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One of the most important elements of furnaces, boilers and other heating units is the structure (lining), usually made of silica-alumina, basic or special refractories. The basic refractories are materials that are increasingly in demand and whose manufacturing involves necessarily the use of MgO and CaO. In this article, the description and characterization of magnesite (MgCO 3) and dolomite (Mg,Ca(CO 3) 2) and their contribution in industrial ceramics-refractories have been reviewed.

Five mixtures (M1 to M5) of silica-alumina geomaterials and two varieties of alumina (A P and A R ) were used for the elaboration of mullite refractory materials between 1500˚C and 1600˚C. 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 A R obtained from waste of silica-alumina bricks proves to be efficient for an eventual use.

Production of porous and light-weight bricks with acceptable flexural strength is accomplished. Sawdust was used as an additive to an earthenware brick to produce the pores. SEM-EDS, XRD and XRF analysis of the raw materials and the elaborated refractory were performed. Mixtures containing sawdust were prepared at different proportions (up to 30%). Apparent porosity at 1600 °C was investigated with the bulk density, water absorption, firing shrinkage and flexural strength. Microstructural investigation was carried out by both natural light microscopy and polarized light microscopy. The results obtained showed that the samples tested here maintained their shape without undergoing any deformation up to 1600 °C. The use of sawdust decreased the fired density of the bricks down to 1.24 g/cm³.

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