MICROSTRUCTURE AND PROPERTIES OF COLLOIDAL SILICA BONDED MAGNESITE CASTABLE REFRACTORIES

Abstract: Efforts have been carried out in order to use microsilica to develop a forsterite bond rather than other types of binders in the basic refractory castables. According to the higher drying rate and sinterability of colloidal silica, it has been proposed in the recent years. In the present work, effects of replacement of microsilica by colloidal silica evolution of forsterite bond have been studied in magnesia based refractory castables. In this way, Physical properties of prepared samples with different amount of colloidal silica versus temperature were investigated. In addition, phase variation and microstructural evolution of sintered specimens at 1000, 1200 and 1400 °C were studied by X-ray diffraction (XRD) and scanning electron microscope (SEM) respectively. Results showed that, due to Reaction of magnesia with microsilica and colloidal silica, magnesium hydrate and magnesium silicate hydrate formed in the dried samples strengthening the texture of the samples while forsterite formed from about 1000 °C and gradually increased with temperature rise. Also, better forsterite formation would be appeared by increasing the colloidal silica content. Further investigation carried out on the type of silica addition on properties of the castable refractory samples. It was found that the presence of micro silica and colloidal silica simultaneously (MS3C3 sample) at 1400 °C, caused modifying mechanical strength in compare with sample with only micro silica (MS sample).