No / Solvent influences on the crystallization of polymorph and hydrate forms of the nootropic drug piracetam (2-oxo-pyrrolidineacetamide) were investigated from water, methanol, 2-propanol, isobutanol, and nitromethane. Crystal growth profiles of piracetam polymorphs were constructed using time-resolved diffraction snapshots collected for each solvent system. Measurements were performed by in situ energy dispersive X-ray diffraction recorded in Station 16.4 at the synchrotron radiation source (SRS) at Daresbury Laboratory, CCLRC UK. Crystallizations from methanol, 2-propanol, isobutanol, and nitromethane progressed in a similar fashion with the initial formation of form I which then converted relatively quickly to form II with form III being generated upon further cooling. However, considerable differences were observed for the polymorphs lifetime and both the rate and temperature of conversion using the different solvents. The thermodynamically unstable form I was kinetically favored in isobutanol and nitromethane where traces of this polymorph were observed below 10°C. In contrast, the transformation of form II and subsequent growth of form III were inhibited in 2-propanol and nitromethane solutions. Aqueous solutions produced hydrate forms of piracetam which are different from the reported monohydrate; this crystallization evolved through successive generation of transient structures which transformed upon exchange of intramolecular water between the liquid and crystalline phases

O câncer de mama é o tipo de câncer mais frequente entre as mulheres, sendo a mamografia a técnica mais utilizada para sua detecção. No entanto, essa técnica possui algumas limitações, como o baixo contraste, o qual pode ser associado, dentre outros fatores, a radiação espalhada. Apesar desse fato, novas técnicas baseadas na detecção do espalhamento vêm sendo empregadas em um vasto campo de aplicação, como na caracterização de materiais e tecidos biológicos. Há na literatura diversos estudos sobre perfil de espalhamento para a caracterização de tecidos mamários, porém ainda são poucos os estudos sobre imagem por espalhamento de mama e de otimização de contraste. Além disso, essas imagens são realizadas apenas em pequenas amostras de mama. Uma das possibilidades para o estudo de mamas de dimensões reais é a aplicação do método Monte Carlo (MC). Neste trabalho, foi estudado e otimizado um sistema de difração de raios X dispersivo em energia (SDRXDE) para medidas de perfis de espalhamento e um sistema para formação de imagens por espalhamento utilizando estas informações. O SDRXDE foi caracterizado experimentalmente, analiticamente e por simulação Monte Carlo, enquanto que o segundo sistema foi caracterizado analiticamente e por simulação Monte Carlo. Os resultados obtidos mostraram que as principais correções para o SDRXDE foram auto-atenuação, o espectro incidente, eficiência de detecção e múltiplo espalhamento. Outro fator importante que afeta o perfil de espalhamento resultante é a resolução de momento do sistema, o qual depende dos parâmetros geométricos (abertura dos colimadores, distâncias, ângulo de espalhamento e espessura da amostra) e da resolução de energia do detector. Os resultados para o sistema de imagem mostram claramente a capacidade dessas imagens na detecção de um nódulo no interior da mama. A respeito da otimização das condições de irradiação da mama e detecção da radiação espalhada, os resultados alcançados demostram a viabilidade experimental da geração destas imagens num ambiente clínico. / Breast cancer is the most frequent type of cancer among women, being mammography the technique more used for its detection. However, this technique presents some limitations, such as low contrast, which may be associated with scattered radiation. Thus, new scatterinng detection techniques have been employed in different fields such as characterization of biological materials and tissues, such as characterization of scattering profile for breast tissue, although there are still few studies on breast image and contrast optimization. Moreover, the images are originated from small breast samples. In this context, one of the possibilities for the study of actual breast dimensions is the application of the Monte Carlo method. Thus, this work studied optimized an energy X ray diffraction system (EDXRD) for measures of scattering profile and developed a system for imaging using this information. The EDXRD system was studied and optimized by experimentally, analytically and Monte Carlo simulation, while the image system was studied analytically and simulated by Monte Carlo. The results showed that the main corrections for the EDXRD system are self-attenuation, incident spectrum, detection eficiency and multiple scattering. Another important factor that affects scattering profile is the system momentum resolution, which depends on geometric parameters (collimator aperture, distances, scattering angle and sample thickness) and detector energy resolution. The results for the imaging system showed that a nodule could be detected within the breast. Finaly the optimizations of breast radiation conditions and radiation detection showed the viability of generating experimental scattering images in clinical environment.

