Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第15377号 / 工博第3256号 / 新制||工||1490(附属図書館) / 27855 / 京都大学大学院工学研究科材料工学専攻 / (主査)教授 松原 英一郎, 教授 田中 功, 准教授 宇田 哲也 / 学位規則第4条第1項該当

This contribution addresses recent advances in the experimental investigation of the phase stability, microstructural integrity and stress evolution of metal/metal (Cu/W) [1] and metal/ceramic (Ag/AlN, Ag60wt.%Cu40at.%/AlN, AgGe10at% /AlN) NML coatings during heating by advanced in-situ diffraction methods in combination with XPS, SEM and TEM analysis.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第17887号 / 工博第3796号 / 新制||工||1581(附属図書館) / 30707 / 京都大学大学院工学研究科材料工学専攻 / (主査)教授 田中 功, 教授 酒井 明, 教授 邑瀬 邦明 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Disordered multicomponent nitride thin film can be used for various applications. The focus of this Licentiate Thesis lies on the theoretical study of piezoelectric properties, phase stability and surface diffusion in multifunctional hard coating nitrides using density functional theory (DFT). Piezoelectric thin films show great promise for microelectromechanical systems (MEMS), such as surface acoustic wave resonators or energy harvesters. One of the main benefits of nitride based piezoelectric devices is the much higher thermal stability compared to the commonly used lead zirconate titanate (PZT) based materials. This makes the nitride based material more suitable for application in, e.g., jet engines. The discovery that alloying AlN with ScN can increase the piezoelectric response more than 500% due to a phase competition between the wurtzite phase in AlN and the hexagonal phase in ScN, provides a fundamental basis for constructing highly responsive piezoelectric thin films. This approach was utilized on the neighboring nitride binaries, where ScN or YN was alloyed with AlN, GaN, or InN. It established the general role of volume matching the binaries to easily achieve a structural instability in order to obtain a maximum increase of the piezoelectric response. For Sc0.5Ga0.5N this increase is more than 900%, compared to GaN. Y1-xInxN is, however, the most promising alloy with the highest resulting piezoelectric response seconded only by Sc0.5Al0.5N. Phase stability and lattice parameters (stress-strain states) of the Y1-xAlxN alloy have been calculated in combination with experimental synthesis. Hard protective coatings based on nitride thin films have been used in industrial applications for a long time. Two of the most successful coatings are TiN and the metastable Ti1-xAlxN. Although these two materials have been extensively investigated both experimentally and theoretically, at the atomic level little is known about Ti1-xAlxN diffusion properties. This is in large part due to problems with configurational disorder in the alloy, because Ti and Al atoms are placed randomly at cation positions in the lattice, considerably increasing the complexity of the problem. To deal with this issues, we have used special quasi-random structure (SQS) models, as well as studying dilute concentrations of Al. One of the most important mechanisms related to the growth of Ti1-xAlxN is surface diffusion. Because Ti1-xAlxN is a metastable material it has to be grown as a thin film with methods such as physical vapor deposition (PVD), in which surface diffusion plays a pivotal role in determining the microstructure evolution of the film. In this work, the surface energetics and mobility of Ti and Al adatoms on a disordered Ti0.5Al0.5N(001) surface are studied. Also the effects on the adatom energetics of Ti, Al, and N by the substitution of one Ti with an Al surface atom in TiN(001), TiN(011), and TiN(111) surfaces is studied. This provides an indepth atomistic understanding of how the energetics behind surface diffusion changes as TiN transitions into Ti0.5Al0.5N. The investigations revealed many interesting results. i) That Ti adatom mobilities are dramatically reduced on the TiN and Ti0.5Al0.5N(001) surfaces while Al adatoms are largely unaffected. ii) The reverse effect is found on the TiN(111) surface, Al adatom migration is reduced while Ti adatom migration is unaffected. iii) The magnetic spin polarization of Ti adatoms is shown to have an important effect on binding energies and diffusion path, e.g., the adsorption energy at bulk sites is increased by 0.14 eV.

