Die vorliegende Arbeit beschäftigt sich mit dem Einfluss der NMDA-Rezeptorantagonisten, Memantin, MK-801, CGS und Ifenprodil auf die hypoxieinduzierte Zellschädigung an kortikalen Zellen der Ratte. Außerdem wurde der Einfluss von subtoxischen Konzentrationen von NMDA sowie von Roscovitin, einem Hemmer Cyclin-abhängiger Kinasen, auf die hypoxiebedingte Zellschädigung untersucht. Ziel dieser Arbeit war es, die neuroprotektive Wirkung dieser Substanzen zu erfassen. Zur Untersuchung der hypoxischen Schädigung wurden zwei 48-Well-Zellkulturplatten mit 15 Tage alten kortikalen Zellen der Ratte verwendet. Eine Kulturplatte wurde für vier Stunden mit HEPES(N-2-Hydroxyethylpiperazine-N’-2-Ethansulfonsäure)-Puffer (ohne Glucose) unter hypoxischen Bedingungen inkubiert. Die zweite Platte, mit glukorisiertem HEPES-Puffer, wurde für vier Stunden unter normoxischen Bedingungen inkubiert. Der HEPES-Puffer wurde nach vier Stunden entfernt, die Kulturplatten mit Dulbecco’s Modified Eagle Medium (DMEM) gewaschen und mit diesem Medium für 24 Stunden unter normoxischen Bedingungen inkubiert. Anschließend wurde das Medium ent¬fernt, durch NMDA, Memantin, Roscovitin, CGS und Ifenprodil ersetzt und die Ansätze für weitere 24 Stunden unter normoxischen Bedingungen inkubiert. Zur Beurteilung der Zellschädigung wurden der Aktivitätsanstieg der Laktat-Dehydrogenase (LDH), die Freisetzung freier Sauerstoffradikale und die Steigerung der Caspase-Aktivität bestimmt. Während die Bestimmung der LDH-Aktivität und die Freisetzung der freien Sauer¬stoff¬radikale nekrotische Veränderungen der Zellen charakterisiert, zeigt eine Zunahme der Caspase-Aktivität apoptotische Vorgänge an. LDH ist ein stabiles zytoplasmatisches Enzym, das in fast allen Körperzellen vorkommt. Beim Absterben der Zelle wird das Enzym durch die Schädigung der Plasmamembran aus der Zelle freigesetzt, so dass es zu einem Anstieg der LDH-Aktivität proportional zur Anzahl der toten Zellen kommt. Diese Aktivität wurde spektrophotometrisch mit einem Mikrotiterplatten-Lesegerät bestimmt. Die Ergebnisse des LDH-Tests zeigen, dass nach der 24-stündigen Behandlung der Zellen mit MK-801 die LDH-Aktivität um 11%, bei Roscovitin um 13%, bei Memantin (5 µM) um 56%, bei Memantin (0,5 µM) um 52% und mit NMDA (5 µM) um 44% signifikant vermindert wurde. Bei einer hypoxiebedingten Schädigung kortikaler Zellen kommt es auch zur Bildung freier Sauer¬stoff¬radikale. 2’,7’-Dichlorfluorescein Diacetat (2’,7’-H2DCF-DA) wird von den Zellen auf¬ge¬nommen und intrazellulär mit Sauerstoff- und Stickstoffspezies zum Fluoreszenz¬farb-stoff 2’,7’-Dichlorodihydrofluorescein (DCF) deacetyliert. DCF verbleibt dabei in den Zellen, so dass die Messung der Fluoreszenz der Zellen als Maß für intrazelluläre Oxidationsprozesse verwendet werden kann. Die DCF-Fluoreszenz-Änderung wurde mittels eines Fluorimeters gemessen und die daraus resultierenden Daten mit einer im Fluorimeter integrierten Software bearbeitet. Die Ergebnisse zeigen, dass die Freisetzung der freien Sauerstoffradikale, der hypoxiegeschädigten Zellen, signifikant durch Ifenprodil (10 µM) um 119%, Memantin (50 µM) um 88% und NMDA (5 µM) um 134% reduziert wurde. Die hypoxieinduzierte Zellmembranschädigung führt desweiteren zu einem Anstieg der Caspase-Aktivität. Mit Hilfe des Apo-One Homogeneous Caspase-3/7-Assays (Promega) wurde die Aktivität der Caspasen 3 und 7 fluorimetrisch bestimmt. Um die unterschiedliche Zelldichte in den Kulturschalen zu berücksichtigen, wurde eine Proteinbestimmung nach der Bicinchoninsäure-Methode (Smith et al. 1985) durchgeführt. Einen protektiven Effekt auf die Zellschädigung zeigen Memantin und NMDA in Bezug auf die Beeinflussung dieser Caspase-Aktivität. Der hypoxiebedingte Anstieg der Caspase-3-Aktivität konnte nach 24-stündiger Inkubation mit Memantin (5 µM) um 24%, mit Memantin (0,5 µM) um 28% und mit NMDA (5 µM) um 24% vermindert werden. CGS hat in diesen Versuchen keinen protektiven Einfluss auf die hypoxie¬induzierte Zellschädigung. Diese Arbeit zeigt, dass die Applikation niedriger NMDA-Konzentrationen neuroprotektive Effekte auf die Entwicklung der hypoxischen Schädigung von kortikalen Zellen der Ratte hat. Darüber hinaus wird vermutet, dass NMDA sogar einen trophischen Effekt auf das Über-leben der kortikalen Neurone ausübt. Dieser schützende Mechanismus von NMDA scheint denselben, wenn nicht sogar einen größeren protektiven Effekt wie Memantin zu induzieren. Um die Therapiemöglichkeiten der zerebralen Hypoxie durch neuroprotektive Medikamente zu optimieren, wären jedoch weitergehende Untersuchungen besonders als In-vivo-Modelle wünschenswert.

