Marek Potoczek

A new polyurethane binder providing high green strength of dry-pressed alumina

Abstract The effect of a new polyurethane binder on green strength of dry-pressed alumina bodies was studied. The alumina compacts showed exceptionally high green strength. Depending on binder concentration (1–5 wt.%) the tensile and flexural strength were 1.6-7.0 MPa and 2.0–12.7 MPa, respectively. The high green strength was controlled by polymer–ceramics interactions, as was revealed by IR study. The glass transition temperature of polymer influenced the binder behaviour in ceramic processing. To achieve high green density some residual moisture was needed but then samples had to be dried to obtain high green strength. The binder burnout was characterized by TGA and DTA study in air and in nitrogen. The polyurethane binder had a gradual burnout with a low char residue in both types of atmosphere. The thermal decomposition in air was caused by oxidation reactions, while in nitrogen, the polyurethane binder underwent depolymerization process.

Microstructural, mechanical and thermal characterization of alumina gel-cast foams manufactured with the use of agarose as gelling agent

Alumina gel-cast foams manufactured by using agarose as gelling agent were examined in terms of microstructural, mechanical and thermal properties. The microstructural SEM measurements of alumina foams were compared with X-ray micro tomography investigations also on the pore network. Young’s modulus of alumina foams was determined by impulse excitation and ultrasonic sound velocity measurements. These two independent techniques showed similar results. Gibson and Ashby’s model of completely open-cell and closed-cell foams was compared with experimental data from compression tests. The thermal conductivity measurements using laser-flash analysis were correlated with the pore network in the alumina foam structure.