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Orientadores: Rubens Maciel Filho, Maria Izabel Maretti Silveira Bueno / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-18T14:39:31Z (GMT). No. of bitstreams: 1 Henriques_ClaudeteBernardo_D.pdf: 9506603 bytes, checksum: 875e508c591361025ae37d3b9ac0f432 (MD5) Previous issue date: 2011 / Resumo: Esta tese tem como objetivo apresentar um estudo detalhado para a caracterização de petróleos, tanto no âmbito do desenvolvimento de modelos capazes de prever propriedades físico-químicas clássicas, como também avaliar os fenômenos associados a instabilidades decorrentes de características químicas. Para alcançar este objetivo, duas ações foram executadas: (1) Obter a curva de destilação do ponto de ebulição verdadeiro (PEV) através de simulação, por espectrometria de espalhamento de raios-X (EERX) aliada ao algoritmo denominado máquina vetor de suporte (SVM), com o propósito de prever o rendimento do processo de refino, e (2) Caracterizar o petróleo em relação ao fenômeno de agregação dos asfaltenos, para assim possibilitar a previsão da qualidade do processo de refino. Foram avaliadas amostras de petróleos com propriedades distintas, com o intuito de fornecer amplitude e robustez ao estudo. A primeira abordagem foi à análise classificatória dos petróleos em relação às suas propriedades intrínsecas (teor de enxofre, Grau API e ponto de ebulição verdadeiro), com aplicação de métodos multivariados de classificação. Com estas classificações em mãos, foram desenvolvidos modelos para previsão da curva PEV e do Grau API, utilizando o algoritmo SVM (segunda abordagem). Os dados tratados por meio deste algoritmo apresentaram um perfil de não linearidade. Os resultados obtidos para a caracterização das cargas a partir dos modelos não foram significativamente diferentes dos valores experimentais, permitindo o desenvolvimento de estudos computacionais usando o software comercial Petro-SIM®, para caracterização, aquisição das curvas das misturas de petróleos e, finalmente, previsão dos rendimentos dos cortes na simulação de uma torre de destilação atmosférica. A partir destes resultados, é muito importante ressaltar que, ao contrário da maioria das modelagens quimiométricas, um pequeno grupo de amostras foi necessário para o desenvolvimento do modelo (13 amostras). Vale também serem mencionadas a alta capacidade de previsão do modelo, a rápida e eficiente previsão de curvas PEV de amostras de petróleos puros, processados nas refinarias e, finalmente, a aplicação com sucesso destes modelos em simuladores de processo. A terceira abordagem do trabalho foi à avaliação dos aspectos relacionados à existência de formas coloidais dos asfaltenos, peptizados por resinas e dos efeitos relacionados à presença de outros solventes nos petróleos, que podem causar mudanças na cinética de floculação dos asfaltenos. A composição dos solventes (petróleos diluentes) e dos petróleos pesados foi correlacionada com os resultados do estudo cinético, obtido por meio da avaliação da transmitância por varredura óptica da camada de precipitação dos particulados e da floculação dos asfaltenos, como também por modelos dinâmicos. Para isto, foram elaboradas misturas de petróleos e observou-se que os efeitos associados ao fenômeno de agregação estão diretamente correlacionados com a composição dos petróleos, assim como com a presença de particulados nas misturas. A caracterização adequada dos constituintes de petróleo é uma informação indispensável para garantir o processamento adequado nas refinarias. A reprodução do cenário real do processo, por meio da simulação, foram promissores, mostrando que a caracterização da carga é possível ao se trabalhar com os modelos desenvolvidos, reforçando a relevância das técnicas aplicadas para descrição dos fenômenos químicos associados ao cenário de produção nacional / Abstract: This work aims to present a detailed study for petroleum characterization, through model developments able to preview physical chemical properties and also to evaluate the associate phenomena due to instability in current chemical characteristics. For this purpose two actions were executed: (1) To obtain the curve true boiling point (TPB) through the simulation by spectrometry X-ray scattering (EERX) combined with the algorithm called support vector machine (SVM), in order to predict the yield of the refining process, and (2) to characterize the petroleum in respect to asphaltene aggregation phenomena, making possible the prediction of the quality of the refining process. For these purposes, the petroleum samples were evaluated with different properties, providing amplitute and robustness to the study. The first approach was the classificatory analisis of petroleum in relation to intrinsic properties (sulfur contents, API degrees and