Effect of CaF2 and MgO on sintering of cement clinker

CaF2 (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 degrees C for 112 min. Clinker samples were cooled to room temperature and the amount of free lime (CaOf) 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 CaF2-added samples and the amount of belite increased. The CaOf 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 CaOf. 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. (C) 1999 Elsevier Science Ltd. All rights reserved.