Development of densification-resistant castable porous structures from in situ mullite

Ceramic porous structures are technologically important materials for several high-temperature applications. Many recent studies have aimed at increasing their temperature of use and refractoriness, preserving their pores characteristics (content, shape, and permeability) and creating different forming and placing techniques. The present manuscript reports on the development of highly porous castable structures based on mullite (3Al 2 O 3 ·2SiO 2 ) formed in situ from calcined and hydratable alumina, aluminum hydroxide and amorphous silica. The evolution of their physical properties and microstructure during thermal treatment was evaluated by mechanical (compression strength and elastic modulus) and dilatometric tests, porosity measurements, X-ray diffraction and scanning electron microscopy. The results indicate the mullite׳s intrinsic difficulty for densification (which is a detrimental effect in the production of dense parts) can be a powerful mechanism to prevent porosity loss at high temperatures.