true boiling point curves) with application of classification multivariate methods. With these classifications in hands, models were developed to predict the TBP curve and API gravity, using the algorithm SVM (second approach). The data were processed by this algorithm, showing nonlinear profiles. The results for the blend characterization using the models were not significantly different from the experimental values, allowing the development of computational studies using the commercial software Petro-SIM® for characterization, acquisition of mixtures curves and finally, prediction of the cuts yield in the simulation of an atmospheric distillation tower. From these results, it is important to emphasize that a small group of samples was necessary for the model development (13 samples). It is also worth to mention the high predictive ability of the model, the rapid and efficient prediction of TBP curves of crude oil samples, processed in the refineries and finally, the successful application of these models in process simulators. The third approach of this work was to evaluate the aspects related to the existence of colloidal forms of asphaltenes, peptized by resins and of effects related to the presence of other solvents in oils, which can cause changes in the kinetics of flocculation of asphaltenes. The composition of solvents (thinner oil) and of heavy crude oils were correlated with the results of kinetic study, obtained by evaluating the transmittance for optical scanning of the layer of precipitation of particles and the flocculation of asphaltenes, but also by dynamic models. For this, petroleum mixtures were prepared and it was observed that the effects associated to aggregation phenomena are correlated with the petroleum composition as well as the particulate presence in mixtures. The adequate characterization of petroleum constituents is essential information to ensure proper processing in refineries. The reproduction of real scenario of the process, through the simulation, were promising, showing that the blend characterization is possible when working with these developed models, reinforcing the relevance of the techniques applied for describing the chemical phenomena associated with the setting of national production / Doutorado / Desenvolvimento de Processos Químicos / Doutor em Engenharia Química

In order to elucidate the effects of nanostructuring on electron behavior in vanadium oxides, a suite of x-ray spectroscopy techniques was employed to comprehensively characterize the electronic structures of V2O5 and VO2 nanoparticles and compare them to their bulk counterparts. V2O5 and VO2 nanoparticle powders were characterized via PXRD, TEM, and HR-TEM to confirm size, purity, and crystallinity. Additionally, DSC and temperature-varied PXRD measurements on both VO2 samples confirmed the structural aspect of the monoclinic to rutile metal-insulator phase transition, and UV-Vis measurements allowed for Kubelka-Munk analysis on the V2O5 samples. XAS measurements enable the comparison of unoccupied conduction band states, while XES and RIXS measurements reveal occupied valence band states and the individual vanadium and oxygen PDOS below the Fermi level. XPS measurements of both core and valence band states both confirmed the valence band structure revealed by XES and also provide information on core-state energy levels. In the case of V2O5, the valence band O 2p states are upshifted in the nanoparticle sample, while the lowest V 3d conduction band states are unshifting but provide more available unoccupied states for excitation. These changes produce a shrunken bandgap in the V2O5 nanoparticles that is in line with much previous computational work, but unexpected from previous experimental results and defies the Moss-Burstein effect usually observed in V2O5. The resulting changes in band structure are attributed to a higher concentration of oxygen vacancy defects in the nanoparticle sample. Additionally, electron correlation effects in V2O5 nanoparticles are found to be enhanced relative to the bulk, likely due to added electron presence in the V 3d split-off band. In the case of VO2, dramatic changes in both the valence band and conduction band states are observed both below and above the structural phase transition temperature. These changes (lowered unoccupied conduction band states coupled with broadened and upshifted occupied valence band states) also lead to nanoparticle bandgap reduction and enhanced metallicity. The enhanced metallic nature of the VO2 nanoparticles is again attributed to the increased presence of surface oxygen vacancy defects, as well as a V2O3-like surface reconstruction. Additionally, electron correlation effects are found to be reduced in the VO2 nanoparticle samples relative to the bulk, unlike in the case of V2O5.

