付記する学位プログラム名: 京都大学卓越大学院プログラム「先端光・電子デバイス創成学」 / 京都大学 / 新制・課程博士 / 博士(工学) / 甲第23905号 / 工博第4992号 / 新制||工||1779(附属図書館) / 京都大学大学院工学研究科電子工学専攻 / (主査)教授 木本 恒暢, 教授 白石 誠司, 准教授 小林 圭 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

The lifetime of aluminium reduction cells is of considerable importance in the operating economics of an aluminium smelter. Not only are the cell materials costly, but cell life is also key in minimizing production downtime and the waste material generated in the cutting-out and relining of a reduction cell. This lifetime is increasingly driven by two components of the cell lining: the carbon cathode and the sidewall refractories which are the primary containment of the metal and electrolyte. Silicon nitride bonded silicon carbide (SNBSC) refractories are the current state-of-the-art sidewall materials. These materials are formed by encapsulation of SiC particles in a silicon nitride matrix, by nitridation of silicon at high temperatures under a nitrogen atmosphere. In this study the mechanisms of the corrosion of silicon nitride bonded silicon carbide refractories in an aluminium reduction cell environment were examined. Microstructural analysis of SNBSC materials by: X-ray diffraction, solid state NMR, Raman spectroscopy, XPS, and SEM, identified variations in α/β Si3N4 ratio and porosity in the binder phase, with higher porosity levels and β Si3N4 content found in the interior part of the brick. Unreacted metallic silicon was observed only as a crystalline phase inside SiC grains and is not associated with the binder phase. SNBSC samples from eight different commercial refractory manufacturers were tested in an industrial aluminium cell environment, both by immersion in industrial cells and in the laboratory. The samples showed extensive attack and considerable differentiation between the samples. The effects on the corrosion rate of porosity levels, amount of binder, α/β Si3N4 ratio, free Si content in the binder, and different factors in the environment were examined in the laboratory scale trials. A laboratory scale testing rig with some novel features, such as a rotating anode, was developed to examine corrosion resistance of samples under electrolysis conditions in molten cryolite at up to 1000oC. Corrosion test results, supported by thermodynamic calculations, identified the Si3N4 binder as the reactive phase in SNBSC materials, especially in the gas phase above the bath level. High porosity levels and high β Si3N4 fraction in the binder showed a statistically significant contribution to the corrosion rate in lab-scale corrosion trials. Commercial materials are also highly inhomogeneous in the distribution of the β Si3N4 phase as mentioned above, which complicates sample selection and the interpretation of corrosion test results. The crystal morphology of β Si3N4 is suggested as the reason for the high reactivity of these materials. This morphology characterised by elongated rod-like shape crystals with hexagonal cross section, presents a higher surface area compared to α Si3N4 crystals containing mainly flat matte crystals. In the light of this observation, the binder phase in selected samples was deliberately modified to convert a significant fraction of the α Si3N4 to β Si3N4. Corrosion rates measured from these modified samples in general support the argument that the crystallographic form of silicon nitride contributes to corrosion rate. The proposed corrosion mechanism for SNBSC materials in the aluminium reduction cell atmosphere is based on combination of oxidation of the binder followed by attack of corrosive gases to produce volatile SiF4. Thus the binder phase is initially passivated below the electrolyte level on the sidewall, where exposure to corrosive gases is limited, but occurs more rapidly in the area above the electrolyte/air interface. The intrusion of electrolyte into the refractory and capillary transport up the sidewall is a key in accelerating this reaction.