The Council for Geoscience (CGS) is one of the National Science Councils of South Africa and is the legal successor to the Geological Survey of South Africa. The total staff complements numbered 291 as of March 2006, consisting of four executive managers, 18 unit managers, 124 professionals, 84 technicians, 41 administrative personnel, 17 unskilled labourers 3 skilled workers. The strength of the CGS is manifested in its core of competent geoscience and technical staff. The primary business of the CGS is science; therefore scientists, apart from human resources, finance and procurement, are appointed to senior positions in the organisation. The criteria for scientists to qualify for managerial positions are either a masters or doctorate degree in science. Although a sound knowledge of science is needed for these positions, the necessary managerial and leadership characteristics have never played a significant role in the appointment of unit leaders. Therefore, it is the aim of this study to determine the leadership style of the scientists that were appointed as unit leaders. Theories on leadership provide for a variety of potential explanations regarding effective leadership, including personal attributes, contingencies, and the role of subordinates. By analysing managerial leadership, it becomes important to consider and recognise the complex interplay among the structure of organisational life, patterns of behaviour, varied beliefs, values, interests, and initiatives of the individuals who create and work within this structure. Research on organisational leadership has grown systematically with the advance of industrialisation. Large work organisations are associated with bureaucratic and technological complexity that affects the demand for managers and the need for coordination and leadership roles. Leadership theories have evolved over time, becoming more sophisticated and even more applicable for their “innovation”. Different perspectives have featured throughout history. Theories of leadership are primarily analytical, directed at better understanding of the leadership process and the variations among them. The most up- to- date concept within leadership is the theory of transformational and transactional leadership. Transformational leadership comprises five factors — (1) idealised influence: attributed; (2) idealised influence: behaviour; (3) inspirational motivation; (4) intellectual simulation; and (5) individualised consideration — of which the first two factors refer to the concern, power, personal morality, and sacrifice of the leader, as well as his or her ability to instil collective pride in the group’s mission. The third factor relates to motivating the group to accomplish missions through challenging goals and by indicating certainty in areas of uncertainty, which, in turn, arouse individual and team spirit. The fourth factor refers to the leaders’ ability to relate at an individual level to the follower and the fifth factor to intellectual stimulation. Transactional leadership display behaviours associated with constructive and corrective transactions, and comprises three factors— (1) contingent reward leadership; (2) management-by-exception: active; and (3) management-by-exception: passive — of which relates to leaders who involve themselves only when things go wrong, i.e. the constructive style. Their interventions are associated with failure and punishment. The corrective style is labelled management-by-expectation: active, which refers to the closer involvement in monitoring the subordinates’ actions. Contingent reward leadership relates to rewards for work performance. The Multifactor Leadership Questionnaire (MLQ) has become a standard instrument for assessing a variety of transformational, transactional and non-leadership scales and was used to assess the leadership style of scientists of the Council for Geoscience. The instrument measures a broad range of leadership types: passive leaders, leaders who give contingent rewards to subordinates and leaders who transform their subordinates into leaders themselves. The objectives of the study were to (1) determine the leadership style of scientists in positions of unit leaders; (2) how their supervisors, peers and subordinates perceive their leadership style; and (3) whether scientists as unit leaders, perceive their own leadership style differently than do their supervisors, peers and subordinates. The MLQ instrument