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The L10 FePt phase belongs to the most promising hard ferromagnetic materials for high density recording media. The main challenges for thin FePt films are: (i) to lower the process temperature for the transition from the soft magnetic A1 to the hard magnetic L10 phase, (ii) to realize c-axes preferential oriented layers independently from the substrate nature and (iii) to control layer morphology supporting the formation of FePt - L10 self-organized isolated nanoislands towards an increase of the signal-to-noise ratio. In this study, dc magnetron sputtered FePt thin films on amorphous substrates were inve-stigated. The work is focalized on the correlation between structural and magnetic properties with respect to the influence of deposition parameters like growth mode (co-sputtering vs. layer – by - layer) and the variation of the deposition gas (Ar, Xe) or pressure (0.3 - 3 Pa). In low-pressure Ar discharges, high energetic particle impacts support vacancies formation during layer growth lowering the phase transition temperature to (320 +/- 20)°C. By reducing the particle kinetic energy in Xe discharges, highly (001) preferential oriented L10 - FePt films were obtained on a-SiO2 after vacuum annealing. L10 - FePt nano-island formation was supported by the introduction of an Ag matrix, or by random ballistic aggregation and atomic self shadowing realized by FePt depositions at very high pressure (3 Pa). The high coercivity (1.5 T) of granular, magnetic isotropic FePt layers, deposited in Ar discharges, was measured with SQUID magnetometer hysteresis loops. For non-granular films with (001) preferential orientation the coercivity decreased (0.6 T) together with an enhancement of the out-of- plane anisotropy. Nanoislands show a coercive field close to the values obtained for granular layers but exhibit an in-plane easy axis due to shape anisotropy effects. An extensive study with different synchrotron X-ray scattering techniques, mainly performed at the ESRF, BM-20 (ROBL-Beamline), pointed out the importance of in-situ investigations to clearly understand the kinetic mechanism of the A1 to L10 transition and ordering and to control FePt nanoclusters evolution.

This thesis focuses on the theoretical investigation of the electronic structure and magnetic interactions present in 3d and 4d/5d transition metal compounds. We use many-body quantum chemistry methods that provide a theoretical frame for the rigorous construction and systematic improvement of correlated N-electron wave-functions. In Chapter 3 we compute d-d transitions fully ab initio and assign excitation peaks of experimental spectra measured in spin-Peierls TiPO4 compound. In this material we find that the d1 ground state is composed of an admixture of dz2 and dxz orbital character, which is related to the large positive ionic charge at P sites in the xz plane (defining the shortest Ti-P links) and of Ti nearest-neighbors along the z axis. In addition, the magnitude of the nearest-neighbors Heisenberg magnetic coupling calculated by quantum chemistry methods compares well with resonant inelastic X-ray scattering (RIXS) experimental data. We further demonstrate that the intersite exchange is very sensitive to the Ti-Ti interatomic distance, which is relevant in the context of spin-Peierls physics in TiPO4. In Chapter 4 we have studied the magnetic anisotropy of Fe ions within the Li3N lattice. The calculated magnetic anisotropy splitting of 26.3 meV for Fe2+ d6 ions in D6h symmetry compares favorably to values measured or computed by similar theoretical methods for Fe1+ d7 species with linear coordination. This substantial spin-reversal energy barrier of the Fe2+ ion is associated with a a^1_{1g}e^3_{2g}e^2_{1g} ground-state electron configuration. Our study therefore puts into the spotlight the linearly coordinated Fe2+ d6 ion as candidate for viable single molecule magnet behavior. In Chapter 5 we address the effect of electron-lattice interactions on the magnetic properties of 4d and 5d TM ions with a formally degenerate t^1_{2g} electron configuration in the double-perovskite materials Ba2YMoO6, Ba2LiOsO6 and Ba2NaOsO6. Our analysis indicates that the sizable magnetic moments and g-factors found experimentally are due to both strong TM d -- ligand p hybridization and dynamic Jahn-Teller effects. Our results also point out that cation charge imbalance in the double-perovskite structure allows a fine tuning of the gap between the t2g and eg levels. The mechanism has not been explored so far experimentally but seems to hold much potential in the context of orbital engineering in transition metal compounds. In Chapter 6 we report a study of magnetic exchange interactions in the S=3/2 