Five mixtures (M1 to M5) of
silica-alumina geomaterials and two varieties of alumina (AP and AR)
were used for the elaboration of mullite refractory materials between 1500℃ and 1600℃. An X-ray diffraction (XRD) analysis showed that
the refractory samples are composed of mullite, corundum and silica. The length
of the mullite crystals was measured by a method of image analysis of
scanning electron microscopy (SEM). Chemical and mechanical properties of these
materials were investigated and correlated with their microstructure. Resistance towards Acid Attack test showed
that the refractory samples present good resistance, as well as, the alumina
powder AR obtained from waste of silica-alumina bricks proves to be
efficient for an eventual use.
Different mixtures of Moroccan silica-alumina geomaterials were used for the preparation of refractory ceramics. A formula of composition (M2) has allowed obtaining a good quality of refractory. Addition of a small quantity of carbon (1%) to the M2 formula has substantially improved the quality of the refractory. The morphological, textural and mineralogical evolution, through SEM and XRD shows that the addition of carbon, which plays a catalytic role, favors the crystallization of andalusite. Then, from 1200°C, the andalusite starts to transform to primary mullite needles. At 1400°C, the mullite becomes the major mineral phase beside cristobalite and vitreous phase.