Research was performed on the development of metal-supported solid oxide fuel cell (SOFC) electrolytes by suspension and solution precursor plasma spraying (SPS and SPPS). Experiments were conducted to understand the effects of many plasma-, feedstock-, and substrate-related process parameters on the microstructure, permeability, and conductivity of the resulting coatings. Most work was performed with yttria-stabilized zirconia (YSZ), but samaria-doped ceria (SDC) was also considered. The plasma-to-substrate heat flux behaviour of the process is particularly relevant for producing dense electrolytes with low segmentation cracking. Heat flux profiles for various processing conditions were experimentally determined and then used to model temperature distributions in the electrolyte and substrate during deposition. The results showed a strong correlation between segmentation crack severity and the peak temperature difference between the electrolyte surface and the metal support during deposition. Building on these findings, two strategies were developed for improving electrolyte performance. The first strategy is to use a bi-layer electrolyte structure, in which one layer is dense but has segmentation cracks and the other layer is more porous but contains relatively few segmentation cracks. A cell with a bi-layer electrolyte achieved a peak power density of 0.718 W cm-2 at 750 °C using hydrogen as fuel. The second strategy involves reducing the thickness and roughness of the electrode on which the electrolyte is deposited, which first required the development of improved metal supports. A thinner electrode reduces the thermal stresses that drive segmentation cracking and a smoother surface minimizes the formation of concentrated porosity. A cell with a 16 μm thick anode and a 21 μm thick electrolyte achieved an open circuit voltage (OCV) of 1.053 V, a series resistance of 0.284 Ω cm2, and a peak power density of 0.548 W cm-2 at 750 °C using hydrogen as fuel. A separate cell with a 28 μm thick electrolyte achieved an OCV of 1.068 V. At the end of the thesis, cell performance is compared to that of state-of-the-art cells produced in other facilities and using other production methods.

Research was performed on the development of metal-supported solid oxide fuel cell (SOFC) electrolytes by suspension and solution precursor plasma spraying (SPS and SPPS). Experiments were conducted to understand the effects of many plasma-, feedstock-, and substrate-related process parameters on the microstructure, permeability, and conductivity of the resulting coatings. Most work was performed with yttria-stabilized zirconia (YSZ), but samaria-doped ceria (SDC) was also considered. The plasma-to-substrate heat flux behaviour of the process is particularly relevant for producing dense electrolytes with low segmentation cracking. Heat flux profiles for various processing conditions were experimentally determined and then used to model temperature distributions in the electrolyte and substrate during deposition. The results showed a strong correlation between segmentation crack severity and the peak temperature difference between the electrolyte surface and the metal support during deposition. Building on these findings, two strategies were developed for improving electrolyte performance. The first strategy is to use a bi-layer electrolyte structure, in which one layer is dense but has segmentation cracks and the other layer is more porous but contains relatively few segmentation cracks. A cell with a bi-layer electrolyte achieved a peak power density of 0.718 W cm-2 at 750 °C using hydrogen as fuel. The second strategy involves reducing the thickness and roughness of the electrode on which the electrolyte is deposited, which first required the development of improved metal supports. A thinner electrode reduces the thermal stresses that drive segmentation cracking and a smoother surface minimizes the formation of concentrated porosity. A cell with a 16 μm thick anode and a 21 μm thick electrolyte achieved an open circuit voltage (OCV) of 1.053 V, a series resistance of 0.284 Ω cm2, and a peak power density of 0.548 W cm-2 at 750 °C using hydrogen as fuel. A separate cell with a 28 μm thick electrolyte achieved an OCV of 1.068 V. At the end of the thesis, cell performance is compared to that of state-of-the-art cells produced in other facilities and using other production methods.