This thesis presents a study on two types of X-ray diffraction methodologies applied to the characterization of amorphous materials. The purpose of this study was to assess the feasibility of measuring the diffractive spectrum of amorphous materials by Energy-Dispersive X-ray Diffraction (EDXRD) utilizing Cadmium Zinc Telluride detectors. The total scattering intensity (coherent plus incoherent scatter) spectra precisely measured by high-energy Wide-Angle X-ray Scattering (WAXS) were compared to the EDXRD spectra to determine the level of agreement between the two techniques. The EDXRD spectra were constructed by applying a spectra fusing technique which combined the EDXRD spectra collected at different scattering angles rendering a continuous total scattering spectrum. The spectra fusing technique extended the momentum transfer range of the observed scattered spectrum beyond the limitations of the X-ray source and CZT detection efficiencies. Agreement between the WAXS and fused EDXRD spectra was achieved. In addition, this thesis presents the atomic pair correlation functions and coordination numbers of the first coordination shell for four hydrogen peroxide solutions of varying mass concentrations using Empirical Potential Structural Refinement (EPSR). The results are compared to the state-of-the art ad initio quantum mechanical charge field molecular dynamics (QMCF MD) model of the hydrogen peroxide in solution to support the model's predictions on why hydrogen peroxide is stable in water. The EPSR results using the coherent scattering intensity calculated from the WAXS data set predicts a hydration shell of 6.4 molecules of water surrounding hydrogen peroxide. The results also indicate that hydrogen peroxide is more likely to behave as a proton donor than acceptor. These findings are in agreement with QMCF MD model of aqueous hydrogen peroxide. / Physics

<div>In this thesis, the role of location-specific microstructural features in the fatigue performance of the safety-critical aerospace components made of Nickel (Ni)-base superalloys and linear friction welded (LFW) Titanium (Ti) alloys has been studied using crystal plasticity finite element (CPFE) simulations, energy dispersive X-ray diffraction (EDD), backscatter electron (BSE) images and digital image correlation (DIC).</div><div><br></div><div>In order to develop a microstructure-sensitive fatigue life prediction framework, first, it is essential to build trust in the quantitative prediction from CPFE analysis by quantifying uncertainties in the mechanical response from CPFE simulations. Second, it is necessary to construct a unified fatigue life prediction metric, applicable to multiple material systems; and a calibration strategy of the unified fatigue life model parameter accounting for uncertainties originating from CPFE simulations and inherent in the experimental calibration dataset. To achieve the first task, a genetic algorithm framework is used to obtain the statistical distributions of the crystal plasticity (CP) parameters. Subsequently, these distributions are used in a first-order, second-moment method to compute the mean and the standard deviation for the stress along the loading direction (σ_load), plastic strain accumulation (PSA), and stored plastic strain energy density (SPSED). The results suggest that an ~10% variability in σ_load and 20%-25% variability in the PSA and SPSED values may exist due to the uncertainty in the CP parameter estimation. Further, the contribution of a specific CP parameter to the overall uncertainty is path-dependent and varies based on the load step under consideration. To accomplish the second goal, in this thesis, it is postulated that a critical value of the SPSED is associated with fatigue failure in metals and independent of the applied load. Unlike the classical approach of estimating the (homogenized) SPSED as the cumulative area enclosed within the macroscopic stress-strain hysteresis loops, CPFE simulations are used to compute the (local) SPSED at each material point within polycrystalline aggregates of 718Plus, an additively manufactured Ni-base superalloy. A Bayesian inference method is utilized to calibrate the critical SPSED, which is subsequently used to predict fatigue lives at nine different strain ranges, including strain ratios of 0.05 and -1, using nine statistically equivalent microstructures. For each strain range, the predicted lives from all simulated microstructures follow a log-normal distribution; for a given strain ratio, the predicted scatter is seen to be increasing with decreasing strain amplitude and are indicative of the scatter observed in the fatigue experiments. Further, the log-normal mean lives at each strain range are in good agreement with the experimental evidence. Since the critical SPSED captures the experimental data with reasonable accuracy across various loading regimes, it is hypothesized to be a material property and sufficient to predict the fatigue life.