Effect of Nano- sized Fe2O3 on Microstructure and Hydration Resistance of MgO-CaO Refracrories

Magnesia–Doloma refractories are considered as a mixed product of alkali products i.e. sintered (fused) magnesia and doloma in which 50-80wt% magnesia is contained. These refractories enjoy some advantages such as high slag resistance corrosion, high-temperature performance, potential for production of pure molten iron and low cost due to abundance of magnesia and doloma resources in access. However, poor resistance of hydration can be cited that may constrain the amount of this refractory in various industrial applications. in this work the effect of nano-sized Fe2O3 on microstructure and hydration resistance of MgO-CaO refractories with 35wt.% CaO were investigated. MgO-CaO refractories with 35wt.% CaO content were prepared by using dolomite and magnesite calcined as starting material and nano-sized Fe2O3 as additive. Samples were uniaxially pressed in to briquettes at a pressure of 90 MPa. Briquettes after drying at 110 for 24 hr were sintered at 1650 for 3 hr. Hydration resistance was measured at 25oC in 95% relative humidity through the weight gain after 72 hr. according to the results, with the addition of nano-sized Fe2O3, bulk density and hydration resistance of the samples increase while apparent porosity decreased. Densification of MgO-CaO refractories was promoted with increase of nano-sized Fe2O3 content. nano- sized Fe2O3 addition lead to formation low melting phases such as C2F(2CaO.Fe2O3), CF(CaO.Fe2O3) and C3A(3CaO.Al2O3). Formation of this low melting point surrounding the CaO and MgO grain and grain boundaries and promoted densification of MgO-CaO refractories. The nature of nano-sized Fe2O3 promoting densification is promoting the liquid phase sintering.