MgO–CaZrO3-based refractories for cement kilns

Two series of refractory materials were prepared, taking into account the phase equilibrium relationships, to obtain MgO-CaZrO3-Ca2SiO4-Ca3Mg(SiO4)2 or MgO-CaZrO3-Ca3Mg(SiO4)2-c-ZrO2 as the final crystalline phases. Specimens were fabricated by reaction sintering of natural dolomite and zircon with dead burned magnesia aggregates. Different relationships between the proportion and sizes of the fines and the aggregates were explored. The microstructure of the materials was characterised in terms of density, crystalline phases and phase distribution and morphology. A combination of XRD, reflected light optical microscopy and SEM with microanalysis was 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 were found for initial matrix fractions higher than those for non-reactive systems. The mechanical behaviour was 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, was calculated from the load-displacement curves of stable fracture tests. For optimum starting mixtures, materials with E (60-80 GPa), MOR (4-6 and about 10 MPa at 25 and 1100 C, respectively) and WOF (40-70 J/m2) values in the range of those of other magnesia-based refractories have been obtained.