Preparation Of ZrO₂ Porous Ceramics Using Egg White Foaming Method

Ceramic foams are known to have applications in diverse areas, and there are several processes for fabrication of them. The present study prepared ceramic foam by a direct foaming and casting process--protein coagulation casting (PCC). The ovalalbumin has a good foaming ability, and it is also an environmentally friendly low-cost binder for gelcasting of ceramic foams.The egg white extracted from fresh hen's eggs was used instead of ovalalbumin as both foamer and binder to produce zirconia foams, and the source was added to adjust slurry properties. The slurries were prepared with different solid loadings (20-50vol % ) and egg white contents. Thermal consolidation was done in a conventional drying oven at 80℃, and in a conventional household microwave oven for comparesion.Decomposition behaviour of egg white containing foam was investigated by TG/DTA. Microstructure of specimens, including pore distribution and size, was investigated using Scanning Electron Microscopy. Both compressive strength and bend strength were measured. The specimens were sintered at an optimized temperature schedule as followd: from room temperture to 800℃at lower rate (1K·min^-1) with holds at 150℃for 30min, 200℃for 60min, 230℃for 30min and 360℃for 30min, and then from 800℃to 1550℃at a higher rate (3K·min^-1) with hold at highest temperture for 2 hours.Based on slurries with different solid contents, Porous ceramic samples with porosity ranging from 94.55% to 77.24% were prepared. It was illustration that the slurry viscosity increased with the increasing of solid content and egg white content, which led to a decreasing of cell size and cell wall thickness, as well a increasing of strength of sintered samples and fractions of closed porosity. With increasing addition of source, slurry viscosity reduced at fitst and followed increased, meanwhile, the source served as a binder because of its web structure, relating with both separating and joining effects. Foaming ability of egg white was depended on slurry viscosity in great extent, which in turn governes both microstructure and properties of porous ceramics. It was also showed that the microstructures of samples solidified in a conventional household microwave oven were more homogeneous compared with those solidified in conventional drying oven.