Effect of Nano-Sized Fe2O3 on Microstructure and Hydration Resistance of MgO-CaO Refractories

In this work the effect of Nano-sized Fe2O3 on microstructure and hydration resistance of MgO-CaO refractories with 35 wt% CaO was investigated. MgO-CaO refractories with  35 wt% CaO content was prepared by using dolomite and magnesite calcined as starting materials and Nano-sized Fe2O3 (2,4, 6 and 8 wt%) as an additive. Samples were pressed into briquettes at a pressure of 90 MPa. Briquettes after drying at 110 oC for 24 hours were sintered at 1650 oC for 3 hours. Hydration resistance was measured at 25 oC in 95% relative humidity through the weight gain after 72 hours. According to the results, it is observed that when the amount of Nano-sizedFe2O3 added increased to 8 wt% the bulk density increased to 3.14 gr/cm3 and apparent porosity decreased to 8.20%. For the sample without addition, the mass gain after 72 hours was 1.76, which sharply decreased to 1.27 with increasing the amount of Nano-sized Fe2O3. With the addition of Nano-sized Fe2O3, bulk density and hydration resistance of the samples increased while apparent porosity decreased. Densification of MgO-CaO refractories was promoted to increase of Nano-sized Fe2O3 content. Nano-sized Fe2O3 addition led to formation of low melting phases such as C2F (2CaO.Fe2O3), CF (CaO.Fe2O3) and C3A (3CaO.Al2O3). The formation of this low melting point phases 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 increasing the liquid phase sintering.