orthorhombic perovskite NaOsO3. We mapped the ab initio quantum chemistry results onto model Hamiltonians including both isotropic Heisenberg interactions and anisotropic Dzyaloshinskii-Moriya exchange. We found antiferromagnetic nearest-neighbors Heisenberg exchange interactions of J_ac = 24.4 meV and J_b = 20.9 meV, twice larger than the J extracted from the magnon excitation spectra. The quantum chemistry results motivate further experimental measurements or theoretical analysis to clarify the magnitude of the nearest-neighbors Heisenberg couplings. In Chapter 7 we provide valuable insights on the effective magnetic interactions in 5d and 4d oxides with face-sharing oxygen octahedra, BaIrO3 and BaRhO3, for different bond-angles and bond-lengths. The large antiferromagnetic Heisenberg interactions computed here emphasize the subtle interplay among strong spin-orbit interactions, direct intersite orbital overlap and orbital bonding, and couplings to the lattice degrees of freedom in face-sharing compounds. In Chapter 8 we apply a computational scheme for computing intensities as measured in X-ray absorption and RIXS experiments. We take into account the readjustment of the charge distribution in the vicinity of an excited electron for the modeling of RIXS. For L3-edge spectra of Cu2+ 3d9 ions in KCuF3, we discuss the way to consider orbital ordering effects (alternately occupied d_x2-z2 and d_y2-z2 orbitals). For L3-edge spectra of Ni2+ 3d8 ions in La2NiO4, the computed spectra reproduce trends found experimentally for the incoming-photon incident-angle and polarization dependence.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18780号 / 理博第4038号 / 新制||理||1581(附属図書館) / 31731 / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)准教授 戸塚 圭介, 教授 川上 則雄, 教授 佐々 真一 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第21124号 / 工博第4488号 / 新制||工||1697(附属図書館) / 京都大学大学院工学研究科高分子化学専攻 / (主査)教授 辻井 敬亘, 教授 山子 茂, 教授 竹中 幹人 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

The relationship between microstructure and mechanical properties of semicrystalline polymer materials has been a hot topic since many years in materials science and engineering. Isotactic polypropylene (iPP) is frequently used as a model material, due to its good mechanical properties and wide applications. In the past few years, numerous studies have been performed in the field of structural evolution during deformation. Previous results revealed that phase transition from crystal to mesophase happens in the crystal scale, lamellae orientation and fragmentation occurs in the lamellae scale, and even cavitation behavior exists in the larger scale. Although abundant work has been done, some problems remain under debate, for instance the relationship between lamellae deformation and cavitation behavior, the role of phase transition on the void formation, et al. In this study, well defined microstructure of iPP is obtained by annealing or adding nucleating agent. Afterward, the structural evolution under three types of mechanical load modes (including uniaxial stretching, creep, and stress relaxation) is in-situ monitored by synchrotron X-ray scattering. During uniaxial stretching, we revealed, for the first time, how lamellae deformation occurs in the time scales of elastic deformation, intra-lamellar slip, and melting-recrystallization, separated by three critical strains which were only rarely found to be influenced by annealing. Strain I (a Hencky strain value of 0.1) marks the end of elastic deformation and the onset of intra-lamellar slip. Strain II (a Hencky strain value of 0.45) signifies the start of the recrystallization process, from where the long period in the stretching direction begins to decrease from its maximum and the polymer chains in the crystal start to orient along the stretching direction. The energy required by melting arises from the friction between the fragmented lamellae. Strain III (a Hencky strain value of 0.95) denotes the end of the recrystallization process. Beyond the strain of 0.95, the long period and the crystal size remain nearly unchanged. During further stretching, the extension of the polymer chains anchored by lamellae triggers the strain hardening behavior. On the other hand, annealing significantly decreases the critical strain for voids formation and increases the voids number, but restricts the void size. For those samples annealed at a temperature lower than 90 oC, voids are formed between strain II and strain III. The voids are oriented in the stretching direction once they are formed. For those samples annealed at a temperature higher than 105 oC, voids are formed between strain I and strain II. The voids are initially oriented with their longitudinal axis perpendicular to the stretching direction and