Chemical microreactors offer opportunities for portable power generation, on-site waste remediation and point-of-use chemical synthesis. Much of the existing development of microreactor devices involves silicon-based microfabrication techniques. It is recognized that new refractory materials are important to realizing high-temperature microreactors. Requirements of these materials include high-temperature resistance, chemical inertness and low-cost microfabrication. Advances in multilayer ceramics hold promise for the fabrication of microreactor structures from ceramic tape. Problems include creep, moderate levels of densification, and volumetric shrinkage, all of which can lead to dimensional instability. Intermetallics are another class of refractory materials which may hold some promise for high-temperature microreactor development. In this paper, a new method of forming microchannel arrays from thin layers of intermetallics is demonstrated. This method has the advantage of eliminating volumetric shrinkage due to binder removal. Various iterations of NiAl intermetallic conversion and bonding are presented. Results show that the NiAl system may be suitable as a substrate for microchannel reactor designs. / Graduation date: 2002

The miniaturization of energy, chemical and biological systems for distributed and portable applications, known as process intensification, is realized by the enhancement in heat and mass transfer performance within high surface-to-volume ratio microchannels. Fabrication of devices for process intensification is achieved in part by microlamination techniques. These techniques consist of patterning, aligning, and bonding thin layers of material into monolithic devices. Even though the fabrication techniques used in microlamination are generally accurate and consistent, small amounts of dimensional variation in microlaminated structures can strongly affect the device performance. One significant finding of this dissertation is that fin warpage, which is commonly induced during bonding, generally has more adverse device performance effects than misalignment. A heat exchanger that contains fin warpage as small as 25 percent of the microchannel height (on the order of 10 ��m) needs to almost double the number of flow channels to gain the same thermal effectiveness as the uniform one. Therefore, the focus of this dissertation is to investigate, understand, and learn how to control the cause and effect of buckling warpage produced within microlaminated structures. The microlamination discussed in this dissertation is performed with a thermally-controlled registration process, which facilitates metallic bonding at elevated temperatures. Another finding of this dissertation is that the tolerance limits of the fixture used in this registration process exceed the accuracy of the machine tools used to produce the fixture. Fixture tolerance limits on the order of 10 ��m are necessary to align and bond laminae with thicknesses below 100 ��m. An alternative technique based on the compliance of the fixture is proposed in order to improve these limits. This technique helps compensate for the excessive registration force due to over-constrained bonding, which extends the range of fixture tolerance limit to over 100 ��m well within current process capability of machine tools. Another approach to controlling fin warpage, based on the induction of higher modes of fin buckling, is also discussed. An analytical evaluation shows that the effect of fin warpage is minor as the mode of buckling reaches mode 10. A preliminary experiment confirms that the induction of fin buckling into a higher mode can be achieved by constraining the fin at specific locations along the fin during microlamination. / Graduation date: 2002

Graduation date: 2005

Thesis (Ph. D.)--Oregon State University, 2009. / Printout. Includes bibliographical references. Also available on the World Wide Web.

Microchannel process technology (MPT) components are chemical unit operations which exploit highly-parallel arrays of microchannels to process large fluid volumes for portable and distributed applications. Microchannel heat exchangers (MCHXs) have demonstrated 3 to 5 times higher heat fluxes when compared to conventional heat exchangers resulting in proportionate reductions in size and weight. The most common fabrication approach for producing MPT components is microchannel lamination, or microlamination, in which thin layers of metal or polymer are patterned with microchannel features, registered, and bonded to produce monolithic components. Currently, the most common microlamination architecture involves the photochemical machining and diffusion bonding of metal foils. Prior work has established that the yields in diffusion bonding often drive the costs of MCHXs. Laser keyhole welding has been proposed as an alternative bonding technology providing the potential for faster cycle times, smaller weld widths and layer-to-layer evaluation of hermeticity leading to higher yields. Furthermore, laser weldments have small heat-affected zones providing excellent mechanical strength. In this study, efforts are made to evaluate the feasibility of using laser welding in the microlamination of a high-temperature counter-flow heat exchanger made of a Ni superalloy. Preliminary efforts were focused on the development and validation of weld strength estimation models. These models were then used to narrow down the range of process parameters and a final set of process parameters was determined through the use of a full factorial experiment with weld strength, joining efficiency and weld gap as response variables. The most acceptable parameter set was used to demonstrate the fabrication of a Haynes 214 microchannel array with adequate bond strength and hermeticity and minimal thermal warpage. / Graduation date: 2013

