, sharif university
In this study, the effect of variety of Nano- additives doping on the hydration resistance of the MgO-CaO system was investigated. Samples were prepared from calcined dolomite and magnesite. Nano-additives that contained cations with various valences (trivalent and tetravalent) used as a dopant. The bulk density, apparent porosity and hydration resitance were studied and evaluated. Also, phase analysis of samples was conducted by using X-ray diffraction (XRD) and the microstructure investigation was done by scanning electron microscopy (SEM). The use of both additives improved the hydration resistance. However, the important role of the higher-valence cation in improvmnt of the hydration resistance of MgO-CaO materials was revealed. This behavior is believed to be due to the formation of vacancies in solid solution of CaO or MgO with higher–valence cation. Zr4+ cation form a solid solution with CaO, which reduce the Ca2+ concentration and leads to the improved hydration resistance of the MgO-CaO system. Also trivalent cation led to the formation of some low melting phases such as C2F (2CaO.Fe2O3), CF (CaO.Fe2O3), C3A (3CaO.Al2O3). The formation of these low melting point phases surrounded the CaO and MgO grain, grain-boundaries and thus promoted densification and hydration resistance of the MgO-CaO system.