Estudo do processamento da alumina como gradiente funcional de porosidade pelo método de consolidação por amido

Abstract

This work aimed to study the starch consolidation casting technique in the production of monolithic and layered porous alumina ceramics. Suspensions were produced using alumina, corn starch, distilled and deionized water and ammonium polyacrylate dispersant. Solids’ volume were fixed at 40%, with an amount of starch varying from 5 to 15% in volume. The samples were consolidated at 70 and 80oC and sintered at 1500°C. Characterization was made by shrinkage measures, apparent porosity, mercury porosimetry, microstructure analysis and mechanical behavior under compression. Monolithic samples were also produced by uniaxial pressing, using starch as a sacrifice phase, for comparison. Starch gelling was observed by optical microscopy, showing the swelling of the granules with the water absorption. The shrinkage was higher for the samples consolidated at higher temperature (80°C), with consequently higher densities for them. Porosity had the opposite behavior, with higher values for monolithic samples consolidated at 70°C. The increase in porosity generated a decrease in mechanical strength, but in general, the values obtained in the compression test were very significant, approaching 210 MPa for monolithic samples consolidated at 80°C and 60 MPa for layered samples produced by Starch Consolidation Casting. A toughening effect was observed in the sample fracture test. In layered samples, it was possible to observe the differentiation in the amount of porous between layers and interfaces were presented without cracks and imperfections.