O presente trabalho apresenta a análise da resistência ao desgaste abrasivo de um revestimento duro e do aço SAE 5160. O revestimento foi obtido pela deposição de uma liga ferrosa através de processo de soldagem \"TIG\" sobre um aço ABNT 1020. Aliga foi desenvolvida com a utilização de CR e Nb como elementos formadores de carbonetos, proporcionando uma microestrutura constituída, no estado bruto de fusão, de uma rede de carbonetos (Cr, Fe)7C3 interdendríticos e NbC dispersos em uma matriz austenítica. Corpos de prova revestidos foram submetidos a tratamentos térmicos de normalização, têmpera, sub-zero e revenido, visando a obtenção de diferentes microestruturas na matriz, enquanto que o aço SAE 5160 foi temperado e revenido de acordo com o procedimento utilizado na confecção de ferramentas agrícolas com este material. A resistência ao desgaste do revestimento foi superior à do aço SAE 5160 nos dois tipos de ensaios de abrasão realizados, sendo os melhores desempenhos apresentados pelo revestimento temperado no ensaio realizado com equipamento do tipo pino sobre lixa e pelo revestimento temperado e revenido no ensaio do tipo roda de borracha/areia seca. A identificação dos mecanismos de remoção de material predominantes nos ensaios abrasivos foi possibilitada pela observação das superfícies desgastadas dos corpos de prova através de microscopia eletrônica de varredura. / The present work presents an analysis of the abrasive wear resistance of a hardfacing and of the SAE 5160 steel. The hardfacing was obtained by the deposition of a iron based alloy through \"TIG\" welding on a ABNT 1020 steel. This alloy was developed with the use of Cr and Nb as carbide forming elements , resulting in a microstructure formed by a carbide net of M7C3 interdendritic in a austenitic matrix. The hardfacing samples suffered heat treatment of normalizing, hardening, tempering and subzero, viewing the achievement of differents microstructure, while the SAE 5160 steel suffered hardening and tempering according to the production process used in the agricutural tool manufacturing. The wear resistance of the hardfacing overcame the SAE 5160 steel in both types of abrasion wear tests, and the best performances were presented by hardening hardfacing in the pin wear test and by the tempering hardfacing in the rubber wheel/dry sand test. The identification of the material removal mechanisms in the abrasive tests was made by the observation of the worn surfaces of the samples through the scanning eletronic microscopy.

Orientador: Eduardo Granado Monteiro da Silva / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-09-01T17:31:34Z (GMT). No. of bitstreams: 1 Kaneko_UlissesFerreira_D.pdf: 51229533 bytes, checksum: 3d39a6722771458fa1812d75c31661b4 (MD5) Previous issue date: 2017 / Resumo: Nesta tese, empregamos espectroscopia Raman para realizar um estudo detalhado dos fônons e das respostas eletrônicas em monocristais de LaFeAsO. Nós observamos as simetrias e frequências dos fônons nas fases tetragonal e ortorrômbica e também a dependência com a temperatura de um pico quase-elástico (do inglês: QEP) na simetria B1g com intensidade máxima em torno da transição magnética TN . A área e a altura do QEP B1g foram atribuídas às flutuações nemáticas de spin, enquanto que a largura do QEP B1g foi relacionada com taxa de relaxação dessas flutuações. Através da análise da largura do QEP B1g propomos que a transição estrutural esté relacionada a um congelamento gradual das flutuaçõees nemáticas de spin, o que deve ser um fenômeno geral presente nos demais supercondutores à base de Fe. Esse estudo foi complementado por medidas de espectroscopia Raman em BaFe2As2 e de difração de raios-X com luz síncrotron em LaFeAsO, BaFe2As2 e SrFe2As2 dopado com Co. Paralelamente, nós estudamos as estruturas cristalinas e magnéticas em compostos da série Ba1?xLaxTi1/2Mn1/2O3 através da técnica de difração de nêutrons / Abstract: In this thesis, we employed Raman spectroscopy to perform a detailed study of the phonons and electronic responses in single crystals of the LaFeAsO. We observed the symmetries and frequencies of the phonons in the tetragonal and orthorhombic phases and also the temperature dependence of the quasi-elastic peak (QEP) in the B 1g symmetry with maximum intensity around the magnetic transition T N . The B 1g QEP area and height were ascribed to spin nematic fluctuations, while the B 1g QEP width was related to the relaxation rate of these fluctuations. From the B 1g QEP width analysis we propose that the structural transition is related to a gradual freezing of the spin nematic fluctuations, which may be a general phenomenon present in other Fe-based superconductors. This study was complemented by measurements of Raman spectroscopy in BaFe2As2 and synchrotron X-ray diffraction in LaFeAsO, BaFe2As2 and Co-doped SrFe2As2 . In parallel, we studied the crystal and magnetic structures in compounds of the series Ba1?xLaxTi1/2Mn1/2O3 through the neutron diffraction technique / Doutorado / Física / Doutor em Ciências / 140978/2012-7 / CNPQ

