MgO–CaZrO 3-based refractories for cement kilns

Abstract

Two series of refractory materials have been designed taking into account the phase equilibrium relationships to obtain MgO–CaZrO 3–Ca 2SiO 4–Ca 3Mg(SiO 4) 2 or MgO–CaZrO 3–Ca 3Mg(SiO 4) 2–c-ZrO 2 as final crystalline phases. Specimens have been fabricated by reaction sintering of natural dolomite and zircon and with dead burned magnesia aggregates. Different relationships between the proportion and sizes of the fines and the aggregates have been explored. The microstructure of the materials has been characterized in terms of density, crystalline phases and phase distribution and morphology. A combination of X-ray diffraction (XRD) analyses and reflected light optical microscopy and scanning electron microscopy with microanalysis have been used. The phases present in the materials are those expected from the phase equilibrium relationships in the quaternary system. The optimum microstructures, i.e. minimum porosity and adequate matrix content to constitute the bonding between the aggregates are found for initial matrix fractions higher than those for non-reactive systems. The mechanical behaviour has been determined in terms of the room temperature dynamic Young's modulus, E, and the three point bending modulus of rupture, MOR, at 25 and 1100 °C. Additionally, the work of fracture, WOF, has been calculated from the load–displacement curves of stable fracture tests. For optimum starting mixtures, materials with E (60–80 GPa), MOR (4–6 and ∼10 MPa at 25 and 1100 °C, respectively) and WOF (40–70 J m −2) values in the range of those of other magnesia-based refractories have been obtained.