfer large amount of energy between the PCM and heat transfer fluid (HTF) and (b) increase the heat transfer area of interaction between the HTF and PCM by incorporating the PCM mixture in small capsules using suitable encapsulation techniques.   The second portion of the research focuses on numerical modeling of large scale latent thermal storage systems integrated to a CSP plant with the aforementioned enhancement techniques and cascaded with more than one PCM to maximize the exergetic efficiency. Based on systematic parametric analysis on the various performance metrics of the two types of LTES, feasible operating regimes and design parameters are identified to meet the U.S. Department of Energy SunShot Initiative requirements including storage cost < $15/kWht and exergetic efficiency > 95%, for a minimum storage capacity of 14 h, in order to reduce subsidy-free levelized cost of electricity (LCE) of CSP plants from 21¢/kWh (2010 baseline) to 6¢/kWh, to be on par with the LCE associated with fossil fuel plants. / Ph. D.

No description available.

Increasing storage for energy is one of the most important challenges today to overcome in order to enable higher penetration of renewable energy in the existing energy systems. Thermal storage is one category of energy storage that has been successfully demonstrated in a number of engineering projects and is showing promising potential in the future. However, a technology cannot be widespread if it is not economically feasible and sustainable in the long run. Bottom up cost analysis can be used to assess economic viability of a technology. For newer technologies, the top-down cost calculation is not always possible due to the limited amount of data. The aim of this thesis is to investigate the best practices in performing bottom up cost calculation and to propose a methodology with the purpose of enabling it to be implemented over thermal energy storage bottom up economic evaluations. To achieve this, two proven applications, molten salt storage for concentrated solar power and ice thermal storage for building cooling, were examined as the basis of the bottom up state of the art calculation models. It was found that in the ice storage case, the models were often done in a hybrid bottom up-top down approach which limits a fully detailed cost analysis. Instead these are referred as case studies instead because of the few elements needed in their calculation. The constructed specialized models and case studies are then compared against other external sources to validate the proposed economic analysis procedure. The numerical results showed some discrepancies when compared to external resources. A compilation of a general bottom up cost model with detailed step by step model to perform a bottom up calculation for thermal storages is finally proposed in this work. / Att förbättra möjligheterna att lagra energi är en av dagens viktigaste utmaningar för att kunna öka andelen förnybar energi i vårt energisystem. Termisk energilagring eller värmelagring är en typ av energilagring som använts framgångsrikt i flera områden och visar hög potential i ett flertal ytterligare teknologier. En teknologi kan dock inte få en omfattande påverkan om den inte är ekonomiskt hållbar. En bottom-up kostnadsanalys kan användas för att uppskatta genomförbarheten för teknologin. För nya teknologier är en top-down kostnadsanalys inte alltid möjlig, vilket är beroende på den begränsade tillgången till data. Syftet med den här uppsatsen är att undersöka de vanligaste tillvägagångssätten i att utföra en bottom-up kostnadsanalys och föreslå en metodologi som har ändamålet att användas i bottom-up kostnadsanalyser för värmelagringstekniker. För att uppnå detta har två beprövade tekniker, smält saltlagring i koncentrerad solkraft och islagring för kylning av byggnader, undersökts som modeller för moderna bottom-up kostnadsanalyser. Efter undersökning fann man att i islagringsteknologi genomförs kostnadsanalysen vanligen i ett hybrid bottom up-top down upplägg, vilket begränsar möjligheten att rekonstruera en fullt detaljerad bottom-up kostnadsanalys. Dessa kommer istället att refereras som fallstudier eftersom endast ett fåtal objekt behövdes i en kostnadsberäkning. Specialiserade kostnadsmodeller som konstruerats och fallstudier jämförs med externa källor för att bekräfta den föreslagna analysproceduren för kostnadsberäkningar. Jämförelsen med externa källor visade viss spridning i numeriska resultat. En sammanställning av en generell bottom-up kostnadsmodell med detaljerad steg för steg-beskrivning för att genomföra en bottom-up kostnadsanalys är dessutom föreslagen i detta arbete.