The crystalline iron-based nanowires encapsulated by multiwalled carbon nanotubes have been the subject of numerous studies owing to the range of potential applications. The presence of a-Fe (bcc)/y -Fe(fcc) junctions o ers the possibility of exploitation of the exchange bias effect, an interfacial magnetic phenomenon that plays a major role in magnetocaloric cooling, spintronic and high-density magnetic storage devices. This work is concerned with the synthesis and microstructural characterization of Fe-based and NiFe nanowires encapsulated by multiwall carbon nanotube radial structures. The known attributes of these structures are well matched to the magnetocaloric application. The primary aim of this work was to determine the unknown microstructural details of the encapsulated nanowire that are of relevance to the magnetocaloric application (junction types, location and orientation relative to the nanotube axis). The secondary aim was to explore the modi cation of the synthesis route to promote desirable attributes. This is the first report of a-Fe/y -Fe sequential junctions and a-Fe/Fe3C concentric junctions in encapsulated Fe-based nanowires. The presence of a-Fe/y -Fe junctions was inferred from the observation of a-Fe nanowires terminated by a ~100 nm length y-Fe crystallites of larger diameter. The a-Fe/Fe3C junctions exhibit the Bagaryatski orientation relationship: [110 ]bcck[100 ]orth. The degree of substrate roughness was found to be a means of tailoring details of the structure and composition of the encapsulated nanowires. NiFe encapsulated nanowires were found to contain crystallites of a-NiFe, y-NiFe and Ni3Fe and the sequential junctions -NiFe/Ni3Fe and a-NiFe/y-NiFe junctions.

The origin of the nematic phase in the iron-based superconductors is still unknown, and an understanding of its microscopic mechanism could have important implications on the unconventional superconductivity in these materials. This thesis describes a series of experiments using scanning tunneling microscopy (STM) and spectroscopy (STS) to visualize the nematic electronic structure in NaFe1-xCoxAs as a function of energy, temperature, strain, and doping. We first start with background material on the iron-based superconductors and the iron pnictides in particular. We then extensively explore the physical details of NaFe1-xCoxAs which is the main material of study in this thesis. Additional attention is paid to the electronic structure due to its relation to quasiparticle interference (QPI) measurements made with STS. The theoretical underpinnings of STM and STS are then derived as well as further details of QPI. Many of the experiments described in this thesis were performed on a custom-built, low temperature STM which the author helped build. We describe the design of this system and report on benchmarking tests that were used to characterize the system's performance. Both pristine, undoped NaFeAs and LiFeAs were measured by STM, and we compare and contrast these two materials which come from the same structural family. The electronic local density of states (LDOS) of NaFeAs was measured at various temperatures in all three phases of the material (tetragonal paramagnetic, orthorhombic paramagnetic, and orthorhombic spin density wave (SDW)). The electronic structure in the SDW phase is highly anisotropic. QPI signals in this phase are found to be well-explained by comparison to a joint density of states (JDOS) model using the reconstructed bandstructure fit to angle-resolved photoemission spectroscopy data. The electronic anisotropy is found to persist into the nominally tetragonal phase. This persistence arises from built-in crystallographic strain coupling to high amplitude, unidirectional, antiferroic fluctuations. These fluctuations renormalize the bare Green's function which gives rise to anisotropic scattering. We then describe the construction of a novel device created for variable-strain STS. Antiphase domains in NaFeAs are visualized and found to change in size as a function of unidirectional strain. These domains are tracked as a function of temperature and found to disappear at exactly the nematic transition temperature proving that this is the temperature at which long-range order is lost. By measuring Co-doped samples, we find that the domains disappear before optimal doping in an underdoped sample with superconducting transition temperature of 18 K. However, the electronic structure remains anisotropic implying that nematic fluctuations persist. These fluctuations are found even in overdoped samples and disappear with superconductivity at heavy doping.