The lifetime of aluminium reduction cells is of considerable importance in the operating economics of an aluminium smelter. Not only are the cell materials costly, but cell life is also key in minimizing production downtime and the waste material generated in the cutting-out and relining of a reduction cell. This lifetime is increasingly driven by two components of the cell lining: the carbon cathode and the sidewall refractories which are the primary containment of the metal and electrolyte. Silicon nitride bonded silicon carbide (SNBSC) refractories are the current state-of-the-art sidewall materials. These materials are formed by encapsulation of SiC particles in a silicon nitride matrix, by nitridation of silicon at high temperatures under a nitrogen atmosphere. In this study the mechanisms of the corrosion of silicon nitride bonded silicon carbide refractories in an aluminium reduction cell environment were examined. Microstructural analysis of SNBSC materials by: X-ray diffraction, solid state NMR, Raman spectroscopy, XPS, and SEM, identified variations in α/β Si3N4 ratio and porosity in the binder phase, with higher porosity levels and β Si3N4 content found in the interior part of the brick. Unreacted metallic silicon was observed only as a crystalline phase inside SiC grains and is not associated with the binder phase. SNBSC samples from eight different commercial refractory manufacturers were tested in an industrial aluminium cell environment, both by immersion in industrial cells and in the laboratory. The samples showed extensive attack and considerable differentiation between the samples. The effects on the corrosion rate of porosity levels, amount of binder, α/β Si3N4 ratio, free Si content in the binder, and different factors in the environment were examined in the laboratory scale trials. A laboratory scale testing rig with some novel features, such as a rotating anode, was developed to examine corrosion resistance of samples under electrolysis conditions in molten cryolite at up to 1000oC. Corrosion test results, supported by thermodynamic calculations, identified the Si3N4 binder as the reactive phase in SNBSC materials, especially in the gas phase above the bath level. High porosity levels and high β Si3N4 fraction in the binder showed a statistically significant contribution to the corrosion rate in lab-scale corrosion trials. Commercial materials are also highly inhomogeneous in the distribution of the β Si3N4 phase as mentioned above, which complicates sample selection and the interpretation of corrosion test results. The crystal morphology of β Si3N4 is suggested as the reason for the high reactivity of these materials. This morphology characterised by elongated rod-like shape crystals with hexagonal cross section, presents a higher surface area compared to α Si3N4 crystals containing mainly flat matte crystals. In the light of this observation, the binder phase in selected samples was deliberately modified to convert a significant fraction of the α Si3N4 to β Si3N4. Corrosion rates measured from these modified samples in general support the argument that the crystallographic form of silicon nitride contributes to corrosion rate. The proposed corrosion mechanism for SNBSC materials in the aluminium reduction cell atmosphere is based on combination of oxidation of the binder followed by attack of corrosive gases to produce volatile SiF4. Thus the binder phase is initially passivated below the electrolyte level on the sidewall, where exposure to corrosive gases is limited, but occurs more rapidly in the area above the electrolyte/air interface. The intrusion of electrolyte into the refractory and capillary transport up the sidewall is a key in accelerating this reaction.

The lifetime of aluminium reduction cells is of considerable importance in the operating economics of an aluminium smelter. Not only are the cell materials costly, but cell life is also key in minimizing production downtime and the waste material generated in the cutting-out and relining of a reduction cell. This lifetime is increasingly driven by two components of the cell lining: the carbon cathode and the sidewall refractories which are the primary containment of the metal and electrolyte. Silicon nitride bonded silicon carbide (SNBSC) refractories are the current state-of-the-art sidewall materials. These materials are formed by encapsulation of SiC particles in a silicon nitride matrix, by nitridation of silicon at high temperatures under a nitrogen atmosphere. In this study the mechanisms of the corrosion of silicon nitride bonded silicon carbide refractories in an aluminium reduction cell environment were examined. Microstructural analysis of SNBSC materials by: X-ray diffraction, solid state NMR, Raman spectroscopy, XPS, and SEM, identified variations in α/β Si3N4 ratio and porosity in the binder phase, with higher porosity levels and β Si3N4 content found in the interior part of the brick. Unreacted metallic silicon was observed only as a crystalline phase inside SiC grains and is not associated with the binder phase. SNBSC samples from eight different commercial refractory manufacturers were tested in an industrial aluminium cell environment, both by immersion in industrial cells and in the laboratory. The samples showed extensive attack and considerable differentiation between the samples. The effects on the corrosion rate of porosity levels, amount of binder, α/β Si3N4 ratio, free Si content in the binder, and different factors in the environment were examined in the laboratory scale trials. A laboratory scale testing rig with some novel features, such as a rotating anode, was developed to examine corrosion resistance of samples under electrolysis conditions in molten cryolite at up to 1000oC. Corrosion test results, supported by thermodynamic calculations, identified the Si3N4 binder as the reactive phase in SNBSC materials, especially in the gas phase above the bath level. High porosity levels and high β Si3N4 fraction in the binder showed a statistically significant contribution to the corrosion rate in lab-scale corrosion trials. Commercial materials are also highly inhomogeneous in the distribution of the β Si3N4 phase as mentioned above, which complicates sample selection and the interpretation of corrosion test results. The crystal morphology of β Si3N4 is suggested as the reason for the high reactivity of these materials. This morphology characterised by elongated rod-like shape crystals with hexagonal cross section, presents a higher surface area compared to α Si3N4 crystals containing mainly flat matte crystals. In the light of this observation, the binder phase in selected samples was deliberately modified to convert a significant fraction of the α Si3N4 to β Si3N4. Corrosion rates measured from these modified samples in general support the argument that the crystallographic form of silicon nitride contributes to corrosion rate. The proposed corrosion mechanism for SNBSC materials in the aluminium reduction cell atmosphere is based on combination of oxidation of the binder followed by attack of corrosive gases to produce volatile SiF4. Thus the binder phase is initially passivated below the electrolyte level on the sidewall, where exposure to corrosive gases is limited, but occurs more rapidly in the area above the electrolyte/air interface. The intrusion of electrolyte into the refractory and capillary transport up the sidewall is a key in accelerating this reaction.