then transferred along stretching direction via voids coalescence. Additionally, the formation of voids influences neither the critical strains for lamellae deformation, nor the final long period, the orientation of polymer chains or the crystal size. β-iPP is a kind of metastable phase which can be induced only under special condition. By adjusting the morphology of N,N'-dicyclohexyl-2,6-naphthalene dicarboxamide (NJS) through self-assembly, the relative content of β-iPP (Kβ) is successfully controlled, under the condition that the weight content of NJS in the composite keeps at 0.3 wt. %. The microstructural evolution of the iPP/NJS composites with different Kβ during uniaxial stretching is studied. The results show that a higher Kβ could increase the number of the voids. However, the size of the voids is similar regardless of the NJS morphology. The β-α phase transition takes place after voids formation. During intralamellar and inter-lamellar slip, no obvious polymer chains orientation can be found for α-iPP. In the strain range of 0.1~0.6, the c-axis of the β-iPP crystal tends to orient perpendicular to the stretching direction due to lamellae twisting, which is a unique deformation mode of β-iPP lamellae. And the lamellae twisting are proposed to be responsible for the intense voids formation of the composite with higher Kβ. During creep, the evolution of the long period can be divided into four stages (primary creep, transition stage, secondary creep, and tertiary creep). This fits quite well with the macroscopic displacement and strain evolution. In primary creep, the long period along loading direction (L_p^∥) increases with time due to the stretching of amorphous phase, whereas the long period perpendicular to loading direction (L_p^⊥) decreases slightly. In secondary creep, strain increases linearly with time. Both L_p^∥ and L_p^⊥ exhibit the same tendency with strain. The increase of the long period is caused by lamellae thickening, which is a kind of cooperative motion of molecular chains with their neighbors onto the lamellae surface. The increasing rate of L_p^∥ is larger than that of L_p^⊥, indicating that the orientation of molecular chains along loading direction decreases the energy barrier for the cooperative motion. In tertiary creep, strain grows dramatically within a limited time. The lamellae are tilted and rotated, and then disaggregated. In addition, fibrillary structure is formed during lamellae breaking. The length of the fibrillary structure increases from 364 nm to 497 nm but its width stays at 102 nm as creep time increases. During stress relaxation, the local deformation behavior of the long period is affine with the macroscopic stress relaxation. However, the evolution of the crystal orientation and the void size lag behind the macroscopic stress relaxation. The decrease of the long period is mainly caused by the relaxation of the strained polymer chains in the amorphous phase. The retardation of the evolution of the crystal orientation is probably caused by the phase transition from stable α-iPP to metastable mesomorphic-iPP. By phase transition, the highly oriented α-iPP is transferred to weakly oriented mesomorphic-iPP. Due to the fact that the void is confined by the network of the strained polymer chains where lamellae blocks serve as the physical anchoring points, the phase transition contributes greatly to the viscoplastic deformation of the network. Consequently, the evolution of the voids size shows a similar trend with that of the phase transition. With this thesis, we gained a deeper insight into the relationship between structure and properties of semicrystalline polymers. The current study will not only benefit the understanding of polymer materials science but also serve as guidance for the processing of semicrystalline polymers for engineering applications.:1 Introduction 1 1.1 Isotactic polypropylene (iPP) 1 1.1.1 Chain structure of PP 1 1.1.2 Crystal forms of iPP 2 1.1.3 Lamellae of iPP 4 1.1.4 The morphology of the supra-structure of iPP 4 1.2 Structural evolution during deformation 5 1.2.1 Deformation process of semicrystalline polymers 5 1.2.2 Cavitation behavior of semicrystalline polymers 7 1.3 Synchrotron X-ray scattering 9 1.3.1 X-ray and its sources 9 1.3.2 The interaction between X-rays and objects 11 1.3.3 Wide angle X-ray scattering 12 1.3.4 Small angle X-ray scattering 13 2 Motivation and objectives 15 3 Samples preparation and basic characterization 17 3.1 Materials and samples preparation 17 3.1.1 Preparation of iPP films with single layer of spherulites and transcrystalline regions 17 3.1.2 Preparation of iPP plates crystallized with different thermal histories 17 3.1.3 Preparation of iPP/NJS plates with different morphologies of NJS 18 