Evaluation of the porogenic behavior of aluminum hydroxide particles of different size distributions in castable high-alumina structures

The combination of Al2O3 and Al(OH)3 produces high refractoriness porous structures. The evolution of these ceramics during the first heating is a competition between pore generation by Al(OH)3 dehydroxilation, and densification by sintering. Previous studies have reported the size of Al(OH)3 particles affect both events. In this study, we evaluate the porogenic behavior of three grades of α-Al(OH)3 (gibbsite) of different average particle sizes (0.9, 10 and, 107 μm). The particles were thermally treated (300-1500 °C) for the investigation of changes in their physical properties and microstructures. Amounts of 67.5 vol% of each grade were added to aqueous castable alumina suspensions. After rheological tests and casting, the sintered samples (1100-1500 °C) were tested for porosity, pore size, and strength and examined by electron microscopy. The particles of the three grades exhibited similar evolution during thermal treatment. When they were added to the alumina matrix, structures of different porosity and strength were obtained.