contains 45 items that identify and measure key leadership and effectiveness behaviours. A five point rating scale (0: 1: 2: 3: 4) is used for rating the frequency of observed leader behaviour where 0=not at all, and 4=frequently, if not always. The average scores of the MLQ questionnaire for the Council for Geoscience ranged from 2 to 3 on the transformational leadership factors. Participants in general perceive scientists in unit leader positions more as transformational leaders as apposed to transactional leaders. The 2.5 rating on transformational leadership indicates that the unit leaders are often influential in the awareness of what is important. The ratings of scientists as unit leaders were similar to the ratings of their peers and 'others'. Supervisors and subordinates, however, rated them lower. Transactional leadership ratings for the majority of leaders were between 2.0–3.0 on CR, and MBEA and 1.0–2.0 on MBEP. The ratings obtained, indicate that unit leaders would be seen as people wwho prefer to monitor and take action before failures occur. Supervisors, peers and others rated the scientists as unit leaders higher on transactional leadership, except for subordinates who rated them lower. Leaders are rated 0–1 on laissez-faire leadership style. Supervisors, peers and subordinates rated scientists as unit leaders higher on laissez-faire leadership style than the rating they gave themselves (self-rating). The low rating on the laissez-faire leadership style confirms that leaders do get involved in important issues and have a need to be involved in the decision-making process. Scientists as unit leaders, however, perceive themselves to be more involved than do supervisors and subordinates. Attribution ratings (extra-effort, effectiveness and satisfaction) varied from 2.0–3.0. For attribution dimensions, supervisors and subordinates rated the scientists as unit leaders lower on extra-effort, effectiveness and satisfaction, whereas peers rated them higher. The satisfaction dimension indicates that unit leaders often work with others in a satisfactory way. For attribution dimensions, supervisors and subordinates rated the scientists as unit leaders lower on extra-effort, effectiveness and satisfaction, whereas peers rated them higher. Supervisors are less satisfied with the leaders than subordinates are. The results obtained from the MLQ questionnaire for the leadership style of scientists in the Council for Geoscience are slightly different from those of United States companies. The Council for Geoscience, compared with United States (US) companies, rated lower on both transformational leadership and attribution dimensions (extra-effort, effectiveness and satisfaction) and higher on both transactional and laissez-faire leadership styles. This seems to indicate that the Council for Geoscience tends to follow a less inspirational and influential leadership style with more objective setting and less satisfying methods of leadership, compared with US companies. Transformational leadership development is recommended for the scientists as unit leaders of the Council for Geoscience. It is important to note that false transformational leaders (seemingly transformational leaders with a self-absorbed tendency) should be distinguished from the genuine ones. Optimism and employee frustration can be used in future surveys by the Council for Geoscience to determine the progress of transformational leadership development in the organisation. The leadership of an organisation influences the organisational culture. Upper management is responsible for the implementation of the necessary changes to promote transformational leadership. The culture of an organisation is a reflection of upper management. If upper management does not realise the importance of transformational leadership, the chances for the rest of the organisation to promote a transformational leadership culture in the organisation are not good. One recommendation to consider is for the Council for Geoscience to employ people with adequate managerial skills in unit leader positions. These skills would include leadership traits, operational skills, financial skills, etc. A decision needs to be taken by the Council for Geoscience that when scientists are employed as unit leaders or as members of the upper management cadre, they must have adequate managerial and leadership skills, and all parties have to agree with the competency and be satisfied with the management styles. / Graduate School of Business Leadership / M.B.L.