3.1.4 Preparation of microinjection molded iPP/NJS sample 18 3.2 Characterization 18 3.2.1 Differential scanning calorimetry (DSC) 18 3.2.2 Dynamic mechanical analysis (DMA) 19 3.2.3 Scanning electron microscopy (SEM) 19 3.2.4 Polarized optical microscopy (POM) 20 3.2.5 Rheology test 20 3.2.6 Gel Permeation Chromatography (GPC) 21 3.2.7 In situ synchrotron X-ray scattering measurements 21 3.2.8 X-ray scattering pattern processing and calculation 24 4 Microstructure characterization in a single iPP spherulite by synchrotron microfocus wide angle X-ray scattering 29 4.1 Introduction 30 4.2 The nucleation efficiency of the carbon fiber on iPP 31 4.3 Morphology of iPP spherulites and transcrystalline region 32 4.4 Defining of the position of the carbon fiber 33 4.5 Microstructure studies of the spherulite 34 4.5.1 Crystallinity in the spherulite 35 4.5.2 The ratio between “daughter” lamellae and “mother” lamellae in the spherulite 36 4.5.3 The orientation of the crystal axis in the spherulite 37 4.6 Conclusion 39 5 Influence of annealing on the mechanical αc-relaxation of iPP: a study from the intermediate phase perspective 41 5.1 Introduction 42 5.2 Crystal form of water cooled and annealed iPP 44 5.3 Microstructure of iPP with different thermal history 45 5.4 Melting behavior of iPP with different thermal history 50 5.5 Mechanical relaxation behavior of iPP with different thermal history 52 5.6 Conclusion 57 6 Critical strains for lamellae deformation and cavitation during uniaxial stretching of annealed iPP 59 6.1 Introduction 60 6.2 The true stress-strain curves of iPP uniaxial stretched at 75 oC 61 6.3 In Situ SAXS and WAXS Results 63 6.3.1 Synchronize mechanical test and in-situ SAXS/WAXS measurement 66 6.4 Lamellae deformation 67 6.4.1 The evolution of the long period 67 6.4.2 The evolution of the crystal size 69 6.4.3 The orientation of the c-axis of the crystal 71 6.4.4 The evolution of the crystallinity 72 6.5 Cavitation behavior 74 6.5.1 The onset strain of the voids formation and the voids direction transition 74 6.5.2 The evolution of the voids size 75 6.5.3 The scattering invariant (Q) of the voids 76 6.5.4 The morphology of voids 77 6.6 Final discussion 79 6.7 Conclusion 82 7 Accelerating shear-induced crystallization and enhancing crystal orientation of iPP by controlling the morphology of N,N'-dicyclohexyl-2,6-naphthalene dicarboxamide 83 7.1 Introduction 84 7.2 The self-assembly process of N,N'-dicyclohexyl-2,6-naphthalene dicarboxamide 85 7.3 Rheological behavior 88 7.3.1 Frequency sweep test 88 7.3.2 Strain sweep test 88 7.3.3 Steady-state shear test 89 7.4 Shear-induced crystallization 91 7.4.1 Crystallization kinetics studied by rheological method 91 7.4.2 In-situ SAXS measurement 93 7.4.3 Microstructure of iPP after shear-induced crystallization 96 7.4.4 The morphology of the sample 98 7.4.5 The crystallization mechanism 99 7.5 Conclusion 100 8 Influence of nucleating agent self-assembly on structural evolution of iPP during uniaxial stretching 101 8.1 Introduction 102 8.2 The morphology of the NJS in the compression molded iPP 103 8.3 Microstructure of iPP with different NJS morphologies 104 8.4 In-situ SAXS results 105 8.4.1 Cavitation behavior 107 8.4.2 Evolution of the long period 110 8.5 In-situ WAXS results 111 8.5.1 The β-α phase transition behavior 112 8.5.2 The orientation of the crystal 115 8.6 Conclusion 117 9 Microstructural evolution of iPP during creep: an in-situ study by synchrotron SAXS 119 9.1 Introduction 120 9.2 The creep curve 121 9.3 In-situ SAXS results 123 9.3.1 Evolution of long period and domain thickness 125 9.3.2 Lamellae tilting and rotation 128 9.3.3 Lamellae orientation and fibrillary structure formation 129 9.4 Conclusions 132 10 Microstructural evolution of iPP during stress relaxation 133 10.1 Introduction 134 10.1.1 The structural evolution during stress relaxation at 60 oC 135 10.1.2 The structural evolution during stress relaxation at 90 oC 140 10.2 Conclusion 145 11 Conclusion and outlook 146 12 References 148 13 Appendix 158 13.1 List of symbols and abbreviations 158 13.2 List of figures and tables 163 13.3 List of publications 171 14 Acknowledgements 173 15 Eidesstattliche Erklärung 175

Recent resonant inelastic x-ray scattering (RIXS) experiments have detected a significant high-energy spin-excitation anisotropy in the nematic phase of the enigmatic iron-based superconductor FeSe, whose origin remains controversial. We apply an itinerant model previously used to describe the spin-excitation anisotropy as measured by neutron scattering measurements, with magnetic fluctuations included within the RPA approximation. The calculated RIXS cross section exhibits overall agreement with the RIXS data, including the high energy spin-excitation anisotropy