Processing and Analysis of Ceramic Mesoscale Combustors Fabricated by Co-Extrusion
In this work, millimeter-scale tubular combustion channels were fabricated from ceramic precursor materials. Co-extrusion of structured feedrods holds promise for the development of multi-layered, functionally graded and/or textured combustor walls, but requires a polymer binder that is difficult to remove before structures can be sintered to full density. In conventional thermal debinding, cracking is a major issue, where crack formation is attributed to a lack of pore space for outgassing of pyrolysis products. The main focus of this study is to validate a manufacturing process that uses a combination of solvent de-binding and thermal debinding, which is applied to a simple combustor geometry. Alumina powder was batched with a mixture of polyethylene butyl-acrylate (PEBA) and polyethylene glycol (PEG) in a torque rheometer. A 19mm feedrod, consisting of a carbon-black/binder mixture as core, and a surrounding ceramic/binder mixture forming the wall, was extruded through a 5.84 mm die. The binder removal involves two processing steps, where the PEG content was removed by solvent extraction (SE) to initiate pore formation, after which thermal de-binding by pyrolysis removes the remaining binder and carbon-black. Solvent extraction was performed in water at three different temperatures for various times. The 1:1 mixture of PEG:PEBA showed the highest PEG removal of 80wt% for 6 hrs extraction. The thermal de-binding cycle was designed based on thermo-gravimetric analysis (TGA) and successfully performed with a ramping rate of 1.25°C/min to 1000°C without any crack formation. After de-binding, samples were sintered at 1600°C for 1 hr. SEM analysis showed some void spaces in the solvent extracted samples but confirmed that solvent extraction followed by thermal de-binding yielded the best results. The viability of sintered ceramic tubes was tested for conditions typical for thermal cycling in a combustion environment.
Publication Source (Journal or Book title)
ASME 2013 International Mechanical Engineering Congress and Exposition
Schoegl, I. (2013). Processing and Analysis of Ceramic Mesoscale Combustors Fabricated by Co-Extrusion. ASME 2013 International Mechanical Engineering Congress and Exposition https://doi.org/10.1115/imece2013-64866