In this work, physical phenomena related to the growth and phase formation of alumina, Al2O3, are investigated by experiments and computer calculations. Alumina finds applications in a wide variety of areas, due to many beneficial properties and several existing crystalline phases. For example, the α and κ phases are widely used as wear-resistant coatings due to their hardness and thermal stability, while, e.g., the metastable γ and θ phases find applications as catalysts or catalyst supports, since their surface energies are low and, hence, they have large surface areas available for catalytic reactions. The metastable phases are involved in transition sequences, which all irreversibly end in the transformation to the stable α phase at about 1050 °C. As a consequence, the metastable aluminas, which can be grown at low temperatures, cannot be used in high temperature applications, since they are destroyed by the transformation into α. In contrast, α-alumina, which is the only thermodynamically stable phase, typically require high growth temperatures (~1000 °C), prohibiting the use of temperature sensitive substrates. Thus, there is a need for increasing the thermal stability of metastable alumina and decreasing the growth temperature of the α phase. In the experimental part of this work, hard and single-phased α-alumina thin films were grown by magnetron sputtering at temperatures down to 280 °C. This dramaticdecrease in growth temperature was achieved by two main factors. Firstly, the nucleation stage of growth was controlled by pre-depositing a chromia “template” layer, which is demonstrated to promote nucleation of α-alumina. Secondly, it is shown that energetic bombardment was needed to sustain growth of the α phase. Energy-resolved mass spectrometry measurements demonstrate that the likely source of energetic bombardment, in the present case, was oxygen ions/atoms originating from the target surface. Overall, these results demonstrate that low-temperature α-alumina growth is possible by controlling both the nucleation step of growth as well as the energetic bombardment of the growing film. In addition, the mass spectrometry studies showed that a large fraction of the deposition flux consisted of AlO molecules, which were sputtered from the target. Since the film is formed by chemical bonding between the depositing species, this observation is important for the fundamental understanding of alumina thin film growth. In the computational part of the work, the effect of additives on the phase stability of α- and θ-alumina was investigated by density functional theory calculations. A systematic study was performed of a large number of substitutional dopants in the alumina lattices. Most tested dopants tended to reverse the stability between α- and θ-alumina; so that, e.g., Modoping made the θ phase energetically favored. Thus, it is possible to stabilize the metastable phases by additives. An important reason for this is the physical size of the dopant ions with respect to the space available within the alumina lattices. For example, large ions induced θ stabilization, while ions only slightly larger than Al, e.g., Co and Cu, gave a slight increase in the relative stability of the α phase. We also studied the stability of some of these compounds with respect to pure alumina and other phases, containing the dopants, with the result that phase separations are energetically favored and will most likely occur at elevated temperatures.

Fundamental thermodynamic investigations have been carried out regarding the phase equilibria of La0.8Sr0.2MnO3±δ (LSM), a cathode of a solid oxide fuel cell (SOFC), utilizing the CALculation of PHAse Diagram (CALPHAD) approach. The assessed thermodynamic databases developed for LSM perovskite in contact with YSZ fluorite and the other species have been discussed. The application of computational thermodynamics to the cathode is comprehensively explained in detail, including the defect chemistry analysis as well as the quantitative Brouwer diagrams, electronic conductivity, cathode/electrolyte interface stability, thermomechanical properties of the cathode and the impact of gas impurities, such as CO2 as well as humidity, on the phase stability of the cathode. The quantitative Brouwer diagrams for LSM at different temperatures are developed and the detailed analysis of the Mn3+ charge disproportionation behavior and the electronic conductivity in the temperature range of 1000-1200°C revealed a good agreement with the available experimental observations. The effects of temperature, CO2 partial pressure, O2 partial pressure, humidity level and the cathode composition on the formation of secondary phases have been investigated and correlated with the available experimental results found in the literature. It has been indicated that the CO2 exposure does not change the electronic/ionic carriers’ concentration in the perovskite phase. The observed electrical conductivity drop is predicted to occur due to the formation of secondary phases such as LaZr2O7, SrZrO3, SrCO3 and Mn oxides at the LSM/YSZ interface, resulting in the blocking of the electron/ion transfer paths. For the thermo-mechanical properties of LSM, a new weight loss Mechanism for (La0.8Sr0.2)0.98MnO3±δ using the La-Sr-Mn-O thermodynamic database is modeled with respect to the compound energy formalism model. This newly proposed mechanism comprehensively explains the defect formation as a result of volume/weight change during the thermal cycles. According to the proposed mechanism the impact of cation vacancies regarding the volume change of cathode was explained.

No description available.