Universiẗat, Diss.--Passau, 2007. / Literaturverz. S. 141 - 150.

Thesis (doctoral)--Universität Erlangen.

Zugl.: Rostock, Univ., Diss., 2007

Master-Arbeit Univ. St. Gallen, 2006.

Ce travail entendait examiner le fonctionnement de la sainteté dans la théologie politique biblique juive, et ce en se servant de la méthodologie sociologique (au sens large) à l'étude de la politique. L'objet de notre recherche n'est pas l'action de la Divinité, mais les actions des hommes qui agissent à partir d'une certaine représentation de la Divinité et de leurs relations face à elle. Notre étude a montré que la conception de la sainteté, telle qu'elle fut appréhendée dans la recherche (chez Durkheim, Otto, Eliade, James, Underhill, Zehner, Comstock, Berger) ne permet pas d'expliquer la sainteté biblique. En effet, ces savants partagent tous l'axiome d'une séparation de la sainteté et du profane, ainsi que l'idée que le message religieux vise à transférer la sainteté, qui se limite elle-même, vers le profane, et ainsi à exercer ses effets sur ce qui l'entoure. Toutefois, comme l'a indiqué Dan, cette conception échoue à rendre compte de la pensée biblique parce que dans sa nature, la réalité ne se divise pas en deux domaines séparés, le profane et le saint. Notre étude a indiqué que l'idée de sainteté biblique dérive de l'idée d'alliance. Celle-ci, représentant le système des relations entre le transcendant et l'immanent, donne son impulsion à la dimension du politique, et reflète l'exigence adressée au peuple d'Israël de fonder une Histoire théocentrique sanctifiant l'espace public. La sainteté, qui est imposée à l'individu, s'inscrit dans le cadre d'une finalité à l'échelle collective exigeant tant de l'individu que du collectif un travail morale sur soi. Elle comprend une série de présuppositions philosophiques, qui concernent les relations matière-esprit et le rôle du libre choix. La finalité de la sainteté n'est donc pas individuelle, mais collective: elle est destinée à "produire" la sainteté collective d'une nation politique. Cette nation possède, selon le récit biblique, une finalité d'existence universelle. Ce travail contribue à mieux comprendre la philosophie politique biblique, et la place de la sainteté collective ainsi que ses effets sur les cérémonies, les institutions et la Constitution. Notre recherche aide également à mieux appréhender la notion de sainteté dans la mesure où la Bible oppose l'impureté à la sainteté et à la pureté, en elles-mêmes deux notions distinctes, tandis que le profane n'y joue qu'un rôle secondaire. / This research has examined the function of the concept of Holiness in biblical political theology, by using methodology from the fields of sociology (in its broadest sense) to study politics. The topic of this research is not the activity of God, but rather the activity of human beings in their relationship with the Divine. The research revealed that the concept of Holiness (in the thoughts of: Durkheim, Otto, Eliade, James, Underhill, Zehner, Comstock, Berger) does not fully explain Holiness is it appears in the Bible. These thinkers and authors share common assumptions that divided the Holy from the secular, and then posit that the Holy seeks to influence the secular, and the Gospel aims to bring the Holy toward the secular. However, as pointed out by Dan, their formulations do not reflect clearly the biblical thought because, in the Bible, reality does not split into two sections: Holy and secular. The concept of Holiness in the Bible, as this research has shown, emerges from the notion of covenant—i.e., reflecting a promised relationship between the transcendental and the immanent, stimulating the political realm, and animating a demand from "Am Israel" to establish theocentric history that consecrates the public space. This Holiness expects and demands intensive work by the individual as well as the collective to advance the understanding and practice of morals to the standards of the Holy. The biblical concept of Holiness includes a series of philosophical assumptions regarding the relationship between matter and spirit and the role of human free choice, but it is not purposed toward individual aims; rather, it establishes as the purpose of existence the creation of collective Holiness; first, nationally, and ultimately, universally. This paper contributes to the understanding of biblical political philosophy, and to a better grasp of the concept of collective Holiness, its place and its implications upon rituals, institutions and the Constitution. The research also contributes to the understanding of the concept of Holiness by examining the use of the term in the Bible, and pointing out that Impurity is the opposing term to both Purity and Holiness, and that all three of these terms have meaning separate and apart from what is considered to be within the concept of secular.