Gegenstand dieser Arbeit ist die Entwicklung, Herstellung und Charakterisierung verschiedener glasbildender Eisenbasislegierungen, mit dem Ziel: 1. durch umfangreiche Charakterisierung der Startlegierung Fe44,63Cr4,93Co4,93Mo12,61Mn11,03C15,56B5,81Y1,5 (at.%) Möglichkeiten zu evaluieren mit dieser Legierung Komposite aus amorpher Matrix und kristalliner Zweitphase herzustellen, 2. den Einfluss der Legierungselemente Kobalt, Chrom und Molybdän auf die strukturellen, thermischen und mechanischen Eigenschaften des Startlegierungstyps zu bestimmen und 3. auf Grundlage der Startlegierung Glasmatrixkomposite mit Zusatzelementen herzustellen. Die Erkenntnisse sollen als Grundlage für die Verbesserung der plastischen Eigenschaften der hochfesten aber auch außerordentlich spröden amorphen Eisenbasislegierungen dienen. Für den Beginn der Forschungsarbeiten wurde die von Lu et al. publizierte Legierung mit der Zusammensetzung Fe44,63Cr4,93Co4,93Mo12,61Mn11,03C15,56B5,81Y1,5 at. % und einem kritischen Gießdurchmesser von 12 mm gewählt [Lu04], da aufgrund der hohen Anzahl von Legierungselementen, stark unterschiedlichen Atomgrößen und dem internen Sauerstoffgetter Yttrium zu erwarten ist, dass die Glasbildungsfähigkeit auch nach Legierungsmodifikationen hoch bleibt. Dadurch ist es möglich, die Auswirkungen von Zusammensetzungsveränderungen auf die Eigenschaften der amorphen Legierungen und Glasmatrixkomposite zu studieren. Als erstes wurde die Startlegierung umfangreich strukturell, thermisch und mechanisch charakterisiert (Kapitel 5). Daran schließt sich die Untersuchung des Einflusses der Elemente Kobalt, Chrom und Molybdän auf die thermischen, strukturellen und mechanischen Eigenschaften an (Kapitel 6). Das Kapitel 7 hat zum Ziel zu zeigen, welche Arten von Glasmatrixkompositen auf der Basis der Startlegierung herstellbar sind. Es wurden Komposite mit Zirkoniumkarbid, Titankarbid, Niobkarbid, Silber und Kupfer hergestellt und charakterisiert.

O presente trabalho apresenta a análise da resistência ao desgaste abrasivo de um revestimento duro e do aço SAE 5160. O revestimento foi obtido pela deposição de uma liga ferrosa através de processo de soldagem \"TIG\" sobre um aço ABNT 1020. Aliga foi desenvolvida com a utilização de CR e Nb como elementos formadores de carbonetos, proporcionando uma microestrutura constituída, no estado bruto de fusão, de uma rede de carbonetos (Cr, Fe)7C3 interdendríticos e NbC dispersos em uma matriz austenítica. Corpos de prova revestidos foram submetidos a tratamentos térmicos de normalização, têmpera, sub-zero e revenido, visando a obtenção de diferentes microestruturas na matriz, enquanto que o aço SAE 5160 foi temperado e revenido de acordo com o procedimento utilizado na confecção de ferramentas agrícolas com este material. A resistência ao desgaste do revestimento foi superior à do aço SAE 5160 nos dois tipos de ensaios de abrasão realizados, sendo os melhores desempenhos apresentados pelo revestimento temperado no ensaio realizado com equipamento do tipo pino sobre lixa e pelo revestimento temperado e revenido no ensaio do tipo roda de borracha/areia seca. A identificação dos mecanismos de remoção de material predominantes nos ensaios abrasivos foi possibilitada pela observação das superfícies desgastadas dos corpos de prova através de microscopia eletrônica de varredura. / The present work presents an analysis of the abrasive wear resistance of a hardfacing and of the SAE 5160 steel. The hardfacing was obtained by the deposition of a iron based alloy through \"TIG\" welding on a ABNT 1020 steel. This alloy was developed with the use of Cr and Nb as carbide forming elements , resulting in a microstructure formed by a carbide net of M7C3 interdendritic in a austenitic matrix. The hardfacing samples suffered heat treatment of normalizing, hardening, tempering and subzero, viewing the achievement of differents microstructure, while the SAE 5160 steel suffered hardening and tempering according to the production process used in the agricutural tool manufacturing. The wear resistance of the hardfacing overcame the SAE 5160 steel in both types of abrasion wear tests, and the best performances were presented by hardening hardfacing in the pin wear test and by the tempering hardfacing in the rubber wheel/dry sand test. The identification of the material removal mechanisms in the abrasive tests was made by the observation of the worn surfaces of the samples through the scanning eletronic microscopy.

