In this paper, the phases in the Mg-Ti-O system using the 1:1 formulation of MgO:TiO2 mixing synthetic brucite of Mexican origin with TiO2 microparticles of high purity and with a heat treatment at 1100°C for 1 h were studied. The raw materials and formulation by XPS and DRX techniques were characterized. The results demonstrate the presence of different oxidation states in titania and the formation of different oxides in the Mg-Ti-O system when mixed and calcined at 1100°C; additionally, the formation of vacancies in the crystal lattice during the transformation from hexagonal brucite to magnesia with a cubic structure centered on the faces is estimated. With the results, its thermal behavior is warned based on the MgO-TiO2 phase diagram.

The regenerated magnesia-calcium brick samples that had added 0, 1.5, 3.0 wt.% aluminium oxide (Al2O3) were prepared by using spent magnesia-calcium bricks, fused magnesia and Al2O3 powder additive as the main raw materials. The phases, microstructures, room temperature and hot flexural strength, resistance to cement clinker corrosion and strength of coating adherence were investigated respectively. It indicated that the addition of Al2O3 increased mainly resulting in the content of tetracalcium aluminoferrite (C4AF) and tricalcium aluminate (C3A) increased in the regenerate samples. The bulk density, the room temperature flexural strength and the strength of coating adherence all increased, while the hot flexural strength and corrosion resistance both deteriorated along with the increase of Al2O3 addition. It was because that on the one hand the low melting point phases of C4AF and C3A improved the sinterability of the regenerated samples during the burning stage, on the other hand they melted or existed in liquid phase during the experimental temperature (1573 K and 1823 K) which degraded hot flexural strength and corrosion resistance, and enhanced the strength of coating adherence as the wettability of the liquid phase. The content of Al2O3 in the regenerated magnesia-calcium brick should not be higher than 1.1 wt.%, considering its room and high-temperature performances for cement rotary kiln.