Development and characterization of porous moldable refractory structures of the alumina-mullite-quartz system

Efforts to reduce energy consumption have led to the increasing use of microporous refractory ceramics as high-temperature thermal insulation materials. One of the techniques to produce these materials is based on the generation of pores through the phase transformation of hydroxyl or carbonate compounds. This method does not release toxic volatiles but prolonged use at high temperatures limits its use, because the transition compounds that are formed after dehydroxylation/decarbonation tend to accelerate densification, reducing the system's total porosity. The aim of this work was to produce porous moldable ceramics from alumina, aluminum hydroxide and a source of silica (quartz), using the reaction of alumina and quartz in order to form mullite, a compound that is able to decrease densification rates at high temperatures. The samples were sintered between 1100 °C and 1500 °C and characterized by porosity measurements, modulus of elasticity, compressive strength, X-ray diffraction, dilatometry, mercury porosimetry, and scanning electron microscopy. The results indicated that high levels of porosity were preserved up to 1500 °C owing to the formation of mullite.