Abstract: Isobutylene is a high demand chemical that contributes to the production of fuel, plastic, and rubbers. It is produced industrially by different processes, as a byproduct of steam cracking of naphtha or a fluidized catalytic cracking or by isobutane dehydrogenation. Catalytic dehydrogenation of isobutane is in increasing importance because of the growing demand for isobutylene and the better economic advantage compared to other isobutylene production processes. Isobutane dehydrogenation is an endothermic reaction and to achieve good yields; it is preferred to work at higher temperatures. At these temperatures, carbon deposition leads to catalyst deactivation, which requires the catalyst to be regenerated on a frequent basis. Most of the current processes to produce isobutylene use either expensive platinum-based metal or toxic chromium-based catalysis. Hence, there is a demand to search for alternative catalysts that are a relatively cheap and non-toxic. To achieve this goal, Zirconia-supported Iron catalysts were prepared. To study the effect of active phase distribution, different iron loadings were tested for impregnation (3% to 10%) and co-precipitation (10%-20%). The catalysts show promising results that can achieve an isobutylene selectivity and yield of 91% and 31%, respectively, with isobutane conversion of 35%.

In this thesis, the results of analyzing the electronic structure of two iron-based superconductors: FeSe and LiFeAs are presented. To access the electronic structure, angle-resolved photoemission spectroscopy was used. In our analysis, we focus on the structure of the superconducting gap and the influence of nematicity on the electronic structure. We have revealed changes in the electronic structure of FeSe caused by nematicity in all parts of the Brillouin zone. A scale of these changes is smaller than it was believed earlier. Also, we have observed an anomalous shift of the dispersions in opposite directions with temperature in this material. We have observed anisotropic superconducting gap on all sheets of the Fermi surfaces of both: FeSe and LiFeAs. We have shown that in LiFeAs, rotational symmetry is broken in the superconducting state, which manifests not only in the gap symmetry but also in the shapes of the Fermi surfaces sheets. This result indicates a realization of a novel phenomenon of superconductivity-induced nematicity:1 Iron-based superconductors 1.1 Introduction to iron-based superconductors 1.2 LiFeAs - special iron-based superconductor 1.3 FeSe - structurally simplest iron-based superconductor 2 Angle-Resolved Photoemission 3 Temperature evolution of the electronic structure of FeSe 3.1 Effects of nematicity from low-temperature measurements 3.2 Temperature dependent shift of the dispersions 3.3 Discussion and conclusions 4 Three-dimensional superconducting gap in FeSe 4.1 Superconducting gap on the electron-like pockets 4.2 Superconducting gap on the hole-like pocket 4.3 Discussion and conclusions 5 Superconductivity-induced nematicity in LiFeAs 5.1 Superconducting gap 5.2 Nematicity 5.3 Discussion and conclusions Summary

This project was a cooperation between the division of Chemical Technology at KTH, Cortus Energy and Haldor Topsoe A/S. The goal was to build up a totally new setup for converting and deoxygenate pyrolysis bio-oil, in order to increase the performance of Cortus Energy’s WoodRoll process. Therefore an iron based catalyst from Haldor Topsoe was used. The building up of the new setup with all reactors and the control panel was a complicated and time-consuming work. This led to an only short time slot for performing experiments, which means that more work needs to be done to get more valuable results. The most important success of this project was to get all the knowledge about the system and to make everything (the whole experimental setup) running properly. However, the sampling system needs to be improved before making further experiments. The experiments which have been done show promising results and that the iron based catalyst was working well for converting the bio-oil. During the two hour long experiment there were not shown any indications of deactivation, when looking at the gas compositions, but the results from temperature programmed oxidation (TPO) show carbon deposition on the catalyst and the BET surface also shows a slight decrease in surface area.

京都大学 / 0048 / 新制・論文博士 / 博士(理学) / 乙第12996号 / 論理博第1552号 / 新制||理||1604(附属図書館) / 32924 / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 松田 祐司, 教授 前野 悦輝, 教授 石田 憲二 / 学位規則第4条第2項該当 / Doctor of Science / Kyoto University / DGAM