Mullite (3Al2O3·2SiO2) ceramics obtained by reaction sintering of rice husk ash and alumina, phase evolution, sintering and microstructure

The use of industrial waste (by-products) as raw materials in the ceramic industry has been under study for decades due to the economical, energy, tax and environmental advantages. The specificity of the waste requires a basic characterization and technology thereof.The applicability of rice husk ash (RHA), as silica (SiO2) source, in refractory and porous materials withpotential structural, insulating and/or filtering applications was carried out by characterizing the ceramicbehavior of stoichiometric mixtures of calcined alumina (Al2O3) and RHA. A reaction-sintering frameworkcan be defined in the (Al2O3–SiO2) system. The sinterability and conversion during the reaction sinteringprocesses were studied in order to obtain mullite (3Al2O3·2SiO2) ceramics. Also some microstructural fea-tures of the developed materials were studied in the 1100–1600ºC range. The mullitization was studiedquantitatively.Partial densification was achieved (30%) and highly converted materials were obtained. The developedmicrostructure consisted in a dense ceramic matrix with homogenous interconnected porosity, with anarrow pore size distribution below 20 μm. The developed material gives enough information for design-ing mullite ceramics materials with either porous or dense microstructures with structural, insulating orfiltering applications employing RHA as silica source and calcined alumina as the only other raw material.