L’apparition de fibres de SiC de haute pureté au cours des années 1990 a permis de considérer leur utilisation dans les réacteurs nucléaires en tant que renfort des composites à matrice SiC, dits composites SiC/SiC. Envisagés en tant que matériau de cœur des réacteurs du futur (SFR, GFR) et en remplacement des gaines en zirconium des réacteurs REP, la compatibilité thermochimique du SiC et des composites SiC/SiC avec l’environnement de tels réacteurs a été examinée. Des traitements thermiques en systèmes ouvert et fermé entre le SiC et l’UO2 ont montré une réactivité marquée au-delà de 1200°C avec la formation principalement de CO et de siliciures d’uranium dans la phase condensée, voire l’apparition d’une phase liquide entre 1500 et 1650°C. L’exposition au sodium liquide à 550°C jusqu’à 2000h a été étudiée en fonction de la concentration en oxygène. Une amélioration des propriétés mécaniques des composites SiC/SiC fabriqués pour cette étude (déformations et contraintes à rupture plus importantes) a été mise en évidence après immersion quelle que soit la concentration en oxygène du sodium liquide. Enfin, les compositions et les cinétiques de croissance des zones de réaction du SiC avec le niobium et le tantale (métaux utilisés pour assurer l’étanchéité d’une gaine en composite SiC/SiC) ont été mesurées entre 1050 et 1500°C. / The development of high purity SiC fibers during the nineties has led to their consideration as nuclear reactors components through the use of SiC/SiC composites. SiC and SiC/SiC composites are considered as core materials of future nuclear reactors (SFR, GFR) and as a potential replacement for the zirconium cladding of PWR. Therefore, the thermochemical compatibility of these materials with typical environments of those nuclear reactors has been studied. The composition and the growth kinetics of the reaction zone of SiC towards niobium and tantalum (considered as materials to ensure the leak-tightness of a SiC/SiC cladding for GFR) have been studied between 1050 and 1500°C. High temperature heat treatments in open and closed systems between SiC and UO2 have shown a significant reactivity over 1200°C characterized by the formation of CO and uranium silicides. Moreover, a liquid phase has been detected between 1500 and 1650°C. The exposure of SiC/SiC to liquid sodium (550°C, up to 2000h) has been studied as a function of the oxygen concentration dissolved in liquid sodium. An improvement of the mechanical properties of the composites elaborated for this study (increase of the tensile strength and strain at failure) has been highlighted after immersion in the liquid sodium independently of its oxygen concentration. It is believed that this phenomenon is due to the presence of residual sodium in the material.