Identifier

etd-11132015-133833

Degree

Doctor of Philosophy (PhD)

Department

Mechanical Engineering

Document Type

Dissertation

Abstract

The objective of this work is to develop an improved manufacturing process for microstructured ceramic components that is based on co-extrusion. Co-extrusion of structured feedrods holds promise for development of multi-layered, functionally graded and/or textured structures. However, it requires a polymer binder that is difficult to remove before structures can be sintered to full density. A two-step debinding is introduced to eliminate debinding defects that are commonly observed in thermal debinding (TD). Cracking is a major issue due to a lack of pore spaces for outgassing of pyrolysis products in traditional TD. In two-step debinding, a soluble binder is removed partially by solvent extraction (SE) which creates a porous network and allows gases to escape in subsequent TD of remaining binder components. The feasibility of solvent extraction (SE) is documented for the extrusion of solid ceramic rods and co-extrusion of tubes, where alumina powder was batched with polyethylene butyl acrylate (PEBA) as backbone polymer and polyethylene glycol (PEG) as water soluble binder. SE for specimens with varying PEBA:PEG ratios were tested in water at three different temperatures for various times. Experiments were also performed with different grades of PEBA and EVA to investigate the effect of thermoplastics on SE. The 1:1 mixture showed a PEG removal up to 80wt.% of the original PEG content after 6h extraction. After subsequent thermal debinding, rods and tubes were sintered successfully without defects, demonstrating the viability of the process. Scanning electron microscopy and optical analysis were performed to characterize the process. In order to illustrate potential applications, microfluidic devices were manufactured using extrusion followed by hot embossing. Ceramic microfabricated components have advantages over silicon, glass or polymer devices in terms of their ability to sustain high temperatures without compromising their functional capabilities. Flat tapes were extruded to create substrates, which were subsequently embossing micro patterns using a brass metal mold. To seal the microchanneled feature, a glass slide was attached to the chip by thermal bonding. Though a good bond was obtained, small portions were found where poor bonding was observed. To check leakage, colored water was forced to flow through the channel,and no leakage of water was found. A low temperature sintered ceramic material was fabricated as a potential alternative to the commercial low temperature co-fired ceramic (LTCC) tape. Overall, the study describes new possibilities for microstructure fabrication on ceramic based substrate and established the embossing process as a promising technique for fabrication.

Date

2015

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Schoegl, Ingmar

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