</div><div><br></div><div>Inclusions are unavoidable in Ni-base superalloys, which lead to two competing failure modes, namely inclusion- and matrix-driven failures. Each factor related to the inclusion, which may contribute to crack initiation, is isolated and systematically investigated within RR1000, a powder metallurgy produced Ni-base superalloy, using CPFE simulations. Specifically, the role of the inclusion stiffness, loading regime, loading direction, a debonded region in the inclusion-matrix interface, microstructural variability around the inclusion, inclusion size, dissimilar coefficient of thermal expansion (CTE), temperature, residual stress, and distance of the inclusion from the free surface are studied in the emergence of two failure modes. The CPFE analysis indicates that the emergence of a failure mode is an outcome of the complex interaction between the aforementioned factors. However, the possibility of a higher probability of failure due to inclusions is observed with increasing temperature, if the CTE of the inclusion is higher than the matrix, and vice versa. Any overall correlation between the inclusion size and its propensity for damage is not found, based on inclusion that is of the order of the mean grain size. Further, the CPFE simulations indicate that the surface inclusions are more damaging than the interior inclusions for similar surrounding microstructures. These observations are utilized to instantiate twenty realistic statistically equivalent microstructures of RR1000 – ten containing inclusions and remaining ten without inclusions. Using CPFE simulations with these microstructures at four different temperatures and three strain ranges for each temperature, the critical SPSED is calibrated as a function of temperature for RR1000. The results suggest that critical SPSED decreases almost linearly with increasing temperature and is appropriate to predict the realistic emergence of the competing failure modes as a function of applied strain range and temperature.</div><div><br></div><div>LFW process leads to the development of significant residual stress in the components, and the role of residual stress in the fatigue performance of materials cannot be overstated. Hence, to ensure fatigue performance of the LFW Ti alloys, residual strains in LFW of similar (Ti-6Al-4V welded to Ti-6Al-4V or Ti64-Ti64) and dissimilar (Ti-6Al-4V welded to Ti-5Al-5V-5Mo-3Cr or Ti64-Ti5553) Ti alloys have been characterized using EDD. For each type of LFW, one sample is chosen in the as-welded (AW) condition and another sample is selected after a post-weld heat treatment (HT). Residual strains have been separately studied in the alpha and beta phases of the material, and five components (three axial and two shear) have been reported in each case. In-plane axial components of the residual strains show a smooth and symmetric behavior about the weld center for the Ti64-Ti64 LFW samples in the AW condition, whereas these components in the Ti64-Ti5553 LFW sample show a symmetric trend with jump discontinuities. Such jump discontinuities, observed in both the AW and HT conditions of the Ti64-Ti5553 samples, suggest different strain-free lattice parameters in the weld region and the parent material. In contrast, the results from the Ti64-Ti64 LFW samples in both AW and HT conditions suggest nearly uniform strain-free lattice parameters throughout the weld region. The observed trends in the in-plane axial residual strain components have been rationalized by the corresponding microstructural changes and variations across the weld region via BSE images. </div><div><br></div><div>In the literature, fatigue crack initiation in the LFW Ti-6Al-4V specimens does not usually take place in the seemingly weakest location, i.e., the weld region. From the BSE images, Ti-6Al-4V microstructure, at a distance from the weld-center, which is typically associated with crack initiation in the literature, are identified in both AW and HT samples and found to be identical, specifically, equiaxed alpha grains with beta phases present at the alpha grain boundaries and triple points. Hence, subsequent fatigue performance in LFW Ti-6Al-4V is analyzed considering the equiaxed alpha microstructure.</div><div><br></div><div>The LFW components made of Ti-6Al-4V are often designed for high cycle fatigue performance under high mean stress or high R ratios. In engineering practice, mean stress corrections are employed to assess the fatigue performance of a material or structure; albeit this is problematic for Ti-6Al-4V, which experiences anomalous behavior at high R ratios. To address this problem, high cycle fatigue analyses are performed on two Ti-6Al-4V specimens with equiaxed alpha microstructures at a high R ratio. In one specimen, two micro-textured regions (MTRs) having their c-axes near-parallel and perpendicular to the loading direction are identified. High-resolution DIC is performed in the MTRs to study grain-level strain localization. In the other specimen, DIC is performed on a larger area, and crack initiation is observed in a random-textured region. To accompany the experiments, CPFE simulations are performed to investigate the mechanistic aspects of crack initiation, and the relative activity of different families of slip systems as a function of R ratio. A critical soft-hard-soft grain combination is associated with crack initiation indicating possible dwell effect at high R ratios, which could be attributed to the high-applied mean stress and high creep sensitivity of Ti-6Al-4V at room temperature. Further, simulations indicated more heterogeneous deformation, specifically the activation of multiple families of slip systems with fewer grains being plasticized, at higher R ratios. Such behavior is exacerbated within MTRs, especially the MTR composed of grains with their c-axes near parallel to the loading direction. These features of micro-plasticity make the high R ratio regime more vulnerable to fatigue damage accumulation and justify the anomalous mean stress behavior experienced by Ti-6Al-4V at high R ratios.</div><div><br></div>