Submitted by Alison Vanceto (alison-vanceto@hotmail.com) on 2016-10-25T10:51:21Z No. of bitstreams: 1 TeseRHP.pdf: 8778601 bytes, checksum: eb4553a13387041c0fd36d153b524c3c (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-11-08T19:10:09Z (GMT) No. of bitstreams: 1 TeseRHP.pdf: 8778601 bytes, checksum: eb4553a13387041c0fd36d153b524c3c (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-11-08T19:10:15Z (GMT) No. of bitstreams: 1 TeseRHP.pdf: 8778601 bytes, checksum: eb4553a13387041c0fd36d153b524c3c (MD5) / Made available in DSpace on 2016-11-08T19:10:21Z (GMT). No. of bitstreams: 1 TeseRHP.pdf: 8778601 bytes, checksum: eb4553a13387041c0fd36d153b524c3c (MD5) Previous issue date: 2016-09-30 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / InO1.5-stabilized zirconia (InSZ) is a potential hot corrosion resistant thermal barrier coating (TBC). However, the thermal instability prevents real applications of InSZ-based TBC. This thesis investigates the hypothesis of co-doping using the charge compensation to improve the phase stability of InSZ. Four co-doping systems were synthesized by coprecipitation and studied: (ZrO2)1-(x+y)(InO1.5)x(MOz)y with MOz = TaO2.5, NbO2.5, MoO3, or WO3. After synthesis, 9 mol% of InO1.5 plus the charge-compensating oxides was sufficient to stabilize the tetragonal phase. Specific surface area up to 106.1 m2.g-1 and crystallite size ~11 nm were achieved using ethanol washing followed by azeotropic distillation as dehydration technique in the precipitates. In these powders, initial thermal stability analysis indicated instability of the tetragonal phase, with extension of the t→m transformation less detrimental in the InMoSZ system. Further increase in the concentration of InO1.5:MoO3 results in monophasic samples with retention of cubic phase in the InMoSZ. Cubic InMoSZ exhibited hardness and thermal expansion coefficient of 13.5% and 9% higher than those of InSZ, respectively. However, thermal treatments at T ≥ 1200 °C showed that the InMoSZ is also passive to destabilization of the high temperature cubic polymorph. Although the cubic InMoSZ was the most promising system found in this thesis, the stability results do not support its application as TBC for temperatures ≥ 1000 ºC. A deep evaluation of the phase transformations between 1000 to 1200 °C indicated that the instability of the proposed systems is due to a progressive c→t→m destabilization of the polymorphs. This c→t→m transformation is directly associated with the reduction of the InO1.5 stabilizer in solid solution by volatilization as In2O during heat treatment. At temperatures ≤ 800 ºC, the c→t phase transformation do not occurs, then, InSZ-based TBC is stable in these conditions. / A zircônia estabilizada com InO1,5 (InSZ) é um material com potencial aplicação como revestimentos para barreira térmica (TBC) resistentes à corrosão. Contudo, a instabilidade de fases impede aplicações industriais da InSZ. Esta tese investiga a ação da co-dopagem por compensação de cargas como uma estratégia para aumentar a estabilidade de fases da InSZ. Quatro sistemas de co-dopagem foram sintetizados por co-precipitação e estudados: (ZrO2)1-(x+y)(InO1,5)x(MOz)y com MOz = TaO2,5, NbO2,5, MoO3 ou WO3. Após a síntese, 9 %mol de InO1,5 somado a concentração de óxidos compensadores de carga foi suficiente para estabilização da fase tetragonal. Área superficial específica de até 106,1 m2.g‒1 e tamanho de cristalitos de ~11 nm foram obtidos utilizando a lavagem com etanol seguida por destilação azeotrópica como técnica de desidratação dos precipitados. Para estes pós, testes de estabilidade térmica indicaram instabilidade da fase tetragonal, com extensão de transformação t→m menos detrimental no sistema InMoSZ. Aumentando gradativamente a concentração de InO1,5-MoO3 na InMoSZ resulta em amostras monofásicas com retenção da fase cúbica. A InMoSZ cúbica exibiu dureza e coeficiente de expansão térmica até 13,5% e 9% superiores aos valores da InSZ, respectivamente. No entanto, tratamentos em temperaturas ≥ 1200 ºC indicaram que a InMoSZ é também suscetível a desestabilização da fase cúbica. Embora a InMoSZ cúbica tenha sido o sistema mais promissor obtido nesta tese, os resultados de estabilidade indicam que sua aplicação como TBC não é possível em temperaturas ≥ 1000 ºC. Uma avaliação detalhada das fases formadas após os tratamentos entre 1000 a 1200 ºC demonstrou que a instabilidade dos sistemas estudados é decorrente de uma transformação progressiva tipo c→t→m. A origem da transformação c→t→m é associada a redução da concentração do estabilizador InO1,5 em solução sólida por volatilização como In2O durante os testes de estabilidade térmica. Em temperaturas ≤ 800 ºC, a transformação c→m não ocorre, neste caso, TBCs baseadas em InSZ são estáveis termicamente para aplicações industriais.

Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2016-06-22T12:43:46Z No. of bitstreams: 0 / Made available in DSpace on 2016-06-22T12:43:46Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2016-06-22T12:43:46Z No. of bitstreams: 0 / Made available in DSpace on 2016-06-22T12:43:46Z (GMT). No. of bitstreams: 0 / Neste trabalho foi estabelecido um sistema padrão primário para raios X de energias baixas (10 kV a 50 kV), utilizando uma câmara de ionização de ar livre de cilindros concêntricos da marca Victoreen (modelo 481-5) no Laboratório de Calibração de Instrumentos (LCI) do Instituto de Pesquisas Energéticas e Nucleares (IPEN/CNEN-SP). Para isso foi desenvolvido um novo protocolo de alinhamento da câmara de ionização no sistema de radiação e foi feita uma modificação no suporte dos micrômetros utilizados para o movimento dos cilindros internos. Os resultados obtidos nos testes de estabilidade e de caracterização ficaram dentro dos limites estabelecidos pelas normas IEC 61674 e IEC 60731. Foram determinados também os fatores de correção para atenuação de fótons no ar, transmissão e espalhamento no diafragma, espalhamento e fluorescência, e recombinação iônica. Esses valores foram comparados com os valores obtidos pelo laboratório padrão primário alemão,Physikalisch-Technische Bundesanstalt (PTB), mostrando boa concordância. Por último, foi determinado o valor absoluto da grandeza taxa de kerma no ar para as qualidades padronizadas de mamografia de feixes diretos WMV28 e WMV35 e feixes atenuados WMH28 e WMH35; os resultados são compatíveis, com diferença máxima de 3,8% com os valores obtidos utilizando o sistema padrão secundário do LCI. / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP