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Mikrocharakterisierung nanokristalliner Nickel-Phosphor- und Eisen-Silber-Legierungen mit der Tomographischen AtomsondeFärber, Boye 27 April 2000 (has links)
No description available.
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Bimetallic aerogels for electrocatalytic applications / Bimetallische Aerogele für elektrokatalytische AnwendungenKühn, Laura 26 June 2017 (has links) (PDF)
Polymer electrolyte fuel cells (PEFCs) have emerged as a promising renewable emission-free technology to solve the worldwide increasing demand for clean and efficient energy conversion. Despite large efforts in academia and automotive industry, the commercialization of PEFC vehicles still remains a great challenge. Critical issues are high material costs, insufficient catalytic activity as well as longterm durability. Especially due to the sluggish kinetics of the oxygen reduction reaction (ORR), high Pt loadings on the cathode are still necessary which leads to elevated costs.
Alloys of Pt with other less precious metals (Co, Ni, Fe, Cu, etc.) show improved ORR activities compared to pure Pt catalysts. However, state-of-the-art carbon-supported catalysts suffer from severe Pt and carbon corrosion during the standard operation of PEFCs, affecting their reliability and long-term efficiency.
Multimetallic aerogels constitute excellent candidates to overcome these issues. Due to their large open pores and high inner surface areas combined with electrical conductivity, they are ideal for applications in electrocatalysis. In addition, they can be employed without any catalyst support. Therefore, the fabrication of bimetallic Pt-M (M=Ni, Cu, Co, Fe) aerogels for applications in fuel cell catalysis was the focus of this thesis.
Based on a previously published synthesis for Pt–Pd aerogels, a facile one-step procedure at ambient conditions in aqueous solution was developed. Bimetallic aerogels with nanochain diameters of as small as 4 nm and Brunauer-Emmett-Teller (BET) surface areas of up to 60 m2/g could be obtained.
Extensive structure analysis of Pt–Ni and Pt–Cu aerogels by powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), scanning transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy (STEM-EDX) and electrochemical techniques showed that both metals were predominantly present in their metallic state and formed homogeneous alloys. However, metal (hydr)oxide byproducts were observed in aerogels with higher contents of non-precious metal (>25 %). Moreover, electronic and geometric structures were similar to those of carbon-supported Pt alloy catalysts.
As a result, ORR activites were comparable, too. A threefold improvement in surface-specific activity over Pt/C catalysts was achieved. The mass-specific activites met or exceeded the U.S. Department of Energy (DOE) target for automotive PEFC applications. Furthermore, a direct correlation between non-precious metal content in the alloy and ORR activity was discovered. Aerogels with nonprecious metal contents >25% turned out to be susceptible to dealloying in acid leaching experiments, but there was no indication for the formation of extended surface structures like Pt-skeletons.
A Pt3Ni aerogel was successfully employed as the cathode catalyst layer in a differential fuel cell (1 cm2), which is a crucial step towards technical application. This was the first time an unsupported metallic aerogel was implemented in a PEFC. Accelerated stress tests that are usually applied to investigate the support stability of fuel cell catalysts revealed the excellent stability of Pt3Ni alloyed aerogels. In summary, the Pt alloy aerogels prepared in the context of this work have proven to be highly active oxygen reduction catalysts with remarkable stability.
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Aufbau eines Hochtemperaturviskosimeters und Messung der Viskosität von Schmelzen des Systems Aluminium-NickelKehr, Mirko 12 November 2009 (has links) (PDF)
Das System Aluminium-Nickel besitzt als Modellsystem
in der Wissenschaft sowie als ein Basissystem von
sogenannten Superlegierungen in der Technik eine
große Bedeutung. Aufgrund der hohen Liquidustemperaturen
von bis zu 1638°C sind die thermophysikalischen
Eigenschaften der Schmelzen bisher nur in den
Randbereichen des Systems bekannt. Die Viskosität
ist eine der thermophysikalischen Größen und sowohl
von der Zusammensetzung als auch von der Temperatur
abhängig. Sie besitzt eine große Bedeutung als
Eingabeparameter für Simulationsrechnungen zur
Erstarrung von Schmelzen sowie bei der Optimierung
von Herstellungsprozessen metallischer Werkstoffe.
Die Viskosität der Schmelzen im System Aluminium-Nickel
wurde nach Kenntnis des Autors bisher nur einmal
gemessen. Durch den vorliegenden Datensatz war jedoch
nicht der gesamte Konzentrationsbereich im System Aluminium-Nickel
abgedeckt. Besonders im Bereich der technologisch
interessanten hochschmelzenden Legierungen bestanden
Lücken. Mit bisherigen Viskosimetern war die Messung
der Viskositäten im gesamten System nicht möglich, da
die Liquidustemperaturen des Systems Aluminium-Nickel
die maximalen Arbeitstemperaturen überstiegen.
Im Rahmen der Arbeit wurde ein neues Schwingtiegelviskosimeter
mit hängendem Tiegel konzipiert, aufgebaut und mit
Viskositätsmessungen an reinen Metallen mit bekannter
Viskosität bei Temperaturen bis 1800°C erfolgreich
getestet. Mit weiteren Modifikationen sind mit dem
neu aufgebauten Viskosimeter Temperaturen bis 2300°C
erreichbar. Für den Betrieb des Viskosimeters wurde
ein umfangreiches Mess- und Steuerprogramm entwickelt
sowie erfolgreich getestet. Zur Berechnung der
Viskosität wurden im Messprogramm verschiedene
Arbeitsgleichungen implementiert. Für die Detektion
der Schwingung des Torsionspendels wurde ebenfalls
eine neue Methode angewendet, die eine quasikontinuierliche
und damit genauere Messung Erfassung der Schwingung
erlaubt.
Die Viskosität der Schmelzen des Systems Aluminium-Nickel
konnte erfolgreich bestimmt werden, womit experimentelles
Neuland betreten wurde. Die gemessenen Verläufe zeigen eine
gute Übereinstimmung mit den wenigen bekannten Daten
zur Viskosität von Aluminium-Nickel Schmelzen. Ebenso
gut ist die Übereinstimmung mit wenigen weiteren vorhandenen
Messdaten der Diffusionskonstanten sowie mit Daten aus
Computersimulationen. Mit verschiedenen Modellen zur
Vorhersage der Viskosität von Legierungen wurden
Viskositätsverläufe im System Aluminium-Nickel berechnet.
Der Vergleich mit den Messdaten hat gezeigt, dass nur wenige
der Modelle zur Vorhersage der Viskosität im System
Aluminium-Nickel geeignet sind. / The system aluminium-nickel is of importance as a
model-system in materials science as well as a
basic system for superalloys in technical applications.
The knowledge of the thermophysical properties of
the system aluminium-nickel has been limited to the
areas close to the pure elements mainly related to
the high melting temperatures of up to 1638°C. The viscosity, which is one of these
thermophysical properties, depends on alloy composition as
well as on temperature. The viscosity is of importance as
an input parameter in computer simulations and for
improving casting processes of metallic alloys.
The viscosity of aluminium-nickel melts has been
measured only once so far. However, not the whole
concentration range of the aluminium-nickel system
was covered by these data. In particular the viscosity
values of the high melting alloys, which are of
technological interest, were unknown. The measurement
of the missing values was not possible due to the
high melting temperatures using existing viscometers.
A new oscillating cup viscometer has been constructed
within this work. The viscometer has been tested
measuring the viscosity values of pure metals, which
are well known in literature. The test measurements
have been done at temperatures up to 1800°C. A
temperature of 2300°C is achievable with slight
modifications. A new software for controlling the
device and evaluation of the measured data has been
developed. Several working equations for calculating
the viscosity have been implemented. Furthermore a
new approach has been used for detecting the damping
of the oscillation of the pendulum containing the
liquid sample.
The viscosity of aluminium-nickel melts have been
measured successfully. The measured values are in
good agreement with the little number of known
values. A good agreement with values calculated
from diffusion experiments and computer simulations
was observed as well. Several models for calculating
the viscosity of liquid alloys have been tested and
compared with the experimental values measured in
this work. Not all the tested models can predict
the viscosity values of aluminium-nickel melts
plausibly.
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Aufbau eines Hochtemperaturviskosimeters und Messung der Viskosität von Schmelzen des Systems Aluminium-NickelKehr, Mirko 29 October 2009 (has links)
Das System Aluminium-Nickel besitzt als Modellsystem
in der Wissenschaft sowie als ein Basissystem von
sogenannten Superlegierungen in der Technik eine
große Bedeutung. Aufgrund der hohen Liquidustemperaturen
von bis zu 1638°C sind die thermophysikalischen
Eigenschaften der Schmelzen bisher nur in den
Randbereichen des Systems bekannt. Die Viskosität
ist eine der thermophysikalischen Größen und sowohl
von der Zusammensetzung als auch von der Temperatur
abhängig. Sie besitzt eine große Bedeutung als
Eingabeparameter für Simulationsrechnungen zur
Erstarrung von Schmelzen sowie bei der Optimierung
von Herstellungsprozessen metallischer Werkstoffe.
Die Viskosität der Schmelzen im System Aluminium-Nickel
wurde nach Kenntnis des Autors bisher nur einmal
gemessen. Durch den vorliegenden Datensatz war jedoch
nicht der gesamte Konzentrationsbereich im System Aluminium-Nickel
abgedeckt. Besonders im Bereich der technologisch
interessanten hochschmelzenden Legierungen bestanden
Lücken. Mit bisherigen Viskosimetern war die Messung
der Viskositäten im gesamten System nicht möglich, da
die Liquidustemperaturen des Systems Aluminium-Nickel
die maximalen Arbeitstemperaturen überstiegen.
Im Rahmen der Arbeit wurde ein neues Schwingtiegelviskosimeter
mit hängendem Tiegel konzipiert, aufgebaut und mit
Viskositätsmessungen an reinen Metallen mit bekannter
Viskosität bei Temperaturen bis 1800°C erfolgreich
getestet. Mit weiteren Modifikationen sind mit dem
neu aufgebauten Viskosimeter Temperaturen bis 2300°C
erreichbar. Für den Betrieb des Viskosimeters wurde
ein umfangreiches Mess- und Steuerprogramm entwickelt
sowie erfolgreich getestet. Zur Berechnung der
Viskosität wurden im Messprogramm verschiedene
Arbeitsgleichungen implementiert. Für die Detektion
der Schwingung des Torsionspendels wurde ebenfalls
eine neue Methode angewendet, die eine quasikontinuierliche
und damit genauere Messung Erfassung der Schwingung
erlaubt.
Die Viskosität der Schmelzen des Systems Aluminium-Nickel
konnte erfolgreich bestimmt werden, womit experimentelles
Neuland betreten wurde. Die gemessenen Verläufe zeigen eine
gute Übereinstimmung mit den wenigen bekannten Daten
zur Viskosität von Aluminium-Nickel Schmelzen. Ebenso
gut ist die Übereinstimmung mit wenigen weiteren vorhandenen
Messdaten der Diffusionskonstanten sowie mit Daten aus
Computersimulationen. Mit verschiedenen Modellen zur
Vorhersage der Viskosität von Legierungen wurden
Viskositätsverläufe im System Aluminium-Nickel berechnet.
Der Vergleich mit den Messdaten hat gezeigt, dass nur wenige
der Modelle zur Vorhersage der Viskosität im System
Aluminium-Nickel geeignet sind. / The system aluminium-nickel is of importance as a
model-system in materials science as well as a
basic system for superalloys in technical applications.
The knowledge of the thermophysical properties of
the system aluminium-nickel has been limited to the
areas close to the pure elements mainly related to
the high melting temperatures of up to 1638°C. The viscosity, which is one of these
thermophysical properties, depends on alloy composition as
well as on temperature. The viscosity is of importance as
an input parameter in computer simulations and for
improving casting processes of metallic alloys.
The viscosity of aluminium-nickel melts has been
measured only once so far. However, not the whole
concentration range of the aluminium-nickel system
was covered by these data. In particular the viscosity
values of the high melting alloys, which are of
technological interest, were unknown. The measurement
of the missing values was not possible due to the
high melting temperatures using existing viscometers.
A new oscillating cup viscometer has been constructed
within this work. The viscometer has been tested
measuring the viscosity values of pure metals, which
are well known in literature. The test measurements
have been done at temperatures up to 1800°C. A
temperature of 2300°C is achievable with slight
modifications. A new software for controlling the
device and evaluation of the measured data has been
developed. Several working equations for calculating
the viscosity have been implemented. Furthermore a
new approach has been used for detecting the damping
of the oscillation of the pendulum containing the
liquid sample.
The viscosity of aluminium-nickel melts have been
measured successfully. The measured values are in
good agreement with the little number of known
values. A good agreement with values calculated
from diffusion experiments and computer simulations
was observed as well. Several models for calculating
the viscosity of liquid alloys have been tested and
compared with the experimental values measured in
this work. Not all the tested models can predict
the viscosity values of aluminium-nickel melts
plausibly.
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Preparation, Processing and Characterization of Noble Metal Nanoparticle-based Aerogels / Darstellung, Prozessierung und Charakterisierung von Edelmetallnanopartikel-basierten AerogelenHerrmann, Anne-Kristin 05 January 2015 (has links) (PDF)
New challenges in nanotechnology arise in the assembly of nanoobjects into three-dimensional superstructures, which may carry synergetic properties and open up new application fields. Within this new class of materials nanostructured, porous functional metals are of great interest since they combine high surface area, gas permeability, electrical conductivity, plasmonic behavior and size-enhanced catalytic reactivity. Even though a large variety of preparation pathways for the fabrication of porous noble metals has already been established, several limitations are still to be addressed by research developments.
The new and versatile approach that is presented in this work makes use of a templatefree self-assembly process for the fabrication of highly porous, metallic nanostructures. Thereby, nanochains are formed by the controlled coalescence of noble metal NPs in aqueous media and their interconnection and interpenetration leads to the formation of a self-supported network with macroscopic dimensions. Subsequently, the supercritical drying technique is used to remove the solvent from the pores of the network without causing a collapse of the fragile structure. The resulting highly porous, low-weighted, three-dimensional nanostructured solids are named aerogels. The exceptional properties of these materials originate from the conjunction of the unique properties of nanomaterials magnified by macroscale assembly.
Moreover, the combination of different metals may lead to synergetic effects regarding for example their catalytic activity. Therefore, the synthesis of multimetallic gels and the characterization of their structural peculiarities are in the focus of the investigations. In the case of the developed preparation pathways the gelation process starts from preformed, stable colloidal solutions of citrate capped, spherical noble metal (Au, Ag, Pt, Pd) NPs. In order to face various requirements several methods for the initiation of the controlled destabilization and coalescence of the nanosized building blocks were developed and synthesis conditions were optimized, respectively. Multimetallic structures with tunable composition are obtained by mixing different kinds of monometallic NP solutions and performing a joint gel formation.
The characterization of the resulting materials by means of electron microscopy reveals the formation of a highly porous network of branched nanochains that provide a polycrystalline nature and diameters in the size range of the initial NPs. Furthermore, synthesis conditions for the spontaneous gel formation of glucose stabilized Au and Pd NPs were investigated. In order to gain a detailed knowledge of the structural properties of bimetallic aerogel structures a versatile set of characterization techniques was applied. A broad pore size distribution dominated by meso- and macropores and remarkably high inner surface areas were concluded from the N2 physisorption isotherms and density measurements. As investigated, a specific thermal treatment could be used to tune the ligament size of Au-Ag aerogels, whereas Au-Pd and Pt-Pd structures provide thermal stability under mild conditions.
Further investigations aimed to the enlightenment of the elemental distribution and phase composition within the nanochains of multimetallic gel structures. The different approaches provide complementary and consistent results. Phase analyses based on XRD measurements revealed separated phases of each metal in the case of Ag-Pd and Au-Pd aerogels. They further proved the possibility of temperature induced phase modifications that lead to complete alloying of Au and Pd. In addition, separated domains of Pt and Pd were established from the EXAFS analysis of the corresponding aerogel. STEM EDX high resolution elemental mappings confirmed the separated domains of different metals in the case of Au-Pd and Pt-Pd aerogels. Moreover, a complete interdiffusion and alloy formation of Au and Ag within the corresponding aerogel structure is suggested from STEM EDX results.
Finally, the presented investigations further promote the field of metallic aerogels by addressing the challenging issue of processability and device fabrication. Hybrid materials with organic polymers as well as various kinds of coatings on glass substrates and glassy carbon electrodes were prepared whereas the network structure was preserved throughout all processing steps. Moreover, it was illustrated that the NP-based aerogels carry metallic properties as expressed by their low Seebeck coefficients and high electrical conductivities.
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Oberflächenvorbehandlung von Fügeteilen zur Optimierung adhäsiver Verbindungen im Konstruktiven Glasbau / Surface Modification Methods for Improving Adhesive Joints in Glass StructuresKothe, Christiane 25 February 2014 (has links) (PDF)
Die moderne Architektur ist durch gläserne Fassaden und ausgefallene Konstruktionen aus Glas geprägt. Dabei wird Glas nicht nur als raumabschließendes Element verwendet, sondern auch konstruktiv eingesetzt und zunehmend an der Lastabtragung beteiligt. Die Integration von Glaselementen in die Baukonstruktion erfolgt über linien- oder punktförmige Lagerungen. Dabei können mechanisch ausgeführte Halterungen lokale Beanspruchungen und damit Glasversagen verursachen. Eine Alternative bilden Klebverbindungen, welche ein materialgerechtes Konstruieren im Glasbau ermöglichen. Kommerziell wird hierfür eine Vielzahl von Klebstoffen angeboten.
Neben der Auswahl eines geeigneten Klebstoffsystems können dauerhafte adhäsive Verbindungen aber meist nur mit Hilfe von Oberflächenvorbehandlungen der Fügeteile gewährleistet werden. Aufgrund der langen Standzeiten von Bauwerken sind große Beständigkeiten von geklebten Verbindungen notwendig, welche nur durch den Aufbau von möglichst hohen Haftungskräften zwischen Fügeteiloberflächen und Klebstoffpolymer erreichbar sind. Spezielle Vorbehandlungsverfahren sorgen für eine bessere Benetzbarkeit der Oberflächen und schaffen zudem energetisch aktive Zentren, die mit den Klebstoffen in Wechselwirkung treten können. Viele der insbesondere für metallische Materialien industriell etablierten Oberflächenvorbehandlungen sind allerdings wenig zukunftsträchtig, da diese Verfahren häufig den Einsatz ätzender, hochgiftiger und umweltgefährdender Substanzen notwendig machen.
Hierin liegt der Ansatzpunkt der vorliegenden Arbeit. In verschiedenen Industriebereichen, wie dem Automobilbau, der Elektrotechnik und der Dentalmedizin werden bereits neu entwickelte Oberflächenvorbehandlungsverfahren auf Basis von Plasma- und Abscheidungstechnologien eingesetzt. Daraus ergibt sich die Fragestellung nach der Anwendbarkeit solcher Verfahren auf Fügeteilmaterialien des Konstruktiven Glasbaus und nach dem Nutzen dieser Oberflächenvorbehandlungen in Bezug auf die Optimierung von strukturellen Klebungen.
Für die Ermittlung optimaler Eigenschaften von Oberflächen für den klebtechnischen Prozess werden ausgewählte Fügeteile aus Edelstahl, Aluminium und Messing sowie Einscheibensicherheitglas aus Kalk-Natronsilikatglas physikalischen und chemischen Oberflächenanalysen vor und nach der Anwendung von vier verschiedenen Oberflächenvorbehandlungsverfahren unterzogen. Zudem werden die Haftungseigenschaften nach der Vorbehandlung an geklebten Prüfkörpern vor und nach Alterung untersucht. Aus den daraus erhaltenen Ergebnissen wird der Einfluss der Oberflächenbeschaffenheit auf die Festigkeit der Klebverbindungen bestimmt.
Die durchgeführten Untersuchungen ergeben sehr unterschiedliche, stark substrat- und klebstoffabhängige Wirkungsweisen der einzelnen Oberflächenvorbehandlungen. Als geeignetes Verfahren in Bezug auf die Verbesserungen des Adhäsionsvermögens und der Alterungsbeständigkeit, die Integrierbarkeit in maschinelle Herstellungsprozesse und die Vermeidung optischer Veränderung der Oberflächen stellt sich die Flammensilikatisierung heraus. Die mit dieser Oberflächenvorbehandlung aufgebrachte, dichte Silikatschicht und deren chemische Aktivität sowie deren vollständige Benetzbarkeit bieten beste Voraussetzungen für die Verklebung verschiedener Fügeteilmaterialien mit unterschiedlichsten Klebstoffen. / The modern architecture is affected by glass facades and novel glass structures. Therein glass is not only used as space enclosing element, rather it finds more and more constructive application and it is increasingly involved in load transfer. State of the art for the integration of glass elements in buildings are mechanically designed point and linear fixings. But they may cause local stresses followed by glass breakage. An alternative to these fixations are adhesive joints which more respect the specific requirements of the fragile material glass. A wide variety of adhesives is already available for this purpose.
For strong adhesive joints not only the selection of a suitable adhesive is essential. The surface quality, which can be enhanced by surface treatments, is just as important for a very good adhesion. Due to the long life expectancy of buildings, a permanently aging resistance of the adhesive joints is necessary. For that, a formation of the highest possible adhesion forces between adhesive polymer and adherend surface is essential. Special surface treatment processes ensure a better wettability of the surfaces and also create energetically active sites that can interact with the adhesive molecules. However, many of the industrially established surface pretreatments, especially those for metallic materials, are not sustainable, since these methods often use corrosive, highly toxic and environmentally hazardous substances.
This is the basis of the present dissertation. In various industries, such as automotive, electrical engineering and dentistry, newly developed surface treatment methods based on plasma and deposition technologies are already used. This raises the question of the applicability of such methods on materials for glass constructions and of their benefit to the optimization of structural adhesive joints.
The effect of four different surface treatment methods used on the surfaces of stainless steel, aluminum, brass and toughened safety glass made from soda-lime glass is investigated in experimental studies. Physical and chemical surface analyses are performed before and after the applications. In addition, the adhesion properties of bonded specimens with pretreated surfaces are examined before and after aging. The influence of the surface conditions on the strength of the adhesive joints is determined from the obtained results.
The results show very different effects of the individual surface treatment methods with high dependences on substrate and adhesive. With regard to an increase of adhesion strength, a good aging resistance, an uncomplicated integration into automated production processes and an avoidance of changing the optical surface properties, the investigated combustion chemical vapour deposition is the most suitable method. With this pretreatment, a dense silicate layer is deposite on the surface. Its high chemical activity and its complete wettability offer the best conditions for bonding a variety of materials with different adhesives.
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Bimetallic aerogels for electrocatalytic applicationsKühn, Laura 29 May 2017 (has links)
Polymer electrolyte fuel cells (PEFCs) have emerged as a promising renewable emission-free technology to solve the worldwide increasing demand for clean and efficient energy conversion. Despite large efforts in academia and automotive industry, the commercialization of PEFC vehicles still remains a great challenge. Critical issues are high material costs, insufficient catalytic activity as well as longterm durability. Especially due to the sluggish kinetics of the oxygen reduction reaction (ORR), high Pt loadings on the cathode are still necessary which leads to elevated costs.
Alloys of Pt with other less precious metals (Co, Ni, Fe, Cu, etc.) show improved ORR activities compared to pure Pt catalysts. However, state-of-the-art carbon-supported catalysts suffer from severe Pt and carbon corrosion during the standard operation of PEFCs, affecting their reliability and long-term efficiency.
Multimetallic aerogels constitute excellent candidates to overcome these issues. Due to their large open pores and high inner surface areas combined with electrical conductivity, they are ideal for applications in electrocatalysis. In addition, they can be employed without any catalyst support. Therefore, the fabrication of bimetallic Pt-M (M=Ni, Cu, Co, Fe) aerogels for applications in fuel cell catalysis was the focus of this thesis.
Based on a previously published synthesis for Pt–Pd aerogels, a facile one-step procedure at ambient conditions in aqueous solution was developed. Bimetallic aerogels with nanochain diameters of as small as 4 nm and Brunauer-Emmett-Teller (BET) surface areas of up to 60 m2/g could be obtained.
Extensive structure analysis of Pt–Ni and Pt–Cu aerogels by powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), scanning transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy (STEM-EDX) and electrochemical techniques showed that both metals were predominantly present in their metallic state and formed homogeneous alloys. However, metal (hydr)oxide byproducts were observed in aerogels with higher contents of non-precious metal (>25 %). Moreover, electronic and geometric structures were similar to those of carbon-supported Pt alloy catalysts.
As a result, ORR activites were comparable, too. A threefold improvement in surface-specific activity over Pt/C catalysts was achieved. The mass-specific activites met or exceeded the U.S. Department of Energy (DOE) target for automotive PEFC applications. Furthermore, a direct correlation between non-precious metal content in the alloy and ORR activity was discovered. Aerogels with nonprecious metal contents >25% turned out to be susceptible to dealloying in acid leaching experiments, but there was no indication for the formation of extended surface structures like Pt-skeletons.
A Pt3Ni aerogel was successfully employed as the cathode catalyst layer in a differential fuel cell (1 cm2), which is a crucial step towards technical application. This was the first time an unsupported metallic aerogel was implemented in a PEFC. Accelerated stress tests that are usually applied to investigate the support stability of fuel cell catalysts revealed the excellent stability of Pt3Ni alloyed aerogels. In summary, the Pt alloy aerogels prepared in the context of this work have proven to be highly active oxygen reduction catalysts with remarkable stability.
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Laser nitriding of metals:Influences of the ambient pressure and the pulse duration / Influences of the ambient pressure and the pulse duration / Lasernitrieren von Metallen: / Einfluss des Umgebungsdrucks und der PulsdauerHan, Meng 17 December 2001 (has links)
No description available.
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Synthesis and X-ray Structural Characterization of Oxygen Bridged Complexes for Olefin Polymerization: A Theoretical Interpretation of Structure and Activity RelationshipPrabhuodeyara Matada, Gurubasavaraj 30 October 2007 (has links)
No description available.
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Mikrostruktur und elektrischer Transport von Sr<sub>1-x</sub>Ca<sub>x</sub>RuO<sub>3</sub>-Dünnfilmen – Der Weg zur Aufdeckung des Fermiflüssigkeitgrundzustandes in CaRuO<sub>3</sub> / Microstructur and electrical transport in Sr<sub1-x</sub>Ca<sub>x</sub>RuO<sub>3</sub> thin films – The way of revelation of fermi liquid groundstate in CaRuO<sub>3</sub>Srba, Melanie 20 July 2018 (has links)
No description available.
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