Degradation mechanisms of periclase-magnesium aluminate spinel refractory bricks used in the upper transition zone of a cement rotary kiln

•The degradation mechanisms of periclase- spinel bricks were investigated.•The brick was taken from the upper transition zone of the cement rotary kiln.•Combined effects of cement clinker and alkali vapor on bricks were studied.•Thermomechanical stresses from the changing temperature field were clarified. In this study, the degradation mechanisms of dense periclase-magnesium aluminate spinel refractory bricks used in the upper transition zone of cement rotary kilns were investigated by XRD, SEM and EDS. And the results indicated that the damage of the used brick was main due to the structural spalling as well as the formation and extension of cracks, caused by the corrosion of cement clinker, the deposition of alkali salts and thermal stress resulted from changing temperature field. The bricks reacted with the cement clinker forming a liquid phase at the reacting interface, and then the penetration of this liquid phase by reaction sintering altered the microstructure and compositions of bricks. Additionally, the constantly changing temperature field and the precipitation of alkali salts with the high thermal expansion coefficient in colder zones led to tremendous thermomechanical stress. Thus, joint effects of these factors caused the structural spalling and deterioration of refractory linings.