RESEARCH PROGRAMS IN THE ION BEAMS GROUP
Large-area Filtered Arc Plasma Source Ion
Deposition Technology for Corrosion Resistant Coatings on Bi-Polar Plates in
Planar Solid Oxide fuel Cells
Supported by
DOE in collaboration with Pacific Northwest National Laboratory and the
Electrochemical Engineering Center at Montana State University
Project Summary
The goal of this project is to determine the feasibility of using the large-area filtered arc plasma source ion deposition
(FAPSID) technology for the production of corrosion-resistant bipolar plates in planar solid-oxide fuel cells
(SOFC). Work will include application-specific modifications and improvements in the critical hardware components, demonstration of consistent and reliable equipment performance, and production and testing of experimental quantities of multi-layer coated corrosion resistant bipolar plates. The need to reduce cost for components in the SOFC suggests using inexpensive metallic alloys for the interconnecting plate between adjacent cells in a SOFC stack. Most metals will fail quickly due to corrosion in the gaseous environment of the cell, resulting in potentially catastrophic gas leaks. Multilayer coatings on these plates are proposed as a solution to provide oxidation resistance and chemical stability with adjacent components. The bonding characteristics and integrity of the coatings against thermal cycling (>800 o C) will be determined. This project will exploit the capability of FAPSID to grow extremely smooth surfaces of multi-layer coatings with a low pinhole density, providing improved corrosion resistance. The corrosion resistant coatings will be optimized as a function of several parameters, including substrate material and surface preparation and substrate temperature, number and composition of individual layers, addition of ultra-thin diffusion barriers. The physical, chemical, and electrical integrity of the coated plates will be tested at elevated temperatures in wet and oxidizing conditions. Ultimately, the coating process will be tested for production size prototype bipolar plates at operating temperatures in collaboration with PNNL scientists.
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Use of Metallic Interlayers to Promote Metal/Metal Epitaxial
Growth
Supported by NSF - Department of Materials Research
Project Summary
The objective of the proposed research is to investigate the potential for ultra-thin, metal inter-layers to stabilize the interface in multi-layered,
thin-film structures. The work will identify those metals which when deposited in mono-layer amounts at the interface make possible abrupt,
epitaxial interfaces in systems that are otherwise characterized by inter-diffusion or roughness. The interlayer materials, unlike
surfactants, will remain at the interface to promote chemical, thermal, and structural stability. The work is directed primarily at improving the
interfaces in thin-film magnetic tunneling junctions and giant magneto-resistive structures being considered for magnetic memory or
sensing applications, where it is felt that more abrupt interfaces will result in devices with better magnetic switching characteristics and
lower total resistance. The interlayer should be atomically thin, unlike conventional diffusion barriers, to minimize the impact on any magnetic
properties of the device. Since current fabrication techniques for tunnel junctions involve the oxidation of Al films grown on various ferromagnetic
metals (Fe, Co, Ni, and their alloys), the structure and thermal stability of these interfaces will be characterized first. The effect of the
interlayer on these structures will then be studied. Previous work suggests that Ti,
Zr, and perhaps Ta have the potential for serving as stabilizing, ultra-thin inter-layers in aluminum/transition metal
interfaces. The structure and stability of these magnetic films on oxidized Al surfaces, with and without an interlayer, will also be
studied. The measurements will characterize the degree of ordered growth or inter-diffusion at the interface using high-energy ion backscattering
and channeling, low energy electron diffraction, low-energy ion scattering, and x-ray photoelectron diffraction. Core-level photoelectron binding
energies will serve to identify compound formation at the interface. Monte Carlo computer simulations, using embedded atom potentials to calculate
total energies, will guide the structure analysis. Test structures will be fabricated using those materials that appear to have the most stable and
abrupt interfaces, and the magnetic switching and tunneling properties of these structures will be measured. The results of this research will
provide a better understanding of, and ability to predict and grow abrupt epitaxial metal/metal interfaces.
How would an interlayer work?
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