Effect of CaF 2 and MgO on sintering of cement clinker

Abstract

CaF 2 (0.25, 0.50, and 1%) and MgO (1, 2, and 3%) was added to a mixture composed from limestone, sand, and loam, then burned at 1410°C for 112 min. Clinker samples were cooled to room temperature and the amount of free lime (CaO f) was determined by titration while the relative amounts of alite and belite were determined by X-ray diffraction (XRD). Microstructure was investigated by scanning electron microscopy (SEM). The amount of alite decreased in CaF 2-added samples and the amount of belite increased. The CaO f content of the sample containing 1% MgO was less than that of the pure sample. For the other MgO-added samples, due to the increase in lime saturation factor value no evident change was detected in the amount of CaO f. Both XRD and SEM analyses showed a decrease of the amount of alite and an increase of the amount of belite in MgO-added samples when compared to pure samples. The reason for the decrease in amount of alite in MgO-added samples is believed to be coarse belite crystals. Due to the prolonged holding time at the alite formation temperature, coarse belite crystals were formed. Because of the high diffusion rate at this period, belite crystals lose their surface activity and consequently alite formation was hindered.