The Council for Geoscience (CGS) is one of the National Science Councils of South Africa and is the legal successor to the Geological Survey of South Africa. The total staff complements numbered 291 as of March 2006, consisting of four executive managers, 18 unit managers, 124 professionals, 84 technicians, 41 administrative personnel, 17 unskilled labourers 3 skilled workers. The strength of the CGS is manifested in its core of competent geoscience and technical staff. The primary business of the CGS is science; therefore scientists, apart from human resources, finance and procurement, are appointed to senior positions in the organisation. The criteria for scientists to qualify for managerial positions are either a masters or doctorate degree in science. Although a sound knowledge of science is needed for these positions, the necessary managerial and leadership characteristics have never played a significant role in the appointment of unit leaders. Therefore, it is the aim of this study to determine the leadership style of the scientists that were appointed as unit leaders. Theories on leadership provide for a variety of potential explanations regarding effective leadership, including personal attributes, contingencies, and the role of subordinates. By analysing managerial leadership, it becomes important to consider and recognise the complex interplay among the structure of organisational life, patterns of behaviour, varied beliefs, values, interests, and initiatives of the individuals who create and work within this structure. Research on organisational leadership has grown systematically with the advance of industrialisation. Large work organisations are associated with bureaucratic and technological complexity that affects the demand for managers and the need for coordination and leadership roles. Leadership theories have evolved over time, becoming more sophisticated and even more applicable for their “innovation”. Different perspectives have featured throughout history. Theories of leadership are primarily analytical, directed at better understanding of the leadership process and the variations among them. The most up- to- date concept within leadership is the theory of transformational and transactional leadership. Transformational leadership comprises five factors — (1) idealised influence: attributed; (2) idealised influence: behaviour; (3) inspirational motivation; (4) intellectual simulation; and (5) individualised consideration — of which the first two factors refer to the concern, power, personal morality, and sacrifice of the leader, as well as his or her ability to instil collective pride in the group’s mission. The third factor relates to motivating the group to accomplish missions through challenging goals and by indicating certainty in areas of uncertainty, which, in turn, arouse individual and team spirit. The fourth factor refers to the leaders’ ability to relate at an individual level to the follower and the fifth factor to intellectual stimulation. Transactional leadership display behaviours associated with constructive and corrective transactions, and comprises three factors— (1) contingent reward leadership; (2) management-by-exception: active; and (3) management-by-exception: passive — of which relates to leaders who involve themselves only when things go wrong, i.e. the constructive style. Their interventions are associated with failure and punishment. The corrective style is labelled management-by-expectation: active, which refers to the closer involvement in monitoring the subordinates’ actions. Contingent reward leadership relates to rewards for work performance. The Multifactor Leadership Questionnaire (MLQ) has become a standard instrument for assessing a variety of transformational, transactional and non-leadership scales and was used to assess the leadership style of scientists of the Council for Geoscience. The instrument measures a broad range of leadership types: passive leaders, leaders who give contingent rewards to subordinates and leaders who transform their subordinates into leaders themselves. The objectives of the study were to (1) determine the leadership style of scientists in positions of unit leaders; (2) how their supervisors, peers and subordinates perceive their leadership style; and (3) whether scientists as unit leaders, perceive their own leadership style differently than do their supervisors, peers and subordinates. The MLQ instrument contains 45 items that identify and measure key leadership and effectiveness behaviours. A five point rating scale (0: 1: 2: 3: 4) is used for