A new adhesive bonding method is introduced for microlamination architectures, for producing low-temperature microchannel arrays in a wide variety of metals. Sheet metal embossing and chemical etching processes have been used to produce sealing bosses and flow features, resulting in approximately 50% fewer laminae over traditional methods. These lamina designs are enabled by reduced bonding pressures required for the new method. An assembly process using adhesive dispense and cure is outlined to produce leak-free devices. Feasible fill ratios were determined to be 1.1 in general and 1.25 around fluid headers, largely due to gaps between faying surfaces caused by surface roughness. Bond strength investigation reveals robustness to surface conditions and a bond strength of 5.5-8.5 MPa using a 3X safety factor. Dimensional characterization reveals a two sigma (95%) post-bonded channel height tolerance under 10% (9.6%) after bonding. Patterning tolerance and surface roughness of the faying laminae were found to have a significant influence on the final postbonded channel height. Leakage and burst pressure testing on several samples has established confidence that adhesive bonding can produce leak-free joints. Operating pressures up to 413 kPa have been satisfied, equating to tensile pressure on bond joints of 1.9 MPa. Higher operating pressures can be accommodated by increasing the bond area of devices. A two-fluid counterflow microchannel heat exchanger has been redesigned, fabricated and tested to demonstrate feasibility of the new method. Results show greater effectiveness and higher heat transfer rates, suggesting a smaller device than the original heat exchanger. A maximum effectiveness of 82.5% was achieved with good agreement between theoretical and experimental values. Although thermal performance was improved, higher pressure drops were noted. Pressure drops were predicted with a maximum error of 16% between theoretical and experimental values. Much of the pressure drop was found to be in the device manifolds, which can be improved in subsequent designs. Fluid flow simulation results show a 45-65X reduction in fluid leakage velocity past sealing bosses, thereby mitigating adhesive erosion concerns. Theoretical models indicate that the worst-case adhesive erosion rate is 1/12th the rate of aluminum and 1/7th the rate of stainless steel, implying satisfactory reliability in high fluid velocity applications. Economic comparison indicates an 83% reduction in material cost and 71% reduction in assembly cost with the new adhesive bonding process, when compared to diffusion bonding for the recuperator investigated in this study. Adhesive compatibility with common refrigerants is reviewed through literature references, with no adverse compatibility issues noted. The findings of this research suggest a fairly quick path to commercialization for the new bonding method. Future studies required to pursue commercialization are liquid and gas permeability evaluations, and long term strength and performance testing of adhesives in targeted applications. / Graduation date: 2012 / Access restricted to the OSU Community at author's request from Mar. 26, 2012 - Mar. 26, 2013

The objective of this dissertation is to develop amorphous metal thin films (AMTFs) for two-terminal electrical device and nanolaminate applications. Two AMTFs, ZrCuAlNi and TiAl, are investigated in both two-terminal electrical device and nanolaminate applications. Material properties including composition, atomic order, surface morphology, surface potential, and electrical resistivity are explored. Application of AMTFs as electrodes in tunneling MIM diodes leverages the ultra-smooth AMTF surface morphology which results from the amorphous atomic order of AMTFs. Analysis methodologies using tunneling MIM diode I-V characteristics are described. A methodology used to estimate potential barrier heights is applied to tunneling MIM diode with differing lower electrode material, upper electrode material and upper electrode deposition technique. A second methodology used to estimate relative tunneling MIM diode insulator thickness is also presented. The presented I-V characteristic analysis methodologies illustrate that tunneling MIM diodes fabricated with AMTF lower electrodes possess tunable I-V characteristics. Nanolaminates are layered materials fabricated with alternating dissimilar thin-film layers. The flexibility of AMTF nanolaminates is illustrated through the presentation of amorphous metal/oxide nanolaminates fabricated with differing AMTFs and aqueous solution deposited oxides. TEM and XPS depth profile analysis of realized nanolaminates are presented. The optical dielectric response of ZrCuAlNi/aluminum phosphate oxide (AlPO) and TiAl/AlPO nanolaminates are evaluated through polarized reflectance measurements and effective medium theory. The optical dielectric response of the nanolaminates differ from the optical dielectric response of the component layers. ZrCuAlNi/AlPO and TiAl/AlPO nanolaminates therefore satisfy the definition of metamaterials. / Graduation date: 2012 / Access restricted to the OSU Community at author's request from May 9, 2012 - May 9, 2013