Extensive research efforts are underway to generate composite coatings including carbon nanotubes (CNT) in order to improve the properties of the bulk coat. The present project concentrates on possible methods that would allow the plasma spraying of CNT-based nano-composite coatings. Various methods for producing metal-CNT composite powders for thermal plasma spraying are studied in this project. The first method discussed is based on CNT dispersion followed by an agglomeration procedure using a polymer binder. The second and more promising technique gets around the problems associated with handling, separating, and transporting the nanotubes to the substrate through a direct synthesis of the CNT on the particles to be sprayed. In the present context, this synthesis is made on pretreated stainless steel SS304 powders by chemical vapor deposition (CVD). A parametric study is made for the various steps of the thermal CVD process by varying parameters such as the etching time in the pre-treatment sequence, while the reaction temperature, the annealing temperature, the growth phase duration and the acetylene injection time are varied for the CVD sequence. The composite powders are analyzed using high resolution electron microscopy images (FEGSEM), thermogravimetric analyses (TGA), Raman spectroscopy, and BET surface area analyses. This study provided the parametric optimization of the thermal CVD procedure with respect to CNT production. The composite powders generated show a dense, fully covered, and uniform CNT forest with a purity of CNT to amorphous carbon of 86% based on the micro-Raman spectra obtained.

Thesis (Ph. D.)--Oregon Graduate Institute of Science and Technology, 1996.

Thesis (Ph. D.)--Ohio State University, 2007. / Full text release at OhioLINK's ETD Center delayed at author's request

No description available.

Rolling contact is experienced by a large number of components in mechanical designs. Examples include roller bearings and ink distribution rollers in the printing industry. Rolling contact results in surface wear. It is however possible to reduce rolling contact wear rates and surface fatigue by performing a surface modification such as powdered metal coating [35]. Powder coating methods such as Laser cladding and Plasma coating are two application processes that are completely different in method and therefore create different coating microstructures and bonding mechanisms between the coating and substrate. The aim of the research was to investigate the comparative rolling contact performance of two coating processes and two separate metal powder compositions. The coatings were applied to British standard En 9 steel test specimens. En 9 was selected due to its popular use in the manufacture of shafts, cylinders and rollers. Under rolling contact, material is removed from the surface as a result of wear and surface fatigue. Through testing and evaluation, the performance of the coating application processes were evaluated relative to one another and relative to the uncoated steel under rolling contact. The performance of the coating compositions were also evaluated against one another for a given coating application process. Results used to determine the performance of the coatings and coating processes were, the number of cycles to failure and the wear rates of the coated surface. Microstructure pictures of the coated surface were taken prior to testing and following testing. The pictures were used to qualitatively determine the effects of the rolling contact on the surfaces. Through the study of rolling contact, an explanation of the stresses induced in the contact area and the position of the maximum values were determined. The boundaries for the deformation regimes were identified through the understanding of the position of first yield and the shakedown limit under rolling contact. The theories of rolling contact fatigue are covered briefly as part of a better understanding of the failure mechanism however the experimentation is largely comparative based. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2008.

No description available.

No description available.

The research work performed in this thesis has been carried out at the Production Tech-nology Centre where the Thermal Spray research group of University West has its work-shop and labs. This research work has been performed in collaboration with the International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad, India. First of all, I would like to express my sincere thanks and gratitude to my supervisors Dr. Nicolaie Markocsan and Dr. Nicholas Curry for their guidance, great support and valuable suggestions without which this work could not have been possible. I would also like to thanks Prof. Per Nylén for keeping faith in me and providing me an opportunity to work at PTC, which is a great place to perform research. It is my pleasure being their student and I wish I would keep learning from all of them, both on academic and personal grounds. I would also like to thank my colleagues at PTC Mr. Mohit Gupta and Mr. Stefan Björklund, for their help and support during this work. I would like to acknowledge the H.C. Starck Company for its financial support for the pro-ject; Dr. Filofteia-Laura TOMA at Fraunhofer IWS, Dresden to help us in spraying suspen-sion sprayed YSZ top coats, G Shivkumar from ARCI to help us in spraying solution pre-cursor sprayed top coats and Toni Bogdanoff, Jönköping University to help us in conduct-ing the LFA experiment