rating the frequency of observed leader behaviour where 0=not at all, and 4=frequently, if not always. The average scores of the MLQ questionnaire for the Council for Geoscience ranged from 2 to 3 on the transformational leadership factors. Participants in general perceive scientists in unit leader positions more as transformational leaders as apposed to transactional leaders. The 2.5 rating on transformational leadership indicates that the unit leaders are often influential in the awareness of what is important. The ratings of scientists as unit leaders were similar to the ratings of their peers and 'others'. Supervisors and subordinates, however, rated them lower. Transactional leadership ratings for the majority of leaders were between 2.0–3.0 on CR, and MBEA and 1.0–2.0 on MBEP. The ratings obtained, indicate that unit leaders would be seen as people wwho prefer to monitor and take action before failures occur. Supervisors, peers and others rated the scientists as unit leaders higher on transactional leadership, except for subordinates who rated them lower. Leaders are rated 0–1 on laissez-faire leadership style. Supervisors, peers and subordinates rated scientists as unit leaders higher on laissez-faire leadership style than the rating they gave themselves (self-rating). The low rating on the laissez-faire leadership style confirms that leaders do get involved in important issues and have a need to be involved in the decision-making process. Scientists as unit leaders, however, perceive themselves to be more involved than do supervisors and subordinates. Attribution ratings (extra-effort, effectiveness and satisfaction) varied from 2.0–3.0. For attribution dimensions, supervisors and subordinates rated the scientists as unit leaders lower on extra-effort, effectiveness and satisfaction, whereas peers rated them higher. The satisfaction dimension indicates that unit leaders often work with others in a satisfactory way. For attribution dimensions, supervisors and subordinates rated the scientists as unit leaders lower on extra-effort, effectiveness and satisfaction, whereas peers rated them higher. Supervisors are less satisfied with the leaders than subordinates are. The results obtained from the MLQ questionnaire for the leadership style of scientists in the Council for Geoscience are slightly different from those of United States companies. The Council for Geoscience, compared with United States (US) companies, rated lower on both transformational leadership and attribution dimensions (extra-effort, effectiveness and satisfaction) and higher on both transactional and laissez-faire leadership styles. This seems to indicate that the Council for Geoscience tends to follow a less inspirational and influential leadership style with more objective setting and less satisfying methods of leadership, compared with US companies. Transformational leadership development is recommended for the scientists as unit leaders of the Council for Geoscience. It is important to note that false transformational leaders (seemingly transformational leaders with a self-absorbed tendency) should be distinguished from the genuine ones. Optimism and employee frustration can be used in future surveys by the Council for Geoscience to determine the progress of transformational leadership development in the organisation. The leadership of an organisation influences the organisational culture. Upper management is responsible for the implementation of the necessary changes to promote transformational leadership. The culture of an organisation is a reflection of upper management. If upper management does not realise the importance of transformational leadership, the chances for the rest of the organisation to promote a transformational leadership culture in the organisation are not good. One recommendation to consider is for the Council for Geoscience to employ people with adequate managerial skills in unit leader positions. These skills would include leadership traits, operational skills, financial skills, etc. A decision needs to be taken by the Council for Geoscience that when scientists are employed as unit leaders or as members of the upper management cadre, they must have adequate managerial and leadership skills, and all parties have to agree with the competency and be satisfied with the management styles. / Graduate School of Business Leadership / M.B.L.

