Hercynite and magnesium aluminate spinels acting as a ceramic bonding in an electrofused MgO–CaZrO3 refractory brick for the cement industry

Innovative chrome-free basic refractory bricks have been design based on electrofused magnesia–calcium zirconate (MgO-CaZrO3) technology using as ceramic bonding magnesium aluminate spinel (MgAl2O4) and hercynite spinel (FeAl2O4) in order to improve their properties. Industrial refractory bricks have been manufactured by solid state sintering of magnesium and calcium zirconate aggregates with MgAl2O4 and FeAl2O4 spinels at 1650 °C in a tunnel kiln. Physical and microstructural characteristics of new refractory bricks have been characterised in terms of density, porosity, crystalline phases, phase distribution and morphology. X-ray diffraction (XRD) analyses and scanning electron microscopy (SEM) with microanalysis (using energy dispersive spectroscopy analysis -EDS) have been used. The mechanical behaviour has been evaluated in terms of cold crushing strength (CCS) at room temperature and three point bending modulus of rupture (MOR) at 25 and 1260 °C. Static and dynamic resistance test by chemical attack of clinker raw meal constituents have been carried out at 1450 °C. Results have shown that thermo-mechanical properties of new refractory bricks significantly improved with increasing both type of spinel in content. Microstructural analysis revealed that spinel phases aided to develop a strong bond between the magnesia and calcium zirconate refractory aggregates. Finally, these refractory matrixes exhibit a good thermal stability and an excellent chemical resistance against clinker raw meal.