Abstract
The present work demonstrates a new method for fabrication of thin‐walled tubular alumina substrate by combining the principles of gelcasting and freeform fabrication. A tube made up of filter paper or organic preform was filled with 4N nitric acid and dipped in a 55 vol% alumina (average particle size 0.34 μm) slurry containing methylolurea and urea. A thin layer of alumina slurry was gelled on the filter paper tube by in situ polymerization of methylolurea and urea monomers present in the slurry by delivering the acid through the walls of the filter paper tube. The thickness of the alumina tube obtained depended on the dipping time. Alumina tubes with thicknesses in the range 0.7–2 mm were obtained for dipping times in the range 1–8 min. The tubes obtained had good surface finishes and profiles. These tubes were sintered at 1150°C and microstructural observation indicated uniform grain size and pore morphology. A porosity of 40% and an average pore size of 300 nm were obtained.
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