>Magister Scientiae - MSc / The Sea Point contact, Cape Town, South Africa, exposes the contact between the Neoproterozoic Malmesbury Group metasedimentary rocks of the Pan-African Saldania belt and the intrusive S-type Peninsula Granite of the Neoproterozoic-Paleozoic Cape Granite Suite (CGS). The exposure outcrops over an area of approximately 170 m × 60 m with the northern end of the exposure being characterized by the country rock–microgranite intrusive contact. Heading further south, the outcrop transitions to the main contact zone, which is a predominantly gradational zone marked by sheets of compositionally variable granitic injections (collectively referred to as hybrid granite phases) concordant to the country rock structure, before reaching the main pluton area comprising the voluminous coarse-grained porphyritic granite. Using a combined study incorporating field, structural, geochemical, isotopic and U-Pb geochronological data, the intrusive contact is investigated to determine the construction history of the pluton and delineate possible emplacement mechanisms. The granitic phases, which vary from fine-grained leucocratic, medium-grained porphyritic to coarse-grained porphyritic, are peraluminous, magnesian to ferroan, and alkali-calcic. Based on the linear trends between the whole-rock major and trace element content of the granites vs. maficity (molar Fe + Mg), their initial Sr ratios and εNd(t) values, the granites of the study area are consistent with the currently proposed petrogenetic model for the CGS (e.g. Stevens et al., 2007; Villaros et al., 2009a; Harris & Vogeli, 2010); i.e., they are crustally derived and their chemical variability is controlled primarily by peritectic assemblage entrainment. The fractional crystallization of K-feldspar is identified as the primary mechanism for the local geochemical variability of the granites. The fractionation of K-feldspar as a mechanism of variability was evaluated using binary log-log diagrams of Ba, Sr and Eu and is interpreted to have taken place at levels close to the emplacement site after source entrainment processes. Although there is outcrop evidence, particularly in the main contact zone, to suggest that local assimilation and filter pressing took place, this was not reflected by the whole-rock and isotope geochemistry of the granites. This suggests that these processes are very localized and will need further rigorous testing to ascertain the extent to which they caused variability. Outcrop evidence for assimilation includes gradational country rock-granite contacts and the ductile behaviour of the country rock, whereas the occurrence of K-feldspar megacrysts embedded in the country rock at the main contact zone suggests melt accumulation and escape consistent with the filter pressing mechanism. In the case of the latter, the melt fraction of the granite was easily mobilized and driven out compared to the crystal fraction (K-feldspars) during the emplacement of the granites. Field relationships and the structural interpretation of the Malmesbury Group country rocks and the granites reveal that: (1) the various granites are late syn-tectonic and (2) were emplaced as incrementally assembled, repeated pulses of inclined granitic sheets more or less normal (i.e. at high angles) to the regional NE-SW shortening (D1) of the Malmesbury forearc during the Saldanian orogeny. Given the lack of a controlling shear zone in facilitating granite emplacement in the study area, the pre-existing planar anisotropies (bedding planes and foliations) in the country rock provided preferential pathways for magma emplacement and propagation during deformation. This implies that the tensile strength normal and parallel to the bedding and foliation anisotropy of the country rock was larger than the regional differential stress (σ1 – σ3, with σ1 ≥ σ2 ≥ σ3), allowing for magma emplacement relative to shortening. Sheet propagation is interpreted to have occurred through the balance of the following conditions: (1) density contrasts between host rocks and magmas, (2) the pressure differential along the subvertical fractures/sheets, and (3) the melt pressure equalling the lithostatic pressure to keep the magma pathways open and being sufficiently high such that it exceeds the sum of σ1 and the tensile strength of the rock parallel to σ1. The crystallization ages of the dated granite samples are identical within error and vary between 538.7 ± 3.6 Ma and 542.7 ± 2.9 Ma. They, therefore, cannot prove which granite phase intruded first and which one proceeded and so forth. Field relationships, however, suggests that the microgranites were first to intrude given their fine-grained nature and the localized chilled contacts they show with the country rock. The various coarser-grained and porphyritic phases were next to intrude, with their coarse grain-sizes and lack of chilled margins with the country rock suggesting that the time interval between their successive emplacements was not too long; this prevented the country rock from completely cooling down between each magma batch. Magma stoping and the ductile flow of the host material (owing to highly viscous magma flow) to accommodate granite emplacement are interpreted to be secondary emplacement processes.

In der vorliegenden Arbeit wird ausgehend vom Stand der Wissenschaft und Technik für Verfahren und Werkstoffe des Titanlötens das Kaltgasspritzen in seiner Eignung als Vorbelotungsprozess beim löttechnischen Fügen von Titanlegierungen untersucht und qualifiziert. Die Parameter des Beschichtungsvorgangs werden dabei mit den resultierenden Schichtgefügen und späteren Lötergebnissen korreliert, wodurch eine Bewertung ermöglicht und ein Beitrag zum Verständnis der Mechanismen einer spritztechnischen Vorbelotung geliefert wird. Es werden dabei sowohl materialografische als auch mechanische Charakterisierungen durchgeführt. Ergänzt werden die Arbeitspunkte durch eine hochauflösende TEM-Untersuchung der Grenzfläche von kaltgasgespritzten Zink-Schichten und Aluminium-Substraten, die der Überprüfung theoretischer Erkenntnisse zum Haftungsmechanismus kaltgasgespritzter metallischer Schichten auf Leichtmetallsubstraten dient. Die Arbeit schließt mit einer Diskussion und Folgerung und gibt Empfehlungen für weiterführende Forschungen auf diesem Gebiet.:1 Einleitung und Problemstellung 2 Stand der Wissenschaft und Technik 2.1 Leichtmetalle als Konstruktionswerkstoffe 2.1.1 Aluminium 2.1.2 Magnesium 2.1.3 Titan 2.2 Titan und Titanlegierungen als Konstruktionswerkstoffe 2.3 Stoffschlüssiges Fügen von Titan und Titanlegierungen 2.3.1 Kleben und Schweißen von Titanwerkstoffen 2.3.2 Löten von Titanwerkstoffen 2.3.2.1 Begriffe des Lötens 2.3.2.2 Löten von Titan und Titanlegierungen 2.3.2.3 Hartlote zum Löten von Titan und Titanlegierungen 2.3.2.4 Das Dreistoffsystem Titan-Kupfer-Nickel 2.4 Thermisches Spritzen 2.4.1 Begriffe des Thermischen Spritzens 2.4.2 Verfahren des Thermischen Spritzens 2.4.3 Kaltgasspritzen 2.4.3.1 Prozesstechnische und physikalische Grundlagen des Kaltgasspritzprozesses 2.4.3.2 Haftungsmechanismen kaltgasgespritzter Schichten 2.4.3.3 Eigenschaften kaltgasgespritzter Schichten 3 Folgerungen aus dem Stand der Wissenschaft und Technik 4 Zielsetzung 5 Versuchsdurchführung 5.1 Voruntersuchungen mit Aluminiumsubstraten 5.1.1 Metallografische TEM-Untersuchungen 5.2 Untersuchungen mit TiAl 6 V 4-Substraten 5.2.1 Versuchsplanung 5.2.2 Kaltgasspritzen von Lotschichten 5.2.3 Vakuumdiffusionslöten 5.2.4 Metallografische Charakterisierung 5.2.5 Mechanische Charakterisierung der Lötverbindungen 6 Ergebnisse 6.1 Voruntersuchungen mit Aluminiumsubstraten 6.1.1 AlSi 12-CGS-Lotschichten 6.1.2 Zn-basierte CGS-Lotschichten 6.1.3 Metallografische TEM-Untersuchungen 6.1.4 Zusammenfassung der Untersuchungsergebnisse mit Aluminiumsubstraten 6.2 Untersuchungen mit TiAl 6 V 4-Substraten 6.2.1 Kaltgasspritzen von Lotschichten 6.2.2 Lötverbindungen 6.2.2.1 Metallografische Charakterisierung der Ti-Cu-Ni-Schichtlotfolien 6.2.2.2 Metallografische Charakterisierung der Lötverbindungen 6.2.2.3 Mechanische Charakterisierung der Lötverbindungen 7 Ergebnisdiskussion 7.1 Kaltgasspritzen von Lotschichten auf TiAl 6 V 4-Substraten 7.2 Charakterisierung von TiAl 6 V 4-Lötverbindungen 7.3 Bewertung der Ergebnisse mit TiAl 6 V 4-Substraten 8 Folgerungen 9 Zusammenfassung 10 Quellennachweis / The present work qualifies the cold gas dynamic spray process (CGS) as a process for the application of braze filler coatings onto titanium alloy substrates. The work program results from needs and problems that were identified in the state-of-the-art of science and technology. The parameters of the coating process are correlated with the resulting coating microstructures and the posterior brazing results. Materialographic and mechanic characterisations of the filler coatings and braze seams are carried out. Thereby, an evaluation of the braze filler application by cold gas spraying is permitted. In addition, high-resolution TEM investigations within the interfaces of a cold sprayed zinc coating and an aluminium base material proof the theory of the bonding mechanisms of CGS coatings on light weight metals. The work discusses the achieved results and gives an outlook to continuative investigations in this field of science.:1 Einleitung und Problemstellung 2 Stand der Wissenschaft und Technik 2.1 Leichtmetalle als Konstruktionswerkstoffe 2.1.1 Aluminium 2.1.2 Magnesium 2.1.3 Titan 2.2 Titan und Titanlegierungen als Konstruktionswerkstoffe 2.3 Stoffschlüssiges Fügen von Titan und Titanlegierungen 2.3.1 Kleben und Schweißen von Titanwerkstoffen 2.3.2 Löten von Titanwerkstoffen 2.3.2.1 Begriffe des Lötens 2.3.2.2 Löten von Titan und Titanlegierungen 2.3.2.3 Hartlote zum Löten von Titan und Titanlegierungen 2.3.2.4 Das Dreistoffsystem Titan-Kupfer-Nickel 2.4 Thermisches Spritzen 2.4.1 Begriffe des Thermischen Spritzens 2.4.2 Verfahren des Thermischen Spritzens 2.4.3 Kaltgasspritzen 2.4.3.1 Prozesstechnische und physikalische Grundlagen des Kaltgasspritzprozesses 2.4.3.2 Haftungsmechanismen kaltgasgespritzter Schichten 2.4.3.3 Eigenschaften kaltgasgespritzter Schichten 3 Folgerungen aus dem Stand der Wissenschaft und Technik 4 Zielsetzung 5 Versuchsdurchführung 5.1 Voruntersuchungen mit Aluminiumsubstraten 5.1.1 Metallografische TEM-Untersuchungen 5.2 Untersuchungen mit TiAl 6 V 4-Substraten 5.2.1 Versuchsplanung 5.2.2 Kaltgasspritzen von Lotschichten 5.2.3 Vakuumdiffusionslöten 5.2.4 Metallografische Charakterisierung 5.2.5 Mechanische Charakterisierung der Lötverbindungen 6 Ergebnisse 6.1 Voruntersuchungen mit Aluminiumsubstraten 6.1.1 AlSi 12-CGS-Lotschichten 6.1.2 Zn-basierte CGS-Lotschichten 6.1.3 Metallografische TEM-Untersuchungen 6.1.4 Zusammenfassung der Untersuchungsergebnisse mit Aluminiumsubstraten 6.2 Untersuchungen mit TiAl 6 V 4-Substraten 6.2.1 Kaltgasspritzen von Lotschichten 6.2.2 Lötverbindungen 6.2.2.1 Metallografische Charakterisierung der Ti-Cu-Ni-Schichtlotfolien 6.2.2.2 Metallografische Charakterisierung der Lötverbindungen 6.2.2.3 Mechanische Charakterisierung der Lötverbindungen 7 Ergebnisdiskussion 7.1 Kaltgasspritzen von Lotschichten auf TiAl 6 V 4-Substraten 7.2 Charakterisierung von TiAl 6 V 4-Lötverbindungen 7.3 Bewertung der Ergebnisse mit TiAl 6 V 4-Substraten 8 Folgerungen 9 Zusammenfassung 10 Quellennachweis

Includes vita. / Title from PDF of title page. / Document formatted into pages; contains 204 pages. / Thesis (Ph.D.)--University of South Florida, 2003. / Includes bibliographical references. / Text (Electronic thesis) in PDF format. / ABSTRACT: The goal of this research project was to contribute to the understanding of CuGaSe2/CdS photovoltaic devices, and to improve the performance of these devices. The initial part of the research dealt with the optimization of a Sequential Deposition process for CuIn(Ga)Se2 absorber formation. As an extension of this, a recipe (Type I Process) for CuGaSe2 absorber layer fabrication was developed, and the deposition parameters were optimized. Electrical characterization of the thin films and completed devices was carried out using techniques such as Two-Probe and Three-Probe Current-Voltage, Capacitance-Frequency, Capacitance-Voltage, and Spectral Response measurements. Structural/chemical characterization was done using XRD and EDS analysis. Current densities of up to 15.2 mA/cm2, and Fill Factors of up to 58% were obtained using the Type I CuGaSe2 Process. VOC's, however, were limited to less than 700 mV. / ABSTRACT: Several process variations, such as changes in the rate/order/temperature of depositions and changes in the thickness of layers, resulted in little improvement. With the aim of breaking through this VOC performance ceiling, a new absorber recipe (Type II Process) was developed. VOC's of up to 735 mV without annealing, and those of up to 775 mV after annealing, were observed. Fill Factors were comparable to those obtained with Type I Process, whereas the Current Densities were found to be reduced (typically, 10-12 mA/cm2, with the best value of 12.6 mA/cm2). This performance of Type II devices was correlated to a better intermixing of the elements during the absorber formation. To gain an understanding of the performance limitations, two simulation techniques, viz. SCAPS and AMPS, were used to model our devices. / ABSTRACT: Several processing experiments and SCAPS modeling indicate that a defective interface between CuGaSe2 and CdS, and perhaps a defective absorber layer, are the cause of the VOC limitation. AMPS simulation studies, on the other hand, suggest that the back contact is limiting the performance. Attempts to change the physical back contact, by changes in the absorber processing, were unsuccessful. Processing experiments and simulations also suggest that the CuGaSe2/CdS solar cell involves a true heterojunction between these two layers. / System requirements: World Wide Web browser and PDF reader. / Mode of access: World Wide Web.